Anti-tachycardia pacing implantable medical device

Abstract

An implantable medical device (IMD) and method for anti-tachycardia pacing of a heart is described. The IMD comprises at least one electrode pole that senses electrical signals and delivers electrical pulses to the heart. A stimulation unit applies therapy sequences consisting of electrical pulses, while a detection unit analyzes sensed signals to identify tachycardia conditions based on tachycardia cycle lengths from detected events. Upon identification of a first tachycardia condition, the implantable medical device delivers a first therapy sequence. If a subsequent tachycardia condition is detected with a second tachycardia cycle length, the detection unit determines a phase offset between the initial and subsequent detected events. Based on this phase offset, a control unit generates a second therapy sequence tailored to the detected offset and delivers it via the stimulation unit. The IMD adapts therapy in real time by measuring the phase offset created by the first therapy sequence and using that information to shape the next therapy sequence. This shortens the path to an effective ATP configuration and can reduce repeated ineffective attempts.

Description

[0001] Anmelder: BIOTRONIK SE & Co. KG

[0002] Datum: 11.03.2026

[0003] Unser Zeichen: 23.163P-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 asan atrial tachyarrhythmia being greater than or equal to a first detection threshold. The processor is configured to 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] In an embodiment, an implantable medical device (IMD) for ATP of a heart comprises at least one electrode pole that senses electrical signals and delivers electrical pulses to the heart. A stimulation unit applies therapy sequences consisting of electrical pulses, while a detection unit analyzes sensed signals to identify tachycardia conditions based on tachycardia cycle lengths from detected events. Upon identification of a first tachycardia condition, the implantable medical device delivers a first therapy sequence. If a subsequent tachycardia condition is detected with a second tachycardia cycle length, the detection unit determines a phase offset between the initial and subsequent detected events. Based on this phase offset, a control unit generates a second therapy sequence tailored to the detected offset and delivers it via the stimulation unit.

[0012] The IMD adapts therapy in real time by measuring the phase offset created by the first therapy sequence and using that information to shape the next therapy sequence. This shortens the path to an effective ATP configuration and can reduce repeated ineffective attempts.

[0013] In an embodiment of the IMD according to the invention, a tachycardia condition is detected if:

[0014] The time intervals between the events have a tachycardia cycle length (TCL) shorter than a tachycardia threshold, and

[0015] The time intervals between the events fulfill at least one stability parameter.

[0016] 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.Combining a fast TCL with stability reduces false detections and ensures the therapy targets sustained tachycardia. According to embodiments, tachycardia cycle lengths are calculated in defined windows and interval stability is verified before delivering ATP and before evaluating phase offset.

[0017] 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:

[0018] Ventricular tachycardia (VT) zone 1 is defined as tachycardias equal to or greater than lOObpm, preferably greater than 150bpm.

[0019] VT zone 2 is defined as tachycardias equal to or greater than 187bpm.

[0020] VF zone 3 is defined as tachycardias equal to or greater than 250bpm, preferably greater than 222bpm.

[0021] In an embodiment, the implantable device determines 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 of tachycardia events before confirming a tachycardia condition.

[0022] Standard deviation, dominant frequency, and autocorrelation provide robust measures of rhythm regularity.

[0023] 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 TCL.

[0024] 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.

[0025] In 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.Excluding values near 0% and near 100% reduces near-neutral cases, making the phase evidence clearer.

[0026] In an embodiment, the detection unit determines the phase offset between tachycardia events only when the first and second tachycardia cycle lengths are considered similar, facilitating meaningful comparison and therapy adjustment.

[0027] Phase comparison is more meaningful when tachycardia cycle lengths match closely. According to an embodiment, TCL1 and TCL2 are computed in adjacent windows and proceeding with offset determination only when they are similar.

[0028] According to an embodiment, a similar TCL 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 10ms.

[0029] In alternative or additional embodiments, the events can also be derived from impedance, pressure, Sp02curves, or cardiac sounds, and sensing may be performed across multiple vectors formed by the electrode poles.

[0030] 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 30ms, preferably 10ms for purposes of phase offset determination.

[0031] Moreover, according to an alternative, the similarity of tachycardia cycle lengths is defined as the relative difference between the first and second tachycardia cycle lengths being less than or equal to 10% for purposes of phase offset determination.

[0032] 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 a relative difference of 10% and / or an absolute difference of 30ms for purposes of phase offset determination.According to an aspect, the similarity of tachycardia cycle lengths is defined such that the difference between the first and second tachycardia cycle lengths must be less than or equal to the smaller of the two thresholds: (1) a relative difference of 10% or (2) an absolute difference of 30ms, whichever yields the smaller absolute value, for purposes of phase-offset determination.

[0033] A tight tolerance improves confidence that changes are due to the therapy sequence rather than rate drift.

[0034] In an embodiment, the detection unit calculates the phase offset by virtually extending the timeline of first detected events through estimated events spaced by the initial TCL. The offset is then computed as the temporal deviation between one estimated event and its nearest subsequent second event, normalized to the initial tachycardia cycle length. The temporal deviation is called offset time interval in the following.

[0035] Virtual continuation provides a normalized phase measure even when intermediate events are missing.

