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(Circulation. 1999;100:1125-1130.)
© 1999 American Heart Association, Inc.

Basic Science Reports

Relation of Atrial Refractoriness to Upper and Lower Limits of Vulnerability for Atrial Fibrillation/Flutter Following Implantable Ventricular Defibrillator Shocks

Amos Katz, MD; Robert J. Sweeney, PhD; Robert M. Gill, BS; Philip R. Reid, MD; Eric N. Prystowsky, MD

From the Cardiology Department, Soroka Medical Center, Beer-Sheva, Israel (A.K.); the Department of Electrophysiology Research, Lilly Research Laboratory Division, Eli Lilly and Company (R.J.S., R.M.G., P.R.R.); and Indiana Heart Institute, Indianapolis, Ind (E.N.P.).

Correspondence to Amos Katz, MD, Cardiology Department, Soroka Medical Center, POB 151, Beer-Sheva 84101, Israel. E-mail amoskatz{at}bgumail.bgu.ac.il

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.

Methods and 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.

Key Words: atrium • defibrillation • electrophysiology • fibrillation