Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/38—Applying electric currents by contact electrodes alternating or intermittent currents for producing shock effects
  • A61N1/385—Devices for inducing an abnormal cardiac function, e.g. fibrillation
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
  • A61N1/00—Electrotherapy; Circuits therefor
  • A61N1/18—Applying electric currents by contact electrodes
  • A61N1/32—Applying electric currents by contact electrodes alternating or intermittent currents
  • A61N1/36—Applying electric currents by contact electrodes alternating or intermittent currents for stimulation
  • A61N1/362—Heart stimulators
  • A61N1/37—Monitoring; Protecting
  • A61N1/371—Capture, i.e. successful stimulation

Definitions

• the present invention relates generally to cardiac electrophysiological testing in a medical device, and more particularly to a method and apparatus for validating a pacing train delivered prior to a T- shock such that the T-wave shock is delivered with a high probability of occurring during the vulnerable period.
• the vulnerable period encompasses the repolarization phase of the myocardial action potential, also referred to as the "recovery phase", and a period immediately following it.
• the repolarization phase is observed as the T-wave portion of a cardiac ECG or EGM.
• the ventricles are in an inhomogeneous state where certain regions are excitable and certain regions are refractory to stimuli. Delivery of a stimulation pulse, or "T-shock", during this inhomogeneous state can initiate disorganized depolarization wave fronts causing fibrillation.
• Defibrillation threshold the minimum shock energy required to terminate VF
• DFT defibrillation threshold
• determination of the defibrillation threshold in a patient typically involved delivering a T-shock during the vulnerable period to induce VF and delivering a defibrillation shock there after to terminate the induced VF.
• a series of defibrillation shocks increasing or decreasing in energy can be delivered to determine the lowest energy that successfully defibrillates the heart.
• the minimum T-shock energy at which VF induction does not occur is referred to as the "upper limit of vulnerability.”
• the upper limit of vulnerability has been shown to be a predictor of the defibrillation threshold in a patient. Determination of the ULV could be substituted for defibrillation threshold testing at the time of ICD implantation.
• the implanting physician only needs to know if the patient meets the ICD implant criteria, i.e. if the patient's defibrillation threshold is acceptably below the maximum defibrillation shock energy available from the ICD.
• a clinician may select a shock energy that would be an acceptable DFT for a particular ICD and lead configuration. IfVF is not induced by a T-shock delivered at the selected shock energy, the energy is assumed to be at or above the ULV for that patient. The clinician can therefore conclude that the selected shock energy is at or above the patient's DFT and thereby make the determination that the patient meets the ICD implant criteria.
• a determination that a patient meets ICD implant criteria may be made by delivering as few as one T-shock without actually inducing VF.
• Such methods potentially improve the safety of ICD implantation procedures since actual VF induction may be avoided.
• a T-shock that is less than the ULV will normally induce VF in susceptible patients when it is properly timed during the vulnerable period.
• a T- shock delivered outside the vulnerable period may not induce VF, potentially misleading a clinician to think the T-shock.
• energy is greater than the ULV.
• a T-shock is typically delivered following a train of pacing pulses delivered at a rate greater than the patient's intrinsic heart rate.
• the T-shock is delivered following the last pacing pulse at a coupling interval that corresponds to a previously measured time interval between a pacing pulse and a subsequent T- wave. If all of the pacing pulses in the pulse train capture the heart, the pace-T-wave interval will be consistent and a T-shock delivered at that interval following the last pacing pulse will fall into the vulnerable period.
• the timing of the vulnerable period may change relative to the last pacing pulse of the pacing train.
• the T-shock may fail to induce VF irrespective of its amplitude.
• a clinician may inappropriately conclude that the T-shock energy is above the patient's ULV. Inappropriate ULV determination may cause a clinician to determine that a patient's DFT is lower than it actually is and that the patient meets ICD implant criteria when he/she may not.
• Methods are needed for promoting reliable T-shock delivery during the vulnerable period in order to take advantage of using ULV determination during ICD implantation procedures.
• the present invention provides a method and apparatus for validating a pacing pulse train, also referred to herein as an "Sl train", which precedes a T-shock.
• a pacing pulse train also referred to herein as an "Sl train”
• the last pacing pulse must capture the heart and other intervening intrinsic events between the last Sl pulse and the T-shock should not be present. If one or more of the S 1 pacing pulses fail to capture or if an intervening intrinsic event occurs during the Sl train, a previously set pace-T-shock interval may no longer be the correct coupling interval for timing the T-shock during the vulnerable period.
• One aspect of the invention is a T-shock delivery method that includes validation of the Sl train.
• Validation of the Sl train includes verifying capture of at least the last pulse of the Sl train. Capture verification may be performed for all or any portion of the Sl pulses that includes the last Sl pulse.
• capture verification includes detection of an evoked response (ER) during an ER sensing window.
• capture verification of an Sl pulse includes morphological analysis of a sensed event for verifying the sensed event is an ER.
