Implantable medical device configured to provide an intracardiac function - Patent Application 20070122997

Abstract

An implantable medical device 1 configured to provide an intracardiac function, the implantable medical device 1 comprising: a body 10; a sensor arrangement disposed on the body 10 and configured to receive cardiac sensed signals; and processing circuitry 15 operatively connected to the sensor arrangement. The processing circuitry 15 is configured to process the cardiac sensed signals received using the sensor arrangement to detect signal deflections that may be indicative of an atrial event As caused by atrial activity to obtain an atrial detection, detect signal deflections indicative of a ventricular event Vx caused by ventricular activity subsequent to said atrial detection, determine an atrial-ventricular interval AVI representing a time between the atrial detection and the ventricular event Vx, and identify whether the atrial detection is valid or invalid based on the atrial-ventricular interval AVI.

Description

[Technical Field]

[0001] The present invention relates generally to implantable medical devices for providing intracardiac functions, particularly pacing functions such as ventricular pacing, and in particular VDD pacing. [Background technology]

[0002] In an implantable medical device, for example in the form of a leadless pacemaker device or a cardiac stimulation device that uses a subcutaneously implanted pulse generator and one or more leads extending into a patient's heart, it may be desirable to provide stimulation to a ventricle of the patient's heart, e.g., the right ventricle, in synchronization with atrial activity. Thus, ventricular pacing takes into account atrial sensed signals, for example in a so-called VDD pacing mode, to control ventricular pacing based on atrial events indicative of atrial activity.

[0003] In recent years, leadless pacemakers have attracted increasing attention. In contrast to subcutaneously implanted pacemakers, which use leads that extend into the heart via veins, leadless pacemakers do not use leads because the pacemaker device itself is implanted intracardially and the pacemaker is shaped like a capsule for implantation in cardiac tissue, particularly the right ventricle. Such leadless pacemakers offer the inherent advantage of being lead-free, thereby reducing patient risks associated with leads that extend into the heart via veins, such as pneumothorax, lead migration, cardiac perforation, and venous thrombosis.

[0004] Leadless pacemaker or stimulation device leads may be specifically designed for implantation in the right ventricle, for example, by positioning them near the apex of the right ventricle during implantation. Ventricular pacing may be required, for example, when AV node dysfunction occurs but sinus node function is intact and adequate. In such cases, so-called VDD pacing may be particularly desirable, which involves ventricular pacing with atrial tracking, which requires sensing atrial activity to pace the ventricles based on intrinsic atrial contractions.

[0005] VDD pacing is specifically motivated by the hemodynamic benefits to the patient: maximizing ventricular preload, limiting AV valve regurgitation, maintaining low mean atrial pressure, and atrioventricular (AV) synchronization by utilizing adequate sinus node function to trigger ventricular pacing, which may allow modulation of autonomic neurohumoral reflexes.

[0006] Solutions using modalities for detecting the mechanical event of atrial contraction, including sensing motion, sound, and pressure, have been explored in the literature (see, for example, U.S. Patent No. 6,273,999, which discloses a leadless cardiac pacemaker including a pressure sensor and / or an 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 the implantable medical device is located within the ventricle and therefore quite far from the atrium whose contraction is to be sensed. Furthermore, wall motion and blood movement caused by atrial contraction may not be transmitted directly to the ventricle, and cardiac hemodynamic signals, such as motion, heart sounds, and pressure, are easily affected by external factors such as posture and patient activity.

[0007] A further drawback of mechanical sensing can result from the signal being mixed with ventricular activity signals at a lower rate than is possible with electrical sensing. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Application Publication No. 2018 / 0021581 Summary of the Invention [Problem to be solved by the invention]

[0009] In particular, it is an object to provide an implantable medical device, and a method for operating an implantable medical device, that enables ventricular pacing that involves atrioventricular synchrony and therefore requires reliable sensing of atrial events in order to provide ventricular pacing based on such events. [Means for solving the problem]

[0010] Such needs are addressed by an implantable medical device configured to provide an intracardiac function having the features of claim 1.

[0011] In one aspect, an implantable medical device configured to provide an intracardiac function comprises a body, a sensor arrangement disposed on the body and configured to receive cardiac sensed signals, and processing circuitry operatively connected to the sensor arrangement. The processing circuitry is configured to process the cardiac sensed signals received using the sensor arrangement to: detect signal deflections that may be indicative of an atrial event caused by atrial activity to obtain an atrial detection; detect signal deflections that are indicative of a ventricular event caused by subsequent ventricular activity of the atrium; determine an atrial-ventricular interval representing the time between the atrial detection and the ventricular event; and identify whether the atrial detection is valid or invalid based on the atrial-ventricular interval.

[0012] In implantable medical devices, processing circuitry is used to process and analyze cardiac sensed signals to detect atrial events indicative of atrial activity. Atrial event detection typically involves comparing a cardiac sensed signal to a threshold within an appropriate sensing window for sensing atrial activity, and assuming an atrial event if the threshold is crossed. However, because this sensing occurs within the ventricle by a sensor arrangement located on the device body implanted within the ventricle, atrial activity occurs in the far-field, and thus the atrial sensed signal is received at the sensor arrangement as a far-field signal with a relatively small signal amplitude. Therefore, there is a risk of oversensing near-field signals, particularly those associated with ventricular activity, such as the QRS complex in an intracardiac electrogram (IEGM).

