Implantable medical device enabling a stepwise reduction of the atrioventricular interval

Abstract

The present invention relates to an implantable medical device (1) for stimulating a human or animal heart. During operation, the implantable medical device (1) executes a method comprising the following steps: a) determining a temporal difference between i) a current atrioventricular interval (AV) having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval (AV) having a second length that is shorter than the first length, wherein the target atrioventricular interval (AV) is to be applied in a subsequent cardiac cycle; and b) stepwise reducing a length of the atrioventricular interval (AV) in at least two cardiac cycles following the first cardiac cycle from the first length to the second length, wherein the length of the atrioventricular interval (AV) is reduced in one step of a plurality of reduction steps by at most 50 % of the temporal difference.

Description

[0001] Applicant: BIOTRONIK SE & Co. KG

[0002] Date: 09.03.2026

[0003] Our Reference: 22.271P-WO

[0004] Implantable medical device enabling a stepwise reduction of the atrioventricular interval

[0005] The present invention relates to an implantable medical device according to the preamble of claim 1 and to a method for operating an implantable medical device according to the preamble of claim 9.

[0006] Implantable medical devices for stimulating a human or animal heart, such as pacemakers, have been known for a long time. They can perform different functions. Different stimulation programs can be carried out by an appropriate pacemaker to restore the treated heart to a normal state.

[0007] To give an example, pacemakers can be used for cardiac resynchronization therapy (CRT) in which they apply stimulation pulses to a de-synchronized heart in order to resynchronize the heart again.

[0008] In pacemaker modes with programmed biventricular or left ventricular pacing a situation can occur (e. g., by an atrial or a ventricular extrasystole or by a change of timing parameters of the pacing program) that leads to an inhibition of the delivery of a left ventricular pace. If due to the missing pace an occurring left ventricular depolarization (i.e., a left ventricular sense event, LVs) retriggers a protective interval, then the next left ventricular pace delivery can be inhibited again and so on. A so-called lock-in situation is generated. This phenomenon is also described, e.g., by Barold and Kucher (Barold, S. Serge, and Andreas Kucher. “Interruption of cardiac resynchronization therapy by atrial premature complexes.” Journal of Electrocardiology 51.2 (2018): 247-251).Prior art pacemakers employing CRT pursue different strategies to avoid such a lock-in situation. Some of the prior art pacemakers do not enable the retriggering of the protective interval by left ventricular sense events. However, this reduces the patient comfort provided by such CRT devices irrespective of the cardiac rhythm of the patient. If, e.g., the parameter “LV T-wave protection” (that prevents a left ventricular stimulation during the T wave which could cause frequently experienced palpitations) is turned off permanently there is an increased risk of left ventricular pacing into the vulnerable phase of the left ventricle. This can have severe side effects for the patient.

[0009] Barold et al. (Barold, S. Serge, et al. “Desynchronization in a cardiac resynchronization device induced by a pacemaker-mediated tachycardia algorithm.” Indian Pacing and Electrophysiology Journal 18.3 (2018): 108-111) describes the occurrence of desynchronization in a patient with a cardiac resynchronization device programmed with an active pacemaker-mediated tachycardia (PMT) algorithm based on atrioventricular (AV) delay modification. The desynchronization was precipitated by sinus tachycardia and the abrupt return of the prevailing AV delay that followed the periodic prolongation of the AV delay mandated by activity of the PMT algorithm. The authors concluded that a prevention of desynchronization in this setting would require programming a right ventricular upper rate interval longer than the sum of the programmed ventriculoarterial interval and the AV delay.

[0010] It is an object of the present invention to provide a device for cardiac resynchronization therapy that enables safe cardiac resynchronization therapy and employs preventive measures against a desynchronization induced, e.g., by an active PMT algorithm.

[0011] This object is achieved with an implantable medical device for stimulating a human or animal heart according to claim 1. Such an implantable medical device comprises a processor, a memory unit, a stimulation unit, a detection unit, and at least a first electrode and a second electrode connected with the stimulation unit and the detection unit. The stimulation unit serves for stimulating a human or animal heart. The detection unit serves for detecting an electric signal of the same heart, i.e., a cardiac electric signal. The first electrode is configured to sense atrial electric signals and / or to deliver atrial stimulation

[0012] 22.271P-WO / 09.03.2026pulses. The second electrode is configured to sense ventricular electric signals and to deliver ventricular stimulation pulses.

[0013] According to an aspect of the present invention, the memory unit comprises a computer-readable program that causes the processor to perform the steps explained in the following when being executed on the processor.

[0014] In a first step, a temporal difference between i) a current atrioventricular interval having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval having a second length that is shorter than the first length is determined. In this context, the target atrioventricular interval is to be applied in a subsequent cardiac cycle.

[0015] The atrioventricular interval denotes a time interval between an atrial sense event or an atrial stimulation event on the one hand and a succeeding ventricular stimulation event on the other hand.

[0016] Afterwards, a stepwise (iterative) reduction of a length of the atrioventricular interval from the first length to the second length is carried out. This is done during at least two cardiac cycles directly or indirectly following the first cardiac cycle. The at least two cardiac cycles can be directly adjacent cycles or can be interrupted by one or more cardiac cycles during which the length of the atrioventricular interval is not reduced. In any case, the length of the atrioventricular interval is reduced in one step of a plurality (two or more) of reduction steps by at most 50 % of the temporal difference.

