Implantable medical devices configured to provide intracardiac function

Abstract

The implantable medical device (1) configured to provide an intracardiac function comprises a body (10), a sensor device disposed on the body (10) and configured to receive a cardiac sense signal (S2), and a processing circuit (15) operatively connected to the sensor device. The processing circuit (15) is configured to process the cardiac sense signal (S2) received using the sensor device to detect a signal deflection in the cardiac sense signal (S2) potentially indicative of an atrial event (As) caused by atrial activity, and to initiate a peak detection window (PDW) based on detecting the signal deflection to determine a peak amplitude (PA) associated with the atrial event (As). The peak detection window (PDW) may include one or more sub-windows (P i , P i+1 , ...), and the processing circuit (15) processes each of the sub-windows (P i , P i+1 , ...) to determine candidate peak values ​​within one or more consecutive subwindows (P i , P i+1 , ...) based on valid candidate peak values.

Description

[Technical Field]

[0001] The present invention generally relates to an implantable medical device for providing intracardiac function, particularly pacing function, such as ventricular pacing, specifically VDD pacing. [Background technology]

[0002] In the form of implantable medical devices, such as leadless pacemakers or cardiac stimulators using a subcutaneously implanted pulse generator and one or more leads extending into the patient's heart, it may be desirable to provide stimulation to the ventricles of the patient's heart, such as the right ventricle, in synchronization with atrial activity. For this purpose, ventricular pacing should take into account atrial sense signals to control ventricular pacing based on atrial events indicating atrial activity, for example, in a so-called VDD pacing mode.

[0003] In recent years, leadless pacemakers have been gaining attention. In contrast to pacemakers that are implanted subcutaneously using lead wires that extend transvenously into the heart, leadless pacemakers avoid lead wires by having the pacemaker device itself implanted in the heart, and having the shape of a capsule for implantation in cardiac tissue, particularly in the right ventricle. Such leadless pacemakers offer the inherent advantage of not using lead wires, thereby reducing patient risks associated with lead wires that access the heart transvenously, such as pneumothorax, lead dislodgement, cardiac perforation, and venous thrombosis.

[0004] Leadless pacemakers, or the leads of stimulators, may be specifically designed to be implanted in the right ventricle, in which case they are positioned, for example, near the apex of the right ventricle during implantation. For example, ventricular pacing may be ordered when there is dysfunction in the AV node, but sinoatrial node function is intact and adequate. In such cases, so-called VDD pacing may be preferable, in particular, which involves ventricular pacing with atrial tracking and therefore requires a sense of atrial activity to pace the ventricle based on intrinsic atrial contraction.

[0005] VDD pacing is particularly motivated by the hemodynamic benefits for atrioventricular (AV)-synchronous patients by leveraging appropriate sinoatrial node function to trigger ventricular pacing, potentially maximizing ventricular preload, limiting AV valve regurgitation, maintaining low mean atrial pressure, and modulating autonomic and neurohumoral reflexes.

[0006] Cardiology publications are exploring solutions that use modalities to detect mechanical events of atrial contraction, including motion, sound, and pressure sensing (see, for example, U.S. Patent Application Publication 2018 / 0021581, which discloses a leadless cardiac pacemaker including a pressure sensor and / or accelerometer for determining atrial contraction timing). Because mechanical events generally exhibit small signal volumes, signal detection based on mechanical events, such as motion, sound, or pressure, can be difficult to sense, especially when implantable medical devices are placed in the ventricles and are therefore quite far from the atria where contractions will be sensed. Furthermore, the movement of the heart wall and blood movement generated by atrial contraction may not be directly translated into the ventricles, and cardiac hemodynamic signals such as motion, heart sounds, and pressure are likely to be affected by external factors such as posture and patient activity. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2018 / 0021581 SUMMARY OF THE INVENTION

[0008] In particular, an object is to provide an implantable medical device that enables ventricular pacing with atrioventricular synchrony and thus requires a reliable sense of atrial events to provide ventricular pacing based on such atrial events, and a method of operating the implantable medical device.

[0009] Such a need is addressed by an implantable medical device configured to provide an intracardiac function having the features of claim 1.

[0010] In one aspect, an implantable medical device configured to provide an intracardiac function includes a body, a sensor device disposed on the body and configured to receive a cardiac sense signal, and a processing circuit operably connected to the sensor device. The processing circuit processes the cardiac sense signal received using the sensor device to detect a signal deflection of the cardiac sense signal that potentially indicates an atrial event caused by atrial activity, and starts a peak detection window based on detecting the signal deflection to determine a peak amplitude associated with the atrial event. The peak detection window includes one or more sub-windows, and the processing circuit is configured to determine candidate peak values within each sub-window and set the peak amplitude based on valid candidate peak values of one or more consecutive sub-windows or the maximum value of valid candidate peak values.

[0011] Generally, in order to be able to provide cardiac functions such as a cardiac pacing function, it may be desirable to sense atrial events so that the pacing operation can be provided with atrioventricular (AV) synchrony, for example, in the VDD pacing mode. When an implantable medical device is implanted, for example, in a ventricle, such as the right ventricle, however, the cardiac sense signal related to atrial activity is generated in a far-field, and thus the signal amplitude may be weak and there may be a lot of noise.

[0012] When an atrial event is detected, the peak amplitude associated with the atrial event will be determined. Based on this peak amplitude, for example, a subsequent sense threshold is determined and used in subsequent cardiac cycles to detect atrial events. By dynamically adapting the sense threshold based on the actual peak amplitude measured for the atrial event, the reliability of sensing atrial events over a series of cardiac cycles can be enhanced, thus limiting the number of failure cycles in which atrial events are not detected and increasing the likelihood that true atrial events are detected.

[0013] For example, an atrial event is detected by comparing a cardiac sense signal with a sense threshold, and it is assumed that an atrial event exists when a crossing of the sense threshold based on one or more signal values is identified.

[0014] If an atrial event is detected near a subsequent ventricular event, the signal portion related to the atrial event may be corrupted by a subsequent signal deflection related to ventricular activity. In this case, since ventricular activity is detected in the near field, the ventricular signal deflection is generally much larger.