[0013] In particular, when the sensor configuration is an electrode configuration for sensing electrical IEGM signals, the onset of the QRS complex (due to signals in the near field caused by ventricular activity) may be mistaken for an atrial sensed signal, and an atrial detection may then be erroneously identified as an atrial event determined based on a threshold crossing by a signal associated with the QRS complex.

[0014] For this reason, it is proposed to assume that an atrial detection is valid only if it occurs with a sufficient timing period relative to a subsequent ventricular event. To this end, when processing a cardiac sensed signal, it is determined whether a signal deflection in the cardiac sensed signal may indicate an atrial event. A ventricular event is then detected, and an atrial-ventricular interval indicating the timing period between the assumed atrial event and the subsequent ventricular event is determined. The atrial-ventricular interval is then evaluated, and based on the atrial-ventricular interval, it is determined whether the atrial detection is valid or invalid. In this manner, it is possible to determine, inter alia, whether an atrial event is detected with a sufficient time period from a subsequent ventricular event, and only if so, is the atrial event assumed to be a true, valid atrial event. Otherwise, the putative atrial event is classified as invalid because the atrial detection may possibly be too close to a subsequent ventricular event and thus may be caused, for example, by a cardiac sensed signal waveform due to ventricular activity, such as the onset of a QRS complex in an intracardiac electrocardiogram.

[0015] The sensor arrangement may in particular be formed by an electrode arrangement of one or more electrodes arranged on the body, such that electrical signals can be received by the sensor arrangement, such electrical signals representing an intracardiac electrocardiogram recording and thus indicative of cardiac activity.

[0016] In another example, the sensor arrangement may be configured to sense cardiac signals in the form of pressure signals, acoustic signals, ultrasound signals, motion signals, and / or impedance signals.

[0017] In one embodiment, the body of the implantable medical device may be formed by a lead connectable to a generator of the implantable medical device. In this case, the generator is implanted in the patient, e.g., subcutaneously, away from the heart, and the lead may form a body extending from the generator into the heart, where the body having the sensor arrangement disposed thereon is placed within the heart, e.g., within the right ventricle, for engaging tissue therein.

[0018] In another example, the body can be formed by a leadless pacemaker device housing, where the implantable medical device is formed as a leadless device but without leads extending from a location outside the heart into the heart for providing stimulation and / or sensing within the heart. The leadless pacemaker device housing can have a distal end formed by the housing that is positionable on tissue, with the sensor arrangement, for example, positioned (at least partially) on or near the distal end and engaging tissue when the distal end of the leadless pacemaker device is placed on tissue.

[0019] When the implantable medical device is a leadless pacemaker device, the housing encapsulates the implantable medical device, which contains all components necessary for autonomous operation, e.g., processing circuitry, energy storage such as a battery, electrical and electronic circuitry, etc. The housing is fluid-tight, allowing the implantable medical device to be implanted in cardiac tissue and maintained therein for an extended period of time to provide long-term continuous cardiac pacing operation.

[0020] In one embodiment, the processing circuitry is configured to compare the atrial-ventricular interval with the exclusion interval and identify atrial detection as valid if the atrial-ventricular interval is greater than the exclusion interval. Alternatively, atrial detection is identified as invalid if the atrial-ventricular interval is less than the exclusion interval. This is based on the observation that if a detected atrial event is too close to a subsequent ventricular event, the atrial event is likely to be due to a signal of non-atrial origin, such as a ventricular near-field signal, e.g., the onset of a QRS complex in an intracardiac electrocardiogram. Therefore, the timing interval relative to the subsequent ventricular event can be used to disqualify and discard a suspected atrial event that is likely to be a false positive. With regard to disqualifying atrial detection, the timing between the atrial detection and the subsequent ventricular event, i.e., the atrial-ventricular interval, is compared to a threshold, i.e., the atrial exclusion interval. Atrial detection is considered valid only if the time interval between the atrial detection and the subsequent ventricular event is greater than the exclusion interval. Otherwise, the atrial detection is considered invalid.

[0021] This criterion for determining atrial events is particularly simple compared to that of prior art methods and is therefore particularly suitable for use in leadless pacemakers where resource-saving algorithms are advantageous.

[0022] In one example, the processing circuitry is configured to determine a peak amplitude associated with an atrial event if atrial detection is identified as valid. If atrial detection is identified as valid, recorded data related to the atrial event is analyzed to determine the peak amplitude. For example, an atrial event is identified as the point in time when the cardiac sensed signal crosses a sensing threshold, also referred to as the atrial detection threshold. A peak detection window is initiated beginning with the crossing of the sensing threshold, and the largest signal amplitude value within the peak detection window is assumed to be the peak amplitude of that detection.

[0023] In one example, the processing circuitry is configured to determine whether the peak detection window overlaps with an exclusion interval. The peak detection window may have, for example, a fixed length. If the peak detection window overlaps with an exclusion interval that precedes and ends with a subsequent ventricular event, data associated with the overlapping portion of the peak detection window is discarded and not used in determining the peak amplitude. This is based on the assumption that a portion of the cardiac sensed signal within the exclusion interval may not be associated with atrial activity but may be associated with near-field signals due to, for example, ventricular activity, and therefore should be discarded and not processed to analyze atrial activity.

[0024] The exclusion interval can range from 0 ms to 175 ms.