• capture verification of an Sl pulse includes analyzing the temporal relationship of sensed events occurring on multiple EGM signal sources for verifying the sensed events represent an ER.
• Validation of the S 1 train may further include sensing for intrinsic ventricular events during or after the Sl train, prior to T-shock delivery.
• a sensed event that occurs outside an ER sensing window is determined to be an intrinsic event.
• a sensed event that is not confirmed to be an ER based on morphological analysis or the temporal relationship of events on multiple EGM signals is determined to be an intrinsic event.
• An Sl train is declared valid if a capture requirement is met and intrinsic events that might alter the refractory period of the heart relative to the last Sl pacing pulse are not sensed.
• Another aspect of the invention is a T-shock delivery method that includes a response to a detection of an invalid Sl train. Detection of an invalid Sl train may be based on failure of an Sl train to meet a previously defined capture requirement.
• Detection of an invalid Sl train may also be based on sensing of an intrinsic ventricular event during the Sl train, preceding a scheduled T-shock.
• the response to an invalid Sl train includes the generation an alert signal to notify a user of the invalid Sl train.
• the response to an invalid Sl train includes canceling a scheduled T-shock.
• the invalid Sl train response includes automatically extending the duration of the Sl train or repeating delivery of the Sl train.
• the invalid Sl train response includes adjustment of the Sl pacing train parameters.
• the apparatus includes control circuitry for controlling the delivery of an Sl pacing train generated by low- voltage output circuitry and for controlling the delivery of a subsequent T-shock pulse generated by high voltage output circuitry.
• the apparatus includes low-voltage cardiac pacing electrodes adapted for coupling to the low voltage output circuitry and high-voltage electrodes adapted for coupling to the high voltage output circuitry.
• the apparatus further includes sensing circuitry for receiving EGM or ECG signals from one or more sources using the low and/or high voltage electrodes for sensing ventricular events. Sensed signals are provided to processing circuitry for identifying a sensed event as an ER or as an intrinsic event.
• Processing circuitry is used to validate an Sl pacing train based on an Sl capture requirement and criteria regarding the occurrence of sensed intrinsic events.
• Another aspect of the invention is a computer-readable medium containing instructions. The instructions cause a programmable processor to control a defibrillator to deliver an Sl pacing train; validate the Sl pacing train by performing capture verification methods and sensing for intrinsic ventricular events during the Sl pacing train prior to T-shock delivery; deliver a T-shock at a predetermined pace-T-shock interval if an Sl pacing train is validated; and provide an invalid Sl pacing train response if an Sl pacing train is invalidated.
• a response to an invalid Sl pacing train may include any of: generating an alert; withholding a T-shock; extending the Sl pacing train; repeating the Sl pacing train, adjusting a pacing train parameter.
• FIG. 1 is a schematic diagram of an exemplary medical device suitable for practicing the present invention
• FIG. 2 is a functional block diagram of the medical device of FIG. 1 ;
• FIG. 3 is a timing diagram illustrating the delivery of an Sl pacing train and subsequent T-shock
• FIG. 4 is a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to the present invention
• FIG. 5 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention
• FIG. 6 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention
• FIG. 7 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention
• FIG. 8 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention.
• the present invention is directed toward providing an apparatus and method for validating an Sl pacing train preceding a T-shock.
• T-shock delivery for inducing VF during DFT testing could be repeated until VF was successfully induced.
• the goal was to induce VF. If a T-shock failed to induce, the timing or the T- shock energy could be adjusted until VF induction was successful.
• the present invention provides a method and apparatus for verifying capture and detecting intrinsic ventricular events during an Sl pacing train and prior to T-shock delivery.
• the present invention may be implemented in an ICD system, for example, for use during DFT testing or ULV measurements used to determine if a patient meets ICD implant requirements.
• the invention may alternatively be implemented in an automatic external defibrillator (AED).
• AEDs are increasingly provided for use in public and private environments.
• the S 1 pacing train validation methods described herein may be implemented in an AED having T-shock delivery features that may be used for inducing VF, measuring DFT or measuring ULV.
• FIG. 1 is a schematic diagram of an exemplary medical device suitable for practicing the present invention.
• a medical device according to the present invention may include an ICD 10 coupled to a patient's heart by way of three leads 6, 15, and 16, for example.
• a connector block 12 receives the proximal end of a right ventricular lead 16, a right atrial lead 15 and a coronary sinus lead 6, used for positioning electrodes for sensing and stimulation in three or four heart chambers.
• the right ventricular lead 16 is positioned such that its distal end is in the right ventricle for sensing right ventricular cardiac signals and delivering pacing or shocking pulses in the right ventricle.
• right ventricular lead 16 is equipped with a ring electrode 24, a tip electrode 26, and a coil electrode 20, each of which are connected to an insulated conductor contained within the body of lead 16.
• the proximal end of the insulated conductors are coupled to corresponding connectors carried by a connector assemblyl4 at the proximal end of lead 16 for providing electrical connection to the ICD 10.
