WO2007059383A2

WO2007059383A2 - Pacing device for minimizing ventricular pauses after delivery of atrial anti-tachycardia pacing therapy

Info

Publication number: WO2007059383A2
Application number: PCT/US2006/060513
Authority: WO
Inventors: Paul D. Ziegler; Douglas A. Hettrick; Paul G. Krause; Katherine H. Anderson
Original assignee: Medtronic, Inc.
Priority date: 2005-11-10
Filing date: 2006-11-03
Publication date: 2007-05-24
Also published as: EP1996286A2; US20070106334A1; WO2007059383A3; US7689279B2; EP1996286B1

Abstract

A pacing control is used in a multiple-chamber cardiac pacing system, which, upon detecting an atrial arrhythmia, automatically switches to a special therapy mode and administers a selected anti-tachycardia pacing (ATP) therapy in the atrium, and which switches to a standard pacing mode following delivery of the ATP therapy. The pacing control adjusts the timing of pacing pulses to be delivered to the atrium and/or the ventricle to minimize any potential ventricular pauses that may result from the switch from the therapy mode to the standard pacing mode.

Description

PACING DEVICE FOR MINIMIZING VENTRICULAR PAUSES AFTER DELIVERY OF ATRIAL ANTI-TACHYCARDIA PACING

THERAPY

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of cardiac pacing systems, and more particularly to a cardiac pacing device having pacing control for minimizing a ventricular pause that can follow the delivery of an atrial anti-tachycardia pacing (ATP) therapy.

Modern cardiac pacing devices and systems, such as implantable pacemakers and cardioverter-defibrillators, are designed for efficient dual or multiple chamber pacing, as well as for detection and treatment of dangerous cardiac arrhythmias. A dual chamber pacing device commonly provides an atrial tracking, synchronous pacing mode (such as DDD or DDDR), whereby the ventricle is paced in synchrony with sensed and/or paced atrial activity. This type of pacing scheme approximates the normal healthy coordination between the atrium and the ventricle and, thus, optimizes cardiac output of the heart.

If the atrium is seized with an arrhythmia, however, most modern pacing devices will switch from an atrial tracking, synchronous pacing mode (such as DDD) to a non- tracking, atrial-ventricular (AV) sequential pacing mode (such as DDI), in which the ventricle is paced in response to pulsed atrial activity but not sensed atrial activity. To combat the atrial arrhythmia, the pacing device commonly will select and administer an ATP therapy comprising a plurality of carefully controlled, rapidly administered pulses to the atrium. During delivery of the ATP therapy to the atrium, the pacing device will switch to a special therapy mode (such as AOO with VVI backup) in which the ventricle is paced independent of atrial activity. That is, neither paced nor sensed atrial events trigger pacing in the ventricle. During the special therapy mode, the ventricle is commonly paced at a patient-specific lower iate interval (LRI), or at a sensor rate if the patient's current activity levels justify a higher rate,

Upon delivery of the last atrial pacing pulse of the ATP therapy, the pacing device commonly reverts back to the non-tracking, AV sequential pacing mode (e.g., DDI). This transition back, however, may result in a ventricular pulsc-to-ventricular pulse (V-V) interval between the last ventricular pulse delivered prior to the cessation of the ATP ATP therapy that is significantly longer than the LRi. This is especially true if the last atria! poise of the ATP therapy occurs immediately prior to tlie next scheduled ventricular pulse. Tills long V-V interval experienced upon transition between the pacing device's therapy mode and αon.-tracMπg, AV sequential mode is referred to herein as a ventricular pause,

A ventricular pause that is greater than the LRI presents three potentially negative effects, First, the long -ventricular pause roay produce undesirable symptoms in some patients. Second, alternating between relatively short and long ventricular intervals could be potentially pro-arrhythmic. Third, the long ventricular pause may result m confusion for the patient's physician because data stored in the device .may appear as though the patient was paced at a rate lower than, the programmed LRI.

BMEf SUMMARY OF THE INVENTION

The present invention introduces a pacing control for use in a multiple-chamber cardiac pacing system, which, iψon detecting an atrial arrhythmia, aiitornatically switches to a special therapy mode and administers a selected anti-tachycardia pacing (ATP) therapy in the atriura, and which switches to a standard pacing mode following delivery of the ATP therapy. The pacing control adjusts ibs timing of pacing pulses to be delivered to the atrium and/or the ventricle to minimize arsy potential ventricular pauses that may result from the switch from the therapy mode to the standard pacing mode.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of an implantable medical device and lead set of a type in which the present invention may be practiced.