[0025] The exclusion interval may be programmed as a fixed value, or alternatively, may be adaptive, for example depending on the actual or average heart rate, or on an activity parameter indicative of patient activity.

[0026] Using the peak amplitude, the processing circuitry may be configured to update the sensing threshold for detecting subsequent atrial events. In particular, the processing circuitry may use the average threshold reference value and the percentage ratio to calculate the following equation: ST(t)=PC·ATR(t) where ST is the current sense threshold for cycle t, PC is a percentage ratio, and ATR(t) is the current average threshold reference for cycle t. The percentage ratio may be in a range between 0% and 100%, for example.

[0027] It should be noted that the above formula can be used for setting the sensing threshold for some or all cycles, but in that case more complex schemes can be employed, including, for example, step-down techniques for adapting the sensing threshold.

[0028] The average threshold reference value is based on the peak amplitude and is calculated using the following formula: ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) where W denotes an update weight that determines how much to change the average threshold reference value based on the preceding peak amplitude, PA(t-1) is the peak amplitude determined for the preceding cycle t-1, and ATR(t-1) is the preceding average threshold reference value. In the actual cycle t, the average threshold reference value is determined based on the previously determined valid peak amplitude and the preceding average threshold reference value for cycle t-1. Therefore, the average threshold reference value is updated and newly calculated for each cycle, and as a result, the average threshold reference value is dynamically adjusted for each cycle.

[0029] Peak amplitudes are determined only for atrial detections that qualify as valid based on a comparison of the atrio-ventricular interval with, for example, an exclusion interval. If an atrial detection is classified as invalid, peak amplitudes are not determined and the average threshold reference value is not updated. In this case, the cycle is counted as a missed cycle, i.e., a cycle in which no atrial activity was sensed. In this way, the possibility that false detection of an atrial event due to near-field signals, such as the onset of a QRS complex in an intracardiac electrogram, could erroneously lead to an increase in the average threshold reference value used to set the sensing threshold for the next cycle is particularly prevented.

[0030] In one embodiment, the processing circuitry comprises a first processing channel having a first gain for processing a first processed signal derived from a sensor signal received via the sensor arrangement, and a second processing channel having a second gain for processing a second processed signal derived from the sensor signal received via the sensor arrangement, the second gain being higher than the first gain.

[0031] In general, an implantable medical device can be configured to process various processed signals. To obtain such processed signals, a sensor arrangement is provided, the sensor arrangement including, for example, one or more electrodes for receiving electrical signals from which the processed signals are derived. Here, the processed signals can each be obtained, for example, using one electrode pair, and the same or different electrode pairs can be used to obtain different processed signals. In this first case, a single electrical signal, such as an intracardiac electrocardiogram, can be obtained from which different processed signals, i.e., first and second processed signals that are processed separately, are derived. In the latter case, separate electrical signals, e.g., related to a ventricular sensed signal and an atrial sensed signal (i.e., by applying sensing optimized for atrial sensing), can be received to derive first and second processed signals from such different electrical signals, the different electrical signals being received, for example, using different electrode pairs of the sensor arrangement.

[0032] The different processed signals are processed in different processing paths of the processing circuitry in one embodiment, such that the processing circuitry comprises a first processing channel for processing a first processed signal, the first processed signal relating to, for example, a near-field (particularly ventricular) sensed signal that may be of such strength that the first processing channel may exhibit a fairly low gain depending on the placement of the implantable medical device, for example, within a ventricle of a patient's heart.

[0033] The processing circuitry further includes a second processing channel for processing a second processed signal, which may be related to, for example, a far-field atrial sensed signal, the amplitude of which may be reduced when an implantable medical device is placed within a ventricle due to the distance between the implant location and the source of the signal. To enable reliable processing of the second processed signal, the second processing channel exhibits a gain higher than that of the first processing channel to enable proper analysis of features related to atrial activity within the received signal.

[0034] For example, when placing an implantable medical device in a ventricle, it may be difficult to discern atrial events in a standard ventricular sensed signal (e.g., obtained by a standard ventricular QRS sensing channel) because atrial activity occurs in the far-field and the P waves resulting from the atrial activity may exhibit small amplitudes relative to the QRS and T waves. For this reason, signal portions associated with far-field activity may be processed separately from signals associated with near-field activity in the second processing channel, such that far-field events may be detected in the second processing channel with greater reliability and improved timing accuracy.

[0035] In one aspect, the implantable medical device will be placed in whole or in part within the right or left ventricle.

[0036] In one aspect, the sensor arrangement is formed by an electrode arrangement including a first electrode disposed near a distal end of the body, the first electrode being disposed on cardiac tissue when the implantable medical device is implanted, the first electrode being in contact with the cardiac tissue in a location effective to, for example, inject a stimulation signal into the cardiac tissue to cause a pacing action, particularly ventricular pacing.

[0037] In one embodiment, the electrode configuration includes a second electrode formed by an electrode ring extending circumferentially around the body. Alternatively, the second electrode may be formed by, for example, a patch or another conductive area formed on the body. The second electrode is located at a distance from the distal end of the body and thus from the first electrode located at the distal end.

