WO2024104706A1

WO2024104706A1 - Implantable medical device having an automatic surgery recognition mode

Info

Publication number: WO2024104706A1
Application number: PCT/EP2023/079211
Authority: WO
Inventors: Bjoern Henrik Diem; Thomas Doerr
Original assignee: Biotronik Se & Co. Kg
Priority date: 2022-11-18
Filing date: 2023-10-20
Publication date: 2024-05-23

Abstract

The invention relates to an implantable medical device (4) for stimulating a human or animal tissue or organ, comprising a processor (11), a memory unit (12), a stimulation unit (8) configured to stimulate a human or animal tissue or organ, and a detection unit (9) configured to detect an electric signal of the same tissue or organ. The memory unit (12) comprises a computer-readable program that causes the processor (11) to perform the following steps when executed on the processor (11): a) detecting, with the detection unit (9), an electromagnetic field having a frequency lying in a range of from 100 kHz to 5 MHz; b) reading device activity data from the memory unit (12), the device activity data indicating whether the stimulation unit (8) emitted a stimulation pulse within a first time window, the first time window covering up to 48 hours prior to the detection of the electromagnetic filed in step a); and c) automatically switching an operation of the implantable medical device (4) from a first operational mode (23) to a second operational mode (22A, 22B), wherein the device activity data read in step b) is at least co-decisive for the chosen second operational mode (22A, 22B).

Description

IMPLANTABLE MEDICAL DEVICE HAVING AN AUTOMATIC SURGERY RECOGNITION MODE

The present invention relates to an implantable medical device according to the preamble of claim 1, to an arrangement comprising such an implantable medical device according to claim 11, and to a method for operating such a medical device according to the preamble of claim 15.

Implantable medical devices are used for many applications in stimulating tissue or organs. For this purpose, the implantable medical devices senses electric signals from the tissue or organ to be stimulated and applies a stimulation only in such cases in which the stimulation is indeed needed. Thus, it is mandatory for such implantable medical devices to finely detect electric signals from the tissue or organ to be stimulated.

If a patient carrying an implantable medical device is subjected to an electrosurgical procedure (such as electrocautery), strong electric fields can act upon the patient and the implantable medical device implanted to the patient. These electromagnetic fields can negatively influence the functioning of the implantable medical device. To avoid any malfunctioning, implantable medical devices are typically manually reprogrammed or deactivated prior to such electrosurgical procedure and again reprogrammed or reactivated after having terminated that electrosurgical procedure. By this quite laborious process steps, malfunctioning of an implantable medical device such as inadequate shocks in case of implantable cardioverter defibrillators (ICDs) or the inhibition of the stimulation function in case of implantable pulse generators (IPGs) are avoided. However, it would be desirable to provide a less laborious possibility of avoiding malfunctioning due to electrosurgical procedures. EP 2 338 561 Bl addresses this problem and discloses an implantable medical device that is transferred into an asynchronous operating state upon detecting electromagnetic interference fields, wherein the asynchronous operating state is always associated with a change of the stimulation amplitude and/or the stimulation pulse width.

It is an object of the present invention to provide an implantable medical device that avoids a malfunctioning during an electrosurgical procedure while minimizing any restrictions of the usability of the implantable medical device that are associated with prior art solutions.

This object is achieved with an implantable medical device having the claim elements of claim 1. Such an implantable medical device serves for stimulating a human or animal tissue or a human or animal organ. The implantable medical device comprises a processor, a memory unit, a stimulation unit, and a detection unit. The stimulation unit is configured to stimulate a human or animal tissue or organ. The detection unit is configured to detect an electric signal of the same tissue or organ.

According to an aspect of the present invention, the memory unit comprises a computer- readable program that causes the processor to perform the steps explained in the following when being executed on the processor.

In a first step, an electromagnetic field is detected with the detection unit. This electromagnetic field has a frequency lying in a range of from 100 kHz to 5 MHz, in particular of from 200 kHz to 4.5 MHz, in particular from 250 kHz to 4 MHz, in particular from 300 kHz to 3.5 MHz, in particular from 350 kHz to 3 MHz, in particular from 400 kHz to 2.5 MHz, in particular from 500 kHz to 2 MHz, in particular from 600 kHz to 1.5 MHz, in particular from 700 kHz to 1 MHz, in particular from 800 kHz to 900 kHz.