• the right atrial lead 15 is positioned such that its distal end is in the vicinity of the right atrium and the superior vena cava.
• Lead 15 is equipped with a ring electrode 21 and a tip electrode 17 for sensing and pacing in the right atrium.
• Lead 15 is further equipped with a coil electrode 23 for delivering high-energy shock therapy.
• the ring electrode 21, the tip electrode 17 and the coil electrode 23 are each connected to an insulated conductor with the body of the right atrial lead 15.
• Each insulated conductor is coupled at its proximal end to a connector within connector assembly 13 adapted for electrical connection to ICD 10.
• the coronary sinus lead 6 is advanced within the vasculature of the left side of the heart via the coronary sinus and great cardiac vein.
• the coronary sinus lead 6 is shown in the embodiment of FIG. 1 as having a defibrillation coil electrode 8 that may be used in combination with either the coil electrode 20 or the coil electrode 23 for delivering electrical shocks for cardioversion and defibrillation therapies.
• coronary sinus lead 6 may also be equipped with a distal tip electrode and ring electrode for pacing and sensing functions in the left chambers of the heart.
• the coil electrode 8 is coupled to an insulated conductor within the body of lead 6, which provides connection to the proximal connector 4.
• the electrodes 17 and 21 or 24 and 26 may be used as bipolar pairs, commonly referred to as a "tip-to-ring” configuration, or individually in a unipolar configuration with the device housing 11 serving as the indifferent electrode, commonly referred to as the "can" or “case” electrode.
• the device housing 11 may also serve as a subcutaneous defibrillation electrode in combination with one or more of the defibrillation coil electrodes 8, 20 or 23 for defibrillation of the atria or ventricles.
• the right ventricular tip electrode 24 is used with either ring electrode 26 or housing 11 to deliver a primary Sl pacing pulse train to the ventricles to facilitate timing of a T-shock during the vulnerable period.
• Any of the available ventricular electrodes 24 and 26, coil electrodes 8, 20 and 23, and housing 11 may be used in various unipolar or bipolar sensing configurations for obtaining one or more EGM signals during Sl pacing train delivery for use in validating the Sl train.
• a T-shock is delivered using any of the coil electrodes 8, 20, or 23 and may utilize the device housing 11 as a "can" electrode. It is recognized that alternate lead systems may be substituted for the three lead system illustrated in FIG. 1.
• any available ventricular pacing and sensing electrodes may be used for delivering and validating the Sl train according to the methods described in detail below, and any available high-voltage electrodes may be used for delivering the T-shock as well as for sensing EGM signals for Sl train validation.
• subcutaneous electrodes may be provided and used for applying Sl pacing pulses and T-shocks.
• stimulation may be delivered using the "can" electrode and a subcutaneous electrode carried by a lead extending from the ICD.
• Subcutaneous electrode pairs may be incorporated in or on the ICD housing or provided on a subcutaneous lead and could be used for sensing intrinsic ventricular events and evoked responses.
• a hybrid system including subcutaneous electrodes and either transvenous electrodes or epicardial electrodes may be used.
• transvenous leads may be used to position electrodes within the heart for accurate sensing of cardiac activity and evoked responses during Sl pacing train delivery
• subcutaneous electrodes may be positioned for delivering Sl pacing pulses and T-shocks.
• the invention may alternatively be implemented in a "leadless" implantable device.
• a "leadless" implantable device Reference is made, for example, to the subcutaneous ICD generally disclosed in U.S. Pat. No. 6,647,292, issued to Bardy et al., incorporated herein by reference in its entirety.
• the Sl pacing train could be delivered through a subcutaneous defibrillation pathway and the same electrodes or alternate electrodes implanted subcutaneously could be used for sensing an evoked response following the Sl pulses.
• the methods provided herein would increase the likelihood that a T-shock would induce VF for DFT testing and would promote reliable ULV measurements. While a particular multi-chamber ICD and lead system is illustrated in FIG. 1, methodologies provided by the present invention may be adapted for use with other single chamber, dual chamber, or multichamber ICD systems. Atrial chamber sensing and stimulation capabilities are not necessary for practicing the invention.
• FIG. 2 is a functional block diagram of the medical device of FIG. 1.
• This functional diagram is exemplary of the type of device in which the invention may be implemented, however, the invention may usefully be practiced in a variety of device implementations, including devices used for electrophysiological studies, implantable or external devices which deliver electrical stimulation therapies, and implantable or external devices which deliver other forms of cardiac rhythm therapies such as nerve stimulation or drug administration.
• the disclosed embodiment shown in FIG. 2 is a microprocessor-controlled device, but the methods of the present invention may also be practiced with devices employing dedicated analog or digital circuitry for controlling device functions.
• the ICD 10 is provided with a number of connection terminals for achieving electrical connection to the cardiac leads 6, 15, and 16 and their respective electrodes.
• the connection terminal 311 provides electrical connection to the housing 11 for use as the indifferent electrode during unipolar stimulation or sensing.