[0038] In one embodiment, the processing circuitry is configured to process a first signal sensed between a first electrode and a second electrode as the first processed signal. Such a first signal may be represented as a near-field vector received between a pair of electrodes consisting of the first electrode and the second electrode. Because the first electrode and the second electrode may be located at a fairly close distance to each other in one embodiment, such an electrode pair is primarily suitable for receiving signals in close proximity to an implantable medical device, i.e., within a near-field region within a cardiac chamber when the implantable medical device is implanted within a cardiac chamber. The sensed signal received between the first electrode and the second electrode is provided to a first processing channel for processing, for example, to detect near-field (e.g., ventricular) events in the signal.

[0039] In one embodiment, the body comprises a remote location remote from the tip (e.g., at a distal end of a leadless pacemaker device housing), and the electrode configuration comprises a third electrode disposed on the body at the remote location operatively connected to the processing circuitry to enable the processing circuitry to receive and process signals received via the third electrode.

[0040] In one aspect, the processing circuitry is configured to process, as the second processed signal, a second signal sensed between the first electrode and the third electrode. Such a second signal vector arising between the first electrode and the third electrode may be referred to as a far-field vector, with the first electrode and the third electrode exhibiting a greater distance from each other than the first and second electrodes. The second signal may be processed to detect an event in the far-field, i.e., an atrial contraction, so that the second signal can capture intrinsic atrial activity prior to injection of a pacing stimulus when the implantable medical device is placed within a ventricle.

[0041] A second signal sensed between the first and third electrodes can be used to sense intrinsic atrial contractions to effect atrial-ventricular synchronization by injecting a timely stimulus following an atrial contraction at the implanted site of the pacemaker device in the ventricle. The second signal is provided to a second processing channel for processing the signal and detecting atrial events therefrom for the purpose of providing a pacing action based on the detected atrial events, thereby enabling ventricular pacing with atrioventricular (AV) synchronization.

[0042] In one embodiment, the second processing channel includes a processing stage for distinguishing wave portions from other wave portions in the second processed signal. The processing stage may be configured to apply at least one of band-pass filtering, a blanking window to exclude portions of the second signal from further processing, moving average filtering, and rectification to the second processed signal. The processing stage isolates and / or emphasizes wave portions in the signal to be processed that may indicate, for example, atrial events. When an implantable medical device is placed within a ventricle of a patient's heart, signal portions associated with far-field atrial activity may have a much smaller amplitude than signal portions associated with near-field ventricular activity. In this manner, the processing serves to distinguish between different signal portions to identify signal portions that may include signals associated with far-field atrial activity.

[0043] For example, to isolate P waves in an intracardiac electrogram, bandpass filtering may be applied to distinguish wave portions associated with P waves from wave portions specifically associated with QRS and T waves resulting from ventricular activity. Alternatively or additionally, blanking techniques may be applied to nullify certain portions of the second processed signal, i.e., portions containing signals resulting from events other than far-field atrial activity. In this case, a blanking window serves to mask signal portions that are not important to far-field activity but may interfere with the detection of far-field activity. The blanking window thus excludes portions of the signal not associated with far-field atrial activity from processing, limiting processing to signal portions likely associated with far-field activity. Alternatively or additionally, other methods may be applied, such as moving average filtering, finite differences, or signal rectification. A moving average filter may be used herein to smooth the processed signal. Rectification may facilitate comparison of the processed signal to a (single) threshold to identify when the signal magnitude exceeds a predefined threshold.

[0044] In one embodiment, the first processing channel includes a first detection stage for detecting at least one near-field event in the first signal. Herein, the processing stage of the second processing channel may be configured to determine at least one limit value of a blanking window for excluding 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 processes the signal with a lower gain to detect near-field events, i.e., events resulting from activity in close proximity to an implanted implantable medical device, e.g., in the ventricle in which the implantable medical device is implanted. Since near-field events will also be included in the second processed signal, it is advantageous to null signal portions associated with near-field activity, i.e., the QRS complex and T wave when the implantable medical device is located in the ventricle. Detected near-field events may be taken into account for purposes of properly positioning the blanking window, e.g., to determine the standard timing between atrial and ventricular events. From the detected near-field event, it can be determined within what time range after the far-field event the near-field event will typically occur so that a blanking window defined by a start time and a stop time can be appropriately set to null out portions of the second processed signal that are associated with near-field ventricular events.

[0045] For example, to conserve power in the second high-gain processing channel, the second processing channel may be at least partially turned off during the blanking window. The second processing channel may, for example, comprise an amplifier stage for amplifying the second processed signal, and the amplifier stage may be turned off during the blanking window so that no power is consumed by amplification during the time interval of the blanking window.

[0046] Detection of far-field atrial events occurs in a detection window outside the blanking window. This detection window may begin (immediately) at the end of the preceding blanking window or may end at the start of the next blanking window. However, it is also contemplated that the detection window may begin, for example, some time delay after the end of the preceding blanking window. Between the end of the blanking window and the start of the detection window, the second processing channel may be fully functional and may process the associated second processed signal, but in this case, no far-field (atrial) event detection occurs until the start of the detection window.

[0047] In one embodiment, the second processing channel comprises a second detection stage for detecting atrial events in the second processed signal, which may be logically located after the processing stage of the second processing channel such that the second detection stage receives the processed signal from the processing stage of the second processing channel, where the second detection stage serves to identify far-field atrial events in the second processed signal to output information related to the timing of the detected atrial events.

