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 arrangement disposed on the body 10 and configured to receive cardiac sensing signals, and a processing circuitry 15 operatively connected to the sensor arrangement. The processing circuitry 15 is configured to process the cardiac sensing signals received using the sensor arrangement to detect an atrial event As caused by atrial activity based on a comparison of the cardiac sensing signal to a sensing threshold ST for a number of cardiac cycles, evaluate whether the reduction criterion is met when an atrial event As has not been detected in X1 out of Y1 cardiac cycles, X1 being a natural number equal to or greater than 1, and reduce the sensing threshold ST if the reduction criterion is met.

Description

[Technical Field]

[0001] The present invention relates to an implantable medical device for providing intracardiac functions in general, and more particularly to pacing functions such as ventricular pacing, specifically VDD pacing. [Background technology]

[0002] For example, in implantable medical devices such as leadless pacemakers or cardiac stimulators that use a subcutaneously implanted pulse generator and one or more leads extending into the patient's heart, it may be desirable to provide stimulation in the ventricles of the patient's heart, for example, the right ventricle, in synchronization with atrial activity. To this end, ventricular pacing is controlled based on atrial events that indicate atrial activity, for example, in a so-called VDD pacing mode, taking atrial sensing signals into consideration.

[0003] In recent years, leadless pacemakers have been gaining increasing attention. In contrast to subcutaneously implanted pacemakers that use leads that extend into the heart via veins, leadless pacemakers do not use leads because the pacemaker device itself is implanted inside the heart. These pacemakers have a capsule shape for implantation into cardiac tissue, particularly the right ventricle. Such leadless pacemakers offer the inherent advantage of not using leads, which reduces the risks for patients involved with leads that approach the heart via veins, such as pneumothorax, lead dislodgement, cardiac perforation, and venous thrombosis.

[0004] The leads of a leadless pacemaker, or stimulator, 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. Ventricular pacing may be applied, for example, when there is dysfunction in the atrioventricular node but the sinoatrial node function is intact and normal. In such cases, so-called VDD pacing may be particularly desirable, which requires ventricular pacing with atrial tracking and therefore requires sensing of atrial activity in order to pace the ventricle based on intrinsic atrial contraction.

[0005] VDD pacing is particularly motivated by the patient's hemodynamic benefits, which include atrioventricular (AV) synchronization through the use of appropriate sinoatrial node function to induce ventricular pacing, enabling maximization of ventricular preload, limitation of atrioventricular valve regurgitation, maintenance of low mean atrial pressure, and regulation of autonomic and neurohumoral reflexes.

[0006] In the literature, solutions have been explored for using modalities to detect mechanical events of atrial contraction, including motion, sound, and pressure sensing (see, for example, U.S. Patent Application Publication 2018 / 0021581(A1) disclosing a leadless intracardiac pacemaker including a pressure sensor and / or accelerometer for determining the timing of atrial contraction). Since mechanical events generally produce small signal quantities, signal detection based on mechanical events such as motion, sound, or pressure can be difficult, especially when the implanted medical device is placed in the ventricle and is therefore quite far from the atrium where the contraction will be sensed. Furthermore, wall motion and blood movement resulting from atrial contraction may not be directly transmitted to the ventricle, and cardiac hemodynamic signals such as motion, heart sounds, and blood pressure are susceptible to 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(A1) [Overview of the project] [Problems that the invention aims to solve]

[0008] In particular, the objective is to provide an implantable medical device that requires reliable sensing of atrial events in order to enable ventricular pacing with atrioventricular synchronization and thus provide ventricular pacing based on atrial events, and a method for operating the implantable medical device. [Means for solving the problem]

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

[0010] In one embodiment, an implantable medical device configured to provide intracardiac function comprises a main unit, a sensor configuration configured to receive cardiac sensing signals on the main unit, and a processing circuit configuration operably connected to the sensor configuration. The processing circuit configuration processes the cardiac sensing signals received using the sensor configuration to detect atrial events caused by atrial activity for several cardiac cycles based on a comparison of the cardiac sensing signals with a sensing threshold. The circuit configuration is configured to evaluate whether the reduction criterion is met when no atrial events are detected in X1 out of Y1 cardiac cycles, and when X1 is a natural number greater than or equal to 1 and Y1 is a natural number greater than or equal to X1, and to reduce the sensing threshold if the reduction criterion is met.

[0011] A sensing threshold is generally used to detect atrial events. Generally, an atrial event is assumed to be present when a cardiac sensing signal associated with atrial activity crosses the sensing threshold. In this specification, assuming, for example, that an implantable medical device is implanted in the ventricle, e.g., the right ventricle of the patient's heart, a processing method such as a windowing scheme can be used to distinguish between the signal portion associated with remote-field atrial activity and the signal portion associated with near-field ventricular activity.

[0012] To reliably detect atrial activity, a fixed sensing threshold may be insufficient because the sensing signals associated with atrial activity may change. In this specification, if an atrial event is missed, i.e., if an atrial event is not detected for one or more cardiac cycles, for example, because the threshold crossover of the corresponding sensing signal is not identified, the sensing threshold can be adjusted so that the atrial event is recaptured, thus enabling reliable steady-state detection operation, for example, in the context of atrioventricular synchronized pacing.

[0013] Therefore, this specification proposes using an approach in which the sensing threshold is dynamically adjusted, in particular an approach that is reduced based on one or more reduction criteria that take into account atrial events missed in several cardiac cycles.

[0014] In particular, it is evaluated whether the reduction criteria are met, which are met if no atrial events are detected in X1 out of Y1 cardiac cycles. In this specification, X1 is a natural number greater than or equal to 1. Y1 is also a natural number greater than or equal to X1.

[0015] Reduction criteria may be defined as short-term or long-term criteria.

[0016] Within the short-term criteria, it is checked whether an atrial event was missed in the most recent cardiac cycle. For the short-term criteria, Y1 may be a value between 1 and 4, for example, 2. X1 may also have a value between 1 and Y1, for example. For example, within the reduced criteria, it is possible to check whether one of the two cardiac cycles immediately preceding the current cardiac cycle was missed, or whether both of the two cardiac cycles immediately preceding the current cardiac cycle were missed.

[0017] Within the long-term criteria, for example, it is possible to check whether a significant number of atrial events are being missed as the number of cardiac cycles increases. For the long-term criteria, Y1 may be a value between 4 and 16, for example, 8. X1 may also be a value between 3 and Y1, for example, 5. Within the long-term criteria, for example, it is possible to check whether five of the eight cardiac cycles immediately preceding the current cardiac cycle have been missed.