• the connection terminals 320, 310, and 318 provide electrical connection to coil electrodes 20, 8 and 23 respectively.
• Each of these connection terminals 311, 320, 310, and 318 are coupled to the high voltage output circuit 234 to facilitate the delivery of high energy shocking pulses to the heart using one or more of the coil electrodes 8, 20, and 23 and optionally the housing 11.
• connection terminals 317 and 321 provide electrical connection to the tip electrode 17 and the ring electrode 21 positioned in the right atrium.
• the connection terminals 317 and 321 are further coupled to an atrial sense amplifier 204 for sensing atrial signals such as P-waves.
• the connection terminals 326 and 324 provide electrical connection to the tip electrode 26 and the ring electrode 24 positioned in the right ventricle.
• the connection terminals 326 and 324 are further coupled to a ventricular sense amplifier 200 for sensing ventricular signals.
• the atrial sense amplifier 204 and the ventricular sense amplifier 200 may be embodied as automatic gain controlled amplifiers with adjustable sensing thresholds.
• the general operation of the ventricular sense amplifier 200 and the atrial sense amplifier 204 may correspond to that disclosed in U.S. Pat. No. 5,117,824, by Keimel, 2006/014761
• a signal received by atrial sense amplifier 204 exceeds an atrial sensing threshold a signal is generated on the P-out signal line 206.
• a signal received by the ventricular sense amplifier 200 exceeds a ventricular sensing threshold a signal is generated on the R-out signal line 202.
• generation of a signal on R-out signal line during an ER sensing window can be used in verifying capture of an Sl pacing pulse. Capture verification of at least the last Sl pacing pulse is used in validating an Sl pacing train.
• Switch matrix 208 is used to select which of the available electrodes are coupled to a wide band amplifier 210 for use in digital signal analysis. Selection of the electrodes is controlled by the microprocessor 224 via data/address bus 218. The selected electrode configuration may be varied as desired for the various sensing, pacing, cardioversion and defibrillation functions of the ICD 10. Signals from the electrodes selected for coupling to bandpass amplifier 210 are provided to multiplexer
• A/D converter 222 for storage in random access memory 226 under control of direct memory access circuit 228.
• Microprocessor 224 may employ the digitized EGM signals stored in random access memory 226 in conjunction with Sl capture verification methods for validating an Sl train in accordance with the present invention.
• the microprocessor 224 may analyze a ventricular EGM signal acquired following an Sl pulse or verifying capture of the Sl pulse.
• digitized EGM signals are used to sense a ventricular event occurring during an ER sensing window following an Sl pacing pulse to verify capture of the Sl pacing pulse.
• the morphology of a digitized sensed event signal following an Sl pulse is compared to a previously determined ER morphology stored in RAM 226 for verifying that the sensed event is an actual ER and not an intrinsic event.
• the temporal relationship of sensed events occurring on different EGM sources following an Sl pulse is compared to a known ER temporal relationship for verifying that the sensed events represent an actual ER to the Sl pulse.
• the operation of the microprocessor 224 in perfo ⁇ ning the Sl train validation methods provided by the present invention can be controlled by executable software stored in ROM, associated with microprocessor 224.
• the telemetry circuit 330 receives downlink telemetry from and sends uplink telemetry to an external programmer, as is conventional in implantable anti-arrhythmia devices, by means of an antenna 332. Data to be uplinked to the programmer and control signals for the telemetry circuit 330 are provided by microprocessor 224 via address/data bus 218.
• Received telemetry is provided to microprocessor 224 via multiplexer 220. Any type of telemetry system known for use in implantable devices may be used.
• the remainder of circuitry illustrated in FIG. 2 is dedicated to the provision of cardiac pacing, cardioversion and defibrillation therapies.
• the pacer timing and control circuitry 212 includes programmable digital counters which control the basic time intervals associated with various single, dual or multi-chamber pacing modes or anti-tachycardia pacing therapies delivered in the atria or ventricles. Pacer circuitry 212 also determines the amplitude of the cardiac pacing pulses under the control of microprocessor 224.
• escape interval counters within pacer timing and control circuitry 212 are reset upon sensing of R- waves or P-waves as indicated by signals on lines 202 and 206, respectively.
• pacing pulses are generated by atrial pacer output circuit 214 and ventricular pacer output circuit 216.
• the pacer output circuits 214 and 216 axe coupled to the desired electrodes for pacing via switch matrix 208.
• the escape interval counters are reset upon generation of pacing pulses, and thereby control the basic timing of cardiac pacing functions, including anti-tachycardia pacing.
• pacer timing and control circuitry 212 is used to control the delivery of an S 1 pacing train at an overdrive rate, slightly greater than a sensed intrinsic heart rate.
• the durations of the escape intervals are determined by microprocessor 224 via data/address bus 218.
• the value of the count present in the escape interval counters when reset by sensed R-waves or P-waves can be used to measure R-R intervals, P-P intervals, P-R intervals, and R-P intervals, which measures are stored in memory 226 and used in conjunction with the present invention to diagnose the occurrence of a variety of arrhythmias.
