Video imaging of atrial defibrillation in the sheep heart

The effects of defibrillatory shocks on the organization of atrial fibrillation (AF) have not been studied previously. In this study, we examined the events that precede, accompany, and follow the application of atrial defibrillatory shocks.

We used video imaging to study the sequence of activation on the surface of the atria in the Langendorff-perfused sheep heart. We recorded transmembrane potentials simultaneously from > 20000 sites on the epicardium during AF as well as during and after biphasic shocks applied by a programmable atrial defibrillator. Defibrillatory shocks (1.2 +/- 0.6 J; n = 6) depolarized all epicardial regions of the atria, and asynchronous repolarization 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 by termination, and (4) organized activity followed by degeneration back into AF. Types 2 through 4 involved a quiescent period lasting 110 +/- 28 ms immediately after the shock, then an activation sequence similar 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 (144 +/- 33 ms). Repolarization time after a shock was significantly longer for successful compared with unsuccessful shocks.

These results indicate that the shock depolarized the entire atrial epicardial surface, followed by a quiescent period, after which organized activation emanated from the sinoatrial pacemaker region.