[0017] By such a stepwise reduction of the atrioventricular interval a cardiac desynchronization due to a lock-in situation during which no proper cardiac resynchronization therapy can be applied is effectively avoided. This increases the general CRT success. At the same time, the permanent LV T-wave protection remains fully active.

[0018] In an embodiment, the length of the atrioventricular interval is reduced in one step of a plurality (two or more) of reduction steps by 10 % to 50 %, 20 % to 40 %, 20 % or 30 % or 25 % of the temporal difference.

[0019] 22.271P-WO / 09.03.2026Prior art CRT devices currently record intracardiac electrogram (IEGM) episodes of the type “end of CRT pacing”. In particular if a pacemaker-mediated tachycardia (PMT) algorithm is applied more often than usual, a plurality of such IEGM episodes (partly even everyday) can be generated that are entered into a log file or that are sent to a remote service center. Expressed in other words, these IEGM episodes result from an undesired temporal interruption of CRT due to the lacking possibility of preventing a desynchronization of the heartbeat. It would generally be desirable to reduce the number of such IEGM episodes to a minimum to clearly identify critical IEGM episodes or to not store or present rather uncritical IEGM episodes representing a (short) interruption of CRT. By preventing a cardiac desynchronization due to the stepwise reduction of the atrioventricular interval (i.e., of a specific timing parameter of the implantable medical device), the number of such IEGM episodes can be significantly reduced. This reduces the amount of physiologically irrelevant or less relevant IEGM episodes and allows an easy identification of relevant IEGM episodes that require separate or additional therapy.

[0020] In an embodiment, the current atrioventricular interval has its first length (which is longer than a typical length of previous atrioventricular intervals) due to the application of an algorithm aiming at identifying a pacemaker-mediated tachycardia (PMT). In an embodiment, the current atrioventricular interval has its first length due to operating the CRT device in a sense-amplitude-measurement and AV-conduction-test mode with deactivated left ventricular triggering (LV triggering “off’). In an embodiment, the target atrioventricular interval is chosen to be shorter than the current atrioventricular interval due to changing the operational mode of the implantable medical device, in particular due to changing from PMT-identification mode or from sense-amplitude-measurement and AV-conduction-test mode with enabled left ventricular triggering (switching LV triggering from “off’ to “on”).

[0021] In an embodiment, the temporal difference lies in a range of from 10 ms to 400 ms, in particular 10 ms to 350 ms, in particular 10 ms to 250 ms, in particular from 20 ms to 240 ms, in particular from 30 ms to 230 ms, in particular from 40 ms to 220 ms, in particular from 50 ms to 210 ms, in particular from 60 ms to 200 ms, in particular from 70 ms to 190 ms, in particular from 80 ms to 180 ms, in particular from 90 ms to 170 ms, in particular

[0022] 22.271P-WO / 09.03.2026from 100 ms to 160 ms, in particular from 110 ms to 150 ms, in particular from 120 ms to 140 ms, in particular from 125 ms to 130 ms.

[0023] In an embodiment, the computer-readable program causes the processor to reduce the atrioventricular interval in a single step of the plurality of reduction steps by 5 ms to 60 ms, in particular 5 ms to 55 ms, in particular 5 ms to 50 ms, in particular by 10 ms to 45 ms, in particular by 15 ms to 40 ms, in particular by 20 ms to 35 ms, in particular by 25 ms to 30 ms. It turned out that a reduction by such a value efficiently prevents the CRT device from entering a lock-in situation during which no proper resynchronization therapy can be applied anymore to a patient in need thereof.

[0024] Generally, it is possible to reduce the atrioventricular interval in the individual steps of the plurality of reduction steps to a different extent (this corresponds to an embodiment of the CRT device). To give an example, a stronger reduction is applied first, wherein afterwards a less pronounced reduction is applied. However, such an unequal distribution of the reduction may lead to individual cardiac cycles during which the reduction of the atrioventricular interval is too high to securely avoid a lock-in situation. Therefore, in an embodiment, the computer-readable program causes the processor to reduce the atrioventricular interval in each step of the plurality of reduction steps by the same length. Then, the reduction of the atrioventricular interval is uniformly distributed over time.

[0025] In an embodiment, the plurality of reduction steps comprises 2 to 10, in particular 3 to 9, in particular 4 to 8, in particular 5 to 7, in particular 6 reduction steps.

[0026] In an embodiment, the computer-readable program causes the processor to keep a predeterminable protective interval constant. This predeterminable protective interval serves for preventing a left ventricular pacing into a vulnerable phase of the left ventricle. Expressed in other words, the predeterminable protective interval allows the delivery of a left ventricular pacing pulse only if the left ventricle is in a physiologic state in which a contraction would occur under natural conditions. E.g., the predeterminable protective interval prevents a left ventricular pacing that could cause more frequently experienced palpitations. The predeterminable protective interval is initiated by one of three possible

[0027] 22.271P-WO / 09.03.2026events. The first event is a preceding left ventricular pacing pulse delivered with the second electrode. The second event is a preceding left ventricular depolarization detected with the second electrode. The third event is a preceding logic event that is triggered instead of a preceding left ventricular pacing pulse at the same time at which the preceding left ventricular pacing pulse was scheduled to be delivered. Such a logic event can also be denoted as phantom pace or phantom pacing pulse. It replaces a real pacing pulse in case that the conditions for delivering the real pacing pulse are not met (e.g., because of a nonterminated predeterminable protective interval). In this context, “preceding” refers to an event that directly or indirectly precedes the left ventricular pacing pulse that was scheduled to be delivered (but being subject to the conditions to be met). By keeping the predeterminable protective interval constant while stepwise reducing the atrioventricular interval, a particular appropriate prevention of cardiac desynchronization can be achieved.