In another method step, device activity data is read from the memory unit. The device activity data indicates whether the stimulation unit has emitted a stimulation pulse within a first time window. In this context, the first time window covers up to 48 hours, in particular 1 hour to 48 hours, in particular 2 hours to 42 hours, in particular 3 hours to 36 hours, in particular 4 hours to 30 hours, in particular 5 hours to 24 hours, in particular 6 hours to 18 hours, in particular 7 hours to 12 hours prior to the detection of the electromagnetic field in the precedingly explained step. Expressed in other words, the device activity data indicates whether or not the implantable medical device has been active in a predefined time period lying temporarily before the detection of the electromagnetic field.

In a further method step, an operation of the implantable medical device is automatically switched from a first operational mode to a second operational mode. In this context, the device activity data read in the precedingly explained step is at least co-decisive, in particular the only decision-making parameter, for the chosen second operational mode. Thus, it is possible to choose one of different variants of the second operational mode, wherein the choice is an automatic choice that is based on the device activity data.

The implantable medical device enables to carry out electrosurgical procedures on patients to whom such an implantable medical device has been implanted without making it necessary to manually reprogram the implantable medical device to avoid a malfunctioning of the implantable medical device due to electromagnetic interference by the electrosurgical procedure. In this context, an automatic smart reprogramming of the implantable medical device is carried out the takes into consideration the concrete use of the implantable medical device by the patient to whom the device is implanted. If the patient’s body has not required an activity of the implantable medical device within the first time window, it is not necessary (or even be unfavorable) if the implantable medical device would apply an unspecific stimulation to the patient in the second operational mode of the implantable medical device during the procedure that generates an electromagnetic field in the above-mentioned frequency range. Rather, it is favorable in such a case if the stimulation function of the stimulation unit of the implantable medical device simply deactivated. While such deactivation may be highly dangerous for patients requiring regular stimulation by the implantable medical device, it does not present a specific risk for patients that have not required an assistance by the implantable medical device within the first time window. Therefore, the device activity data used for making a decision on which of the possible second operational states is chosen significantly increases the safety and usability of the implantable medical device, yet allowing a patient-specific adaptation of the functions and operations of the implantable medical device during surgical or other operations being connected to the occurrence of electromagnetic fields in the above-mentioned frequency range.

Due to the automatic detection of the electromagnetic field and the automatic switching of the operational mode of the implantable medical device, it is not necessary to manually reprogram the implantable medical device prior to and after a surgical intervention or another intervention making use of such electromagnetic fields. Therefore, the preparation time prior to subjecting the patient carrying the implantable medical device to electromagnetic fields having the above-mentioned frequency range is significantly shortened. Consequently, the implantable medical device is operated in the second operational state only during a shorter period of time than in case of implantable medical devices that require manual reprogramming. As a result, the patient can take advantage of the full functionality of the implantable medical device for longer period of time, i.e., until shortly before being subjected to an electromagnetic field in the above-mentioned frequency range and already shortly after the termination of the procedure that causes the emission of electromagnetic fields in the above-mentioned frequency range.

In an embodiment, the computer-readable program causes the processor to detect signals emitted from an electrocautery. Such electrocauteries are typically used for cauterization procedures; they emit electromagnetic fields having a frequency lying in the above- mentioned frequency range. In an embodiment, the detection unit is specifically arranged and designed to detect and optionally to evaluate an electromagnetic field of an electrocautery. This can be done, e.g., by detecting interfering signals imprinted into the physiologic electric signal read from the patient.

In an embodiment, the second operational mode is an operational mode in which a stimulation function of the stimulation unit is deactivated and/or an operational mode in which a recording of data detected by the detection unit is deactivated, if the device activity data indicated that the stimulation unit did not emit a stimulation pulse within the first time window. In such a case, the patient obviously does not require, in its current health state, stimulation by the implantable medical device. Therefore, it is generally possible to deactivate more relevant functions of the implantable medical device than in other cases in which the patient regularly requires a stimulation by the implantable medical device. The stimulation function of the stimulation unit can be deactivated, e.g., if the implantable medical device is an implantable pulse generator (IPG), an implantable cardioverter defibrillator (ICD), a device for cardiac resynchronization therapy (CRT) or a neural stimulator.