• Microprocessor 224 operates as an interrupt driven device, and is responsive to interrupts from pacer timing and control circuitry 212 corresponding to the occurrences of sensed P-waves and R-waves and corresponding to the generation of cardiac pacing pulses. These interrupts are provided via data address bus 218.
• microprocessor 224 Any necessary mathematical calculation or logic operations to be performed by microprocessor 224, including those to be described in greater detail below, and any updating of values or intervals controlled by pacer timing and control circuitry 212 take place following such interrupts. These operations are performed under the control of software stored in ROM associated with microprocessor 224.
• a portion of the random access memory 226 may be configured as a number of recirculating buffers capable of holding a series of measured intervals, which may be analyzed in response to a pace or sense interrupt by microprocessor 224 for diagnosing an arrhythmia.
• an anti- tachycardia pacing therapy may be delivered if desired by loading a regimen from microcontroller 224 into the pacer timing and control circuitry 212 according to the type of tachycardia detected.
• microprocessor 224 activates the cardioversion and defibrillation control circuitry 230 to initiate charging of the high voltage capacitors 246 and 248 via charging circuit 236 under the control of high voltage charging control line 240.
• the voltage on the high voltage capacitors 246 and 248 is monitored via a voltage capacitor (VCAP) line 244, which is passed through the multiplexer 220.
• VCAP voltage capacitor
• the defibrillation or cardioversion pulse is delivered to the heart by high voltage output circuit 234 under the control of the pacer timing and control circuitry 212 via a control bus 238.
• the output circuit 234 determines the electrodes used for delivering the cardioversion or defibrillation pulse and the pulse wave shape. Examples of high- voltage cardioversion or defibrillation output circuitry are generally disclosed in U.S. Pat. No. 4,727,877 issued to Kallok, and U.S. Pat No. 5,163,427 issued to Keimel, both incorporated herein by reference in their entirety.
• pacer timing and control circuitry 212 controls the delivery of an Sl train while cardioversion and defibrillation control circuitry 230 initiates charging of the high voltage capacitors .246 and 248 for T-shock delivery.
• the pacer timing and control circuitry controls the delivery of a T-shock by output circuit 234 following the last Sl pacing pulse at a predetermined pace-T-shock interval.
• the pace-T-shock interval is set based on a previous measurement of the time between an
• Sl pacing pulse and a subsequently sensed T-wave or other measurement of the patient's refractory period or Q-T interval may be implemented according to methods known in the art, for example as generally disclosed in U.S. Pat. No. 5,129,392 issued to Bardy, et al, incorporated herein by reference in its entirety.
• the present invention provides a method for validating the Sl train to increase the likelihood that the T-shock has been properly delivered during the vulnerable period.
• FIG. 3 is a timing diagram illustrating the delivery of an Sl pacing train and subsequent T-shock.
• Intrinsic R- waves 50 and 55 are sensed at the intrinsic heart rate by the ICD ventricular sensing circuitry.
• Timing and control circuitry will set the Sl pacing train interval 62 such that the Sl pacing rate will be greater than the intrinsic ventricular rate.
• a train of Sl pulses 60 are delivered at the overdrive pacing rate corresponding to interval 62.
• the Sl pulses are set to a pulse amplitude and width that is above the pacing threshold required to capture the ventricle.
• the pacing threshold is determined previously using threshold testing methods known in the art.
• each of the Sl pulses are followed by an evoked response (ER) 64 indicating that the Sl pulses have successfully captured the ventricle.
• ER evoked response
• a T-shock 65 is delivered at a pace-T-shock interval 70 previously set such that the T-shock will be delivered during the vulnerable period following the last Sl pulse.
• the T-shock will have a high probability of being coupled to the cardiac cycle during the vulnerable period when each of the Sl pulses of Sl train 60 has captured the ventricle.
• Sl train validation includes verifying capture of at least the last Sl pulse 67 and may include verifying capture of any portion or all of the Sl pulses.
• the Sl train validation method further includes sensing for any intervening intrinsic ventricular events that could alter the timing of the refractory period relative to the last Sl pulse 67.
• intrinsic ventricular events that occur after the last Sl pulse and prior to T-shock delivery will invalidate the Sl train.
• intrinsic events occurring during the Sl train prior to the last Sl pulse 67 may also invalidate the Sl train.
• FIG. 4 is a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to the present invention.
• the steps included in the various methods described herein may be incorporated in software or firmware executed by a microprocessor for controlling ICD, AED or other appropriate medical device functions. Some functions performed during execution of the methods described herein may be embodied in dedicated integrated circuitry.
• a method 100 of validating a pacing train includes defining an Sl train validation requirement, step 101.
• the S 1 validation requirement includes an S 1 capture requirement and may include requirements regarding intrinsic ventricular event sensing.
• the Sl capture requirement for validating an Sl train requires capture by the last Sl pacing pulse prior to scheduled T-shock delivery. In other embodiments, capture by a selected portion of the Sl pulses including the last Sl pulse is required to validate the Sl train.