[0028] In an embodiment, the predeterminable protective interval has a duration lying in a range of from 275 ms to 700 ms, in particular from 300 ms to 675 ms, in particular from 325 ms to 675 ms, in particular from 350 ms to 650 ms, in particular from 375 ms to 625 ms, in particular from 400 ms to 600 ms, in particular from 425 ms to 575 ms, in particular from 450 ms to 550 ms, in particular from 475 ms to 525 ms or from 275 ms to 400 ms. A duration of the predeterminable protective interval of 300 ms corresponds to a cardiac rate of 200 bpm. I.e., as long as the cardiac rate is not higher than 200 bpm, than a predeterminable protective interval of 300 ms will allow the delivery of a left ventricular pacing pulse. A duration of the predeterminable protective interval of 700 ms corresponds to a cardiac rate of approximately 86 bpm. The intermediate variations of the predeterminable protective intervals correspond to intermediate cardiac rates. The cardiac rate in beats per minute can be calculated as l / (duration in milliseconds)*60,000. The regular (non-reduced) predeterminable protective interval typically has a duration at the upper end of the beforementioned interval, e.g., in a range from 500 ms to 700 ms, in particular from 550 ms to 675 ms, in particular from 600 ms to 650 ms.

[0029] In an embodiment, the second electrode is a left ventricular electrode configured to be implanted in the left ventricle for detecting left ventricular electric signals and for delivering left ventricular stimulation pulses.

[0030] 22.271P-WO / 09.03.2026In an embodiment, the implantable medical device comprises a third electrode, the third electrode being a right ventricular electrode configured to be implanted in the right ventricle for detecting right ventricular signals and for delivering right ventricular stimulation pulses.

[0031] In an embodiment, the computer-readable program causes the processor to detect at least one right ventricular depolarization with the third electrode. In an embodiment, the computer-readable program causes the processor to deliver at least one right ventricular pacing pulse with the third electrode.

[0032] In an embodiment, the computer-readable program causes the processor to deliver at least one left ventricular pacing pulse with the second electrode.

[0033] In an embodiment, a condition needs to be met for delivering a left ventricular pacing pulse. According to this condition, a predeterminable interventricular interval (representing the regular delay of contraction of the left ventricle in relation to a contraction of the right ventricle) needs to be expired. This interventricular interval is typically rather short since both the right ventricle and the left ventricle depolarize quite simultaneously.

[0034] In an embodiment, the computer-readable program causes the processor to temporary prolong (extend) the pacing interval (i.e., the distance between two adjacent atrial pacing pulses, two adjacent right ventricular pacing pulses, or two adjacent left ventricular pacing pulses). Such an extension of the pacing interval can assist the stepwise reduction of the atrioventricular interval for achieving a prevention of a desynchronization of the heart and the stable application of a resynchronization therapy.

[0035] In an embodiment, the computer-readable program causes the processor to determine a current cardiac interval from the detected at least one right ventricular depolarization or the delivered at least one right ventricular pacing pulse on the one hand and at least one detected left ventricular depolarization on the other hand. The detected left ventricular depolarization is typically a left ventricular depolarization directly succeeding the detected right ventricular depolarization or delivered right ventricular pacing pulse. Then, an immediate information

[0036] 22.271P-WO / 09.03.2026on the actual cardiac interval is obtained that reflects in real time the current physiological state of the heart to be treated.

[0037] In an embodiment, the implantable medical device comprises a data communication unit that serves for transferring data to a remote monitoring system in a wireless manner. All standard data transmission protocols or specifications are appropriate for such a wireless data communication. Examples of standard data transmission protocols or specifications are the Medical Device Radiocommunications Service (MICS), the Bluetooth Low Energy (BLE) protocol, the Zigbee specification, the long range wide area network (LoRaWAN) protocol, the wireless personal area network (WPAN) specification, the low-power wide-area network (LPWAN) specification, the wireless local area network (WLAN) specification, the Global System for Mobile Communications (GSM) specification, the Long-Term Evolution (LTE) standard, and the fifth-generation technology standard for broadband cellular networks (5G).

[0038] In an aspect, the present invention relates to a method for operating an implantable medical device for stimulating a human or animal heart, in particular an implantable medical device according to the preceding explanations. In this context, the method comprises the steps explained in the following.

[0039] In a first step, a temporal difference between i) a current atrioventricular interval having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval having a second length that is shorter than the first length is determined. In this context, the target atrioventricular interval is to be applied in a subsequent cardiac cycle.

[0040] Afterwards, a stepwise (iterative) reduction of a length of the atrioventricular interval from the first length to the second length is carried out. This is done during at least two cardiac cycles directly or indirectly following the first cardiac cycle. The at least two cardiac cycles can be directly adjacent cycles or can be interrupted by one or more cardiac cycles during which the length of the atrioventricular interval is not reduced. In any case, the length of the atrioventricular interval is reduced in one step of a plurality (two or more) of reduction steps by at most 50 % of the temporal difference.

[0041] 22.271P-WO / 09.03.2026In an aspect, the present invention relates to a method for preventing an interruption of an effective cardiac resynchronization therapy applied to a patient in need thereof with an implantable medical device for stimulating a human or animal heart, in particular an implantable medical device according to the preceding explanations. In this context, the method comprises the steps explained in the following.