In an embodiment, the deactivated stimulation function of the stimulation unit is a defibrillation function. Such a defibrillation function is typically employed by ICDs and CRT devices. In an embodiment, the deactivated stimulation function is an antitachycardiac stimulation. Such an antitachycardiac stimulation is typically employed by an IPG, an ICD or a CRT device. In an embodiment, the deactivated stimulation function is a biventricular stimulation. Such a biventricular stimulation is typically employed by a CRT device. The deactivation of the stimulation function can also be performed if the implantable medical device is a neural stimulator. Then, no neural stimulation will be possible as long as the implantable medical device is operated in the second operational state.

If the patient does, in his actual health state, apparently - based on the device activity data - not require stimulation by the implantable medical device, it is also not necessary to record data detected by the detection unit since the recorded data will be interfered by the electromagnetic field. To give a specific example, electrocardiogram (ECG) recordings (which are regularly done by IPGs, ICDs, and/or CRT devices) are deactivated in an embodiment.

In an embodiment, the second operational mode is an operational mode featuring an asynchronous stimulation function of the stimulation unit and/or an operational mode featuring an increase of the stimulation pulse amplitude and/or an operational mode featuring an increase of the stimulation pulse which and/or an operational mode in which a biventricular stimulation by the stimulation unit is activated, if the device activity data indicated that the stimulation unit emitted a stimulation pulse within the first time window. In such a case, the patient apparently requires stimulation by the implantable medical device so that the core functionality of the implantable medical device is not to be deactivated during the surgical or other procedure that causes a generation of the electromagnetic field. An asynchronous stimulation function of the stimulation unit is, e.g., employed in an IPG, an ICD or a CRT device. Such an asynchronous stimulation function guarantees stable stimulation of the patient’s tissue or organ to be stimulated (such as the patient’s heart) even though the detection unit cannot properly detect electrical signals from the patient because of the electromagnetic field. However, such asynchronous stimulation function should not be generally applied since many patients do not require any stimulation during a surgical procedure, as explained above. Therefore, the additional consideration of the device activity data significantly increases the safety and usability of the implantable medical device - the relevant functionality of the implantable medical device is not deactivated if the patient required the implantable medical device’s function in a short time window prior to starting the surgical or other procedure that generates the detected electromagnetic fields.

It should be noted that the device activity data does not consider a time window in which the surgical or other procedure generating the electromagnetic field has already been started, but only relies on a time window that lies before the occurrence and detection of the electromagnetic field. Thus, any negative or positive impact of the electromagnetic field onto the patient is excluded from consideration when deciding in which second operational state the implantable medical device is operated.

An increase of the stimulation pulse amplitude increases the chances that the stimulation pulse is indeed capable of stimulating the patient’s organ or tissue even in presence of the electromagnetic field that may attenuate the efficacy of the stimulation pulse. Likewise, an increase of the stimulation pulse with increases the total energy of the stimulation pulse (which is calculated as the integral of the stimulation pulse) and thus reduces the risk that stimulation pulse would not result in the desired physiologic effect. An activation of a biventricular stimulation (instead of a stimulation of the left ventricle only) can also increase the efficacy of the stimulation. Such biventricular stimulation is typically applied by a CRT device for cardiac resynchronization applications.

In an embodiment, the computer-readable program causes the processor to activate an electrical protection circuit of the implantable medical device. This electrical protection circuit protects the implantable medical device from damages due to an energy input from the detected electromagnetic field. Since such device protection is helpful irrespective of the patient’s need regarding stimulation, the activation of the electrical protection circuit is independent on the detected device activity data.

In an embodiment, the computer-readable program causes the processor to detect, with the detection unit, an energy of the electromagnetic field. In this embodiment, the computer- readable program causes the processor furthermore to automatically switch the operation of the implantable medical device from the first operational mode to the second operational mode only if the detected energy exceeds a predetermined threshold. Thus, in this embodiment, an energy of the electromagnetic field exceeding a predetermined threshold is a prerequisite for switching the implantable medical device into the second operational state. The kind or variant of the second operational state is then chosen on the basis of at least the device activity data. However, if the energy of the detected electromagnetic field is low (i.e., lies below the predetermined threshold), no interference of the electromagnetic field with the proper functioning of the implantable medical device is to be feared. Therefore, the implantable medical device can be further operated in its first operational state in such a situation.

In an embodiment, the detection unit comprises a separate detection channel that serves for detecting the electromagnetic field. This separate detection channel does not serve for detecting the electrical signals from the tissue or organ of the patient (i.e., the core functionality of the implantable medical device). Rather, the regular physiologic signals are detected with a first detection channel and the electromagnetic field is detected with the separate detection channel. By separating the detection functionalities of the detection unit, the detection sensitivity can be increased.

