Follow-up of patients with unexplained syncope and inducible ventricular tachyarrhythmias: Analysis of the AVID registry and an AVID substudy

Introduction: A prospective registry and substudy were conducted in the Ant iarrhythmics Versus Implantable Defibrillators (AVID) Study to clarify the prognosis and recurrent event rate, risk factors, and impact of implantable cardioverter defibrillator (ICD) therapy in patients with unexplained sync ope, structural heart disease, and inducible ventricular tachyarrhythmias. Methods and Results: Included in the AVID registry were patients from all p articipating sites who had "out of hospital syncope with structural heart d isease and EP-inducible VT/VF with symptoms." In addition, 13 collaborating sites provided more in-depth clinical and electrophysiologic data as part of a formal prospective substudy. Patients in the substudy were followed by local investigators for recurrent arrhythmic events and mortality. Registr y patients were tracked for fatal outcomes by the National Death Index. A t otal of 429 patients with syncope were entered in the AVID registry, of who m 80 participated in the substudy. Of the substudy patients, 21 patients (2 6%) had inducible polymorphic ventricular tachycardia/ventricular fibrillat ion (VT/VF), 11 patients (14%) had sustained monomorphic VT <200 beats/min, and 48 patients (60%) had sustained monomorphic VT <greater than or equal to>200 beats/min. The ICD was used as sole therapy in 75% of the syncope su bstudy patients (and with antiarrhythmic drug in an additional 9%) and in 5 9% of the syncope registry patients. Survival rates at 1 and 3 years were 9 3% and 74% for the substudy patients and 90% and 74% for the registry patie nts, respectively. Survival of the syncope substudy patients (predominantly treated by ICD) was similar to the VT patients treated by ICD and superior to the VT patients treated by an antiarrhythmic drug (P=0.05) in the rando mized main trial. Mortality events in the substudy were marginally predicte d by ejection fraction (P=0.06) but not by electrophysiologic study-induced arrhythmia. The significant predictor of increased mortality in the regist ry was age (P=0.003) and of reduced mortality was treatment with ICD (P=0.0 06). Conclusion: The results of these analyses support the role of the ICD as pr imary antiarrhythmic therapy in patients with unexplained syncope, structur al heart disease, and inducible VT/VF at electrophysiologic study.