[0018] Based on an evaluation of reduction criteria, the detection threshold is reduced. If the reduction criteria are found to be met, the detection threshold is reduced in a predetermined manner. If the reduction criteria are not met, the detection threshold is not reduced based on the reduction criteria, but may be fitted in another predetermined manner, for example, based on the peak amplitude determined for atrial events. The detection threshold may have an excessively high value beforehand, resulting in a significant amount of missed atrial events in the previous cardiac cycle. By reducing the detection threshold, it may be possible to reliably detect atrial events for subsequent cardiac cycles. Therefore, by dynamically adjusting the detection threshold based on each cycle, atrial detection can be improved and the loss of atrial events can be limited.

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

[0020] In another embodiment, the sensor assembly may be configured to sense cardiac 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 can be formed by a lead connectable to the generator of the implantable medical device. In this case, the generator may be implanted, for example, subcutaneously away from the heart within the patient's body, and the lead forms a body that extends from the generator into the heart such that the body on which the sensor assembly is disposed engages tissue within the heart, such as in the right ventricle.

[0022] In another embodiment, the body can be formed by the housing of a leadless pacemaker device. In this case, the implantable medical device is formed as a leadless device and does not include a lead that extends from a position outside the heart into the heart to provide stimulation and / or sensing within the heart. The housing of the leadless pacemaker device may be disposed on tissue having a distal end formed by the housing, and the sensor assembly is disposed (at least in part) on or in the vicinity of the distal end and engages the tissue when the leadless pacemaker device is disposed on the tissue having the distal end.

[0023] When the implantable medical device is a leadless pacemaker device, the housing provides encapsulation of the implantable medical device, and the implantable medical device includes, within the housing, all the components necessary for autonomous operation, such as a processing circuit configuration, an energy storage unit such as a battery, and an electrical and electronic circuit configuration. The implantable medical device can be implanted into the heart tissue and held within the heart tissue over a long period to provide long-term continuous cardiac pacing operation, and the housing is liquid-tight.

[0024] In one embodiment, the processing circuit configuration is configured to reduce the sensing threshold for detecting atrial events in the current cycle if it is found that the reduction criterion is met in the current cycle. The reduction criterion is met if no atrial events are detected in X1 of Y preceding cardiac cycles. Therefore, in the current cycle, it is checked whether the reduction criterion is met for the cardiac cycle immediately preceding the current cycle. In this specification, Y preceding cardiac cycles are examined, and it is checked whether no atrial events are detected in X1 of these Y cardiac cycles. If no atrial events are detected, the reduction criterion is met, and the sensing threshold is appropriately reduced. Otherwise, the reduction criterion is not met, and the sensing threshold is not reduced according to a predetermined method associated with the reduction criterion.

[0025] In one embodiment, the processing circuit configuration is configured to reduce the sensing threshold by a reduction coefficient when the reduction criterion is met. The reduction coefficient may be a percentage value applied to calculate the sensing threshold when the reduction criterion is met. The reduction coefficient can be programmed in steps of, for example, 6.25% between 5% and 10%, and can take values ​​between 0% and 100%.

[0026] The reduction factor may be applied, for example, to an average threshold reference value, and the sensing threshold is generally set based on it. Alternatively, the reduction factor may be applied to a pre-existing sensing threshold.

[0027] In one embodiment, in addition to reducing the sensing threshold by a predefined reduction factor, an additional step factor may be applied if the reduction criterion is met for two or more consecutive cycles. Generally, the reduction factor is applied if the reduction criterion is met for the current cycle. An additional step factor may be applied if the reduction criterion is met again for at least one subsequent cardiac cycle. If the reduction criterion is met again for the next cardiac cycle, the step factor may be applied again, and as a result, the step factor may be applied repeatedly if the reduction criterion is met for multiple cardiac cycles.

[0028] The step coefficient can take the form of a percentage value, can be programmed, for example, between 5 and 10%, or even 6.25% in steps, and can take values ​​between 0 and 100%.

[0029] The additional step coefficient may be applied, for example, to a pre-valid sensing threshold, particularly to the sensing threshold after the application of a reduction coefficient.

[0030] In one embodiment, multiple reduction criteria may be applied. For example, in addition to the reduction criteria described above, a second reduction criterion may be applied, for which it is evaluated whether an atrial event was detected in X2 out of Y2 cardiac cycles. In this specification, X2 is a natural number greater than X1, and Y2 is a natural number greater than Y1.

[0031] Since X2 and Y2 are larger than X1 and Y1, the second reduction criterion is a long-term criterion to check whether a significant number of atrial events within a cardiac cycle have been missed over a long period. The first reduction criterion, which assesses whether atrial events have been missed in X1 cardiac cycles out of Y1 cardiac cycles, may in this case be a short-term criterion to assess whether a significant number of atrial events have been missed in a small number of recent cardiac cycles.

[0032] If the second reduction criterion is met, the processing circuit configuration may, in one embodiment, be configured to reduce the sensing threshold by a second reduction coefficient associated with the second reduction criterion. The second reduction coefficient is generally larger than the first reduction coefficient associated with the first reduction criterion, and can be programmed in steps of, for example, 5 to 10%, for example, 6.25%, and can take values ​​between 0 and 100%.

[0033] The second reduction factor may be applied, for example, to an average threshold reference value, and the sensing threshold is generally set based on it. Alternatively, the second reduction factor may be applied to a pre-valid sensing threshold.

[0034] In one embodiment, if both the first and second reduction criteria are met, only the second reduction criterion is applied. Therefore, the second reduction criterion takes precedence over the first reduction criterion, and as a result, if both reduction criteria are met, the sensing threshold is reduced by the second reduction coefficient.

[0035] In one embodiment, in addition to reducing the sensing threshold by a predefined second reduction factor, an additional second step factor may be applied if the second reduction criterion is met for two or more consecutive cycles. Generally, the second reduction factor is applied for the current cycle if the second reduction criterion is met. If the second reduction criterion is met again for subsequent cardiac cycles or multiple cardiac cycles, an additional second step factor may be applied. If the second reduction criterion is met again for the next cardiac cycle, the second step factor may be applied again, and as a result, the second step factor may be repeatedly applied for multiple cardiac cycles if the second reduction criterion is met.

[0036] The second step coefficient can also take a percentage value, for example, between 5 and 10%, or programmed with a step of 6.25%, and can take a value between 0 and 100%.

[0037] The additional step coefficient may be applied, for example, to the pre-applied sensing threshold setting, in particular to the sensing threshold after the application of a second reduction coefficient.

[0038] In one embodiment, the processing circuit configuration is set up so as not to reduce the sensing threshold beyond the lower absolute threshold. Therefore, the sensing threshold is limited to the lower limit defined by the lower absolute threshold. While the sensing threshold is at the lower limit, even if the first reduction criterion and / or the second reduction criterion are (repeatedly) met, no further reduction of the sensing threshold occurs.

[0039] In one embodiment, the processing circuit configuration is configured to determine the peak amplitude associated with a detected valid atrial event. When an atrial event is detected, the data recorded for the atrial event is analyzed to determine the peak amplitude. For example, an atrial event is identified as the point at which the cardiac sensing signal crosses the sensing threshold, and is also denoted as the atrial detection threshold. Starting from the crossing of the sensing threshold, a peak detection window is initiated, the maximum sensing signal value within the peak detection window is searched for, and this is then taken as the peak amplitude.