FlG. 2 ΪS a functional Mock diagram of the circuitry of the implantable medical device ofHG. 1.

FiG, 3 is an. example of a timing diagram for illustrating a ventricular pause that caa follow the deliver}' of an atrial anti-tachycardia pacing therapy.

FIGS. 4, 5A aid 5B are examples of timing diagrams for illustrating a pacing control in accordance with the present invention ΪOΪ use in ih& implantable medical device. DETAILED DESCRIPTION

FlG. 1 is a. diagram of implantable medical άevicβ (IMD) 10 capable of providing pacing therapy to heart H in accordance with the present invention. IMD 10 is presented herein as one embodiment of a cardiac pacing system that embodies the pacing control of the present invention. However, the pacing control of the present invention may be adapted for use with any multiple chamber pacing or defibrillation system which- upon detecting an atrial arrhythmia, automatically switches from an atrial synchronous pacing mode to a nou-tracMng pacing .mode and administers an anii -tachycardia pacing (ATP) therapy in the atrium, and which reverts to the atrial synchronous pacing mode upon successful termination of the atrial arrhythmia by the ATP therapy.

Ia the embodiment illustrated in FIG. I, IMD 10 includes heπneticaHy-seafed housing .12. header .14. right atrial (RA) lead 16. and right ventricular (RV) lead 18, IMD 10 further includes circuitry and a power source;, which are located within housing 12, for controlling the operation of ΪMD 10. The circuitry, which includes the pacing control of the present invention, communicates %vith leads 16 and 18 through electrical connectors within header 14. Leads 16 and .18 extend from header 14 to right atrium RA and right ventricle RV, respectively, of heart H, Leads 16 and 18 carry one or more sensors/electrodes for sensing electrical signals attendant .o the depolarization and repolarization of heart H, and further for providing pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof, As shown in PIG; L atrial electrodes 20 and 22 are disposed at the distal end of RA lead 16 mύ are located in right atrium RA. Similarly, ventricular electrodes 24 and 26 are disposed at the distal end of RV lead 18 and are located in right ventricle RV.

FIO. 2 is a functional block diagram of the circuit!}' located within IMD K). This block diagram is irjfendθd to be merely exemplary and corresponds only to a general functional organisation of most presently available IMDs, "The circuitry generally includes microcomputer circuit 5O₅ input/output circuit 52, and data communications bus 54.

Microcomputer circuit 50 includes microprocessor 56. system clock 58, on-boarø- RAM memory 60, on-board ROM memory 62, off-board RAM/ROM, memory 64 and digital controller/timer circtwt 66 collected to microprocessor 56 and ofi-boarci RAM/jRϋM memory 64 via data communications bus 54, Microcomputer circuit 50 communicates with input/output circuit 52 to monitor electrical activity in heart H as well as Io deliver appropriately-timed pulses to the various electrodes. Digital controHer/tirπer circuit 66 includes digital timers and counters xssed to determine time between successive depolarizations in the atria and. ventricles, as well as to provide various refractory, blanking, and other timing windows used to determine delivery of paced pulses to the alria and ventricles. Digital controller/timer circuit 66 receives sensed activity signals and causes pacing pulses to be delivered via connections to leads .16 mά 1 S.

RA lead 16 is connected to digital controller/timer circuit 66 via output pulse generator 68, electrogram (EGM) amplifier 70, and sensing circuitry 72. Sensing circuitry 72 includes sense amplifier 74 and peak sense arid threshold measurement circuitry 76, Sense amplifier 74 amplifies electrical cardiac signals sensed by RA lead i6 and provides an amplified signal to peak sense and threshold measurement circuitry 76, which in turn provides an indication of sensed cardiac events and measured sense amplifier threshold voltages to digital controller/timer circuit 66. Electrical signals sensed by RA lead 16 provide microcomputer 50 with information regarding depolarizations in right atrium RA. Signals received by RA lead 16 are also provided to EOM amplifier 70 and are converted into digital values by sualog-to-digital converter (ADC) and multiplexer 77. The output of ADC and multiplexer 77 provides a digitized version of the EOM signal, which ΪMD 10 may transmit to an external programmer (not shown) when interrogated by the external programmer to transmit a representation of a cardiac EGM. tinder the control of microcomputer circuit 50 and digital controller/timer circuit 66, output pulse generator 68 provides pacing pulses to RA lead 16.

