EP4669423A1

EP4669423A1 - DEVICE AND METHOD FOR FABRIC CONDUCTION COMMUNICATION

Info

Publication number: EP4669423A1
Application number: EP24704259.1A
Authority: EP
Inventors: Evan S. Johnson; David J. Peichel; Jonathan D. EDMONSON
Original assignee: Medtronic Inc
Current assignee: Medtronic Inc
Priority date: 2023-02-24
Filing date: 2024-02-06
Publication date: 2025-12-31
Also published as: WO2024176028A1

Abstract

A device having a tissue conductance communication (TCC) circuit is configured to perform a set up procedure that includes determining at least one signal strength metric of a received TCC signal corresponding to each of multiple time points of one or more cycles of the cyclical physiological signal. The device may establish a time window of the cyclical physiological signal for performing TCC based on the signal strength metrics.

Description

APPARATUS AND METHOD FOR TISSUE CONDUCTION COMMUNICATION

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63/486,735, filed February 24, 2023, the entire content of which is incorporated herein by reference.

TECHNICAE FIELD

[0002] The disclosure relates generally to devices, systems and methods for communication between two or more devices using tissue conduction communication.

BACKGROUND

[0003] Communication between two or more devices associated with a living subject, e.g., implanted within the subject and/or attached to or otherwise contacting the subject, may be desirable in a number of applications, such as for monitoring or managing health of a patient. Communication between these devices may, for example, enable the exchange of information, coordinated monitoring of a health condition and/or coordinated therapy to treat health conditions. Such systems, some examples of which are described below, may communicate using tissue conduction communication (TCC). TCC may use the human body as the medium of communication. TCC may sometimes be referred to as human body conduction (HBC) or intrabody communication.

[0004] A wide variety of implantable medical devices (IMDs) for delivering a therapy to or monitoring a physiological condition of a patient have been used clinically or proposed for clinical use in patients. Examples include IMDs that deliver therapy to and/or monitor conditions associated with the heart, muscle, nerve, brain, stomach or other tissue. Some therapies include the delivery of electrical stimulation to such tissues. Some IMDs may employ electrodes for the delivery of therapeutic electrical signals to such organs or tissues, electrodes for sensing intrinsic physiological electrical signals within the patient, which may be propagated by such organs or tissue, and/or other sensors for sensing physiological signals of a patient.

[0005] Implantable cardioverter defibrillators (ICDs), for example, may be used to deliver high energy defibrillation and/or cardioversion shocks to a patient's heart when ventricular tachyarrhythmia, e.g., tachycardia or fibrillation, is detected. An ICD may detect a tachyarrhythmia based on an analysis of a cardiac electrogram (EGM) or electrocardiogram (ECG) sensed via electrodes, and may deliver anti-tachyarrhythmia shocks, e.g., defibrillation shocks and/or cardioversion shocks, via electrodes. An ICD or an implantable cardiac pacemaker, as another example, may provide cardiac pacing therapy to the heart when the natural pacemaker and/or conduction system of the heart fails to provide synchronized atrial and ventricular contractions at rates and intervals sufficient to sustain healthy patient function. ICDs and cardiac pacemakers may also provide overdrive cardiac pacing, referred to as anti-tachycardia pacing (ATP), to suppress or convert detected tachyarrhythmias in an effort to avoid cardioversion/defibrillation shocks.

[0006] Some IMDs are coupled to one or more of the electrodes used to sense electrical physiological signals and deliver electrical stimulation via one or more leads. A medical electrical lead carrying sensing and/or electrical therapy delivery electrodes allow the IMD housing to be positioned a location spaced apart from the target site for sensing and/or stimulation delivery. For example, a subcutaneously or sub-muscularly implanted housing of an ICD or implantable cardiac pacemaker may be coupled to endocardial electrodes via one or more medical electrical leads that extend transvenously to the patient’s heart. Other ICDs are not necessarily coupled to any intracardiac leads, and instead sense and deliver shocks via electrodes implanted away from the patient’s heart, e.g., implanted subcutaneously or substernally. Extra-cardiac electrodes may be provided along the housing of an IMD and/or coupled to an IMD via one or more leads extending subcutaneously, submuscularly, substernally or transvenously from the housing but remain outside the heart.

[0007] Leadless IMDs may also be used to deliver therapy to a patient, and/or sense physiological parameters of a patient to provide important patient monitoring functions. In some examples, a leadless IMD may include one or more electrodes on its outer housing to deliver therapeutic electrical stimulation to the patient, and/or sense intrinsic electrical signals of patient. For example, a leadless pacemaker may be used to sense intrinsic depolarizations or other physiological parameters of the patient, and/or deliver therapeutic electrical stimulation to the heart. A leadless pacemaker may be positioned within the heart and, in some examples, may be anchored to a wall of the heart via a fixation mechanism. [0008] In some situations, two or more medical devices are implanted within and/or worn by a single patient. It may be desirable for the two or more medical devices to be able to communicate with each other, e.g., to coordinate, or cooperatively provide, sensing for monitoring the patient and/or therapy delivery.

SUMMARY

[0009] The techniques of this disclosure generally relate to TCC techniques performed by a device in contact with or implanted in a living subject. The techniques of this disclosure are described in the context of one IMD communicating with another IMD. However, the techniques can be utilized by any device that is implanted, worn externally with surface or skin electrodes in contact with the patient, or worn externally with electrodes that are implanted transcutaneously for communicating with another device using TCC.

[0010] The techniques disclosed herein can used in optimizing TCC performance between two medical devices when at least one of the two medical devices is subjected to body or tissue motion that is cyclical in nature, e.g., cardiac motion, respiratory motion, repetitive physical body motion or other cyclical motion, including cyclical motion that may vary in period and/or amplitude of an associated cyclical signal. A medical device operating according to the techniques disclosed herein may sense a cyclical signal and receive a TCC signal from another medical device throughout, or at multiple time points, during one or more cycles of the cyclical signal. The medical device may determine a time window that can be defined relative to the cyclical signal that is associated with a relatively high received TCC signal strength compared to other time points in a cycle of the cyclical signal. The medical device may schedule a TCC window for transmitting TCC signals to and/or receiving TCC signals from another medical device during the TCC window of one or more future cycles of the cyclical signal for exchanging data, commands or other information that may be used in monitoring a medical condition of the patient and/or providing a therapy to the patient.

[0011] In one example, the disclosure provides a device that includes sensing circuitry configured to sense a cyclical physiological signal and TCC circuitry configured to receive a test TCC signal. The device includes processing circuitry configured to identify one or more cycles of the cyclical physiological signal and, during a set up procedure, determine at least one signal strength metric of the received test TCC signal at each of multiple time points relative to the identified one or more cycles of the cyclical physiological signal. The processing circuitry may, based on the signal strength metrics, establish a TCC time window of the cyclical physiological signal for performing TCC. The TCC circuitry can be configured to perform TCC during the established TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0012] In another example, the disclosure provides a method including sensing a cyclical physiological signal, receiving a test TCC signal, identifying one or more cycles of the cyclical physiological signal, and, during a set up procedure, determining at least one signal strength metric of the received test TCC signal at each of multiple time points relative to the identified one or more cycles of the cyclical physiological signal. The method may include, based on the signal strength metrics, establishing a TCC time window of the cyclical physiological signal for performing TCC. The method may include performing TCC during the TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0013] A non-transitory computer-readable medium comprising a set of instructions that, when executed by processing circuitry of a device cause the device to sense a cyclical physiological signal, receive a test TCC signal, identify one or more cycles of the cyclical physiological signal, and, during a set up procedure, determine at least one signal strength metric of the received test TCC signal at each of multiple time points relative to the identified one or more cycles of the cyclical physiological signal. The instructions may further cause the device to, based on the signal strength metrics, establish a TCC time window of the cyclical physiological signal for performing TCC. The instructions may cause the device to perform TCC signal during the TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0014] The details of one or more aspects of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the techniques described in this disclosure will be apparent from the description and drawings, and from the claims. BRIEF DESCRIPTION OF DRAWINGS

[0015] FIG. 1 is a conceptual diagram of a variety of devices capable of performing TCC techniques and various body locations that such devices may be implanted in or positioned on a patient’s body.

[0016] FIG. 2 is a conceptual diagram of an IMD system capable of TCC according to one example.

[0017] FIG. 3 is a conceptual diagram of a leadless pacemaker that may be included in a system configured to communicate via TCC according to some examples.

[0018] FIG. 4 is a conceptual diagram of a sensor that may be configured to perform TCC according to one example.

[0019] FIG. 5 is a conceptual diagram of an IMD capable of performing TCC according to some examples.

[0020] FIG. 6 is a conceptual diagram of a TCC transmitter that may be included in TCC circuitry of a device according to some examples.

[0021] FIG. 7 is a flow chart of a method that may be performed by a medical device included in a device system configured to communicate via TCC.

[0022] FIG. 8 is a diagram of a test TCC signal that may be transmitted by a secondary device during a TCC setup procedure and the corresponding TCC signal that may be received by a primary device according to some examples.

[0023] FIG. 9 is a diagram of a test TCC signal that may be transmitted by a secondary device during a TCC set up procedure and the corresponding received TCC signal received by a primary device according to another example.

[0024] FIG. 10 is a flow chart of a TCC set up procedure according to another example.

[0025] FIG. 11 is a flow chart of a method for performing TCC by a medical device system according to some examples.

[0026] FIG. 12 is a diagram that depicts TCC windows and that may be scheduled during a cyclical signal after completing the TCC set up procedure.

DETAILED DESCRIPTION

[0027] Wireless communication between two or more devices in contact with a living subject may be desired for a number of reasons, including to exchange data and/or to coordinate or cooperatively provide sensing of physiological signals, collection of physiological data, and/or therapy delivery. TCC signals may be wirelessly transmitted from one device to one or more other devices co-implanted within a patient and/or to an external medical device having surface or transcutaneous electrodes coupled to the patient for transmitting and/or receiving TCC signals.

[0028] A device configured to perform TCC may be implanted or attached to the patient such that electrodes used for transmitting and receiving TCC signals are subjected to cyclical motion due to a cyclical physiological function, such as the heartbeat or respiration. In some instances, cyclical body motion, such as walking, bicycling, jogging, stair stepping, swimming or the like may expose a device to cyclical motion. The relative proximity and alignment of TCC transmitting electrodes of one device and TCC receiving electrodes of a second device may therefore fluctuate, in a cyclical manner, during a TCC session due to this cyclical motion of one or both of the transmitting device electrodes and/or the receiving device electrodes. The cyclical motion of the transmitting device electrodes and/or receiving device electrodes may cause the strength of the TCC signal received by a TCC receiver to fluctuate and/or drop out during a communication session. TCC techniques disclosed herein are provided for reducing the likelihood of signal drop out or reduced or variable signal strength of a received TCC signal due to cyclical motion imparted on one or both of the transmitting and receiving electrodes.

[0029] FIG. 1 is a conceptual diagram 1 of example body locations that devices capable of performing TCC techniques may be implanted in or positioned on a patient 12. As illustrative examples, a patient may be implanted with a cranial device 2, which may be implanted in or on the cranium or positioned externally in a cranial location. Cranial device 2 may be positioned for monitoring an electroencephalogram (EEG) signal and/or delivering electrical stimulation to the patient’s brain. A medical device 3 may be implanted in the neck of the patient 12 to provide neurostimulation and/or monitoring of nervous system signals or other physiological signals. Medical device 3 may represent, as examples, a spinal cord stimulator, EEG monitor, or an upper airway stimulation device (e.g., for treating sleep apnea) as examples.

[0030] Patient 12 may be implanted with one or more leadless sensors 4 and 250, which may be implanted or worn cutaneously, transcutaneously, subcutaneously, submuscularly or transvenously, for sensing one or more physiological signals, such as cardiac, neurological, respiratory or other signals. For example, sensor 4 may be a cardiac monitor configured to sense an electrocardiogram (ECG) signal using electrodes on the sensor housing that encloses electronics configured to perform sensor functions such as sensing the ECG signal, determining a heart rhythm and performing TCC. Sensor 4 may generally correspond to the REVEAL LINQ™ Insertable Cardiac Monitor available from Medtronic, Inc., Dublin Ireland, adapted to perform the TCC techniques as disclosed herein for example. In the example shown, sensor 4 is implanted away from the heart such that electrodes on the sensor housing (and/or on a lead extending from the housing but not making contact with the patient’s heart) can be used for recording an ECG signal. In other examples, sensor 4 may include housing-based and/or lead-based electrodes that can be implanted in contact with the heart for sensing a cardiac electrogram (EGM) signal. Sensor 250 may be a wireless blood pressure sensor that may be implanted in an arterial location, e.g., in the pulmonary artery as shown in FIG. 1, for monitoring a patient’s blood pressure. Sensor 250 is described below in conjunction with FIG. 4.

[0031] Patient 12 is shown implanted with an atrial intracardiac, leadless pacemaker 112 and an intraventricular, leadless pacemaker 114 implanted in the patient’s heart 8. Pacemakers 112 and 114 may be configured to sense cardiac electrical signals and deliver atrial and/or ventricular pacing to promote a regular heart rhythm. Pacemaker 114 may generally correspond to the MICRA™ Transcatheter Pacemaker available from Medtronic, Inc., Dublin Ireland, for example. An example leadless pacemaker is described below in conjunction with FIG. 4.

[0032] In some examples, patient 12 may be implanted with a pacemaker or ICD 5 that may be positioned in a subcutaneous or submuscular pocket in a pectoral region and coupled to one or more transvenous leads (not shown in FIG. 1 for the sake of clarity) tunneled from the patient’s heart to the implant pocket. The one or more transvenous leads can be used to position electrodes in one or more chambers of heart 8. Sometimes a pacemaker or ICD may be implanted in a pocket formed in an abdominal location rather than a pectoral location. In other examples, patient 12 may receive an ICD 14 that may be implanted in a lateral location, e.g., along the ribcage of the patient, that is coupled to one or more extracardiac leads (not shown in FIG. 1 for the sake of clarity) that may extend subcutaneously, submuscularly, substernally and/or transvenously to position electrodes for sensing cardiac electrical signals, delivering cardiac stimulation pulses which may include cardiac pacing pulses and/or cardioversion/defibrillation (CV/DF) shocks. An example of an extra-cardiac ICD system is described below in conjunction with FIG. 2. [0033] In some cases, patient 12 may receive a device that is implanted or worn in an abdominal location, pelvic location or a peripheral limb location as generally illustrated by devices 6, 7, 9a, 9b and 9c. Abdominal device 6 may be an implanted or external pacemaker, diaphragm stimulator, gastric stimulator, drug pump, or glucose monitor as examples. Pelvic device 7 may be a neurostimulator used for treating incontinence for example. Limb devices 9a, 9b and 9c may represent a variety of implanted or externally worn devices configured to sense a physiological signal, e.g., a glucose monitor, ECG monitor, pulse oximeter, activity tracker, etc., and/or deliver a therapy, e.g., as a drug pump or a neurostimulator.

[0034] As can be seen from FIG. 1, a wide variety of devices may be worn by or implanted in a patient that may be configured to sense a physiological signal and/or deliver a therapy and be capable of TCC with another device in contact with or implanted in the patient 12. The techniques disclosed herein for improving TCC between two devices are not limited to being implemented in a particular type of device. Any device including at least one pair of electrodes in contact with body tissue for transmitting and receiving TCC signals can be configured to perform techniques disclosed herein in a TCC device system.

[0035] The techniques disclosed herein can be particularly beneficial when at least one of the two devices communicating with another device via TCC is subjected to cyclical motion of the patient’s body or tissues, such as cardiac motion or respiratory motion or other cyclical body motion. At least one of the two devices may be configured for sensing a cyclical physiological signal associated with the cyclical body motion. Among examples of cyclical physiological signals that may be sensed by a device performing the TCC techniques disclosed herein are, but not limited to: an ECG signal; EGM signal; tissue oxygen saturation or pulse oximetry signal; blood pressure signal; heart sounds signal; respiration sounds signal; cardiac acceleration signal; arterial wall motion signal; cardiac impedance signal; arterial impedance signal; thoracic impedance signal; blood flow signal; respiratory air flow signal; temperature signal; pH signal; or physical body acceleration signal. [0036] As described below, a device configured to sense a cyclical physiological signal associated with cyclical body or tissue motion imparted on one or both of the devices communicating via TCC can analyze a received TCC signal at multiple times relative to one or more cycles of the cyclical physiological signal. For example, during a TCC set up procedure, a first device may determine at least one signal strength metric of a TCC signal received from another device at multiple time points relative to one or more cycles of the cyclical physiological signal sensed by the first device. The motion caused by the sensed cyclical physiological signal may cause motion of the TCC electrodes of the first device and/or the TCC electrodes of the second device that communicates with the first device via TCC. Based on the signal strength metrics, the first device may establish a time window of the cyclical physiological signal, e.g., relative to the cycle length of the cyclical physiological signal, for performing TCC with the second device. For example, the first device may establish the time window to correspond with the portion of the cyclical physiological signal during which the TCC signal was the strongest or at least above a particular threshold as further described below. The TCC circuitry of the first device and/or second device can be configured to transmit and/or receive a TCC signal during the established time window of one or more cycles of the cyclical physiological signal after the TCC set up procedure.

[0037] It is to be understood that the “set up procedure” performed for establishing the timing of a TCC window relative to a cyclical signal can be performed at any time that the TCC window needs to be established or re-established. The set up procedure is not limited to being performed only once or at a particular time such as at device implant. The set up procedure can be performed multiple times over the life of the device, e.g., at device implant or installation, during a patient follow up visit with a clinician, in response to receiving a command from an external device or programmer, and/or according to a specified schedule (e.g., once per hour, once per day, once per week or other scheduled frequency). In some examples, the set up procedure may be performed in response to a command received from another device, e.g., an external or implantable device, which may or may not be the other device with which TCC is being performed during the subsequently established TCC time windows. The set up procedure may be performed by a device in a TCC system in response to detecting a set up procedure triggering event such as a failed TCC communication, a change in patient posture, a change in patient physical activity, a change in the rate (e.g., period) or amplitude of the cyclical signal or other conditions that may be associated with a change in the received TCC signal strength at a receiving device during a TCC session. The set up procedure disclosed herein for establishing a TCC time window during a cycle of a cyclical signal provides improvements in medical device communication systems by increasing the likelihood of successful communication between two devices and/or enabling optimization of TCC control parameters such as TCC electrodes, transmit power and/or receiving sensitivity that conserve power of the devices communicating via TCC, thereby conserving the useful life the devices.

[0038] FIG. 2 is a conceptual diagram of an IMD system 10 capable of TCC according to one example. IMD system 10 includes an ICD 14, an extra-cardiac electrical stimulation and sensing lead 16 coupled to ICD 14, and an intra-cardiac pacemaker 114. ICD 14 and pacemaker 114 may be enabled to communicate via TCC for transmitting a variety of data or commands. For example, ICD 14 and pacemaker 114 may be configured to communicate via TCC to confirm detected cardiac events or a detected heart rhythm and/or coordinate delivery of cardiac pacing pulses for bradycardia pacing, ATP therapy, cardioversion/defibrillation (CV/DF) shocks, post-shock pacing, cardiac re synchronization therapy (CRT) or other electrical stimulation therapies in response to an abnormal heart rhythm being detected by one or both of the ICD 14 and pacemaker 114.

[0039] IMD system 10 senses cardiac electrical signals, such as R-waves attendant to ventricular depolarizations and/or P- waves attendant to atrial depolarizations, for detecting abnormal heart rhythms with high sensitivity and specificity to enable IMD system 10 to deliver (or withhold) appropriate therapies at appropriate times. TCC signals transmitted by pacemaker 114 and received by ICD 14 or vice versa may vary in signal strength due to cardiac and/or respiratory motion imparted on the TCC electrodes used by pacemaker 114 and/or ICD 14. Variation in the received TCC signal strength may result in failed communications. The TCC signal transmission techniques disclosed herein promote a reliable received signal strength during TCC and may enable optimization of TCC control parameters such as transmit power and/or receiving sensitivity for conserving the power sources and thereby increasing the useful life of ICD 14 and/or pacemaker 114.

[0040] FIG. 2 is described in the context of an IMD system 10 including ICD 14 and pacemaker 114 capable of sensing cardiac electrical signals produced by the patient’s heart 8 and delivering CV/DF shocks and cardiac pacing pulses to the patient’s heart 8. In some examples, the TCC communication may be “one-way” communication, e.g., transmission only from ICD 14 to pacemaker 114 or transmission only from pacemaker 114 to ICD 14. In other examples, the TCC communication may be “two-way” communication between ICD 14 and pacemaker 114 such that each of pacemaker 114 and ICD 14 can receive and transmit information.

[0041] ICD 14 includes a housing 15 that forms a hermetic seal that protects internal components of ICD 14. The housing 15 of ICD 14 may be formed of a conductive material, such as titanium or titanium alloy. The housing 15 may function as an electrode (sometimes referred to as a “can” electrode). In other instances, the housing 15 of ICD 14 may include a plurality of electrodes on an outer portion of the housing. The outer portion(s) of the housing 15 functioning as an electrode(s) may be coated with a material, such as titanium nitride for reducing post-stimulation polarization artifact. Housing 15 may be used as an active can electrode for use in delivering CV/DF shocks or other high voltage pulses delivered using a high voltage therapy circuit. In other examples, housing 15 may be available for use in delivering relatively lower voltage cardiac pacing pulses and/or for sensing cardiac electrical signals in combination with electrodes carried by lead 16. In any of these examples, housing 15 may be used in a transmitting and/or receiving electrode vector for transmitting and/or receiving TCC signals according to the techniques disclosed herein.

