Anti-tachycardia pacing implantable medical device

Abstract

An implantable medical device (IMD) for anti-tachycardia pacing ATP is described. The IMD comprises a detection unit configured to detect events in the sensed electrical signals, to analyze time intervals between the events, and to detect a tachycardia condition. Moreover, the IMD comprises a control unit configured to generate the therapy sequence and to derive at least one parameter to adjust the therapy sequence, and a memory unit. The stimulation unit is configured to deliver a first therapy sequence TS1 if the detection unit detects a first tachycardia condition based on first events. The control unit is configured to store a first therapy information in the memory unit, wherein the first therapy information is determined delivery of the first therapy sequence TS1. If the detection unit detects a second tachycardia condition based on second events, the control unit is configured to generate a second therapy sequence TS2 based on the first therapy information.

Description

[0001] Anmelder: BIOTRONIK SE & Co. KG

[0002] Datum: 20.03.2026

[0003] Unser Zeichen: 25.045P-WO

[0004] ANTI-TACHYCARDIA PACING IMPLANTABLE MEDICAL DEVICE

[0005] This invention generally relates to devices and methods for anti-tachycardia pacing (ATP) of the heart.

[0006] Implantable cardioverter-defibrillators (ICDs) are widely used to prevent sudden cardiac death in patients at risk of life-threatening ventricular arrhythmias. These devices deliver two primary therapies: high-energy shocks and anti -tachycardia pacing (ATP). ATP is generally preferred as a first-line therapy for terminating atrial and ventricular tachycardias because it is painless and conserves device battery life compared to shocks. Conventional ATP strategies, such as Burst and Ramp pacing, deliver a predefined sequence of pacing pulses at intervals shorter than the tachycardia cycle length (TCL) in an attempt to interrupt the reentrant circuit responsible for tachycardia.

[0007] Despite its clinical benefits, conventional ATP has limitations. Current algorithms typically rely on fixed or preprogrammed parameters, such as the number of pulses, coupling intervals, and sequence structure, which are determined by the physician prior to implantation or during follow-up. These settings do not adapt to the dynamic electrophysiological characteristics of tachycardia at the time of therapy delivery. As a result, ATP may fail to terminate tachycardia or, in some cases, accelerate the arrhythmia, necessitating painful shock therapy. Furthermore, repeated unsuccessful ATP attempts can prolong therapy duration and delay defibrillation, increasing patient risk.

[0008] To address these shortcomings, adaptive ATP algorithms have been introduced. However, existing adaptive approaches remain limited in scope and may require multiple iterations to converge on an effective configuration. This can result in prolonged therapy and does not fully exploit the information available from the patient’s response to prior ATP attempts.

[0009] US Patent 11,134,881 B2 describes a system for detecting an atrial tachyarrhythmia episode that includes a medical device having sensing circuitry configured to receive a cardiac electrical signal from electrodes coupled to the medical device and a processor configured to detect an atrial tachyarrhythmia episode in response to a time duration of the cardiac electrical signal classified as an atrial tachyarrhythmia being greater than or equal to a first detection threshold. The processor is configuredto determine if detection threshold adjustment criteria are met based on at least the detected first atrial tachyarrhythmia episode and adjust the first detection threshold to a second detection threshold different than the first detection threshold in response to the detection threshold adjustment criteria being met.

[0010] Accordingly, there is a need for improved methods and systems that dynamically adjust ATP therapy to the patient’s real-time arrhythmic state. In particular, there is a need for approaches that utilize timing information — such as intervals between delivered pulses and subsequent intrinsic ventricular events — after an initial ATP attempt to optimize the configuration of subsequent ATP sequences. Such adaptive strategies have the potential to increase the likelihood of tachycardia termination, reduce the number of unsuccessful attempts, and minimize the need for high-energy shocks.

[0011] The following presents a simplified summary in order to provide a basic understanding of some aspects of the disclosed subject matter. This summary is not an extensive overview, and it is not intended to identify key / critical elements or to delineate the scope thereof. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.

[0012] An implantable medical device (IMD) for anti-tachycardia pacing ATP of a heart of a patient is described. The IMD comprises at least one electrode pole configured to sense electrical signals of the heart and apply electrical pulses to the heart, a stimulation unit configured to deliver the electrical pulses to the heart via the electrode pole, wherein the stimulation unit is configured to deliver at least one therapy sequence to the heart, the therapy sequence comprising at least one electrical pulse. The IMD further comprises a detection unit configured to detect events in the sensed electrical signals, to analyze time intervals between the events, and to detect a tachycardia condition based on the events. Moreover, the IMD comprises a control unit configured to generate the at least one therapy sequence and to derive at least one parameter to adjust the therapy sequence based on the events, and a memory unit. The stimulation unit is configured to deliver a first therapy sequence TS 1 to the heart if the detection unit detects a first tachycardia condition based on a plurality of first events. The control unit is configured to store a first therapy information in the memory unit, wherein the first therapy information is determined around the time of delivery of the first therapy sequence TS 1. If the detection unit detects a second tachycardia condition based on a plurality of second events after delivery of the first therapy sequence TS 1, the control unit is configured to generate a second therapy sequence TS2 based on the first therapy information.

[0013] According to an embodiment, the first therapy information is associated with at least one of: the first therapy sequence TS1, an IMD parameter, and a patient parameter. The first therapy information is

[0014] 25.045P-WO / / 20.03.2026determined around the time of delivery of the first therapy sequence TS1, which can be within a time frame that starts prior to delivery of the first therapy sequence TS1, e.g. with the detection of the first tachycardia condition, and ends after the delivery of the first therapy sequence TS1, as for instance after expiration of a predetermined time after delivery of the first therapy sequence (e.g. 5 seconds to 5 minutes after the last pulse of the first therapy sequence). Alternatively or in addition, the time frame ends if a termination of the tachycardia condition has been detected as a result of the delivery of the first therapy sequence.

[0015] The IMD is configured to apply stored information related to prior therapy sequences from a prior tachycardia episode to select parameters for a later therapy sequence. This may support more efficient therapy delivery in subsequent tachycardia episodes.

[0016] For example, the IMD is configured such that the control unit generates the second therapy sequence TS2 such that at least one therapy parameter of the second therapy sequence TS2 is equal to at least one therapy parameter of the first therapy sequence TS 1.

[0017] By reusing at least one therapy parameter, computational effort for re-parameterization at the start of a later therapy sequence may be reduced.

[0018] In the context of the present invention, generating the second therapy sequence TS2 such that at least one therapy parameter of the second therapy sequence TS2 is equal to at least one therapy parameter of the first therapy sequence TS 1 is to be understood as permitting deviations that arise solely from regular device manufacturing tolerances, which are considered irrelevant.

[0019] According to an embodiment of the present invention, a therapy sequence comprises at least one pulse train, whereby a pulse train comprises at least a plurality of electrical pulses. In an example, a therapy sequence comprises a plurality of pulse trains, wherein two successive pulse trains are separated by an inter-train interval.

[0020] According to an aspect, the first therapy sequence TS 1 comprises at least one pulse train, wherein the therapy parameter of the first therapy sequence TS1 is one therapy parameter of the pulse train (e.g. the number of pulses of one pulse train, the inter-pulse intervals applied within the pulse train, etc.). In an example, the first therapy sequence TS1 comprises a plurality of pulse trains, wherein the therapy parameter of the first therapy sequence TS 1 is one therapy parameter associated with the plurality of pulse trains (e.g. the number of pulse trains).

[0021] 25.045P-WO / / 20.03.2026In an embodiment, at least one therapy parameter of the first pulse train of the second therapy sequence is equal to at least one therapy parameter of the first therapy sequence TS1, e.g. a therapy parameter associated with the last pulse train of the first therapy sequence TS 1.

[0022] In an embodiment, the control unit is configured to generate at least one therapy sequence TSi (i being an index for the number of the therapy sequence) by adjusting at least one of the following therapy parameters:

[0023] - A duration of the therapy sequence,

[0024] - A number of pulses of a therapy sequence,

[0025] - A number of pulse trains of a therapy sequence,

[0026] - An inter-pulse interval between at least two pulses of a therapy sequence,

[0027] - A coupling interval RSi between the last detected intrinsic tachycardia event and the first pulse of a therapy sequence,

[0028] - A maximum number of therapy sequences,

[0029] - A maximum duration of the therapy sequence,

[0030] - A minimum and / or maximum duration between successive therapy sequences.

[0031] According to an embodiment of the present invention,

[0032] - The number of therapy sequences is 10, 20, 30 or 40,

[0033] - The duration of a therapy sequence or a series of therapy sequences ranges between 60s to 3600s. - The minimum duration between successive therapy sequences is 0.6s.

[0034] According to an aspect of the invention, the control unit is configured to generate at least one therapy sequence TSi by adjusting at least one of the following parameters:

[0035] - a maximum number of therapy sequences,

[0036] - a maximum duration of the therapy sequence,

[0037] - a minimum and / or maximum duration between therapy sequences.

[0038] In an example, a maximum number of therapy sequences is 40. In that example, a maximum of 2x10 sequences are delivered for a VT zone, 2x10 therapy sequences are delivered for a ventricular fibrillation (VF) zone.

[0039] According to an embodiment, a maximum duration of the therapy sequence is 3600s.

[0040] Moreover, according to an aspect, the minimum duration is 600ms.

[0041] 25.045P-WO / / 20.03.2026Adjustment of at least one therapy parameter from a selection of multiple therapy parameters allows customization of therapy delivery and provides flexibility to tailor anti-tachycardia pacing to individual patient cardiac dynamics.

[0042] According to an embodiment, the control unit is further configured to store therapy sequences that have been identified as unsuitable for reuse, in particular therapy sequences for which a loss-of-capture (LOC) condition was detected. The control unit may be configured to explicitly exclude such stored unsuitable therapy sequences from selection when generating / parametrizing a subsequent therapy sequence for a later tachycardia episode. This may prevent reuse of therapy configurations that previously failed to capture the myocardium and therefore reduce the likelihood of ineffective or detrimental ATP attempts.

[0043] According to an aspect, the IMD is configured such that the control unit generates the second therapy sequence TS2 based on the first therapy information if the first therapy information is sufficiently similar to at least one second therapy information. The second therapy information is determined prior to the time of the planned delivery of the second therapy sequence TS2. That solution may avoid application of non-matching settings to a different therapy or cardiac rhythm situation. This may support more targeted initialization of the second therapy sequence.

[0044] According to an embodiment, the second therapy information is associated with at least one of an IMD parameter or a patient parameter. The second therapy information is determined in advance of the planned delivery of the second therapy sequence TS2, and may begin, for example, at the time of detection of the second tachycardia condition. Alternatively or additionally, the second therapy information is determined retrospectively with respect to the detection of the second tachycardia condition, for example within a window from about 2 minutes to about 5 seconds prior to the detection time.

[0045] According to an embodiment, the IMD is configured such that the first therapy information and / or the second therapy information is based on at least one of:

[0046] - sensed electrical signals,

[0047] - events in the sensed electrical signals,

[0048] - time intervals between the events,

[0049] - a tachycardia condition based on the events,

[0050] - one sensor of the IMD,

[0051] - one programming parameter, and

[0052] - a physiological patient parameter.

[0053] 25.045P-WO / / 20.03.2026Providing multiple sources as a basis for the stored therapy information may provide a broader description of the rhythm situation and device or patient context. This may support improved selection or parametrization of therapy sequences for later ATP attempts.