[0048] The second detection stage of the second processing channel may be particularly 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 may be concluded that a far-field atrial event is present. This processing may be performed on a rectified signal, which allows for the application of a single threshold that can be compared to the rectified signal. However, it is also possible to identify a far-field atrial event in an unrectified signal by applying, for example, two thresholds, i.e., a positive threshold and a negative threshold, in which case a far-field atrial event is identified if the positive signal portion exceeds the positive threshold and / or the negative signal portion (magnitude) exceeds the negative threshold.

[0049] The various features and advantages of the present invention may be more readily understood by reference to the following detailed description and the examples illustrated in the drawings. [Brief explanation of the drawings]

[0050] [Figure 1] Schematic representation of a human heart with an implantable medical device in the form of a leadless pacemaker device implanted within it. [Figure 2] 1 is a schematic diagram of an implantable medical device. [Figure 3] FIG. 1 is a schematic diagram of an implantable medical device showing signal vectors between different electrodes of the implantable medical device. [Figure 4] FIG. 1 is a schematic diagram of processing circuitry for an embodiment of an implantable medical device. [Figure 5A] FIG. 2 illustrates a first processed signal in the form of an intracardiac electrocardiogram (IEGM) processed by a first processing channel of the processing circuitry. [Figure 5B] FIG. 10 illustrates a second processed signal processed by a second processing channel of the processing circuitry. [Figure 6] 1 is a schematic diagram of a human heart with an implantable medical device in the form of a cardiac stimulation device with a lead implanted in the right ventricle. DETAILED DESCRIPTION OF THE INVENTION

[0051] Next, embodiments of the present invention will be described in detail with reference to the drawings, in which like reference numerals indicate like structural elements.

[0052] It should be noted that these examples do not limit the present invention, but merely represent illustrative examples.

[0053] In the present invention it is proposed to provide an implantable medical device that provides an intracardiac function, in particular ventricular pacing, in particular so-called VDD pacing.

[0054] 1 shows a schematic diagram of a human heart, comprising the right atrium (RA), right ventricle (RV), left atrium (LA), and left ventricle (LV), with the so-called sinoatrial node (SAN) located in the wall of the right atrium (RA), which is formed by a group of cells capable of spontaneously generating electrical impulses that travel through the cardiac electrical conduction system and thereby cause the heart to contract to pump blood through the heart. The atrioventricular node (AVN), which regulates electrical conduction between the atria and ventricles, is located near the opening of the coronary sinus in the dorsal-inferior region of the interatrial septum. Extending from the atrioventricular node (AVN) is the so-called HIS bundle (H), which is composed exclusively of electrically conducting cardiac muscle cells and forms part of the electrical conduction system that transmits electrical impulses from the atrioventricular node (AVN) around the right ventricle (RV) via the so-called right bundle branch (RBB) and around the left ventricle (LV) via the so-called left bundle branch (LBB).

[0055] When there is a block in the atrioventricular node (AVN), the intrinsic electrical conduction system of the heart (H) may be disrupted, which may result in insufficient stimulation of ventricular activity, i.e., insufficient or irregular contractions of the right ventricle (RV) and / or left ventricle (LV). In such cases, pacing of ventricular activity with a pacemaker device may be required, which stimulates ventricular activity by injecting stimulation energy into intracardiac tissue, particularly the myocardium (M).

[0056] In one embodiment, as shown schematically in FIGURE 1 , an implantable medical device 1 is provided in the form of a leadless cardiac pacemaker device for ventricular pacing having a body 10 formed by a leadless pacemaker device housing.

[0057] In another embodiment, as shown in FIG. 6, the implantable medical device 1 may be a stimulation device having a generator 18 and at least one lead that forms the body 10 of the implantable medical device 1 and extends from the generator 18 into the patient's heart via a vein.

[0058] Although typical implantable medical devices are designed to sense ventricular activity by receiving electrical signals from the ventricle (RV) in which they are placed, it may be desirable to provide pacing that achieves atrioventricular (AV) synchrony by providing pacing in the ventricle synchronized with intrinsic atrial activity. In such a pacing mode, also referred to as a VDD pacing mode, it is necessary to sense atrial activity and identify such atrial events as related to atrial contraction in order to pace the ventricle based on atrial events.

[0059] 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 a VDD pacing mode, comprises a housing 10 enclosing electrical and electronic components for operating the implantable medical device 1. In particular, processing circuitry 15 is enclosed within the housing 10, which also includes a communication interface for communicating with an external device, e.g., a programmer wand. Further electrical and electronic components are enclosed within the housing 10, such as an energy storage unit in the form of a battery. The housing 10 provides encapsulation of the components contained therein, and the housing 10 has the shape of, e.g., a cylindrical shaft, e.g., having a length of several centimeters.

[0060] The implantable medical device 1 is intended to be implanted directly onto the intracardiac tissue M. To this end, the implantable medical device 1 comprises in the region of the distal end 100 a fixation device 14, e.g. in the form of a nitinol wire, for engaging the intracardiac tissue M in order to hold the implantable medical device 1 fixedly on the tissue in the implanted state.

[0061] The implantable medical device 1 in the embodiment of Figures 2 and 3 does not comprise a lead, but receives signals related to cardiac activity by means of an electrode arrangement disposed on the housing 10, and also emits stimulation signals by means of such an electrode arrangement. In the embodiment of Figures 2 and 3, the implantable medical device 1 comprises different electrodes 11, 12, 13 that constitute the electrode arrangement and serve to emit pacing signals to the intracardiac tissue M for providing pacing, as well as to sense electrical signals indicative of cardiac activity, in particular atrial and ventricular contractions.