[0042] ICD 14 includes a connector assembly 17 (also referred to as a connector block or header) that includes electrical feedthroughs crossing housing 15 to provide electrical connections between conductors extending within the lead body 18 of lead 16 and electronic components included within the housing 15 of ICD 14. As will be described in further detail herein, housing 15 may house one or more processors, memories, transceivers, cardiac electrical signal sensing circuitry, therapy delivery circuitry, TCC transmitting and receiving circuitry, power sources, other optional sensors and/or other components for sensing cardiac electrical signals, detecting a heart rhythm, and controlling and delivering electrical stimulation pulses to treat an abnormal heart rhythm and for transmitting and receiving TCC signals to/from pacemaker 114.

[0043] Lead 16 includes an elongated lead body 18 having a proximal end 27 that includes a lead connector (not shown) configured to be connected to ICD connector assembly 17 and a distal portion 25 that includes one or more electrodes. In the example illustrated in FIG. 1, the distal portion 25 of lead body 18 includes defibrillation electrodes 24 and 26 and pace/sense electrodes 28 and 30. In some cases, defibrillation electrodes 24 and 26 may together form a defibrillation electrode in that they may be configured to be activated concurrently. Alternatively, defibrillation electrodes 24 and 26 may form separate defibrillation electrodes in which case each of the electrodes 24 and 26 may be selectively activated independently.

[0044] Electrodes 24 and 26 (and in some examples housing 15) are referred to herein as defibrillation electrodes because they are utilized, individually or collectively, for delivering high voltage stimulation therapy (e.g., cardioversion or defibrillation shocks). Electrodes 24 and 26 may be elongated coil electrodes and generally have a relatively high surface area for delivering high voltage electrical stimulation pulses compared to pacing and sensing electrodes 28 and 30. However, electrodes 24 and 26 and housing 15 may also be utilized to provide pacing functionality, sensing functionality, and/or TCC signal transmission and receiving in addition to or instead of high voltage stimulation therapy. In this sense, the use of the term “defibrillation electrode” herein should not be considered as limiting the electrodes 24 and 26 for use in only high voltage cardioversion/defibrillation shock therapy applications. For example, electrodes 24 and 26 may be used in a sensing vector used to sense cardiac electrical signals and detect and discriminate tachyarrhythmias. Electrodes 24 and 26 may be used in a TCC signal transmitting electrode vector in combination with each other, collectively with housing 15, or individually with housing 15. When ICD 14 operates in a receiving mode for receiving TCC signals from pacemaker 114, electrodes 24, 26 and/or housing 15 may be used in a TCC receiving electrode vector. The TCC transmitting and receiving electrode vectors may be the same or different vectors.

[0045] Electrodes 28 and 30 are relatively smaller surface area electrodes which are available for use in sensing electrode vectors for sensing cardiac electrical signals and may be used for delivering relatively low voltage pacing pulses in some configurations. Electrodes 28 and 30 are referred to as pace/sense electrodes because they are generally configured for use in low voltage applications, e.g., delivery of relatively low voltage pacing pulses and/or sensing of cardiac electrical signals, as opposed to delivering high voltage cardioversion defibrillation shocks. In some instances, electrodes 28 and 30 may provide only pacing functionality, only sensing functionality or both. Furthermore, one or both of electrodes 28 and 30 may be used for TCC signal transmission and/or receiving in some examples, together or in combination with any of electrodes 24, 26 and/or housing 15. In the example illustrated in FIG. 1, electrode 28 is located proximal to defibrillation electrode 24, and electrode 30 is located between defibrillation electrodes 24 and 26. Electrodes 28 and 30 may be ring electrodes, short coil electrodes, hemispherical electrodes, or the like. Electrodes 28 and 30 may be positioned at other locations along lead body 18 and are not limited to the positions shown. In other examples, lead 16 may include none, one or more pace/sense electrodes and/or one or more defibrillation electrodes.

[0046] ICD 14 may obtain cardiac electrical signals corresponding to electrical activity of heart 8 via a combination of sensing electrode vectors that include combinations of electrodes 24, 26, 28, 30 and/or housing 15. Various sensing electrode vectors utilizing combinations of electrodes 24, 26, 28, and 30 may be selected by sensing circuitry included in ICD 14 for receiving a cardiac electrical signal via one or more sensing electrode vectors. As described below, ICD 14 may function as a primary device during a TCC set up procedure by sensing a cardiac electrical signal and determining signal strength metrics from a TCC signal received from pacemaker 114 at multiple time points relative to one or more cycles of the cardiac electrical signal. Based on the determined signal strength metrics, processing circuitry of ICD 14 may establish a TCC window for performing TCC.

[0047] A TCC transmitting/receiving electrode vector may be selected from the available electrodes, e.g., defibrillation electrodes 24, 26, 28, 30 and housing 15 of ICD 14. The TCC transmitting/receiving electrode vector may be used for transmitting TCC signals produced by a TCC transmitter included in ICD 14 and for receiving TCC signals from another device, e.g., pacemaker 114. During the TCC set up procedure described herein, TCC signals may be transmitted by ICD 14 via multiple TCC transmission electrode vectors and/or received by multiple TCC receiving electrode vectors for use in identifying the TCC transmitting/receiving electrode vector that is associated with the highest (or at least acceptable) TCC signal strength at a receiving device.

[0048] Electrodes, such as defibrillation electrodes 24 and 26 and housing 15, having a relatively large surface area may be used to transmit TCC signals to minimize the impedance of the transmitting electrode vector. A low impedance of the transmitting electrode vector maximizes the injected current signal. The TCC transmitting electrode vector may be selected to both minimize impedance of the transmitting electrode vector and maximize transimpedance from the transmitting electrode vector to the intended receiving electrode vector. As used herein, the term “transimpedance” refers to the voltage received at a TCC signal receiving electrode vector divided by the transmitted current (voltage out divided by current in). As such, the transimpedance for a given TCC communication electrode vector for each of two devices configured to communicate bidirectionally is the same for communication in both directions for a given set of transmitting and receiving electrode vectors. By maximizing transimpedance, the voltage signal at the intended receiving electrodes is maximized for a given current signal injected into the tissue conductance pathway. As such, a low impedance of the transmitting electrode vector and high transimpedance of the TCC pathway increases the received TCC signal strength (voltage signal) at the receiving electrode vector.

[0049] Among the factors that may contribute to a maximized transimpedance of the TCC pathway are a substantially parallel electrical configuration of the transmitting and receiving electrode vectors, relatively wide spacing of the transmitting electrodes, relatively wide spacing of the receiving electrodes, and close proximity of the transmitting electrode vector to the receiving electrode vector. A transmitting electrode vector closer in proximity to the receiving electrode vector improves the strength of the TCC signal compared to a larger separation of the transmitting and receiving electrode vectors. The optimal orientation for the receiving electrode vector is parallel to the conductive tissue pathway of the current flow. A transmitting electrode vector that is substantially electrically parallel to the receiving electrode vector improves the strength of the TCC signal compared to the receiving electrode vector being orthogonal to the pathway of the current flow through the body tissue, which may result in a null signal.

[0050] A parallel electrical configuration between the transmitting and receiving electrode vectors may coincide with physically parallel electrode pairs. The physical electrode vectors may be viewed in some cases as the line the extends from one electrode of the vector to the other electrode of the vector to determine orientation of the transmitting and receiving vectors relative to one another. In some instances, however, physically parallel electrode pairs may not be electrically parallel depending on the electrical conduction properties of the intervening tissues. For example, a body tissue having relatively low electrical conductance, such as lung tissue, compared to other surrounding tissues, may require a physical electrode configuration that is not necessarily parallel in order to achieve an electrical configuration that is substantially parallel.

[0051] Due to motion of the patient’s body and tissues, e.g., due to cardiac motion, lung motion or physical activity, the alignment and proximity of the transmitting and receiving electrodes of ICD 14 and pacemaker 114 may vary due to cyclical motion imparted on the transmitting and/or receiving electrodes. This cyclical variation may result in time-varying signal strength and/or signal margin relative to baseline noise. The techniques disclosed herein enable ICD 14 and pacemaker 114 to communicate via TCC during time windows of the cardiac cycle, for example, that promotes a high signal strength and/or signal margin for reliable communication between the two devices. In some examples, time windows during a cyclical signal corresponding to cardiac or respiratory motion, for example, may be identified as time windows during which TCC is least desirable, e.g., due to a relatively low or variable received signal strength at the receiving electrodes. Thus in some examples, the set up procedure may include a determination of a time window during a cyclical signal that TCC is avoided so that the established TCC time window can exclude undesired time windows.

[0052] The TCC transmitting electrode vector may be selected to include electrodes that are not coupled to ICD sensing circuitry, e.g., a cardiac event detector configured to sense R-waves and/or P-waves from a cardiac electrical signal received by a sensing electrode vector. Use of an electrode for TCC signal transmission that is also coupled to a cardiac electrical event detector or other electrical signal sensing circuitry may increase interference with cardiac event detection or other electrical signal monitoring. The transmitting electrode pair may be selected to include at least one or both electrodes that are not coupled to the cardiac electrical event detector circuit of ICD 14, at least at the time of TCC transmission, so that TCC signals that are unintentionally received by the cardiac event detector are received via a transimpedance pathway from the transmitting electrode vector to the sensing electrode vector rather than directly through the sensing electrode impedance.

[0053] In other examples, however, the TCC transmitting electrode vector may include one or more electrodes coupled to a cardiac electrical event detector included in ICD 14. A transmitting electrode vector may include electrodes coupled to the ICD sensing circuitry when the resulting transmitting electrode vector is optimal in other ways, e.g., low impedance and high transimpedance. Transmission of TCC signals using one or both electrodes included in a sensing electrode vector coupled to a cardiac event detector circuit may be selected in a trade-off for optimizing other considerations in achieving reliable TCC signal transmission and reception.

[0054] In one example, defibrillation electrode 24 may be selected in combination with housing 15 for transmitting TCC signals to pacemaker 114. In other examples, TCC signals may be transmitted by ICD 14 using defibrillation electrode 26 and housing 15 or using two defibrillation electrodes 24 and 26. The transmitting electrode vector impedance (delivered voltage divided by delivered current) may be up to hundreds of ohms. The transimpedance of the TCC pathway that includes a transmitting electrode vector including one defibrillation electrode 24 or 26 paired with housing 15 may be less than 10 ohms and even less than 1 ohm. A high transimpedance at the TCC signal transmission frequency is desired to produce a relatively high voltage on the receiving electrodes for a given injected current of the TCC signal.

[0055] The electrode pair selected for transmitting TCC signals may include one or both of pace/sense electrodes 28 and 30 in some examples. For example, the pace/sense electrode 28 or 30 may be paired with housing 15, defibrillation electrode 24 or defibrillation electrode 26 for transmitting TCC signals. The impedance of the transmitting electrode vector may be increased due to the relatively smaller surface area of pace/sense electrodes 28 and 30, which may have the effect of lowering the injected current during TCC signal transmission and thereby lowering the received voltage signal at the receiving electrode vector.

[0056] ICD 14 may be configured to select a TCC transmitting electrode vector from among multiple possible vectors using electrodes 24, 26, 28, 30 and housing 15 to achieve the highest TCC signal strength at the receiving electrodes of pacemaker 114 and/or minimize TCC signal interference with cardiac event detection, impedance monitoring, or other functions performed by the ICD sensing circuit and/or by a sensing circuit of pacemaker 114. In some examples, multiple vectors may be used to transmit TCC signals to cover different angles in three-dimensional space to achieve at least one TCC transmitting electrode vector that is substantially electrically parallel to the receiving electrode vector during a time window of the cardiac cycle and/or respiration cycle. Multiple TCC transmitting/receiving electrode vectors may be tested during the set up procedure for identifying a TCC vector that is associated with optimized TCC communication during at least a portion of cycle of cyclical signal.

[0057] TCC performance may be considered optimized based on a number of factors such as relatively high TCC signal strength received by the receiving device, relatively high signal margin or any other signal strength metric described herein, relatively low TCC power required by the receiving and/or transmitting medical device for achieving a specified signal margin, relatively low TCC failure rate, or tradeoff combinations of any of the foregoing. TCC performance may be optimized using techniques disclosed herein within time constraints of a particular application which may require communication that occurs at least a given time interval prior to the start of the next cycle of a cyclical signal or other timing related constraints that enable coordination of monitoring and/or therapy delivery functions between two devices, e.g., ICD 14 and pacemaker 114.

[0058] In the example shown, lead 16 extends subcutaneously or submuscularly over the ribcage 32 medially from the connector assembly 27 of ICD 14 toward a center of the torso of patient 12, e.g., toward xiphoid process 20 of patient 12. At a location near xiphoid process 20, lead 16 bends or turns and extends superiorly, e.g., subcutaneously or submuscularly over the ribcage and/or sternum or substernally under the ribcage and/or sternum 22. Although illustrated in FIG. 2 as being offset laterally from and extending substantially parallel to sternum 22, the distal portion 25 of lead 16 may be implanted at other locations, such as over sternum 22, offset to the right or left of sternum 22, angled laterally from sternum 22 toward the left or the right, or the like. Alternatively, lead 16 may be placed along other subcutaneous, submuscular or substernal paths. The path of extra-cardiovascular lead 16 may depend on the location of ICD 14, the arrangement and position of electrodes carried by the lead body 18, and/or other factors.

[0059] The lead body 18 of lead 16 may be formed from a non-conductive material and shaped to form one or more lumens within which the one or more conductors extend. Lead body 18 may be a flexible lead body that conforms to an implant pathway. In other examples, lead body 18 may include one or more preformed curves. Electrical conductors (not illustrated) extend through one or more lumens of the elongated lead body 18 of lead 16 from the lead connector at the proximal lead end 27 to electrodes 24, 26, 28, and 30 located along the distal portion 25 of the lead body 18. The elongated electrical conductors contained within the lead body 18 are each electrically coupled with respective defibrillation electrodes 24 and 26 and pace/sense electrodes 28 and 30, which may be separate respective insulated conductors within the lead body 18. The respective conductors electrically couple the electrodes 24, 26, 28, and 30 to circuitry of ICD 14, such as a signal generator for therapy delivery and TCC signal transmission and/or a sensing circuit for sensing cardiac electrical signals and/or receiving TCC signals, via connections in the connector assembly 17, including associated electrical feedthroughs crossing housing 15.

[0060] The electrical conductors may transmit therapy from a therapy delivery circuit within ICD 14 to one or more of defibrillation electrodes 24 and 26 and/or pace/sense electrodes 28 and 30 and transmit sensed electrical signals from one or more of defibrillation electrodes 24 and 26 and/or pace/sense electrodes 28 and 30 to the sensing circuit within ICD 14. The electrical conductors also transmit TCC signals from a TCC transmitter to electrodes selected for transmitting the TCC signals. ICD 14 may receive TCC signals from pacemaker 114 conducted from a receiving pair of electrodes of ICD 14 to a TCC signal receiver enclosed by housing 15.

[0061] ICD 14 analyzes the cardiac electrical signals received from one or more sensing electrode vectors to monitor for abnormal rhythms, such as bradycardia, tachycardia or fibrillation. ICD 14 may analyze the heart rate and morphology of the cardiac electrical signals to monitor for tachyarrhythmia in accordance with any of a number of tachyarrhythmia detection techniques. ICD 14 generates and delivers electrical stimulation therapy in response to detecting a tachyarrhythmia, e.g., ventricular tachycardia (VT) or ventricular fibrillation (VF), using a therapy delivery electrode vector which may be selected from any of the available electrodes 24, 26, 28 30 and/or housing 15. ICD 14 may deliver ATP in response to VT detection, and in some cases may deliver ATP prior to a CV/DF shock or during high voltage capacitor charging in an attempt to avert the need for delivering a CV/DF shock. If ATP does not successfully terminate VT or when VF is detected, ICD 14 may deliver one or more CV/DF shocks via one or both of defibrillation electrodes 24 and 26 and/or housing 15. ICD 14 may generate and deliver other types of electrical stimulation pulses such as post-shock pacing pulses or bradycardia pacing pulses using a pacing electrode vector that includes any of electrodes 24, 26, 28, and 30 and/or the housing 15 of ICD 14.

[0062] ICD 14 is shown implanted subcutaneously on the left side of patient 12 along the ribcage 32. ICD 14 may, in some instances, be implanted between the left posterior axillary line and the left anterior axillary line of patient 12. ICD 14 may, however, be implanted at other subcutaneous or submuscular locations in patient 12. For example, ICD 14 may be implanted in a subcutaneous pocket in the pectoral region. In this case, lead 16 may extend subcutaneously or submuscularly from ICD 14 toward the manubrium of sternum 22 and bend or turn and extend inferiorly from the manubrium to the desired location subcutaneously or submuscularly. In yet another example, ICD 14 may be placed abdominally.

[0063] Pacemaker 114 is shown as a leadless intracardiac pacemaker configured to communicate via TCC with ICD 14 via housing-based electrodes in the examples presented herein. Pacemaker 114 may be delivered transvenously and anchored by a fixation member at an intracardiac pacing and sensing site. For example, pacemaker 114 may be implanted in an atrial or ventricular chamber of the patient’s heart. In other examples, pacemaker 114 may be attached to an external surface of heart 8 (e.g., in contact with the pericardium and/or epicardium) such that pacemaker 114 is disposed outside of heart 8.

[0064] Pacemaker 114 is configured to deliver cardiac pacing pulses via a pair of housingbased electrodes and may be configured to sense cardiac electrical signals for determining the need and timing of a delivered pacing pulse. For example, pacemaker 114 may deliver bradycardia pacing pulses, rate responsive pacing pulses, ATP, post-shock pacing pulses and/or other pacing therapies. Pacemaker 114 may include a TCC receiver that receives and demodulates TCC signals transmitted from ICD 14 and received by pacemaker 114 via housing-based electrodes. Pacemaker 114 may include a TCC transmitter that transmits TCC signals to ICD 14 via the housing-based electrodes. Pacemaker 114 may operate as a primary device during the set up procedure for establishing a TCC window by sensing a cardiac signal, e.g., an EGM signal or an accelerometer signal, for example, and analyzing a TCC signal received from ICD 14 throughout or at multiple time points of one or more cardiac cycles. Pacemaker 114 may transmit the timing of the TCC window to ICD 14, directly or indirectly via another implanted or external device (e.g., via external device 50 described below), using TCC or another communication method. In other examples, as described above, ICD 14 may operate as the primary device for establishing a TCC window based on analysis of a TCC signal received from pacemaker 114. Techniques for establishing a TCC window relative to a cycle of a cyclical signal such as a cardiac signal are described below, e.g., in conjunction with FIG. 7 and 10.

[0065] Pacemaker 114 may be implanted in the right atrium or the right ventricle of heart 8 to sense electrical activity of heart 8 and deliver pacing therapy. Pacemaker 114 may be implanted in the ventricle for sensing a ventricular EGM signal and deliver ventricular pacing pulses. In some examples, pacemaker 114 is implanted in the right atrium and configured for sensing a ventricular EGM signal and delivering ventricular pacing pulses. When implanted in the right atrium, pacemaker 114 may additionally or alternatively sense an atrial EGM signal and/or deliver atrial pacing pulses. ICD 14 may be configured to transmit TCC signals to pacemaker 114 implanted within the patient’s heart 8 to coordinate electrical stimulation therapy delivery and/or sensing and detection of cardiac rhythms. For example, ICD 14 may transmit command signals to cause pacemaker 114 to deliver a cardiac pacing pulse, ATP therapy, or request confirmation of sensed cardiac electrical events or a tachyarrhythmia detection.

[0066] An external device 50 is shown in telemetric communication with ICD 14 by a wireless communication link 42 and pacemaker 114 via a wireless communication link 44. External device 50 may include a processor 52, memory 53, display unit 54, user interface 56, telemetry unit 58 and other components for communicating with ICD 14 and/or pacemaker 114 for transmitting and receiving data via communication link 42 and 44, respectively. Communication link 42 or 44 may be established between ICD 14 or pacemaker 114, respectively, and external device 50 using a radio frequency (RF) link such as BLUETOOTH®, Wi-Fi, or Medical Implant Communication Service (MICS) or other RF or communication frequency bandwidth. In some examples, ICD 14 and/or pacemaker 114 may communicate with external device 50 using TCC, e.g., using TCC transmitting/receiving electrodes coupled to external device 50 and placed externally on patient 12.

[0067] External device 50 may be embodied as a programmer used in a hospital, clinic or physician’s office to retrieve data from ICD 14 and/or pacemaker 114 and to program operating parameters and algorithms in ICD 14 for controlling ICD functions and/or pacemaker 114 for controlling pacemaker functions. External device 50 may be used to program cardiac event sensing parameters (e.g., R-wave sensing parameters), cardiac rhythm detection parameters (e.g., VT and VF detection parameters) and therapy control parameters used by ICD 14. Data stored or acquired by ICD 14, including physiological signals or associated data derived therefrom, results of device diagnostics, and histories of detected rhythm episodes and delivered therapies, may be retrieved from ICD 14 by external device 50 following an interrogation command. External device 50 may alternatively be embodied as a home monitor or hand-held device, such as a smart phone, tablet or other hand-held device.

[0068] In some examples, pacemaker 114 may not be capable of bidirectional communication with external device 50. For example, due to size and/or power capacity limitations, pacemaker 114 may not communicate via RF telemetry with external device 50. ICD 14 may operate as a control device and pacemaker 114 as a responder. Pacemaker 114 may receive TCC communication signals from ICD 14 that include operating control data and commands (which may be transmitted from external device 50 to ICD 14) so that RF telemetry circuitry need not be included in pacemaker 114. Pacemaker 114 may transmit data, such as information related to delivered pacing therapy and/or acquired cardiac electrical signals on command from ICD 14 via TCC transmissions. ICD 14 may transmit data received from pacemaker 114 to external device 50 via RF communication. Alternatively, pacemaker 114 may periodically transmit data to ICD 14, which stores it until receiving a request from external device 50.