In an embodiment, the separate detection channel is an integral part of at least one electrical sensing functionality of the implantable medical device.

In an embodiment, the computer-readable program causes the processor to evaluate an additional criterion being indicative for a surgical intervention, in particular an electrosurgical intervention, to be performed on a patient to whom the implantable medical device is implanted. Such additional criterion is, e.g., the position (or posture) of the patient (e.g., a horizontal position of the patient) and/or impedance measuring signals of the detection unit or an external ECG monitor. The position of the patient is preferably determined by means of a 3D accelerometer or motion sensor in the implant. 3D accelerometers for position determination are already used in implants, for example in implants configured for heart failure monitoring. During or after implantation, these sensors may be calibrated once with regard to their position information individually for each patient. After calibration such sensors can reliably provide the patient's position information. Since the surgical situation is usually always associated with a lying position of the patient, the use of an additional criterion as position of the patient would make the indication for a surgical intervention more reliable. In addition, by means of an impedance measuring cell present in the implant, the typical signals of external ECG monitors may be detected, which could be fed in by the external monitors in order to monitor the correct contact of the external ECG electrodes by means of an impedance measurement. Narrow spikes of a current injection by the external ECG monitor may be used as additional criterion being indicative for surgical intervention. The additional criterion further increases the probability that the detected electromagnetic field indeed originates from a surgical device such as an electrocautery. Therefore, considering the additional criterion further increases the safety of the implantable medical device since its functions will only be adapted if the probability of a surgical intervention has been proven to be high.

In an embodiment, the computer-readable program causes the processor to automatically switch the operation of the implantable medical device from the first operational mode to the second operational mode if the device activity data comprises a pattern of stimulation pulses within the first time window that fulfils a predefinable pattern criterion. Thus, it is not only possible to rely on a single signal or a single stimulation activity in the past, but rather on a patterned activity. Such patterned activity can comprise much more complex device activity data than data on single individual stimulation events. Therefore, different patterns of stimulation pulses can be assigned to different health conditions of the patient carrying the implantable medical device so that a very appropriate choice of the second operational mode can be made in view of the health condition of the patient. Once again, this significantly increases the usability of the implantable medical device and the treatment comfort conveyed by the implantable medical device. The pattern of stimulation pulses can have, e.g., qualitative and/or qualitative information. Thus, a specific amount of stimulation pulses within a predefinable time period indicates a frequency of stimulation and thus the general stimulation need of the patient. Specific sequences of pulses can also make up the pattern of stimulation pulses and can be indicative for a specific health condition of the patient. By relying on the pattern of stimulation pulses, statistical data regarding the stimulation unit activity is considered for choosing an appropriate second operational mode for the operation of the implantable medical device.

In an embodiment, the computer-readable program causes the processor to automatically switch the operation of the implantable medical device from the second operational mode back to the first operational mode after a second time period has passed. The second time period is, e.g., a predetermined or predeterminable time period. The second time period serves for a temporal hysteresis with respect to switching back from the second operational mode to the first operational mode.

In an embodiment, it is necessary that no electromagnetic field has been detected during the second time period in order to achieve a switch back from the second operational mode to the first operational mode. Generally, it would also be possible to allow such switch back to the first operational mode after the second time period has elapsed, wherein the operational mode would again be switched to the second operational mode immediately after detecting again an electromagnetic field. The operative result with respect to the functionality of the implantable medical device would be basically the same. However, avoiding a switch back to the first operational mode and an immediate switch back again to the second operational mode might be connected to an increased energy consumption of the implantable medical device. Such additional energy consumption is typically not favorable with respect to the longevity of the implantable medical device, considering that the battery capacity of the implantable medical device is one of the critical parameters for the longevity of the implantable medical device. In an embodiment, the implantable medical device comprises a communication unit by which the implantable medical device can be connected with a remote monitoring system in a wireless manner for transferring data to the remote monitoring system in a wireless manner. All standard data transmission protocols or specifications are appropriate for such a wireless data communication. Examples of standard data transmission protocols or specifications are the Medical Device Radiocommunications Service (MICS), the Bluetooth Low Energy (BLE) protocol and the Zigbee specification. Such a remote monitoring system can significantly increase the safety of the implantable medical device since its status and the activated operational state can be monitored from remote even during a surgical intervention.