[0036] In an embodiment, the detection unit computes the phase offset by measuring the interval between the last event of the detected first events and the first event of the second events, dividing this interval by the first TCL1, 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.

[0037] 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.

[0038] According to an embodiment of the present invention, the phase offset PS is determined by an angle calculated by

[0039] PS = OTI / TCL1 * 2*Pi

[0040] or

[0041] PS = ((I-OTI) / TCL1) * 2

[0042] whereby OTI is the offset time interval.

[0043] Furthermore, according to an aspect of the invention, the TCL is a mean or median interval length which is determined across at least 3 events of the first events or the second events.[Claim 10]:

[0044] In an embodiment, the control unit is configured to generate at least one therapy sequence TSi by adjusting at least one of the following parameters:

[0045] - A duration of the therapy sequence,

[0046] - A number of pulses of a therapy sequence,

[0047] - An inter-pulse interval between at least two pulses of a therapy sequence,

[0048] - A coupling interval between the last pulse of the events having a tachycardia condition and the first pulse of a therapy sequence,

[0049] - A maximum number of therapy sequences,

[0050] - A maximum duration of the therapy sequence,

[0051] - A minimum and / or maximum duration between successive therapy sequences,

[0052] - An amplitude of at least one pulse of a therapy sequence,

[0053] - A polarity of at least one pulse of a therapy sequence,

[0054] - A specific charge of at least one pulse of a therapy sequence,

[0055] wherein the stimulation unit is configured to deliver the second therapy sequence to the heart.

[0056] Adjustable duration, pulse count, timing, and energy enable targeted interaction with the tachycardia circuit.

[0057] In an embodiment, the coupling interval is computed as a product of a scaling factor rs (where 0.5 < rs < 1) and the TCL, while inter-pulse intervals are computed as products of inter-pulse-interval coupling factor ipi and the tachycardia cycle length ipi*TCL, with ipi less than or equal to rs.

[0058] According to an embodiment, at least a first group of inter-pulse intervals within a therapy sequence are maintained equal.

[0059] Normalizing timing to TCL makes the therapy rate-adaptive and consistent across different tachycardia rates.

[0060] 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.

[0061] In an embodiment, the control unit confirms a positive therapeutic effect of the first therapy sequence if the phase offset exceeds a lower threshold or is less than an upper threshold, and stores the corresponding therapy parameters in memory for future reference.

[0062] This positive therapeutic effect is also called "entrainment". Entrainment is the process of capturing and “over-driving” a reentrant tachycardia circuit by pacing slightly faster than the tachycardia cycle length. When the pacing rate is just faster than the ongoing ventricular tachycardia (VT), 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.

[0063] A threshold-based confirmation avoids uncertain results and preserves successful parameter sets for future use. According to an embodiment, confirmed configurations are written to memory for later retrieval and reuse in similar tachycardia conditions.

[0064] In an embodiment, the control unit is configured to determine at least a first set of parameters for a therapy sequence that lead to a phase offset lower than the lower threshold or higher than the upper threshold, and for which the positive effect of the second therapy cannot be determined unambiguously. Moreover, the control unit is configured to generate a second therapy sequence that has a set of parameters that differs from the at least one first set of parameters.

[0065] This strategy avoids uncertain therapy results by excluding ineffective pulse counts, thus increasing the reliability of therapy adjustments.

[0066] 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.

[0067] According to an aspect, of the present invention, a method of operating an implantable medical device is proposed. The method involves detecting an initial tachycardia condition from sensedelectrical signals based on a first TCL, delivering a first therapy sequence, detecting a subsequent tachycardia condition with a second tachycardia cycle length, determining the phase offset between the first and second events, and generating a second therapy sequence based on this phase offset.

[0068] The method establishes a closed-loop mechanism in which the TCL is measured, the therapy is delivered, the result is measured, and the next therapy sequence is adapted from the measured phase offset. The loop repeats until termination criteria are met or escalation rules apply.

[0069] 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.

[0070] 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.

[0071] According to an embodiment, 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.

[0072] According to an aspect of the invention, assessments of the 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.

[0073] All embodiments of the implantable medical device can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the described method. Likewise, all embodiments of the described method can be combined in any desired way and can be transferred either individually or in any arbitrary combination to the implantable medical device.

[0074] The term „IMD" as used herein refers to an implantable medical device configured for sensing cardiac electrical signals and delivering electrical pulses to the heart for ATP therapy.The term „electrode pole" as used herein refers to a component of the implantable medical device designed to both sense electrical signals from the heart and deliver electrical pulses to the heart tissue.

[0075] The term „electrical pulses" as used herein refers to programmed electrical stimuli delivered via electrode poles to the heart to modify cardiac rhythm during ATP therapy.

[0076] The term „heart" as used herein refers to the human or animal cardiac organ whose electrical activity is monitored and therapeutically influenced by the implantable medical device.

[0077] The term „electrical pulse" as used herein refers to a single therapeutic electrical pulse delivered to the heart as part of a therapy sequence.