[0069] In other examples, pacemaker 114 may be configured to communicate with external device 50 via an RF communication method, e.g., BEUETOOTH®, and may be configured for one-way TCC communication with ICD 14 for receiving TCC signals from ICD 14. ICD 14 may transmit pacing commands (e.g., to trigger, schedule or withhold a pacing pulse) to coordinate therapy between ICD 14 and pacemaker 114 when an arrhythmia is detected by ICD 14. Pacemaker 114 may receive TCC signals from ICD 14 during a TCC window that is established by pacemaker 114 or ICD 14 according to the techniques disclosed herein.

[0070] FIG. 3 is a conceptual diagram of a leadless pacemaker 114 that may be included in a system configured to communicate via TCC according to some examples. The pacemaker shown in FIG. 3 may correspond to pacemaker 114 shown implanted in a ventricular heart chamber in FIGs. 1 and 2. However, in some examples pacemaker 114 may be configured for implantation in the right atrium (e.g., as pacemaker 112 shown in FIG. 1) for providing atrial pacing and/or ventricular pacing from a right atrial approach. Pacemaker 112 shown in FIG. 1 implanted in the right atrium and pacemaker 114 shown implanted in the right ventricle in FIGs. 1 and 2 may each include a housing 150 carrying housing based electrodes that do not require attachment of a lead as generally described in conjunction with FIG. 3. The type and location of housing based electrodes may be adapted for a particular implant location and sensing/pacing application. Other features of a leadless pacemaker such as fixation members, size, etc. may be adapted as necessary for a particular pacing and sensing application. As such, pacemaker 114 shown in FIG. 3 is illustrative in nature of a leadless pacemaker that can be one type of device that may be subjected to cyclical motion and can be included in a device system configured to perform TCC according to the techniques disclosed herein and is not intended to be limiting, particularly with regard to a specific implant location or features adapted for that implant location.

[0071] Pacemaker 114 includes a housing 150 having a distal end face 102 and a proximal end face 104. The lateral sidewall 170 of housing 150 extending from distal end face 102 to proximal end face 104 may be generally cylindrical to facilitate transvenous delivery, e.g., via a catheter, of pacemaker 114 to an implant site. Distal end face 102 is referred to as “distal” in that it is expected to be the leading end as pacemaker 114 is advanced through a delivery tool, such as a catheter, and placed against a targeted implant site. In other examples, housing 150 may have a generally prismatic shape. The housing 150 encloses the electronics and a power supply for sensing cardiac signals, producing pacing pulses and controlling therapy delivery and other functions of pacemaker 114 as described herein.

[0072] Pacemaker 114 is shown including electrodes 162, 164 and 165 spaced apart along the housing 150 of pacemaker 114 for sensing cardiac electrical signals and delivering pacing pulses. Pacemaker 114 may have more than or fewer than three electrodes, however. In another example, pacemaker 114 may only include electrodes 162 and 165 or only electrodes 162 and 164 for instance. Electrodes 162, 164 and 165 may be, without limitation, titanium, platinum, iridium or alloys thereof and may include a low polarizing coating, such as titanium nitride, iridium oxide, ruthenium oxide, platinum black, among others. Electrode 164, also referred to herein as “tip electrode” 164, is shown extending from distal end face 102 of housing 150. Tip electrode 164 is shown as a screw-in helical electrode which may provide fixation of pacemaker 114 at an implant site as well as serving as a pacing and sensing electrode. In some examples, pacemaker 114 may be implanted in the right atrium so that electrode 164 can be advanced from within the right atrial chamber to a ventricular pacing site, e.g., toward or into the interventricular septum, for delivering pacing to the His-Purkinje conduction system and/or for pacing of ventricular septal myocardial tissue. A proximal portion of tip electrode 164, nearest housing distal end face 102, may be provided with an electrically insulative coating. The more distal portion of tip electrode 164, positioned at a target pacing site, may be uninsulated to function as the electrically conductive portion of tip electrode 164 for pacing pulse delivery and for sensing cardiac electrical signals, e.g., a ventricular EGM signal. Examples of insulating coatings that may be provided on the proximal portion of tip electrode 164 include parylene, urethane, poly ether ether ketone (PEEK), or polyimide, among others. In other examples, tip electrode 164 is not necessarily a tissue piercing electrode as shown in this example. When implemented as a non-tissue piercing electrode, tip electrode 164 may be implanted in intimate proximity to myocardial tissue and held in a stable position via other fixation means, e.g., anchored in the atrium or the ventricle via fixation tines, for pacing atrial myocardium or ventricular myocardium respectively. [0073] Electrode 165 is shown as a ring electrode along the lateral sidewall 170 of housing 150. In other examples, electrode 165 may be a dot, button, ring, hemispherical, segmented or other type of electrode positioned on the distal end face 102 of housing 150 and/or along the lateral sidewall 170. Electrode 162 is shown as a ring electrode along the lateral sidewall 170 of housing 150 spaced proximally from electrode 165, toward proximal end face 104 of housing 150. In other examples, electrode 162 may be a dot, button, ring, hemispherical, segmented or other type of electrode positioned on the proximal end face 104 of housing 150 and/or along the lateral sidewall 170, spaced proximally and/or laterally from electrode 165. Electrodes 162 and 165 may both be ring electrodes circumscribing the lateral sidewall 170 in some examples, e.g., adjacent proximal end face 104 and adjacent distal end face 102, respectively. Other portions of housing 150 may be electrically insulated by an insulating coating. [0074] Tip electrode 164 may serve as a cathode electrode with ring electrode 162 serving as a return anode for delivering ventricular pacing pulses, which may be delivered to capture of at least a portion of the His-Purkinje system and/or ventricular myocardium. Tip electrode 164 and ring electrode 162 may be used as a bipolar pair for ventricular pacing and for receiving a ventricular electrical signal from which R-waves can be sensed by sensing circuitry enclosed by housing 150. When pacemaker 114 is implanted in the right atrium, electrodes 165 and 162 may form a second cathode and return anode pair for bipolar atrial pacing and sensing an atrial electrical signal from which P-waves can be sensed by the sensing circuitry enclosed by housing 150. In some examples, any combination of electrodes 162, 164 and 165 may be used in an electrode sensing vector for sensing one or more cardiac electrical signals from which P-waves and/or R-waves may be sensed.

[0075] Electrodes 162, 164 and 165 may be positioned at locations along pacemaker 114 other than the locations shown. Furthermore, in some examples, pacemaker 114 includes a distal tip electrode 164 and one proximal electrode 162 or 165. A TCC transmitting electrode pair and a TCC receiving electrode pair (which may or may not be the same electrode pair) may be selected from the available electrodes 162, 164 and 165. A sensing/pacing electrode pair and the TCC electrode pair carried by housing 150 may include no shared electrodes, one shared electrode or two shared electrodes in various examples. In some examples, at least one electrode pair may be carried by housing 150 for sensing cardiac signals and delivering cardiac pacing and another electrode pair may be carried by housing 150 as a TCC electrode pair. The sensing/pacing electrode pair and the TCC electrode pair may be dedicated electrode pairs or selectable from available electrodes carried by housing 150.

[0076] Pacemaker 114 may be configured to communicate with another leadless pacemaker implanted in the patient’s heart. For example, as shown in FIG. 1, one leadless pacemaker 112 may be implanted in the right atrium and one leadless pacemaker 114 may be implanted in the right ventricle. Pacemakers 112 and 114 may communicate via TCC for coordinating sensing of cardiac event signals and/or delivery of pacing pulses. For example, a pacemaker 112 implanted in the right atrium as shown in FIG. 1 may transmit a TCC signal to the second pacemaker 114 implanted in the right ventricle for coordinating atrial synchronous ventricular pacing and thereby provide a two-device dual chamber pacing system.

[0077] Housing 150 is formed from a biocompatible material, such as a stainless steel or titanium alloy. In some examples, the housing 150 may include an insulating coating. Examples of insulating coatings include parylene, urethane, PEEK, or polyimide, among others. The entirety of the housing 150 may be insulated, but only electrodes 162, 164 and 165 uninsulated. Electrodes 162, 164 and 165 are electrically coupled to internal circuitry, e.g., a pacing pulse generator and cardiac electrical signal sensing circuitry, enclosed by housing 150. Electrodes 162 and 165 may be formed as a conductive portion of housing 150 defining respective electrodes that are electrically isolated from each other and from the other portions of the housing 150 as generally shown in FIG. 3.

[0078] Pacemaker 114 may include features for facilitating deployment to and fixation at an implant site. For example, pacemaker 114 may optionally include a delivery tool interface 158. Delivery tool interface 158 may be located at the proximal end 104 of pacemaker 114 and is configured to connect to a delivery device, such as a catheter, guidewire or other tool used to position pacemaker 114 at an implant location during an implantation procedure. The delivery tool interface may enable a clinician to advance, retract and steer pacemaker 114 to an implant site and rotate pacemaker 114 to advance the helical tip electrode 164 into the cardiac tissue. Helical tip electrode 164 in this example provides fixation of pacemaker 114 at the implant site. In other examples, however, pacemaker 114 may include a set of fixation tines, hooks or other fixation members to secure pacemaker 114 to cardiac tissue. Numerous types of active and/or passive fixation members may be employed for anchoring or stabilizing pacemaker 114 in an implant position.

[0079] As generally described in conjunction with FIG. 5 below, a device included in a TCC system such as pacemaker 114 may include processing and control circuitry, memory, pulse generating circuitry for generating therapeutic electrical stimulation pulses, sensing circuitry for sensing physiological signals, TCC circuitry for transmitting and receiving TCC signals and a power source. In some examples, a pulse generator of pacemaker 114 includes a TCC transmitter (standalone or as part of a transceiver), such as the transmitter described below in conjunction with FIG. 6, for generating TCC signals transmitted via electrodes 162, 164 and/or 165. [0080] Pacemaker 114 may be configured for sensing cardiac electrical signals, e.g., R- waves or P-waves, attendant to intrinsic depolarizations of the myocardial tissue. In this way, pacemaker 114 may function as a primary device configured to sense a cyclical cardiac signal, identify cardiac cycles, and assess a received TCC signal strength during one or more identified cardiac cycles during a TCC set up procedure. The pacemaker 114 may establish a TCC window for conducting TCC communication with another device, e.g., pacemaker 112, ICD 14, or any other examples devices shown or described in conjunction with FIG. 1.

[0081] Pacemaker 114 may include a TCC receiver for receiving and detecting a TCC signal transmitted by another medical device, e.g., pacemaker 112, ICD 14 or any of the other examples described herein. A voltage potential that develops across an electrode pair, e.g., tip electrode 164 and ring electrode 162 or between ring electrodes 162 and 165, in response to current conducted via a tissue pathway during TCC signal transmission from another medical device. The voltage signal may be received and demodulated by the TCC receiver and decoded by processing circuitry of pacemaker 114. The TCC receiver may include amplifiers, filters, analog-to-digital converters, rectifiers, comparators, counters, a phase locked loop and/or other circuitry configured to detect a wakeup signal from a transmitting device and detect and demodulate a modulated carrier signal transmitted in data packets including encoded data. For example, a TCC receiver of pacemaker 114 (and other TCC receivers referred to herein) may include a pre-amplifier and a high-Q filter tuned to the carrier frequency of a carrier signal that is used to transmit wake up signals and data signals during a TCC session. The filter may be followed by another amplifier and a demodulator that converts the received signals to a binary signal representing coded data.

[0082] The circuitry of a TCC receiver may include circuitry shared with electrical signal sensing circuitry in some examples. The filters included in a TCC receiver and cardiac electrical signal sensing circuitry, however, are expected to operate at different passbands, for example, for detecting different signal frequencies. The TCC signals may be transmitted with a carrier frequency in the range of 33 to 250 kHz, in the range of 60 to 200 kHz, or at 100 kHz as examples. Cardiac electrical signals generated by heart 8 are generally less than 100 Hz. [0083] FIG. 4 illustrates a perspective view of a sensor 250 that may be configured to perform TCC according to one example. Sensor 250 is a pressure sensor but may be configured to additionally or alternatively sense temperature, pH, oxygen saturation, heart and/or respiration sounds, acceleration, impedance, or other physiological signals. As shown in FIG. 4, sensor 250 includes an elongated housing 251 having a sensing window 252 that exposes sensor elements to the surrounding environment to facilitate physiological signal sensing. In this example, sensing window 252 may be a pressure sensitive diaphragm that exposes a pressure sensitive element within housing 251 to the surrounding pressure, e.g., blood pressure when sensor 250 is implanted in the heart or a blood vessel. Electrodes 260 and 262 may be secured to opposite ends of housing 251 and may be electrically insulated from housing 251 to form an electrode pair for transmitting and/or receiving TCC signals. Electrodes 260 and 262 may be coupled to TCC circuitry enclosed by housing 251. TCC circuitry that may be included in sensor 250 is generally described below, e.g., in conjunction with FIGs. 5 and 6.

[0084] Housing 251 may enclose a battery, physiological signal sensing circuitry such as a pressure sensing circuit, a TCC transceiver, processing and control circuitry, and memory for storing operating parameters such as TCC control parameters and data such as pressure signal data, etc. In some examples, the pressure sensing circuit includes an air gap capacitive element and associated circuitry, which may include temperature compensation circuitry, for producing a signal correlated to pressure along window 252. The pressure sensing circuit may include a micro electro-mechanical system (MEMS) device in some examples. A fixation member 270 extends from housing 251 and may include a selfexpanding stent or one or more self-expanding loops 272 that stabilize the position of sensor 250, e.g., along an arterial lumen, such as within the pulmonary artery, by gently pressing against the interior walls of the artery. When deployed in an arterial location, sensor 250 may sense and store pressure signals correlated to arterial blood pressure. [0085] Sensor 250 may include a TCC transmitter or transceiver, such as the transmitter shown in FIG. 6 below, for transmitting TCC signals to another medical device, such as ICD 14, pacemaker 114 or external device 50. Sensor 250 may transmit data extracted from a pressure signal and/or other sensed physiological signal(s) and/or other communication data in a TCC signal via electrodes 260 and 262. For instance, sensor 250 may include a TCC transmitter or transceiver for at least producing acknowledgment and/or confirmation signals transmitted back to a transmitting device, e.g., ICD 14 or pacemaker 114, in response to receiving a TCC signal to confirm detection of a wakeup signal and/or reception of transmitted data packets.

[0086] FIG. 5 is a conceptual diagram of a device 214 capable of performing TCC according to some examples. For the sake of convenience, the device 214 of FIG. 5 is generally described as being a cardiac pacing device or ICD coupled to electrodes 224, 226, 228, and 230, with the device housing 215 represented conceptually as an electrode available for sensing, electrical stimulation pulse delivery and, in some examples, as a receiving and/or transmitting electrode during TCC. As such, device 214 is referred to herein as an “implantable medical device” or IMD 214. It is to be understood, however, that the circuitry and components shown in FIG. 5 may generally correspond to circuitry included in any of the example devices referred to herein and can be adapted for performing physiological signal sensing and/or therapy delivery functions according to a particular clinical application for signal monitoring and/or therapy delivery. For instance, a device configured to perform TCC functions disclosed herein may have more or fewer electrodes than the four electrodes 224, 226, 228 and 230 shown in FIG. 5. At least two electrodes are available for performing TCC transmission and receiving functions. The TCC electrodes may be leadless, housing-based electrodes and/or carried by a lead extending away from the device housing. Furthermore, as described above, in other examples the electrodes may be skin or surface electrodes or transcutaneous electrodes when device 214 is an external device.

[0087] IMD 214 may include a control circuit 80, memory 82, therapy delivery circuit 84, sensing circuit 86, sensors 87, RF telemetry circuit 88, TCC circuit 90 and power source 89. Power source 89 provides power to the circuitry of IMD 214, including each of the circuits 80, 82, 84, 86, 87, 88 and 90 as needed. Power source 89 may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between power source 89 and each of the other circuits 80, 82, 84, 86, 87, 88 and 90 are to be understood from the general block diagram of FIG. 5 but are not shown for the sake of clarity. For example, power source 89 may be coupled to charging circuits included in therapy delivery circuit 84 for charging capacitors or other charge storage devices and activating output switching circuitry included in therapy delivery circuit 84 for producing electrical stimulation pulses such as CV/DF shock pulses and pacing pulses. Power source 89 is coupled to TCC circuit 90 for providing power for generating TCC signals by transmitter 91 and powering TCC receiver 92. Power source 89 provides power to processors and other components of control circuit 80, memory 82, amplifiers, analog-to-digital converters and other components of sensing circuit 86, any additional sensors 87 optionally included in IMD 214 and a transceiver of RF telemetry circuit 88, when included, as examples.

[0088] Memory 82 may store computer-readable instructions that, when executed by a processor included in control circuit 80, cause IMD 214 to perform various functions attributed to IMD 214 (e.g., sensing physiological signals, TCC communication with another device, and/or delivery of an electrical stimulation therapy). Memory 82 may include any volatile, non-volatile, magnetic, optical, or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically erasable programmable ROM (EEPROM), flash memory, or any other digital or analog media.

[0089] Control circuit 80 may communicate with therapy delivery circuit 84 and sensing circuit 86 for sensing cardiac electrical activity, detecting cardiac rhythms, and controlling delivery of cardiac electrical stimulation therapies in response to sensed cardiac signals. The functional blocks shown in FIG. 5 represent functionality included in IMD 214 and may include any discrete and/or integrated electronic circuit components that implement analog and/or digital circuits capable of producing the functions attributed to IMD 214 herein. Providing software, hardware, and/or firmware to accomplish the described functionality in the context of any modem medical device system, given the disclosure herein, is within the abilities of one of skill in the art.

[0090] Sensing circuit 86 may be selectively coupled to electrodes 224, 226, 228, 230 and/or housing 215 in order to monitor electrical activity of the patient’s heart. Sensing circuit 86 may include switching circuitry for selecting which of electrodes 224, 226, 228, 230 and housing 215 are coupled to sense amplifiers or other cardiac event detection circuitry included in event detector 85. Switching circuitry may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple sense amplifiers to selected electrodes. The event detector 85 within sensing circuit 86 may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), or other analog or digital components configured to detect a feature from a sensed physiological signal to enable processing circuitry of control circuit 80 to identify cycles of a cyclical physiological signal. In the example of IMD 214 sensing one or more cardiac electrical signals (e.g., an ECG or EGM), cardiac electrical event signals attendant to myocardial depolarizations, e.g., P- waves attendant to atrial depolarizations and/or R-waves attendant to ventricular depolarizations, may be sensed from a cardiac electrical signal received via a sensing electrode vector for use in identifying cardiac cycles by control circuit 80.

[0091] In some examples, sensing circuit 86 includes multiple sensing channels for acquiring cardiac electrical signals from multiple sensing vectors selected from electrodes 224, 226, 228, 230 and housing 215. Each sensing channel may be configured to amplify, filter, digitize and rectify the cardiac electrical signal received from selected electrodes coupled to the respective sensing channel to improve the signal quality for sensing cardiac event signals, e.g., P-waves and/or R-waves. For example, each sensing channel in sensing circuit 86 may include an input or pre-filter and amplifier for receiving a cardiac electrical signal developed across a selected sensing electrode vector, an analog-to-digital converter, a post-amplifier and filter, and a rectifier to produce a filtered, digitized, rectified and amplified cardiac electrical signal that is passed to event detector 85. The event detector 85 may include a sense amplifier, comparator or other circuitry for comparing the cardiac electrical signal to a cardiac event sensing threshold, such as a P-wave sensing threshold amplitude or an R-wave sensing threshold amplitude, which may be an auto-adjusting threshold. Event detector 85 may produce a sensed cardiac event signal in response to a sensing threshold crossing. The sensed cardiac events, e.g., R-waves and/or P-waves, can be used by control circuit 80 for determining a heart rate, detecting cardiac rhythms and determining a need for a pacing and/or CV/DF therapy.

[0092] TCC circuit 90 may receive sensed cardiac event signals directly from sensing circuit 86 or from control circuit 80 for use in establishing TCC windows by processing circuitry included in TCC circuit 90 during a TCC set up procedure as described below. In other examples, TCC circuit 90 and control circuit 80 may operate cooperatively for establishing TCC windows based on sensed event signals received from sensing circuit 86 for identifying cycles of a cardiac signal (or other cyclical signal sensed by sensor(s) 87) and TCC signals received from a transmitting device during the TCC set up procedure. TCC circuit 90 may control TCC receiver 92 and/or transmitter 91 to receive and/or transmit TCC signals, respectively, during a scheduled TCC window applied during one or more cardiac cycles during a TCC session based on the timing of sensed event signals produced by sensing circuit 86.

[0093] Control circuit 80 may include interval counters, which may be reset upon receipt of a cardiac sensed event signal from sensing circuit 86. The value of the count present in an interval counter when reset by a sensed R-wave or P-wave, for example, may be used by control circuit 80 to measure the cardiac cycle length, e.g., durations of R-R intervals, or P-P intervals, which are measurements that may be stored in memory 82. Control circuit 80 may use the count in the interval counters to detect a tachyarrhythmia event, such as fibrillation or tachycardia. These intervals may also be used in establishing, scheduling and applying TCC windows used by TCC circuit 90 for transmitting and/or receiving TCC signals.