[0042] In a first step, a temporal difference between i) a current atrioventricular interval having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval having a second length that is shorter than the first length is determined. In this context, the target atrioventricular interval is to be applied in a subsequent cardiac cycle.

[0043] Afterwards, a stepwise (iterative) reduction of a length of the atrioventricular interval from the first length to the second length is carried out. This is done during at least two cardiac cycles directly or indirectly following the first cardiac cycle. The at least two cardiac cycles can be directly adjacent cycles can be interrupted by one or more cardiac cycles during which the length of the atrioventricular interval is not reduced. In any case, the length of the atrioventricular interval is reduced in one step of a plurality (two or more) of reduction steps by at most 50 % of the temporal difference.

[0044] In another step, a ventricular pacing pulse is delivered to the patient after expiration of at least one of the atrioventricular intervals that has a length being shorter than the first length.

[0045] All embodiments of the implantable medical device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described methods. Likewise, all embodiments of the described methods can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device or the respective other method.

[0046] Further details of aspects of the present invention will be explained in the following making reference to exemplary embodiments and accompanying Figures. In the Figures:

[0047] Figure 1 A schematically shows a system comprising an implantable medical device;

[0048] 22.271P-WO / 09.03.2026Figure IB schematically shows different components of the implantable medical device of Figure 1A;

[0049] Figure 2A shows a first schematic illustration of cardiac events sensed by a prior art CRT device and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device;

[0050] Figure 2B shows a second schematic illustration of cardiac events sensed by an exemplary embodiment of a CRT device according to the present disclosure and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device;

[0051] Figure 3A shows a third schematic illustration of the cardiac events sensed by a prior art CRT device and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device;

[0052] Figure 3B shows a fourth schematic illustration of cardiac events sensed by an exemplary embodiment of a CRT device according to the present disclosure and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device;

[0053] Figure 4A shows a fifth schematic illustration of cardiac events sensed by a prior art CRT device and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device; and

[0054] Figure 4B shows a sixth schematic illustration of the cardiac events sensed by an exemplary embodiment of a CRT device according to the present disclosure and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device.

[0055] 22.271P-WO / 09.03.2026Figure 1 A shows a system comprising a device for cardiac resynchronization therapy (CRT) 1 as example of an implantable medical device for stimulating the human or animal heart. The system further comprises a home monitoring system 2 serving as remote system. It is possible for the CRT device 1 to establish a wireless data communication with the home monitoring system 2.

[0056] The CRT device 1 comprises a housing 3 with a header 4 and a first electrode 13 connected to the header 4. The first electrode 13 comprises a first tip electrode pole 14 and a first ring electrode pole 15 that is proximally arranged from the first tip electrode pole 14. A first sensing vector 16 is defined from the first ring electrode pole 15 to the first tip electrode pole 14. Electric cardiac signals sensed between the first tip electrode pole 14 and first the ring electrode pole 15, i.e., along the first sensing vector 16, are directly recorded within a heart chamber, typically the right atrium. Thus, the first electrode 13 is designed and arranged to sense right atrial electric signals and to deliver stimulation pulses to the right atrium.

[0057] The CRT device 1 further comprises a second electrode 9 that is also connected to the header 4. The second electrode 9 comprises a second tip electrode pole 10 and a second ring electrode pole 11 that is proximally arranged from the second tip electrode pole 10. A second sensing vector 12 is defined from the second ring electrode pole 11 to the second tip electrode pole 10. Electric cardiac signals sensed between the second tip electrode pole 10 and the second ring electrode pole 11, i.e., along the second sensing vector 12, are also directly recorded within a heart chamber, typically the left ventricle. Thus, the second electrode 9 is designed and arranged to sense left ventricular electric signals and to deliver stimulation pulses to the left ventricle.

[0058] The CRT device 1 additionally comprises a third electrode 5 connected to the header 4. The third electrode 5 comprises a first tip electrode pole 6 and a first ring electrode pole 7 that is proximally arranged from the first tip electrode pole 6. A first sensing vector 8 is defined from the first ring electrode pole 7 to the first tip electrode pole 6. Electric cardiac signals sensed between the first tip electrode pole 6 and first the ring electrode pole 7, i.e., along the first sensing vector 8, are directly recorded within a heart chamber, typically the right

[0059] 22.271P-WO / 09.03.2026ventricle. Thus, the first electrode 5 is designed and arranged to sense right ventricular electric signals and to deliver stimulation pulses to the right ventricle.

[0060] Figure IB schematically illustrates individual components of the CRT device 1 that are comprised within the housing 3. In this and in all following Figures, similar elements will be denoted with the same numeral reference. The housing 3 houses a detection unit 31 (also referred to as sensing unit) that typically comprises an analog-to-digital converter, a bandpass filter, and an offset compensation. The detection unit 31 is operatively connected with a processor 32 that has access to a memory unit 33. The memory unit 33 serves for storing instructions for the processor 32 as well as data detected by the detection unit 31. The housing 3 further comprises an evaluation unit 34 that can also be part of the processor 32 and that serves for extracting features from the detected cardiac electric signal. The housing 3 further comprises a stimulation unit 35 that serves for stimulating the heart from which the detection unit 31 detects electric signals. The first electrode 13 along with its first tip electrode pole 14 and first ring electrode pole 15 as well as the second electrode 9 along with its second tip electrode 10 and second ring electrode 11 and the third electrode 5 along with its third tip electrode 6 and third ring electrode 7 (confer Figure 1A) are operatively connected to and / or form part of the detection unit 31 and of the stimulation unit 35. Additionally, the housing 3 comprises a data communication unit 36 that serves for data transfer to the home monitoring system 2 (confer Figure 1 A).