[0078] The term „post-pacing interval" as used herein refers to a time interval measured from the last delivered electrical pulse of a therapy sequence to the first subsequent intrinsic cardiac event. The term difference D" as used herein refers to the calculated difference between two consecutively measured post-pacing intervals used as a relation parameter for adjusting therapy.

[0079] The term „events" as used herein refers to distinct cardiac electrical occurrences detected in sensed signals, including intrinsic cardiac actions and delivered pulses.

[0080] The term ..stimulation unit" as used herein refers to the component of the implantable medical device that delivers programmed electrical pulses to the heart via electrode poles.

[0081] The term „Implantable medical device" as used herein refers to a device implanted in the body that monitors cardiac electrical signals and provides electrical pacing therapy to treat tachycardia.

[0082] The term „first tachycardia condition" as used herein refers to an initial detection of a tachycardia state identified by analyzing cardiac events and intervals which triggers delivery of a first therapy sequence.

[0083] The term „time intervals" as used herein refers to measured durations between detected cardiac electrical events used to assess cardiac rhythm conditions.

[0084] The term "estimated events in succession" as used herein refers to computed event timings created by extending the timeline of detected events spaced by the TCL to facilitate phase offset calculation.The term „electrical signal" as used herein refers to the cardiac electrical activity recorded by the implantable medical device's sensing electrodes.

[0085] The term „second therapy sequence TS2" as used herein refers to the subsequent therapy sequence delivered after the first, in response to persistent tachycardia, consisting of one or more electrical pulses.

[0086] The term „memory unit" as used herein refers to the storage component of the implantable medical device that retains therapy parameters and measurement data such as pulse counts and post-pacing intervals.

[0087] The term „cardiac pacemaker" as used herein refers to a type of implantable medical device that provides electrical pacing to regulate the heart rhythm.

[0088] The term "remainder" as used herein refers to the fractional part left over when dividing the interval between detected events by the TCL, used to derive the phase offset.

[0089] The term „control unit" as used herein refers to the implantable medical device component responsible for analyzing detected cardiac events, computing parameters, and adjusting therapy sequences dynamically.

[0090] The term „ICD" as used herein refers to an implantable cardioverter-defibrillator device capable of delivering ATP and high-energy shocks to treat arrhythmias.

[0091] The term "dominant frequency" as used herein refers to the main frequency component derived from frequency analysis of detected cardiac events, indicative of rhythm regularity in tachycardia.

[0092] The term „coupling interval RSi" as used herein refers to the time interval between the last intrinsic tachycardia event and the first pulse of a therapy sequence, typically expressed as a fraction of the TCL. “I” is an index number.

[0093] The term „second tachycardia condition" as used herein refers to a subsequent detection of tachycardia after delivery of a preceding therapy sequence, triggering further therapy actions.The term „first relation parameter" as used herein refers to a computed value derived from comparing two post-pacing intervals that guides adjustment of subsequent therapy sequences.

[0094] The term „therapy sequence TSi" as used herein refers to a series of one or more electrical pulses delivered to the heart as a coordinated therapeutic intervention indexed by i.

[0095] The term „therapy sequence" as used herein refers generally to a group of electrical pulses delivered in succession to interrupt tachycardia.

[0096] The term „first therapy sequence TSI" as used herein refers to the initial sequence of electrical pulses delivered upon detecting the first tachycardia condition.

[0097] The term „electrical signals" as used herein refers to the cardiac electrical activity continuously sensed by the implantable medical device for rhythm analysis.

[0098] The term „second post-pacing interval PI2" as used herein refers to the time interval measured between the last pulse of the second therapy sequence and the first intrinsic cardiac event detected thereafter.

[0099] The term „inter-pulse interval IPIi" as used herein refers to the time interval between consecutive pulses within a therapy sequence or between the tachycardia pulse and the first pulse of a singlepulse therapy sequence. “I” is an index number.

[0100] The term „PI2" as used herein refers synonymously to the second post-pacing interval measured after the second therapy sequence.

[0101] The term „ATP" as used herein refers to anti -tachycardia pacing, a therapy involving electrical pulses to terminate tachycardia by interrupting abnormal cardiac rhythms.

[0102] The term ..parameter" as used herein refers to a quantifiable characteristic or variable used by the control unit to configure or adjust therapy sequences.

[0103] The term „detection unit" as used herein refers to the implantable medical device component responsible for sensing cardiac electrical events and analyzing them to identify tachycardia conditions.The term „anti-tachycardia pacing" as used herein refers to a therapeutic technique using controlled electrical pulses to halt tachycardia by resetting the pathological cardiac electrical circuit.

[0104] The term „sensed electrical signals" as used herein refers to the electrical cardiac signals recorded by the implantable medical device's electrode poles for rhythm detection.

[0105] The term „first events" as used herein refers to the plurality of cardiac electrical events detected prior to and triggering the first therapy sequence.

[0106] The term „tachycardia condition" as used herein refers to a state of abnormally fast cardiac rhythm identified by analyzing intervals and characteristics of detected cardiac events.

[0107] The term „first detected intrinsic cardiac event" as used herein refers to the earliest intrinsic (natural) cardiac electrical occurrence detected following the last pulse of a therapy sequence.