[0094] The therapy delivery circuit 84 is configured to generate cardiac electrical stimulation pulses, e.g., CV/DF shock pulses and cardiac pacing pulses for delivery to the patient’s heart via selected electrodes 224, 226, 228, 230 and/or 215. Therapy delivery circuit 84 may include one or more energy storage elements, such as one or more capacitors, configured to store the energy required for a therapeutic CV/DF shock or pacing pulse. In response to detecting a shockable tachyarrhythmia, control circuit 80 controls therapy delivery circuit 84 to charge the energy storage element(s) to prepare for delivering a CV/DF shock. Therapy delivery circuit 84 may include other pulse generating circuitry, such as a transformer, charge pump, charge storage capacitors and switches to couple the charge storage capacitors to electrode terminals via an output capacitor or other output circuitry such as an H-bridge to discharge and deliver the electrical stimulation pulses. Therapy delivery circuit 84 may include voltage level- shifting circuitry, switches, transistors, diodes, or other circuitry as needed for generating and delivering electrical stimulation pulses. In some examples, therapy delivery circuit 84 may include both a low voltage therapy circuit for generating and delivering relatively low voltage therapy pulses, such as cardiac pacing or other neurostimulation pulses, and a high voltage therapy circuit for generating and delivering CV/DF shocks or other relatively higher voltage stimulation pulses which may include cardiac pacing pulses delivered via extra-cardiac electrodes as described in conjunction with FIG. 2. [0095] In some examples, IMD 214 can be configured to monitor the impedance of an electrode vector. For example, therapy delivery circuit 84 may apply a current drive signal to a pair of electrodes coupled to IMD 214. Sensing circuit 86 may detect the resulting voltage developed across the pair of electrodes. Impedance monitoring may be performed for detecting a lead or electrode issue and for selecting a therapy delivery electrode vector, a TCC transmitting or receiving electrode vector, or a sensing electrode vector based at least in part on the lead/electrode impedance. In other examples, IMD 214 may be configured to monitor bioimpedance in a tissue volume, e.g., thoracic impedance or cardiac impedance, for monitoring a patient condition. The impedance signal may be a cyclical physiological signal sensed by IMD 214. The impedance signal may be used for identifying cardiac and/or respiration cycles that may cause motion of TCC electrodes. The impedance signal may be sensed by IMD 214 for identifying cycles of a cyclical physiological signal during a TCC set up procedure and for scheduling TCC sessions as described below.

[0096] TCC transmitter 91 is configured to generate TCC signals for transmission from a transmitting electrode vector selected from the electrodes 224, 226, 228, 230 and housing 215 via a conductive tissue pathway. TCC transmitter 91 is configured to generate and transmit a TCC signal to communicate with another implanted or external device. In some examples, TCC circuit 90 includes switching circuitry for selectively coupling TCC transmitter 91 to a selected transmitting electrode vector, e.g., using any two or more of electrodes 224, 226, 228, 230 and housing 215.

[0097] The TCC signal may be transmitted by TCC circuit 90 having a carrier signal, which may have a peak-to-peak amplitude and carrier frequency selected to avoid stimulation of excitable tissue, e.g., nerve, smooth muscle, skeletal muscle or cardiac tissue, of the patient. In some examples, the carrier frequency of the TCC signal may be 100 kilohertz (kHz) or higher. A TCC signal emitted or received, for example by a TCC electrode pair, at a frequency of at least approximately 100 kHz may be less likely to stimulate nearby tissue, e.g., muscles or nerves, or cause pain than lower frequency waveforms. Consequently, a TCC signal having a frequency of at least approximately 100 kHz may have a higher amplitude than a lower frequency signal without causing extraneous nerve or muscle stimulation. A relatively higher amplitude signal may increase the likelihood that another medical device successfully receives the TCC signal from IMD 214. The peak-to-peak amplitude of the TCC signal may be within a range from approximately 100 microamps to 10 milliamps (mA) or more, such as within a range from approximately 1 mA to approximately 10 mA. In some examples, the amplitude of the TCC signal may be approximately 3 mA. A TCC signal having a frequency of at least approximately 100 kHz and an amplitude no greater than approximately 10 mA may be unlikely to stimulate nearby tissue, e.g., muscles or nerves, or cause pain. For a transmitting electrode vector having an impedance of 200 ohms injecting a current signal having an amplitude of 10 mA peak-to-peak, the voltage signal at the transmitting electrode vector may be 2 Volts peak-to-peak. The voltage developed at the receiving electrode vector may be in the range of 0.1 to 100 millivolts peak-to-peak, as illustrative examples. However, it is contemplated that other frequencies and amplitudes of TCC signals may be used in conjunction with the techniques disclosed herein.

[0098] The TCC circuit 90 may transmit a TCC signal as a modulated signal in some examples. Amplitude modulation (AM), frequency modulation (FM), or digital modulation (DM), such as frequency- shift keying (FSK) or phase-shift keying (PSK) may be performed by TCC circuit 90. In some examples, the modulation can be FM toggling between two frequencies, e.g., toggling between approximately 100-150 kHz and approximately 200-250 kHz. In some examples, the TCC signal has a frequency of 150- 200 kHz and is modulated using FSK modulation at 12.5 kbps. In other examples, a TCC signal having a carrier frequency of 100 kHz is modulated to encode data using binary phase shift keying (BPSK). Balanced pulses of opposite polarity may be used to shift the phase of the TCC signal, e.g., by 180 degrees positively or negatively, and balance the charge injected into the body tissue during the phase shift to minimize the likelihood of interfering with cardiac event sensing operations of sensing circuit 86. Techniques for BPSK modulation of the TCC carrier signal using charge balanced phase shifts are disclosed in U.S. Patent No. 11,110,279 (Roberts, et al.), incorporated herein by reference in its entirety. The data modulated on TCC signals, e.g., being sent to another device, may include wake up signals, commands to deliver a therapy, and/or commands to collect or send physiological signal data, as examples.

[0099] The TCC transmitter 91 illustrated in FIG. 5 may provide “one-way” or unidirectional TCC in some examples. Such a configuration may be used if, for example, the IMD 214 is configured as a control device to transmit a command or request to another device configured as a responder, e.g., to pacemaker 114 (FIGs. 1 and 2) or sensor 250 (FIGs. 1 and 3), to provide commands for pacing delivery or pressure signal acquisition, for instance. In other examples, TCC circuit 90 includes TCC receiver 92 to facilitate “two-way” TCC between IMD 214 and another device. IMD 214 may be configured to receive confirmation signals from the intended receiving device to confirm that a transmitted TCC signal was successfully received. In other examples, IMD 214 may receive commands or data via TCC receiver 92 from another device. A modulated or nonmodulated carrier signal may be received by TCC receiver 92 via TCC receiving electrodes (e.g., any of electrodes 224, 226, 228, 230 and/or housing 215) selectively coupled to TCC circuit 90. TCC receiver 92 may include an amplifier, filter and demodulator to pass the demodulated signal, e.g., as a stream of digital values, to control circuit 80 for decoding of the received signal and further processing as needed. In other examples, TCC receiver 92 may be included in or share sensing circuitry with sensing circuit 86. TCC transmitter 91 may be included in or share signal generating circuitry with therapy delivery circuit 84.

[0100] Memory 82 may be configured to store a variety of operational parameters, therapy parameters, sensed and detected data, and any other information related to the monitoring, therapy and treatment of the patient. Memory 82 may store, for example, thresholds and parameters used in determining a need for therapy from a sensed physiological signal and control parameters used in controlling therapy delivery. Memory 82 may store communications transmitted to and/or received from another device via TCC.

[0101] As described below, memory 82 may store signal strength data determined from a received test TCC signal during a set up procedure. Signal strength data may be stored for each of multiple time points relative to a cycle of a cyclical signal that causes motion of the IMD 214 or another device that IMD 214 is capable of communicating with via TCC. Processing circuitry of control circuit 80 may analyze the received TCC signal to determine signal strength metrics for establishing a TCC window of the cyclical cycle during which TCC is conducted after the set up procedure is completed. The processing circuitry may determine an optimal transmit power, receiver sensitivity, and/or data rate in addition to establishing a TCC window. These TCC control parameters may be stored in memory 82 for use by control circuit 80 and TCC circuit 90 for performing TCC. [0102] IMD 214 may be equipped with one or more other physiological sensors 87 for sensing physiological signals, such as an accelerometer, pressure sensor, temperature sensor, oxygen saturation sensor, gyroscope, heart sound sensor or the like. In some examples, IMD 214 includes a multi-axis, e.g., three dimensional, accelerometer for sensing patient posture. The alignment and proximity of TCC electrodes used by IMD 214 with the TCC electrodes of a second device communication with IMD 214 may be influenced by patient posture changes. During the TCC set up procedure, a TCC window of a cyclical signal may be established for each of multiple different patient postures. The TCC window may be stored in memory 82 with an associated patient posture determined at the time of the set up procedure. At the time of a TCC session scheduled after the set up procedure, processing circuitry of control circuit 80 may redetermine the patient posture from an accelerometer signal received from sensors 87. TCC circuit 90 may operate to transmit and/or receive TCC data during the TCC window of the cyclical signal that is established for the corresponding patient posture.

[0103] In some examples, the TCC transmitting and receiving TCC electrode vectors that result in a relatively high received TCC signal strength at the receiving TCC electrode pair may be different for one patient posture than for another patient posture. As such, the TCC set up procedure may include testing multiple combinations of transmitting and/or receiving TCC electrode vectors and identifying a transmitting electrode vector and/or receiving electrode vector associated with a received signal strength at the receiving electrode vector that is the highest or at least greater than a specified level or signal margin. At the time of a TCC session scheduled after the set up procedure, processing circuitry of control circuit 80 may redetermine the patient posture from an accelerometer signal received from sensors 87. TCC circuit 90 may operate to transmit and/or receive TCC data during the TCC window of the cyclical signal that is established for the corresponding patient posture using a TCC electrode vector identified as being optimal or acceptable for the given patient posture.

[0104] In other examples, IMD 214 includes at least a single axis accelerometer for sensing patient physical activity. The optimal TCC window and/or other TCC control parameters may change with changing patient physical activity level. For example, a decreased data rate or increased transmit power to offset a reduced or variable received TCC signal margin may be used during a high level of patient activity. [0105] IMD 214 may optionally have an RF telemetry circuit 88 including an antenna and transceiver for RF telemetry communication with another implanted or external device, e.g., with external device 50 shown in FIG. 2. RF telemetry circuit 88 may include an oscillator and/or other circuitry configured to generate a carrier signal at the desired frequency. RF telemetry circuit 88 further includes circuitry configured to modulate data, e.g., stored physiological and/or therapy delivery data, on the carrier signal. The modulation of RF telemetry signals may be, as examples, AM, FM, or DM, such as FSK or PSK.

[0106] In some examples, RF telemetry circuit 88 is configured to modulate the TCC signal for transmission by TCC transmitter 91. Although RF telemetry circuit 88 may be configured to modulate and/or demodulate both RF telemetry signals and TCC signals within the same frequency band, e.g., within a range from approximately 150 kHz to approximately 200 kHz, the modulation techniques for the two signals may be different. In other examples, TCC transmitter 91 includes a modulator for modulating the TCC signal. [0107] FIG. 6 is a conceptual diagram of TCC transmitter 91 of TCC circuitry that may be included in a device performing TCC according to some examples. TCC transmitter 91 may include a controller 93, drive signal circuit 94, polarity switching circuit 95, alternating current (AC) coupling capacitor 96, protection circuit 97 and voltage holding circuit 98. In other examples, TCC transmitter 91 may include fewer or more components than the circuits and components shown in FIG. 6. IMD power source 89 is shown coupled to TCC transmitter 91 to provide power necessary to generate TCC signals. While the controller 93, drive signal circuit 94, polarity switching circuit 95, AC coupling capacitor 96, protection circuit 97 and voltage holding circuit 98 are shown as discrete circuits by the blocks in FIG. 6, it is recognized that these circuits may include common components or a common circuit may perform the functions attributed to the separate circuit blocks shown in FIG. 6. For example, generating a carrier signal having a carrier frequency and a peak-to-peak amplitude may be performed by drive signal circuit 94 and polarity switching circuit 95 under the control of controller 93.

[0108] Controller 93 may include a processor, logic circuitry, data registers, a clock circuit and/or other circuitry or structures for providing the functionality attributed to controller 93 herein. Controller 93 may include a dedicated clock circuit 93 for generating clock signals used to control the frequency of the transmitted TCC signals. In other examples, controller 93 may be implemented within control circuit 80. Controller 93 may include a clock circuit configured to provide a clock signal that may be used to transmit the TCC signal during an established TCC window of a cyclical physiological signal and may be used for transmitting the TCC signal using more than one frequency. For example, TCC transmitter 91 may be configured to provide a clock signal that may be used to transmit the TCC signal using at least three different frequencies, the TCC signal being modulated using FSK during a wakeup mode (e.g., modulating the signal using two different frequencies) and switch to a data transmission mode that includes transmitting data packets using a carrier signal at a third frequency (e.g., modulated using BPSK or other modulation technique). To illustrate, a wake up or beacon signal for establishing a communication session may be transmitted using high and low alternating frequencies, which may be centered on the frequency of the carrier signal. The wake up signal may be followed by a request to establish a TCC session, sometimes referred to as an “OPEN” request or command, transmitted at the carrier frequency. A clock signal generated by controller 93 may be required to enable generation of at least three different frequencies of the TCC signal produced by drive signal circuit 94 and polarity switching circuit 95 and passed to AC coupling capacitor 96 in this particular example.

[0109] After switching from the wakeup mode to a data transmission mode, e.g., after receiving an acknowledgement signal from the other device, the TCC transmitter 91 may be configured to transmit subsequent TCC signals at the carrier frequency, different than the distinct high and low frequencies used during the wake up signal transmission. The carrier signal can be modulated using BPSK in some examples such that the TCC signals are transmitted using a single frequency during the data transmission mode. In some examples, a wakeup mode during which a wake up or beacon signal is transmitted and received by two devices communicating via TCC is optional in that the two devices may power up TCC circuitry for transmitting and/or receiving according to a scheduled TCC window relative to a sensed cyclical signal, which may be sensed by both devices. [0110] TCC transmitter 91 is shown coupled to a transmitting electrode vector 99 including electrode 224 and housing 215 in this example. It is to be understood that TCC transmitter 91 may be coupled to one or more TCC transmitting electrode vectors selected from any of the available electrodes coupled to the transmitting device via switching circuitry included in TCC circuit 90. Controller 93 may be configured to switchably connect a transmitting electrode vector 99 to TCC transmitter 91 for transmission of TCC signals, e.g., by controlling switches included in TCC circuit 90. Controller 93 may select a transmitting electrode vector from among multiple electrodes coupled to the transmitting device, which may include electrodes carried by the housing of the transmitting device, a transvenous or non-transvenous lead, or in some cases cutaneous or surface electrodes. The transmitting electrode vector 99 may be selected based on a patient posture determined by control circuit 80 based on a signal from sensor(s) 87.

[0111] Drive signal circuit 94 may include a voltage source and/or a current source powered by power source 89. In one example, drive signal circuit 94 may be an active drive signal circuit generating a balanced, bi-directional drive current signal to balance the return current with the drive current for a net zero DC current injected into the body tissue via transmitting electrode vector 99. In another example, the drive signal circuit 94 may include a charge pump and a holding capacitor that is charged by the charge pump to generate a current signal that is coupled to the transmitting electrode vector 99. In yet another example, drive signal circuit 94 may include a current source that is used to charge a holding capacitor included in drive signal circuit 94.

[0112] The drive signal generated by drive signal circuit 94 may be a voltage signal in some examples. In the illustrative examples presented herein, the drive signal circuit 94 generates a current signal to deliver TCC signal current through the transmitting electrode vector 99 having a desired peak-to-peak amplitude, e.g., high enough to produce a voltage signal on receiving electrodes of a receiving device that is detectable by the receiving device, which may be any of the example devices listed herein. The peak-to-peak current amplitude is low enough to avoid or minimize the likelihood of stimulation of tissue. A carrier signal that may be generated by drive signal circuit 94 and polarity switching circuit 95 may have a peak-to-peak amplitude in a range from approximately 1 mA to approximately 10 mA, such as approximately 3 mA peak-to-peak, as discussed above. The voltage developed at the receiving electrode vector may be in the range of 0.1 to 100 millivolts peak-to-peak.

[0113] Polarity switching circuit 95 receives the drive signal from drive signal circuit 94 and includes circuitry configured to switch the polarity of the drive signal current at a carrier frequency of the TCC signal. For example, polarity switching circuit 95 may include transistors and/or switches configured to switch the polarity of the drive current signal at the frequency of the TCC signal. In some examples, polarity switching circuit includes a respective one or more transistors and/or switches coupled to each of electrode 224 and housing 215, and the on-off states of the respective transistor(s) and/or switch(es) are alternated to switch the polarity of the TCC signal current between the electrodes at the carrier frequency. As discussed above, the carrier frequency may be approximately 100 kHz. For example, the carrier frequency may be within a range from approximately 33 kHz to approximately 250 kHz.

[0114] In some examples, RF telemetry circuit 88 (FIG. 5) may include a mixed signal integrated circuit or other circuitry configured to provide a digital version of the modulated TCC signal to controller 93. In other examples, controller 93 is configured to produce the digital input signal for modulating the TCC carrier signal to encode communication data in the transmitted signal. Controller 93 controls one or both of drive signal circuit 94 and polarity switching circuit 95 to modulate the TCC carrier frequency signal to generate the modulated TCC signal with an amplitude, phase shifts and/or frequency according to the encoding. For example, controller 93 may control polarity switching circuit 95 to toggle the frequency of the carrier signal according to FSK modulation to encode the communication data. In another example, controller 93 may control polarity switching circuit 95 to switch the polarity of the current signal after a desired portion of the carrier frequency cycle length to shift the phase of the current signal by 180 degrees according to BPSK modulation.

[0115] Polarity switching circuit 95 is capacitively coupled to the transmitting electrode vector 99 (e.g., electrode 224 and housing 215 in the example shown) via AC coupling capacitor 96. AC coupling capacitor 96 couples the current signal output from polarity switching circuit 95 to the transmitting electrode vector 99 to inject the current into the conductive body tissue pathway. AC coupling capacitor 96 may include one or more capacitors coupled in series with one or each of the electrodes included in electrode vector 99. The AC coupling capacitor 96 is charged to a DC operating voltage at the beginning of a TCC signal. AC coupling capacitor 96 is selected to have a minimum capacitance that is based on the frequency and the peak-to-peak current amplitude of the carrier signal being used to transmit wake up and data signals. As examples, AC coupling capacitor 96 may have a capacitance of at least one nanofarad and up to ten microfarads for coupling a carrier signal having a frequency between 25 kHz and 250 kHz and peak-to-peak current amplitude of 100 microamps to 10 milliamps. Larger capacitances may be used but may increase the time required to charge the AC coupling capacitor to a DC operating voltage. [0116] During a ‘ ‘cold start,” e.g., at the beginning of a TCC transmission session when AC coupling capacitor 96 is uncharged, the charging of AC coupling capacitor 96 to the DC operating voltage may result in a low frequency current being injected into the body through the transmitting electrode vector. This low frequency current is more likely to interfere with the operation of sensing circuitry, e.g., sensing circuit 86 of FIG. 5, or other electrophysiological signal sensing circuits included in co-implanted IMDs or external devices coupled to the patient. Electrophysiological signal sensing circuits of intended or unintended receiving devices may operate in a low frequency band, e.g., 1 to 100 Hz. As such, low frequency artifact at the start of TCC signal transmission, during charging of the AC coupling capacitor 96, may interfere with electrophysiological signal sensing. After the DC operating voltage is established on AC coupling capacitor 96, the high frequency carrier signal, e.g., 100 kHz, is typically above the operating bandwidth of electrophysiological sensing circuitry and unlikely to cause interference or false event detection.

[0117] TCC transmitter 91 may include a voltage holding circuit 98 coupled to AC coupling capacitor 96. Voltage holding circuit 98 may be configured to hold the AC coupling capacitor 96 at the DC operating voltage between transmitted TCC signals during a TCC transmission session, e.g., between TCC windows established according to the techniques described below) and/or between TCC transmission sessions. By holding the AC coupling capacitor at a DC voltage during time intervals between TCC signal transmissions, interference with sensing circuitry that may otherwise occur due to the low frequency artifact injected during charging of the AC coupling capacitor 96 to the DC operating voltage is minimized or avoided.

[0118] Examples of circuitry that can be included in voltage holding circuit 98 are described in U.S. Patent No. 11,213,684 (Peichel, et al), incorporated herein by reference in its entirety. In some examples, voltage holding circuit 98 may include circuitry for floating AC coupling capacitor 96 at the DC voltage between TCC signal transmissions. In other examples, voltage holding circuit 98 may include circuitry to actively hold the AC coupling capacitor 96 at a DC voltage between TCC signal transmissions, e.g., between TCC windows of different cycles of a cyclical signal. A variety of circuitry may be conceived for preventing or minimizing discharging of AC coupling capacitor 96 between TCC signal transmissions. In this way, at the start of transmitting the next TCC signal the AC coupling capacitor 96 is already at or near the DC operating voltage. Without having to re-establish the DC voltage on the AC coupling capacitor 96, low frequency artifact injected into the TCC tissue pathway at the onset of the next TCC signal transmission is avoided or minimized. It is recognized that leakage currents may still exist within TCC transmitter 91 and may cause some discharge of AC coupling capacitor 96 between signal transmissions. Voltage holding circuit 98 may be used to minimize any discharge of AC coupling capacitor 96 between transmitted TCC signals to minimize low frequency interference with sensing circuit 86 (FIG. 5) of the transmitting device as well as sensing circuits of other co-implanted IMDs and/or external device coupled to the patient.

[0119] In other examples, TCC transmitter 91 may be configured to generate individual TCC signal pulses, each having a pulse width and a pulse amplitude, that may be delivered as a single pulse or as a series or train of pulses that may be encoded based on amplitude, pulse number, pulse frequency, time intervals between individual pulses or pulse trains or other attributes of the TCC signal pulses for communicating data or commands to another device. TCC transmitter 91 may generate TCC signal pulses without necessarily generating a carrier signal that oscillates at a carrier frequency about a central amplitude (e.g., zero amplitude).