[0054] According to an embodiment, the sensor of the IMD can be at least one of an impedance, pressure, oxygen, and cardiac sound sensor.

[0055] For example, the IMD is configured such that the first therapy information and / or the second therapy information comprises at least one of:

[0056] a mean cardiac cycle length,

[0057] a stability of a cardiac rhythm,

[0058] a morphological signal metric derived from the sensed electrical signal, an impedance value,

[0059] a patient posture,

[0060] a mean heart rate, and

[0061] a patient activity level.

[0062] According to one embodiment, an accelerometer may be used to determine the patient posture or patient activity level.

[0063] For example, the first therapy information and / or the second therapy information further comprises at least one of: a current time of day / night, a current (e.g. daily) value related to Cardiac Resynchronization Therapy (CRT) pacing, Right Atrial (RA) pacing, Right Ventricular (RV) pacing, a current pacing threshold, a mean heart rate (e.g. for the day), a number of recorded tachycardia episodes of certain types (e.g. Supra Ventricular Tachycardia, Ventricular Tachycardia (VT), Ventricular Fibrillation (VF), Non-Sustained Ventricular Tachycardia (NSVT)) that can be normalized for a programmable time period (e.g. 1 month), and a relative fluctuation of selected morphological signal metrics (e.g. difference of the median of all maximum values and the median of the minimum values of the normalized QRS area that have been stored on an hourly basis) for a programmable comparison time period (e.g. one day).

[0064] According to an aspect, impedance values can be obtained from an impedance sensor. Impedance measurements can be used to determine, for instance, fluid balance of an organ or a part of the patient’s body.

[0065] 25.045P-WO / / 20.03.2026In general, storing information that is related to the cardiac rhythm, IMD device parameters or physiological patient parameters may support comparing a current tachycardia episode to prior tachycardia episodes. This may enable selection and / or parametrization of therapy sequences that are more appropriate for the current tachycardia condition.

[0066] According to an aspect, the IMD is configured such that the morphological signal metric comprises at least one of: a wave difference vector (e.g. a normalized wave difference vector), a peak-to-peak amplitude (e.g. a maximum peak-to-peak amplitude), a width of a QRS complex, and an area under a curve (e.g. a normalized area under the curve).

[0067] According to embodiments of the present invention, the following definitions apply:

[0068] a wave difference vector represents a metric a difference between two segments of the sensed electrical signal, for example by comparing the morphology of a current signal segment to a reference segment to quantify changes in waveform shape.

[0069] a peak-to-peak amplitude represents a voltage difference between a maximum and a minimum amplitude within the sensed electrical signal.

[0070] a width of a QRS complex represents a time duration of a QRS complex in the sensed electrical signal, indicating how long ventricular depolarization extends.

[0071] an area under a curve represents an integrated signal amplitude over time for a defined portion of the sensed electrical signal.

[0072] Using morphological signal metrics may support discrimination between rhythm situations that have similar rates but different characteristics of the sensed electrical signal (e.g. electrogram). This may improve identification of a sufficiently similar tachycardia condition for selection and / or parametrization of a further therapy sequence.

[0073] According to an embodiment, the IMD is configured such that the control unit stores the first therapy information if the delivery of the first therapy sequence TS1 resulted in a termination of the first tachycardia condition for at least a predetermined time, or if the delivery of the first therapy sequence resulted in detection of an entrainment condition.

[0074] Storing the therapy sequences which lead to a termination of a tachycardia condition, or that reached an entrainment condition will ensure selection of starting configurations for further therapy sequences with higher likelihood of tachycardia termination.

[0075] 25.045P-WO / / 20.03.2026Generally speaking, entrainment is defined as the process of capturing and “over-driving” a reentrant tachycardia circuit by delivering ATP paces that are slightly faster than the tachycardia cycle length. When the pacing rate is just faster than the ongoing tachycardia, each paced beat enters the circuit’s excitable gap, drives the circuit at the pacing rate, and can ultimately terminate the tachycardia — typically by causing the paced wavefronts to collide and extinguish within the circuit. It is therefore desirable to provide ATP delivery that can be adapted in response to intrinsic cardiac activity detected during therapy. However, if the ATP pacing interval is set shorter than a critical boundary interval, entrainment may be lost and intrinsic events corresponding to the underlying tachycardia may reappear.

[0076] For example, the IMD is configured such that an entrainment condition is detected if the first therapy sequence succeeded in capturing the heart. This provides an objective criterion for identifying effective interaction between the therapy sequence delivery and the cardiac tissue, and enables selection and / or parameterization of further therapy sequences with a higher likelihood of tachycardia termination.

[0077] For instance, the entrainment condition is detected if the detection unit detects a post-pacing interval between a last pulse of a previous therapy sequence preceding the first therapy sequence and a first detected intrinsic cardiac event after the last pulse of the previous therapy sequence, wherein the length of the post-pacing interval exceeds an entrainment threshold, and / or if the control unit is configured to control the timing of at least one therapy sequence based on at least one propagation time. The propagation time is a time span between the delivery of at least one first electrical pulse until arrival of the first electrical pulse at a target area of the heart. The control unit is configured to determine the propagation time based on at least one signal parameter from the sensed electrical signals. Entrainment detection may additionally and / or alternatively be performed via an additional electrode pole, wherein the first electrode pole is located on a first electrode lead and the second electrode pole is located on a second electrode lead. In an embodiment, the control unit confirms an entrainment condition of the previous therapy sequence if a phase offset exceeds a lower threshold or is less than an upper threshold, and stores the corresponding therapy parameters of the previous therapy sequence in a memory unit for future reference.

[0078] According to an embodiment, the propagation time PT is defined as a time span between the delivery of at least one first electrical pulse and the arrival of the electrical pulse at a target area of the heart. For assessing PT, the detection unit of the implantable medical device detects events in sensed electrical signals and analyzes time intervals between the events. The detection unit extracts at least one signal parameter SP from the sensed electrical signals prior to delivering the first electrical pulse and / or during

[0079] 25.045P-WO / / 20.03.2026a specific operation mode. The signal parameter SP comprises at least one of a runtime between two events measured in the electrical signals, wherein a first event is measured via a first electrode pole and a second event is measured via a second electrode pole. The control unit determines a QRS width in the electrical signals, a distance between extrema in the electrical signals, and / or an area under a curve.

[0080] According to an embodiment, the control unit determines the propagation time PT based on the at least one signal parameter SP, including by generating a weighted sum comprising a plurality of weights. Alternatively or in combination, the control unit is configured to determine a QRS width and / or an RV-LV delay that indicates a time delay between a right ventricular depolarization and a left ventricular depolarization in the sensed electrical signals. PT can be determined using the RV-LV delay and / or by PT = QRS width * x, wherein x is a correction factor for the measurement inaccuracy of QRS width.

[0081] According to an aspect, the IMD is configured such that the control unit stores a ranking of delivered therapy sequences and / or of a delivered series of therapy sequences in the memory unit. The ranking is based on at least one of: a success rate for termination of a tachycardia, a time until termination of a tachycardia, a number of electrical pulses of a therapy sequence, a battery consumption level of the therapy sequence, and a time elapsed since delivery of a delivered therapy sequence. The stimulation unit is configured to deliver at least one following therapy sequence based on the ranking.

[0082] Ranking previous therapy sequences or series of therapy sequences according to their success rate may facilitate prioritizing therapy sequences that increase the likelihood for tachycardia termination for selection and / or parameterization of further therapy sequences. This may reduce the number of ineffective ATP attempts in later tachycardia episodes.

[0083] According to an example, ranking previously delivered therapy sequences based on the time elapsed since their delivery can be implemented such that a more recent therapy sequence is ranked higher than a therapy sequence delivered further in the past. More recent therapy sequences may exhibit a higher success rate due to their increased applicability to the current cardiac state.

[0084] According to an embodiment, the IMD is configured such that the detection unit determines a first postpacing interval PI 1 between the last delivered pulse of the first therapy sequence TS 1 and a first detected intrinsic cardiac event after the last delivered pulse of the first therapy sequence TS 1. The stimulation unit is configured to deliver a second therapy sequence TS2 to the heart. If the detection unit detects a third tachycardia condition based on a plurality of third events after delivery of the second therapy sequence TS2, the detection unit is configured to determine a second post-pacing interval PI2 between

[0085] 25.045P-WO / / 20.03.2026the last delivered pulse of the second therapy sequence TS2 and a first detected intrinsic cardiac event after the last delivered pulse of the second therapy sequence TS2. The control unit is configured to compute a first relation parameter RP1 between PI1 and PI2. The control unit is configured to generate a third therapy sequence TS3 depending on the first relation parameter RP1, and / or to detect at least one phase offset between the first events and the second events, and / or between the second events and the third events. The control unit is configured to generate the second therapy sequence TS2 and / or the third therapy sequence TS3 based on the phase offset. Advantage: Using post-pacing interval information and / or phase offset information may support feedback-based adaptation of subsequent therapy sequences. This may improve responsiveness of therapy selection to measured outcomes.

[0086] An intrinsic event according to the invention is for instance an intrinsic tachycardia beat.

[0087] According to these embodiments, the IMD is additionally configured to adapt ATP therapy by measuring post-pacing intervals caused by at least two successive therapy sequences and / or a phase offset caused by at least one therapy sequence and using that information to shape the next, e.g. the second or third, therapy sequence. This increases the likelihood for a termination of a tachycardia condition and can reduce repeated ineffective ATP attempts.

[0088] In an embodiment of the invention,

[0089] - the coupling interval RSi is computed by scaling factor rs*TCL, whereby 0.5 < rs < 1;

[0090] - the inter-pulse-interval IPIi is computed by factor ipi*TCL, whereby ipi < rs, and i is the index number of the therapy sequence,

[0091] - whereby all inter-pulse-intervals of a therapy sequence are of equal length.

[0092] These timing regimes ensure that therapy delivery is adjusted according to the intrinsic cardiac cycle, and according to systematical dynamic adaptation of the anti -tachycardia pacing in successive attempts, with the target to enhance the effectiveness of anti -tachycardia pacing.

[0093] According to an aspect, if a previously delivered conventional ATP (cATP) therapy sequence in a prior episode successfully terminated a tachycardia, the IMD may initialize a dynamic ATP attempt from parameters derived from that cATP therapy sequence. In particular, when the prior cATP was a ramp type ATP, the IMD is configured to set a burst pulse count NS1 to 1 for the initial therapy sequence, adopts the cATP ramp decrement as the S2 ramp factor, and sets maximum number of ramp pulse count NS2_max for the dynamic therapy sequence equal to the total number of pulses of the successful cATP. If such initialization does not result in a termination of the tachycardia condition, subsequent therapy

[0094] 25.045P-WO / / 20.03.2026sequences may fall back to programmed defaults as described herein. Optionally, when the stored success stems from cATP, an automatic determination of the SI coupling factor rs may be applied for the initial therapy sequence.

[0095] Conventional anti-tachycardia pacing (cATP) is understood as the pre-programmed delivery of pacing pulses to terminate a reentrant tachycardia using fixed parameters chosen by the clinician in advance, typically without adapting those parameters in real time based on the patient’s response.

[0096] In a further embodiment, the IMD is configured to determine the initial S 1 count NS 1 for the first therapy sequence from a minimum duration constraint. Assuming the minimum duration constraint is at least 6*meanRRi, where meanRRi is the average of at least five pre -therapy RR intervals. With the coupling of the first SI pulse defined by the factor rs (RSI = rs TCL or equivalently rs- meanRRi in this context), the initial SI count is computed as NS1 = 6 / rs.