[0108] The term ..conduction system pacing (CSP) device" as used herein refers to a cardiac pacing system designed to deliver electrical stimulation directly to the heart’s intrinsic conduction system — primarily the His bundle or the left bundle branch area — rather than to the right ventricular myocardium.

[0109] The term "stability parameter" as used herein refers to a quantitative measure for evaluating the consistency and regularity of tachycardia events for accurate detection.

[0110] The term „ cardiac rhythm management therapy (CRT) device " as used herein refers to an implantable pacemaker — sometimes combined with a defibrillator (CRT-P / CRT-D) — that delivers coordinated pacing to both ventricles (and often the right atrium) to resynchronize heart contractions in selected heart-failure patients with electrical conduction delays, improving pump efficiency and symptoms.

[0111] The term „therapy module" as used herein refers to a type of therapeutic measure of a cardiac pacing system designed to deliver electrical stimulation.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 :

[0112] Fig. 1 illustrates a schematic view of an implantable medical device interacting with a heart.

[0113] Fig. 2 shows a schematic of intrinsic rhythm, tachycardia detection, and delivery of a first ATP therapy sequence.

[0114] Fig. 3a illustrates the determination of phase offset via the temporal deviation by calculation of an offset time interval.

[0115] Fig. 3b illustrates a first example for the determination of phase offset via the temporal deviation by calculation of an offset time interval under consideration of a detection threshold.

[0116] Fig. 4 illustrates a further example of the determination of a phase offset via the temporal deviation by calculation of an offset time interval.

[0117] Fig . 5 illustrates a second example for the determination of phase offset via the temporal deviation by calculation of an offset time interval under consideration of a detection threshold.

[0118] Fig. 6 illustrates an exemplary control flow diagram for the ATP therapy according to embodiments of the present invention.

[0119] Fig. 7 depicts an exemplary detailed view of evaluation step 700 executed by the implantable medical device according to embodiments of the present invention.

[0120] Fig. 8 depicts an exemplary detailed view of evaluation step 800 executed by the implantable medical device according to embodiments of the present invention.

[0121] Fig. 9a depicts an exemplary detailed view of evaluation step 900 executed by the implantable medical device according to embodiments of the present invention.Fig. 9b shows an exemplary detail view of an additional evaluation logic applied during the configuration for the next ATP attempt to avoid therapy sequence configurations that would likely yield ambiguous phase offset results.

[0122] 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. Fig. 1 shows alternative configurations whereby 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.

[0123] 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 RS 1 220. 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 SISI 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.

[0124] 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 ormore 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.

[0125] Figure 3a illustrates the evaluation of a subsequent tachycardia having tachycardia cycle length TCL 321 in observation window 320 with respect to its phase relation to a preceding tachycardia detected in observation window 300 having TCL 301 and the derivation of a phase offset used to adapt anti-tachycardia therapy. The implantable medical device first verifies that a tachycardia condition is present in observation window 300 with predefined characteristics, for example that the tachycardia cycle length TCL 301 or a mean interval length TCLm calculated from the cardiac events of the tachycardia in observation window 300 lies within programmed zone boundaries and that stability criteria are met (TCLs within stability limits). The intrinsic tachycardia events are indicated by 302. The implantable medical device then delivers a therapy sequence 310 that is coupled to the last intrinsic tachycardia event R via a coupling interval.

[0126] After the therapy sequence 310, the implantable medical device checks whether a tachycardia condition is present in observation window 320 with the predefined characteristics and whether its cycle length 321 is sufficiently similar to that of the preceding tachycardia of observation window 300. If so, the rhythm of the tachycardia of observation window 300 with tachycardia cycle length TCL 301 is virtually continued to the time position of the subsequent tachycardia of observation window 320. The virtually continued or constructed continuation is denoted estimated events 330, having the estimated inter-pulse interval 331 which is equal to TCL 301.

[0127] To determine the phase offset, the implantable medical device measures the temporal deviation by means of offset time interval 340 between the cardiac events of tachycardia in observation window 320 and the expected event positions of the estimated events 330. Preferably, the offset time interval 340 is normalized to TCL 301 (forming the quotient: offset time interval / TCL) and expressed as a phase measure in which TCL 301 corresponds to 360°. Preferably, a normalized phase value(1 - offset time interval / TCL) is computed; the value lies between 0 and 1 and represents the position of tachycardia in observation window 320 relative to the extrapolated pattern of the estimated events 330.

[0128] According to an embodiment, a positive phase offset is defined in the negative time direction. When entrainment exists, the cardiac events of the tachycardia in observation window 320 occur earlier than those of the estimated events 330. Phase offsets near 360° are treated like offsets near 0° as approximately no phase offset. According to an embodiment, the computation of the estimated events uses the mean interval length TCLm calculated from the cardiac events of the tachycardia in observation window 300 instead of TCL 301, preferably determined across at least three tachycardia cycles.