[0015] In another scenario, an atrial event may be erroneously detected, for example, based on a signal portion related to the T wave of an intracardiac electrogram signal. The T wave corresponds to ventricular repolarization and thus occurs in the near field, so the T wave may also exhibit a larger signal amplitude than the signal deflection related to atrial activity. If a portion of the T wave is erroneously identified as an atrial event, the atrial event may be detected early, and in a general approach, it may be impossible to obtain a reliable value of the peak amplitude associated with the true atrial event.

[0016] If the peak amplitude is erroneously determined based on the detection of an atrial event, this can result in an incorrect update of the sense threshold and an unreliable detection of atrial events in subsequent cycles.

[0017] Therefore, this specification proposes a method for determining peak amplitude in which the peak detection window is divided into multiple sub-windows. Candidate peak values ​​are determined in each sub-window, and then the actual peak amplitude is set based on the candidate peak values ​​determined in the sub-windows. By dividing the peak detection window into different sub-windows, different sub-windows can be processed separately to determine different candidate peak values, and the overall peak amplitude can be reliably determined from these different candidate peak values, thus simplifying the processing.

[0018] In particular, by dividing the peak detection window into subwindows, it may be possible to identify subwindows that may be too early within the atrial detection window and therefore too close to the preceding T wave, or too late within the atrial detection window and therefore too close to the subsequent QRS wave morphology associated with ventricular activity. Subwindows that may lead to erroneous results may be declared invalid and discarded, and the calculation of peak amplitude can be improved by using only subwindows declared as valid. A valid subwindow may be any subwindow that is not discarded for being too close to a T or QRS wave.

[0019] The sensor device may be formed in particular by an electrode device of one or more electrodes arranged on a main body. Thus, the sensor device can receive electrical signals, which represent an intracardiac electrogram recording and therefore indicate cardiac activity.

[0020] In another embodiment, the sensor device may be configured to sense cardiac sense signals in the form of pressure signals, acoustic signals, ultrasonic signals, motion signals, and / or impedance signals.

[0021] In one embodiment, the body of the implantable medical device may be formed by lead wires that can be connected to the generator of the implantable medical device. In this case, the generator may be implanted in the patient subcutaneously, for example, away from the heart, and the lead wires forming the body extend from the generator into the heart, and the body on which the sensor device is located is positioned within the heart, for example in the right ventricle, to engage with the tissue of the right ventricle.

[0022] In another embodiment, the main body may be formed by the housing of a leadless pacemaker device. In this case, the implantable medical device is formed as a leadless device that does not include lead wires extending from an external location to the heart for providing stimulation and / or sensing within the heart. The housing of the leadless pacemaker device may be placed on tissue using the distal end formed by the housing, and a sensor device may be placed, for example, on or near the distal end to engage with the tissue when the leadless pacemaker device is placed on the tissue using its distal end.

[0023] If the implantable medical device is a leadless pacemaker device, the housing provides encapsulation for the implantable medical device, which contains all the components necessary for autonomous operation, such as processing circuits, energy storage units such as batteries, and electrical and electronic circuits. Because the housing is liquid-tight, the implantable medical device can be implanted in cardiac tissue and maintained within the cardiac tissue for extended periods, providing long-term, continuous cardiac pacing.

[0024] In one embodiment, the processing circuit is configured to detect signal deflection in the cardiac sense signal that potentially indicates an atrial event, based on a comparison of the cardiac sense signal with a sense threshold. If the cardiac sense signal is observed to cross the sense threshold, an atrial event can be identified, and a peak detection window may be initiated based on the atrial event. The sense threshold herein may be set based on the previous peak amplitude in the previous cardiac cycle.

[0025] In one embodiment, the candidate peak value of a subwindow corresponds to the maximum value of the cardiac sense signal within that subwindow. Thus, the cardiac sense signal is tracked within the subwindow, and the candidate peak value is set to the maximum value of the sense signal within that subwindow. This is repeated for all subwindows, and based on the candidate peak values ​​of all (valid) subwindows, the overall peak amplitude can be determined, for example, by setting the peak amplitude to the maximum value of the candidate peak values ​​of all (valid) subwindows. Subwindows that are discarded due to suspected contamination from near-field ventricular activity are considered invalid, and all subwindows included in the peak amplitude calculation are considered valid.

[0026] Therefore, a subwindow (i.e., at least one subwindow) can be considered a valid subwindow if it is not discarded because it is close to the T or QRS complex and / or because of suspected contamination from near-field ventricular activity. Therefore, a candidate peak value (i.e., at least one candidate peak value) can be considered a valid candidate peak value if the candidate peak value lies within a valid subwindow.

[0027] In one embodiment, the processing circuit is configured to start another subwindow at the end of one subwindow. Thus, the length of the peak detection window may not be fixed initially, but the overall length of the peak detection window is adaptive in that one subwindow is followed by the next subwindow until further tracking of the cardiac sense signal to determine the peak amplitude is no longer performed. The subwindows herein are consecutive, with one subwindow being followed by the next without gaps, and a consecutive peak detection window is formed by a plurality of consecutive subwindows.

[0028] In one embodiment, the processing circuit is configured to detect signal deflections in the cardiac sense signal that potentially indicate an atrial event within an atrial detection window. A windowing method can be used to process the cardiac sense signal for detecting atrial events. In particular, signal portions that are likely to cause signal deflections related to ventricular activity (such as the T wave or QRS waveform of the intracardiac electrocardiogram signal) can be blanked by applying a blanking window so that only the portion of the cardiac sense signal that is likely to cause signal deflections related to atrial activity and is not impaired by signals unrelated to atrial activity is processed. Thus, an atrial detection window is defined, and signal deflections related to atrial activity are searched only within the atrial detection window, and atrial events are identified, for example, based on the crossover of sense thresholds by the cardiac sense signal.

[0029] The atrial detection window may be initiated with a predetermined duration relative to the previous ventricular event. Alternatively, the atrial detection window may be initiated adaptively, for example, based on analysis of cardiac sense signals and identification of T waves in the intracardiac electrocardiogram, prior to the deflection of the atrial signal. The atrial detection window may be terminated after a fixed duration relative to the previous ventricular event. Alternatively, the duration of the atrial detection window may be dynamic, for example, with a fixed duration relative to the dynamic initiation of the atrial detection window, or alternatively, it may be adaptive and extended until a subsequent ventricular event.

[0030] For example, the start of the atrial detection window may be set based on comparing the cardiac sense signal with a start threshold. The start threshold may have the same value as the sense threshold subsequently used to detect atrial events, or it may have a different value. By monitoring whether the cardiac sense signal crosses the start threshold, in particular whether it becomes smaller than the start threshold, it can be identified that the previous waveform, such as the previous T wave, has ended, and therefore the atrial detection window can be started to detect atrial events.