Ih a similar fashion, RV lead 18 is also connected to digital controller/timer circuit 66 via output pulse generator 78_r EGM amplifier 80, and sensing circuitry 82. Sensing circuitry 82 includes sense amplifier 84 and peak sense and threshold measurement circuitry 86. Sense amplifier 84 amplifies electrical cardiac signals sensed by RV lead .1 B and provides an amplified signal to peak sense and threshold measurβraent circuitry 86, which in turn provides an indication of sensed cardiac events and measured sense amplifier threshold voltages to digital controller/timer circuit 66, Electrical signals sensed by RV lead 18 provide microcomputer 50 with information regarding depolarizations in right ventricle RV, Signals received by RV lead 18 are also provided to EOM amplifier 80 mά are converted to a digital value by ADC sad multiplexer 87. The output of the ADC and multiplexer 87 provides s digitized version of the EGM, signal, which IMD 10 may transmit to fee external programmer when interrogated by the external programmer to transmit a representation of a cardiac EGM. Under the control of microcomputer circuit 50 and digital controHer/timer circuit 66, output pulse generator 78 provides pacing pulses to RY lead IB.

In the embodiment shown ?.o FIG, 2, LMD 10 also includes activity sensor 90 mύ accebromeier 92 or activity crystal, which provide input to digital controller/timer circuit 66 regarding a patient's metabolic requirements. Digital controller/timer circuit 66 takes into account input from activity sensor 90 and aecelerometer 92 in deciding an appropriate rate at which to provide pulses to RA lead 16^' and RV lead IS, However, the patient preferably is not paced at a rate lower than a programmed, patient-specific, lowest rate interval (LRl).

IMD 10 also includes RF transmitter nnά receiver 94 and antenna.96, which allows IMD 10 to be programmed by means of an external programming unit (not shown). Power is supplied to all systems of JMD 10 by power supply 98.

ΪMD 10 may implement any of a number of different pacing modes depending on the situation. Digital controller/timer circuit 66 of FIG. 2 includes programmable digital counters that control the basic timing intervals associated with each of the various pacing modes. Each mode can be described by a three-lettør (or sometimes four) code as described in the following table:

For example, when operating in a DDD mode (known as a tracking πrødε), IMD U⁾ may pace either the atrium or the ventricle and senses in either the atrium or the ventricle, ϊn response to sensed depølarkaέions, pulses may be triggered or inhibited. Thus, IMD 10 operating in the DDB mode may deliver pacing pulses to right, ventricle RV in response to electrical activity sensed (intrinsic or paced) in right atrium RA. During norma! operation of IMD 10, this tracking mode is a -common pacing strategy to maintain a one-to-one coordination between atrial mid ventricular contractions.

FiG. 3 is an example of a. timing diagram illustrating atria! pacing pulses APl- AP16 (collectively AP) and ventricular pacing pulses VP1-VP6 (collectively YP) for delivery by IMD .10 to right atrium RA and right ventricle RV, respectively, as a function of time over first, second, and third periods Tl-O.

During first and third periods Tl aadT3. IMD 10 operates in a non-tracking, AV sequential pacing mode such as DDI. This mode is commonly used, when JMD 10 is following detection of an atrial arrhythmia. During the non-tracking. AV sequential mode, ventricular pacing pulses VP are delivered by 1MB IO only m response to paced atrial pulses, and not to sensed atrial pulses.

In the example shown to FlG. 3, IMD K) detects an. arrhythmia (not shown.) in right atrium RA prior to first time period Tl. Upon detection of this atrial arrhythmia, IMD IO automatically switches to a non-tracking, AV sequential mads (period J). To combat the atrial arrhythmia, IMD 10 automatically selects an appropriate ATP therapy ami begins delivery of the selected ATP therapy to right atrium RA during second time period T2, At the onset of period T2, IMD 10 switches modes to a special therapy mode in which ventricular pacing pulses VP are provided independent of atrial pulses AP (i.e., a non-tracking mode with no AV syπchroiύ/atioa). ATP therapies may vary depending upon the device^'s programmed setting and the detection rate of the arrhythmia, but generally include a carefully controlled, rapidly paced sequence of pacing pulses, ϊn this example, the selected ATP therapy consists of rapidly-paced pulses AP3-.AP14. independent: of this activity in right atrium RA, IMD JO paces right ventricle RV at a constant, paiietu-specific lower rate interval (LRI) representing the lowest rate at which the patient should be paced, ϊf justified by the patient's current activity levels, however, right ventricle RV may he paced at a higher aciivity-hased rate.