[0097] According to an embodiment of the present invention, the at least one therapy sequence TSi comprises a number of pulses Ni having a first inter-pulse-interval IPIi, that is followed by at least one further pulse S2. An inter-pulse-interval IPIis2 between the last pulse of the at least one Ni pulses and the at least one further pulse S2 is shorter than IPIi. In other words, the further pulse S2 is coupled to the last pulse of the Ni pulses by inter-pulse-interval IPIs2, that is shorter than IPIi. The control unit is configured to determine IPIis2 on the basis of the difference D and / or on the basis of the phase offset.

[0098] In an embodiment of the invention, the at least one therapy sequence TSi comprises a plurality of further pulses S2...Sn, wherein the inter-pulse-intervals IPIis2... IPIisn decrease in length. The control unit is configured to determine the lengths of the inter-pulse-intervals IPIis2... IPIisn on the basis of the difference D and / or on the basis of the phase offset.

[0099] For instance, the control unit is configured to determine the decrease in lengths by successively shortening each inter-pulse-interval IPIis2... IPIisn by a pre-determined time period or by a percentage value PV in relation to the preceding inter-pulse interval.

[0100] Said phase of at least one shorter pulse interval at the end of a therapy sequence is called the ramp phase. According to embodiments of the present invention, each therapy sequence includes a burst phase with equidistant inter-pulse intervals IPIi and, optionally, a so-called ramp phase in which one or more terminal inter-pulse intervals IPIis2 are progressively shortened relative to IPIi. In an exemplary embodiment, IPIi is constant over the burst phase, while the ramp phase shortens the terminal intervals

[0101] 25.045P-WO / / 20.03.2026according to a programmed S2 ramp factor. The counts NS1 (burst) and NS2 (ramp), along with IPIi, and the ramp factor, provide degrees of freedom for dynamically adapting therapy from attempt to attempt. According to an embodiment, the ramp factor refers to the percentage value PV, wherein the length of the inter-pulse interval from the preceding pulse to the S2 pulse is defined by the preceding inter-pulse interval times the ramp factor.

[0102] Furthermore, according to an embodiment of the present invention, the at least one therapy sequence TSi comprises a number of pulses Ni, wherein the control unit is configured to determine Ni on the basis of the phase offset and / or on the basis of the difference D.

[0103] According to an exemplary embodiment of the present invention, the control unit is configured to store in a memory unit the smallest number of pulses Ns of a therapy sequence TSs out of a number of therapy sequences n, wherein Ns leads to a longest post-pacing interval Pls between the last pulse of the therapy sequence TSs and a first detected intrinsic cardiac event after the last pulse of the therapy sequence out of a number n of post-pacing intervals.

[0104] Retaining the minimal effective pulse count that maximizes post-pacing interval allows the device to optimize therapy efficiency, reducing unnecessary stimulation while maintaining efficacy.

[0105] According to an embodiment, Ns is the number of SI pulses required for the therapy sequence to take control over the reentry — known in the scientific literature as entrainment.

[0106] If entrainment is detected, this fact is reported along with the corresponding therapy sequence parameters, for example:

[0107] - to the control unit, which takes this into account when configuring subsequent therapy sequences, - made available to external entities,

[0108] - stored for later processing or retrieval.

[0109] In particular, the value Ns is made available for further processing.

[0110] According to a further embodiment, when a Loss-of-Capture (LOC) scenario is recognized during a therapy sequence (e.g. if a post-pacing interval is shorter than the mean tachycardia cycle length TCLm and / or a negative post-pacing interval difference D beyond tolerance), a subsequent reset or re-initialization may use its starting configuration from the last parameter set preceding the LOC-positive therapy sequence. In doing so, the IMD preserves the most promising configuration

[0111] 25.045P-WO / / 20.03.2026discovered so far while avoiding the coupling aggressiveness that caused a LOC, and may additionally constrain initial inter-pulse intervals to be equal to or longer than the shortest intervals that did not cause the LOC condition.

[0112] For example, the IMD is configured such that a tachycardia condition is detected if the time intervals between the events have a tachycardia cycle length TCL shorter than a tachycardia threshold, and if the time intervals between the events fulfill at least one stability parameter.

[0113] This approach enhances detection accuracy by incorporating both timing and stability metrics, reducing false positives and ensuring appropriate initiation of therapy only during confirmed tachycardia episodes.

[0114] In an embodiment, the implantable device is configured to determine stability parameters such as a difference between a predetermined number of preceding tachycardia cycle lengths and a stability threshold value, a standard deviation, a dominant frequency derived from frequency analysis, or autocorrelation-based parameters to assess the stability consistency of tachycardia events before confirming a tachycardia condition.

[0115] According to an embodiment the tachycardia threshold is set to a value from the range of 100-250 bpm. For example, with higher tachycardia rates, multiple tachycardia thresholds can be programmed depending on the tachycardia rate, defining different tachycardia zones, as for instance:

[0116] Ventricular tachycardia (VT) zone 1 is defined as tachycardias equal to or greater than 150bpm.

[0117] VT zone 2 is defined as tachycardias equal to or greater than 187bpm.

[0118] VF zone 3 is defined as tachycardias equal to or greater than 222bpm.

[0119] In an embodiment, the control unit generates an inter-pulse interval that is shorter than the tachycardia cycle length of preceding cardiac events. This interval is defined either between pulses within a therapy sequence if multiple pulses are present or between the tachycardia pulse and the first pulse of the therapy sequence if only one pulse is delivered.

[0120] Implementing inter-pulse intervals shorter than the tachycardia cycle length improves the likelihood of successfully interrupting tachycardias, thereby enhancing therapy efficacy.

[0121] According to an aspect, the IMD is configured such that the relation parameter is a difference D between two successively measured post-pacing intervals Pli.

[0122] 25.045P-WO / / 20.03.2026Using the difference between two successively measured post-pacing intervals enables precise assessment of therapy impact, facilitating optimized adjustment of therapy sequences in response to real-time measurements of cardiac activity.

[0123] According to an embodiment, the IMD is configured such that the detection unit determines the phase offset if the time intervals between the first events and the time intervals between the second events have a similar length. A similar length is confirmed if a difference of an interval length of the time intervals between the first events and the interval length of the time intervals between the second events is smaller than a threshold difference.

[0124] In an embodiment, a similar length is confirmed if a difference between a mean interval length of the first events and a mean interval length of the second events is smaller than a threshold difference.

[0125] For example, the threshold difference is 10 ms.

[0126] For example, the IMD is configured such that the detection unit determines the phase offset by virtually continuing the first events by adding a plurality of estimated events in succession to the first events, the estimated events each having a first tachycardia cycle length TCL 1 to the preceding event. The detection unit further calculates an offset time interval between one estimated event and one neighboring second event. The detection unit further determines the phase offset based on the offset time interval in relation to the first tachycardia cycle length TCL1. Advantage: Virtual continuation with estimated events may enable a phase offset calculation referenced to the tachycardia cycle length. This may support consistent phase-offset computation for use in therapy sequence generation.

[0127] In an embodiment, the control unit confirms an entrainment condition of the previous therapy sequence if a phase offset exceeds a lower threshold or is less than an upper threshold, and stores the corresponding therapy parameters of the previous therapy sequence in a memory unit for future reference.

[0128] In an embodiment, the control unit generates a second therapy sequence based on the determined phase offset only when the phase offset falls within a specified percentage range of the initial tachycardia cycle length.

[0129] Restricting adaptation to a defined phase window avoids ambiguous timing results and supports consistent decisions. According to an embodiment, a normalized offset is checked whether it lies inside an allowed range before changing therapy parameters.

[0130] 25.045P-WO / / 20.03.2026In an embodiment, the percentage range used to determine the applicability of phase offset-based therapy adjustment is set between 10% and 90% of the initial TCL.

[0131] In an embodiment, the detection unit determines the phase offset between tachycardia events only when the first tachycardia cycle length, tied to the first tachycardia condition, and a second tachycardia cycle length, tied to the second tachycardia condition, are considered similar, facilitating meaningful comparison and therapy adjustment.

[0132] According to an embodiment, a similar tachycardia cycle length is confirmed if the difference between at least one interval length between two consecutive events of the first events and an interval length between two consecutive events of the second events is smaller than a threshold difference, or if the difference between a mean interval length of the first events and a mean interval length of the second events is smaller than a threshold difference. For example, the threshold difference is 10 ms.

[0133] In an embodiment, the similarity of tachycardia cycle lengths is defined as the difference between the first and second tachycardia cycle lengths being less than or equal to 10 milliseconds for phase offset determination.

[0134] In an embodiment, the detection unit computes the phase offset by measuring the interval between the last event of the first detected intrinsic cardiac events and the first event of the second detected intrinsic cardiac events, dividing this interval by the first tachycardia cycle length, and defining the remainder of this division as the offset time interval. The phase offset is then derived relative to the initial tachycardia cycle length.

[0135] Using the remainder of the division yields the same normalized phase regardless of how many full cycles elapse between windows. According to an embodiment, a modulo-based computation is simple and efficient for embedded processing.

[0136] According to an embodiment of the present invention, the phase offset PS is determined by an angle calculated by

[0137] PS = OTI / TCLl*2*7i

[0138] or

[0139] PS = (l-OTI / TCLl)*2*7i

[0140] whereby OTI is the offset time interval and TCL1 is the first tachycardia cycle length.

[0141] 25.045P-WO / / 20.03.2026Furthermore, according to an aspect of the invention, the tachycardia cycle length is a mean or median interval length which is determined across at least 3 events of the first events or the second events.

[0142] In an embodiment, the second therapy sequence includes the same number of electrical pulses as the first therapy sequence, plus one additional pulse. The inter-pulse intervals for the initial pulses are uniform, while the interval between the additional pulse and the last of the initial pulses is shorter if a non-zero phase offset is detected, or equal if the phase offset is zero. Adding one pulse and shortening only the terminal interval when a non-zero offset is present provides a minimal yet targeted change that increases the likelihood of effective interaction. According to an embodiment, the initial ipi is kept constant and the final interval selectively shortened when the measured phase offset indicates a therapeutic benefit.

[0143] According to an embodiment, the detection unit is configured to detect at least one intrinsic event of the heart in the sensed electrical signals during the delivery of the first therapy sequence, wherein the intrinsic event indicates that a tachycardia condition is present. The control unit is configured to generate at least a first parameter based on the intrinsic event. The control unit is configured to adjust the first therapy sequence based on the first parameter during the delivery of the therapy sequence, and / or to generate at least one second therapy sequence based on the first parameter.

[0144] The IMD according to the invention enables the detection of an intrinsic event during ATP delivery, followed by a dynamic adaptation of therapy based on the intrinsic event by adjustment of the first therapy sequence during delivery of the same, and / or by adjustment of the second therapy sequence. The solution according to the invention can lead to improved ATP therapy success by implementing a dynamic optimization of the inter-pulse interval (SISI or S1S2) interval and avoidance of progressing a lost entrainment, while increasing patient safety due to avoiding further tachycardia acceleration.

[0145] An intrinsic event may lead to acceleration of a tachycardia because the intrinsic excitation disrupts the intended entrainment, causing loss of ATP pacing control and fracturing of excitation fronts. This timing scenario allows the reentrant circuit to resume or even shorten its cycle length, enabling intrinsic tachycardia events to reappear more rapidly and potentially destabilizing the rhythm.

