Epicardial activation times after defibrillation in open-chest dogs using unipolar DC-coupled activation recordings

The widespread clinical application of implantable electrical defibrillation devices has engendered considerable interest into the mechanism of action of such devices. In addition, better means of rapid detection of postshock efficacy have been sought. The authors performed this study to test the following hypotheses: (1) postshock epicardial activation times may be used to differentiate successful from unsuccessful defibrillation attempts; and (2) successful defibrillation can be characterized by whether two or more activation wavefronts are simultaneously present on the epicardium after a defibrillation attempt. Unipolar Ag AgCl sintered electrodes were directly coupled from 120 recording sites that covered both right and left ventricular surfaces. This technique was applied to 203 defibrillation attempts in 6 open-chest dogs during electrically induced ventricular fibrillation. There were 139 successful and 64 unsuccessful defibrillation attempts. The difference between the first and second post-shock activation times was significantly different between the successful and unsuccessful attempts. This difference was secondary to the activation time delay of the second post-shock activation cycle relative to the first post-shock activation cycle. When the first-to-second post-shock time delay was greater than 140 ms, the defibrillation attempt was found to be uniformly successful. In no case of successful defibrillation accompanied by total termination of ventricular fibrillation were more than two wavefronts simultaneously present on the heart after shock. In contrast, successful defibrillation accompanied by transient residual fibrillating activity or unsuccessful defibrillation attempts were observed to present with either two simultaneous activation wavefronts or an activation wavefront in temporal isolation. In summary, the first two post-shock epicardial activation sequences can determine the eventual outcome of a defibrillation attempt if the delay between them exceeds 140 ms, but they are unable to determine the outcome if the delay is less than 140 ms.