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(Circulation. 1998;97:1613-1622.)
© 1998 American Heart Association, Inc.

Basic Science Reports

Effects of Atrial Defibrillation Shocks on the Ventricles in Isolated Sheep Hearts

Richard A. Gray, PhD; ; José Jalife, MD

From the Department of Pharmacology, SUNY Health Science Center at Syracuse, NY.

Correspondence to José Jalife, MD, Department of Pharmacology, SUNY Health Science Center at Syracuse, 766 Irving Ave, Syracuse, NY 13210.

Background—The effects of cardioversion of atrial fibrillation on the activation sequence of the ventricles have not been previously studied. In this study we examined the events in the ventricle that follow the application of atrial defibrillatory shocks.

Methods and Results—We used video imaging technology to study the sequence of activation on the surface of the ventricles in the Langendorff-perfused sheep heart. We recorded transmembrane potentials simultaneously from over 20 000 sites on the epicardium before and after biphasic shocks applied by a programmable atrial defibrillator. The first epicardial activation after the shock depended on both the voltage and timing of the shock. During ventricular diastole shocks as low as 10 V produced ventricular excitation, although the time between the shock and the first epicardial activation (latency) was 30 ms. As the shock voltage was increased to 120 V, latency decreased to zero and the entire epicardium was depolarized within 30 ms. For 120-V shocks delivered late in systole, the depolarization sequence produced by the shock was similar to the previous repolarization sequence. Shocks of 120 V applied 150 to 300 ms after the previous ventricular excitation induced ventricular fibrillation. Ventricular fibrillation was induced by multiple focal beats after the shock, which produced waves that propagated but broke down into reentry within regions of high repolarization gradients.

Conclusions—These results demonstrate that atrial defibrillation shocks excite the ventricles even at low shock voltages. In addition, ventricular fibrillation can be induced by shocks given in the vulnerable period by producing focal patterns that break down into reentrant waves.

Key Words: cardioversion • defibrillation • fibrillation • ventricles