[0146] According to an embodiment of the present invention, the detection unit is configured to detect the intrinsic event via the first pair of electrode poles, or via a second pair of electrode poles. At least one

[0147] 25.045P-WO / / 20.03.2026electrode pole of the second pair of electrode poles is different from the electrode poles of the first pair of electrode poles, which provides flexibility in sensing configurations for detecting the intrinsic event.

[0148] According to an aspect of the invention, the first therapy sequence comprises a plurality of inter-pulse intervals. The control unit can be configured to adjust the first therapy sequence by prolonging at least one inter-pulse interval of the first therapy sequence. The prolonged inter-pulse interval immediately succeeds the intrinsic event. The prolonged inter-pulse interval is longer than the inter-pulse interval directly preceding the intrinsic event.

[0149] By adjusting the running therapy sequence, the chances of tachycardia termination can be increased immediately after detection of the intrinsic event.

[0150] According to an embodiment, the first therapy sequence comprises a plurality of inter-pulse intervals. The control unit can be configured to adjust the first therapy sequence by scheduling an electrical pulse that directly succeeds the intrinsic event such that the inter-pulse interval between the electrical pulse that is delivered directly prior to the intrinsic event and the electrical pulse that directly succeeds the intrinsic event is prolonged. The prolonged inter-pulse interval is longer than the inter-pulse interval that directly precedes the detection of the intrinsic event.

[0151] Said embodiment allows a controlled prolongation of that inter-pulse interval in which the intrinsic event occurs, which additionally increases the chances of tachycardia termination immediately after detection of the intrinsic event.

[0152] According to an aspect of the present invention, the second therapy sequence comprises a plurality of inter-pulse intervals. The control unit can be configured to adjust the second therapy sequence by prolonging at least one inter-pulse interval of the second therapy sequence. The prolonged inter-pulse interval of the second therapy sequence has a position in the second therapy sequence which is the same position as, the same position minus one, or the same position plus one as the position of the prolonged inter-pulse interval in the first therapy sequence. The prolonged inter-pulse interval of the second therapy sequence is longer than the inter-pulse interval of the first therapy sequence which directly precedes the detection of the intrinsic event.

[0153] The embodiment allows a consistent adjustment across therapy sequences using related interval positions, which increases the chances of tachycardia termination in following ATP attempts after delivery of the first therapy sequence.

[0154] 25.045P-WO / / 20.03.2026Moreover, according to an embodiment, the control unit is configured to cancel the delivery of the first therapy sequence if the detection unit detects the intrinsic event.

[0155] The detection of the intrinsic event indicates that a tachycardia condition has occurred is still persistent, which leads to the conclusion that the ongoing therapy sequence cannot effectively terminate the tachycardia. Moreover, the one or more intrinsic events disturb the stimulation timing of the ATP therapy sequences, i.e. the intrinsic event can cause a fracturing of the excitation fronts that are generated by the electrical pulses of the therapy sequence, that may cause a ventricular fibrillation in the heart. An immediate cancellation of the therapy sequence can prevent this scenario, and in addition, saves IMD battery life and time for therapy optimization.

[0156] In an embodiment of the present invention, the control unit is configured to generate the first and / or second therapy sequence such that it comprises at least a succession of inter-pulse intervals having a decreasing length. The control unit can be configured to generate no further decrease of an inter-pulse interval succeeding the detection of the intrinsic event.

[0157] Successively reducing the inter-pulse interval length, also called "ramp", until the intrinsic event occurs enables determining the shortest allowable inter-pulse interval that results effective an ATP therapy. If further shortening of inter-pulse intervals smaller than such boundary interval length is prevented, the effectiveness of the ATP therapy can be increased.

[0158] Moreover, according to an embodiment, the control unit is configured to generate at least one inter-pulse interval of the first therapy sequence or second therapy sequence that succeeds the detection of the intrinsic event. The at least one inter-pulse interval is of equal length or longer than the shortest interpulse interval that preceded the detection of the intrinsic event and which did not lead to detection of the intrinsic event.

[0159] By establishing that lower bound on inter-pulse intervals for the ATP therapy after the detection of the intrinsic event, the effectiveness of the succeeding ATP attempts can be increased.

[0160] According to an aspect of the present invention, the control unit is configured to store the inter-pulse interval which directly preceded the detection of the intrinsic event in a memory unit. The control unit can be configured to adjust at least one of the first, second or a further therapy sequence such that at least one inter-pulse interval of the therapy sequence is longer than the stored inter-pulse interval.

[0161] 25.045P-WO / / 20.03.2026For example, a group of said stored inter-pulse intervals is arranged at the beginning of at least one further therapy sequence, which may increase the chances for a fast termination of a tachycardia condition.

[0162] According to an aspect, a method for operating an implantable medical device IMD for stimulating a heart of a patient comprises detecting a first tachycardia condition based on a plurality of first events in an electrical signal of the heart. The method further comprises delivering a first therapy sequence TS 1 comprising at least one electrical pulse to the heart. The method further comprises storing a first therapy information, wherein the first therapy information is associated with at least one of: the first therapy sequence TS 1 , an IMD parameter, and a patient parameter around the time of delivery of the first therapy sequence TS 1. If a second tachycardia condition is detected based on a plurality of second events after delivery of the first therapy sequence TS1, the method further comprises generating a second therapy sequence TS2 based on the first therapy information.

[0163] By storing the therapy information and using it later for selection and / or parametrization of further therapy sequence (e.g. a second therapy sequence), a higher likelihood of tachycardia termination is enabled for the further ATP attempt. This allows an improved initialization of therapy sequences for later detected tachycardia conditions.

[0164] According to an aspect of the present invention, the at least one electrode pole can be assigned to different vectors for sensing signals of the heart and applying electrical pulses to the heart. Moreover, the detection unit is for instance configured to associate events to time points in the signals of the heart via trigger thresholds and morphological landmarks such as steepest slope, extrema, curvature -conditioned extrema, inflection points, or centroids. Tachycardia identification can further make use of morphological comparisons to reference patterns.

[0165] As an example, parameters subject to adjustment encompass the number of pulses, inter-pulse intervals, amplitude, polarity, pulse width, charge amount, and tilt, in addition to therapy sequence characteristics such as sequence count, total duration, and timing be-tween therapy sequences. Therapy sequences may differ or be repeated for confirmation measurement purposes. Time interval determination may utilize signals from identical or differing vectors or alternative physiological signals.

[0166] The described device and method apply to ventricular and / or atrial tachycardias, transvenous or non -transvenous ICDs, and implants or temporary devices that provide ATP therapy options.

[0167] 25.045P-WO / / 20.03.2026According to an embodiment, therapy information, post pacing intervals, relation parameters, phase offset values, tachycardia characteristics, and therapy parameters can be stored in the memory unit, read out via a programmer device, and transmitted remotely for further evaluation.

[0168] According to an embodiment of the present invention, the IMD is a cardiac pacemaker, an implantable cardioverter-defibrillator (ICD), a cardiac rhythm management therapy (CRT) device, or a conduction system pacing (CSP) device.

[0169] According to an aspect of the invention, assessments of the therapy information, post pacing intervals, relation parameters, phase offset and the derivation of therapy parameters may alternatively or additionally be performed by an external instance such as the programmer system or web / app-based platform, automatically or by trained clinical staff.

[0170] Features that are described in the context of separate aspects and embodiments of the invention may be used together and / or be interchangeable. Similarly, features described in the context of a single embodiment may also be provided separately or in any suitable subcombination.

[0171] DEFINITIONS

[0172] An observation window denotes a defined span of detected intrinsic events used to compute rate and stability before or after a therapy sequence.

[0173] The tachycardia cycle length (TCL) denotes the interval between consecutive intrinsic tachycardia events.

[0174] The stability measure (TCLs) denotes a classification based on whether recent inter-event intervals lie within a programmable tolerance band.

[0175] The coupling interval RSI denotes the delay from the last intrinsic event to the first SI pulse.

[0176] The burst interval SISI denotes the equidistant intra-burst inter-pulse interval.

[0177] The ramp intervals S1S2 and S2S2 denote terminal intervals that are progressively shortened relative to the preceding interval according to a ramp factor.

[0178] 25.045P-WO / / 20.03.2026NS 1 denotes the number of S 1 pulses in the burst and NS2 denotes the number of S2 pulses in the ramp.

[0179] The post-pacing interval denotes the time from the last pulse of sequence to the first subsequent intrinsic cardiac event sensed.

[0180] The PI difference D denotes the difference between consecutive valid post-pacing intervals.

[0181] The intermittent interval used for phase analysis denotes the interval from the last intrinsic event before a sequence to the first intrinsic event after the sequence.

[0182] The phase offset denotes the normalized displacement of post-therapy sequence intrinsic timing relative to a virtual continuation of the former tachycardia condition.

[0183] Entrainment denotes a state in which pacing captures and overdrives the reentrant circuit.

[0184] Loss of capture (LOC) denotes a condition inferred when the pacing pulse is delivered by a pacemaker / ICD but does not depolarize the myocardium.

[0185] Propagation time (PT) denotes the time from a delivered pulse to its arrival at a target area.

[0186] Similarity denotes a condition where current and stored therapy information match within programmed criteria.

[0187] The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:

[0188] Fig. 1 illustrates a schematic view of an implantable medical device interacting with a heart.

[0189] Fig. 2 shows a schematic of intrinsic rhythm, tachycardia detection, and delivery of a first ATP therapy sequence.

[0190] Fig. 3 shows an exemplary therapy sequence delivered during a tachycardia episode according to embodiments of the invention.

[0191] 25.045P-WO / / 20.03.2026Fig. 4 illustrates an embodiment for determining the stability measure TCLs by the detection unit at the time the stability check is executed.

[0192] Fig. 5a illustrates an exemplary succession of therapy sequences delivered along a continuous time axis during one tachycardia episode.

[0193] Fig. 5b depicts an exemplary sequence comprising four consecutive therapy sequences delivered along a continuous time axis according to embodiments of the invention.

[0194] Fig. 5c illustrates an exemplary view in which a therapy sequence for a current tachycardia episode is parametrized according to a prior therapy sequence that successfully terminated a prior tachycardia episode.

[0195] Fig. 6 illustrates an exemplary control flow diagram for the ATP therapy according to embodiments of the present invention.

[0196] Fig. 6a illustrates an exemplary control flow diagram for the ATP therapy based on the control flow diagram in Fig. 6. in which a therapy sequence for a current tachycardia episode may be parametrized according to a prior therapy sequence that successfully terminated a prior tachycardia episode.

[0197] Fig. 7 depicts an exemplary detailed view of evaluation step 700 executed by the implantable medical device according to embodiments of the present invention.

[0198] Fig. 8 depicts an exemplary detailed view of evaluation step 800 executed by the implantable medical device according to embodiments of the present invention.

[0199] Fig. 9 depicts an exemplary detailed view of evaluation step 900 executed by the implantable medical device according to embodiments of the present invention.

[0200] Fig. 9a depicts an exemplary detailed view of an embodiment of the workflow shown in Fig. 9, that includes the option to select an initial parameterization for a subsequent therapy sequence based on stored parameters from previous ATP attempts.

[0201] 25.045P-WO / / 20.03.2026Fig. 10 illustrates the improvement in therapy success rate achieved by the ATP therapy according to the present invention.

[0202] Before the present compositions, articles, devices, and / or methods are disclosed and described, it is to be understood that the aspects described below are not limited to specific methods as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and is not intended to be limiting.