As shown in FIG. 3- expected ventricular pacing pulse EVP is scheduled for delivery shortly after last atrial pulse API 4 of the ATP therapy. However, foflowfog delivery of the ATP therapy, IMD 10 switches back to its non-tracking, AV sequential mode in which, ventricular pacing pulses VP lag beMnd atrial pacing pislses AP. delivered by IMD device 10, by Hie A-V interval During the mode transition between the therapy mode and the non-tracking.. AV sequential mode, IMD 10 enforces "A-A timing", m which atrial pulses are provided at the programmed rate at: the expense of providing ventricular pulses at the programmed rate. Therefore, atria! pulse AP 15 is delivered after the last atria! pulse k\ the ATF therapy (,AP 14) at an interval defined by the atrial programmed rate. This mode transition, with A-A timing enforced, causes expected ventricular pulse EVP to not bs delivered to the ventricle and feus results in a V-V interval between ventricular pacing pulses VP4 and VP5 that is significantly longer than the LRI. Il is this long interval thai Is referred to herein as ventricular pause VPP.

Conventionally, atrial ATP therapies were delivered without any consideration of potential ventricular pauses VP?, As described above, however, this long V-V interval, or ventricular pause VPP, may have some undesirable effects,

FI6. 4 is an example of a timing diagram for illustrating a pacing control of IMD 10 for minimizing potential ventricular pauses in accordance with, the present invention. The pacing control of the present invention is based upon the premise that IMD 10 can calculate the timing of a selected atrial ATP therapy and can adjust the timing of pacing pulses to he delivered to right atrium RA arid/or right ventricle RV to minimize the ventricular pause VPP.

As shown in FiG, 4, the therapy delivery duration {TDD) of a selected atrial ATP therapy is a function of the number (n) of ATP pulses comprising the ATP therapy and the mean A-A interval (MAa,t«mii_.) between successive ATP pulses as follows; TDD ^« n * MAj₈W

By adding this duration to an initial V-A interval (VAΪ), a$i atrial activity duration (AAD) can be determined as follows: AAD ^« TDD + VAΪ * n * M A^*; + VAI in this formula, the V-A interval (VAI) is the interval occurring between the ventricular pulse delivered just prior to ATP therapy delivery (VfZ) and the first ATP pulse of the ATP therapy (AP3). A corresponding ventricular activity duration (VAD) during this ATP therapy delivery can be determined as a function of the number of ventricular beats (Z) that would normally occiir in the selected ATP therapy and the V-V interval (VW-vai_.) between successive ventricular pulses as follows: The pacing control of the present invention then attempts to minimize potential ventricular pauses VPP by selecting a value for one of the five variables, of which the atrial activity duration (AAD) and the ventricular activity duration (VAD) are a function, that best equalizes these two durations as follows: ϊl * MAύaβfvaJ + VAJ ~ Z * Vfatiavrf

In other words, the goal in this embodiment is to cause the last ventricular pirtse provided during deliver)' of the ATP therapy to fall sϊmuilaneøus with, or shortly before, the last ATP pulse of the selected ATP therapy, in alternate embodiments, the final ventricular pulse may occur at a prescribed offset with respect to the final ATP therapy pulse. However, this offset should be minimized to keep the potential ventricular pause as small as possible.

Following m& s©\?era! approaches by which a selected atrial ATP therapy and/or ventricular pacing schedule may be adjusted in accordance with the present invention to minimize potential ventricular pauses. In each, of the hypothetical examples presented below, the default values defining the ATP therapy are as follows: the mean A-A interval (MAmtemj) is 150 milliseconds, the number of atrial. ATP pulses {») is 25, the initial V-A interval (YAI) is .1.10 milliseconds, and the V-V interval (V_«to_rv_aø is 1000 milliseconds. Approach 1: _.. V^ Interval

A first approach provides that an alternate Y-V interval {V^^i) be determined for pacing ventricular pulses VP during deliver}' of the atrial ATP therapy, hi many pacing systems, the V-V interval CVWvaø is a pre-programmed value determined by the physician for a particular patient. To prevent the physician^'s settings from being overridden by the pacing control of the pacing system, the pacing system aaay instead request that the physician program a range of acceptable V-V intervals (\W_rvu!) for the patient, In this scenario, the first step is then to determine an. intermediate number of ventricular pacing pulses (Z^!) that will result in a V-Y interval (Vj,«_amj) in the acceptable range of Y-V intervals OW-rot). In. the hypothetical example presented above, this calculation would be as follows; Z' - <μ * MA_toi + VAI) / \W_at X « {(25 * 150 ins) + i 10 vas] I U⁾OO røs - 3.86 pulses The fact that this result is a non-integer value indicates that a ventricular pause would exist if none of the above variables were adjusted. Rather, in accordance with the present invention, the number of ventricular pacing pulses (Z) is determined by rounding the intermediate number of ventricular pacing pulses (Z') to an integer value.

