Electrophysiological and pharmacological studies on the mechanisms of ventricular tachycardia.

Employing electrophysiological and pharmacological methods, the mechanisms of recurrent ventricular tachycardia were studied in 31 patients, 18 with old myocardial infarction and 13 with idiopathic ventricular tachycardia. In the cases of ventricular tachycardia with old myocardial infraction, the initiation and termination of the tachycardia could be achieved by programmed electrical stimulation in 13 out of 18 patients. Endocardial mapping showed that the earliest excitation site during tachycardia was at the border zone of infarction, where the diastolic fragmented activity was detected. Programmed electrical stimulation sometimes provoked more than two kinds of QRS morphology of tachycardia in the same patient. Class IA antiarrhythmic agents were effective in terminating tachycardia. These data suggest that there are multiple reentrant pathways consisting of partially depressed fast fibers at the border zone of infarction. In the cases with idiopathic ventricular tachycardia, the induction and termination of tachycardia was effected by electrical stimulation in 8 out of 13 patients. For the termination of tachycardia, long overdrive pacing was sometimes necessary. The diastolic fragmented activity could not be detected by endocardial mapping. A class IV drug such as verapamil was more effective for the termination of tachycardia than class I drugs, and there were repetitive short runs of ventricular extrasystole observed until the final termination. These data support the reentrant pathways containing slow with enhanced automaticity as the circuit of idiopathic ventricular tachycardia.