[0203] For purposes of reading the description of the various implementations below, the following descriptions of the sections of the Specification and their respective contents may be helpful:

[0204] Figure 1 shows the implantable medical device 100 connected to a heart 110 via electrode poles 111. The implantable medical device consists of a stimulation unit 120, detection unit 130, control unit 140 and memory unit 150. These components are enclosed within the implantable medical device housing for device 100. Fig. 1 shows the stimulation unit 120 delivering electrical pulses to the heart 110 through the electrode poles 111, enabling detection of cardiac events via the detection unit 130. The detection unit 130 analyzes time intervals between cardiac events to recognize tachycardia conditions and feeds this information to the control unit 140. Fig. 1 shows the control unit 140 in a closed-loop configuration with the detection unit 130 and stimulation unit 120, allowing dynamic adjustment of therapy sequences based on real-time cardiac event analysis. The memory unit 150 stores parameters such as post-pacing intervals, contributing to therapy sequence adjustments. The control unit 140 might receive enhanced feedback from additional sensors or employ advanced algorithms to predict and adjust therapy sequences, optimizing therapy outcomes, and adapting to patient-specific needs.

[0205] The stimulation unit may deliver at least one therapy sequence TSi, 170, i being an index number. TSi 170 can be composed of two phases, a first burst phase 171 that is characterized by a number of equidistant stimulation pulses SISI, and a ramp phase 172, that is characterized by at least one pulse with a coupling interval that decreases in length to the previous inter-pulse-interval S1S2 / S2S2.

[0206] After a therapy sequence TSi has been delivered, the detection unit may determine:

[0207] ■ The post-pacing interval Pli between the last delivered pulse of TSi and the first sensed cardiac event thereafter,

[0208] ■ The difference D of post-pacing intervals for consecutively delivered therapy sequences, D = Pli - Pl(i-l); and

[0209] 25.045P-WO / / 20.03.2026■ The phase offset of the tachycardia before and after Pli, that may be induced or modified by the delivered therapy sequence.

[0210] Figure 2 shows a time -based schematic of intrinsic rhythm, tachycardia detection, and delivery of a first therapy sequence, along with the timing quantities used for algorithmic control. A baseline healthy rhythm exhibits a cycle length CL 209. A ventricular tachycardia (VT) then occurs with a tachycardia cycle length TCL 210, which is assessed within an observation window 210b to confirm onset and stability of the arrhythmia. Upon detection of a qualifying tachycardia, the implantable medical device delivers a therapy sequence 200 (a first therapy sequence TSi), which is coupled to the last detected intrinsic event via a coupling interval RSI 220. Successive pulses within the therapy sequence are separated by an intra-therapy sequence pulse interval SISI 230 (e.g., an inter-pulse-interval chosen as a fraction of the preceding TCL). This phase of equidistant pulse intervals of the therapy sequence is called the burst phase. Optionally, at least one last pulse of therapy sequence 200 can be separated by an inter-pulse interval 231 that is shorter than S 1 S 1 230. This phase of at least one shorter pulse interval at the end of a therapy sequence is called the ramp phase. If the therapy attempt is not yet successful, the tachycardia persists with a tachycardia cycle length TCL 211, which is again verified within a corresponding observation window 211b.

[0211] According to embodiments of the present invention, each therapy sequence includes a burst phase with equidistant inter-pulse intervals SISI and, optionally, a so-called ramp phase in which one or more terminal inter-pulse intervals S1S2 / S2S2 are progressively shortened relative to SISI. The therapy sequence is coupled to the last intrinsic tachycardia event via a coupling interval RSI, and parameters are conveniently normalized to the tachycardia cycle length: RSI = rs TCL with scaling factor 0.5 < rs < 1, and SISI = ipi TCL with ipi as inter-pulse-interval coupling factor and wherein ipi < rs. In preferred implementations SISI is constant over the burst, while the ramp phase shortens the terminal intervals according to a programmed S2 ramp factor. The counts NS1 (burst) and NS2 (ramp), along with RSI, SISI, and the ramp factor, provide principal degrees of freedom for dynamically adapting therapy from attempt to attempt. According to an embodiment, the ramp factor is a percentage value, wherein the length of the inter-pulse interval from the preceding pulse to the S2 pulse is defined by the preceding inter-pulse interval times the ramp factor.

[0212] In an example, a sliding observation window 242 can be utilized to determine a redetection of a tachycardia, for instance if x-out-of-y inter-pulse intervals fall below a below a programmed tachycardia zone threshold.

[0213] 25.045P-WO / / 20.03.2026Figure 3 shows a therapy sequence delivered along a continuous time axis during a tachycardia episode together with the observation windows and timing parameters used for analysis according to embodiments of the invention. Immediately prior to the therapy attempt, an observation window 210a is evaluated to confirm the rhythm and to determine the tachycardia cycle length TCL1 and a stability measure TCLs. In addition, a further observation window 350 ends at the first overlap with window 210a, providing additional context for estimating the ongoing tachycardia characteristics. For instance, the tachycardia is considered sufficiently stable if the difference between a mean tachycardia cycle length determined from the inter-pulse intervals from window 210a and a mean tachycardia cycle length determined from window 350 does not exceed a programmable threshold, e.g. 10ms. The value 301 designates the cycle length TCL1 determined in these windows. TCL1 can be a mean tachycardia cycle length TCLm.

[0214] The depicted therapy sequence comprises two phases. A first burst phase 171 contains a number NS1 of SI pulses that are equidistantly coupled relative to TCL1. The inter-pulse intervals of this burst are denoted 230 (SISI) and remain constant across the burst. According to one implementation, they are computed based on TCLm and a programmable SI coupling factor. A subsequent ramp phase 172 contains NS2 S2 pulses whose coupling intervals are successively shortened with respect to their immediate predecessors according to a ramp factor. The corresponding intervals are denoted 231 (S1S2 / S2S2) and decrease stepwise over the ramp. This two-portion structure allows the therapy to start with stable inter-pulse intervals and then tighten terminal coupling to increase the likelihood of interacting with the tachycardia circuit.

[0215] Following delivery of the last stimulus of the therapy sequence, the device identifies the first intrinsic event 360. The post-pacing interval 310 (PI) is measured as the time interval from the last delivered pulse of the series to this first intrinsic event 360. In parallel, the quantity 320 represents the intermittent interval between the last intrinsic event prior to the therapy sequence and the first intrinsic event after the therapy sequence. To support phase offset analysis, the device forms a virtual continuation 321 of the pre -therapy tachycardia at TCL1, extrapolating expected intrinsic event positions from the last pre -therapy intrinsic event. Based on the relationship between the intermittent interval 320 and TCL1 301, the device determines a phase offset 322 that represents the displacement of the post-therapy intrinsic timing relative to the virtually continued tachycardia. The phase offset can be expressed as a fraction or percentage of TCL1 (and, where useful, as an equivalent angular measure).

[0216] 25.045P-WO / / 20.03.2026After the therapy sequence, a post-therapy observation window 300a is evaluated to verify persistence of tachycardia, to reassess TCLm and TCLs under comparable conditions, and to validate the measurements for ATP therapy adaptation. When rhythm characteristics before and after ATP therapy are sufficiently similar, the combination of PI 310 and phase offset 322 provides a measure to the effectiveness of the therapy attempt.

[0217] Figure 4 illustrates an embodiment for determining the stability measure TCLs by the detection unit at the time the stability check is executed. The assessment is based on the most recent five detected cardiac events and thus the four immediately preceding inter-event intervals. Proceeding from the interval length of the current scenario 401, a tolerance band is spanned symmetrically around this interval; the band is delimited by an upper limit value 410a and a lower limit value 410b obtained by adding and subtracting, respectively, a programmable relative percentage of the last interval length — preferably within 4% to 30%, with 12% as a preferred value. The three direct predecessor interval lengths 402, 403, 404 are compared with this tolerance band: if all three he within the band, the rhythm is classified as stable in the sense of TCLs; if any one of them lies outside, the rhythm is classified as unstable. In the example shown, interval 403 falls outside the tolerance band, so the evaluation classifies the rhythm as unstable.

[0218] Figure 5a illustrates an exemplary succession of therapy sequences delivered along a continuous time axis during one tachycardia episode, in which the control unit incrementally adapts the pulse counts of a two-portion sequence comprising a burst phase 171 with equidistant SI pulses (inter-pulse interval SISI) and a ramp phase 172 with S2 pulses whose coupling intervals (S1S2 / S2S2) are progressively shortened according to a programmed ramp factor; all coupling is normalized to the tachycardia cycle length (TCL1 which is for instance TCLm) via RSI and an inter-pulse-interval coupling factor for consistency with the application terminology. In the initial series of attempts 171a / 172a 171b / 172a 171c / 172a , the device increases the number of SI pulses NS1 in the burst phase from attempt to attempt while keeping the ramp configuration unchanged at 172a; after each attempt, the detection unit derives the phase offset from the intermittent interval using a virtual continuation of the pre -therapy tachycardia at TCL1, and entrainment is confirmed when the phase offset lies within the programmed detection window, the smallest burst count that achieves entrainment being recorded as Ns (depicted at 171c / 172a). Once Ns has been found and entrainment continues to be confirmed, the strategy holds NS1 constant at Ns (thus the burst portion remains 171c) and escalates the number of S2 pulses NS2 in the ramp portion across subsequent attempts ( 17 lc / 172b, then 171c / 172c, and so forth) to intensify terminal coupling.

[0219] 25.045P-WO / / 20.03.2026Figure 5b depicts an exemplary sequence 501 comprising four consecutive therapy sequences 200a-200d delivered along a continuous time axis, beginning with recognition of tachycardia events 510 that trigger detection at time 500. Immediately prior to the first therapy sequence, the device evaluates observation window 210a (that for example comprises four inter-event intervals) to determine the initial tachycardia cycle length TCL initial, the mean tachycardia cycle length TCLm, and the stability measure TCLs, upon which the initial parameterization is applied with NS1 = 8 SI pulses in the burst and NS2 = 1 S2 pulse in the ramp phase (configuration 171a / 172a). The SISI inter-pulse intervals during the burst 171a are computed by the control unit using the programmed SI coupling factor referenced to TCLm from window 210. The terminal S1S2 interval (that is the coupling interval from the last SI pulse of the burst phase to the first S2 pulse from the ramp phase) in the ramp phase 172a is derived from the immediate preceding SISI via the programmed S2 ramp factor. After each delivered therapy sequence, at the first intrinsic event that follows the sequence (times 503a-503d), the device determines the post-pacing interval Pli, I being an index number, and its difference Di relative to the prior attempt (i.e., the difference D between two consecutive Pls), computes the phase offset using the intermittent interval and a virtual continuation of the pre -therapy rhythm, and performs validity checks as outlined for the next-attempt configuration (see e.g. Fig. 9). If the checks pass, the control unit obtains information as to whether entrainment was achieved and whether a loss-of-capture (LOC) scenario is indicated for the preceding therapy sequence. In the illustrated course, following 200a, the device continues to sense tachycardia and enters a redetection phase 503a (shown shortened), which for instance comprises at least eight intrinsic tachycardia events, typically more than twelve, in accordance with the device’s programmed redetection criterion. Because no entrainment is detected at 503a, the control strategy increases the burst count NS 1 by the programmed increment S l_Incr (here S l_Incr = 3) for the next attempt 200b, while the ramp remains consistent with the previous attempt. At 503b, entrainment is now recognized, yet tachycardia redetection still occurs (redetection phase 503b), so for 200c the device refreshes TCLm and TCLs from the new observation window 210c and keeps NS1 at the entrainment-achieving value Ns for the burst 171c, while increasing NS2 in the ramp 172c to intensify terminal coupling. After a further redetection in 503c, the device refreshes TCLm and TCLs from the new observation window 210d and delivers 200d analogously with the validated burst / ramp timing 17 ld / 172d (i.e. burst held at Ns, NS2 increased as permitted by limits). At 503d, the device senses a non-tachycardia event 511 at time 502, and the termination criterion (shown in shortened form, preferably an X-out-of-Y rule such as 5 of 12) is met so that 200d constitutes a successful ATP therapy for the episode, consistent with the adaptive evaluation and modification approach based on PI / D and phase -offset measurements according to embodiments of the invention.