[0061] Figure 2A shows a first schematic illustration of cardiac events sensed by a prior art CRT device and pacing pulses delivered by this CRT device together with selected timing parameters of the CRT device. The CRT device is programmed to be operated as DDD BiV-LV type device (i.e., it employs a dual stimulation, a dual sensing, and a dual (inhibiting and triggered) operating mode; in addition, it performs a biventricular stimulation, wherein the left ventricle is the first paced ventricle).

[0062] Upon detecting an atrial depolarization (atrial sense, As), an atrioventricular interval AV is started. Upon termination of this atrioventricular interval AV, a left ventricular pacing pulse LVp is delivered. This initiates a small interventricular interval, the so-called interventricular

[0063] 22.271P-WO / 09.03.2026delay after pace VVp. Upon termination of the interventricular delay after pace VVp, a right ventricular pacing pulse RVp is applied by the CRT device.

[0064] With the delivery of the initial left ventricular pacing pulse LVp, an upper rate interval UTI and a left ventricular upper resynchronization interval LVURI (an embodiment of the predeterminable protective interval) are started. The left ventricular upper resynchronization interval LVURI has a twofold function. On the one hand, it defines the maximum left ventricular pacing rate in CRT devices employing biventricular cardiac resynchronization. Under this aspect, the left ventricular upper resynchronization interval LVURI is utilized to prevent sensible patients from experiencing palpitations at elevated resynchronization rates. On the other hand, the left ventricular upper resynchronization interval LVURI serves as protection against competitive left ventricular pacing after detected left ventricular senses.

[0065] The length of the left ventricular upper resynchronization interval LVURI is adjusted to the cardiac rate of the patient’s heart to be treated with the CRT device. Typically, the left ventricular upper resynchronization interval LVURI ends prior to the end of a pacing interval PP. Thus, after another left ventricular pacing pulse LVp, another upper rate interval UTI and another interventricular delay after pace VVp are initiated. Furthermore, a novel right ventricular pacing pulse RVpis delivered by the CRT device.

[0066] The CRT device then applies an algorithm to detect a pacemaker-mediated tachycardia (PMT) and extends the atrioventricular interval AV by 50 ms, as illustrated by the vertically hatched section of the atrioventricular interval AV in the third pacing cycle. Consequently, the directly subsequent applied left ventricular pacing pulse LVp and right ventricular pacing pulse RVpare shifted by 50 ms to the right. Because the following atrial depolarization As does not follow this shifted ventricular pace, the interval between the ventricular pace and the atrial depolarization differs from the respective interval between ventricular paces and atrial depolarizations of prior cardiac cycles (i.e., the interval is not stable). This indicates that PMT is not confirmed by the applied PMT algorithm. Therefore, the atrioventricular interval shall be set back to its previous value. This reduction of atrioventricular interval AV by 50 ms to its previous value is typically done in the next pacing cycle (indicated by the arrow pointing to the left). However, then a left ventricular pacing pulse is scheduled to be

[0067] 22.271P-WO / 09.03.2026delivered at a time point at which a left ventricular upper resynchronization interval LVURI still persists. During this left ventricular upper resynchronization interval LVURI the delivery of a further left ventricular pacing pulse is inhibited. Consequently, only a logical event, namely a left ventricular phantom pacing pulse LVp(PH) is emitted. In addition, a left ventricular timing window T LVs is initiated that lasts until the detection of an intrinsic left ventricular depolarization LVs. The time between the right ventricular depolarization RVs and the left ventricular depolarization LVs is also referred to as interventricular sense delay IVSD.

[0068] Both the left ventricular phantom pacing pulse LVp(PH) and the sensed left ventricular depolarization LVs initiate further left ventricular upper resynchronization intervals LVURI. Consequently, different left ventricular upper resynchronization intervals LVURI overlap and inhibit the further delivery of a left ventricular pacing pulse LVp. A so-called LVURI lock-in situation has occurred that persistently prevents left ventricular resynchronization pacing. It will not be possible for the CRT device to terminate the LVURI lock-in situation. Thus, the CRT device cannot perform its cardiac resynchronization functionality any longer; a cardiac desynchronization results.

[0069] Figure 2B shows a similar schematic illustration, however, not for a prior art device, but for an embodiment of an implantable medical device according to the present disclosure. This implantable medical device is a CRT device that is also programmed to be operated as DDD BiV-LV type device (like the CRT device in Figure 2A). The situation in the first three pacing cycles is identical to the situation explained with respect to Figure 2A. In the third pacing cycle, the atrioventricular interval is extended for carrying out the PMT detection algorithm. However, afterwards, the extended atrioventricular interval is not reduced in a single step, by reducing the atrioventricular interval AV by 50 ms (as in case of the comparative example of Figure 2A), but rather in three subsequent steps, wherein in each step the atrioventricular interval is reduced by e.g. 50 / 3 ms. In an alternative embodiment, the reduction can differ in each of the three steps, but lies in a range of from 2 to 25 ms.