[0062] The first electrode 11 is designated herein as a pacing electrode. The first electrode 11 is located at the distal end 100 of the housing 10 and is configured to engage cardiac tissue M.

[0063] The second electrode 12 is represented here 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 for generating a pacing signal directed toward the intracardiac tissue M.

[0064] Furthermore, the second electrode 12 serves as a sensing electrode for sensing signals particularly related to ventricular contractions, and a signal vector V is generated between the second electrode 12 and the first electrode 11, and this signal vector V is represented as a near-field vector.

[0065] The second electrode 12 is disposed at a distance from the first electrode 11 and has, for example, the shape of a ring extending circumferentially around the housing 10. The second electrode 12 is disposed, for example, at a distance of about 1 cm from the tip 100 of the housing 10 where the first electrode 11 is disposed.

[0066] 2 and 3, the implantable medical device 1 further comprises a third electrode 13 located at the distal end 101 of the housing 10, which serves as a sensing electrode for sensing signals indicative of cardiac activity in the far field. In particular, a signal vector A arises between the third electrode 13 and the first electrode 11, and the signal vector A includes a signal indicative of, for example, an atrial contraction and is referred to as a far-field vector.

[0067] The electrodes 11, 12, 13 are operatively connected to processing circuitry 15, which is configured to cause the first electrode 11 and the second electrode 12 to emit pacing signals for stimulating the ventricles of the heart. The processing circuitry 15 is also configured to process signals received via the electrodes 11, 12, 13 to sense cardiac activity, particularly atrial and ventricular contractions.

[0068] If the implantable medical device 1 has the form of a stimulation device comprising a generator 18 and leads extending from the generator 18, as shown in the embodiment of Figure 6, a similar electrode arrangement comprising, for example, three electrodes 11, 12, 13 may be disposed on a lead implanted in and extending to the right ventricle RV, as shown in Figure 6, in which case the above also applies to embodiments of the implantable medical device 1 having leads extending into the patient's heart. In this case, the processing circuitry 15 may be part of the generator 18 and may be operatively connected to the electrode arrangement disposed on the lead.

[0069] To provide pacing in the ventricle in which the implantable medical device 1 is placed, particularly to enable pacing in VDD mode, sensing of atrial activity is necessary to enable detection of atrial sense markers for timing pacing in the ventricle to achieve atrioventricular (AV) synchrony. Thus, far-field signals from the right ventricle RV (see FIGS. 1 and 6) in particular will be sensed to enable synchronous pacing in the right ventricle RV by the implantable medical device 1 implanted on endocardial tissue M within the right ventricle RV.

[0070] 4, the processing circuitry 15, in one embodiment, comprises two processing channels 16, 17 for processing different processed signals associated with ventricular and atrial activity. As used herein, an intracardiac electrocardiogram (IEGM) typically includes signal portions associated with ventricular activity (particularly QRS complexes) and atrial activity (particularly P waves), as well as signal portions associated with atrial activity but arising from far-field sources and therefore much less prominent and having much smaller amplitudes than signal portions associated with ventricular activity in the near-field, i.e., in close proximity to the implanted implantable 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 serving to process a first processed signal to identify ventricular events Vx with a fairly low gain G1, and the second processing channel 17 configured to process a second processed signal to identify atrial events with a significantly higher gain G2.

[0071] In particular, the first processing channel 16 is connected to the electrode configuration consisting of the electrodes 11, 12, and 13, and the first processing channel 16 is particularly configured to sense and process signals (near-field vector V in FIGS. 2 and 3) received via the electrodes 11, 12. The first processing channel 16 comprises a first amplification stage 161 having a gain G1, and is followed by a detection stage 162 configured to identify a ventricular sensing marker Vx from the first processed signal processed in the first processing channel 16.

[0072] The second processing channel 17 is similarly connected to the electrode arrangement consisting of electrodes 11, 12, 13, and is specifically configured to process signals sensed via the far-field vector A between the electrodes 11, 13 located at the distal end 100 and distal end 101 of the housing 10, as shown in Figures 2 and 3. The second processing channel 17 comprises a second amplification stage 171 having a second gain G2, followed by a processing stage 172 and a second detection stage 173.

[0073] The processing stage 172 serves to pre-process the amplified second processed signal. The detection stage 173 then serves to evaluate and analyze the processed signal to identify atrial events within the second processed signal, and the second processing channel 17 then outputs an atrial sense marker As indicative of an atrial event detected in the processed signal.

[0074] Processing circuitry 15 further includes a timing stage 174 that uses timing information received from first processing channel 16 and second processing channel 17 to provide pacing timing, particularly VDD timing, for achieving atrial-ventricular synchronous pacing.

[0075] In order 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 related to atrial events, but it is necessary to distinguish such signal portions related to atrial events from other signal portions, in particular signal portions related to ventricular events Vx in the near field and therefore much stronger than signal portions originating from atrial events in the far field.

[0076] For example, bandpass filtering, windowing (e.g., partial blanking), smoothing by moving average filtering, and rectification may be performed within processing stage 172. First- or second-order differencing may be applied to remove non-zero baselines while enhancing P-wave defections.

[0077] 5A and 5B show examples of signals S1, S2 processed by different processing channels 16, 17, with the upper Fig. 5A showing signal S1 processed by the first processing channel 16 and the lower Fig. 5B showing signal S2 processed by the second processing channel 17. As a result of the processing, ventricular events Vx and atrial events As are identified and corresponding markers are output.

