Incidence and characteristics of type-2 breaks in response to antitachycardia pacing therapy in implantable cardioverter defibrillator patients.
BACKGROUND
Antitachycardia pacing (ATP) effectively treats monomorphic ventricular tachycardia (VT). The VT may cease immediately upon ATP completion (type-1 break), or it may persist or change to another tachyarrhythmia for one or more beats before termination (type-2 break). We investigated the prevalence and characteristics of type-2 breaks in ICD patients.


RESULTS
We analyzed VT episodes with stored electrograms that had at least one ATP therapy delivered in PainFREE Rx trial, a multicenter trial with 220 coronary artery disease patients. Further subanalysis was performed by classifying the VT as slow or fast based on the cycle length (CL); slow VT: CL >320 ms, fast VT: 240 < or =CL < or =320 ms. To assess the effect of ATP on VT, comparison was performed of pre-ATP and post-ATP CL variability, average CL, and morphology. A total of 514 episodes (264 slow VT and 250 fast VT) were analyzed. The burst ATP terminated 457 (89%; 239 slow VT and 218 fast VT) of 514 episodes. Forty five (10%) episodes in 18 (32%) patients had type-2 breaks. The mean number of beats during type-2 breaks was 5.4 +/- 3.1 (median 4). The mean time for episode termination measured from the end of ATP to return of first sinus/paced beat was 2.9 +/- 1.2 seconds (median 2.6). The VT CL variability increased by 150% after ATP delivery. The ATP affected either VT CL or morphology, or both of 36 (80%) type-2 breaks (9% accelerated, 47% decelerated, 22% changed in morphology only). Among the 9 (20%) episodes that remained unchanged in morphology and CL, four episodes (9%) were unaffected by ATP.


CONCLUSIONS
Approximately 10% of VT episodes that were successfully terminated with burst ATP therapy had type-2 breaks. Type-2 breaks are associated with an increase in CL variability. Approximately 9% of all type-2 episodes may be spontaneously terminating nonsustained VT given that ATP did not affect these episodes in any way.
Sharma
Vinod
V
Tachyarrhythmia Research, Medtronic Inc., 7000 Central Avenue N.E., Minneapolis, MN 55432, USA. vinod.sharma@medtronic.com
DeGroot
Paul J
PJ
Wathen
Mark S
MS
D002304:Cardiac Pacing, Artificial / Q000379:methods* / Q000706:statistics & numerical data*; D015897:Comorbidity; D003324:Coronary Artery Disease / Q000453:epidemiology* / Q000628:therapy*; D017147:Defibrillators, Implantable; D006801:Humans; D015994:Incidence; D012189:Retrospective Studies; D017180:Tachycardia, Ventricular / Q000145:classification / Q000453:epidemiology* / Q000628:therapy*; D016896:Treatment Outcome; D014481:United States / Q000453:epidemiology