[0120] The TCC transmitter 91 may include protection circuit 97 that allows the delivery of the TCC signal via electrodes coupled to other IMD circuitry but protects the TCC transmitter 91 and other circuitry of the IMD 214 from voltages that may develop across the electrodes, e.g., during a CV/DF shock delivered by therapy delivery circuit 84 or an external defibrillator as well as high voltages that may develop across the TCC transmitting electrode vector during other situations such as an electrocautery procedure or magnetic resonance imaging. The circuitry within housing 215 of IMD 214 protected by protection circuit 97 may include circuitry of any of the components of IMD 214 illustrated in FIG. 5, such as control circuit 80, memory 82, sensing circuit 86, therapy delivery circuit 84, and RF telemetry circuit 88.

[0121] Protection circuit 97 may be coupled between drive signal circuit 94 and the transmitting electrode vector 99, e.g., between AC coupling capacitor 96 and electrode vector 99 as shown. In some examples, protection circuit 97 may include circuitry before and/or after AC coupling capacitor 96. Protection circuit 97 may include, as examples, capacitors, inductors, switches, resistors, and/or diodes. Examples of TCC signal generation and protection circuitry that may be utilized in conjunction with the signal transmission techniques disclosed herein are generally described in U.S. Patent No. 9,636,511 (Carney, et al.), incorporated herein by reference in its entirety.

[0122] TCC transmitter 91 may be controlled by control circuit 80 to transmit data via TCC during TCC windows of a cyclical signal, e.g., during one or more cardiac cycles or respiration cycles. The TCC windows can be identified as being time windows associated with an optimized TCC signal strength, which may or may not be a maximized TCC signal strength, received by the receiving device. In some examples, TCC transmitter 92 may be controlled by control circuit 80 to transmit TCC signals using a transmit power that is selected based on the strength of the received signal during the TCC window of a cyclical signal. The TCC window and the TCC transmit power may be optimized to produce a received TCC signal at a receiving pair of electrodes that at least meets a minimum specified signal margin. In some cases, the TCC transmit power is minimized to conserve power source 89 (FIG. 5) while promoting at least a minimum specified signal margin of the TCC signal received by another device during an established TCC window. In other examples, the TCC transmit power may be selected to maximize the received TCC signal strength at a receiving pair of electrodes of another device.

[0123] FIG. 7 is a flow chart 300 of a method that may be performed by a medical device included in a device system configured to communicate via TCC. For the sake of convenience the process of FIG. 7 is described with reference to a “primary device” and a “secondary device.” The primary device is configured to sense a cyclical signal associated with a physiological function that subjects the primary device and/or the secondary device to cyclical motion. The cyclical motion such as cardiac motion or respiratory motion may cause cyclical changes in the alignment of the TCC transmitting and receiving electrodes of the primary and secondary devices during a TCC session. Accordingly, during the TCC set up procedure of FIG. 7, the primary device, e.g., IMD 214 of FIG. 5, may determine one or more time points in a cycle of the cyclical signal that are associated with at least an acceptable received TCC signal strength, e.g., a specified threshold amplitude, signal margin or other specified signal strength metric. The one or more time points may be used for scheduling future TCC sessions by the primary and/or the secondary device. [0124] A device in the TCC system is designated as the “primary device” for the purposes of the TCC set up process of FIG. 7 when it is configured to sense a cyclical physiological signal that corresponds to body or tissue motion that is imparted on the primary and/or secondary device. In some cases, the secondary device may be subjected to the cyclical motion but may not be configured to sense the cyclical signal. In other instances, the primary device is subjected to the cyclical motion and configured to sense the cyclical signal. In still other examples, both the primary device and the secondary device may be subjected to the cyclical motion and be configured to sense the associated cyclical signal. In this case, the selection of which device is the primary device may be arbitrary or may be based on other device capabilities or capacity. For example, when both the primary and the secondary devices are subjected to cardiac motion and are configured to sense a cardiac signal, the primary device may have greater memory capacity, processing capacity and/or power capacity than the secondary device and therefore be configured to operate as the primary device for analyzing received TCC signals during the TCC set up procedure of FIG. 7 for establishing a TCC window for subsequent or future TCC sessions.

[0125] When the primary device and/or secondary device is implanted in or on the heart, within the thoracic cavity, in or along an artery, or another location that subjects the primary device and/or secondary device to cardiac motion or pulsatile motion associated with the heartbeat, the primary device may be configured to sense a cardiac signal, e.g., a cardiac electrical signal such as an EGM or ECG, a blood pressure signal, a heart sound signal, a cardiac motion signal such as an accelerometer signal, gyroscope signal, impedance signal or another signal that varies cyclically with the heartbeat.

[0126] The primary device and/or the secondary device may additionally or alternatively be subjected to respiratory motion. In this case, the primary device may be configured to sense a physiological signal that varies cyclically with the respiration cycle, e.g., a thoracic impedance signal or any of the cardiac signals listed above that may be filtered to remove the cardiac cycle changes to obtain cyclical baseline variations due the respiration cycle. [0127] While examples described in conjunction with FIGs. 7-9 primarily refer to sensing a cyclical physiological signal using electrodes or other sensors, it is to be understood that when the primary device delivers an electrical stimulation therapy, e.g., cardiac pacing or diaphragm pacing, the cycles of the cyclical signal may be identified based on the timing of the delivered pacing pulses. As such, when cycles of a cyclical signal are identified by a primary device performing the method of FIG. 7, for example, the cycles may be pacing evoked cycles or intrinsic cycles, e.g., of a cardiac or respiration cycle.

[0128] In some cases, the primary device and the secondary device may both be configured to sense a cyclical signal associated with body or tissue motion that may cause cyclical changes in the relative alignment and/or proximity of the TCC transmitting and receiving electrodes of each device. In this case, the process of FIG. 7 may optionally be performed with a first device designated as the primary device and a second device designated as the secondary device and then repeated with the first device designated as the secondary device and the second device designated as the primary device.

[0129] At block 302, a TCC session is initiated for setting up TCC parameters that promote reliable signal reception at a receiving device during TCC sessions. The TCC parameters may be selected for reducing system power consumption required for TCC and/or promoting at least a specified signal strength or signal margin at the receiving electrodes of a receiving device during TCC. The TCC session is initiated at block 302 by enabling the secondary device to be the transmitting device and enabling the primary device to be the receiving device. The TCC session may be initiated at block 302 upon user command or at a scheduled time of day or at scheduled TCC set up intervals. For example, the process of flow chart 300 may be performed once per hour, once per day, once per week or at other scheduled time intervals to promote reliable TCC when subsequent TCC sessions are scheduled during one or more future cycles of the cyclical signal for transmitting data between the primary and secondary devices. In other instances, the process of flow chart 300 may be triggered when a failed communication is identified or, for example, when a transmitting device fails to receive a confirmation signal from a receiving device or when a receiving device has not received an expected communication. Other triggering conditions may include detecting a physiological condition that may alter the received TCC signal strength such as patient posture, patient physical activity, thoracic impedance (e.g., due to changes in lung wetness or dryness or cardiac volume), patient weight, a change in the rate and/or amplitude of the cyclical physiological signal, or any other condition that may alter the impedance of a TCC transmission pathway and/or the alignment of TCC electrodes between the two communicating devices.

[0130] When the TCC session is initiated, the secondary device may begin transmitting a test TCC signal at block 302. In some examples, the test TCC signal is a continuous signal that is transmitted for a specified time interval that is expected to encompass at least one cycle of the cyclical signal being sensed by the primary signal. In other examples, the test TCC signal may be a transmitted according to a duty cycle for a specified time period that is expected to encompass at least one cycle of the cyclical signal. Multiples duty cycles may occur during the specified time period such that multiple duty cycles may occur during each cycle of the cyclical signal. The test TCC signal may be transmitted at a maximum transmit power, minimum transmit power or at a nominal or default transmit power in various examples.

[0131] The test TCC signal may be a modulated or non-modulated carrier signal or series of TCC pulses. For instance, the test TCC signal may be a frequency modulated signal to enable the primary device to positively confirm receipt of the test TCC signal and distinguish the test TCC signal from noise or other electrical signals that may be received at the TCC receiving electrodes of the primary device. In some examples, the test TCC signal may be a frequency shift keying (FSK) or phase shift keying (PSK) modulated signal, e.g., a binary phase shift keying (BPSK) modulated signal, to enable the TCC receiver of the primary device to demodulate the received TCC signal for confirming that the signal is the expected test TCC signal and not noise or other electrical signal artifact at the TCC receiving electrodes.

[0132] The primary device senses the cyclical, physiological signal associated with cyclical motion that may be imparted on the primary device and/or secondary device at block 304. The cyclical signal may be any of a number of cyclical physiological signals that may be sensed by the primary device and associated with body or tissue motion imparted on the primary and/or secondary device, such as any of the example cyclical physiological signals listed or referred to herein.

[0133] At block 306, the primary device receives the TCC signal transmitted by the secondary device during at least a portion of each of one or more cycles of the sensed cyclical signal. The primary device may be configured to enable its TCC receiver to receive a TCC signal during a receiving window that begins at an identified starting point of a cycle of the cyclical signal and ends at the identified starting point of the next cycle of the cyclical signal. In other examples, the primary device TCC receiver may be enabled to receive the TCC during multiple consecutive or non-consecutive cycles of the sensed cyclical signal. In some examples, one continuous receiving window is applied during at least a portion of each of one or more cycles of the cyclical signal. In other examples, the primary device TCC receiver may be enabled to receive according to a duty cycle so that the transmitted test TCC signal can be received during multiple spaced apart receiving windows distributed through each of one or more cycles of the sensed cyclical signal. The primary device may enable the TCC receiver for multiple time windows that randomly or chronologically march through multiple cycles of the cyclical signal so that the TCC test signal can be received at different time points during each of multiple cycles of the cyclical signal. In some examples, the test TCC signal is received at multiple time points relative to the cardiac cycle during one or more respiration cycle, e.g., during multiple cardiac cycles that occur at different time points of the respiration cycle. The TCC receiver sensitivity may be set to a greatest sensitivity, a lowest sensitivity or a nominal or default sensitivity for receiving the TCC test signal.

[0134] At block 308, processing circuitry of the primary device may determine one or more signal strength metrics of the received test TCC signal at multiple time points or intervals of the cyclical signal. As an illustrative example, the processing circuitry may determine a signal strength metric at 10 ms, 20 ms, 50 ms, 100 ms or 200 ms intervals relative to a starting time of a cycle of the cyclical signal. It is to be understood that the size of the sampling intervals at which the received test TCC signal is analyzed may depend on the cycle length of the cyclical signal and other factors. The signal strength metrics determined for each sample time or interval by the processing circuitry of the primary device may include a peak-to-peak amplitude, a maximum peak amplitude, a baseline noise amplitude, a signal margin (e.g., determined as the difference between the baseline noise amplitude and the maximum peak amplitude), a margin factor determined as the ratio of the peak signal amplitude to the TCC receiver sensitivity, and/or a signal to noise ratio (e.g., determined as the ratio of the maximum peak amplitude to the baseline noise amplitude). With reference to FIG. 5, the control circuit 80 may determine the signal metric(s) from the test TCC signal received at multiple time points of the cyclical signal and store the determined signal metrics in memory 82 with a corresponding reference time relative to the starting time of a cycle of the cyclical signal, which may be stored as an absolute time from the starting time of the cycle or as percentage of the cycle length.

[0135] The signal metrics may be determined from the received test TCC signal at multiple time points within a given cycle of the cyclical signal. The signal metrics may be determined from the received test TCC signal at multiple time points received during multiple cycles of the cyclical signal. In other examples, the signal strength metric(s) may be determined from the received test TCC signal at one time point per cycle of the cyclical signal for multiple cycles. The time point at which the signal strength metric(s) is/are determined during each individual cycle may be varied between the multiple cycles to obtain a sampling of the received TCC signal strength at different time points relative to the repeating cycle, e.g., the cardiac cycle or respiration cycle. In some examples, the signal strength metrics may be determined at multiple time points relative to a cardiac cycle and relative to a respiration cycle. For example, the signal strength metrics may be determined for multiple time points relative to a cardiac cycle for multiple cardiac cycles occurring at different times relative to a respiration cycle.

[0136] At block 310, the processing circuitry of the primary device may determine a maximum signal strength metric from the signal strength metrics determined at block 308. The maximum signal strength metric may be the greatest peak amplitude, greatest peak-to- peak amplitude, greatest signal margin, greatest margin factor, or greatest signal to noise ratio identified from the signal strength metrics determined at block 308 and stored in device memory. It is recognized that if a baseline noise amplitude is determined as a signal strength metric at different time points in the cyclical signal, the minimum (rather than the maximum) baseline noise amplitude may be identified at block 310. The processing circuitry may determine if the maximum signal strength metric meets at least a specified minimum threshold at block 310. If not, the transmit power of the secondary device may be increased (in response to a signal transmitted from the primary device) and/or receiver sensitivity may be increased by the primary device at block 314. The process may return to block 306 to receive the TCC signal during one or more cycles of the cyclical signal.

[0137] In other examples, instead of or in addition to determining a maximum signal strength metric, the processing circuitry of the primary device may identify the signal strength metrics that meet at least a minimum acceptable threshold, e.g., a minimum acceptable signal margin or margin factor. The processing circuitry may identify each time point relative to a cycle of the cyclical signal at which the signal strength metric(s) meet at least a specified minimum acceptable threshold at block 310. For example, each time point in a cycle of the cyclical signal that is associated with a specified minimum margin factor may be identified at block 310. [0138] In some examples, the process of flow chart 300 may be performed with the TCC transmit power of the secondary device at a minimum and/or the TCC receiver sensitivity at a minimum in order to identify time points in a cycle of the cyclical signal associated with at least a specified minimum signal margin (or other signal strength metric) when TCC power requirements for transmitting and/or receiving are minimized. When the specified minimum signal margin (and/or other signal strength metric) is not met at any time during a cycle of the cyclical signal, or at any time of the cycle that is a feasible communication time for the clinical application of interest, the transmit power (of the secondary device) and/or receiver sensitivity (of the primary device) may be increased, and the process of flow chart 300 may be repeated. A feasible communication time for a given clinical application may depend on other operations being performed by the two communicating devices that may interfere with TCC communications or tie up processing circuitry for other functions. A feasible communication time for a given clinical application may relate to coordinating timing of events or operations performed by the communicating devices based on the TCC communication. For instance, a latest time point in a cardiac cycle may be defined for transmitting a pace command for triggering or scheduling a pacing pulse to be delivered by a receiving device before the next intrinsic cardiac cycle begins.

[0139] In some examples, if a different transmitting electrode pair (of the secondary device) and/or receiving electrode pair (of the primary device) is available, a different transmitting and/or receiving electrode pair may be selected at block 314 when the signal strength metrics do not meet a specified minimum at any time point of the cycle of the cyclical signal being evaluated. Various combinations of transmitted electrode vector, receiving electrode vector, transmit power and/or receiver sensitivity may be tested during the process of flow chart 300 until at least one time point of the cycle of the cyclical signal is identified as being associated with signal strength metrics that meet at least a specified signal margin, margin factor, received signal amplitude, or other criteria for acceptable received TCC signal strength or any combination thereof.

[0140] It is to be understood that the process of transmitting test TCC signals that are received at block 306, determining signal metrics, and comparing signal metrics to each other and/or to minimally acceptable thresholds may be performed multiple times for multiple available transmitting electrode vectors, multiple available receiving electrode vectors, multiple transmit powers and/or multiple receiving sensitivities. In some examples, when all combinations to be tested is complete, the processing circuitry may identify a combination associated with at least one time point in a cycle of the cyclical signal that is associated with a maximized signal strength metric or a signal strength metric that at least meets a specified minimum. In other examples, the process of receiving the test TCC signal at block 306 and determining signal strength metrics for different transmit powers, transmitting electrode vectors, receiver sensitivities, and/or receiving electrode vectors may be repeated only when a first combination results in signal strength metrics that do not meet a specified minimum threshold at any time during the cycle of the cyclical signal, as determined at block 310.

[0141] At block 312, the primary device processing circuitry may establish one or more TCC windows during a cycle of the cyclical signal based on the signal strength metric(s) determined at block 308. A TCC window can be determined as a time interval during a cycle of the cyclical signal during which TCC signals may be transmitted and received with the greatest received signal strength. In other examples, the TCC window can be determined as one or more time intervals during a cycle of the cyclical signal during which the signal strength metrics meet at least a specified minimum value. The TCC window(s) established at block 312 may be used by the primary device and/or transmitted to the secondary device for use in scheduling future TCC sessions. A TCC window may be established having a starting time, center time or ending time, for example, based on a time point stored in the primary device memory in association with an identified maximum or acceptable signal strength metric.

[0142] In an illustrative example, when a maximum signal strength metric identified at block 310 occurs at 600 ms from the start of a cardiac cycle, the primary device processing circuitry may establish a TCC window that begins or is centered at 600 ms (plus or minus any desired offset). In some examples, the primary device processing circuitry may determine the TCC window as having a starting time that is scheduled at a percentage of the cycle length of the cyclical signal. To illustrate, if the maximum signal strength metric is identified when 60% of the cardiac cycle length has elapsed, the TCC window established at block 312 may have a starting or center time at 60% of the cardiac cycle length (plus or minus any desired offset). Sixty percent of the cardiac cycle length may be determined in milliseconds based on a preceding cardiac cycle when a TCC window is being scheduled for a future TCC session.

[0143] It is recognized that in some instances, the signal strength metrics determined at block 308 may be relatively constant throughout the cycle of the cyclical signal or meet at least a specified minimum value throughout the cycle. In this case, setting a TCC window relative to the cycle of the cyclical signal may be optional or arbitrary. TCC transmission may be started at any desired time relative to the cycle or independent of the timing of cycles of the cyclical signal. A trade off may exist between scheduling a relatively narrow TCC window during a limited portion of a physiological signal cycle for performing TCC when the received TCC signal strength is known to be maximized or relatively high (allowing minimized or reduced TCC power requirements for conserving the longevity of the power sources of one or both devices) and scheduling a relatively wide TCC window that may require higher transmit power and/or receiver sensitivity with greater power consumption but perhaps a likelihood of higher successful TCC transmission rates. As such, in some cases, when the signal strength metrics indicate an acceptable received signal strength through a cycle of the cyclical signal for a given TCC transmit and receiving electrode vector combination, TCC may be scheduled at any desired time during the cycles of the cyclical signal and may be independent of the timing of the cyclical signal events.

[0144] FIG. 8 is a diagram 400 of a test TCC signal 402 that may be transmitted by the secondary device during a TCC setup procedure and the corresponding received TCC signal 430 that may be received by the primary device according to some examples. The TCC transmitter of the secondary device may be configured to transmit a modulated or non-modulated beacon or other specified test signal, which may be transmitted with a maximum or relatively high transmit power during the TCC set up procedure, e.g., beginning at block 302 of FIG. 7. A relatively high transmit power may be used in order to promote a high likelihood of the TCC receiver of the primary device receiving the signal during at least a portion of the cyclical signal being sensed by the primary device. In other examples, a minimum or nominal or default transmit power may be used to transmit the test TCC signal.

[0145] The secondary device may transmit the TCC signal 402 as a continuous, nonmodulated signal, e.g., a continuous carrier signal having a constant frequency and amplitude. In other examples, the secondary device may transmit the TCC signal 402 as a continuous, modulated signal, e.g., a frequency or phase modulated signal such as an FSK, PSK or BPSK modulated signal as described above. In the example shown in FIG. 8, the test TCC signal 402 is a non-modulated signal, e.g., a carrier signal having a carrier frequency of oscillations about a central amplitude and between a maximum and minimum peak amplitude. In other examples, the test TCC signal may be series of signal pulses having a signal amplitude and pulse width that are transmitted as train(s) of pulses that can be separated by an inter-pulse interval.

[0146] In various examples, the secondary device may transmit the test TCC signal 402 in a manner that reduces the likelihood of electrical interference with physiological signal sensing circuitry of the secondary device and/or the primary device. In the example shown, TCC signal 402 is transmitted at a constant carrier frequency and amplitude 404 after a starting ramp up interval 406 and until an ending ramp down interval 408. The test TCC signal 402 may be a ramped signal, e.g., having a peak to peak amplitude that is ramped up over the starting ramp up interval 406. For instance, test TCC signal 402 may be digitally controlled to step up the peak-to-peak amplitude of the carrier signal in a manner that minimizes any low frequency current that may be received at sensing electrodes used for sensing electrophysiological signals, e.g., ECG, EGM, electroencephalogram signals or other neurological or muscle signals, or the like, to avoid interfering with electrophysiological signal sensing. The test TCC signal 402 may be stepped up in amplitude according to a step increment and step up interval over the ramp up interval 406 that results in changes in the voltage potential developed at a sensing electrode vector that can be below the sensitivity of the electrical signal sensing circuitry of the secondary and/or primary device. Examples of ramped TCC signals that may be implemented as test TCC signals transmitted by the secondary device during a TCC setup procedure are generally disclosed in U.S. Patent No. 11,045,654 (Peichel, et al.), incorporated herein by reference in its entirety. It is to be understood, however, that the amplitude of the test TCC signal is not necessarily ramped up or down in some examples. [0147] In other examples, the test TCC signal 402 transmitted by the secondary device during the TCC set up process of FIG. 7 may include an initial carrier cycle that is a quarter cycle of the carrier signal frequency. TCC signal 402 can be started with an initial pulse and ended with an ending pulse that each have a pulse duration that is one-quarter of the carrier frequency cycle length. In this way, the average DC voltage signal of a low pass filtered signal provided as input to sensing circuitry, e.g., cardiac electrical signal circuitry of the primary device, does not include a DC voltage shift (or only a negligible DC voltage shift). By delivering a starting pulse of TCC signal 402 having a net charge that is one-quarter the cycle charge of the carrier signal, the net charge injected into the body tissues via the transmitting electrode vector of the secondary device is quickly balanced during the next, second pulse of the TCC signal, which has the opposite polarity of the starting pulse and a pulse width that is half of the carrier signal cycle length. Any DC voltage shift at a receiving electrode vector coupled to sensing circuitry of the primary or secondary device is reduced, avoided or minimized. It is to be understood that when the initial cycle is a quarter cycle of the carrier frequency cycle length, a ramp up interval 406 of the test TCC signal 402 is not required. The initial cycle may have an amplitude that is half of the peak to peak amplitude 404 of the test TCC signal. The ramp off interval 408 may be optional. TCC signal 402 may have an ending amplitude that is equal to the peak- to-peak amplitude 404. The ending cycle may be a quarter cycle with an amplitude that is half of the peak to peak amplitude 404. Examples of TCC signals having a starting pulse that is a quarter cycle pulse of the carrier cycle that may be used in transmitting a test TCC signal are generally disclosed in the above-incorporated U.S. Patent No. 11,110,279 (Roberts, et al.).