[0031] To reliably detect the end of the previous waveform, it may be determined whether a predetermined number of signal values, for example, a number between 1 and 20, or four signal sample values, are below a starting threshold. The signal values ​​may be consecutive or non-consecutive. By determining whether a pre-requested number of signal values ​​are below the starting threshold, it is determined whether the previous waveform has ended, and the atrial detection window can be initiated to search for signal deviations that may be associated with an atrial event.

[0032] The peak detection window can have a total length that extends substantially over the entire remainder of the atrial detection window from the time of atrial event detection. For this reason, another subwindow may be started at the end of each subwindow until the end of the atrial detection window is reached. In particular, additional subwindows are added unless the atrial detection window has already expired. If the (last) subwindow extends beyond the atrial event detection window, the subwindow can still be considered, and candidate peak values ​​can be determined for that subwindow based on tracking cardiac sense signals within the portion of the subwindow over which the atrial detection window has not yet expired.

[0033] In one embodiment, the processing circuit is configured to detect signal deflections indicating ventricular events caused by ventricular activity following an atrial event, and to define exclusion intervals based on the ventricular events. In particular, when identifying ventricular events, the exclusion interval may be set to correspond to the time interval immediately preceding the ventricular event. It can then be determined whether one or more subwindows are contained by or reach the exclusion interval, in which case the subwindows are discarded, and the candidate peak values ​​determined for those subwindows are not considered when determining the overall peak amplitude.

[0034] In particular, the processing circuit may be configured to exclude candidate peak values ​​obtained within subwindows that at least partially overlap with the exclusion interval. This may be the case for one or more subwindows, and candidate peak values ​​from one or more subwindows may be discarded when determining the overall peak amplitude.

[0035] The length or boundary of any one of the atrial detection window, peak detection window, subwindow, and exclusion interval may be programmable.

[0036] In one embodiment, the exclusion interval has a first length, and each subwindow has a second length corresponding to 1 / Z times the first length, where Z is a natural number greater than or equal to 1. Therefore, Z subwindows fit within the exclusion interval.

[0037] For example, at least some of the subwindows may have a length of 3ms to 100ms, for example, 12ms to 35ms. Here, all subwindows may have the same length, or different subwindows may have different lengths. For example, the lengths of the subwindows may gradually increase or decrease.

[0038] Based on the method described herein, peak amplitude can be determined for atrial events in a reliable and accurate manner. In this specification, peak amplitude can be determined regardless of whether the atrial event was correctly identified or not. In particular, even if an atrial event is misidentified, for example, due to signal deflection from a preceding T wave, the peak amplitude associated with the actual peak related to the actual subsequent atrial event can be correctly determined based on signal tracking within different subwindows.

[0039] Using the peak amplitude, the processing circuit may be configured to calculate a sense threshold for detecting atrial events in subsequent cardiac cycles. In particular, the processing circuit may use the following equation ST = PC·ATR(t) (In the formula, ST is the current sense threshold, PC is the percentage ratio, and ATR(t) is the current average threshold reference for period t.) The sense threshold may be configured to update using an average threshold criterion and a percentage ratio accordingly. The percentage ratio may be in the range of, for example, 0% to 100%, and may be programmable.

[0040] In another embodiment, the average threshold criterion is given by the following formula ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) (In the formula, W represents the update weight that determines how much the mean threshold criterion should change based on the previous peak amplitude, PA(t-1) is the peak amplitude determined for the previous period t-1, and ATR(t-1) is the previous mean threshold criterion.) It can be calculated based on the peak amplitude PA. Therefore, for the current period t, the mean threshold criterion is determined based on the peak amplitude PA determined for that period t and the previous valid mean threshold criterion in period t-1. Thus, for each period in which an atrial event As is detected, the mean threshold criterion is updated and recalculated so that it is dynamically adjusted period by period.

[0041] The average threshold criterion can be calculated, for example, as the average of the peak amplitudes over a predetermined number of cardiac cycles in which atrial events were detected, such as 2 to 6 cardiac cycles, or 4 cardiac cycles.

[0042] In one embodiment, the processing circuit includes a first processing channel having a first gain for processing a first processing signal derived from a sensor signal received via a sensor device, and a second processing channel having a second gain for processing a second processing signal derived from a sensor signal received via a sensor device, wherein the second gain is higher than the first gain.

[0043] Generally, implantable medical devices may be configured to process different processing signals. To acquire such processing signals, a sensor device is provided, which comprises, for example, one or more electrodes for receiving electrical signals from which the processing signals are derived. The processing signals herein can each be acquired, for example, using a pair of electrodes, and to acquire different processing signals, the same pair of electrodes or different pairs of electrodes can be used. In the first case, a single electrical signal, such as an intracardiac electrogram, can be acquired from which different processing signals, namely a first processing signal and a second processing signal, can be derived for separate processing. In the latter case, separate electrical signals can be received, for example, related to a ventricular sense signal and an atrial sense signal (i.e., by applying a sense optimized for atrial sense), in order to derive the first and second processing signals from such different electrical signals, and the different electrical signals are received, for example, using different pairs of electrodes of a sensor device.

[0044] In one embodiment, different processing signals are processed by different processing paths of a processing circuit. For this purpose, the processing circuit includes a first processing channel for processing a first processing signal, which relates to a near-field (particularly ventricular) sense signal, which can be increased to such an extent that the first processing channel exhibits a fairly low gain, for example, depending on the placement of an implanted medical device in the ventricle of a patient's heart.

[0045] Furthermore, the processing circuit includes a second processing channel for processing a second processing signal, the second processing channel may relate to a far-field atrial sense signal, which may have a small amplitude due to the distance between the implantation site and the signal source, for example, when an implantable medical device is placed in the ventricle. To enable reliable processing of the second processing signal, the second processing channel exhibits a higher gain than the first processing channel so that features related to atrial activity can be properly analyzed within the received signal.

[0046] When an implantable medical device is placed, for example, in the ventricle, atrial activity occurs in the far field, and the P waves resulting from atrial activity may have small amplitudes relative to the QRS and T waves. Therefore, it may be difficult to distinguish atrial events within a normal ventricular sense signal (e.g., acquired from a normal ventricular QRS sense channel). For this reason, the signal portion related to far-field activity can be processed separately from the signal related to near-field activity in a second processing channel, thereby enabling detection of far-field events with higher reliability and improved timing accuracy within the second processing channel.