[0040] A crossover of the sensing threshold occurs when one value of the (processed) cardiac sensing signal is greater than the atrial detection threshold. Since the remote field atrial signal may contain noise, in another embodiment, an atrial event can be assumed to be present when two or more samples are greater than the sensing threshold, and only when they are greater than the threshold, and these instances may be consecutive or not.

[0041] Using the peak amplitude, the processing circuit configuration may be configured to update the sensing threshold to detect subsequent atrial events. In particular, the processing circuit configuration may be configured to update the sensing threshold using an average threshold criterion and a percentage ratio according to the following formula. ST = PC·ATR(t) Here, ST is the current sensing threshold, PC is the percentage ratio, and ATR(t) is the current average threshold reference over period t. The percentage ratio can be in the range of, for example, 0% to 100%, and can be programmed.

[0042] The average threshold criterion can be calculated and updated based on the peak amplitude according to the following formula. ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) Here, 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.

[0043] Therefore, for an actual period t, the average threshold criterion is determined based on the peak amplitude determined for that period and based on the average threshold that was previously effective in period t-1. Thus, for each period, the average threshold criterion is updated and recalculated, and as a result, the average threshold criterion is dynamically adjusted based on each period.

[0044] In another embodiment, the mean threshold criterion may be determined as the average value of the peak amplitude over a predefined number of cardiac cycles in which an atrial event was detected, e.g., a number between 2 and 6, e.g., four cardiac cycles.

[0045] The peak amplitude is determined only if a (valid) atrial event is detected. If no atrial event is detected, the peak amplitude is not determined, and the mean threshold criterion is not updated. In this case, the period is counted as a missed period, i.e., a period in which no atrial activity is detected.

[0046] In one embodiment, the processing circuit configuration includes a first processing channel having a first gain for processing a first processing signal derived from a signal received via a sensor configuration, and a second processing channel having a second gain for processing a second processing signal derived from a signal received via a sensor configuration, wherein the second gain is higher than the first gain.

[0047] In general, implantable medical devices may be configured to process different processing signals. To obtain such processing signals, a sensor configuration 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 may each be obtained, for example, using one electrode pair each, and the same or different electrode pairs may be used to obtain different processing signals. In the first case, a single electrical signal, such as an intracardiac electrophysiogram, may be obtained from which different processing signals, namely a first processing signal and a second processing signal, are derived for separate processing. In the latter case, for example, separate electrical signals associated with ventricular sensing signals and atrial sensing signals (i.e., by applying sensing optimized for atrial sensing) may be received to derive the first and second processing signals from such different electrical signals, and the different electrical signals may be received, for example, using different electrode pairs of a sensor configuration.

[0048] In one embodiment, different processing signals are processed by different processing paths in a processing circuit configuration. For this purpose, the processing circuit configuration includes a first processing channel for processing a first processing signal, which is related to, for example, a near-field (particularly ventricular) sensing signal, and which can be of a magnitude such that the first processing channel exhibits a fairly low gain, depending on the placement of the implanted medical device within the ventricle of the patient's heart.

[0049] Furthermore, the processing circuit configuration includes a second processing channel for processing a second processing signal, which may relate to a remote atrial sensing signal whose amplitude may decrease depending on the distance between the implantation site and the signal source, for example, in the case of an implantable medical device 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, and as a result, features related to atrial activity in the received signal can be appropriately analyzed.

[0050] For example, due to the placement of implantable medical devices within the ventricle, atrial activity occurs in the remote field. As a result, P waves originating from atrial activity may exhibit smaller amplitudes compared to QRS and T waves, making it difficult to distinguish atrial events within a normal ventricular sensing signal (e.g., obtained from a normal ventricular QRS sensing channel). Therefore, the signal portion related to remote field activity may be processed separately from the signal related to near-field activity in the second processing channel. Consequently, remote field events can be detected in the second processing channel with greater reliability and improved timing accuracy.

[0051] In one embodiment, the implantable medical device is positioned entirely or partially within the right ventricle or the left ventricle.

[0052] In one embodiment, the sensor structure is formed by an electrode structure, the electrode structure comprising a first electrode positioned near the tip of the main body. The first electrode is placed on the cardiac tissue when the implantable medical device is implanted, and as a result, the first electrode contacts the cardiac tissue in a position effective for injecting a stimulating signal into the cardiac tissue to induce, for example, pacing, particularly ventricular pacing.

[0053] In one embodiment, the electrode structure comprises a second electrode formed by an electrode ring extending circumferentially around the 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 slightly away from the tip of the main body, and therefore slightly away from the first electrode positioned at the tip.

[0054] In one embodiment, the processing circuit configuration 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 to be received between an electrode pair consisting of a first electrode and a second electrode. In one embodiment, the first and second electrodes may be placed fairly close to each other so that such an electrode pair is primarily suitable for 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 sensed 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.

[0055] In one embodiment, the main body has a remote position away from the tip (for example, the far end of the housing of a leadless pacemaker device), and the electrode configuration includes a third electrode positioned on the main body at the remote position. The third electrode is operably connected to a processing circuit configuration, which in turn enables the processing circuit configuration to receive and process signals received through the third electrode.

[0056] In one embodiment, the processing circuit configuration 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 generated between the first electrode and the third electrode can be called a remote field vector, and the first electrode and the third electrode are at a greater distance from each other than the first and second electrodes. The second signal can be processed to detect remote field events, i.e., atrial contractions, in particular when the implantable medical device is placed in the ventricle, and as a result, intrinsic atrial activity before the injection of pacing stimuli can be captured by the second signal.

[0057] Intrinsic atrial contractions can be sensed using a second signal sensed between a first electrode and a third electrode to bring atrioventricular synchronization by timely injecting stimuli at the ventricular location of the implanted pacemaker device following atrial contractions. The second signal is provided to a second processing channel to process the signal and detect atrial events from the signal, with the aim of providing pacing action based on the detected atrial event, thereby enabling ventricular pacing under atrioventricular (AV) synchronization.

[0058] In one embodiment, the second processing channel includes a processing step for distinguishing one wave portion from another in the second processed signal. The processing step may be configured to apply at least one of bandpass filtering, a blanking window for excluding a portion of the second 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 remote-field atrial activity may have a much smaller amplitude than signal portions related to near-field ventricular activity. Therefore, this processing plays a role in distinguishing different signal portions in order to identify such signal portions that may contain signals related to remote-field atrial activity.

