title: Relation of atrial refractoriness to upper and lower limits of vulnerability for atrial fibrillation/flutter following implantable ventricular defibrillator shocks.
abstract: BACKGROUND
  Implantable ventricular cardioverter defibrillator (ICD) shocks can cause atrial fibrillation/flutter (AF). This study investigated the pathogenesis of AF after ICD shocks in a canine model.
  
  
  RESULTS
  The study was conducted in 8 dogs. In 5 dogs (group 1), truncated exponential (8 ms, 78% tilt) monophasic and biphasic shocks were delivered through a bipolar epicardial (patch) or endocardial lead. After the last S1 of atrial pacing at a cycle length of 350 ms, shocks of 0.1 to 7.6 A (0.005 to 27.7 J) were delivered, timed to the atrial effective refractory period (AERP). Ventricular defibrillation thresholds were also determined. In 3 dogs (group 2), the effect of the open versus closed chest technique on AF induction was tested in the endocardial biphasic shock configuration. AF was induced in all 8 dogs and in all waveforms and configurations. Mean AF duration was 11.5+/-6 s, with a mean ventricular rate of 184+/-37 bpm. Ventricular shocks could induce AF only if they were timed between an AERP of -60 to 40 ms, -40 to 60 ms, -40 to 60 ms, and -20 to 60 ms in the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively. The mean+/-SD of the upper limit of vulnerability (ULV) for AF induction (in J) was 5. 2+/-0.6, 3.5+/-0.4, 5.2+/-1.2, and 2.5+/-0.1 for the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively (P<0.05). The lower limit of vulnerability (LLV) was 0.8+/-0.1, 0.8+/-0.1, 0.9+/-0, and 0.6+/-0 for the epicardial monophasic, epicardial biphasic, endocardial monophasic, and endocardial biphasic configurations, respectively (P=NS). The ventricular defibrillation threshold (in J) for all wave forms and configurations was higher than the ULV (P<0. 05).
  
  
  CONCLUSIONS
  (1) An atrial LLV and ULV exist for ventricular ICD shock-induced AF; (2) the shock-induced AF is related to both shock intensity and its timing to AERP; and (3) avoiding this atrial window of vulnerability may minimize the risk of post-ICD shock AF.
authors.affiliation: Cardiology Department, Soroka Medical Center, Beer-Sheva, Israel. amoskatz@bgumail.bgu.ac.il
authors.forename: A
authors.initials: A
authors.lastname: Katz
authors.forename: R J
authors.initials: RJ
authors.lastname: Sweeney
authors.forename: R M
authors.initials: RM
authors.lastname: Gill
authors.forename: P R
authors.initials: PR
authors.lastname: Reid
authors.forename: E N
authors.initials: EN
authors.lastname: Prystowsky
mesh_terms: D000818:Animals; D001281:Atrial Fibrillation / Q000503:physiopathology* / Q000628:therapy*; D001282:Atrial Flutter / Q000503:physiopathology* / Q000628:therapy*; D016275:Atrial Function; D004056:Differential Threshold; D004198:Disease Susceptibility; D004285:Dogs; D004554:Electric Countershock; D012032:Refractory Period, Electrophysiological; D013997:Time Factors