In an aspect, the present invention relates to an arrangement that comprises an implantable medical device according to the preceding explanations as well as a remote monitoring system operatively coupled to the implantable medical device. Such an arrangement enables a trained person (such as trained medical staff) to remotely monitor the status of the implantable medical device and to be able to inform the patient or a medical doctor in the patient’s vicinity on any (assumed) malfunctioning of the implantable medical device or any abnormal behavior of the implantable medical device that may lead to a malfunction.

In an embodiment, the computer-readable program causes the processor to transfer data indicative on an activated operational mode of the implantable medical device to the remote monitoring system. Then, it is particularly easy to observe the activated operational mode of the implantable medical device from a remote location.

In an embodiment, the computer-readable program causes the processor to automatically perform an integrity check upon switching the operation of the implantable medical device from the second operational mode to the first operational mode and to transfer data obtained by the integrity check to the remote monitoring system. By such integrity check, it can be assured that the implantable medical device is proper functioning even in its “standard” operational mode, i.e., the first operational mode after having been operated for a time period such as the second time period in the second operational mode. Such an integrity check will provide information on the further proper functioning of the implantable medical device during an extended time period, namely, after a surgical or other intervention on the patient that led to the occurrence of the electromagnetic field has been terminated. Since the first operational mode is an operational mode in which the implantable medical device is intended to be operated during months or even years, it is particularly helpful for medical staff and the patient to have positive knowledge on a proper functioning of the implantable medical device in the first operational mode.

In an embodiment, the computer-readable program causes the processor to automatically perform an additional integrity check upon switching the operation of the implantable medical device from the first operational mode to the second operational mode and/or during operation of the implantable medical device in the second operational mode. In this embodiment, the computer-readable program causes the processor further to automatically transfer data obtained by the additional integrity check to the remote monitoring system. This additional integrity check also ensures proper functioning of the implantable medical device during its operation in the second operational state. However, since the implantable medical device is typically only operated in the second operational state for a couple of minutes or hours, the additional integrity check does typically not have the same impact for the functionality or monitoring of the implantable medical device as the integrity check optionally performed when switching the operational mode of the implantable medical device back from the second operational mode to the first operational mode.

In an aspect, the present invention relates to a method for operating an implantable medical device according to the preceding explanations. This method comprises the steps explained in the following.

In one method step, a detection unit of the implantable medical device is used for detecting an electromagnetic field having a frequency in a range of from 100 kHz to 5 MHz.

In another method step, device activity data is read from a memory unit of the implantable medical device. This device activity data indicates whether a stimulation unit of the implantable medical device has emitted stimulation pulse within a first time window. In this context, the first time window covers up to 48 hours prior to the detection of the electromagnetic field in the precedingly explained step. In a further method step, an operation of the implantable medical device is automatically switched from a first operational mode to a second operational mode. In this context, the device activity data read in the precedingly explained step is at least co-decisive for the chosen second operational mode.

All embodiments of the implantable medical device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the arrangement and to the method. Likewise, all embodiments of the arrangement can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device and to the method. Finally, all embodiments of the method can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device and to the arrangement.

Further details of aspects of the present invention will be explained in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

Figure 1 schematically illustrates a typical workflow known from prior art for manually reprogramming an implantable medical device;

Figure 2 schematically illustrates a workflow for reprogramming an embodiment of an implantable medical device;

Figure 3 schematically illustrates a block diagram of an embodiment of an implantable medical device; and

Figure 4 schematically illustrates a flowchart for automatically adapting the operational state of an implantable medical device to a detected electrosurgical procedure.

Figure 5 Exemplary electrical protection circuit of the implantable medical device according to embodiments of the invention Figure 1 schematically illustrates a prior art workflow for manually reprogramming an implantable pulse generator (IPG) as example of an implantable medical device.

A patient 1 that will be subjected to an electrosurgical procedure 3 has first to visit an implant specialist 2 who will carry out a reprogramming of the implantable medical device implanted to the patient 1 prior to the electrosurgical procedure 3, e.g. in a preparation room (left box in Figure 1). The implant specialist 2 will typically activate an asynchronous stimulation mode if the patient 1 generally requires the pacing functionality of the implant. The implant specialist may alternatively, e.g., deactivate a shocking function of an implantable cardioverter-defibrillator (ICD) to avoid an undesired inhibition of the ICD or inadequate shock delivery during the electrosurgical procedure 3.

Subsequently, the patient 1 is subjected to the electrosurgical procedure 3 (central box in Figure 1). The implant will work according to the reprogramming performed by the implant specialist 2.