[0059] In an intracardiac electrophysiogram, bandpass filtering may be applied, for example, to separate the P wave, thereby distinguishing between the wave portion associated with the P wave and the wave portion particularly associated with the QRS and T waves, which originate from ventricular activity. Alternatively, a blanking method may be applied to neutralize a specific portion of the second processed signal, i.e., such portions containing signals originating from events other than remote-field atrial activity. For this purpose, a blanking window functions to silence signal portions that are not subject to remote-field activity, but rather may interfere with the detection of remote-field activity. Thus, the blanking window excludes such portions of the signal that are not related to remote-field atrial activity from processing, and as a result, processing is limited to these signal portions that are (likely) related to remote-field activity. Alternatively, other methods such as moving average filtering, finite difference filtering, or signal rectification may be applied. In this specification, moving average filtering can be used to smooth the processed signal. Rectification can serve to easily compare the processed signal to a (single) threshold in order to identify the point in time when the magnitude of the signal exceeds a predefined threshold.

[0060] In one embodiment, the first processing channel comprises a first detection stage for detecting at least one near-field event in the first signal. Hereinafter, the processing stage of the second processing channel may be configured to determine at least one limit value for a blanking window to exclude a portion of the second signal from further processing, based on the near-field (e.g., ventricular) event detected by the first detection stage of the first processing channel. The first processing channel plays a role in processing the processing signal with a lower gain to detect near-field events, i.e., events resulting from activity in close proximity to the implanted medical device, for example, in the ventricle where the medical device is implanted. Since near-field events are also picked up within the second processing signal, it is advantageous to nullify such signal portions related to near-field activity, i.e., QRS waves and T waves when the medical device is placed in the ventricle. To precisely position the blanking window, for example, detected near-field events may be considered to determine a certain timing between atrial and ventricular events. From the detected near-field events, it is possible to determine the time range in which near-field events typically occur after far-field events, and as a result, a blanking window defined by the start and end times can be appropriately set to disable such portions of the second processing signal related to near-field ventricular events.

[0061] For example, in order to conserve power in the second high-gain processing channel, the second processing channel may be switched off at least partially during the blanking window. The second processing channel may include, for example, an amplification stage for amplifying the second processing signal, and the amplification stage may be switched off during the blanking window so that power is not consumed by amplification during the time interval of the blanking window.

[0062] Remote-field atrial events are detected in a detection window outside the blanking window. In this specification, the detection window may begin (immediately) at the end of the previous blanking window, or it may end at the beginning of the next blanking window. However, the detection window may also begin with a time delay, for example, after the end of the previous blanking window. Between the end of the blanking window and the start of the detection window, a second processing channel may be fully functional and process associated second processing signals, but remote-field (atrial) event detection does not occur until the start of the detection window.

[0063] In one embodiment, the second processing channel comprises a second detection stage for detecting atrial events within the second processed signal. The second detection stage may be logically positioned behind the processing stage of the second processing channel, so that the second detection stage receives the signal processed from the processing stage of the second processing channel. The second detection stage in this specification plays a role in identifying remote field atrial events in the second processed signal in order to output information related to the timing of the detected atrial events.

[0064] The second detection stage of the second processing channel may be configured to detect an atrial event by comparing the second processed signal with a sensing threshold. If the magnitude of the second processed signal exceeds the sensing threshold, it can be concluded that a remote-field atrial event is present. The processing described herein may be performed on a rectified signal, thereby allowing the application of a single threshold that can be compared to the rectified signal. However, it is also possible to identify a remote-field atrial event in an unrectified signal by applying, for example, two thresholds, namely a positive threshold and a negative threshold, where the remote-field atrial event is identified if the positive signal portion exceeds the positive threshold and / or if the magnitude of the negative signal portion exceeds the negative threshold.

[0065] In another embodiment, a method for operating an implantable medical device for providing intracardiac function includes receiving cardiac sensing signals using a sensor configuration disposed on the main body of the implantable medical device, processing the cardiac sensing signals received using the sensor configuration using a processing circuit configuration operably connected to the sensor configuration to detect atrial events caused by atrial activity for several cardiac cycles based on a comparison of cardiac sensing signals with a sensing threshold, evaluating whether a reduction criterion is met when no atrial events are detected in X1 out of Y1 cardiac cycles, when X1 is a natural number greater than or equal to 1 and Y1 is a natural number greater than or equal to X1, and reducing the sensing threshold if the reduction criterion is met.

[0066] The advantages and favorable embodiments described above for the apparatus can also be applied to methods such as those mentioned above.

[0067] The 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]

[0068] [Figure 1] This is a schematic diagram of a human heart with an implantable device, a leadless pacemaker, embedded inside. [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 the processing circuit configuration of one embodiment of an implantable medical device. [Figure 5A] This figure shows the shape of the intracardiac electrogram (IEGM) processed by the first processing channel of the processing circuit configuration as the first processed signal. [Figure 5B] This figure shows the second processed signal processed by the second processing channel of the processing circuit configuration. [Figure 6] This figure shows an example of a sensing threshold adapted over several cardiac cycles based on peak amplitude and reduction criteria. [Figure 7] This is a schematic diagram illustrating the evaluation of multiple cardiac cycles and one reduction criterion. [Figure 8] This diagram shows a schematic example of evaluating multiple cardiac cycles and two reduction criteria. [Figure 9] This is a schematic diagram of a human heart in which an implantable medical device in the shape of an intracardiac stimulator with leads has been implanted in the right ventricle. [Modes for carrying out the invention]

[0069] Next, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, similar reference numerals indicate similar components.

[0070] It should be noted that the examples provided are not intended to limit the present invention, but merely represent illustrative examples.

[0071] The present invention proposes to provide an implantable medical device that provides intracardiac function, particularly ventricular pacing, specifically so-called VDD pacing.

[0072] Figure 1 is a schematic diagram of a human heart, which consists of the right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV). The sinoatrial node (SAN) is located in the wall of the right atrium (RA), and is composed of a group of cells that have the ability to travel through the heart's electrical conduction system and spontaneously generate electrical impulses that cause 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 on the lower posterior aspect of the interatrial septum near the opening of the coronary sinus. The so-called bundle of His (H) extends from the atrioventricular node (AVN). This bundle of His consists of cardiomyocytes specialized for electrical conduction and forms part of the electrical conduction system for transmitting electrical impulses from the AVN via the so-called right bundle branch (RBB) surrounding the right ventricle (RV) and the left bundle branch (LBB) surrounding the left ventricle (LV).

[0073] In cases of block in the atrioventricular node (AVN), the intrinsic electrical conduction system of the heart (H) may be disrupted, potentially leading to insufficient intrinsic stimulation of ventricular activity, i.e., insufficient or irregular contraction of the right ventricular RV and / or left ventricular LV. In such cases, pacing of ventricular activity with a pacemaker may be applied, which stimulates ventricular activity by injecting stimulating energy into the intracardiac tissue, specifically the myocardium (M).

[0074] In one embodiment, as schematically shown in Figure 1, an implantable medical device 1 in the form of a leadless cardiac pacemaker is provided for ventricular pacing action, and the leadless pacemaker has a body 10 formed by a housing for the leadless pacemaker.