[0220] 25.045P-WO / / 20.03.2026Figure 5c illustrates an example in which the IMD uses stored information from prior tachycardia episodes to generate the parameters for a therapy sequence for a current tachycardia episode . Preferably, the stored information originates from therapy sequences that successfully terminated a prior tachycardia episode. According to an example, such information is considered if an option “Start with last successful pulse series” is activated when programming the IMD. The upper portion of the figure schematically represents past tachycardia episodes 570 including an intrinsic tachycardia event progression and delivered pulse series 571, and further shows an observation window 210d immediately prior to a pulse series that ultimately terminated the tachycardia, wherein the terminating pulse series is represented by a burst portion 17 Id and a ramp portion 172d, followed by a non-tachycardia event 511 indicative of termination. In association with the observation window 210d, the figure further depicts a far-field signal segment 572 and example morphological signal metrics derived therefrom, including an area under a curve feature 573 and a peak-to-peak amplitude feature 574. The lower portion of the figure schematically represents a current tachycardia episode 580 including an intrinsic tachycardia event progression and delivered therapy 581, and further shows an observation window 210e prior to delivery of an initial therapy sequence, together with a corresponding far-field signal segment 582 and example morphological signal metrics including an area under a curve 583 and a peak-to-peak amplitude feature 584. As illustrated, the device compares at least one second therapy information associated with the current tachycardia episode from the observation window 210e to at least one stored first therapy information associated with a prior tachycardia episode e.g., from observation window 210d, that has terminated the prior tachycardia episode successfully. Upon determining a match between the first and the second therapy information, the stored parameter configuration of the stored therapy sequence from the prior successful termination can be selected as a starting configuration for the therapy sequence of the current tachycardia episode . This therapy sequence is represented by a burst portion 171 e and a ramp portion 172e corresponding to the prior successful burst and ramp portions 17 Id, 172d. According to an embodiment, only a part of the parameter configuration from the prior therapy sequence is selected to be applied for the therapy sequence for the current tachycardia episode.

[0221] Figure 6 illustrates an exemplary control flow diagram for the ATP therapy according to embodiments of the present invention. ATP is enabled through the programmer interface 600, which communicates the configuration to the implantable medical device. When a tachycardia condition is detected at 605, the control unit of the system confirms the rhythm characteristics (for example, tachycardia cycle length TCL or mean tachycardia cycle length TCLm and stability TCLs within an observation window) and selects dynamic ATP as the active therapy. The implantable medical device then sets initial parameters at 610, including, for example, the number of SI pulses NS1, the number of S2 pulses NS2 and any initial ramp factor, and selects at 615 the scaling factor rs that is a percentage value and that determines

[0222] 25.045P-WO / / 20.03.2026the coupling interval RS 1 and the inter-pulse intervals of the burst phase SISI relative to TCL or TCLm. According to further aspects, the initial parameterization for dynamic ATP can be derived from (i) a formerly successful configuration recorded for the same patient under comparable tachycardia characteristics, and / or (ii) a population-based parameter set obtained by comparing current tachycardia features to stored data from other patients, such that the control unit loads a closest-match initial set before the first attempt of a sequence. Prior to delivery, the device may perform a suitability check for phase offset determination and optionally skip a therapy sequence or avoid certain parameter combinations of a therapy sequence if the current configuration would likely yield ambiguous phase offset (e.g., unfavorable intermittent-interval timing relative to TCLm), thereby preserving the diagnostic value of the next attempt. With these values, the implantable medical device delivers an initial therapy sequence at 616, which comprises a burst phase with equidistant inter-pulse intervals SISI and, optionally, a ramp phase in which the terminal intervals S1S2 or S2S2 are successively shortened according to the programmed ramp factor. Furthermore, the stability criterion for the tachycardia can be checked in 616.

[0223] During and after delivery of the initial therapy sequence, the implantable medical device executes a next-step evaluation at 700. In 720, the implantable medical device checks for termination of the tachycardia and performs redetection using the programmed termination criterion (for example, an X-out-of-Y intrinsic-interval rule). A successful termination ends the flow at 690. If the tachycardia persists, the implantable medical device performs the following measurements at 750: It determines the post-pacing interval PI from the last pulse of the preceding ATP therapy sequence to the first intrinsic cardiac event, computes the difference D between two consecutive post-pacing intervals across consecutive attempts, and derives the phase offset from the intermittent interval using the pre-therapy TCL or TCLm and a virtual continuation of the prior tachycardia pulses. These metrics allow the implantable medical device to confirm entrainment when the phase offset lies within a programmed detection window and to detect loss of capture LOC (for example, by PKTCLm and / or a negative difference D beyond a tolerance), thereby distinguishing effective, entrainment-achieving configurations from LOC-prone configurations.

[0224] The results from step 750 are used in step 800 to modify the next therapy sequence. Depending on programmed limits, timeouts and rhythm changes, the outcome at 800 selects one of four actions: therapy sequence optimization (continuation with another adapted therapy sequence), reset (reload of the initial configuration within the same therapy module), switch (escalation to a higher-priority therapy module) or break (suspension of further ATP therapy sequences for the ongoing episode). A check in step 760 figures out if further ATP attempts will be taken into consideration. If continued ATP is no

[0225] 25.045P-WO / / 20.03.2026longer effective or permitted, the flow ends at 694. Otherwise, the process will continue with step 615, which has been explained previously. The results will be handed to step 900, in which the control unit adapts at least one timing or other therapy sequence parameter — such as RSI, NS1, NS2, SISI or the S2 ramp factor — based on the measured effects of the prior attempt. The term S2 ramp refers to a pacing strategy used in ATP therapy, wherein a extra pulse S2 is delivered following a sequence of primary pacing pulses S 1. In this approach, the coupling interval of the S2 pulse is progressively shortened across successive attempts, effectively “ramping” the timing closer to the estimated refractory period of the tachycardia circuit. The newly configured therapy sequence is then delivered at 650.

[0226] The post-pacing interval PI and a difference D in two consecutive post-pacing intervals across ATP attempts may be monitored to recognize LOC (for example by PI < TCLm and / or a negative difference D beyond tolerance). According to embodiments, the primary adaptation criterion remains the phase offset; PI and difference D serve as complementary diagnostics that help discriminate entrainment from configurations prone to loss of capture.

[0227] In an example, for modification of a subsequent therapy sequence, the control unit is configured to perform at least one of the following:

[0228] increase the number of S 1 pulses NS 1 if a loss of capture has been previously identified, increasing the number of S2 pulses NS2 by one if entrainment has been confirmed but termination of the tachycardia has not occurred,

[0229] reducing the S2 ramp factor to shorten ramp intervals for a more aggressive approach to terminate tachycardia in case no loss of capture occurred,

[0230] increasing the S2 ramp factor to lengthen ramp intervals when loss of capture is detected during the ramp phase,

[0231] lengthening RSI and the corresponding SISI slightly if loss of capture is attributed to overly short coupling of the burst pulses.

[0232] After each delivered therapy sequence, the loop proceeds by determining a next-attempt configuration at 900, unless termination conditions 690 or 694 apply.

[0233] Throughout the episode, the implantable medical device measures and records data at 695 — such as RSI, NS1, NS2, SISI and S1S2 / S2S2 values, PI, difference D, phase offset and the determinations of entrainment and LOC — for later retrieval and analysis.

[0234] 25.045P-WO / / 20.03.2026Figure 6a illustrates an embodiment of the workflow in Figure 6. It shows an exemplary control flow in which the IMD, upon detection of a tachycardia condition, conditionally generates an initial therapy sequence using a stored parameter configuration associated with a prior successful termination. As shown, a programming device / programmer interface 600 activates the ATP therapy and transmits programmed parameters to the IMD, and the IMD detects a tachycardia condition for which ATP therapy is to be applied in step 605. In an initialization step 610, the IMD sets initial parameters for the initial therapy sequence and, as part of this initialization, checks whether an option “Start with last successful pulse series” is activated in step 660. If the option is activated, the device performs a selection process 661 to identify a suitable stored configuration for the initial therapy sequence and determines whether a suitable configuration is identified in 662. If no suitable configuration is identified or if the option is not activated, the IMD applies programmed initial parameters as global defaults for the initial therapy sequence in step 663. Otherwise, the IMD applies initial parameters based on the selected stored configuration in 664. The device then selects at 615 the scaling factor rs as described previously and delivers the initial therapy sequence in 616. Thereafter, the IMD executes a next-step evaluation 700 including a termination check 720, and, if termination is detected, ends with success in 690. If the tachycardia condition persists, the IMD performs measurements 750 and executes redetection-time checks and therapy sequence modification decisions in 800, including a check whether further therapy sequences are meaningful or allowed 760, and either ends by break 694 or proceeds via next-attempt configuration 900 to deliver a next therapy sequence in 650. The figure further indicates recording of therapy information 695 (for example information for each therapy sequence regarding the number of pulses NS1, number of pulses NS2, SI coupling factor, S2ramp factor, and so forth, and information regarding the last series of therapy sequences in a list, as e.g. a number of therapy sequences in a series, a number of therapy sequences with recognized entrainment, LOC occurrence frequency, and the like).

[0235] Figure 7 depicts an exemplary detail view of evaluation step 700 executed by the implantable medical device to determine the next step during or after an ongoing ATP therapy sequence. The flow begins at 701 after a previously delivered therapy sequence and the associated sensing of cardiac events. Immediately thereafter, the implantable medical device checks for termination and performs redetection at 720 using the programmed termination criterion (for example, an X-out-of-Y intrinsic-interval rule). A successful termination ends the flow at 690. If the tachycardia persists, and if the implantable medical device has performs the measurements at 750 (see Figure 6), the implantable medical device applies the step for modification of the next therapy sequence at 800. In 800, two sets of checks are applied: limit checks 810 and rhythm checks 820.

[0236] 25.045P-WO / / 20.03.2026In the limit checks 810, the implantable medical device verifies whether predefined therapy constraints or safety conditions have been reached for the ongoing sequence. Such conditions can include a programmed maximum number of therapy sequences for the sequence, a maximum elapsed time since the initial detection of the tachycardia, or a previously recorded delivery of a shock therapy within the same episode. Further limits can reflect loss-of-capture (LOC) detections across consecutive attempts, parameter cappings reached in the preceding therapy sequence (for instance minimum allowable inter-pulse intervals in the burst or ramp phase, or a cap on the scaling factor rs that defines the coupling interval RSI), or other device-specific constraints that render a further ATP attempt impractical or inadvisable.

[0237] In the rhythm checks 820, the implantable medical device assesses whether the present tachycardia is still suitable for continuation with dynamic ATP under the assumptions of the current therapy module. To this end, the implantable medical device compares the mean tachycardia cycle length TCLm measured immediately prior to the last therapy sequence with the initial TCLm of the sequence to detect substantial changes in tachycardia cycle length, and it verifies continued stability TCLs within the observation window. Additionally, the implantable medical device can test a minimum TCLm criterion to exclude rhythms that are too fast for safe and effective ATP delivery under the current settings.

