USE OF ISOPROTERENOL AS AN AID TO ELECTRIC INDUCTION OF CHRONIC RECURRENT VENTRICULAR TACHYCARDIA

Initiation of ventricular tachycardia using isoproterenol administration and programmed stimulation of the heart was attempted in 11 patients with recurrent ventricular tachycardia in whom standard stimulation techniques alone failed to induce the tachycardia. Seven patients had nonsustained and four had sustained ventricular tachycardla. In four patients, ventricular tachycardia was induced by exercise; in the remaining seven, tachycardia was not exercise-induced. Before isoproterenol, single and double ventricular premature depolarizations and rapid ventricular pacing failed to induce the tachycardia in all patients. After intravenous administration of small amounts (6 to 16 μg) of isoproterenol, critically timed single and double ventricular premature depolarizations could reproducibly initiate and terminate the tachycardia in six of seven patients with nonsustained ventricular tachycardia and in three of four patients with sustained ventricular tachycardia. Propranolol (0.05 to 0.1 mg/kg body weight) was effective in blocking the arrhythmia-facilitating effect of isoproterenol in four patients and procainamide (10 mg/kg) was effective in three patients. In two patients, neither propranolol nor procainamide was effective. The precise mechanisms underlying the arrhythmogenic effects of isoproterenol in each patient are not obvious. Nonetheless, our results suggest that the administration of isoproterenol is a useful adjunct when attempting to initiate ventricular tachycardia by stimulation techniques. As such, it should be helpful in carrying out studies designed to establish appropriate therapeutic interventions in patients with recurrent ventricular tachycardia. © 1979.