[0075] In another embodiment, as shown in Figure 9, the implantable medical device 1 may be a stimulator having a generator 18 and at least one lead that forms the main body 10 of the implantable medical device 1 and extends from the generator 18 into the heart via the patient's vein.

[0076] While typical implantable medical devices are designed to sense ventricular activity by receiving electrical signals from the ventricular RV and LV in which they are located, it is sometimes desirable to provide pacing that achieves atrioventricular (AV) synchronization by providing pacing in the ventricles that is synchronized with intrinsic atrial activity. For such pacing modes, also known as VDD pacing modes, it is necessary to sense atrial activity and identify such atrial events associated with atrial contraction in order to perform ventricular pacing based on atrial events.

[0077] Referring here to Figures 2 and 3, in one embodiment, an implantable medical device 1 in the form of a leadless pacemaker configured to provide intracardiac pacing, particularly in VDD pacing mode, comprises a housing 10 containing electrical and electronic components for operating the implantable medical device 1. In particular, the housing 10 contains a processing circuit configuration 15, which also includes a communication interface for communicating with external devices, such as a programmer wand. Furthermore, the housing 10 encapsulates electrical and electronic components, such as an energy storage unit in the form of a battery. The housing 10 encapsulates the components housed inside, and the housing 10 has the shape of, for example, a cylindrical shaft, having a length of several centimeters.

[0078] The implantable medical device 1 is to be directly implanted into the intracardiac tissue M. For this purpose, the implantable medical device 1 is equipped with a fixing device 14, for example in the shape of a nitinol wire, within the area of ​​the tip portion 100 in order to engage with the intracardiac tissue M and fixate the implantable medical device 1 on the tissue in an implanted state.

[0079] In the embodiments shown in Figures 2 and 3, the implantable medical device 1 does not have leads, but receives signals related to cardiac activity by an electrode configuration located on the housing 10, and also emits stimulation signals by such an electrode configuration. In the embodiments shown in Figures 2 and 3, the implantable medical device 1 is equipped with different electrodes 11, 12, and 13, which constitute an electrode configuration and emit pacing signals toward the intracardiac tissue M to provide pacing, and also play a role in sensing electrical signals indicating intracardiac activity, particularly atrial and ventricular contractions.

[0080] In this specification, the first electrode 11 is represented as a pacing electrode. The first electrode 11 is positioned at the tip 100 of the housing 10 and is configured to engage with intracardiac tissue M.

[0081] In this specification, the second electrode 12 is represented as a pacing ring. The second electrode 12 acts 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 (P: pacing vector) for emitting a pacing signal toward the intracardiac tissue M.

[0082] Furthermore, the second electrode 12 acts as a sensing electrode to detect signals particularly related to ventricular contraction, generating a signal vector V between the second electrode 12 and the first electrode 11, which is represented as a near-field vector.

[0083] The second electrode 12 is positioned a short distance from the first electrode 11 and, for example, has the shape of a ring extending 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 located.

[0084] In the embodiments shown in Figures 2 and 3, the implantable medical device 1 further comprises a third electrode 13 positioned at the distal end 101 of the housing 10, the third electrode 13 acting as a sensing electrode for sensing signals indicating cardiac activity in the remote field. 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 indicating, for example, atrial contraction and is represented as a remote field vector.

[0085] Electrodes 11, 12, and 13 are operably connected to a processing circuit configuration 15, which is configured so that the first electrode 11 and the second electrode 12 emit pacing signals to provide stimulation to the ventricles. The processing circuit configuration 15 is further configured to process the signals received via electrodes 11, 12, and 13 to sense cardiac activity, particularly atrial and ventricular contractions.

[0086] If the implantable medical device 1 comprises a generator 18 and leads extending from the generator 18, as shown in the embodiment of Figure 9, then a similar electrode configuration comprising, for example, three electrodes 11, 12, and 13 is arranged on leads implanted and extending within the right ventricular RV, as shown in Figure 9. Consequently, the electrode configuration also applies to an embodiment of the implantable medical device 1 having leads extending within the patient's heart. In this case, the processing circuit configuration 15 may be part of the generator 18 and may be operably connected to the electrode configuration arranged on the leads.

[0087] To provide pacing in the ventricle in which the implantable medical device 1 is located, and in particular to enable pacing in VDD mode, sensing atrial activity is required to provide detected atrial sensing markers for timing pacing in the ventricle to achieve atrioventricular (AV) synchronization. For this reason, remote field signals, particularly from the right atrium RA (see Figures 1 and 9), are sensed by the implantable medical device 1, which is implanted on the intracardiac tissue M in the right ventricular RV, to enable synchronized pacing in the right ventricular RV.

[0088] Referring here to Figure 4, in one embodiment, the processing circuit configuration 15 comprises two processing channels 16, 17 for processing different processing signals related to ventricular activity and atrial activity. In this specification, an intracardiac electrogram (IEGM) typically 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 remote-field signal source and is therefore far less prominent and has a much smaller amplitude than the signal portion related to ventricular activity which occurs in the near field, i.e., very close 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 being responsible for processing the first processing signal to identify ventricular events with a fairly low gain G1, and the second processing channel 17 being configured to process the second processing signal to identify atrial events with a significantly higher gain G2.

[0089] In particular, the first processing channel 16 is connected to an electrode configuration consisting of electrodes 11, 12, and 13, and is configured to specifically sense and process signals (near-field vector V in Figures 2 and 3) received via electrodes 11 and 12. The first processing channel 16 comprises a first amplification stage 161 having a gain G1, and a detection stage 162 following the amplification stage 161, configured to identify a ventricular sensing marker Vx from a first processed signal processed within the first processing channel 16.

[0090] A second processing channel 17 is similarly connected to an electrode configuration consisting of electrodes 11, 12, and 13, and the second processing channel 17 may be configured to process signals sensed via a remote field vector A, i.e., between electrodes 11 and 13 located at the front end 100 and 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.

[0091] The processing stage 172 plays the role of pre-processing the amplified second processed signal. Next, the detection stage 173 plays the role of evaluating and analyzing the processed signal in order to identify atrial events in the second processed signal, and then the second processing channel 17 outputs an atrial sensing marker As indicating the atrial events detected in the processed signal.

[0092] Furthermore, the processing circuit configuration 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 atrioventricular synchronous pacing.

[0093] 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 makes it possible to analyze signal portions associated with atrial events, but it is necessary to distinguish such signal portions associated with atrial events from other signal portions, particularly those associated with ventricular events in the near field, which are much stronger than signal portions originating from atrial events in the far field.

[0094] Within the processing stage 172, for example, bandpass filtering, windowing (e.g., partial blanking), smoothing by moving average filtering, and rectification may be performed. A first- or second-order difference may be applied to remove non-zero baselines while augmenting P-wave defects.