A .modified V-V interval iVitaemt') Js then, calculated as: Viβtβvj¹ * (ti * IVLWrf ÷ YAJ ) / 2? VW/ - 1(25 * 150 ΠJS) + 110 jrøsj / 4 ^« 965 xas

Thus, by adjusting the V-V interval (Viaiwύ to 965 milliseconds (rather than the default 1000 milliseconds), fee last ventricular pulse during stria! ATP therapy and the last atrial pulse of the ATP therapy will be delivered at substantially the same time. Further, by founding the unadjusted number of ventricular pulses up to the next highest Integer, the modified V-V interval (V;,_1(!,W} is assured to be shorter {i.e., faster) than the LRL

The method in which IMD 10 rounds the intermediate number of ventricular pacing pulses (Z') to an integer value affects the selected V-V interval <¥«**•«_>]>. 1» a .first method, 1MB 10 rounds the intermediate number of ventricular pacing pulses (Z') to the nearest integer., -causing the V-V interval (Vintm-ai) to be maintained doss to its programmed setting, ϊn a second method, the intermediate number of ventricular pacing pulses (Z') is roaαded to the next highest integer (e.g., 3.25 would be rounded to 4). ensuring the V-V .interval (V_k18,^ is maintained at a rate faster than the lower rate interval (1,RI). Although the second method ensures the V-V interval (Vmtwvai) &\h within accepted parameters., it causes greater deviation from the programmed rate, ϊn on« embodiment, IMD 10 initially employs the first method and rounds the intermediate number of ventricular pacing pulses (Z') to the nearest integer. If the resulting V-V interval {Vjmerwt) (or other modified parameter) tails within an. acceptable raage_? th&a IMD IO proceeds to deliver the ventricular pacing pulses at the modified V-V interval (V^erva))- ϊf however, the resulting V-Y interval (V«,_WW(_!.) does not fall within an acceptable range (e.g.. modified V-V interval (V;_ntem!) is below the LRJ by a sufficient amount), then IMD H⁾ rounds the intermediate number of ventricular pacing pulses (Z^") the next higher integer to ensure a V-V interval within the accepted range. IO

A second approach adjusts (lie number of ATP therapy pulses (») to πiininiix© potential ventricular pauses VPP. Specifically, a small number of the intended ATP therapy pulses are either withheld or added in an attempt to equalize ike atrial activity duration (AAD) with the ventricular activity duration (VAD), Once again, the first step is to determine aa intermediate number of ventricular pacing pulses (Z') that will result in a V-V ύrtervai {Vi,_rtetv;lt) in the acceptable range of V-V intervals {V»m«vai). Taraing to the hypothetical as shown in the first approach presented above, the intermediate number of ventricular pacing pulses (Z¹) is 3,86, which is then rounded to the nearest integer value or the next higher integer value (depending on the method selected by IMD 10) to determine the number of ventricular pacing pulses (Z) to be delivered as four,

A modified number of ATP therapy pulses (a¹) is then calculated as; a¹ - [(Z¹ * Vfatevi) - VAΪJ / NL-W*) jf = [(4 * 1000 røs) - 110 msj / 150 ins - 25.93

As discussed with respect to Approach 1, rounding to the nearest integer results in the modified number of ATP therapy pulses in') being maintained closer to the programmed value. However, this method may result in fewer ATP therapy pukes (n') being delivered. By rounding to the next highest integer,, the modified number of ATP therapy pulses (rT) will always he equal to or greater than the original number of ATP therapy pulses (n). Rounding the number of ventricular pacing pulses to fee nearest integer value (in this case, four) results in twenty-six ATP therapy pulses (rather than the default twenty-five pulses) being delivered to the atrium. Thus, by adding just one additional ATP therapy pulse, the potential ventricular pause VPP is substantially minimized. Because of this iinal rounding of the number of ATP therapy pulses, however, the ventricular pause will aot be completely eliminated. The number of ATP therapy pulses (if) may differ slightly from the programmed number of ATP therapy pulses when using this approach.