• capture verification operations which generally includes ER sensing and may include other methods as described below, are performed following all Sl pulses, and a minimum number of the Sl pulses, including the last Sl pulse, are required to capture the ventricles in order to validate the Sl train.
• the minimum number of Sl pacing pulses required to capture the ventricles may be all of the Sl pacing pulses.
• the Sl train validation requirement defined at step 101 may further include a requirement that no intrinsic ventricular events occur prior to T-shock delivery.
• no intrinsic events may occur between the last Sl pulse and T-shock delivery, i.e. during the pace-T-shock interval.
• intrinsic events sensed at any time during the Sl pacing train will cause the Sl train to be determined to be invalid.
• an Sl pacing train is delivered.
• the Sl pacing train may be delivered during electrophysiological testing for the purposes of VF induction, a DFT measurement or during ULV testing.
• the methods provided by the invention for validating an Sl train are valuable during ULV testing since a failure to induce VF could be due to a T-shock greater than the ULV but could also be due to delivery of the T-shock outside of the vulnerable zone.
• the clinician can be relatively confident that the T-shock was delivered within the vulnerable period and a failure to induce indicates the T-shock energy is greater than the ULV. If the Sl train is invalidated, and a T-shock was delivered but failed to induce VF, the test may be repeated until the Sl train is validated.
• DFT testing validation of the Sl train is useful to the clinician in minimizing the time required for the testing.
• a T-shock fails to induce, the clinician may spend time adjusting the pace-T-shock interval or adjusting the T-shock energy in order to successfully induce VF.
• the failure to induce may have been the result of an invalid Sl train and the T-shock energy and the pace-T-shock interval that were used may have been appropriate for VF induction if the S 1 train had been valid.
• a clinician may spend time making adjustments to the T-shock energy or pace- T-shock interval that then cause the T-shock to fail to induce VF following a valid Sl train.
• Validating the Sl train can therefore save time during DFT testing by preventing unnecessary adjustments of the T-shock energy or pace-T-shock interval. If an Sl train is found to be invalid, the Sl train can be repeated until it is valid.
• the general method summarized by Figure 4 is applicable to ULV testing and DFT testing or any other clinical testing performed which involves T-shock delivery following a pacing train.
• evoked response data is generated, step 107, that is utilized to verify capture of either all of the delivered Sl pacing pulses, at least the last Sl pacing pulse of the delivered Sl pacing train, or any desired portion of the Sl pacing pulses of the delivered Sl pacing train.
• the capture verification data may correspond to evoked response morphology, temporal consistency of the evoked response, or cross correlation of the sensing of the evoked response from multiple EGM sources, for example, as will be described below.
• a determination is then made, based on the generated evoked response data, as to whether associated capture requirements defined at step 101 are satisfied, step 110.
• the Sl train is declared invalid at step 120. For example, if the last Sl pacing pulse results in loss of capture, the Sl train is invalid.
• a T-shock may be delivered at step 135 at a predetermined pace-T-shock interval in response to the valid Sl pacing train.
• an invalid Sl train response is initiated, step 125.
• the invalid Sl train response can include any of, but is not limited to: withholding a scheduled T-shock, extending the Sl pacing pulse train, repeating the Sl pacing pulse train, adjusting the Sl pacing parameters such as rate or pulse energy, and/or generating an alert signal or displayed message on an external programmer to notify a clinician or other user that the Sl train is invalid. The clinician is thereby informed that the response to a delivered T-shock following the invalid S 1 train is unreliable for ULV or DFT measurements and can choose to repeat T-shock tests as necessary.
• FIG. 5 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention.
• capture verification of Sl pacing pulses may include either sensing of an evoked response during a predetermined sensing window during delivery of the Sl pulse train to determine the temporal consistency of the evoked response, verifying that a sensed event occurring after an Sl pulse is an actual evoked response using morphological analysis of the sensed event, or evaluating the temporal relationship between events corresponding to sensing of the evoked response at different EGM sensing locations following an S 1 pulse.
• capture verification of the Sl pacing pulses may include any combination or all three of determining the temporal consistency of the evoked response, determining the evoked response morphology, and evaluating the temporal relationship of sensing of the evoked response from multiple sensing locations.
• an Sl pacing train is delivered, step 205, and an EGM signal corresponding to each of the pulses associated with the delivered Sl pacing train is generated from signals sensed between electrodes 24 and 26, for example, step 260.
• An evoked response is determined for each EGM signal, step 265, and the evoked responses are compared to determine whether they are temporally consistent, step 270.
• the time interval of the evoked response associated with the second evoked response is compared to the time interval of the evoked response associated with the first delivered pulse
• the time interval of the evoked response associated with the third delivered pulse is compared to the time interval of the evoked response associated with the second delivered pulse, and so forth.
• the determination as to whether the evoked responses are temporally consistent is made, step 270, by determining whether the time interval of one of the evoked responses differs from the previous time interval by more than a predetermined time period, such as 10 ms, for example, although any desired time interval could be utilized. Other methods of determining the temporal consistency may also be utilized.