[0095] Figures 5A and 5B show examples of signals S1 and S2 processed by different processing channels 16 and 17. Figure 5A at the top shows signal S1 processed by the first processing channel 16, and Figure 5B at the bottom shows signal S2 processed by the second processing channel 17. As a result of the processing, ventricular event Vx and atrial event As are identified, and corresponding markers are output.

[0096] As shown clearly in Fig. 5B, the sensing of atrial event As uses a windowing scheme that specifically employs a blanking window T to invalidate the signal portion of signal S2 that may potentially be related to ventricular activity. blank

[0097] Specifically, 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 start point and the end point of the blanking window T blank can be set, and thus the signal portion not related to atrial activity can be excluded from the processing. In this way, strong ventricular signals can be suppressed so that the signal portion related to ventricular activity cannot interfere with the detection of atrial events.

[0098] During the blanking window T blank the second processing channel 17 can be turned off. Specifically, the amplification stage 171 of the second processing channel 17 may be switched off to save power.

[0099] Generally, the detection of atrial events is performed outside the blanking window T blank In this specification, the detection window T sense for detecting atrial events may start at the end of the previous blanking window T blank Alternatively, the detection window T sense may be delayed with respect to the end of the previous blanking window T blank as shown in the embodiment of Fig. 5B, and as a result, the signal processing in the second processing channel 17 starts at the end of the previous blanking window T blank but the detection of atrial events starts only after a specific delay.

[0100] Generally, the sensing window T senseIn this case, as shown in Figure 5B, an atrial event As is assumed to exist when the signal S2 crosses the sense threshold ST (ST). The comparison may be based on the rectification of the sense signal S2. Alternatively, positive and negative sense threshold STs may be used, and they may have the same value or their values ​​may be different. In this specification, a threshold crossover can be assumed when one signal value is greater than the sense threshold ST. Alternatively, a sense threshold ST crossover is assumed when a predefined number of signal values ​​are greater than the sense threshold ST, for example, two or more consecutive sample values.

[0101] 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, particularly to update the ST sensing threshold and to achieve atrioventricular synchronized pacing.

[0102] In particular, the atrial event As is considered to be the point in time when the ST crossover at the sensing threshold is identified. At the time of the atrial event As, the peak detection window (PDW) is initiated, 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 on the right in Figure 5B for the second period.

[0103] Furthermore, if an atrial event As is detected, an atrioventricular delay (AVD) may be determined and used for subsequent processing. If a ventricular event Vx is not detected after the course of the atrioventricular delay AVD, a pacing signal can be injected to induce ventricular stimulation.

[0104] In one embodiment, the peak amplitude PA may be used to update the sensing threshold ST. In particular, the processing circuit configuration 15 may be configured to update the sensing threshold ST using an average threshold criterion and a percentage ratio according to the following formula. ST = PC·ATR(t) Here, ST is the current sensing threshold, PC is the percentage ratio, and ATR(t) is the average threshold reference for the current period t. The percentage ratio may be in the range of, for example, 0% to 100%.

[0105] The mean threshold criterion can be determined based on the average values ​​of several previous cardiac cycles, during which atrial events are identified and corresponding peak amplitude values ​​are obtained. In this case, the mean threshold criterion can be determined, for example, as the average of the peak amplitude values ​​in previous cardiac cycles.

[0106] In another embodiment, the average threshold criterion may be calculated based on the peak amplitude PA according to the following formula. ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) Here, 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.

[0107] Therefore, for an actual period t, the average threshold criterion is determined based on the peak amplitude determined for that period t, and is determined based on the average threshold that was previously valid in period t-1. Thus, for each period in which an atrial event As is detected, the average threshold criterion is updated and recalculated, and as a result, the average threshold criterion is dynamically adjusted based on each period.

[0108] If no (valid) atrial event is detected, the peak amplitude PA is not determined, and the mean threshold-based ATR is not updated. In this way, false detection of an atrial event As can lead to a false increase in the sensing threshold ST segment and subsequent loss of atrial activity capture, as is the case in the first cardiac cycle as shown in Figures 5A and 5B, where no crossover of the sensing threshold ST segment is detected, and consequently, no atrial event is identified.

[0109] The ST sensing threshold is generally set based on the peak amplitude value PA of the atrial event As detected in the previous cardiac cycle. Accordingly, the ST sensing threshold can be dynamically increased or decreased in accordance with the peak amplitude value of the previous cardiac cycle.

[0110] However, this applies only when an atrial event As is detected. If an atrial event As is not detected in a cardiac cycle, the peak amplitude PA is not determined, and no dynamic adjustment of the sensing threshold based on the above scheme is performed. However, given the general desire to reliably detect atrial events As and to obtain stable and reliable capture of atrial events As in order to obtain them in as many cycles as possible, measures should be taken to recapture signals related to atrial activity when a significant number of atrial signals are missed. Missing one or more atrial events As in a cardiac cycle may indicate that the sensing threshold ST is too high and therefore should be lowered to recapture atrial activity.

[0111] Therefore, if it is found that a significant number of atrial events As are missed within a cardiac cycle based on one or more reduction criteria, it is proposed to dynamically adjust the sensing threshold ST in a stepwise attenuation procedure. These reduction criteria are formulated as the "X out of Y criterion." If atrial events As are not detected in X out of Y cardiac cycles, the reduction criterion is met accordingly.

[0112] Reduction criteria in this specification may include short-term and long-term criteria.

[0113] The short-term criterion can assess, for example, whether an atrial event As was detected in X1 out of Y1 cardiac cycles. In this case, the short-term criterion is assumed to be true, and the sensing threshold ST is adjusted appropriately. In this specification, X1 and Y1 are natural numbers, where X1 is greater than 0 and Y1 is greater than or equal to X1. Within the short-term criteria of this specification, it is checked whether a significant number of atrial events As have been missed in very recent cardiac cycles. Y1 can take values ​​between 1 and 4, for example, and X1 can be assumed to take values ​​between 1 and Y1.

[0114] For example, Y1 may be equal to 2, and X may be equal to 1 or 2. Therefore, it is checked whether an atrial event was missed in one of the two previous cardiac cycles, or whether both of the two previous cardiac cycles were missed.

[0115] The long-term criterion can be used to assess, for example, whether an atrial event As is detected in two X cycles out of two Y cycles. In this case, the long-term criterion is assumed to be true, and the ST sensing threshold is adjusted appropriately. X2 and Y2 are natural numbers, where Y2 is greater than Y1 and can have a value between 4 and 16, for example, and X2 is greater than X1 and less than or equal to Y2 and can have a value between 3 and 15.

[0116] For example, Y2 may be equal to 8, and X2 may be equal to 5. Therefore, it is checked whether an atrial event As was missed in 5 of the 8 previous cardiac cycles.