In one embodiment the number of ATP therapy pulses (n) to be included in particular ATP therapies may be programmed as discrete range of values rather than exact numbers, allowing flexibility ϊa delermintng the number of ATI? therapy pulses to be included in a particular ATP therapy. A third approach provides that the mean A-A interval (MAi_πtmΛ]) be adjusted so that the atria! activity duration (AAD) substantially equals the- ventricular activity duration (VAD). Once again, an intermediate number of ventricular pulses (Z') is determined to be 3,86 pulses, In this third approach, however; this intermediate value is preferably rounded to the nearest integer value (rather than the next highest integer value). Despite this distinction, the number of ventricular pacing pulses (Z) in this example is still four.

A modified mean. A-A interval (MAfotβrvai') is than, calculated as:

MAiB(RmI* = [(Z' * Vfatewj) - VAIj / 51

MA**™!' ^:::: 1X4 * ICKK.⁾ as) - 110 m\ / 25 ^» 155.6 ns

Depending upon the resolution of the pacing system, this value may need to be rounded to the nearest acceptable value. For example, if the resolution is five milliseconds, the modified mean A-A interval {MA_tatW} would be rounded to .155 milliseconds, but if the resolution were ten milliseconds, ih& modified mean A-A interval (MAtøiW } would be rounded to 160 milliseconds.

Thus, potential ventricular pauses YPP may be minimized by slightly increasing or decreasing the .mean A-A interval (MA_mIe₁V₃O of the ATP therapy pulses. In <ms embodiment, mean A-A interval. {MAi,_ltwV!<;) between the delivered ATP pulses is allowed to vary from programmed values for the A-A intervals between successive ATP pulses. In alternate embodiments, the mean A-A interval {HAmu^O is programmed as a discrete range rather than an exact number. Approach 4; Initial V-A interval

This fourth approach delays the initiation of the ATP therapy by adjusting the initial V-A interval (VA!) to improve the relative timing of the end of the /VTP therapy. Again, an intermediate number of ventricular pxilses (Z') is determined to he 3.86 pulses.. which value is then rounded, to the nearest integer to provide for four ventricular pacing pulses.

A modified initial V-A interval (VAI') is then calculated as: VAF = {T * Va₁WVd) - (n * MAm^₁) YAf « (4 * 1000 xas) - (25 * .150 ms] *= 250 ms

Depending ispon the resolution of the pacing system, this value may need to be rounded to the nearest acceptable value, In implementing this approach, a timer set for Ms value begins running after the last ventricular pulse delivered prior to the delivery of the ATP therapy. Once the timer expires, the pacing system would begm delivering the atrial ATP therapy . By slightly shifting the delivery of the ATP therapy, the duration, of any potential ventricular pause can be minimized. Aββrgatgh S: Shift jPjMjjse M &&fo»w

FiGS. 5A and 58 are timing diagrams illustrating a fifth approach to rainmimrtg potential ventricular pauses following the transition from arson -.racking mode during delivery of an atrial ATP therapy to an. atrial synchronous mode. Rather than adjusting the timing of pacing pulses to be delivered to right atrium RA and/or right ventricle RV during the time the ATP therapy is being delivered, this fifth approach modules the timing of the pacing pulses immediately following the ATP therapy delivery.

As described above, pacing activity in the ventricle, when operating in the atrial synchronous mods, generally tracks pacing activity in. the striian. For this reason, following successful termination of an atrial arrhythmia by an AIP therapy and return to the atrial synchronous mode, conventional pacing systems enforcing A-A timing first schedule an atrial pacing pulse AP, which may then be tracked by & ventricular pacing pulse VP. Because A-A timing does not take into account the ventricular programmed rate., a long -ventricular pause can result following a svvi tch of .modes.

In this fifth approach, following delivery of the ATP therapy, (he pacing system schedules a ventricular pacing pulse VF to occur prior to any atrial pacing pulses AP, As shown in FIG; 5A₅ following the delivery of a successful ATP therapy (and consequent return to the tracking mode), ventricular pacing pulse VP2 is scheduled at the LRI. rate from ventricular pulse VFl, which is the last ventricular pulse delivered during deliver}' of the ATP therapy. First post- ATP atrial pulse API is then scheduled from the first post- ATP ventricular puise YP2, followed by conventional atrial synchronous mode pacing (employing A-A timing) m boih the atrium, ami the ventricle. This approach .may increase the interval between the last atrial pulse delivered as part of the ATP therapy aid the next atrial pulse {e.g., API). It is believed by the present inventors, however, that a potential pause in the atrium is less worrisome than a long pause in the ventricle and that tins mav be a viable option for certain paiienis.