[0238] Checks 810 and 820 are followed by decision step 760 for termination of further ATP attempts and subsequent steps according to Figure 6.

[0239] Figure 8 depicts an exemplary detailed view of evaluation step 800 that determines whether another ATP therapy sequence is delivered and, if so, under which constraints. The process is entered at the step for modification of the next therapy sequence 800 once the implantable medical device has completed redetection and measurements (including PI, difference D and phase offset). Within 800, a first group of limit checks 810 determines whether configured therapy boundaries or safety conditions have been reached. In one exemplary check, the implantable medical device determines at 811 whether the programmed maximum number of pulses for the current therapy sequence would be exceeded by issuing a further attempt. Alternatively or in addition, the implantable medical device determines at 811 whether the programmed maximum number of therapy sequences would be exceeded by issuing a further attempt. Fulfilment of this condition contributes a potential outcome of switch for the resolution in 800. At 812, a timer started with initial tachycardia detection is compared against a programmed maximum; if the maximum time is exceeded and a shock therapy is configured as a follow-up, the implantable medical device marks a potential break so that no further ATP attempts are issued in the ongoing episode. At 813, the implantable medical device tests for a programmable count of consecutive attempts

[0240] 25.045P-WO / / 20.03.2026with detected loss of capture (LOC). The satisfaction of this condition results a potential switch. At 814, the implantable medical device inspects whether the immediately preceding therapy sequence had to be limited by any of the programmed parameter bounds — such as reaching a maximum number of S 1 pulses NSlmax in the burst phase, reaching a minimum allowable inter-pulse interval SISI in the burst phase Tmin_burst, or reaching a minimum allowable inter-pulse interval S1S2 / S2S2 in the ramp phase Tmin ramp. If any of such limitations is present, switch is recorded as a potential outcome. At 815, the implantable medical device applies additional limitation checks for the preceding therapy sequence: For example, ramp-phase intervals must not exceed those of the burst phase, the scaling factor rs must not fall below a programmed maximum relative share of TCLm (ensuring the coupling interval RSI remains capable of capturing myocardium toward the reentry circuit), and the S2 ramp factor is bounded above by a programmed maximum to ensure successive shortening. If any of these constraints is met, a potential switch is indicated, whereas certain configurations can also mark a potential break when ATP would be weaker than a therapy already delivered. At 816, if shock therapy has already been delivered in the current episode, the implantable medical device records a potential break to prevent issuing a weaker therapy thereafter. Finally, at 817, if a previous comparable therapy modality caused a significant acceleration of the rhythm (for example a change from a VT zone into a VF zone), a potential switch is recorded.

[0241] A second group of rhythm checks 820 assesses whether rhythm characteristics of the present tachycardia remains suitable for ATP under the assumptions of the current invention. In 821 , the implantable medical device compares the mean tachycardia cycle length TCLm immediately prior to the most recent therapy sequence with the initial TCLm of the ongoing sequence. Exceeding programmed relative and / or absolute deviation limits indicates a substantial rhythm change and results in a potential reset. In 822, the implantable medical device evaluates stability (for example TCLs within limits in the observation window). Failure of the stability test also contributes to a potential reset. In 823, the implantable medical device verifies that TCLm does not fall below a programmed minimal value. In case the minimal value criterion is not fulfilled, a potential break is recorded to exclude rhythms that are too fast for safe and effective ATP delivery under the current settings.

[0242] Once all checks in 810 and 820 have been applied, the process proceeds to the resolution stage beginning at 801, where the outcomes of the previous steps is reduced to a single action. If at least one potential break is present, 830 resolves the result of 800 to break, and the episode leads to 694 so that no further ATP therapy sequences are attempted in the ongoing episode. If no break is present but at least one potential switch is present, 831 resolves the result of 800 to switch and the control continues to 890, where a higher-priority therapy module is selected. If neither break nor switch applies but at least one

[0243] 25.045P-WO / / 20.03.2026potential reset is present, 832 resolves the result of 800 to reset and the control advances to 891, where the initial parameterization for the current therapy module is reloaded and a new therapy sequence is started. If none of the conditions applies, the default outcome of 800 is sequence optimization, forwarded to 892, whereby the implantable medical device continues the ongoing therapy sequence with another adapted therapy sequence whose configuration is to be determined under the next-attempt configuration step (see 900).

[0244] Figure 9 depicts an exemplary detailed view of the next-attempt configuration 900 executed after each delivered therapy sequence.

[0245] Coming from step 892, the process begins with a validity check at 901, in which the implantable medical device confirms that the post-pacing interval PI can be determined from the last pulse of the preceding therapy sequence to the first intrinsic cardiac event and that the sensing context is suitable for using PI and related quantities (for example first event is intrinsic, not paced). When the basic prerequisites are met, the implantable medical device evaluates loss of capture (LOC) in 905-907. In 906, LOC is detected if PI is shorter than TCLm, which indicates that the last pulse encountered refractory tissue and failed to advance the rhythm. In 907, LOC may alternatively (or additionally) be inferred by a negative difference D between two consecutive post-pacing intervals beyond a programmed tolerance, computed from the difference between the current PI and the PI of the preceding attempt, provided both PI values are valid. These complementary criteria allow robust recognition of LOC both from absolute post-pacing timing and from the trend across consecutive attempts.

[0246] In parallel, the implantable medical device derives and validates the phase offset at 910. To this end, the control unit determines the intermittent interval between the last intrinsic event prior to the preceding therapy sequence and the first intrinsic event thereafter, virtually continues the pre -therapy tachycardia using TCL or TCLm, and computes the phase offset as the deviation (offset time interval) between the expected and the observed event positions. A validity evaluation ensures that the mean tachycardia cycle length TCLm measured in the observation window prior to the last therapy sequence is sufficiently similar to that of the subsequent observation window, i.e. TCLm of the observation window before the last therapy sequence does not deviate from that of the subsequent window by more than a programmed margin, so that the phase offset reflects a comparable rhythm. When valid, phase offset values within a programmable phase window, for example 10% < phase offset < 90%, are treated as evidence of entrainment by the preceding therapy sequence, whereas values near 0% or 100% (or outside the window) indicate absent entrainment or ambiguity and prompt adaptation.

[0247] 25.045P-WO / / 20.03.2026Before selecting concrete modifications, the algorithm may consult a proximity check at 915 to determine whether the number of S2 pulses NS2 used in the preceding therapy sequence was already near a programmed maximum (for example NS2max - 1).

[0248] Based on the measurement outcomes and limit checks, the control unit generates the parameter set for the next therapy sequence using the adaptation steps at 920-924. If entrainment has not yet been achieved, the implantable medical device increases the number of SI pulses in the burst phase at 920 by adding a programmed increment to NS1, thereby improving the likelihood that successive stimuli capture myocardium toward the reentry circuit. If entrainment is present but termination has not occurred and additional aggressiveness in the terminal part of the therapy sequence is warranted, the implantable medical device increases the number of S2 pulses at 921. When the ramp requires stronger shortening to interact with the reentrant circuit, the implantable medical device reduces the S2 ramp factor at 922 so that the S1S2 / S2S2 intervals become successively shorter. Conversely, when LOC is detected during the ramp while entrainment is otherwise present, the implantable medical device relaxes the ramp by increasing the ramp factor at 923, thereby lengthening S1S2 / S2S2 to avoid refractory collisions. If LOC is attributed to coupling that is too aggressive already in the burst, the implantable medical device slows the burst coupling at 924 by increasing the scaling factor rs, which lengthens RS 1 and the ensuing SISI so that capture is re-established without abandoning the closed-loop strategy.

[0249] The measurement of the PI and the phase offset to evaluate the effectiveness of the ATP can be used in combination, parallel or as alternatives. That may have consequences to the available parameters for evaluation of the ATP success and thus modification means for subsequent therapy sequences.

[0250] Finally, coming from step 890, which resolves the result of 800 to switch, the algorithm checks whether the therapy plan foresees ATP as the succeeding higher therapy module at 940. If so, the implantable medical device may select the initial parameterization of that module at 941 to configure the next attempt and continues to the initialization logic 610. When a redetection-time outcome indicates a reset 891, the device likewise continues to the initialization logic 610. That may be a pre-programmed configuration for the purpose of applying ATP as escalation therapy measure. As one step of the initialization, selection of the scaling factor rs as described previously at 615 is performed. The parameter set produced by the logic of Figure 9 is then handed to the delivery step of the main flow (see Figure 6), ensuring that each subsequent therapy sequence reflects the latest PI, difference D and phase offset evidence together with applicable limits.

[0251] 25.045P-WO / / 20.03.2026Figure 9a illustrates an embodiment of the next-attempt configuration in Figure 9. Coming from step 890, which resolves the result of 800 to switch, the algorithm checks whether the therapy plan foresees ATP as the succeeding higher therapy module at 940. If so, the IMD may select the initial parameterization of that module at 941 to configure the next attempt and continues to the initialization logic 610. When a redetection-time outcome indicates a reset 891, the device likewise continues to the initialization logic 610. In 610, a check is performed whether the option “Start with last successful pulse series” is activated 660. Then, a suitable stored configuration is selected in 661, and depending on whether a suitable configuration could be selected in 662, global defaults 663 or the selected stored configuration 664 are applied, before continuing with subsequent selection the scaling factor rs as described previously at 615 and delivering the initial therapy sequence in 616, and proceeding with subsequent delivery of a pulse series 650.

[0252] Figure 10 illustrates the improvement in therapy success rate achieved by the ATP therapy according to the present invention. It shows two graphs that each depict therapy success rates: Graph 1001 represents the success rate of a therapy sequence including a burst and a ramp phase, with S 1 pulses followed by at least one S2 pulse and including feedback / adaptation mechanisms according to embodiments of the invention — Graph 1002 represents the success rate of a therapy sequence that delivers only SI pulses without feedback and merely increments the pulse count between attempts. The ordinate shows the success rate (0... 1), while the abscissa shows ca_mod, a dimensionless measure of the repolarization behavior of diseased cells in the isthmus of an infarct. Across the investigated ca_mod range, the curve for the ATP therapy according to the intention (S 1BS2R, i.e. S l-then-S2-ramp) rises earlier and reaches a higher plateau — approaching unity in the upper ca mod range — whereas the SI -only approach exhibits delayed onset and clearly lower success throughout most of the domain.