[0117] If a first reduction criterion corresponding to a short-term reduction criterion is met, a first reduction factor may be applied. Alternatively, if a second reduction criterion corresponding to a long-term reduction criterion is met, a second reduction factor may be applied, which may result in a stronger reduction than the first reduction factor.

[0118] In this specification, in one embodiment, if the second reduction criterion is met, only the second reduction coefficient applies.

[0119] Both the first and second reduction factors may be percentage values. The reduction factors can be programmed in steps, for example, between 5% and 10%, or between 6.25%. Each reduction factor can take values ​​between 0% and 100%, and the second reduction factor can generally cause a stronger reduction than the first reduction factor.

[0120] Each reduction factor is applied when each reduction criterion is met for the current cardiac cycle. Furthermore, if each reduction criterion is repeatedly met for multiple consecutive cardiac cycles, an additional step factor may be applied in addition to the reduction factor to further reduce the sensing threshold.

[0121] This is shown in Figure 6.

[0122] Generally, if the reduction criteria are not met, the sensing threshold ST is calculated based on the average threshold reference ATR (ATR), which is calculated based on the peak amplitude PA of the previous cardiac cycle, by applying a predefined normal percentage ratio PC (PC), where the percentage ratio is, for example, between 40% and 100%, for example, 80%. The percentage ratio PC is applied as a coefficient, and therefore the sensing threshold ST takes the value of PC × ATR.

[0123] In cardiac cycle i, if, for example, a first reduction criterion corresponding to a short-term reduction criterion is found to be met, the sensing threshold ST is reduced by a first reduction coefficient L1. The first reduction coefficient L1 is applied, for example, to the effective mean threshold criterion ATR, and as a result, the sensing threshold ST is calculated, for example, as the current value of L1 × mean threshold criterion ATR.

[0124] If the first reduction criterion is met in a predefined number of consecutive periods, additional gradual attenuation can be applied by multiplying the currently effective sensing threshold ST by a step coefficient L11, which can be applied repeatedly as shown in Figure 6. The step coefficient L11 can be applied if the reduction criterion is met in two consecutive periods. The step coefficient L11 can also be applied alternatively only if the reduction criterion is met in two or more consecutive periods, as shown in period i+a in Figure 6.

[0125] If an atrial event is detected in cardiac cycle i+b and the first reduction criterion is no longer met, the mean threshold ATR is adjusted according to the now determined peak amplitude PA, and the sensing threshold ST is determined by resetting the step coefficient L11 and by applying the reduction coefficient L1 to the mean threshold ATR.

[0126] If, in period i+c, it is found that the first reduction criterion is again met for a predefined number of consecutive periods, the step coefficient L11 is applied again to reduce the sensing threshold ST.

[0127] In cardiac cycle i+d, the second reduction criterion is also met (potentially in addition to the first reduction criterion), in which case the reduction coefficient L2 associated with the second reduction criterion is applied to calculate the sensing threshold ST. The second reduction coefficient L2 highlights the reduction of the sensing threshold ST, as is evident from Figure 6.

[0128] In cardiac cycle i+e, it is found that the second reduction criterion is met for a predefined number of consecutive cycles, and as a result, an additional step coefficient L21 associated with the second reduction criterion is applied to further reduce the sensing threshold ST.

[0129] In this specification, as is clear from Figure 6, the sensing threshold ST cannot be reduced below the lower absolute threshold LAT (LAT), which acts as the lower limit of the sensing threshold ST and therefore represents the absolute minimum value of the sensing threshold ST.

[0130] In cardiac cycle i+f, an atrial event is detected, and accordingly, the mean threshold ATR is adjusted, the step coefficient L21 is restored, and as a result, the sensing threshold ST is determined by applying only the reduction coefficient L2 associated with the second reduction criterion to the absolute threshold ATR.

[0131] In cardiac cycle i+g, the second reduction criterion is no longer true, an atrial event is detected, and accordingly, the mean threshold criterion ATR increases, and the sensing threshold ST is calculated by applying only the reduction coefficient L1 associated with the first reduction criterion.

[0132] In cardiac cycle i+h, the first reduction criterion is no longer met, an atrial event is detected, and accordingly the mean threshold criterion ATR is adjusted, and the sensing threshold ST is calculated by applying only the percentage ratio PC that indicates normal operation.

[0133] Figure 7 shows an example of adjusting the sensing threshold ST based on a single reduction criterion formulated as X out of Y, where X and Y are equal to 2. Therefore, it is evaluated whether or not an atrial event As is detected in two out of two cardiac cycles.

[0134] In the example shown in Figure 7 (and similarly in the example in Figure 8), the first column shows the cardiac cycles numbered. The second column shows the detected atrial events As and ventricular events Vx. If an atrial event As is not detected, this is indicated by an "x". If it is detected, the peak amplitude (PA) value for the P wave measured in the current cycle is shown.

[0135] In the illustrated example, the reduction criteria are not met in cardiac cycles i to i+3. However, in cardiac cycle i+4, it is found that no atrial events were detected in the current and previous cardiac cycles, and accordingly, the "two of two" reduction criteria are met. Therefore, the reduction coefficient L1 associated with the first reduction criterion is applied, and the sensing threshold ST is calculated by multiplying the currently valid mean threshold criterion value ATR(7.5) by the reduction coefficient L1(0.45). Thus, the threshold ST for cycle i+5 takes the value of 3.4.

[0136] In the following cardiac cycles i+5 and i+6, the reduction criterion is not met, and therefore the sensing threshold ST is recalculated based on the normal percentage ratio PC(0.8). However, in cardiac cycle i+7, the reduction criterion is met again, and the reduction coefficient L1 is applied to calculate the sensing threshold ST for the next cycle i+8.

[0137] In one example shown in the figure, the average threshold ATR is calculated as ATR(i+1)=W*PA(i)+(1-W)*ATR(i), where the update weight W is 0.5.

[0138] In another example shown in Figure 8, two reduction criteria are applied. The first criterion is a short-term criterion, which is met if an atrial event As is detected in one of two cardiac cycles (column 6 in Figure 8). The second reduction criterion is a long-term criterion, which is met if an atrial event As is not detected in five out of eight cardiac cycles (column 7 in Figure 8).

[0139] In the example in Figure 8, the reduction criterion is not met in cardiac cycles i to i+2, and accordingly, the sensing threshold ST is calculated by applying the normal percentage ratio PC(0.8). The first reduction criterion is met in cardiac cycles i+3 and i+4, and accordingly, the reduction coefficient L1(0.6) associated with the first reduction criterion is applied to calculate the sensing threshold ST. In cardiac cycle i+5, the reduction criterion is again not met, and therefore, the normal percentage ratio PC is applied. In cardiac cycles i+6 to i+8, the first reduction criterion is met, and accordingly, the first reduction coefficient L1 is applied to calculate the sensing threshold ST. Then, in cardiac cycle i+9, the second reduction criterion is also met, and the reduction coefficient L2(0.4) associated with the second reduction criterion is applied to calculate the sensing threshold ST. The second reduction criterion is also met in cardiac cycle i+10, whereas in cardiac cycle i+11, the reduction criterion is again not met.