After having terminated the electrosurgical procedure 3, the patient 1 has to return to the implant specialist 2 in the third method step (right box in Figure 1). The implant specialist 2 will then restore the initial implant programming. Since this third step is not necessarily performed directly after having terminated the electrosurgical procedure 3, the implant of the patient 1 may be operated in the operational state that was set in the initial reprogramming step for an extended period of time. This can result in critical health conditions or even lifethreatening situations. Therefore, it is necessary to organize the manual reprogramming step illustrated in figure 1 in the hospital in such a way that not too much time passes between the electrosurgical procedure 3 and the reprogramming performed by the implant specialist 2.

Figure 2 schematically illustrates a workflow that is applied if the patient has been implanted an embodiment of an implantable medical device. In this and in all following figures, similar elements will be denoted with the same numeral reference. Here, the patient 1 can be subjected directly to a electrosurgical procedure 3 without attending the manual reprogramming steps illustrated in Figure 1. The patient 1 carries an implantable pulse generator 4 as implantable medical device. The implantable pulse generator 4 automatically detects the presence of electromagnetic fields having a frequency of 100 kHz to 5 MHz. Such electromagnetic fields are typically generated during the electrosurgical procedure 3 by the electrosurgical devices used during this electrosurgical procedure 3. Data on the status and/or activity of the implantable pulse generator 4 are transferred to a remote monitoring system 5. An implant specialist 2 can all look at the transferred data, e.g., in form of a report 6. Thus, it is possible for the implant specialist 2 to monitor the status of the implantable pulse generator 4 during the electrosurgical procedure 3. Due to the automatic detection of the electromagnetic fields and due to an automatic switch of the operational state of the implantable pulse generator 4, no manual reprogramming prior to and after the electrosurgical procedure 3 is any longer necessary. This significantly saves time for the patient 1 and reduces error sources with respect to a correct programming of the implantable pulse generator 4.

The report 6 comprises at least one of the following: self-test information of the implantable pulse generator 4 that has been automatically obtained by the implantable pulse generator 4 after the electrosurgical procedure 3 has been terminated; data on the electrodes of the implantable pulse generator 4 (such as an impedance, amplitudes, stimulation thresholds, ECG information); technical device data (such as battery voltage, battery impedance, reference voltage prior to and after the electrosurgical procedure 3, error entries in an error table of the implantable pulse generator for).

Figure 3 schematically illustrates a block diagram of an implantable pulse generator 4, e.g., the implantable pulse generator 4 already referred to in Figure 2. The implantable pulse generator 4 comprises an electrode lead 7 that is implanted into or at body tissue of a patient. This electrode lead 7 receives stimulation pulses from a stimulation unit 8 and is able to transfer electrical signals from the patient’s tissue to a detection unit 9. Both the stimulation unit 8 and the detection unit 9 are connected to a control unit 10 that, in turn, is operatively connected to a processor 11. The processor 11 can access a memory unit 12 in which, amongst others, different operational modes of the implantable pulse generator 4 are stored. The detection unit 9 is arranged and designed to detect biological (physiologic) electrical signals of the patient via the electrode lead 7. In addition, the detection unit 9 is arranged and designed to detect an interfering electromagnetic field. If such an electromagnetic field is detected by the detection unit 9, this information is passed by the control unit 10 to the processor 11. The processor 11 then retrieves from the memory unit 12 device activity data being indicative on an activity of the stimulation unit 8 in a predefinable time window prior to the detection of the electromagnetic field. This device activity data illustrates if and to which extent the stimulation of the patient was necessary by the stimulation unit 8 very shortly before the electromagnetic field has been detected. The electromagnetic field is indicative of an electrosurgical procedure during which certain functionalities of the implantable pulse generator 4 should be deactivated or modified in order to avoid malfunctioning of the implantable pulse generator 4 during the electrosurgical procedure. By considering the device activity data retrieved from the memory unit 12, the processor then activates a specific operational mode of the implantable pulse generator 4, the relevant data of which is also stored in the memory unit 12. If the device activity data retrieved from the memory unit 12 indicates that the stimulation unit 8 has not been active in the last 48 hours prior to the detection of the electromagnetic field, the processor 11 will deactivate a stimulation functionality of the stimulation unit 8 for the duration of the electrosurgical procedure (approximated by a predefinable time period).