FlG. 5B illustrates an alternative to Hie method illustrated in FiG, 5A, in which the long atrial pause described with respect to FIG, 5 A is minimised by employing V-V timing, ϊrt V-V timing, ventricular pulses are delivered at the programmed rate (i.e., LR! as shown in FIG. 5B) at the expense of tlie atrial programmed rate, As shown in FΪO. 5B. following the delivery of a successful ATP therapy (and consequent return to the tracking mode), ventricular pacing pulse V.P2 is scheduled at th& LRl fxoxtx ventricular pulse VPi, which is the last ventricular pulse delivered during delivery of the ATP therapy. Because V-V timing is being enforced, a -first posf-ATJ? atrial pulse is scheduled to occur at the pulsed afcriai-vealricular interval (PAV) prior to delivery of the ventricular pulse YP2. The benefit of this method is the return to synchronous pacing directly following delivery of the ATP therapy, as well as a reduction in the atrial pause described with respect to FlG. 5A when A-A timing is enforced. However, because V-V tinting Ls being enforced, the first post- ATP atria) pulse (API) may be delivered close in time with a previous atrial pulse delivered as part of the ATP therapy. Sensed Ventricular Pulses

For sake of simplicity, it is assumed in describing the above approaches that ventricular pacing occurs throughout the duration of the ATP therapy, that is, that no intrinsic pulses are detected in the ventricle. It is possible, however, that intrinsic pulses may be sensed in the ventricle, causing a planned, paced pulse to be inhibited. Where ventricular sensing occurs, the above described calculations could be performed dynamically, or "on the %', to continually adjust the timing of the delivered pacing pulses to minimize potential ventricular pauses. Of course, if intrinsic ventricular pulses are consistently occurring, long ventricular pauses are unlikery to result because the patient would appear to have adequate A-V conduction.

Although the present invention has been described with reference to preferred embodiments;, workers skilled in the an wiil recogflrø that changes may be made in form and detail without departing from the spirit and scope of the invention. For example,, although the present invention, was described above wife respect to en implantable pacemaker device, the invention is equally adaptable for use in both implantable and external, pacing systems. Further, the illustrated embodiments show pacing in only right atrium RA and right ventricle RV, but the present invention applies equally to pacing in all four chambers of the heart.

Claims

1 _% A cardiac pacing device comprising: an atrial lead; a ventricular lead; pulse generation circuitry connected to the atrial and ventricular leads for delivering pacing pulses to an atrium and a ventricle, respectively; and control circuitry for adjusting at least one parameter defining an anti-tachycardia pacing (ATP) therapy and/or a corresponding set of ventricular pacing pulses to affect a ventricular pause following a last ventricular pacing pulse of the set of ventricular pulses, and for causing the poise generation circuitry to deliver the ATP therapy and the set of ventricular pacing pulses, as adjusted, to the atrium and ventricle, respectively.

2. The cardiac pacing device of claim 1 and further comprising: sensing circuitry connected to the atrial and ventricular leads for sensing depolarizations in the atrium and ventricle, respectively.

3. The cardiac pacing device of claim 2, wherein the control circuitry, upon detection of a ventricular depolarization sensed via the ventricular lead, readjusts the at least one parameter to affect, the ventricular pause.

4. The cardiac pacing device of claim 2, wherein the pulse generation circuitry is capable of operating in both an atria! synchronous pacing mode in which synchronized pulses are delivered to the ventricular lead in response to atrial pulses delivered via the atrial lead and a therapy mode in which ventricular pulses are delivered to the ventricular lead independent of atrial pulses sensed or delivered via the atrial lead.

5. The cardiac pacing device of claim 4, wherein the control circuitry causes the pulse generation circuitry, in response to a detected atrial arrhythmia, to switch from the atrial synchronous pacing mode to the therapy pacing mode, and wherein the control circuitry further causes the pulse generation circuitry to revert back to the atrial synchronous pacing mode after a last atrial pulse of the ATP pacing therapy which lias successfully terminated the atrial arrhythmia has been delivered.