[0078] As can be seen from FIG. 5B, sensing of the atrial event As requires the use of a blanking window T to blank out portions of the signal S2 that may be related to ventricular activity. blank A windowing scheme is used, which specifically employs

[0079] In particular, detection of a ventricular event Vx in the first processing channel 16 allows the timing between an atrial event As and a ventricular event Vx to be determined. blank The start and end points of A can be set so that signal portions not associated with atrial activity are excluded from processing. In this way, strong ventricular signals can be suppressed so that signal portions associated with ventricular activity cannot interfere with the detection of atrial events A.

[0080] Blanking window T blank During this time, the second processing channel 17 may be turned off. In particular, the amplifier stage 171 of the second processing channel 17 may be turned off to save power.

[0081] In general, the detection of atrial events As occurs within a blanking window T blank Here, the detection window T for detecting the atrial event As is sense is the leading blanking window T blank Alternatively, the detection window T sense is the time period between the preceding blanking window T blank , in which case the signal processing in the second processing channel 17 may have a delay relative to the end of the preceding blanking window T blank At the end of the atrial pulse, the detection of an atrial event, As, begins, but only after a certain delay.

[0082] Generally, as shown in FIG. 5B, a detection window T senseIf signal S2 crosses a sense threshold ST at , an atrial event As is assumed to be present. This comparison may be based on a rectification of sense signal S2. Alternatively, a positive or negative sense threshold ST may be used, which may have the same value or may be different values.

[0083] As can be seen from Figure 5B, there may be signal portions in the sensed signal S2 that are due to near-field activity, particularly ventricular activity, which may result from, for example, the onset of the QRS complex. Thus, as shown in Figure 5B, it may occur that for the first atrial event As, the threshold crossing is due to near-field effects, and therefore, this threshold crossing may not be due to atrial activity. In that case, the atrial event As may be falsely detected.

[0084] For this reason, it is proposed herein to evaluate an atrial event As based on its timing relative to a subsequent ventricular event Vx.

[0085] In particular, a scheme is proposed in which a possible atrial event As is first determined. Then, a subsequent ventricular event Vx is determined. Based on these two events, an atrial-ventricular interval AVI is determined. The atrial-ventricular interval AVI is compared with a exclusion interval PVI, also referred to as a pre-Vx interval. If the atrial-ventricular interval AVI is found to be smaller than the exclusion interval PVI, the atrial event As is disqualified and deemed invalid, which is the case for the first atrial event As in FIG. 5B. Otherwise, if the atrial-ventricular interval AVI is greater than the exclusion interval PVI, which is the case for the second atrial event As shown in FIG. 5B, the atrial event As is deemed valid.

[0086] Thus, if a detected atrial event As is found to be too close to a subsequent ventricular event Vx, the atrial event As is disqualified and not used for further processing.

[0087] If the atrial event As is determined to be valid, which is the case for the second atrial event As in FIG. 5B, the atrial event As is used for further processing, particularly to update the sensing threshold ST and to achieve atrial-ventricular synchronous pacing.

[0088] In particular, an atrial event As is interpreted as the time when signal S2 crosses sensing threshold ST. A peak detection window PDW is initiated at the time of the atrial event As, and a peak amplitude PA is determined as the maximum signal value within the peak detection window PDW based on the data recorded during that peak detection window PDW. This is shown for the second atrial event As on the right side of Figure 5B.

[0089] Additionally, if the atrial event As is found to be valid, an atrial-ventricular delay AVD may be programmed as an internal delay from the sensing of the atrial event to the initiation of the pace.

[0090] If the peak detection window PDW overlaps with the exclusion interval PVI, the overlapping portion of the peak detection window PDW is excluded from processing such that data recorded within the overlapping portion is discarded and not used to determine the peak amplitude PA (the overlapping portion may, for example, be identified subsequent to determining a subsequent ventricular event Vx, and the peak amplitude PA may, in some cases, only be determined after the detection of the subsequent ventricular event Vx).

[0091] The peak amplitude PA is used to update the sensing threshold ST. In particular, processing circuitry 15 uses the average threshold reference value and the percentage ratio to calculate the following equation: ST = PC ATR(t) where ST is the current sensing threshold, PC is a percentage ratio, and ATR(t) is the average threshold reference value for the current cycle t. The percentage ratio may be in a range between 0% and 100%, for example.

[0092] The average threshold reference value is based on the peak amplitude PA, using the following formula: ATR(t)=W·PA(t-1)+(1-W)·ATR(t-1) where W denotes an update weight that determines how much to change the average threshold reference value based on the preceding peak amplitude, PA(t-1) is the peak amplitude determined for the preceding cycle t-1, and ATR(t-1) is the preceding average threshold reference value. In the actual cycle t, the average threshold reference value is determined based on the previously determined valid peak amplitude and the preceding average threshold reference value for cycle t-1. Therefore, the average threshold reference value is updated and newly calculated for each cycle, and as a result, the average threshold reference value is dynamically adjusted for each cycle.

[0093] If the atrial event As is found to be invalid because the atrioventricular interval AVI is less than the exclusion interval PVI, the peak amplitude PA is not determined and the sensing threshold ST is not updated. In this way, false detection of an atrial event As that would result in a false elevation of the sensing threshold ST and subsequent loss of capture of atrial activity is avoided.