[0047] In one embodiment, the implantable medical device is placed entirely or partially in the right ventricle or left ventricle.

[0048] In one embodiment, the sensor device is formed by an electrode device, the electrode device comprising a first electrode positioned near the tip of the main body. When the implantable medical device is implanted, the first electrode is placed on the cardiac tissue such that it is in contact with the cardiac tissue at a position effective for injecting a stimulating signal into the cardiac tissue to induce, for example, pacing, particularly ventricular pacing.

[0049] In one embodiment, the electrode device comprises a second electrode formed by an electrode ring extending circumferentially around a main body. Alternatively, the second electrode may be formed, for example, by a patch or another conductive region formed on the main body. The second electrode is positioned away from the tip of the main body and therefore away from the first electrode positioned at the tip.

[0050] In one embodiment, the processing circuit is configured to process a first signal sensed between a first electrode and a second electrode as the first processing signal. Such a first signal can be represented as a near-field vector received between a pair of electrodes, the first electrode and the second electrode. In one embodiment, the first and second electrodes may be located at a fairly close distance from each other, so such a pair of electrodes is primarily suited to receiving signals in close proximity to an implantable medical device, i.e., in the near-field region within the ventricle when the implantable medical device is implanted in the ventricle. The sense signal received between the first and second electrodes is provided to a first processing channel for processing, for example, to detect near-field (e.g., ventricular) events in the signal.

[0051] In one embodiment, the main body includes a remote position detached from the tip (e.g., the far end of the housing of a leadless space maker device), and the electrode device includes a third electrode positioned on the main body at the remote position. The third electrode is operably connected to a processing circuit so that the processing circuit can receive and process signals received through the third electrode.

[0052] In one embodiment, the processing circuit is configured to process a second signal sensed between the first electrode and the third electrode as the second processing signal. Such a second signal vector occurring between the first electrode and the third electrode may be called a far-field vector, and the first and third electrodes represent a greater distance from each other than the first and second electrodes. The second signal may be processed in particular to detect far-field events, i.e., atrial contractions when an implantable medical device is placed in the ventricle, so that intrinsic atrial activity prior to the injection of pacing stimuli may be captured by the second signal.

[0053] A second signal sensed between the first and third electrodes may be used to sense intrinsic atrial contraction to provide atrial-ventricular synchronization by timely injecting stimuli into the ventricular position of the implanted pacemaker device after atrial contraction. The second signal is provided to a second processing channel to process the signal and detect atrial events from the signal in order to provide pacing action based on the detected atrial event and thus enable ventricular pacing under atrioventricular (AV) synchronization.

[0054] In one embodiment, the second processing channel includes a processing step for distinguishing one wave portion within the second processed signal from another wave portion. The processing step may be configured to apply at least one of bandpass filtering, blanking windows for excluding portions of the second sensor signal from further processing, moving average filtering, and rectification to the second processed signal. The processing step will, in particular, separate and / or enhance such wave portions within the processed signal, which may, for example, indicate atrial events. When an implantable medical device is placed in the ventricle of a patient's heart, signal portions related to far-field atrial activity may have a much smaller amplitude than signal portions related to near-field ventricular activity. Therefore, processing plays a role in distinguishing between different signal portions in order to identify such signal portions that may contain signals related to far-field atrial activity.

[0055] For example, bandpass filtering can be applied to isolate P waves in an intracardiac electrocardiogram, thereby distinguishing the wave portion associated with P waves from the wave portions associated with QRS and T waves, particularly those attributable to ventricular activity. Alternatively or additionally, a blanking method may be applied to blank a specific portion of a second processed signal, i.e., such portions containing signals attributable to events other than distant-field atrial activity. For this purpose, the blanking window serves to silence signal portions that are not the distant-field activity of interest, but rather may interfere with the detection of distant-field activity. Thus, such signal portions unrelated to distant-field atrial activity are excluded from processing by the blanking window so that processing is limited to signal portions that are (potentially) related to distant-field activity. Alternatively or additionally, other methods such as moving average filtering, difference, or rectification of the signal may be applied. The moving average filter here can be used to smooth the processed signal. Rectification serves to easily compare the processed signal to a (single) threshold in order to identify when the magnitude of the signal exceeds a given threshold.

[0056] In another embodiment, a method for operating an implantable medical device for providing intracardiac function includes the steps of: receiving a cardiac sense signal using a sensor device located on the body of the implantable medical device; and processing the cardiac sense signal received using the sensor device using a processing circuit operably connected to the sensor device to detect a first atrial event candidate in one cardiac cycle based on a comparison of the cardiac sense signal with a sense threshold, determine a modified sense threshold, and monitor whether a second atrial event candidate was detected in the same cardiac cycle by comparing the cardiac sense signal with the modified sense threshold after the detection of the first atrial event candidate.

[0057] The advantages and favorable embodiments of the apparatus described above also apply equally to the methods, as referenced above.

[0058] Various features and advantages of the present invention can be more readily understood by referring to the embodiments shown in the following detailed description and drawings. [Brief explanation of the drawing]

[0059] [Figure 1] This is a schematic diagram of a human heart with an implantable medical device, a leadless pacemaker, implanted. [Figure 2] This is a schematic diagram of an implantable medical device. [Figure 3] This is a schematic diagram of an implantable medical device showing the signal vectors between different electrodes of the implantable medical device. [Figure 4] This is a schematic diagram of a processing circuit for one embodiment of an implantable medical device. [Figure 5A] This figure shows the first processed signal of the shape of the intracardiac electrogram (IEGM) processed by the first processing channel of the processing circuit. [Figure 5B] This figure shows the second processed signal processed by the second processing channel of the processing circuit. [Figure 6] This figure shows an example of a second processing signal within two cardiac cycles. [Figure 7] This is a schematic diagram of a human heart equipped with an implantable medical device in the shape of a cardiac stimulator, with lead wires embedded in the right ventricle. [Modes for carrying out the invention]

[0060] Next, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, similar reference numerals indicate similar structural elements.

[0061] It should be noted that the embodiments are not intended to limit the present invention, but merely to represent illustrative examples.

