Adverse effects of permanent cardiac internal defibrillator patches on external defibrillation.

At the time of left ventricular aneurysm resection, antiarrhythmic operations or other open-heart operative procedures in patients with ventricular dysrhythmia, permanent internal defibrillator patches may be inserted. Insertion of the energy source may be delayed due to its unavailability or to a desire for postoperative electrophysiologic study before its insertion. To assess the effects of permanent internal defibrillator patches on external defibrillation, 7 anesthetized calves were studied. Fibrillation-defibrillation studies were performed before and after insertion of permanent internal defibrillator patches (model L67, 27 cm2, Intec Systems), one on each ventricle. The values of percent successful defibrillation obtained before insertion of the patches, although much lower than values that would be expected in humans, are consistent with the results of an extensive earlier study involving this calf model. Similar values obtained after insertion of the patches are appreciably lower than the values obtained before implantation of the patches, and appreciably lower than the results predicted by the earlier study. A significant decrease in the percent of successful defibrillations (p less than 0.001) was observed for a shock intensity of approximately 400 J. Permanent internal cardiac defibrillator patches on the right and left ventricles reduce the probability of achieving successful defibrillation externally with unidirectional shocks. The wisdom of implanting permanent large internal cardiac defibrillator patches without the energy source is questioned.