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: immediate resumption of a coordinated rhythm, thought to reflect complete depolarization of the myocardium; 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 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.