[0062] The present invention proposes providing an implantable medical device that provides intracardiac function, particularly ventricular pacing, specifically so-called VDD pacing.

[0063] Figure 1 shows a schematic diagram of a human heart including the right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The so-called sinoatrial node (SAN) is located in the wall of the right atrium (RA) and is formed by a group of cells that have the ability to spontaneously generate electrical impulses that travel through the heart's electrical conduction system, thus causing the heart to contract in order to pump blood through it. The atrioventricular node (AVN) plays a role in regulating electrical conduction between the atria and ventricles and is located in the inferior posterior part of the interatrial septum near the opening of the coronary sinus. Extending from the AVN is the so-called bundle of hemispheres (HIS), which is composed of cardiomyocytes specialized in electrical conduction and forms part of the electrical conduction system for transmitting electrical impulses from the AVN via the so-called right bundle bifurcation (RBB) around the right ventricle (RV) and via the left bundle bifurcation (LBB) around the left ventricle (LV).

[0064] In cases of obstruction in the atrioventricular node (AVN), the intrinsic electrical conduction system of the heart is disrupted, potentially leading to insufficient intrinsic stimulation of ventricular activity, i.e., insufficient or irregular contractions of the right ventricular RV and / or left ventricular LV. In such cases, pacing of ventricular activity with a pacemaker device may be instructed, and such a pacemaker device stimulates ventricular activity by injecting stimulating energy into the intracardiac tissue, particularly the myocardium (M).

[0065] In one embodiment, as schematically shown in Figure 1, ventricular pacing action is provided to an implantable medical device 1 in the form of a leadless cardiac pacemaker device, and the leadless pacemaker device has a body 10 formed by a housing for the leadless pacemaker device.

[0066] In another embodiment, as shown in Figure 7, the implantable medical device 1 may be a stimulator having a generator 18 and at least one lead wire forming the body 10 of the implantable medical device 1 and extending transvenously from the generator 18 into the patient's heart.

[0067] While typical implantable medical devices are designed to sense ventricular activity by receiving electrical signals from the ventricular RV and LV where they are implanted, it is sometimes desirable to provide pacing that achieves atrioventricular (AV) synchronization by providing pacing to the ventricles in sync with intrinsic atrial activity. In such pacing modes, also referred to as VDD pacing modes, it is necessary to sense atrial activity and identify atrial events associated with atrial contraction for ventricular pacing based on such atrial events.

[0068] Referring here to Figures 2 and 3, in one embodiment, an implantable medical device 1 in the form of a leadless pacemaker device configured to provide intracardiac pacing, particularly in VDD pacing mode, comprises a housing 10 that encloses the electrical and electronic components for operating the implantable medical device 1. In particular, housing 10 is a processing circuit 15, which also includes a communication interface for communicating with external devices, such as a programmer wand. Furthermore, housing 10 houses electrical and electronic components, such as a battery-shaped energy storage unit. The housing 10 provides encapsulation of the components housed therein, and the housing 10 has the shape of a cylindrical shaft, for example, having a length of several centimeters.

[0069] The implantable medical device 1 will be implanted directly on top of the intracardiac tissue M. For this purpose, the implantable medical device 1 will have a fixation device 14 in the tip 100 region that engages with the intracardiac tissue M to fixate the implantable medical device 1 on the tissue in an implanted state, for example, in the shape of a nitinol wire.

[0070] The implantable medical device 1 in the embodiments of Figures 2 and 3 does not include lead wires but receives signals related to cardiac activity by an electrode device positioned on a housing 10, and also emits stimulating signals by such an electrode device. In the embodiments of Figures 2 and 3, the implantable medical device 1 comprises different electrodes 11, 12, and 13 that constitute an electrode device and are responsible for emitting pacing signals toward intracardiac tissue M to provide pacing and sensing electrical signals indicating cardiac activity, particularly atrial and ventricular contractions.

[0071] In this specification, the first electrode 11 is represented as a pacing electrode. The first electrode 11 is mounted on the tip 100 of the housing 10 and is configured to engage with cardiac tissue M.

[0072] In this specification, the second electrode 12 is represented as a pacing ring. The second electrode 12 functions as a counter electrode to the first electrode 11, and the signal vector P generated between the first electrode 11 and the second electrode 12 provides a pacing vector P for emitting a pacing signal toward the intracardiac tissue M.

[0073] Furthermore, the second electrode 12 functions as a sense electrode to sense signals particularly related to ventricular contraction, and a signal vector V is generated between the second electrode 12 and the first electrode 11, and the signal vector V is represented as a near-field vector.

[0074] The second electrode 12 is positioned away from the first electrode 11 and has a ring shape, for example, that extends circumferentially around the housing 10. The second electrode 12 is positioned, for example, at a distance of about 1 cm from the tip 100 of the housing 10 where the first electrode 11 is installed.

[0075] In the embodiments shown in Figures 2 and 3, the implantable medical device 1 further comprises a third electrode 13 installed at the far end 101 of the housing 10, the third electrode 13 functioning as a sense electrode for sensing signals indicating far-field cardiac activity. In particular, a signal vector A is generated between the third electrode 13 and the first electrode 11, and the signal vector A picks up signals that, for example, indicate atrial contraction and are represented as far-field vectors.

[0076] Electrodes 11, 12, and 13 are operably connected to a processing circuit 15, which is configured to cause the first electrode 11 and the second electrode 12 to emit pacing signals to provide stimulation to the ventricles. The processing circuit 15 is further configured to process the signals received through electrodes 11, 12, and 13 to provide a sense of cardiac activity, particularly atrial and ventricular contractions.

[0077] As shown in the embodiment of Figure 7, if the implantable medical device 1 has the shape of a stimulator comprising a generator 18 and lead wires extending from the generator 18, a similar electrode device comprising, for example, three electrodes 11, 12, and 13 may be implanted in the right ventricular RV and arranged on lead wires extending to the right ventricular RV, as shown in Figure 7, and the above also applies to embodiments of the implantable medical device 1 having lead wires extending to the patient's heart. In this case, the processing circuit 15 may be part of the generator 18 and may be operably connected to the electrode device arranged on the lead wires.