[0070] This is indicated by one arrow pointing to the left in the fourth pacing cycle, two arrows pointing to the left in the fifth pacing cycle, and three arrows pointing to the left in the sixth

[0071] 22.271P-WO / 09.03.2026pacing cycle. Due to this stepwise reduction of the atrioventricular interval and LVURI lock-in situation is avoided. Rather, the stepwise reduction of the atrioventricular interval serves for a stepwise shift of the scheduled left ventricular pacing pulse LVp to the left, but only to such an extent that the scheduled left ventricular pacing pulse LVp is not located within a persisting left ventricular upper resynchronization interval LVURI. Consequently, all scheduled left ventricular pacing pulses LVp can be applied; no left ventricular phantom pacing pulse needs to be emitted. Since an LVURI lock-in situation is avoided by the stepwise reduction of the atrioventricular interval, the CRT device can perform its regular resynchronization therapy. A desynchronization of the heart to be treated is prevented.

[0072] Figure 3A shows another schematic illustration of the cardiac events sensed by a prior art CRT device and pacing pulses delivered by the CRT device together with selected timing parameters of the CRT device. In this comparative example, the CRT device is programmed as DDD BiV-RV type device (i.e., it employs a dual stimulation, a dual sensing, and a dual (inhibiting and triggered) operating mode; in addition, it performs a biventricular stimulation, wherein the right ventricle is the first paced ventricle).

[0073] In this example, an atrial depolarization (atrial sense) As is detected. After expiration of a long atrioventricular interval AV of, e.g., 250 ms, a right ventricular pacing pulse RVp is delivered. This initiates an interventricular delay after pace VVp and an upper rate interval UTI. Upon expiration of the interventricular delay after pace VVp, a left ventricular pacing pulse LVp is delivered to the left ventricle. This left ventricular pacing pulse LVp initiates a left ventricular upper resynchronization interval LVURI.

[0074] In the next cardiac cycle, the atrioventricular interval AV is reduced to a short value of, e.g., 120 ms. The delivered right ventricular pacing pulse RVp initiates again an interventricular delay after pace VVp. Upon expiration of this interventricular delay after pace VVp, the preceding left ventricular upper resynchronization interval LVURI still persists. As a consequence, only a left ventricular phantom pacing pulse LVp(PH) is emitted. This leads to the start of a novel left ventricular upper resynchronization interval LVURI. Shortly afterwards, a left ventricular depolarization LVs is detected in response to the previously applied right ventricular pacing pulse RVp. This left ventricular depolarization LVs starts

[0075] 22.271P-WO / 09.03.2026another left ventricular upper resynchronization interval LVURI. Consequently, different left ventricular upper resynchronization intervals LVURI overlap. One of these left ventricular upper resynchronization intervals LVURI also persists at the time at which the next left ventricular pacing pulse LVp is scheduled due to the prevailing cardiac rate.

[0076] This next scheduled left ventricular pacing pulse LVp falls in a critical desynchronization interval CDI. This critical desynchronization interval CDI is calculated as CDI = T LVs + LVURI, i.e., as the sum of i) the measured time T LVs between the left ventricular phantom pacing pulse LVp(PH) and the next left ventricular depolarization LVs and ii) the left ventricular upper resynchronization interval LVURI. Since T LVs = IV SD - VVp (the difference of the interventricular sense delay IVSD and the interventricular delay after pace VVp), the critical desynchronization interval CDI can also be calculated as CDI = IVSD -VVp + LVURI. If the left ventricular interval is shorter than the critical desynchronization interval CDI, an LVURI lock-in situation can occur.

[0077] This is the case in the situation illustrated in Figure 3A. Once again only a left ventricular phantom pacing pulse LVp(PH) is emitted instead of delivering a left ventricular pacing pulse LVp. Thus, the device has turned into an LVURI lock-in situation from which it cannot return by itself.

[0078] Figure 3B shows a similar schematic illustration, however, not for a prior art device, but for an embodiment of an implantable medical device according to the present disclosure. This implantable medical device is a CRT device that is also programmed to be operated as DDD BiV-RV type device (like the CRT device in Figure 3A). The situation in the first pacing cycle is identical to the situation explained with respect to Figure 3 A. In the second pacing cycle, the extended atrioventricular interval is not reduced in a single step, by reducing the atrioventricular interval AV to 120 ms (as in case of the comparative example of Figure 3 A), but rather in three subsequent steps, wherein in each step the atrioventricular interval is reduced by e.g. 130 / 3 ms. In an alternative embodiment, the reduction can differ in each of the three steps, but lies in a range of from 5 ms to 55 ms.

[0079] 22.271P-WO / 09.03.2026This is indicated by one arrow pointing to the left in the second pacing cycle, two arrows pointing to the left in the third pacing cycle, and three arrows pointing to the left in the fourth pacing cycle. Due to this stepwise reduction of the atrioventricular interval and LVURI lock-in situation is avoided. Rather, the stepwise reduction of the atrioventricular interval serves for a stepwise shift of the scheduled right ventricular pacing pulse RVp to the left, but only to such an extent that the scheduled left ventricular pacing pulse LVp is not located within a persisting left ventricular upper resynchronization interval LVURI. Consequently, all scheduled left ventricular pacing pulses LVp can be applied; no left ventricular phantom pacing pulse needs to be emitted. Since an LVURI lock-in situation is avoided by the stepwise reduction of the atrioventricular interval, the CRT device can perform its regular resynchronization therapy. A desynchronization of the heart to be treated is prevented.