[0094] The atrial sense marker As output by the second processing channel 17 may be used to achieve ventricular synchronous pacing. To this end, following the detected atrial sense marker As, it may be detected whether an intrinsic ventricular sense marker Vx (output by the first processing channel 16) occurs within a predefined time delay window after the atrial sense marker As, in which case no stimulation is required. If the ventricular sense marker Vx is not detected, a stimulation pulse may be emitted to cause synchronous pacing in the ventricles.

[0095] Conversely, asynchronous pacing can also be performed.

[0096] Utilizing far-field electrical signals received by an implantable medical device can provide superior detection of far-field events, particularly atrial events when the implantable medical device is implanted within a ventricle. Tracking far-field events through the use and evaluation of electrical signals can allow for improved consistency and reliability, particularly with respect to external factors such as posture and patient activity. [Explanation of symbols]

[0097] 1 Implantable medical devices 10 Main body (housing) 100 Tip 101 Distal end 11 First electrode (pacing electrode) 12 Second electrode (pacing ring) 13 Third electrode 14 Fixed Devices 15 Processing circuit configuration 16 processing channels 161 Amplification stage 162 Detection stage 17 processing channels 171 Amplification stage 172 Processing Stage 173 Detection stage 174 Timing Stage 18 Generator A signal vector (atrial / far field vector) As atrial event (atrial sense marker) AVD Atrial-Ventricular Delay AVI Atrial-ventricular interval AVN Atrioventricular Node G1, G2 gain H HIS bunch LA Left atrium LBB left leg LV left ventricle M: cardiac tissue (myocardium) P signal vector (pacing vector) PA Peak Amplitude PDW Peak detection window PVI exclusion interval (pre-Vx interval) RA right atrium RBB right leg RV right ventricle S1, S2 signal SAN sinoatrial node ST sensing threshold T blank Blanking Window T sense Sensing window V signal vector (ventricular / near-field vector) Vx Ventricular event (ventricular sensing marker)

Claims

1. A leadless pacemaker (1) configured to provide an intracardiac function, comprising: a body (10) formed by the leadless pacemaker housing; a sensor arrangement implemented as an electrode arrangement disposed on the body (10) and configured to receive an electrical signal as a cardiac sensing signal; a processing circuitry (15) operatively connected to the sensor arrangement for processing cardiac sensed signals received using the sensor arrangement; to detect signal deflections that may indicate atrial events (As) caused by atrial activity to obtain atrial detection; detecting a signal deflection indicative of a ventricular event (Vx) caused by ventricular activity subsequent to said atrial event (As); determining an atrial-ventricular interval (AVI) representing the time between the atrial detection and the ventricular event (Vx); and a processing circuitry (15) configured to process the atrial sensing signal to identify whether the atrial sensing signal is valid or invalid based on the atrial-ventricular interval (AVI); Equipped with the processing circuitry (15) is configured to compare the atrial-ventricular interval (AVI) with a pre-exclusion interval (PVI) and to identify the atrial detection as valid if the atrial-ventricular interval (AVI) is longer than the pre-exclusion interval (PVI) and as invalid if the atrial-ventricular interval (AVI) is shorter than the pre-exclusion interval (PVI); the processing circuitry (15) comprises a first processing channel (16) having a first gain (G1) for processing a first processed signal derived from cardiac sensed signals received via the sensor arrangement, and a second processing channel (17) having a second gain (G2) for processing a second processed signal derived from cardiac sensed signals received via the sensor arrangement, the second gain (G2) being greater than the first gain (G1); the processing circuitry (15) is configured to process the first processed signal to detect ventricular activity and to process the second processed signal to detect atrial activity; the processing stage further configured to apply a blanking window to the second processed signal to exclude a portion of the second processed signal from further processing, the blanking window being positioned by a start time and a stop time based on detected near-field events in the first processing channel.

2. 10. The leadless pacemaker of claim 1, wherein the processing circuitry is configured to determine a peak amplitude (PA) associated with the atrial sense when the atrial sense is identified as valid.

3. 3. The leadless pacemaker of claim 2, wherein the processing circuitry is configured to determine the peak amplitude (PA) associated with the atrial detection within a peak detection window (PDW) following the atrial detection.

4. 4. The leadless pacemaker of claim 3, wherein the processing circuitry is configured to determine whether a portion of the peak detection window (PDW) overlaps with the exclusion interval (PVI) when determining the peak amplitude (PA) and to exclude data received within the portion.

5. 5. The leadless pacemaker of any one of claims 2 to 4, wherein the processing circuitry is configured to use the peak amplitude (PA) to update a sensing threshold (ST) for detecting a subsequent atrial event (As).

6. The processing circuitry (15) uses the average threshold reference value to calculate the following equation: ST(t)=PC・ATR(t) 6. The leadless pacemaker of claim 5 configured to update the sensing threshold (ST) based on:

7. The current average threshold reference value is calculated by the following formula: ATR(t)=W・PA(t-1)+(1-W)・ATR(t-1) where W denotes an update weight, PA(t-1) is the peak amplitude determined for a preceding cycle t-1, and ATR(t-1) is a preceding average threshold reference value.

8. 8. The leadless pacemaker of any one of claims 1 to 7, wherein the processing circuitry is configured to count cardiac cycles in which the atrial sensing occurs as missed cycles if the atrial sensing is identified as invalid.

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