[0078] To provide pacing in the ventricle where the implantable medical device 1 is placed, and in particular to enable pacing in VDD mode, sensing atrial activity is necessary to provide detected atrial sense markers for timing ventricular pacing in order to acquire atrioventricular (AV) synchronous pacing. For this purpose, the implantable medical device 1 is implanted in the intracardiac tissue M within the right ventricular RV, and far-field signals from the right atrium RA (see Figures 1 and 9) are sensed in particular to enable synchronized pacing within the right ventricular RV.

[0079] Referring here to Figure 4, the processing circuit 15, in one embodiment, comprises two processing channels 16, 17 for processing different processing signals related to ventricular activity and atrial activity. Typically, as used herein, an intracardiac electrogram (IEGM) includes signal portions related to ventricular activity (particularly QRS waves) and atrial activity (particularly P waves), but the signal portion related to atrial activity originates from a far-field signal source and is therefore much weaker, having a much smaller amplitude than the signal portion related to near-field ventricular activity, i.e., the signal portion that originates in close proximity to the implanted medical device 1. For this reason, the two processing channels 16, 17 are associated with different gains G1, G2, with the first processing channel 16 playing a role in processing a first processing signal to identify ventricular events Vx at a fairly low gain G1, and the second processing channel 17 processing a second processing signal to identify atrial events at a significantly higher gain G2.

[0080] In particular, the first processing channel 16 is connected to an electrode device consisting of electrodes 11, 12, and 13, and the first processing channel 16 is configured to sense and process signals (near-field vectors V in Figures 2 and 3) received, in particular, via electrodes 11 and 12. The first processing channel 16 includes a first amplification stage 161 having a gain G1, followed by a detection stage 162 configured to identify a ventricular sense marker Vx from a first processed signal processed within the first processing channel 16.

[0081] The second processing channel 17 is similarly connected to an electrode device comprising electrodes 11, 12, and 13, and the second processing channel 17 may be configured to process signals sensed via a far-field vector A between electrode 11 located at the tip 100 and electrode 13 located at the far end 101 of the housing 10, in particular, as shown in Figures 2 and 3. The second processing channel 17 includes a second amplification stage 171 having a second gain G2, followed by a processing stage 172 and a second detection stage 173.

[0082] The processing stage 172 preprocesses the amplified second processed signal. Next, the detection stage 173 evaluates and analyzes the processed signal to identify atrial events within the second processed signal, and then the second processing channel 17 outputs an atrial sense marker As indicating the atrial events detected within the processed signal.

[0083] Furthermore, the processing circuit 15 includes a timing stage 174 that uses timing information received from the first processing channel 16 and the second processing channel 17 to provide pacing timing, in particular VDD timing for achieving atrial-ventricular synchronous pacing.

[0084] To identify and analyze atrial events, the gain G2 of the second processing channel 17 is (significantly) higher than the gain G1 of the first processing channel 16. This generally allows for the analysis of signal segments associated with atrial events, but requires distinguishing such signal segments associated with atrial events from other signal segments, particularly those associated with near-field ventricular events Vx, which are much larger than signal segments originating from far-field atrial events.

[0085] Within the processing stage 172, for example, bandpass filtering, windowing (e.g., partial blanking), smoothing by moving average filtering, and rectification may be performed. First-order or second-order differences can be applied to remove non-zero baselines while enhancing P-wave deflection.

[0086] Figures 5A and 5B show examples of signals S1 and S2 processed by different processing channels 16 and 17, with Figure 5A above showing signal S1 processed by the first processing channel 16, and Figure 5B below showing signal S2 processed by the second processing channel 17. As a result of processing, ventricular event Vx and atrial event As are identified and the corresponding markers are output.

[0087] As shown clearly from FIG. 5B, the sensing of the atrial event As uses a window processing method, particularly the blanking window T ブランク to blank the signal portion of the signal S2 that is potentially related to ventricular activity.

[0088] Particularly, by detecting the ventricular event Vx in the first processing channel 16, the timing between the atrial event As and the ventricular event Vx can be determined. According to such timing, the starting point and the ending point of the blanking window T ブランク can be set, so that the signal portion not related to atrial activity can be excluded from the processing. In this way, a large ventricular signal can be suppressed so that the signal portion related to ventricular activity does not interfere with the detection of atrial events.

[0089] During the blanking window T ブランク the second processing channel 17 may be turned off. Particularly, the amplification stage 171 of the second processing channel 17 may be turned off to save power.

[0090] Generally, the detection of the atrial event As is performed outside the blanking window T ブランク Here, the detection window T センス for detecting the atrial event can start at the ending point of the previous blanking window T ブランク Alternatively, the detection window T センス may have a delay with respect to the ending point of the previous blanking window T ブランク so that the signal processing in the second processing channel 17 starts at the ending point of the previous blanking window T ブランク as shown in the embodiment of FIG. 5B, but the detection of the atrial event As starts only after a specific delay.

[0091] Generally, the atrial event As is within the detection window T センスIn this case, as shown in Figure 5B, it is assumed that a signal S2 exists if it crosses the sense threshold ST. The comparison may be based on the rectification of the sense signal S2. Alternatively, positive and negative sense thresholds ST may be used, which may be the same value or different values. Here, a threshold crossover may be assumed if one signal value is greater than the sense threshold ST. Alternatively, a sense threshold crossover is assumed if a predetermined number of signal values, for example, two or more consecutive or discontinuous (sum) sample values ​​are greater than the sense threshold ST.

[0092] Generally, when an atrial event As is detected, as in the case of the second cardiac cycle in Figure 5B, the atrial event As is used for further processing, specifically updating the sense threshold ST and achieving atrial-ventricular synchronized pacing.

[0093] In particular, the atrial event As is interpreted as the point at which the sense threshold ST crossover is identified. At the time of the atrial event As, the peak detection window PDW begins, and based on the data recorded during that peak detection window PDW, the peak amplitude PA is determined as the maximum signal value within the peak detection window PDW. This is shown in Figure 5B for the second period on the right.

[0094] Furthermore, if an atrial event As is detected, a delayed atrial-ventricular AVD may be determined and used for subsequent processing. If a ventricular event Vx is not detected after the course of the delayed atrial-ventricular AVD, a pacing signal can be injected to induce ventricular stimulation.

[0095] As shown in Figure 5B, the peak amplitude PA is generally determined within the peak detection window PDW after the detection of the atrial event As. Generally, the peak amplitude PA here is determined by tracking the sense signal S2 and thus identifying the maximum value of the sense signal S2 within the peak detection window PDW. The PDW of the first period in Figure 5B is ineligible because it is close to the ventricular event. This concept is further explained in Figure 6.