[0129] Figure 3b illustrates an example of the evaluation of a phase offset according to Fig. 3a. The temporal deviation between the cardiac events of the tachycardia in observation window 320 and the expected event positions of the estimated events 330 is represented by means of offset time interval 340. The offset time interval 340 that represents the phase offset is compared with detection threshold 350. Detection threshold 350 is for instance a lower detection threshold. An offset time interval greater than the detection threshold 350 may indicate entrainment, i.e., the therapy sequence 310 provided sufficient pulses to capture and over-drive the reentry circuit. The phase information is made available for further processing by the control unit 140 and can be stored in a memory unit 150. Alternatively or in addition, a phase offset smaller than a programmable upper threshold can also indicate entrainment. On the other hand, an offset time interval 340 and thus a phase offset below a lower threshold or higher than an upper threshold can indicate that entrainment was not achieved.

[0130] Figure 4 illustrates an example of the evaluation of a phase offset based on Fig. 3a. The intermittent interval 400 between the last intrinsic cardiac event 410 of the tachycardia detected in observation window 300 and the first intrinsic cardiac event 420 of the tachycardia detected in observation window 320 is measured and divided by TCL 301 or a mean interval length TCLm calculated from the cardiac events of the tachycardia in observation window 300. The phase offset results from the fractional part, i.e. the remainder of the division. The fractional part is independent from the number of full intervals TCL 301 included in intermittent interval 400 - the whole cycle portions cancel out in the division. Alternatively, intermittent interval 400 can be determined between other events before and after therapy sequence 310, see for instance time interval 401.

[0131] Figure 5 illustrates an example of the evaluation of a phase offset according to Fig. 3a, 3b and 4.A ventricular tachycardia (VT) occurs with a tachycardia cycle length TCL 301, which is assessed within an observation window 300 to confirm onset and stability of the arrhythmia. Upon detection of a qualifying tachycardia, the implantable medical device delivers a therapy sequence 310 (a first therapy sequence TSi), which is coupled to the last detected intrinsic event 326. Successive pulses within the therapy sequence are separated by an intra-therapy sequence pulse interval SlS1 311 (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 310 can be separated by an inter-pulse interval 312 that is shorter than SISI 311. This phase of at least one shorter pulse interval at the end of a therapy sequence is called the ramp phase. The post-pacing interval 325 is the time interval from the last pulse 327 of therapy sequence 310 to the first cardiac event 360 after the therapy sequence 310. The time to last pulse (T2LS) 328 is the time difference between last detected intrinsic event 326 and last pulse 327 of therapy sequence 310.

[0132] The intermittent interval 324 between the last intrinsic cardiac event 326 of the tachycardia detected in observation window 300 and the first intrinsic cardiac event 360 of the tachycardia detected in observation window 320 is measured and divided by TCL 301 or a mean interval length TCLm calculated from the cardiac events of the tachycardia in observation window 300. The phase offset results from the fractional part, i.e. the remainder of the division. The fractional part is independent from the number of full intervals TCL 301 included in intermittent interval 324 - the whole cycle portions cancel out in the division.

[0133] The temporal deviation between the cardiac events of the tachycardia in observation window 320 and the expected event positions of the estimated events 330 is represented by means of offset time interval 340. The offset time interval 340 that represents the phase offset is compared with detection threshold 350. Detection threshold 350 is for instance a lower detection threshold. An offset time interval greater than the detection threshold 350 may indicate entrainment, i.e., the therapy sequence 310 provided sufficient pulses to capture and over-drive the reentry circuit. The phase information is made available for further processing by control unit 140 and can be stored in a memory unit 150. Alternatively or in addition, a phase offset smaller than a programmable upper threshold can also indicate entrainment. On the other hand, an offset time interval 340 and thus a phase offset below a lower threshold or higher than an upper threshold can indicate that entrainment was not achieved.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 S 1 pulses NS 1 , 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 the coupling interval RSI and the inter-pulse intervals of the burst phase SISI relative to TCL or TCLm. 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.

[0134] 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.

[0135] 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 continuedATP is no longer 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, NS 1, 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.

[0136] 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.

[0137] In an example, for modification of a subsequent therapy sequence, the control unit is configured to perform at least one of the following:

[0138] 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,

[0139] reducing the S2 ramp factor to shorten ramp intervals for a more aggressive approach to terminate tachycardia in case no loss of capture occurred,

[0140] increasing the S2 ramp factor to lengthen ramp intervals when loss of capture is detected during the ramp phase,

[0141] lengthening RS 1 and the corresponding SISI slightly if loss of capture is attributed to overly short coupling of the burst pulses.

[0142] After each delivered therapy sequence, the loop proceeds by determining a next-attempt configuration at 900, unless termination conditions 690 or 694 apply.

[0143] 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 OC — for later retrieval and analysis.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.

[0144] In 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.

[0145] 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.

[0146] Checks 810 and 820 are followed by decision step 760 for termination of further ATP attempts and subsequent steps according to Figure 6.

[0147] 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 hascompleted 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 with 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 SI pulses NSlmax in the burst phase, reaching a minimum allowable inter-pulse interval S 1 S 1 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.

[0148] 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 andresults 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.

[0149] 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 potential 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).

[0150] Figure 9a depicts an exemplary detailed view of the next-attempt configuration 900 executed after each delivered therapy sequence.

[0151] 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.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.

[0152] Before 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).

