title: Incidence and characteristics of type-2 breaks in response to antitachycardia pacing therapy in implantable cardioverter defibrillator patients.
abstract: 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.
authors.affiliation: Tachyarrhythmia Research, Medtronic Inc., 7000 Central Avenue N.E., Minneapolis, MN 55432, USA. vinod.sharma@medtronic.com
authors.forename: Vinod
authors.initials: V
authors.lastname: Sharma
authors.forename: Paul J
authors.initials: PJ
authors.lastname: DeGroot
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wathen
mesh_terms: 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