[0096] Referring now to Figure 6, as shown for one cardiac cycle on the left side of Figure 6, there is a scenario in which the atrial event As is incorrectly determined at a point in the cardiac cycle preceding the actual atrial event. This is because, for example, the endpoint of a preceding signal waveform, such as the T wave of an intracardiac electrographic signal, falls within the atrial detection window T. センス It reaches the atrial detection window T immediately afterward. センス This can occur when a sense threshold ST crossover is identified at the starting point, and therefore an atrial event As is (falsely) detected. In this case, if the peak detection window PDW is too short, it becomes impossible to accurately determine the peak amplitude PA associated with the actual atrial event As that follows (much) later than the falsely identified atrial event As.

[0097] In another scenario shown in the right-hand cardiac cycle of Figure 6, the atrial event As can be correctly determined by identifying the sense threshold ST crossover by the sense signal S2. However, the actual atrial event As may be near the subsequent ventricular event Vx, and the signal deflection associated with the atrial event As may be corrupted by the signal deflection associated with the subsequent ventricular event Vx. In this case, if the peak detection window PDW is too long and reaches the region of subsequent ventricular activity, the peak amplitude PA may again be incorrectly determined due to signal corruption by the subsequent ventricular signal deflection.

[0098] Therefore, according to one embodiment, the peak detection window PDW is a plurality of subwindows P i , P i+1 A method has been proposed in which the signal is divided into, ..., and the signal processing to determine the peak amplitude PA is performed in separate subwindows P i , P i+1 , ... will take place.

[0099] The peak detection window (PDW) generally begins at the detection of atrial event As, as is the case for both the cardiac cycle shown on the left and the cardiac cycle shown on the right in Figure 6. Therefore, a subwindow is started at the detection of atrial event As, and another subwindow is started at the end of the subwindow, and the atrial detection window T センス This is repeated until the endpoint is reached. Therefore, after the detection of an atrial event As, the peak detection window PDW is essentially the atrial detection window T センス It extends to the entire remaining part.

[0100] Here, each subwindow P i , P i+1 ...in subwindow P i , P i+1 ...track the signal S2 within each subwindow P i , P i+1 The candidate peak value is determined by setting the candidate peak value according to the maximum value of the sense signal S2 within .... Then, all (valid) subwindows P are used to determine the peak amplitude PA. i , P i+1 The maximum value of all candidate peak values ​​is determined, and the peak amplitude PA is set to that maximum value.

[0101] As can be seen from Figure 6, one or more subwindows P i , P i+1 ... may completely or partially overlap with an exclusion interval PVI defined before a ventricular event Vx. That is, if a ventricular event Vx is identified following the detection of an atrial event As (which may be an endogenous event or a pacing event), an exclusion interval PVI (also called a pre-Vx interval) is defined, and the exclusion interval PVI defines a time interval immediately preceding the ventricular event Vx such that the exclusion interval PVI ends with the ventricular event Vx.

[0102] In particular, the exclusion interval PVI may be defined to exclude atrial events As that are too close to subsequent ventricular events Vx. Furthermore, the exclusion interval PVI may be defined as a subwindow P of the peak detection window PDW that at least partially overlaps with the exclusion interval PVI. i , P i+1 Defined to exclude ,... Subwindow P i , P i+1 If ... is excluded, then the subwindow P i , P i+1 The candidate peak values ​​determined for ... are not used to determine the overall peak amplitude PA. PDW subwindows that are deemed ineligible because they overlap with the excluded interval PVI are marked with "X" in Figure 6.

[0103] Atrial detection window T センス The duration can be programmable.

[0104] Similarly, the duration of the exclusion interval PVI can be programmable.

[0105] The duration of the peak detection window PDW may also be programmable, and the duration of the peak detection window PDW may be set adaptively. For example, the peak detection window PDW may consist of a series of subwindows P i , P i+1 ...may be determined by the start of the atrial detection window T センス If it extends beyond the endpoint, the peak detection window (PDW) terminates.

[0106] Subwindow P i , P i+1 The duration of the subwindows may be programmable and may have values ​​such as 7ms to 100ms or 12ms to 35ms. The subwindows may have the same duration or their durations may be different.

[0107] In one embodiment, a subwindow of natural numbers fits within the exclusion interval PVI such that the length of the exclusion interval PVI and the length of the subwindow are set in a mutually dependent manner.

[0108] In one embodiment, the peak amplitude PA can be used to update the sense threshold ST for the next cardiac cycle.

[0109] In particular, the processing circuit 15 is given by the following equation ST = PC·ATR(t) (In the formula, ST is the current sense threshold, PC is the percentage ratio, and ATR(t) is the average threshold reference for the current period t.) The sense threshold ST may be configured to update using an average threshold criterion and a percentage ratio accordingly. The percentage ratio may be in the range of, for example, 0% to 100%.

[0110] The mean threshold criterion can be determined based on the average value of several previous cardiac cycles in which atrial events were identified and corresponding peak amplitude values ​​were obtained. In this case, the mean threshold criterion may be determined, for example, as the average of the peak amplitude values ​​in previous cardiac cycles.

[0111] In another embodiment, the average threshold criterion is given by the following formula ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) (In the formula, W represents the update weight that determines how much the mean threshold criterion should change based on the previous peak amplitude, PA(t-1) is the peak amplitude determined for the previous period t-1, and ATR(t-1) is the previous mean threshold criterion.) It can be calculated based on the peak amplitude PA. Therefore, for the current period t, the mean threshold criterion is determined based on the peak amplitude PA determined for that period t and the previous valid mean threshold criterion in period t-1. Thus, for each period in which an atrial event As is detected, the mean threshold criterion is updated and recalculated so that it is dynamically adjusted period by period.

[0112] If no (valid) atrial event As is detected, the peak amplitude PA is not determined, and the mean threshold-based ATR is not updated. In this way, the false detection of atrial event As can lead to a false increase in the sense threshold ST segment and subsequent loss of capture of atrial activity, which is avoided. This is the case for the first cardiac cycle as shown in Figures 5A and 5B, where no crossover of the sense threshold ST segment is detected, and consequently, the atrial event As is not identified.