[0148] Additionally or alternatively, the secondary device may start transmission of the test TCC signal during a blanking period applied to its own sensing circuitry. When the secondary device is configured to sense an electrophysiological signal, e.g., an ECG or EGM signal, a blanking period may be applied to the sensing circuitry during delivery of an electrical stimulation pulse and/or following a sensing threshold crossing during physiological refractory periods, for example. By starting the test TCC signal 402 during a blanking period, interference with electrical signals sensed by the secondary device may be avoided. In some cases, a blanking period applied by the secondary device may coincide with a blanking period applied by the primary device. For instance, if the secondary device delivers a cardiac pacing pulse followed by a post-pace blanking period or senses a cardiac event followed by a post-sense blanking period and the primary device senses a cardiac depolarization subsequent to the delivered pacing pulse or corresponding to the sensed cardiac event, the primary device may apply a post-sense blanking period. In this way, starting the test TCC signal 402 during a blanking period of the secondary device may avoid electrical interference due to electrical potential at sensing electrodes of the secondary and/or primary device that may occur at the onset of the test TCC signal.

[0149] The primary device in this example is configured to sense a cyclical signal as a cardiac electrical signal 410. The primary device may detect the beginning of each cardiac cycle, e.g., based on sensing the QRS waveform 412, or any other selected fiducial point of each cardiac cycle to mark the start of each cycle. For example, cardiac electrical signal sensing circuitry of the primary device may sense an R-wave based on an R-wave sensing threshold crossing by the cardiac electrical signal 410. The cardiac electrical signal sensing circuitry of the primary device may produce a ventricular sensed event signal 414 (denoted as “VS” in FIG. 8). The primary device may enable the TCC receiver to start one or more receiving windows 420 in response to the cardiac electrical signal sensing circuitry detecting the beginning of a cardiac cycle. For example, the control circuitry of the primary device may enable the primary device TCC receiver to power up for receiving a transmitted TCC signal in response to receiving a ventricular sensed event signal 414 from the cardiac electrical signal sensing circuitry.

[0150] In the example shown, the TCC receiver of the primary device may be duty cycled to receive a TCC signal during receiving windows 420 corresponding to an ON time 422. The ON time 422 of each duty cycle may be followed by an OFF time 424. The TCC receiver of the primary device may receive the transmitted test TCC signal 402 during the ON time 422 of each duty cycle as depicted by the received TCC signal 430 of FIG. 8. The TCC receiver of the primary device may be duty cycled to conserve power of the primary device and to provide sampling time intervals, corresponding to the ON time 422 spaced apart by the OFF time 424, for analyzing the received TCC signal 430 for assessing variations in signal strength over the cardiac cycle. However, as shown in the example of FIG. 9, the TCC receiver may be powered on for receiving a TCC signal at a selected starting point of a cycle of a sensed cyclical signal and may remain on in a receiving mode for the duration of one or more cycles of the cyclical signal.

[0151] The received TCC signal 430 may be analyzed by processing circuitry of the primary device for determining a signal strength metric of the received TCC signal at multiple time points during at least one cycle of the sensed cyclical signal. In the example of FIG. 8, a signal strength metric may be determined as the peak to peak amplitude 436 of the received signal during each (or sampled ones) of the receiving windows 420. In other examples, the signal strength metric may be determined as the maximum peak amplitude 435 of the received signal during each receiving window 422. A signal strength metric determined by the primary device processing circuitry may be margin factor determined as the ratio or difference between the received TCC signal amplitude and the receiver sensitivity. In some examples, an average baseline noise amplitude 434 may be determined by the primary device processing circuitry. A signal strength metric may then be determined as the signal margin 435 by determining the difference between the maximum peak amplitude 435 of the received TCC signal 430 during a receiving window and the baseline noise amplitude 434. In still other examples, a signal to noise ratio may be determined as the ratio of the maximum peak amplitude 435 of the received signal during a receiving window to the baseline noise amplitude 434. For the sake of illustration, the baseline noise amplitude 434 is depicted between receiving windows 420, during the OFF time interval 424 of the duty cycled TCC receiver. It is to be understood, however, that baseline noise may be present during the receiving windows 420 and not present during OFF times 424 between the receiving windows 420 when the TCC receiver may be powered down.

[0152] The primary device processing circuitry may store one or more signal strength metrics determined for each of the receiving windows 420 in primary device memory. The signal strength metric(s) stored for a given one of the receiving windows 420 can be stored with a corresponding time interval from the onset of the cardiac cycle. For example, the processing circuitry may store the time from the ventricular sensed event signal 414 to the onset of the respective one of receiving windows 420 with the associated signal strength data. The processing circuitry may be configured to identify one or more receiving windows 420 that correspond to a maximum signal strength metric. For instance, the receiving window 426 may be identified by the processing circuitry as having the greatest peak to peak amplitude 436 of the received TCC signal 430. The associated time interval 440 from the ventricular sensed event signal 414 to the start of receiving window 426 associated with the greatest signal strength metric may be used for establishing a TCC window used for scheduling future TCC sessions.

[0153] The time interval 440 (plus or minus a desired offset) may be used for setting a starting time for a TCC window following a future ventricular sensed event signal for scheduling a future TCC session. The TCC session may be scheduled over multiple cardiac cycles during a transmission or receiving window that is scheduled during each one of the multiple cardiac cycles based on time interval 440. In some examples the time interval 440 may be converted to a percentage of the cardiac cycle length 416 (an RR interval in this example). The percentage of the cardiac cycle length may be used to determine a time following a subsequent ventricular sensed event signal for starting a TCC window.

[0154] In other examples, the processing circuitry may compare the signal strength metrics to a minimum acceptable threshold. For example, threshold 438 may correspond to a minimum acceptable margin factor (e.g., at least a minimum multiple of the receiver sensitivity), minimum acceptable peak amplitude or minimum acceptable signal margin over baseline noise 434. The processing circuitry of the primary device may identify one or more time intervals of the cardiac cycle during which the signal strength metric(s) meet a respective minimum acceptable threshold 438. The time window(s) identified in one cardiac cycle as being associated with a signal strength metric meeting the minimum acceptable threshold 438 may be different than the time window(s) identified in a different cardiac cycle. Variation in identified time windows may occur due to signal strength variation that may occur with respiratory motion, patient physical activity, changes in baseline noise or other factors. As such, the processing circuitry may identify time windows associated with signal strength metrics that consistently meet the minimum acceptable threshold.

[0155] In some examples, the processing circuitry may identify cardiac cycles having relatively fewer or no time windows meeting the minimum acceptable threshold 438. When these cardiac cycles occur at a consistent time relative to the respiration cycle (which may be determined from filtering the cardiac cycle to detect oscillations in the cardiac cycle due to respiration), the relative timing in the respiration cycle may be identified as a time window of the respiration cycle that TCC is not acceptable. The TCC window(s) identified within a cardiac cycle based on signal strength metrics may not be scheduled during unacceptable portions of the respiration cycle to avoid variation due to respiration in the TCC signal strength that may cause signal drop out or failed TCC. Alternatively, time points of the respiration cycle that are associated with relatively higher signal strength metrics may be identified such that the TCC window established for the cardiac cycle can be scheduled for future TCC sessions during cardiac cycles that occur at the desired (e.g., higher signal strength) times of the respiration cycle.

[0156] As such, the test TCC signal 402 may be transmitted over one or more cycles of the sensed cyclical signal so that signal strength metrics may be obtained from multiple cycles of at least one sensed cyclical signal. In the example shown, the test TCC signal 402 is transmitted over more than one cardiac cycle, so that the primary device may accumulate received signal strength data for multiple cardiac cycles. In some cases, the secondary device may start transmitting the test TCC signal 402 at a time that does not necessarily coincide with the start of the receiving windows 420. One or more of the receiving windows 420 may be determined to have a zero signal strength or very low signal margin if transmission of the test TCC signal 402 has not started. In the example shown in FIG. 8, early receiving windows 420 that occur during the ramp up interval 406 may be associated with zero or very low signal strength metrics due to the low amplitude of the test TCC signal 402 during the ramp up interval 406. By transmitting the test TCC signal 402 during a continuous or discontinuous transmission window that encompasses multiple cycles of the cyclical signal, the primary device is enabled to determine signal strength metrics at sampling times or intervals that span a full cycle. The received TCC signal strength may be assessed at sample times throughout the cardiac cycle but those sample times may span more than one cardiac cycle.

[0157] The primary device processing circuitry may determine when receiving windows identified as being associated with the maximum signal strength metric(s) or minimally acceptable signal strengths during two more different cardiac cycles correspond to approximately the same time in the cardiac cycle. For example, in FIG. 8, receiving windows 426 and 428 during different cardiac cycles occur at about the same time in each respective cycle. When the time intervals 440 and 442 corresponding to receiving windows 426 and 428, respectively, are within a threshold difference of each other (e.g., + 10 ms, 20 ms, 50 ms or another defined time or percentage threshold), the primary device processing circuitry may determine a TCC window based on the average of the time intervals 440 and 442. In another example, when each of time intervals 440 and 442 correspond to the nth receiving window following the cycle onset, e.g., following a ventricular sensed event signal, the time intervals 440 and 442 may be averaged for use in establishing a TCC window for scheduling future TCC sessions. [0158] While time intervals 440 and 442 are shown as time intervals extending to the onset of the respective receiving window 426 and 428, it is recognized that the TCC window may be determined based on an average starting time, center time, or ending time of receiving windows 426 and 428 in various examples. The time intervals 440 and 442 may be converted to a percentage of the respective cardiac cycle length 416 and 418. The percentages may be averaged for use in establishing the timing of a TCC window during one or more cardiac cycles during a future TCC session.

[0159] The primary device processing circuitry may identify multiple TCC windows associated with the highest or acceptable signal strength metrics within one cycle of the cyclical signal. A threshold signal strength and/or threshold signal margin may applied to the signal strength metrics determined for each of the receiving windows 420. For example, the peak to peak amplitude 436, maximum peak amplitude 435, signal margin 437 and/or a signal to noise ratio determined for each of receiving windows 420 may be compared to a respective threshold, e.g., minimum acceptable threshold 438. The threshold may be established or specified based on an acceptable signal strength for a programmed, minimum or maximum TCC receiver sensitivity and/or for a programmed, maximum or minimum TCC transmit power being used or available for use by the primary and/or secondary devices. The threshold applied to a given signal strength metric may be based on the maximum value of the respective signal strength metric identified during one or more cycles. In the example of FIG. 8, a second receiving window 427 during the first cardiac cycle and a second receiving window 429 during the second cardiac cycle may be identified by the primary device processing circuitry as having a high or acceptable signal strength based on one or more signal strength metrics. For instance, each of the receiving windows 420 having a signal strength metric that is 80% or 90% or other threshold percentage of the maximum signal strength metric determined for receiving window 426 may be identified as acceptable receiving windows. In other examples, the first and second windows 426, 427, 428 and 429 may be used in establishing two TCC windows (or one longer TCC window) per cardiac cycle when the signal strength metrics for each of the windows 426, 427 238 and 429 meet the minimum acceptable threshold 438. In the example of FIG. 8, the second receiving windows 427 and 429 may be identified during the first and second cardiac cycles, in addition to the first receiving windows 426 and 428, for use in establishing at least one TCC window relative to the starting time of a cardiac cycle by the primary device processing circuitry.

[0160] The second receiving windows 427 and 429 may be used in combination with the first receiving windows 426 and 428 by the primary device processing circuitry for establishing one combined TCC window during each cardiac cycle or two separate TCC windows during each cardiac cycle. For instance, the primary device processing circuitry may establish two TCC windows that can be scheduled during a future cardiac cycle, one based on the timing of the first receiving windows 426 and 428 relative to the start of the cardiac cycle and a second TCC window based on the timing of the second receiving windows 426 and 428.

[0161] In other examples, the primary device processing circuitry may establish one TCC window to be scheduled during a future cardiac cycle based on both of the first and second receiving windows 426 and 427 of the first cardiac cycle and both of the first and second receiving windows 428 and 429 of the second cardiac cycle. For instance, a single TCC window may be established by the primary device processing circuitry that extends from the relative timing within a cardiac cycle of the averaged beginning times of receiving windows 426 and 428 to the relative timing within a cardiac cycle of the averaged ending times of receiving windows 427 and 429. A single TCC window may be established that encompasses the timing of the identified first and second receiving windows 426 and 427, for example. For instance, if receiving window 426 starts at 65% of the cardiac cycle length 416 and receiving window 427 ends at 110% of the cardiac cycle length 416, a TCC window may be established that starts at a time following the onset of a cardiac cycle that is 65% of the preceding cardiac cycle length and ends at a time from the onset of the cardiac cycle that is 110% (or less, e.g., between 70% and 100%) of the preceding cycle length.

[0162] The decision to define a single TCC window based on multiple receiving windows identified within a cardiac cycle as having high or acceptable signal strength based on determined signal strength metrics may be based on the number of intervening receiving window(s) and/or received signal metrics of the intervening receiving window(s). For example, if the signal strength and/or signal margin determined for the intervening receiving window 425 is determined to be at least an acceptable threshold, e.g., at least 50%, 60% or other threshold percentage of the maximum signal strength metric, a single TCC window encompassing the relative timing of receiving windows 425, 426 and 427 during a cardiac cycle may be established to provide a relatively long TCC window with a given cardiac cycle. However, if the signal strength and/or signal margin determined for the intervening receiving window 425 is determined to be less than an acceptable threshold, a single TCC window encompassing receiving windows 426 and 427 may not be established due to risk of signal drop out. Two separate TCC windows corresponding to the relative timing of the first receiving window 426 and the second receiving window 427 may be established, or only one TCC window corresponding to the timing of receiving window 426 having the highest signal strength metric(s) may be established. A decision by primary device processing circuitry to establish a TCC window based on a single receiving window or based on multiple receiving windows identified within a cycle of the cyclical signal may be based on the expected duration of a data packet transmission in some examples. If a relatively longer transmission time is needed than the ON time 422 associated with each of the receiving windows 420, multiple receiving windows identified as having acceptable signal strength metrics may be used in establishing one or more TCC windows scheduled during one or more cardiac cycles for future TCC sessions.

[0163] FIG. 9 is a conceptual diagram 450 of a test TCC signal 452 that may be transmitted during a TCC set up procedure and the received TCC signal 476 according to another example. The test TCC signal 452 is shown as a non-modulated carrier signal (having a carrier frequency of oscillations about a central amplitude) but may be a frequency or phase modulated signal as described above. Test TCC signal 452 may be started at a scheduled time, in response to a programming command or in response to a detected trigger condition, e.g., as further described below in conjunction with FIG. 12. Test TCC signal 452 may be transmitted for a time interval that is expected to extend for at least one cycle of a cyclical signal sensed by the primary device. In other examples, the test TCC signal 452 may be transmitted according to a specified duty cycle having ON and OFF periods that may be fixed or variable to promote receipt of the transmitted test TCC signal by the primary device at a variety of time points during the cyclical signal sensed by the primary device.

[0164] The primary device may be configured to enable its TCC receiver to receive the transmitted test TCC signal during a receiving window 470 that extends the entire duration of one cycle of the cardiac electrical signal 460. Instead of enabling the TCC receiver according to a duty cycle as illustrated in FIG. 8, the primary device may enable the TCC receiver to receive the transmitted test TCC signal 452 throughout the cardiac cycle length 468. Receiving window 470 may be started in response to ventricular sensed event signal 464 and may be terminated upon the next ventricular sensed event signal 466. While the ventricular cycles are defined according to sensed R-waves 462 in the examples described here, it is to be understood that other intrinsic cardiac event signals and/or delivered cardiac pacing pulses may be identified to mark the onset or end of a cardiac cycle.

[0165] The received TCC signal 476 may vary in signal strength over the receiving window 470 as cardiac motion causes variation in the alignment and/or proximity of the transmitting electrode pair of the secondary device and the receiving electrode pair of the primary device. The primary device processing circuitry may sample the received TCC signal 476 at sampling intervals during the receiving window 470 for determining signal strength metrics at each of multiple time points during the receiving window 470. A maximum signal strength metric may be identified, for example the maximum peak to peak amplitude 478, of the received TCC signal 476. A time interval 480 from the onset of the cardiac cycle to a time corresponding to the maximum signal strength metric may be determined by the primary device processing circuitry. The time interval 480 may be used by the processing circuitry for establishing a TCC window used for scheduling future TCC transmission sessions.

[0166] The primary device processing circuitry may determine when the signal strength metric falls below an acceptable threshold 490. The threshold 490 may be defined as a percentage, e.g., 90%, 80%, 70% or other percentage, of the maximum signal strength metric. The time interval 482 from the onset of the cardiac cycle until the time when the signal strength metric of the received TCC signal 476 falls below the threshold 490 may be determined by the primary device processing circuitry. The time interval 482 may be used by the primary device processing circuitry for determining an ending time of a TCC window.

[0167] In other examples, the primary device processing circuitry may identify a starting and ending time point, e.g., based on time intervals 480 and 482 respectively, of a time window during which a signal strength metric of the TCC signal meets at least a threshold 490. In this case, threshold 490 may correspond to a minimum signal amplitude or the received TCC signal amplitude when a minimum acceptable signal margin is met relative to baseline noise or a minimum acceptable margin factor is met relative to the receiver sensitivity as examples. The primary device may establish a TCC window based on time intervals during the cycle of the cyclical signal that a signal strength metric at least meets a minimum acceptable threshold.

[0168] In some examples, when the test TCC signal 452 is terminated, for example after a specified transmission time expires, the secondary device may enable its TCC receiver to listen for a confirmation signal from the primary device during a listening window 456. The primary device may control its TCC transmitter to transmit a cycle completion signal 472 after terminating receiving window 470. In response to receiving the cycle completion signal 472, the secondary device may stop sending test TCC signals, and the TCC set up procedure may be ended. If the cycle completion signal 472 is not received, the secondary device may start another test TCC signal. When the primary device has accumulated signal strength metrics from the received TCC signal 476 over a desired number of cardiac cycles for establishing the TCC window(s), the cycle completion signal 472 may be transmitted. It is to be understood, therefore, that while one cardiac cycle is shown in FIG. 9 for the sake of illustration, one or more test TCC signals may be transmitted over one or more cardiac cycles to enable the primary device to accumulate signal strength metrics determined at multiple time points relative to the cardiac cycle for use in establishing a TCC window.

[0169] FIG. 10 is a flow chart 500 of a TCC set up procedure according to another example. In some instances, the patient’s body posture and/or physical activity level can influence the relative alignment and/or proximity of the transmitting and receiving electrodes of the primary and secondary devices. As a result, the optimal time during a cyclical signal for TCC may change with changes in patient body posture (e.g., upright standing, upright sitting, prone, supine or side lying positions) and/or patient physical activity level (e.g., resting, activities of daily living, or exertion that is a higher level of activity than the activities of daily living range).

[0170] At block 502, the TCC set up procedure may be initiated based on a scheduled time of day, scheduled update time interval, a failed TCC communication, or other triggering condition (e.g., as described below in conjunction with block 512). The secondary device may begin transmitting a test TCC signal according to any of the examples given above. At block 504, at least one or both of the secondary and primary devices may determine a patient condition that may influence the received TCC signal strength. The patient condition may be determined from a signal sensed by sensors 87 (FIG. 5) or from a communication signal received via TCC or via other communication methods, e.g., RF communication.

[0171] In some examples, one or both of the primary and secondary devices may determine a patient condition, which may include determining any of a bioimpedance measurement, patient posture and/or a physical activity metric, e.g., from an accelerometer included in the sensing circuitry (e.g., sensors 87 in FIG. 5) of the respective primary and/or secondary device. For instance, the patient posture and/or the patient physical activity level may be determined by primary device processing circuitry from an accelerometer signal received from the primary device sensing circuitry, e.g., sensor(s) 87 shown in FIG. 5. In other examples, the primary device processing circuitry may determine the patient posture and/or the patient physical activity level from decoded data of a TCC signal received from the secondary device. When the secondary device determines the patient posture and/or patient physical activity level, the secondary device may transmit the determined posture and/or activity level to the primary device during the TCC set up procedure. In some examples, the patient condition may include a rate (or period) and/or amplitude of the cyclical physiological signal.