To safely detect an interfering electromagnetic field originating from an electrosurgical device such as an electrocautery, the detection unit 9 performs, e.g., a wavelet decomposition of the detected signal in order to extract the typical signal of an electrocautery.

Generally, it would also be possible that the stimulation unit 8 is a combined stimulation and detection unit that is specialized in detecting physiologic electrical signals via the electrode lead 7. At the same time, the detection unit 9 could be arranged and designed such to only detect non-physiologic signals in form of electromagnetic fields having a frequency lying in a range of from 100 kHz to 5 MHz. Likewise, the memory unit 12 could have different (logical) program memory entities from which different operational modes for operating the implantable pulse generator 4 in different operational modes could be retrieved. Figure 4 shows a schematic flowchart of a method performed by an embodiment of an implantable medical device, e.g. the implantable pulse generator 4 referred to in Figures 2 and 3.

In a detection step 20, the detection unit of the implantable medical device checks whether there is an electromagnetic field having a frequency lying in a range of from 100 kHz to 5 MHz. If this is the case (Y), device activity data is retrieved from the memory unit of the implantable medical device and is evaluated in a device activity data evaluation step 21. It is then checked if the device activity data indicates that the stimulation unit of the implantable medical device has been active within a first time window (e.g., within 48 hours prior to detecting the electromagnetic field in the detection step 20). If this is the case (Y), a first variant 22A of a second operational mode of the implantable medical device is activated. If the device activity data checked in the device activity data evaluation step 21 indicates that there has been no activity of the stimulation unit within the first time window (N), a second variant 22B of the second operational mode of the implantable medical device is activated.

Both the first variant 22A and the second variant 22B of the second operational mode of the implantable medical device have different functions than a first operational mode 23. Afterwards, a hysteresis timer 24 is activated. This hysteresis timer 24 prohibits a switch back from the first variant 22A or the second variant 22B of the second operational mode to the first operational mode 23. This will be explained in the following in more detail.

If no electromagnetic field having a frequency lying in a range of from 100 kHz to 5 MHz has been detected in the detection step 20 (N), it is checked in a hysteresis timer checking step 25 whether the hysteresis timer 24 is still active. If this is the case (Y), the previously activated first variant 22A or second variant 22B of the second operational mode is maintained. The system moves back to the detection step 20. If, however, it is found in the hysteresis timer checking step 25 that the hysteresis timer 24 is no longer active (N), the system switches back to the first operational state 23 in which the implantable medical device is operated with its usual functionality (without any rigid restrictions). The system moves back to the detection step 20 to safely detect electromagnetic fields occurring in the future. By reading device activity data of the implantable medical device in the device activity data evaluation step 21, the most appropriate variant 22 A or 22B of the second operational state can be chosen to provide the implantable medical device with the best suited functionality during the presence of the electromagnetic field.

Obviously, two variants 22A and 22B of the second operational state only illustrate the minimum functionality of the implantable medical device. Generally, the number of variants of the second operational mode is not limited. Rather, the memory unit of the implantable medical device can store the programming parameters for as many variants of the second operational state as needed to adjust the functionality of the implantable medical device to current and future needs of patients or medical staff.

Referring now to Figure 5, depicted is an exemplary electrical protection circuit 30 of the implantable medical device according to embodiments of the invention. The electrical protection circuit 30 comprises two protection FET transistors 35 and 36. Protection FET transistor 35 is connected to the connector of the lead tip of the electrode lead, wherein protection FET transistor 36 is connected to the connector of the lead ring of the electrode lead. Both protection FET transistors are controlled via control line 37. In case a disturbance electromagnetic field is detected, e.g. caused by a surgery instrument, both protection FET transistors 35, 36 can be switched off by control line 37. Consequently, the disturbance electromagnetic fields cannot couple into the lead neither via the connector of the lead tip nor via the connector of the lead ring, so that the implantable medical device is protected from damages due to an energy input from the disturbance. Electromagnetic Interference (EMI) capacitors 33 and 24 act as additional protection from high frequency signals as with typical EMI signals, since high frequency signals will pass the capacitors to ground due to their low impedance characteristics for high frequencies, whereat low frequency signals are not affected.

