Implantable defibrillator event rates in patients with unexplained syncopeand inducible sustained ventricular tachyarrhythmias - A comparison with patients known to have sustained ventricular tachycardia

OBJECTIVES To assess the clinical significance of inducible ventricular tac hyarrhythmias among patients with unexplained syncope. BACKGROUND Induction of sustained ventricular arrhythmias at electrophysiol ogy study in patients with unexplained syncope and structural heart disease is usually assigned diagnostic significance. However, the true frequency o f subsequent spontaneous ventricular tachyarrhythmias in the absence of ant iarrhythmic medications is unknown. METHODS In a retrospective case-control study, the incidence of implantable cardiac defibrillator (ICD) therapies for sustained ventricular arrhythmia s among patients with unexplained syncope or near syncope (syncope group, n = 22) was compared with that of a control group of patients (n = 32) with clinically documented sustained ventricular tachycardia (VT). Sustained ven tricular arrhythmias were inducible in both groups and neither group receiv ed antiarrhythmic medications. All ICDs had stored electrograms or RR inter vals. Clinical variables were similar between groups except that congestive cardiac failure was more common in the syncope group. RESULTS Kaplan-Meier analysis of the time to first appropriate ICD therapy for syncope and control groups produced overlapping curves (p = 0.9), with 57 +/- 11% and 50 +/- 9%, respectively, receiving ICD therapy by one year. In both groups, the induced arrhythmia was significantly faster than sponta neous arrhythmias, but the cycle lengths of induced and spontaneous arrhyth mias were positively correlated (R = 0.6, p < 0.0001). During follow-up, th ree cardiac transplantations and seven deaths occurred in the syncope group , and two transplantations and five deaths occurred in the control group (3 6-month survival without transplant 52 +/- 11% and 83 +/- 7%, respectively, p = 0.03). CONCLUSIONS In patients with unexplained syncope, structural heart disease and inducible sustained ventricular arrhythmias, spontaneous sustained vent ricular arrhythmias occur commonly and at a similar rate to patients with d ocumented sustained VT. Thus, electrophysiologic testing in unexplained syn cope can identify those at risk of potentially life-threatening tachyarrhyt hmias, and aggressive treatment of these patients is warranted. (C) 1999 by the American College of Cardiology.