VIDEO IMAGING OF ATRIAL DEFIBRILLATION IN THE SHEEP HEART

Background The effects of defibrillatory shocks on the organization of atrial fibrillation (AF) have not been studied previously. In this st udy, we examined the events that precede, accompany, and follow the ap plication of atrial defibrillatory shocks. Methods and Results We used video imaging to study the sequence of activation on the surface of t he atria in the Langendorff-perfused sheep heart. We recorded transmem brane potentials simultaneously from >20 000 sites on the epicardium d uring AF as well as during and after biphasic shocks applied by a prog rammable atrial defibrillator. Defibrillatory shocks (1.2+/-0.6 J; n=6 ) depolarized all epicardial regions of the atria, and asynchronous re polarization occurred. The shocks resulted in four types of responses: (1) immediate cessation of epicardial activity, (2) single postshock activation, (3) organized activation for 0.8 to 1.5 seconds followed b y termination, and (4) organized activity followed by degeneration bac k into AF. Types 2 through 4 involved a quiescent period lasting 110+/ -28 ms immediately after the shock, then an activation sequence simila r to those observed during sinus rhythm. The first cycle length after the shock for types 3 and 4 (170+/-36 ms) was longer than during AF (1 44+/-33 ms). Repolarization time after a shock was significantly longe r for successful compared with unsuccessful shocks. Conclusions These results indicate that the shock depolarized the entire atrial epicardi al surface, followed by a quiescent period, after which organized acti vation emanated from the sinoatrial pacemaker region.