[0080] Figure 4A shows another schematic illustration of the cardiac events sensed by a prior art CRT device and pacing pulses delivered by the CRT device together with selected timing parameters of the CRT device. In this example, the CRT device is programmed as DDD BiV-LV type device.

[0081] In this example, a long atrioventricular interval AV of, e.g., 300 ms, is applied to perform a sense amplitude measurement (SAM) test or an atrioventricular conduction test. After detection of an atrial depolarization (atrial sense) As, the long atrioventricular interval AV is initiated. During this long atrioventricular interval AV, a right ventricular depolarization RVs and a subsequent intrinsic left ventricular depolarization LVs are detected. The left ventricular triggering functionality of the CRT device is turned off during sense amplitude measurement test or atrioventricular conduction test. This means that a left ventricular pacing pulse LVp is not scheduled to be delivered after a right ventricular depolarization RVs. The right ventricular depolarization RVs initiates an upper rate interval UTI, wherein the left ventricular depolarization LVs initiates a left ventricular upper resynchronization interval LVURI.

[0082] After the sense amplitude measurement (SAM) test or atrioventricular conduction test , the atrioventricular interval AV is reduced to a regular shorter value of, e.g., 100 ms. At the same time, the left ventricular triggering is turned on again which means that a left

[0083] 22.271P-WO / 09.03.2026ventricular pacing pulse LVp is scheduled to be delivered after a right ventricular depolarization RVs. However, at the time at which the left ventricular pacing pulse LVp is scheduled, the preceding left ventricular upper resynchronization interval LVURI still persists. As a consequence, only a left ventricular phantom pacing pulse LVp(PH) is emitted. This leads to the start of a novel left ventricular upper resynchronization interval LVURI. in addition, an interventricular delay after pace VVp is initiated. Upon expiration of this interventricular delay after pace VVp, a right ventricular pacing pulse RVp is emitted. In response to this right ventricular pacing pulse RVp, a left ventricular depolarization LVs is detected that starts another left ventricular upper resynchronization interval LVURI. Consequently, different left ventricular upper resynchronization intervals LVURI overlap. One of these left ventricular upper resynchronization intervals LVURI also persists at the time at which the next left ventricular pacing pulse LVp is scheduled. Once again only a left ventricular phantom pacing pulse LVp(PH) is emitted instead of delivering a left ventricular pacing pulse LVp. Thus, the device has turned into an LVURI lock-in situation from which it cannot return by itself.

[0084] Figure 4B shows a similar situation like that of Figure 4A, however, using a CRT device being an embodiment of the present disclosure. This CRT device is again operated as DDD BiV-LV type device.

[0085] Upon detecting an atrial sense As, a long atrioventricular interval AV is initiated. This long atrioventricular interval AV has a length of, e.g., 300 ms and is applied to allow a sense amplitude measurement or an atrioventricular conduction test. It is chosen such to extend over an expected right ventricular depolarization RVs and a left ventricular depolarization LVs. The left ventricular triggering of the CRT device is turned off. Due to the right ventricular depolarization RVs, an intrinsic left ventricular depolarization LVs is detected prior to the expiration of the long atrioventricular interval AV. This left ventricular depolarization LVs starts a left ventricular upper resynchronization interval LVURI.

[0086] In the next cardiac cycles, the atrioventricular interval AV is shortened stepwise to reach its final (target) value. Thus, after detection of the next atrial depolarization As, the first reduction step of the atrioventricular interval AV is carried out. At the same time, the left

[0087] 22.271P-WO / 09.03.2026ventricular triggering of the CRT device is turned on. However, the slightly reduced atrioventricular interval AV is still so long that an intrinsic right ventricular depolarization RVs is detected before a left ventricular pacing pulse LVp is delivered. This right ventricular depolarization RVs initiates an interventricular delay after sense VVs. Upon expiration of this interventricular delay after sense VVs, a left ventricular pacing pulse LVp can be delivered since the previous left ventricular upper resynchronization interval LVURI has already terminated. A novel left ventricular upper resynchronization interval LVURI is started.

[0088] In the next cardiac cycle, again an atrial depolarization As is detected. The atrioventricular interval AV is reduced by a second step, i.e., it is even shorter than in the previous cardiac cycle. However, it is still so long that again an intrinsic right ventricular depolarization RVs is detected that initiates a novel interventricular delay after sense VVs. Upon expiration of this interventricular delay after sense VVs, a novel left ventricular pacing pulse LVp can be delivered.

[0089] In the next cardiac cycle, the atrioventricular interval AV is again reduced. Now, it is shorter than an intrinsic atrioventricular conduction time. Consequently, after detecting an intrinsic atrial depolarization As and upon expiration of the shortened atrioventricular interval AV, a left ventricular pacing pulse LVp can be delivered. This leads to the start of an interventricular delay after pace VVp (and the start of a novel left ventricular upper resynchronization interval LVURI and an upper rate interval UTI). Upon expiration of the interventricular delay after pace VVp, a right ventricular pacing pulse RVp can be delivered. In the next cardiac cycle, the atrioventricular interval AV is again reduced, now to its target value of, e.g., 100 ms. The sequences of pulses is identical to the sequences in the previous cardiac cycle. In the following cardiac cycles, the atrioventricular interval AV is kept constant since it has already reached its target value. Then, the cardiac resynchronization therapy can be applied in a regular way.

