Patterns of Ventricular Activity During Catheter Defibrillation

In order to clarify the mechanism of ventricular catheter defibrillation in which the electrode distribution and the low energy requirements make a simultaneous depolarization of the entire myocardium unlikely, the electrocardiograms recorded during 120 catheter fibrillation-defibrillation episodes in 39 dogs were analyzed. Three distinct, equally distributed defibrillation patterns were observed: 1) immediate resumption of a coordinated rhythm, thought to reflect complete depolarization of the myocardium; 2) increasing coarsening of the fibrillation waveforms interpreted as progressive reduction in the number of fibrillating fibers with reversion when a critical mass of myocardium with synchronized activity is reached, and 3) production of more coordinated “flutter-like’ ventricular complexes probably representing a rhythm distinct from fibrillation and convertible to sinus rhythm by a second subthreshold shock. These observations suggest that total depolarization of the entire myocardium is not a prerequisite for ventricular defibrillation.