[0153] 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 S 1 pulses in the burst phase at 920 by adding a programmed increment to NS 1, 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 S 1 S2 / 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 RSI and the ensuing SISI so that capture is re-established without abandoning the closed-loop strategy.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.

[0154] Finally, comping 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. That may be a pre-programmed configuration for the purpose of applying ATP as escalation therapy measure. The parameter set produced by the logic of Figure 9a 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.

[0155] Figure 9b shows an exemplary detail of an additional evaluation logic applied during the configuration for the next ATP attempt to avoid therapy sequence configurations that would likely yield ambiguous phase offset results. After the implantable medical device has determined the parameters for the next therapy sequence (e.g., NS1, NS2, SISI, S2 ramp factor and RSI) in line with the algorithm of Figure 9a, it invokes the ambiguity -prevention process 950.

[0156] In 950, the control unit predicts whether the forthcoming therapy sequence, even if it achieved entrainment, would produce a phase offset that falls into the programmed window used to determine the applicability of phase offset-based therapy adjustment merely due to timing geometry rather than true therapy interaction.

[0157] To make this prediction, the implantable medical device determines at 951 all programmed parameter bounds of the ongoing therapy module — Tmin burst for the minimum allowable inter-pulse interval SISI in the burst phase, Tmin_ramp for the minimum allowable inter-pulse interval S1S2 / S2S2 in the ramp phase and the cap on the S2 ramp factor. These limits ensure that the prediction reflects what may actually be delivered in the next ATP attempt. In the following, the last intrinsic event before delivery of therapy sequence 326, the last pulse of the therapy sequence 327 and T2LS 328 of Figure 5 and detection threshold 350 are used here for consistency.

[0158] Furthermore, a limited time-to-last-pulse T2LS_Limited is determined in 951, which is a limit for the time-to-last-pulse 328. With T2LS_Limited and a known propagation time PT.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 a 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.

[0159] 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.

[0160] 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.

[0161] The implantable medical device applies the check 960 that evaluates whether there exists a positive integer N such that the phase relation

[0162] 10% > N*TCLm / T2LS_Limited + PT or 90% < N*TCLm / T2LS_Limited + PT

[0163] holds.

[0164] If this condition is true, an estimated event 330 (see Figure 5) of the virtually continued tachycardia (continued from 326 with period TCLm 301) would land inside the phase detection window around 350 even without influence by the forthcoming therapy sequence. In that case, the forthcoming configuration would mimic an entrainment-like phase offset solely by geometry, thereby ambiguous for confirming entrainment.

[0165] If the check at 960 is negative, the implantable medical device proceeds with the prepared configuration unchanged 961. If the check is positive, the implantable medical device modifies the configuration at 962 by adding one S 1 pulse to the burst phase, thereby lengthening the timing of thetherapy sequence (and thus T2LS_Limited) so that the estimated event 330 no longer falls within the tolerance band 350. This adjustment may be repeated if required by the specific limits. In practice, a single additional S 1 pulse typically suffices because commonly used scaling factor rs are below 90%, which shifts the phase geometry enough to avoid ambiguity.

[0166] According to an embodiment, the ATP therapy configuration that does not produce ambiguous phase offset results can be determined as follows:

[0167] The control unit is configured to determine a limited time-to-last-pulse T2LS_Limited, which is a limit for the time interval from the last intrinsic event preceding the therapy sequence to the last pulse of that sequence. The at least one set of parameters is determined with the limited time to last pulse T2LS_Limited and a known propagation time PT.

[0168] 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 a 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.

[0169] 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.

[0170] 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.Moreover, according to an embodiment, the control unit is configured to evaluate whether there exists a positive integer N such that the phase relation

[0171] 10% > N*TCLm / T2LS_Limited + PT or 90% < N*TCLm / T2LS_Limited + PT

[0172] holds.

[0173] A parameter set for a planned therapy sequence that fulfils above phase relation shall not be used for the second therapy sequence. According to an embodiment, a modified set of parameters is chosen instead, e.g. by increasing the number of pulses by one, e.g. adding one pulse in the burst phase SI or adding one pulse in the ramp phase S2.

[0174] According to further exemplary embodiment, the ATP therapy configuration that does not produce ambiguous phase offset results can be determined as follows:

[0175] The control unit is configured to determine a time to last pulse (T2LS) for a forthcoming therapy sequence configured with a burst phase and a ramp phase. The T2LS corresponds to the time interval from the last intrinsic event preceding the therapy sequence to the last pulse of that sequence.

[0176] The quantities are defined as follows:

[0177] Mean tachycardia cycle length TCLm as described previously

[0178] A scaling factor rs S1F specifies the coupling interval RSI relative to TCLm

[0179] An S2 ramp factor S2F specifies successive shortening of the inter-pulse interval in a ramp phase,

[0180] The number of S 1 pulses NS 1 in the burst phase

[0181] Minimum allowable inter-pulse intervals in the burst Tmin burst and ramp phases Tmin ramp

[0182] Propagation time PT, defined as described previously

[0183] According to the embodiment, for a therapy sequence with four S2 pulses and without active limits, T2LS is computed by

[0184] T2LS = TCLm * S1F * (NS1 + S2F + S2FA2 + S2FA3).