Claims

1. Implantable medical device (4) for stimulating a human or animal tissue or organ, comprising a processor (11), a memory unit (12), a stimulation unit (8) configured to stimulate a human or animal tissue or organ, and a detection unit (9) configured to detect an electric signal of the same tissue or organ, characterized in that the memory unit (12) comprises a computer-readable program that causes the processor (11) to perform the following steps when executed on the processor (11): a) detecting, with the detection unit (9), an electromagnetic field having a frequency lying in a range of from 100 kHz to 5 MHz; b) reading device activity data from the memory unit (12), the device activity data indicating whether the stimulation unit (8) emitted a stimulation pulse within a first time window, the first time window covering up to 48 hours prior to the detection of the electromagnetic filed in step a); and c) automatically switching an operation of the implantable medical device (4) from a first operational mode (23) to a second operational mode (22A, 22B), wherein the device activity data read in step b) is at least co-decisive for the chosen second operational mode (22A, 22B).

2. Implantable medical device according to claim 1, characterized in that the second operational mode (22A, 22B) is at least one chosen from the group consisting of an operational mode in which a stimulation function of the stimulation unit is deactivated and an operational mode in which a recording of data detected by the detection unit is deactivated, if the device activity data indicated that the stimulation unit (8) did not emit a stimulation pulse within the first time window. Implantable medical device according to claim 1 or 2, characterized in that the second operational mode (22A, 22B) is at least one chosen from the group consisting of an operational mode featuring an asynchronous stimulation function of the stimulation unit, an operational mode featuring an increase of a stimulation pulse amplitude, an operational mode featuring an increase of a stimulation pulse width, and an operational mode in which a biventricular stimulation by the stimulation unit is activated, if the device activity data indicated that the stimulation unit (8) emitted a stimulation pulse within the first time window. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (11) to activate an electrical protection circuit of the implantable medical device (4) that protects the implantable medical device (4) from damages due to an energy input from the detected electromagnetic field. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (11) to detect, with the detection unit (8), an energy of the electromagnetic field and to automatically switch the operation of the implantable medical device (4) from the first operational mode (23) to the second operational mode (22A, 22B) only if the detected energy exceeds a predeterminable threshold. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (11) to evaluate an additional criterion being indicative for a surgical intervention (3) to be performed on a patient (1) to whom the implantable medical device is implanted. Implantable medical device according to claim 6, characterized in that the additional criterion is at least one of a position of the patient (1) and an impedance measured with the detection unit or an external ECG monitor. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (11) to automatically switch the operation of the implantable medical device (4) from the first operational mode (23) to the second operational mode (22A, 22B) only if the device activity data comprises a pattern of stimulation pulses within the first time window that fulfils a predefinable pattern criterion. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (11) to automatically switch the operation of the implantable medical device (4) from the second operational mode (22A, 22B) to the first operational mode (23) after a second time period has passed. Implantable medical device according to any of the preceding claims, characterized in that the implantable medical device (4) comprises a communication unit by which the implantable medical device can be connected with a remote monitoring system (5) in a wireless manner. Arrangement, comprising an implantable medical device (4) according to any of the preceding claims and a remote monitoring system (5) operatively coupled to the implantable medical device (4). Arrangement according to claim 11, characterized in that the computer-readable program causes the processor (11) to transfer data indicative on an activated operational mode (22A, 22B; 23) of the implantable medical device to the remote monitoring system (5). Arrangement according to claim 11 or 12, characterized in that the computer-readable program causes the processor (11) to automatically perform an integrity check upon switching the operation of the implantable medical device from the second operational mode (22A, 22B) to the first operational mode (23) and to transfer data obtained by the integrity check to the remote monitoring system (5). Arrangement according to claim 13, characterized in that the computer-readable program causes the processor (11) to automatically perform an additional integrity check upon switching the operation of the implantable medical device (4) from the first operational mode (23) to the second operational mode (22A, 22B) and/or during operation of the implantable medical device in the second operational mode (22A, 22B) and to transfer data obtained by the additional integrity check to the remote monitoring system (5). Method for operating an implantable medical device according to any of claims 1 to 10, the method comprising the following steps: a) detecting, with a detection unit (9) of the implantable medical device (4), an electromagnetic field having a frequency lying in a range of from 100 kHz to 5 MHz; b) reading device activity data from a memory unit (12) of the implantable medical device (4), the device activity data indicating whether a stimulation unit (8) of the implantable medical device (4) emitted a stimulation pulse within a first time window, the first time window covering up to 48 hours prior to the detection of the electromagnetic filed in step a); and c) automatically switching an operation of the implantable medical device (4) from a first operational mode (23) to a second operational mode (22A, 22B), wherein the device activity data read in step b) is at least co-decisive for the chosen second operational mode (22A, 22B).