[0140] In cases of missed atrial events (As), adjusting the ST threshold using a stepwise decay method to gradually reduce the ST threshold allows for reliable atrial detection, especially when atrial events are not detected for a significant number of cardiac cycles.

[0141] Ventricular synchronized pacing can be achieved using the atrial sensing marker As output by the second processing channel 17. For this purpose, it is possible to detect whether an intrinsic ventricular sensing marker Vx (output by the first processing channel 16) occurs after the detected atrial sensing marker As, within a predefined time delay window, in which case no stimulation is required. If the ventricular sensing marker Vx is not detected, a stimulation pulse can be issued to induce synchronized pacing in the ventricle.

[0142] Conversely, asynchronous pacing can also be performed.

[0143] By utilizing remote-field electrical signals received by implantable medical devices, excellent detection of remote-field events, particularly atrial events when the medical device is implanted in the ventricle, can be provided. Tracking remote-field events using and evaluating electrical signals can improve consistency and reliability, especially with respect to external factors such as posture and patient activity. [Explanation of symbols]

[0144] 1. Implantable medical devices (leadless pacemaker devices) 10 Main unit (housing) 100 Tip 101 Distal end 11. First electrode (pacing electrode) 12. Second electrode (pacing ring) 13. Third electrode 14 Fixation device 15 Processing Circuit Configuration 16. First processing channel 161 Amplification Stage 162 detection stage 17. Second processing channel 171 Amplification Stage 172 Processing Stages 173 detection stage 174 Timing stage 18 Generators A atrial vector As atrial events AVD (Atrioventricular Delay) AVN Atrioventricular Node G1, G2 gain H His bundle i cardiac cycle L1, L2 Reduction Factor (%) L11, L21 Step Coefficient (%) LA (Left Atrium) LAT Lower Absolute Threshold LBB left leg LV left ventricle M: Cardiac tissue (myocardium) P Pacing Vector PA Peak Amplitude PDW Peak Detection Window RA right atrium RBB right leg RV right ventricle S1, S2 signal SAN sinoatrial node ST Sensing Threshold T blank Blanking window T sense Detection window V ventricular vector Vx ventricular event

Claims

1. An implantable medical device (1) configured to provide intracardiac function, The main unit (10) and A sensor component is placed on the main body (10) and configured to receive heart detection signals, A processing circuit configuration (15) operably connected to the sensor configuration, wherein the processing circuit configuration (15) processes the heart detection signal received using the sensor configuration. For several cardiac cycles, atrial events (As) caused by atrial activity are detected based on a comparison between the cardiac sensing signal and the sensing threshold (ST). The reduction criterion is met when no atrial event (As) is detected in one X cycle out of one Y cycle, and when X1 is a natural number greater than or equal to 1 and Y1 is a natural number greater than or equal to X1, it is evaluated whether the reduction criterion is met. The system is configured to reduce the sensing threshold (ST) in the current cycle if it is found that the reduction criterion is met in the current cycle, and the reduction criterion is met if no atrial event (As) is detected in one of the Y cardiac cycles prior to the current cycle, and comprises a processing circuit configuration (15). Implantable medical device (1).

2. The implantable medical device (1) according to claim 1, wherein the sensor configuration is mounted by an electrode configuration configured to receive an electrical signal as a heart sensing signal.

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

4. The implantable medical device (1) according to claim 1 or 2, wherein the main body (10) is formed by the housing of a leadless pacemaker device.

5. The implantable medical device (1) according to any one of claims 1 to 4, wherein the processing circuit configuration (15) is configured to reduce the sensing threshold (ST) by reduction coefficients (L1, L2) when the reduction criterion is met.

6. The implantable medical device (1) according to claim 5, wherein the processing circuit configuration (15) is configured to further reduce the sensing threshold (ST) by step coefficients (L1, L2) when the reduction criterion is met for at least two consecutive periods.

7. The processing circuit configuration (15) is configured to evaluate whether a further second reduction criterion is met, the further second reduction criterion being met if no atrial event (As) is detected in X2 of Y2 cardiac cycles, where X2 is a natural number greater than X1 and Y2 is a natural number greater than Y1, according to any one of claims 1 to 6.

8. The implantable medical device (1) according to any one of claims 1 to 7, wherein the processing circuit configuration (15) is configured to reduce the sensing threshold (ST) by a second reduction coefficient (L2) associated with the further second reduction criterion.

9. The implantable medical device (1) according to any one of claims 1 to 8, wherein the processing circuit configuration (15) is configured so as not to reduce the sensing threshold (ST) beyond the lower absolute threshold (LAT).

10. The processing circuit configuration (15) is configured to determine the peak amplitude (PA) as the maximum sensing signal value within a peak detection window that starts together with the detected atrial event (As), and the processing circuit configuration (15) is configured by formula ST(t)=PC・ATR(t) Based on this, the system is configured to update the sensing threshold (ST) using an average threshold criterion. Here, ST(t) is the current sensing threshold, PC is the percentage ratio, and ATR(t) is the current average threshold reference. The current average threshold criterion is given by: ATR(t)=W・PA(t-1)+(1-W)・ATR(t-1) Determined by, Herein, W represents an update weight that determines how much the average 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 average threshold criterion, according to any one of claims 1 to 9 (1).

11. The implantable medical device (1) according to any one of claims 1 to 10, wherein the processing circuit configuration (15) comprises a first processing channel (16) having a first gain (G1) for processing a first processing signal derived from a cardiac sensing signal received via the sensor configuration, and a second processing channel (17) having a second gain (G2) for processing a second processing signal derived from a cardiac sensing signal received via the sensor configuration, wherein the second gain (G2) is higher than the first gain (G1).

12. The implantable medical device (1) according to claim 11, wherein the processing circuit configuration (15) is configured to process the first processing signal to detect ventricular activity and to process the second processing signal to detect atrial activity.

13. A method for operating an implantable medical device (1) for providing intracardiac function, The system receives cardiac detection signals using a sensor component placed on the main body (10) of the implantable medical device (1), The heart detection signal received using the sensor configuration is processed using a processing circuit configuration (15) operably connected to the sensor configuration. For several cardiac cycles, atrial events (As) caused by atrial activity are detected based on a comparison between the cardiac sensing signal and the sensing threshold (ST). Evaluate whether the reduction criteria are met, If it is found that the reduction criteria are met in the current cycle, the sensing threshold (ST) in the current cycle is reduced, wherein the reduction criteria are met when no atrial event (As) is detected in X1 of Y1 cardiac cycles prior to the current cycle, and the sensing threshold (ST) is reduced when X1 is a natural number greater than or equal to 1 and Y1 is a natural number greater than or equal to X1. A method for providing this.

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