• the evoked responses may be determined not to be temporally consistent only after the time intervals of more than one of the evoked response differs by more than the predetermined time period.
• the determination of the temporal consistency includes assigning a weighting factor to intervals that differ by more than the predetermined time period based upon where in the delivered pulse train the inconsistent pulse occurs.
• the pulse train is determined to be invalid when the pulse having the time interval that differs from the previous pulse by more than the predetermined time period is positioned at least a predetermined number of pulses or less from the last pulse, such as three for example.
• the pulse train may be determined to be invalid only in response to the time interval associated with the last pulse differing from the previous pulse by more than the predetermined time period.
• determining the temporal consistency of the pulse may also be utilized, such as a combination of the proximity of the evoked response in the pulse train and the number of evoked response intervals that are temporally inconsistent. In addition, it is understood that other methods could be utilized to determine the temporal inconsistency in place of comparing the interval to a previous interval, such as taking an average of the determined evoked response intervals, for example. If the Sl train is determined to be temporally consistent, the Sl train is identified as being a valid pulse train, step 230, and a T-shock may be delivered, step 235, at a predetermined pace-T-shock interval in response to the valid Sl pacing train.
• the Sl train is determined to be invalid, step 220, and an invalid Sl train response is initiated, step 225.
• the invalid Sl train response can include any of, but is not limited to: withholding a scheduled T-shock, extending the Sl pacing pulse train, repeating the Sl pacing pulse train, withholding delivery of the pacing train, adjusting the Sl pacing parameters such as rate or pulse energy, and/or generating an alert signal or displayed message on an external programmer to notify a clinician or other user that the Sl train is invalid. The clinician is thereby informed that the response to a delivered T-shock following the invalid Sl train is unreliable for ULV or DFT measurements and can choose to repeat T-shock tests as necessary.
• FIG. 6 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention.
• capture verification includes the determination of the morphology of the evoked response
• an Sl pacing train is delivered, step 305, and an EGM signal corresponding to each of the pulses associated with the delivered Sl pacing train is generated from signals sensed between electrodes 24 and 26, for example, step 360.
• the morphology of each of the acquired evoked response signals is determined, step 365 and compared to a predetermined morphology template to determine whether the morphology of the individual evoked responses correlate with the morphology template, step 370. In this way, a determination is made as to whether the sensed evoked response corresponds to an intrinsic event and is therefore not a valid evoked response resulting from the associated delivered pulse.
• the morphology parameter may be any evoked response signal feature, such as peak amplitude, signal width, peak slope, or a tpmplate of the evoked response signal.
• determination of an evoked response morphology parameter may include wavelet transform or Fourier Transform analysis. Methods are known in the art for performing morphological comparisons of EGM signals. For example, comparison of digitized EGM signals using wavelet transform analysis is generally described in U.S. Pat. No. 6,393,316 issued to Gillberg, et al., incorporated herein by reference in its entirety.
• the morphology parameter may correspond to an intrinsic event, and therefore the evoked response morphologies are compared to the intrinsic event morphology to determine whether the evoked response is associated with the intrinsic event and is therefore not a valid evoked response resulting from the associated delivered pulse.
• the Sl tain is identified as being an invalid pulse train, step 320.
• the Sl pulses tain could be determined to invalid only after the morphology of more than one of the sensed evoked responses is determined to be not approximately equal to the morphology template.
• the determination of the morphology of the evoked response includes assigning a weighting factor to the determined invalid pulses based upon where in the delivered pulse train the intrinsic event occurs.
• the pulse train is determined to be invalid when the pulse associated with the determined intrinsic event is positioned at least a predetermined number of pulses or less from the last pulse, such as three for example.
• the pulse train may be determined to be invalid only in response to the last pulse being determined to be an intrinsic event.
• morphology may also be utilized, such as a combination of the proximity of the pulse associated with an intrinsic event in the pulse train and the number of evoked responses that do not matches the morphology template, i.e., are determined to be intrinsic events.
• an invalid Sl train response is initiated, step 325.
• the invalid Sl train response can include any of, but is not limited to: withholding a scheduled T-shock, extending the Sl pacing pulse train, repeating the Sl pacing pulse train, withholding delivery of the pacing pulse train, adjusting the Sl pacing parameters such as rate or pulse energy, and/or generating an alert signal or displayed message on an external programmer to notify a clinician or other user that the Sl train is invalid.
• the clinician is thereby informed that the response to a delivered T-shock following the invalid Sl train is unreliable for ULV or DFT measurements and can choose to repeat T-shock tests as necessary.
• the Sl train is identified as being a valid pulse train, step 330, and a T-shock may be delivered, step 335, at a predetermined pace-T-shock interval in response to the valid Sl pacing train.
• FIG. 7 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention.