[0253] 25.045P-WO / / 20.03.2026REFERENCE NUMERAL LIST

[0254] 100 Implantable medical device (IMD)

[0255] 110 Heart

[0256] 111 Electrode pole(s)

[0257] 120 Stimulation unit

[0258] 130 Detection unit

[0259] 140 Control unit

[0260] 150 Memory unit

[0261] 170 Therapy sequence TSi

[0262] 171a-e Burst phase

[0263] 172a-e Ramp phase

[0264] 200 Therapy sequence

[0265] 200a Therapy sequence (example course)

[0266] 200b Therapy sequence (example course)

[0267] 200c Therapy sequence (example course)

[0268] 200d Therapy sequence (example course)

[0269] 209 Baseline cycle length CL

[0270] 210 Tachycardia cycle length TCL

[0271] 210a Pre-therapy observation window

[0272] 210b Observation window for confirming tachycardia

[0273] 210c Observation window prior to a later attempt

[0274] 210d Observation window prior to last attempt before tachycardia termination Observation window prior to the initial therapy sequence of the current 210e tachycardia episode

[0275] 211 Tachycardia cycle length after an attempt

[0276] 211b Post-attempt observation window

[0277] 212 First detected intrinsic cardiac event

[0278] 220 Coupling interval RS 1

[0279] 230 Inter-pulse interval SISI (burst)

[0280] 231 Inter-pulse interval S1S2 / S2S2 (ramp)

[0281] 240 Post-pacing interval PI

[0282] 242 Sliding observation window for redetection criterion

[0283] 300a Post-therapy observation window

[0284] 301 TCL1 / TCL initial

[0285] 25.045P-WO / / 20.03.2026Second therapy sequence TS2

[0286] Post-pacing interval PI

[0287] Post-pacing interval PI

[0288] Intermittent interval

[0289] Virtual continuation of pre -therapy tachycardia Phase offset

[0290] a First detected intrinsic cardiac event (alternate label) Additional pre-therapy observation window

[0291] First intrinsic cardiac event after a therapy sequence Current interval length

[0292] Predecessor interval length

[0293] Predecessor interval length

[0294] Predecessor interval length

[0295] a Upper limit of tolerance band

[0296] b Lower limit of tolerance band

[0297] Detection time

[0298] Block comprising four consecutive therapy sequences Detection time

[0299] a Redetection phase / first-event marker after sequence b Redetection phase / first-event marker after sequence c Redetection phase / first-event marker after sequence d Redetection phase / first-event marker after sequence Recognized tachycardia events triggering detection Non-tachy cardia event

[0300] Past tachycardia episodes

[0301] Delivered pulse series within past tachycardia episodes Far-field signal segment

[0302] Area-under-the-curve morphological metric

[0303] Peak-to-peak amplitude morphological metric Current tachycardia episode

[0304] Delivered therapy during the current episode Far-field signal segment

[0305] Area-under-the-curve morphological metric

[0306] Peak-to-peak amplitude morphological metric Programmer interface

[0307] 25.045P-WO / / 20.03.2026Tachycardia detection step

[0308] Set initial parameters

[0309] Scaling factor rs

[0310] Deliver initial therapy sequence

[0311] Deliver newly configured therapy sequence

[0312] Activation step „Start with last successful pulse series”

[0313] Selection process to identify a suitable stored configuration for the initial therapy sequence

[0314] Identification of suitable configuration

[0315] Application of initial parameters as global defaults

[0316] Application of initial parameters based on the selected stored configuration Termination (successful)

[0317] End (no further ATP)

[0318] Data logging / storage

[0319] Next-step evaluation

[0320] Entry to evaluation after sequence

[0321] Termination / redetection check

[0322] Measurements: PI, D, phase offset

[0323] Decision to continue ATP attempts

[0324] Modification step for next sequence (resolution)

[0325] Beginning of resolution stage

[0326] Limit checks

[0327] Check max pulses / sequences (potential switch)

[0328] Max elapsed time (potential break)

[0329] Consecutive loss-of-capture (LOC) attempts (potential switch) Parameter bound hit (potential switch)

[0330] Additional limits (potential switch / break)

[0331] Shock already delivered (potential break)

[0332] Significant acceleration (e.g., VT^VF) (potential switch)

[0333] Rhythm checks

[0334] TCLm change check (potential reset)

[0335] Stability check (potential reset)

[0336] Minimum TCLm check (potential break)

[0337] Resolve to break

[0338] Resolve to switch

[0339] 25.045P-WO / / 20.03.2026832 Resolve to reset

[0340] 890 Select higher-priority therapy module

[0341] 891 Reload initial parameterization

[0342] 892 Sequence optimization

[0343] 900 Next-attempt configuration

[0344] 901 Validity check for Pl / sensing context

[0345] 905 LOC evaluation block

[0346] 906 LOC by PI < TCLm

[0347] 907 LOC by negative D beyond tolerance

[0348] 910 Derive & validate phase offset

[0349] 915 proximity check (NS2 near max)

[0350] 920 Increase NS1

[0351] 921 Increase NS2

[0352] 922 Reduce S2 ramp factor

[0353] 923 Increase S2 ramp factor

[0354] 924 Increase rs (lengthen RS1 & S1S1)

[0355] 940 Check if succeeding module is ATP

[0356] 941 Select initial parameterization of succeeding module

[0357] 1001 Constant-mode RS 1 coupling factor line

[0358] 1002 'Aggressive' preset curve

[0359] 1003 AUTO rs(TCLm) curve

[0360] 1004 'Offset' preset curve

[0361] 1001 Success-rate curve: Sl+S2-ramp with feedback / adaptation (S1BS2R) 1002 Success-rate curve: SI -only (no feedback)

[0362] 25.045P-WO / / 20.03.2026

Claims

Claims1. Implantable medical device (IMD, 100) for anti-tachycardia pacing (ATP) of a heart (110) of a patient, comprising:- at least one electrode pole (111) configured to sense electrical signals of the heart (110) and apply electrical pulses to the heart,- a stimulation unit (120), configured to deliver the electrical pulses to the heart (110) via the electrode pole (111), wherein the stimulation unit is configured to deliver at least one therapy sequence (200) to the heart, the therapy sequence (200) comprising at least one electrical pulse,- a detection unit (130), configured to detect events in the sensed electrical signals, to analyze time intervals between the events, and to detect a tachycardia condition based on the events,- a control unit (140), configured to generate the at least one therapy sequence (200) and to derive at least one parameter to adjust the therapy sequence (200) based on the events, - a memory unit (150),characterized in thatthe stimulation unit (120) is configured to deliver a first therapy sequence TS1 to the heart (110) if the detection unit (130) detects a first tachycardia condition based on a plurality of first events,wherein the control unit (140) is configured to store a first therapy information in the memory unit (1 0), wherein the first therapy information is determined around the time of delivery of the first therapy sequence TS1,and if the detection unit (130) detects a second tachycardia condition based on a plurality of second events after delivery of the first therapy sequence TS1, the control unit (140) is configured to generate a second therapy sequence TS2 (302) based on the first therapy information.

2. IMD (100) according to claim 1, wherein the control unit (140) is configured to generate the second therapy sequence TS2 (302) such that at least one therapy parameter of the second therapy sequence TS2 (302) is equal to at least one therapy parameter of the first therapy sequence TS 1.

3. IMD (100) according to at least one of the claims 1 or 2, wherein the control unit (140) is configured to generate the second therapy sequence TS2 (302) based on the first therapy25.045P-WO / / 20.03.2026information if the first therapy information is sufficiently similar to at least one second therapy information, wherein the second therapy information is determined prior to the time of the planned delivery of the second therapy sequence TS2 (302).

4. IMD (100) according to at least one of the preceding claims, wherein the first therapy information and / or the second therapy information is based on at least one of:- sensed electrical signals,- events in the sensed electrical signals,- time intervals between the events,- a tachycardia condition based on the events,- one sensor of the IMD,- one programming parameter, and- a physiological patient parameter.

5. IMD (100) according to at least one of the preceding claims, wherein the first therapy information and / or the second therapy information comprises at least one of:a mean cardiac cycle length,a stability of a cardiac rhythm,a morphological signal metric derived from the sensed electrical signal, an impedance value,a patient posture,a mean heart rate, anda patient activity level.

6. IMD (100) according to claim 5, wherein the morphological signal metric comprises at least one of:a wave difference vector,a peak-to-peak amplitude (574, 584),a width of a QRS complex, andan area under a curve (573, 583).

7. IMD (100) according to at least one of the preceding claims, wherein the control unit (140) is configured to store the first therapy information if- the delivery of the first therapy sequence TS1 resulted in a termination of the first tachycardia condition for at least a predetermined time, or if25.045P-WO / / 20.03.2026- the delivery of the first therapy sequence (200) resulted in detection of an entrainment condition.

8. IMD (100) according to claim 7, wherein an entrainment condition is detected if the first therapy sequence (200) succeeded in capturing the heart (110).

9. IMD (100) according to at least one of the previous claims, wherein the control unit (140) is configured to store a ranking of delivered therapy sequences and / or of a delivered series of therapy sequences in the memory unit (150), wherein the ranking is based on at least one of:- a success rate for termination of a tachycardia,- a time until termination of a tachycardia,- a number of electrical pulses of a therapy sequence (200),- a battery consumption level,- a time elapsed since delivery of a delivered therapy sequence,and wherein the stimulation unit (120) is configured to deliver at least one following therapy sequence (200) based on the ranking.

10. IMD (100) according to at least one of the preceding claims, wherein the detection unit (130) is configured to determine a first post-pacing interval PI1 (240) between the last delivered pulse of the first therapy sequence TS1 and a first detected intrinsic cardiac event (212) after the last delivered pulse of the first therapy sequence TS 1,wherein the stimulation unit (120) is configured to deliver a second therapy sequence TS2 (302) to the heart (110),and if the detection unit (130) detects a third tachycardia condition based on a plurality of third events after delivery of the second therapy sequence TS2 (302), the detection unit is configured todetermine a second post-pacing interval PI2 (240) between the last delivered pulse of the second therapy sequence TS2 (302) and a first detected intrinsic cardiac event (212) after the last delivered pulse of the second therapy sequence TS2 (302),wherein the control unit (140) is configured to compute a first relation parameter RP1 between PI1 and PI2, wherein the control unit is configured to generate a third therapy sequence (200) TS3 depending on the first relation parameter RP1, and / ordetect at least one phase offset (322) between the first events and the second events, and / or between the second events and the third events, wherein the control unit (140) is25.045P-WO / / 20.03.2026configured to generate the second therapy sequence TS2 (302) and / or the third therapy sequence (200) TS3 based on the phase offset (322).

11. IMD (100) according to at least one of the preceding claims, wherein a tachycardia condition is detected if- the time intervals between the events have a tachycardia cycle length TCL (210) shorter than a tachycardia threshold, and if- the time intervals between the events fulfill at least one stability parameter.

12. IMD (100) according to claim 10 or 11, wherein the relation parameter is a difference D between two successively measured post-pacing intervals Pli.

13. IMD (100) according to at least one of the claims 10 to 12, wherein the detection unit (130) is configured to determine the phase offset (322) if the time intervals between the first events and the time intervals between the second events have a similar length, wherein a similar length is confirmed if a difference of an interval length of the time intervals between the first events and the interval length of the time intervals between the second events is smaller than a threshold difference.

14. IMD (100) according to at least one of the claims 10 to 13, wherein the detection unit (130) is configured to determine the phase offset (322) by- virtually continuing the first events by adding a plurality of estimated events in succession to the first events, the estimated events each having a first tachycardia cycle length TCL1 (301) to the preceding event,- calculate an offset time interval between one estimated event and one neighboring second event,- determine the phase offset (322) based on the offset time interval in relation to the first tachycardia cycle length TCL1 (301).

15. Method for operating an implantable medical device (IMD, 100) for stimulating a heart (110) of a patient, characterized by the following steps:- detect a first tachycardia condition based on a plurality of first events in an electrical signal of the heart (110),- deliver a first therapy sequence TS 1 comprising at least one electrical pulse to the heart (HO),25.045P-WO / / 20.03.2026- store a first therapy information, wherein the first therapy information is associated with at least one of: the first therapy sequence TS1, an IMD parameter, and a patient parameter around the time of delivery of the first therapy sequence TS 1,- if a second tachycardia condition is detected based on a plurality of second events after delivery of the first therapy sequence TS1, generate a second therapy sequence TS2 (302) based on the first therapy information.25.045P-WO / / 20.03.2026

Images