[0113] Ventricular synchronized pacing can be achieved using the atrial sense marker As output by the processing circuit 15. To this end, it is possible to detect whether the intrinsic ventricular sense marker Vx occurs within a predetermined time delay window (corresponding to the atrial-ventricular delay AVD) following the detected atrial sense marker As, in which case no stimulation is required. If the ventricular sense marker Vx is not detected, a stimulation pulse is released to induce synchronized pacing in the ventricle.

[0114] Conversely, asynchronous pacing can also be performed.

[0115] By utilizing far-field electrical signals received by implantable medical devices, excellent detection of far-field events, particularly atrial events, can be provided when the implantable medical device is implanted in the ventricle. Tracking far-field events using and evaluating electrical signals can enable greater consistency and reliability, especially with respect to external factors such as posture and patient activity. [Explanation of symbols]

[0116] 1. Implantable medical devices 10 Main unit (housing) 100 Tip 101 Far end 11. First electrode (pacing electrode) 12. Second electrode (pacing ring) 13. Third electrode 14 Fixed devices 15 Processing Circuit 16 processing channels 161 Amplification Stage 162 detection stage 17 Processing Channels 171 Amplification Stage 172 Processing Stages 173 detection stage 174 Timing stage 18 Generator A. Signal vector (atrial / far-field vector) As atrial events (atrial sense markers) ATR Mean Threshold Criteria AVD (Atrial-Ventricular Delay) AVN Atrioventricular Node G1, G2 gain H HIS bunch LA (Left Atrium) LAT Lower Absolute Threshold LBB Left Bundle Branch LV left ventricle M Intracardiac tissue (myocardial tissue) P is the signal vector (pacing vector) PA Peak Amplitude PDW Peak Detection Window PVI exclusion interval (Vx pre-interval) P i , P i+1 Subwindow of the peak detection window RA right atrium RBB Right Bundle Branch RV right ventricle S1, S2 signal SAN sinoatrial node ST Sense Threshold T ブランク Blanking window T センス Detection window V signal vector (ventricular / near-field vector) Vx ventricular event (ventricular sense marker)

Claims

1. An implantable medical device (1) configured to provide intracardiac function, Main unit (10), A sensor device disposed on the main body (10) and configured to receive cardiac sense signals (S2), and A processing circuit (15) operably connected to the sensor device, The cardiac sense signal (S2) received using the sensor device is processed, The signal deflection of the cardiac sense signal (S2) which potentially indicates an atrial event (As) caused by atrial activity is detected. A peak detection window (PDW) is initiated based on detecting the signal deflection in order to determine the peak amplitude (PA) associated with the atrial event (As). The processing circuit (15) is configured such that the peak detection window (PDW) has two or more subwindows (P ｉ , P ｉ＋１ , . . ) and the processing circuit (15) includes each subwindow (P ｉ , P ｉ＋１ Determine the candidate peak values ​​within , . . ) and the two or more consecutive subwindows (P ｉ , P ｉ＋１ The system is configured to set the peak amplitude (PA) based on valid candidate peak values ​​within , , , , ), and the valid candidate peak value is a candidate peak value within a valid sub-window, and the sub-window is considered valid if it is not discarded because it is close to a T wave or QRS wave, and / or not discarded because of suspected contamination from near-field ventricular activity. Implantable medical device (1).

2. The implantable medical device (1) according to claim 1, wherein the main body (10) is formed by lead wires that can be connected to the generator (18) of the implantable medical device (1), or the main body (10) is formed by the housing of a leadless pacemaker device.

3. The implantable medical device (1) according to claim 1 or 2, wherein the processing circuit (15) is configured to detect signal deflection of the cardiac sense signal (S2) that potentially indicates an atrial event (As) based on a comparison of the cardiac sense signal (S2) and a sense threshold (ST).

4. Sub-window (P ｉ , P ｉ＋１ ,...) of the candidate peak value is the maximum value of the heart sense signal (S2) within the sub-window (P ｉ , P ｉ＋１ ,...), the implantable medical device (1) according to claim 1.

5. The processing circuit (15) processes the peak amplitude (PA) into the two or more subwindows (P ｉ , P ｉ＋１ The implantable medical device (1) according to claim 1, which is configured to set to the maximum value of the candidate peak values ​​of , . . ).

6. The processing circuit (15) has one subwindow (P ｉ , P ｉ＋１ At the end of , . . ) another subwindow (P ｉ＋１ , P ｉ＋２ An implantable medical device (1) according to claim 1, configured to initiate , . . )

7. The processing circuit (15) determines the atrial detection window (T センス An implantable medical device (1) according to claim 1, configured to detect signal deflection of the cardiac sense signal (S2) which potentially indicates an atrial event (As) within ).

8. The processing circuit (15) determines the atrial detection window (T) based on a comparison between the cardiac sense signal (S2) and the start threshold. センス An implantable medical device (1) according to claim 7, configured to initiate ).

9. The processing circuit (15) controls the atrial detection window (T センス Each subwindow (P ｉ , P ｉ＋１ At the end of , . . ) another subwindow (P ｉ＋１ , P ｉ＋２ An implantable medical device (1) according to claim 7 or 8, configured to initiate , . . )

10. The implantable medical device (1) according to claim 1, wherein the processing circuit (15) is configured to detect a signal deflection indicating a ventricular event (Vx) caused by ventricular activity following the atrial event (As), and to define an exclusion interval (PVI) based on the ventricular event (Vx).

11. The processing circuit (15) has a subwindow (P) that at least partially overlaps with the exclusion section (PVI). ｉ , P ｉ＋１ The implantable medical device (1) according to claim 10, configured to exclude candidate peak values ​​obtained within , . . ).

12. The exclusion interval (PVI) has a first duration, and each subwindow (P ｉ , P ｉ＋１ The implantable medical device (1) according to claim 10 or 11, wherein the , , , ) has a second duration corresponding to 1 / Z times the first length, and Z is a natural number of 1 or more.

13. The aforementioned subwindow (P ｉ , P ｉ＋１ The implantable medical device (1) according to claim 1, wherein at least some of the , , , ) have a length of 3 ms to 100 ms.

14. The implantable medical device (1) according to claim 1, wherein the processing circuit (15) comprises a first processing channel (16) having a first gain (G1) for processing a first processing signal derived from a cardiac sense signal received via the sensor device, and a second processing channel (17) having a second gain (G2) for processing a second processing signal derived from a cardiac sense signal received via the sensor device, wherein the second gain (G2) is higher than the first gain (G1).

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