Electrophysiologic observations during the spontaneous initiation of ischemia-induced ventricular fibrillation.

Electrophysiologic features of spontaneous, ischemia-induced ventricular fibrillation were studied in 17 dogs using multiple endocardial bipoles positioned in normal and ischemic zones and at the border of ischemic myocardium. All dogs showed ventricular tachyarrhythmias prior to the initiation of ventricular fibrillation. The heart rate prior to the fatal arrhythmia in the ventricular fibrillation dogs was significantly faster than that of nonventricular fibrillation dogs. There was no difference in the coupling intervals of the initial premature complex between episodic and sustained ventricular arrhythmia in most dogs. However, shorter coupling intervals initiated sustained arrhythmia in some dogs. Sites of initiation of arrhythmia were mostly in the ischemic zone. Furthermore, diastolic electrical activity was consistently observed in the ischemic zone during fatal arrhythmia in dogs showing diastolic activity. Cycle length during the fatal arrhythmia prior to ventricular fibrillation gradually shortened, whereas cycle length of episodic ventricular tachycardia remained approximately 200 msec followed by lengthening prior to restoration of sinus rhythm. The disparity of local activation (time differences between the earliest and latest onset of the activation in the five recording sites) increased during the fatal arrhythmia. Examples of progressive intraventricular block (Wenckebach-like) between the border and the center of ischemic myocardium leading to ventricular fibrillation are resynchronization of this disparity leading to the termination of ventricular tachycardia are shown. The recording of continuous electrical activity using bipolar electrodes with an interelectrode distance of 1 mm suggests a smaller reentrant pathway during fatal arrhythmia. Our observations confirm the importance of endocardial recordings within ischemic myocardium, and adds new insight into the events leading to both episodic and sustained ventricular tachycardia.