6, The cardiac pacing device of claim 1 , wherein the control circuitry further adjusts the at least one parameter to prevent the last ventricular pacing pulse of the set of ventricular pacing pulses from occurring subsequent to a last atrial pulse of the ATP pacing therapy,

7. The cardiac pacing device of claim 1, wherein the at least one parameter includes a number of ventricular pulses comprising the set of ventricular pacing pulses,

S. The cardiac pacing device of claim 1 , wherein the at least one parameter includes a number of atrial pulses comprising the ATP therapy.

9. The cardiac pacing device of claim. 1, wherein, the at least one parameter includes a time interval between successive ventricular pacing pulses of the set of ventricular pacing pulses.

ΪO. The cardiac pacing device of claim 1 „ wherein the at least one parameter includes a mean time interval between successive atrial pulses comprising the ATP therapy.

1 !, The cardiac pacing device of claim 1, wherein the at least one parameter includes a time interval between a ventricular pulse delivered or sensed prior to delivery of the ATP therapy and the beginning of the ATP therapy.

32, The cardiac pacing device of claim 1, wherein the at least, one parameter includes a time interval between a last atrial pulse of the ATP therapy and a first atrial pacing pulse following the ATP therapy.

13. A method for use with a cardiac pacing device in pacing an atrium and a ventricle of a patient, the method comprising- detecting an atrial arrhythmia; selecting an anti-tachycardia pacing (ATP) therapy and a set of ventricular pulses in response to a detected atrial arrhythmia, adjusting at least one parameter defining the ATP therapy and/or the set of "ventricular pulses to affect a ventricular pause following a last vealriculai pacing pulse of the set of ventricular pulses, and delivering the selected ATP therapy and the set of venvπculai pulses as adjusted, to the patient's atrium and ventricle, respectively

14 ϊ he method of claim 13 and fuithei comprising: sensing depolarizations in the ventricles; and readjusting the ai least one parameter m response to a detected intrinsic depolarization in the ventricle.

15. The method of claim 13 wherein the at least one parameter is further adjusted to prevent the last venlTJculai pacing pulse of the set of ventricular pulses from occumng subsequent to a last atrial pulse of the ATP therapy

16. The method of claim 13 -wherein the at least one parameter is selected from the group consisting of a number of veniriculat pulses comprising the set of ventricular pacing pulses; a number of atrial pulses comprising the A IP therapy; a time interval between successive ventricular pacing pulses of the set of ventricular pacing pulses; a mean time interval between successive atrial pulses comprising the ATP therapy; a time interval between a \ entricujar pulse delivered or sensed prior to delivery of the ATP therapy and the start of the ATP therapy; and a time interval between a last atrial pulse of the ATP theiapy and a first atrial pacing pulse following the ATP therapy.

17. A cardiac pacing device for use with a patient, the cardiac pacing device composing: means for defecting an atrial arrhythmia; means for selecting an anti-tachycardia pacing (AIP) therapy and a set of ventricular pulses in response to a detected atrial arrhythmia; means for adjusting at least one parameter defining the ATf* therapy and/or the set of ventricular pulses to prevent a ventricular pause following a last ventricular pulse of the set of ventricular pulses from, exceeding a lowest rate interval; and means for delivering the selected ATP therapy ami the set. of ventricular pulses, as adjusted, to an atrium and a ventricle, respectively, of the patient

18. The cardiac pacing device of claim 17 and further comprising; means for sensing depolarizations in the ventricle; and means for readjusting the at least one parameter m response to a detected intrinsic depolarization in the ventricle.

19. The cardiac pacing device of claim 1.7, wherein the means for adjusting the at least one parameter defining the ATP therapy and/or the set of ventricular pulses comprising: means for adjusting the at least one parameter defining the ATP therapy and/or the set of ventricular pulses to prevent the last ventricular pacing pulse of the set of ventricular pulses from occurring subsequent to a last, atrial pulse of the ATP therapy.

20. The cardiac pacing device of claim 17 wherein the at least oae parameter is selected from the group consisting of a number of ventricular pulses comprising the set of ventricular pacing pulses; a number of atrial pulses comprising the ATP therapy; a time interval between successive ventricular pacing pulses of the set of ventricular pacing pulses; a mean time interval between successive atrial pulses comprising the ATP therapy; a time interval between a ventricular pulse delivered or sensed prior to delivery of the ATP therapy mά the start of the ATP therapy; and a. iimQ interval between the last atrial pulse of the ATF therapy and a first atrial pacing pulse following the ATI? therapy.