[0090] The stepwise reduction of the atrioventricular interval from its initial long duration to its target shorter duration, as illustrated in Figure 4B by arrows pointing to the left, is performed in four consecutive reduction steps by applying an equal reduction of e.g. 50 ms per step. In

[0091] 22.271P-WO / 09.03.2026other embodiments, the reduction may be different in each step, and / or the number of steps may be different than in the embodiment of Figure 4B. In an alternative embodiment, the reduction per step lies in a range of from 5 to 55 ms, and the number of steps lies in a range of from 2 to 6. The stepwise reduction according to the present invention prevents the CRT device from entering a LVURI lock-in situation. In fact, the CRT device remains able to provide the required cardiac resynchronization therapy, i.e., its normal functionality.

[0092] 22.271P-WO / 09.03.2026

Claims

Claims1. Implantable medical device (1) for stimulating a human or animal heart, comprising a processor (32), a memory unit (33), a stimulation unit (34) configured to stimulate a human or animal heart, a detection unit (31) configured to detect an electric signal of the same heart, and at least a first electrode (13) and a second electrode (9) connected to the detection unit (31) and the stimulation unit (34), wherein the first electrode (13) is configured to sense atrial electric signals and / or to deliver atrial stimulation pulses and the second electrode (9) is configured to sense ventricular electric signals and to deliver ventricular stimulation pulses,characterizedin that the memory unit (33) comprises a computer-readable program that causes the processor (32) to perform the following steps when being executed on the processor (32):a) determining a temporal difference between i) a current atrioventricular interval (AV) having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval (AV) having a second length that is shorter than the first length, wherein the target atrioventricular interval (AV) is to be applied in a subsequent cardiac cycle; andb) stepwise reducing a length of the atrioventricular interval (AV) in at least two cardiac cycles following the first cardiac cycle from the first length to the second length, wherein the length of the atrioventricular interval (AV) is reduced in one step of a plurality of reduction steps by at most 50 % of the temporal difference.

2. Implantable medical device according to claim 1, characterized in that the temporal difference lies in a range of from 10 ms to 350 ms.

3. Implantable medical device according to claims 1 or 2, characterized in that the computer-readable program causes the processor (31) to reduce the atrioventricular interval (AV) in one step of the plurality of reduction steps by 5 ms to 50 ms.22.271P-WO / 09.03.20264. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to reduce the atrioventricular interval (AV) in each step of the plurality of reduction steps by the same length.

5. Implantable medical device according to any of the preceding claims, characterized in that the plurality of reduction steps comprises 2 to 10 reduction steps.

6. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to keep a predeterminable protective interval (LVURI) constant, wherein an expiration of the predeterminable protective interval (LVURI) is a prerequisite for a delivery of a left ventricular pacing pulse (LVp) with the second electrode (9), wherein the predeterminable protective interval (LVURI) is initiated by a preceding left ventricular pacing pulse (LVp) delivered with the second electrode (9), a preceding left ventricular depolarization (LVs) detected with the second electrode (9), or a preceding logic event (LVp(PH)) triggered instead of a preceding left ventricular pacing pulse (LVp) at the same time at which the preceding left ventricular pacing pulse (LVp) was scheduled to be delivered.

7. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to keep all timing parameters of the implantable medical device besides the atrioventricular interval (AV) constant.

8. Implantable medical device according to any of the preceding claims, characterized in that the computer-readable program causes the processor (32) to apply a pacemaker- mediated tachycardia test in the first cardiac cycle.

9. Implantable medical device according to any of the preceding claims, characterized in that the second electrode (9) is a left ventricular electrode configured to be implanted22.271P-WO / 09.03.2026in the left ventricle for detecting left ventricular electric signals and for delivering left ventricular stimulation pulses.

10. Implantable medical device according to any of the preceding claims, characterized by a third electrode (5), the third electrode (5) being a right ventricular electrode configured to be implanted in the right ventricle for detecting right ventricular signals and for delivering right ventricular stimulation pulses.

11. Method for operating an implantable medical device (1) for stimulating a human or animal heart, in particular an implantable medical device (1) according to any of the preceding claims, characterized by the following steps:a) determining a temporal difference between i) a current atrioventricular interval (AV) having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval (AV) having a second length that is shorter than the first length, wherein the target atrioventricular interval (AV) is to be applied in a subsequent cardiac cycle; andb) step-wise reducing a length of the atrioventricular interval (AV) in at least two cardiac cycles following the first cardiac cycle from the first length to the second length, wherein the length of the atrioventricular interval (AV) is reduced in one step of a plurality of reduction steps by at most 50 % of the temporal difference.

12. Method for preventing an interruption of an effective cardiac resynchronization therapy applied to a patient in need thereof with an implantable medical device (1) for stimulating a human or animal heart, in particular an implantable medical device (1) according to any of claims 1 to 10, the method comprising the following steps: a) determining a temporal difference between i) a current atrioventricular interval (AV) having a first length and being applied in a first cardiac cycle and ii) a target atrioventricular interval (AV) having a second length that is shorter than the first length, wherein the target atrioventricular interval (AV) is to be applied in a subsequent cardiac cycle;b) step-wise reducing a length of the atrioventricular interval (AV) in at least two cardiac cycles following the first cardiac cycle from the first length to the second22.271P-WO / 09.03.2026length, wherein the length of the atrioventricular interval (AV) is reduced in one step of a plurality of reduction steps by at most 50 % of the temporal difference; andc) delivering a ventricular pacing pulse (LVp; RVp) to the patient after expiration of at least one of the atrioventricular intervals (AV) that has a length being shorter than the first length.22.271P-WO / 09.03.2026

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