[0172] At block 506, the primary device receives the test TCC signal from the secondary device, while sensing a cyclical signal, for determining signal strength metrics as generally described above in conjunction with FIGs. 7-9. In some examples, more than one TCC receiving electrode vector of the primary device and/or TCC transmitting electrode vector of the secondary device may be tested during the set up procedure. The combination of the TCC receiving electrode vector and TCC transmitting electrode vector that results in a maximum received signal strength or optimized TCC power requirements for achieving at least an acceptable signal strength metric may vary with patient posture, physical activity, bioimpedance, and/or other patient conditions. As such, if a different TCC transmitting electrode vector and/or TCC receiving electrode vector is available, as determined at block 507, the secondary device may transmit test TCC signals using a different selected TCC transmitting electrode vector, and/or the primary device may receive test TCC signals using a different selected TCC receiving electrode vector. The processing circuitry of the primary device may determine signal strength metrics at block 505 for multiple combinations of transmitting and receiving TCC electrode vectors, if available. In other examples, if the signal strength metrics determined for a the first TCC electrode vectors tested, the processing circuitry of the primary device may establish a TCC window for the tested TCC electrode vectors without necessarily testing additional electrode vectors for TCC.

[0173] At block 507, the primary device processing circuitry may determine one or more TCC windows relative to a cycle of the cyclical signal based on a comparative analysis of the determined signal strength metrics according to any of the examples described above. The established TCC window(s) may be determined for the transmitting and receiving TCC electrode vector combination that resulted in the highest signal strength metric(s), longest TCC window associated with signal strength metrics meeting at least an acceptable threshold, minimum variability in received signal strength amplitude and/or other factors that promote reliable and/or power efficient TCC. The established TCC window(s) may be stored in memory with an indication of the determined patient condition, e.g., determined bioimpedance, patient posture, patient physical activity level or other patient condition.

[0174] At block 508, processing circuitry of the primary device and processing circuitry of the secondary device may select the TCC electrode vectors (when multiple vector combinations were tested), a TCC transmit power and/or TCC receiver sensitivity. The TCC transmit power and/or TCC receiver sensitivity which may be based on the received TCC signal strength determined for the established TCC window(s) and/or the power capacity of the primary device and the secondary device and which device is expected to be primarily receiving and which device is expected to be primarily transmitting during TCC sessions.

[0175] For example, if the primary device is expected to primarily be receiving data transmitted from the secondary device and has a higher power source capacity than the secondary device, the secondary device may set a transmit power relatively low and/or a receiver sensitivity relatively low. The primary device may set a receiver sensitivity relatively high and/or a transmit power relatively high. When the primary device has a lower power capacity, the secondary device may set a high transmit power for its TCC transmitter and a high receiver sensitivity so that the primary device may transmit at a relatively low power and receive with a relatively low receiver sensitivity. The processing circuitry of the primary device and/or secondary device may determine an optimal transmit power and receiver sensitivity based on the maximum received signal strength, a desired signal margin, margin factor, or signal to noise ratio and an acceptable power source longevity of each of the primary and secondary devices. An acceptable margin factor may be 1.5, 2, 3, 4, 5 or other selected value, that may be stored in hardware, firmware or software of the medical device and may be user programmable in some examples. The receiver sensitivity may be in the range of 0.001 to 1 root mean square millivolt (mVnns). In an example, the receiver sensitivity may be 0.025 rnVrms. The transmit power may be limited to a current and frequency that does not cause peripheral nerve stimulation or other unwanted excitation of nerve or muscle tissue. Transmit current may be in the range of 0.1 to 10 milliamperes (mA) with a frequency of 100 kHz as an example.

[0176] In some examples, the transmit power and receiver sensitivity may be selected by performing TCC test transmissions at block 508. For example, after establishing the TCC windows, the primary device may transmit a request signal to the secondary device during a TCC window of a subsequent cycle of the cyclical signal using a relatively high or maximum transmit power. Upon receipt of the request signal, the secondary device may transmit a confirmation signal using a relatively low or minimum transmit power. The primary device processing circuitry may verify that the signal strength of the received confirmation signal is at least an acceptable margin, e.g., a threshold percentage or offset greater than the receiver sensitivity. The receiver sensitivity may initially be set high to enable reception of low power TCC signals. The process of transmitting a request signal and receiving a confirmation signal from the secondary device may be repeated during multiple TCC windows to verify an acceptable received signal strength and margin greater than the receiver sensitivity (e.g., at least a specified margin factor of the ratio of the received signal strength to the receiver sensitivity). If the received signal strength is not acceptable, the primary device may transmit a request to the secondary device to increase its TCC transmit power. This process of requesting and receiving confirmation signals from the secondary device, including one or more adjustments to the transmit power by the secondary device as needed, may be repeated until the received signal strength is deemed acceptable by the primary device.

[0177] In other examples, the receiving device may determine an adjustment to the receiver sensitivity or to the transmit power based on a programmed required margin factor and the received margin factor determined from the received signal strength and receiver sensitivity. For instance, if a transmitted signal is determined to be 0.5 decibels higher than a programmed required margin factor, the receiver sensitivity could be reduced by 0.5 dB or the receiving device may transmit a signal to the transmitting device to adjust the transmit power down according to the determined difference.

[0178] Once the TCC window(s) is/are established for the determined patient condition, e.g., bioimpedance, patient posture and/or physical activity level, and the TCC electrode vectors for each of the primary and secondary devices and/or the transmit power and/or receiver sensitivity of one or both of the primary and secondary devices are optionally selected at block 508, these TCC control parameters may be used during future TCC sessions scheduled for exchanging data between the primary and secondary devices at block 510. Example methods for performing TCC according to an established TCC window are described below in conjunction with FIGs. 11 and 12.

[0179] At block 510, the primary device and/or secondary device may re-determine the patient condition, e.g., one or more of bioimpedance, patient posture, patient physical activity level, rate of cyclical signal, and/or amplitude cyclical signal. Prior to or at the start of a TCC session, and optionally during a TCC session, e.g., between TCC windows, the primary device and/or secondary device may re-determine the patient posture and/or physical activity level, bioimpedance or other patient condition for which the TCC control parameters have been established. When the patient condition remains unchanged compared to the condition determined at block 504 at the time that the TCC windows were established, the primary and secondary device may continue to communicate via TCC according to the control parameters established at block 507 and optionally block 508.

[0180] If the patient condition has changed, e.g., if the bioimpedance, patient posture and/or patient physical activity level have changed, the primary device may determine if a different TCC window has been previously established and stored in device memory for the newly detected patient condition. If so, the primary device may retrieve the established TCC control parameters from device memory at block 510 and continue TCC sessions according to the TCC control parameters previously established for the new patient condition.

[0181] It is to be understood that both the primary and the secondary device may be configured to detect a change in patient condition and operate to change to TCC control parameters according to these detected conditions. When only one of the primary device or the secondary is configured to be the detecting device for detecting a change in patient condition, the detecting device may transmit the detected change to the non-detecting device. In this way, if the non-detecting device needs to change a TCC control parameter, e.g., a TCC window and/or TCC electrode vector, it may select the new TCC control parameter(s) as stored in its device memory according to the patient condition information received from the detecting device.

[0182] In some patient positions or postures, the primary and secondary device may detect different postures due to the implant positions of the two devices relative to the patient’s anatomy. For example, in a sitting position a device implanted in the upper torso, head or neck may detect an upright, vertical position. A device implanted in the lower body, however, may detect a horizontal or other non-upright position. During some patient activities, one device may detect a higher level of activity than the other device due to relative differences in acceleration forces imparted on the two devices due to the patient’s body motion during the physical activity. As such, when the TCC window(s), TCC electrode vectors, and optionally the transmit power and/or receiving sensitivity control parameters are established for a given patient posture and/or physical activity level, each of the primary and the secondary device may determine a posture and a physical activity level which may be communicated between the two devices. The combination of postures detected by the two devices and/or the combination of physical activity levels determined by the two devices may be stored in association with the established TCC control parameters used at block 510 whenever the same combination of postures and/or physical activity levels are detected.

[0183] When a new patient condition is detected for which TCC control parameters are not established and stored in memory of the respective primary and/or secondary device, the primary and/or secondary device may detect a TCC set up trigger condition at block 512. The TCC set up procedure may be repeated by returning to block 502 to establish a TCC window and optionally select TCC electrode vectors, transmit power and receiver sensitivity settings for the newly detected patient condition, e.g., a different bioimpedance, patient posture, physical activity level, rate of cyclical signal, and/or amplitude of cyclical signal. In other examples, when a new or different patient condition is detected, TCC communication may be delayed until the same patient condition is redetected for which the TCC window(s) is(are) established. In this way, detection of a patient condition corresponding to an established TCC window may be required by at least one of the two devices communicating via TCC prior to performing TCC during the TCC window of one or more cycles of the cyclical signal.

[0184] The primary device and/or secondary device may be configured to determine if other TCC set up trigger conditions occur at block 512. A TCC set up trigger condition may be identified or detected at block 512 based on a scheduled time of day, expiration of a scheduled update interval, detection of a change in patient posture to a patient posture for which TCC control parameters have not been established as described above, detection of a change in patient physical activity for which TCC control parameters have not been established as described above, a failed TCC transmission, a depletion in a primary or secondary device power source to a replacement level or other threshold level, or other condition that may warrant re-establishing or updating TCC control parameters. In some examples, the primary or secondary device may sense a physiological signal that is related to a patient condition other than (or in addition to) patient posture and/or patient physical activity that could alter the received TCC signal strength during TCC operations. For example, lung wetness, cardiac volume, or tissue edema may be monitored based on a bioimpedance signal. Changes in the bioimpedance or conductivity of the tissue pathway of TCC signals may alter the received TCC signal strength. The primary and/or secondary device may be configured to monitor a patient physiological condition, such as a change in bioimpedance, patient posture, patient physical activity, or other patient condition, which may be detected as a trigger condition at block 512. When a set up trigger condition is detected, the TCC set up procedure may be repeated by returning to block 502. As long as a set up trigger condition is not detected or identified, the primary and secondary device may continue to communicate via TCC at block 510 according to the established TCC control parameters, which may be adjusted as needed between different TCC control parameters established for different patient postures and/or different patient physical activity levels or combinations thereof.

[0185] FIG. 11 is a flow chart 600 of a method for performing TCC by a medical device system according to some examples. At block 602 the primary device determines that it is time for a TCC session The primary device may operate to initiate a TCC session, e.g., by transmitting a wake up signal to the secondary device during one or more TCC windows. As used herein, the term “wake up” signal can refer to a signal transmitted from one device to the other to inform the other device that TCC is commencing and may indicate the timing of the TCC window(s). The “wake up” signal may be referred to as a “beacon signal” in that it provides an alert to the other device that TCC is commencing. The primary device as described above can be the device that is configured to sense the cyclical signal for which the TCC window(s) have been established so that it is enabled to start transmitting a wake up signal during the established TCC window(s) in one or more cardiac cycles to initiate the TCC session. As such, at block 604 of FIG. 7, the primary device may schedule a wake up signal transmission according to the times of the established TCC window(s) during one or more cycles of the sensed cyclical signal until an acknowledgment signal is received from the secondary device confirming receipt of the wake up signal.

[0186] The wake up signal may be transmitted at a relatively high or maximum transmit power to increase the likelihood of successful receipt by the secondary device. In other examples, the wake up signal is transmitted at a transmit power previously selected for optimized TCC, e.g., according to the methods described above in conjunction with FIG. 10. If the secondary device is configured to also sense the cyclical signal sensed by the primary device, the secondary device may schedule listening windows during the sensed cyclical signal that will approximately match the timing of the established TCC windows. In this way, the number of wake up signal transmission attempts may be reduced because the TCC windows scheduled by the primary device for transmitting the wake up signal are expected to be synchronized to listening windows scheduled by the secondary device. The secondary device may schedule a listening window according to the time of TCC windows established by the primary device during each cycle, every nth cycle, one cycle per 10 seconds, one cycle per 30 seconds or at other periodic schedules relative to the cyclical signal. When the primary device transmits a wake up signal repeatedly during the TCC window(s) during one or more cycles of the cyclical signal, the secondary device may receive the wake up signal during a scheduled listening window and can optionally respond to the transmitted wake up signal with an acknowledgement signal.

[0187] In still other examples, the wake up signal may be transmitted during one or more TCC windows and outside the established TCC window times by the primary device. The secondary device may not be configured to sense the cyclical signal and, as such, may power on its TCC receiver to listen for a wake up signal at arbitrarily scheduled listening windows. If the wake up signal is not detected, the secondary device TCC receiver may go back to sleep. If the wake up signal is received, the secondary device sends an acknowledgment signal confirming receipt of the wake up signal establishing the TCC session.

[0188] Furthermore, in some examples, a wake up signal or beacon signal is not required. The primary device may be the primary receiving device during TCC such that it can power on the TCC receiver for receiving transmitted TCC signals from the secondary device during scheduled TCC windows. When the secondary device is the receiving device during TCC, and can sense the same cyclical signal, the secondary device can enable its TCC receiver during the established TCC windows for receiving transmitted signals from the primary device. In other examples, one device that is primarily receiving TCC data may keep its TCC receiver on and enabled continuously or for extended time periods at scheduled times of day or scheduled time intervals such that a wake up signal or beacon signal is not required.

[0189] Once the TCC session is established, data transmission can commence. TCC data transmission between the primary and secondary device may be performed at block 606 during one or more TCC windows scheduled during one or more cycles of the cyclical signal. Data transmitted and received during the TCC window(s) may include therapy delivery commands, e.g., to stop, start or deliver a therapy, and/or a physiological signal and/or data derived therefrom. The number of TCC windows scheduled for the TCC session may depend on the number and length of data packets, the data rate, the duration of each TCC window and other factors. The secondary device may be the primary transmitter with the primary device being the primary receiver once the TCC session is established. As such, the primary device may operate in a receiving mode for receiving TCC data transmitted at least during the TCC window of one or more cycles of the cyclical signal after transmitting a wake up signal. During a receiving mode, the primary device may still transmit acknowledgement or confirmation signals to the transmitting device to confirm successful receipt of transmitted data.

[0190] In other instances, the primary device may be the primary transmitter and the secondary device may be the primary receiver during the TCC session. In this case, the primary device may operate in a transmit mode during at least the TCC window of one or more cycles of the cyclical signal after transmitting the wake up signal. During a transmitting mode, the primary device may still receive acknowledgment or confirmation signals from the receiving device. In some cases, the roles of being primary transmitter and primary receiver may flip during a TCC session when both the primary device and the secondary device have data packets to be transmitted to the other device.

[0191] When the secondary device is configured to sense the cyclical signal that is sensed by the primary device, the secondary device and the primary device may schedule TCC windows according to the TCC window times established previously during the TCC set up procedure described above. Selected TCC transmitting and receiving electrode vectors, TCC transmit power and receiving sensitivities may be employed by each respective device according to TCC control parameters that have been established during the TCC set up procedure. It is to be understood that in performing TCC operations at block 606, the primary device and/or secondary device may determine a patient posture and/or physical activity level or other physiological condition (such as bioimpedance) indicative a patient state that may affect received TCC signal strength and select the corresponding TCC control parameters previously established for the determined posture and activity level or other physiological condition. Posture and/or activity data or other patient condition data may be transmitted from the primary device to the secondary device or vice versa as needed at the onset of the TCC transmission session, e.g., as a header to a first data packet, so that the two devices are using the correct TCC control parameters.

[0192] When the secondary device is configured to sense the cyclical signal that is sensed by the primary device, each device can schedule TCC windows relative to the cyclical signal that are substantially aligned in time to promote successful receipt of transmitted data by the receiving device. When the secondary device is not configured to sense the cyclical signal that is sensed by the primary device, the primary device may transmit a next transmit time to the secondary device in a data packet footer that is transmitted to the secondary device in the current TCC window. If the primary device is operating as the primary receiver during the TCC session, the primary device may transmit a next transmit time to the secondary device in a data confirmation signal that is transmitted to confirm that data transmitted from the secondary device has been successfully received during the current TCC window. In this way, the secondary device may schedule the next TCC window according to a next transmit time received from the primary device. The primary device may determine the next transmit time based on a predicted cycle length of the cyclical signal and the established TCC window. The predicted cycle length may be based on one or more most recent cycle lengths of the sensed cyclical signal.

[0193] In still other examples, when the secondary device is the primary receiver during a TCC session and has a relatively large power source, it is contemplated that once the secondary device is operating in a receiving mode, the TCC receiver remains powered on for receiving data from the primary device transmitted during TCC windows scheduled by the primary device until the primary device transmits a termination signal. The primary device may have a limited power supply and may transmit at a minimum transmit power during the TCC windows. To reduce the likelihood of failed transmission, e.g., due to misaligned TCC windows scheduled by the two devices, the secondary device TCC receiver may remain powered for receiving TCC signals from the time of receiving the wake up signal until a termination signal is received from the primary device.

[0194] During the TCC session, one or both of the primary device and secondary device, may determine that a failed transmission has occurred at block 608. The transmitting device may determine that a transmission failed if a confirmation signal is not received to confirm a successful receipt of the transmitted data or if another expected response by the receiving device is not detected, e.g., a delivered cardiac pacing pulse or other therapy delivery. The receiving device may determine that a failed transmission has occurred if the data packet is incomplete, has errors, signal drop out or other indications of a failed transmission are detected. When a failed transmission is detected, the transmitting device may repeat transmission of the data one or more times using the same TCC control parameters. However, when a threshold number of attempts has been reached, which may be one or more attempts, the primary and/or secondary device may adjust one or more TCC control parameters at block 612.

[0195] A TCC control parameter may be adjusted at block 612 by increasing the duration and/or shifting the start time of a TCC window. In some cases, the TCC windows scheduled by the primary device and the secondary device may be mis-aligned. If one device shifts the TCC window relative to the sensed cyclical signal and/or lengthens the TCC window, the cause of the failed transmission may be corrected. Additionally or alternatively, the transmitting device may increase the transmit power and/or the receiving device may increase the receiving sensitivity. In still other examples, the data rate may decreased, which may reduce noise interference and increase the likelihood of a successful data transmission. The adjusted TCC control parameters applied during the next TCC window after a failed transmission may be used for the remainder of the TCC session in some examples. In some examples, if a different TCC electrode vector is available, the transmitting and/or receiving device may select a different TCC electrode vector or a combination of multiple TCC electrode vectors at block 612 in response to a failed transmission detection.

[0196] As described above in conjunction with FIG. 10, when a failed transmission is detected, the primary and secondary device may re -perform the TCC set up procedure to update the TCC control parameters. The TCC set up procedure may be performed after completed the TCC session that included one or more failed transmission attempts. However, it is to be understood that the TCC session may be terminated in response to a threshold number of failed transmission attempts to enable the TCC set up procedure to be performed. The TCC session may be rescheduled after the TCC set up procedure is performed to establish updated, optimized TCC control parameters.

[0197] Referring again to block 608, if a failed transmission is not detected, but more data is to be transmitted between the primary and secondary devices during the transmission session (as determined at block 610), the devices may return to block 606 to transmit and receive during the next TCC window. If data transmission is complete, the TCC session may be terminated at block 614. The transmitting device during the TCC session may transmit a termination signal so that the receiving device does not schedule another TCC window. The secondary device may return to a listening mode by scheduling listening windows, e.g., as described above, to wait for another wake up signal from the primary device (or vice versa when both devices are configured to sense the cyclical signal for scheduling TCC windows).

[0198] FIG. 12 is a diagram 700 that depicts TCC windows 728 and 730 that may be scheduled during a cyclical signal after the TCC set up procedure. TCC windows 728 and 730 may be scheduled by the primary device. A cardiac electrical signal 710 may be sensed by the primary device. The primary device processing circuitry may determine a cardiac cycle length 702 between successive sensed ventricular event signals 714 and 715. It is to be understood that when the primary device senses a cardiac signal and cardiac pacing is delivered by the primary device or another device, the primary device processing circuitry may detect cardiac cycles and determine cardiac cycle lengths based on the timing of cardiac pacing pulses in combination with any sensed intrinsic cardiac event signals. The cycle length 702 may be determined and used alone or in combination with one or more preceding cycle lengths (not shown in FIG. 12) to determine a representative cycle length of the cyclical cardiac signal. The representative cycle length may be cycle length 702 or may be a median or mean of multiple cycle lengths. In some examples, prior to initiating a TCC session multiple preceding cycle lengths may be evaluated before starting a TCC session to verify that the cycle lengths are stable, e.g., verify a regular heart rate and no arrhythmias.

[0199] The primary device may initiate a TCC session by scheduling a TCC window 728 at a time interval 720 from a cycle onset marker, e.g., ventricular sensed event signal 715, based on the established TCC window time during the TCC set up procedure, e.g., as described in any of the examples given above in conjunction with FIGs. 7-10. The time interval 720 may be determined by calculating a percentage of the preceding cycle length 702, where the percentage corresponds to the time of a TCC window during the cardiac cycle identified during the TCC set up procedure based on an analysis of the signal strength metrics as described above. When the heart rate is relatively stable, the time interval 720 determined as a percentage of the preceding cycle length 702 (or a median or average of recent cycle lengths) may be used to schedule a TCC window 728 at a time following the ventricular sensed event marker 716 that is expected to correspond to a relatively high (or acceptable) signal strength of a received TCC signal. The relative positions and alignment of the transmitting and receiving electrodes of the primary and secondary devices may be optimal for promoting a relatively high received signal strength and acceptable signal margin and margin factor during the TCC window 728.

[0200] The secondary device may or may not sense a cardiac signal. When the secondary device does not sense a cardiac signal, the secondary device may enable its TCC receiver to wake up and listen for a wake up or beacon signal at scheduled time intervals independent of the cardiac cycle. The listening window 740 may begin at an arbitrary or random time relative to the onsets of cardiac cycles, unknown to the secondary device. In the example shown, the secondary device starts the listening window 740 at a scheduled time having a time duration 741 that is expected to extend through a majority or all of at least one cardiac cycle length. In this way, if the primary device transmits a wake up signal during the cardiac cycle, the secondary device is likely to receive it. If the wake up signal is not received, the secondary device TCC receiver may be powered down until the next scheduled listening window. If a wake up signal is not received at an expected time for a TCC session, the listening window 740 may be extended and/or scheduled more often to promote receipt of a transmitted wake up signal.