[0185] When limits apply, the device forms a limited time to last pulse

[0186] T2LS_Limited = max(Tmin_burst, TCLm * SIF limited) * NS1 + max(Tmin_ramp, TCLm * SIF limited * (S2F + S2FA2 + S2FA3)),where SlF_limited is the scaling factor rs after applying programmed bounds. These expressions map the planned SISI burst intervals and the S1S2 / S2S2 ramp intervals to the predicted last-pulse timing under the configured burst-and-ramp geometry and the applicable minima Tmin burst and Tmin ramp.

[0187] Before delivery of the sequence, the device executes check 960 to avoid therapy configurations that could produce an ambiguous phase offset solely due to timing geometry. As previously described, the check is satisfied if there exists a positive integer N such that

[0188] 10% > N*TCLm / T2LS_Limited + PT or 90% < N*TCLm / T2LS_Limited + PT

[0189] A parameter set for a planned therapy sequence that fulfils above phase relation shall not be used for the second therapy sequence. According to an embodiment, a modified set of parameters is chosen instead, e.g. by increasing the number of pulses by one, e.g. adding one pulse in the burst phase SI or adding one pulse in the ramp phase S2.Reference Numeral List

[0190] 100 implantable medical device (IMD)

[0191] 110 heart

[0192] 111 electrode pole(s)

[0193] 120 stimulation unit

[0194] 130 detection unit

[0195] 140 control unit

[0196] 150 memory unit

[0197] 200 therapy sequence

[0198] 209 cycle length CL (baseline rhythm)

[0199] 210 tachycardia cycle length TCL (first window)

[0200] 210b observation window for TCL 210

[0201] 211 tachycardia cycle length TCL (subsequent window)

[0202] 211b observation window for TCL 211

[0203] 220 coupling interval RS 1

[0204] 230 inter-pulse interval SISI (burst)

[0205] 231 shortened inter-pulse interval (ramp)

[0206] 300 observation window (pre -therapy)

[0207] 301 tachycardia cycle length TCL (or mean TCLm) in window 300 302 intrinsic tachycardia events (window 300)

[0208] 310 therapy sequence (first TSi)

[0209] 311 inter-pulse interval SISI (within 310)

[0210] 312 shortened inter-pulse interval (ramp, within 310)

[0211] 320 observation window (post-therapy)

[0212] 321 tachycardia cycle length TCL in window 320

[0213] 324 intermittent interval (last intrinsic before first intrinsic after therapy) 325 post-pacing interval PI (last pulse first intrinsic after)

[0214] 326 last intrinsic cardiac event before therapy sequence

[0215] 327 last pulse of therapy sequence

[0216] 328 time-to-last-pulse T2LS

[0217] 330 estimated events (virtual continuation)

[0218] 331 estimated inter-event interval (equal to TCL 301 / TCLm)

[0219] 340 offset time interval

[0220] 350 detection threshold (phase / offset)

[0221] 360 first intrinsic cardiac event after therapyintermitent interval (general)

[0222] alternative intermitent interval

[0223] last intrinsic cardiac event (Fig. 4)

[0224] first intrinsic cardiac event after therapy (Fig. 4) programmer interface

[0225] tachycardia detection step

[0226] set initial parameters

[0227] scaling factor rs

[0228] deliver initial therapy sequence

[0229] deliver newly configured therapy sequence

[0230] termination (successful)

[0231] end (no further ATP)

[0232] data logging / storage

[0233] next-step evaluation

[0234] entry to evaluation after sequence

[0235] termination / redetection check

[0236] measurements: PI, D, phase offset

[0237] decision to continue ATP atempts

[0238] modification step for next sequence (resolution)

[0239] limit checks

[0240] check max pulses / sequences (potential switch)

[0241] max elapsed time (potential break)

[0242] consecutive loss-of-capture (LOC) atempts (potential switch) parameter bound hit (potential switch)

[0243] additional limits (potential switch / break)

[0244] shock already delivered (potential break)

[0245] significant acceleration (e.g., VT^VF) (potential switch) rhythm checks

[0246] TCLm change check (potential reset)

[0247] stability check (potential reset)

[0248] minimum TCLm check (potential break)

[0249] resolve to break

[0250] resolve to switch

[0251] resolve to reset

[0252] select higher-priority therapy module

[0253] reload initial parameterizationsequence optimization

[0254] next-attempt configuration

[0255] validity check for Pl / sensing context

[0256] LOC evaluation block

[0257] LOC by PI < TCLm

[0258] LOC by negative D beyond tolerance

[0259] derive & validate phase offset

[0260] proximity check (NS2 near max)

[0261] increase NS1

[0262] increase NS2

[0263] reduce S2 ramp factor

[0264] increase S2 ramp factor

[0265] increase rs (lengthen RSI & S1S1)

[0266] check if succeeding module is ATP

[0267] select initial parameterization of succeeding module ambiguity-prevention process

[0268] determine parameter bounds; compute T2LS_Limited; PT setup ambiguity check condition

