Unexpected coexistence of supraventricular and ventricular tachycardia in patients with syncope

The incidence of multiple, inducible sustained arrhythmias during electrophysiologic studies is unknown. We have identified five patients who had several sustained tachycardias, some of which were not previously recognized clinically. Three patients had documented sustained supraventricular tachycardia (one of these also had nonsustained ventricular tachycardia) and two had documented sustained ventricular tachycardia. The clinically documented tachycardia was successfully reproduced in all cases; however, the three cases of supraventricular tachycardia also had sustained ventricular tachycardia initiated, and the two cases of ventricular tachycardia also had sustained supraventricular tachycardia, which had not previously been seen. The underlying common denominators for all five patients were poor left ventricular function due to ischemic heart disease and a history of syncope. In one case of clinical supraventricular tachycardia, the second sustained tachycardia appeared following drug therapy (procainamide), which seemed to convert nonsustained to sustained ventricular tachycardia. In another patient with clinical ventricular tachycardia, the supraventricular tachycardia was also initiated following drug therapy (indecainide). We conclude that: (1) patients with syncope may have multiple arrhythmic etiologies and (2) complete electrophysiologic evaluation, during control studies as well as serial drug studies, are important in the management of these patients.