[0201] The primary device transmits the wake up signal during the TCC window 728. The TCC receiver of the secondary device may receive and acknowledge the wake up signal by terminating the listening window 740 and transmitting an acknowledgment signal 742. The primary device TCC receiver is enabled during a listening window 729 scheduled by the primary device upon termination of the TCC window 728. The primary device can receive the acknowledge signal 742 during the listening window 729 and in this way the TCC session may be established.

[0202] In some examples, particularly when the secondary device does not sense a cyclical signal corresponding to the cyclical signal sensed by the primary device, the primary device may transmit a timing signal 744 after receiving the acknowledgment signal 742 from the secondary device. The timing signal 744 can indicate the cycle length of the sensed cyclical signal or an estimated time to a next TCC window. The secondary device may start a receiving window 746 after transmitting the acknowledgment signal 742 for receiving the timing signal 744. The secondary device may use the timing signal to schedule a next receiving window 750.

[0203] For example, the timing signal 744 may indicate the cardiac cycle length 702 that the primary device used as the basis for scheduling TCC window 728. For the sake of illustration, the primary device may be the primary transmitting device during this TCC session and the secondary device may be the primary receiving device. As such the next TCC window 730 is a transmitting TCC window during which the primary device may transmit one or more data packets. Assuming a stable cycle length, the transmitting TCC window 730 occurs one cycle length after the TCC window 728. Using the transmitted cycle length information received in timing signal 744, the secondary device may be configured to start a receiving TCC window 750 at a time interval 752 from the time 754 that the wake up signal was received from the primary device, for example. The time interval 752 may be set equal to the cycle length received from the primary device. The time interval 752 may be set shorter than the cycle length received from the primary device to account for timing variations due to changes in heart rate, differences in the clock cycles between the primary and secondary devices or other timing variations. [0204] The time duration of the TCC receiving window 750 may be set based on the expected duration of the TCC transmitting window 730 and/or an expected a data packet length that may be indicated in the timing signal 744 or in a preamble of a data packet transmitted by the primary device during the transmitting TCC window 730. In other examples, the secondary device may maintain the TCC receiver in a receiving mode until the primary device transmits a TCC transmission completion signal. In the example shown, signal 748 transmitted by the primary device may be a transmission completion signal, in which case the secondary device terminates the TCC receiving window 750 and returns to scheduling listening windows for sensing the next wake up signal. Listening windows may be scheduled based on the cycle length received in timing signal 744, which may be a typical or resting heart rate for the patient.

[0205] In other examples, when additional data is available for transmitting, the primary device may transmit data during multiple TCC transmit windows. In this case, the transmitted signal 748 may be another timing signal for use by the secondary device in scheduling the next TCC receiving window (not shown in FIG. 12) to coincide in time with the time of the next expected TCC transmitting window of the primary device. In other examples, when the TCC receiving window 750 is started according to timing information received in timing signal 744, the secondary device may maintain the TCC receiver in a receiving mode until a termination signal is received, which may be after multiple TCC transmitting windows that could occur over one or more cycles of the sensed cyclical signal.

[0206] As described above, when one or both of the primary and secondary devices is exposed to respiratory motion, the TCC window 730 may be scheduled during cardiac cycles that occur during a portion of the respiration cycle associated with acceptable received TCC signal strength. Some cardiac cycles may be skipped, e.g., no TCC window scheduled, if they occur during a portion of the respiration cycle that is identified as being associated with relatively low received signal strength or unacceptable signal margin or margin factor. As described above, the respiration cycle may be identified from respiratory-induced oscillations in the cardiac signal, e.g., baseline oscillations or low pass filtering of the cardiac signal. In other examples, the respiration cycle may be identified from a sensed physiological signal such as a thoracic impedance signal.

[0207] While the primary device is represented as the primary transmitter during the TCC session with the secondary device being the primary receiver, it is to be understood that once the TCC session is established, e.g., based on receipt of the acknowledgement signal 742 by the primary device, the secondary device may be the primary transmitter for transmitting data during the TCC window 750 and the primary device may be the primary receiver for receiving data during the respective TCC window 730.

[0208] The timing diagram of FIG. 12 provides an illustrative example of coordination of TCC between two devices of a TCC system configured to communicate during TCC windows scheduled during a cyclical signal. However, it is to be understood that some signals illustrated in FIG. 12, such as wake up, acknowledgment, confirmation or other signals may not be required in some TCC protocols. For example, once the TCC window is established, the primary device and/or secondary device may be configured to schedule TCC windows during each cycle of a sensed cyclical signal for transmitting and/or receiving TCC data without requiring a wake up or beacon signal to establish a communication session and without necessarily requiring acknowledgement or confirmation signals. One or both of the primary device and the secondary device may be configured to power on or enable its TCC circuit during the TCC window and power down or disable the TCC circuit outside of the TCC window. For example, the processing circuitry of one or both of the primary and secondary devices may be configured to power up the TCC circuit at a starting time of the TCC window during a cycle of the cyclical signal after the set up procedure is completed and power down the TCC circuit at an expiration time of the TCC window. The TCC circuit may remain powered down until a starting time (or just before) the next TCC window. The processing circuitry may power up the TCC circuit again for performing TCC at the starting time of the next TCC window during the same or a next cycle of the cyclical signal when TCC data is scheduled to be transmitted during multiple TCC windows over one or more cycles of the cyclical signal.

[0209] Further disclosed herein is the subject matter of the following examples:

[0210] Example 1. A system comprising sensing circuitry configured to sense a cyclical physiological signal, TCC circuitry configured to receive a test TCC signal and processing circuitry configured to identify one or more cycles of the cyclical physiological signal. The processing circuitry may perform a set up procedure during which the processing circuitry may determine at least one signal strength metric of the received test TCC signal at each of a plurality of time points relative to the identified one or more cycles of the cyclical physiological signal. Based on the signal strength metrics, the processing circuitry may establish a TCC time window of the cyclical physiological signal for performing TCC. The TCC circuitry may be configured to perform TCC during the established TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0211] Example 2. The system of example 1 further comprising a therapy delivery circuit configured to deliver an electrical stimulation pulse to evoke a cycle of the cyclical physiological signal wherein the processing circuitry is further configured to identify the at least one cycle of the cyclical physiological signal based on the delivered electrical stimulation pulse.

[0212] Example 3. The system of any of examples 1-2 wherein the processing circuitry is further configured to determine the at least one signal strength metric at each of a plurality of time points by determining at least one of: a maximum signal amplitude; a peak to peak amplitude; a signal margin; a margin factor relative to a receiver sensitivity; or a signal to noise ratio.

[0213] Example 4. The system of any of examples 1-3 wherein the TCC circuitry is further configured to transmit a wake up signal during the TCC time window of the at least one cycle of cyclical physiological signal after the set up procedure.

[0214] Example 5. The system of any of examples 1-4 wherein the TCC circuitry is further configured to operate in at least one of: a receiving mode for receiving TCC data transmitted during the TCC time window of the at least one cycle of the cyclical physiological signal after the TCC set up procedure; or a transmitting mode for transmitting TCC data during the TCC time window of the at least one cycle of the cyclical physiological signal after the TCC set up procedure.

[0215] Example 6. The system of any of examples 1-5 further comprising a memory. The processing circuitry may be further configured to determine a patient condition when the test TCC signal is received, store the determined patient condition in association with the established TCC time window in the memory and redetermine the patient condition after the TCC set up procedure. The processing circuitry may select the TCC time window that is stored in the memory in association with the redetermined patient condition for performing TCC during the established time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

[0216] Example 7. The system of example 6 wherein the processing circuitry is further configured to determine the patient condition by determining at least one of a patient posture, a patient physical activity level, a period of the cyclical physiological signal, an amplitude of the cyclical physiological signal, or a bioimpedance.

[0217] Example 8. The system of any of examples 6-7 wherein the processing circuitry is further configured to determine a plurality of different patient conditions each occurring at different time points and, for each of the plurality of different patient conditions, establish a corresponding TCC time window of a cycle of the cyclical physiological signal for performing TCC. After the set up procedure, the processing circuitry may redetermine the patient condition as being one of the plurality of different patient conditions and select the corresponding TCC time window established for the one of the plurality of different patient conditions that is redetermined as the patient condition for performing the TCC after the set up procedure.

[0218] Example 9. The system of any of examples 1-8 wherein the TCC circuitry is further configured to transmit a timing signal indicating an expected time of a next TCC time window.

[0219] Example 10. The system of any of examples 1-9 wherein the processing circuitry is further configured to determine a failed TCC transmission and, in response to determining the failed TCC transmission, at least one of: a) repeat the set up procedure; or b) adjust at least one of the established TCC time window relative to a cycle of the cyclical physiological signal, a transmit power of the TCC circuitry, a receiver sensitivity of the TCC circuitry, a TCC electrode vector or a data rate.

[0220] Example 11. The system of any of examples 1-10 wherein the processing circuitry is further configured to determine at least one of a TCC electrode vector, a transmit power and a receiver sensitivity based on the at least one signal strength metric, and the TCC circuitry is further configured to utilize at least one of the determined TCC electrode vector, the transmit power or the receiver sensitivity for performing TCC after the set up procedure. [0221] Example 12. The system of any of examples 1-11 wherein the sensing circuitry is configured to sense the cyclical physiological signal by sensing at least one of a cardiac signal or a respiration signal.

[0222] Example 13. The system of any of examples 1-12 wherein the TCC circuitry is further configured to transmit or receive a TCC signal comprising at least one of a therapy delivery command or sensed physiological signal data during the established TCC time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

[0223] Example 14. The system of example 1 further comprising a first device including the sensing circuitry, the TCC circuitry, and the processing circuitry and a second device including second TCC circuitry configured to perform TCC with the first device during the established TCC time window.

[0224] Example 15. The system of any of examples 1-14 wherein the processing circuitry is further configured to repeat the set up procedure in response to at least one of determining a scheduled set up procedure time or detecting a set up procedure trigger condition.

[0225] Example 16. The system of any of examples 1-15 wherein the processing circuitry is further configured to power up the TCC circuitry at a starting time of the TCC window during the at least one cycle of the cyclical physiological signal after the set up procedure and power down the TCC circuitry at an expiration time of the TCC window.

[0226] Example 17. A method comprising sensing a cyclical physiological signal, receiving a test tissue conductance communication (TCC) signal, identifying one or more cycles of the cyclical physiological signal, and, during a set up procedure, determining at least one signal strength metric of the received test TCC signal at each of a plurality of time points relative to the identified one or more cycles of the cyclical physiological signal. The method may further include, based on the signal strength metrics, establishing a TCC time window of the cyclical physiological signal for performing TCC and performing TCC during the TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0227] Example 18. The method of example 17 further comprising delivering an electrical stimulation pulse to evoke a cycle of the cyclical physiological signal and identifying the at least one cycle of the cyclical physiological signal based on the delivered electrical stimulation pulse.

[0228] Example 19. The method of any of examples 17-18 further comprising determining the at least one signal strength metric at each of a plurality of time points by determining at least one of a maximum signal amplitude; a peak to peak amplitude; a signal margin; a margin factor relative to a receiver sensitivity; or a signal to noise ratio.

[0229] Example 20. The method of any of examples 17-19 further comprising transmitting a wake up signal during the TCC time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

[0230] Example 21. The method of any of examples 17-20 further comprising at least one of receiving data transmitted by TCC during at least the TCC time window of the at least one cycle of the cyclical physiological signal identified after the TCC set up procedure or transmitting TCC data during the TCC time window of the at least one cycle of the cyclical physiological signal after the TCC set up procedure.

[0231] Example 22. The method of any of examples 17-21 further comprising determining a patient condition when the test TCC signal is received, storing the determined patient condition in association with the established TCC time window in a device memory, redetermining the patient condition after the TCC set up procedure and selecting the TCC time window that is stored in the device memory in association with the redetermined patient condition for performing TCC during the TCC window of the at least one cycle of the cyclical physiological signal after the set up procedure.

[0232] Example 23. The method of example 22 further comprising determining the patient condition by determining at least one of: a patient posture; a patient physical activity level; a bioimpedance, a period of the cyclical physiological signal, or an amplitude of the cyclical physiological signal.

[0233] Example 24. The method of any of examples 22-23 further comprising determining a plurality of different patient conditions each occurring at different time points and, for each of the plurality of different patient conditions, establishing a corresponding TCC time window of a cycle of the cyclical physiological signal for performing TCC. The method may further include, after the set up procedure, redetermining the patient condition as being one of the plurality of different patient conditions and selecting the corresponding TCC time window established for the one of the plurality of different patient conditions that is redetermined as the patient condition for performing the TCC after the set up procedure.

[0234] Example 25. The method of any of examples 17-24 further comprising transmitting a timing signal indicating an expected time of a next TCC time window.

[0235] Example 26. The method of any of examples 17-25 further comprising determining a failed TCC transmission. The method may include, in response to determining the failed TCC transmission, at least one of: a) repeating the set up procedure; or b) adjusting at least one of the established time window relative to a cycle of the cyclical physiological signal, a transmit power of the TCC circuitry, a receiver sensitivity of the TCC circuitry, a TCC electrode vector or a data rate.

[0236] Example 27. The method of any of examples 17-26 further comprising determining at least one of a TCC electrode vector, a transmit power and a receiver sensitivity based on the at least one signal strength metric. The method may further include utilizing at least one of the determined TCC electrode vector, the transmit power or the receiver sensitivity for performing TCC after the set up procedure.

[0237] Example 28. The method of any of examples 17-27 wherein sensing the cyclical physiological signal comprises sensing one of a cardiac signal or a respiration signal.

[0238] Example 29. The method of any of examples 17-28 further comprising at least one of transmitting or receiving a TCC signal comprising at least one of a therapy delivery command or sensed physiological signal data during the established TCC time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

[0239] Example 30. The method of any of examples 17-29 further comprising repeating the set up procedure in response to at least one of determining a scheduled set up procedure time or detecting a set up procedure trigger condition.

[0240] Example 31. The method of any of examples 17-30 further comprising powering up TCC circuitry at a starting time of the TCC window during the at least one cycle of the cyclical physiological signal after the set up procedure and powering down the TCC circuitry at an expiration time of the TCC window.

[0241] Example 32. A non-transitory computer-readable medium comprising a set of instructions that, when executed by processing circuitry of a system cause the system to sense a cyclical physiological signal, receive a test TCC signal, identify one or more cycles of the cyclical physiological signal, during a set up procedure, and determine at least one signal strength metric of the received test TCC signal at each of a plurality of time points relative to the identified one or more cycles of the cyclical physiological signal. The instructions may further cause the system to establish a TCC time window of the cyclical physiological signal for performing TCC based on the signal strength metrics and perform TCC during the TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

[0242] Example 33. A system comprising processing circuitry configured to receive TCC window information relative to a cyclical physiological signal and schedule a TCC window based on the received TCC window information. The system includes TCC circuitry configured to perform TCC during the TCC time window.

[0243] Example 34. The system of example 33 further comprising sensing circuitry configured to sense the cyclical physiological signal.

[0244] Example 35. The system of any of examples 33-34 wherein the TCC circuitry is configured to receive the TCC window information and the processing circuitry is configured to receive the TCC window information from the TCC circuitry.

[0245] Example 36. The system of any of examples 33-34 further comprising a wireless telemetry circuit configured to receive the TCC window information via a radio frequency communication signal and the processing circuitry is configured to receive the TCC window information from the wireless telemetry circuit.

[0246] Example 37. The system of any of examples 33-36 wherein the TCC circuitry is configured to transmit a test TCC signal and receive the TCC window information subsequent to transmitting the test TCC signal.

[0247] Thus, various examples of a method and apparatus for TCC performed by a medical device system have been presented in the foregoing description with reference to illustrative diagrams and flow charts shown in the drawings. It should be understood that, depending on the example, certain acts or events of any of the methods described herein can be performed in a different sequence, may be added, merged, or left out altogether (e.g., not all described acts or events are necessary for the practice of the method). Moreover, in certain examples, acts or events may be performed concurrently, e.g., through multi-threaded processing, interrupt processing, or multiple processors, rather than sequentially. In addition, while certain aspects of this disclosure are described as being performed by a single device, circuit or component for purposes of clarity, it should be understood that the techniques of this disclosure may be performed by a combination of devices, circuits or components associated with, for example, a medical device system and/or a single circuit or component may perform multiple functions that are represented as separate circuits or components in the accompanying drawings.

[0248] In one or more examples, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored as one or more instructions or code on a computer-readable medium and executed by a hardware -based processing unit. Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media (e.g., RAM, ROM, EEPROM, flash memory, or any other non- transitory computer-readable medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer).

[0249] Instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Accordingly, the terms “processor” and “processing circuitry” as used herein may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein. Also, the techniques could be fully implemented in one or more circuits or logic elements.

[0250] Thus, a system has been presented in the foregoing description with reference to specific examples. It is to be understood that various aspects disclosed herein may be combined in different combinations than the specific combinations presented in the accompanying drawings. It is appreciated that various modifications to the referenced examples may be made without departing from the scope of the disclosure and the following claims.

Claims

WHAT IS CLAIMED IS:

1. A system comprising: sensing circuitry configured to sense a cyclical physiological signal; tissue conductance communication (TCC) circuitry configured to receive a test TCC signal; processing circuitry configured to: identify one or more cycles of the cyclical physiological signal; during a set up procedure, determine at least one signal strength metric of the received test TCC signal at each of a plurality of time points relative to the identified one or more cycles of the cyclical physiological signal; based on the signal strength metrics, establish a TCC time window of the cyclical physiological signal for performing TCC; and the TCC circuitry being configured to perform TCC during the established TCC time window of at least one cycle of the cyclical physiological signal after the set up procedure.

2. The system of claim 1, further comprising a therapy delivery circuit configured to deliver an electrical stimulation pulse to evoke a cycle of the cyclical physiological signal; wherein the processing circuitry is further configured to identify the at least one cycle of the cyclical physiological signal based on the delivered electrical stimulation pulse.

3. The system of any of claims 1-2, wherein the processing circuitry is further configured to determine the at least one signal strength metric at each of a plurality of time points by determining at least one of: a maximum signal amplitude; a peak to peak amplitude; a signal margin; a margin factor relative to a receiver sensitivity; or a signal to noise ratio.

4. The system of any of claims 1-3, wherein the TCC circuitry is further configured to transmit a wake up signal during the TCC time window of the at least one cycle of cyclical physiological signal after the set up procedure.

5. The system of any of claims 1-4, wherein the TCC circuitry is further configured to operate in at least one of: a receiving mode for receiving TCC data transmitted during the TCC time window of the at least one cycle of the cyclical physiological signal after the TCC set up procedure; or a transmitting mode for transmitting TCC data during the TCC time window of the at least one cycle of the cyclical physiological signal after the TCC set up procedure.

6. The system of any of claims 1-5 further comprising a memory, wherein the processing circuitry is further configured to: determine a patient condition when the test TCC signal is received; store the determined patient condition in association with the established TCC time window in the memory; redetermine the patient condition after the TCC set up procedure; and select the TCC time window that is stored in the memory in association with the redetermined patient condition for performing TCC during the established time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

7. The system of claim 6 wherein the processing circuitry is further configured to determine the patient condition by determining at least one of: a patient posture; a patient physical activity level; a period of the cyclical physiological signal; an amplitude of the cyclical physiological signal; or a bioimpedance.

8. The system of any of claims 6-7, wherein the processing circuitry is further configured to: determine a plurality of different patient conditions each occurring at different time points; for each of the plurality of different patient conditions, establish a corresponding TCC time window of a cycle of the cyclical physiological signal for performing TCC; after the set up procedure, redetermine the patient condition as being one of the plurality of different patient conditions; and select the corresponding TCC time window established for the one of the plurality of different patient conditions that is redetermined as the patient condition for performing the TCC after the set up procedure.

9. The system of any of claims 1-8 wherein the TCC circuitry is further configured to transmit a timing signal indicating an expected time of a next TCC time window. .

10. The system of any of claims 1-9, wherein the processing circuitry is further configured to: determine a failed TCC transmission; and in response to determining the failed TCC transmission, at least one of: a) repeat the set up procedure; or b) adjust at least one of the established TCC time window relative to a cycle of the cyclical physiological signal, a transmit power of the TCC circuitry, a receiver sensitivity of the TCC circuitry, a TCC electrode vector or a data rate.

11. The system of any of claims 1-10, wherein: the processing circuitry is further configured to determine at least one of a TCC electrode vector, a transmit power and a receiver sensitivity based on the at least one signal strength metric; and the TCC circuitry is further configured to utilize at least one of the determined TCC electrode vector, the transmit power or the receiver sensitivity for performing TCC after the set up procedure.

12. The system of any of claims 1-11, wherein the sensing circuitry is configured to sense the cyclical physiological signal by sensing at least one of a cardiac signal or a respiration signal.

13. The system of any of claims 1-12, wherein the TCC circuitry is further configured to transmit or receive a TCC signal comprising at least one of a therapy delivery command or sensed physiological signal data during the established TCC time window of the at least one cycle of the cyclical physiological signal after the set up procedure.

14. The system of claim 1, further comprising: a first device comprising the sensing circuitry, the TCC circuitry, and the processing circuitry; and a second device comprising second TCC circuitry configured to perform TCC with the first device during the established TCC time window.

15. The system of any of claims 1-14, wherein the processing circuitry is further configured to repeat the set up procedure in response to at least one of: determining a scheduled set up procedure time; detecting a set up procedure trigger condition.