[0269] proceed unchanged

[0270] modify configuration

Claims

Claims1. Implantable medical device (IMD, 100) for anti -tachycardia pacing (ATP) of a heart (110), comprising:- at least one electrode pole (111) configured to sense electrical signals of the heart (110) and apply electrical pulses to the heart (110),- a stimulation unit (120), configured to deliver the electrical pulses to the heart (110) via the electrode pole (111), wherein the stimulation unit (120) is configured to deliver at least one therapy sequence to the heart (110), the therapy sequence 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 and to derive at least one parameter to adjust the therapy sequence based on the events,characterized in thatthe stimulation unit (120) is configured to deliver a first therapy sequence to the heart (110) if the detection unit (130) detects a first tachycardia condition based on a first tachycardia cycle length TCL1 of a plurality of first events in the sensed electrical signals,and if the detection unit (130) detects a second tachycardia condition based on a second tachycardia cycle length TCL2 of a plurality of second events in the sensed electrical signals after delivery of the first therapy sequence, the detection unit (130) is configured to determine a phase offset between the first events and the second events,wherein the control unit (140) is configured to generate a second therapy sequence based on the phase offset.

2. IMD (100) according to claim 1, wherein a tachycardia condition is detected if- the first and second tachycardia cycle lengths are shorter than a tachycardia threshold, and if- the time intervals between the events fulfill at least one stability parameter.

3. IMD (100) according to claim 2, wherein the stability parameter is at least one of- a difference between a predefined number of preceding tachycardia cycle lengths and a stability threshold value,- a standard deviation,- a dominant frequency from a frequency analysis, or- a parameter determined via an autocorrelation.

4. IMD (100) according to at least one of the preceding claims, wherein the control unit (140) is configured to generate a second therapy sequence based on the phase offset if the phase offset is within a percentage range of the first tachycardia cycle length TCL1.

5. IMD (100) according to claim 4, wherein the percentage range is 10%-90%.

6. IMD (100) according to at least one of the preceding claims, wherein the detection unit (130) is configured to determine the phase offset if the first tachycardia cycle length TCL1 and the second tachycardia cycle length TCL2 are similar.

7. IMD (100) according to claim 6, wherein the first tachycardia cycle length TCL1 and the second tachycardia cycle length TCL2 are considered similar if their difference is smaller or equal to 10ms.

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

9. IMD (100) according to at least one of the claims 1 to 7, wherein the detection unit (130) is configured to determine the phase offset by- Calculating an intermittent interval between the last event of the first events and the first event of the second events,- Dividing the intermittent interval by the first tachycardia cycle length TCL1, - calculating the remainder of the division, wherein the remainder is defined as offset time interval,determine the phase offset based on the offset time interval in relation to the first tachycardia cycle length TCL1.

10. IMD (100) according to at least one of the preceding claims, wherein the control unit (140) is configured to generate the second therapy sequence by adjusting at least one of the following parameters:- a duration of the second therapy sequence,- a number of electrical pulses,- an inter-pulse interval between at least two electrical pulses,- a coupling interval between one of the second events and the first pulse of the second therapy sequence,- An amplitude of at least one pulse of the second therapy sequence,- A polarity of at least one pulse of the second therapy sequence,- A specific charge of at least one pulse of the second therapy sequence,wherein the stimulation unit (120) is configured to deliver the second therapy sequence to the heart (110).

11. IMD (100) according to claim 10, wherein- the coupling interval is computed by scaling factor rs*TCL, whereby 0.5 < rs < 1 and TCL = tachycardia cycle length between the events,- the inter-pulse interval is computed by ipi*TCL, whereby ipi is an inter-pulseinterval coupling factor and wherein ipi < rs.

12. IMD (100) according to claim 10 or 11, wherein the second therapy sequence comprises a first number of electrical pulses which is the same number of pulses as that of the first therapy sequence, plus one additional electrical pulse, wherein the first number of pulses all have inter-pulse intervals of a first length, and wherein the inter-pulse interval between the one additional electrical pulse and the last electrical pulse of the first number of electrical pulses is- shorter than the first length, if the phase offset is not zero, orequal to the first length, if the phase offset is zero.

13. IMD (100) according to at least one of the preceding claims, wherein the control unit (140) is configured to confirm a positive effect of the first therapy sequence if the phase offset is greater than a lower threshold or lower than an upper threshold, wherein the control unit (140) is configured to store the parameters of the associated therapy sequence in a memory unit (150).

14. IMD according to claim 13 referring to claim 10, wherein the control unit is configured to determine at least a first set of parameters for a therapy sequence that lead to a phase offset lower than the lower threshold or higher than the upper threshold, and for which the positive effect of the second therapy cannot be determined unambiguously, and wherein the control unit is configured to generate a second therapy sequence that has a set of parameters that differs from the at least one first set of parameters.

15. Method for operating an implantable medical device (IMD, 100) for stimulating a human or animal heart (110), characterized by the following steps:- detect a first tachycardia condition of the heart (110) based on a first tachycardia cycle length TCL1 of a plurality of first events in sensed electrical signals, - deliver a first therapy sequence to the heart ( 110),- detect a second tachycardia condition based on a second tachycardia cycle length TCL2 of a plurality of second events in the sensed electrical signals, - determine a phase offset between the first events and the second events,- generate a second therapy sequence based on the phase offset.

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