• capture verification includes the determination of the temporal relationship of sensing of the evoked response from multiple sensing locations
• an Sl pacing train is delivered, step 405, and an EGM signal corresponding to each of the pulses associated with the delivered Sl pacing train is generated from signals sensed at two or more sensing locations, step 460, such as between electrodes 24 and 26 positioned along lead 16 and electrodes positioned along coronary sinus lead 6, for example.
• a determination of the sequence of the EGM signals is made, step 465, and based on the EGM sequence, a determination is made as to whether the temporal relationship of the EGM signals sensed from different locations is valid, step 470.
• the evoked response results from the delivered pacing pulse, rather than an intrinsic event, the evoked response will be sensed by the sensing electrode positioned within the apex of the right ventricle prior to being sensed by the electrode positioned along the coronary sinus and the left ventricle.
• the temporal relationship of the sensed EGM signals will be determined to be valid if the evoked response is sensed at the right ventricle prior to being sensed at the left ventricle, and invalid if the evoked response is sensed at the left ventricle prior to being sensed at the right ventricle.
• the Sl train is determined to be associated with a valid EGM temporal relationship, the Sl train is identified as being a valid pulse train, step 430, and a T- shock may be delivered, step 435, at a predetermined pace-T-shock interval in response to the valid Sl pacing train.
• the Sl train is determined not to be associated with a valid EGM temporal relationship, the Sl train is determined to be invalid, step 420, and an invalid Sl train response is initiated, step 425.
• the invalid Sl train response can include any of, but is not limited to: withholding a scheduled T- shock, extending the Sl pacing pulse train, repeating the Sl pacing pulse train, adjusting the Sl pacing parameters such as rate or pulse energy, and/or generating an alert signal or displayed message on an external programmer to notify a clinician or other user that the S 1 train is invalid. The clinician is thereby informed that the response to a delivered T-shock following the invalid Sl train is unreliable for ULV or DFT measurements and can choose to repeat T-shock tests as necessary.
• FIG. 8 a flow chart of a method of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention.
• a method 600 of validating a pacing train associated with the delivery of a high-energy pulse in a medical device according to an embodiment of the present invention is performed during the delivery of an Sl pacing train for validation of the Sl train during DFT or IJLV measurements.
• Capture verification method 600 may be performed in response to the last Sl pacing pulse or in response to any selected portion or all of the Sl pacing pulses, in accordance with a previously defined capture requirement for Sl train validation.
• an ER sensing window is set at step 610.
• the selected EGM sources are sensed at step 615, which may include sensing of one or more EGM sources.
• decision step 620 method 600 determines if an event is sensed from the EGM signal(s). ER sensing circuitry and methods may be generally implemented according to methods known in the art. If no events are sensed following the Sl pulse, loss of capture is declared at step 635. The Sl train may be declared invalid at step 640 according to the Sl capture requirements.
• method 600 determines if the event occurred during the ER sensing window, step 625. If the sensed event occurs outside the ER sensing window, the event is declared an intrinsic event, step 630. If no event is sensed within the ER sensing window and an intrinsic event is sensed outside the ER sensing window, loss of capture is declared, step 635. The Sl train may be declared invalid at step 640 depending on the Sl capture requirements. If the sensed event does occur within the ER window as determined at step 625, a morphological comparison of the sensed event and a previously stoi'ed ER morphology parameter or template is performed, step 645.
• the sensed event morphology is declared an intrinsic event, step 630. Loss of capture is declared, step 635, and the Sl pacing train may be declared invalid, step 640 depending on the Sl capture requirements. If the sensed event morphology is substantially equal to the previously stored ER morphology, the temporal relation between sensed events occurring on different EGM signal sources is determined by comparing the timing of the sensing of the event at the EGM sources, step 650, and a determination is made as to whether a temporal relationship between the sensing of the event at the EGM sources is substantially equal to the ER temporal relationship determined and stored previously, step 655.
• the event is declared an intrinsic event, step 630.
• Loss of capture is declared, step 635, and the Sl train may be determined to be invalid, step 640 depending on the Sl capture requirement.
• capture is declared, step 660.
• the Sl pacing train may be declared valid if all Sl pulses for which capture verification is required are determined to capture the ventricle and no invalidating intrinsic events are sensed as described previously.
• ventricular capture by an Sl pulse may be verified based on sensing a ventricular event during an ER sensing window.
• capture verification includes any combination of sensing an event during an ER sensing window, matching the sensed event morphology to a previously stored ER morphology, and matching the temporal relation between sensed events on multiple EGM signals to a previously determined ER temporal relation. Any combination of these capture verification techniques may be used following one or more Sl pulses to determine if the Sl pacing train capture requirement is met.
• the programmable processor may include one or more individual processors, which may act independently or in concert.
• a "computer-readable medium” includes but is not limited to any type of computer memoiy such as floppy disks, conventional hard disks, CR-ROMS, Flash ROMS, nonvolatile ROMS, RAM and a magnetic or optical storage medium.
• the medium may include instructions for causing a processor to perform any of the features described above for initiating a session of the escape rate variation according to the present invention.

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