Use of the signal-averaged electrocardiogram for predicting inducible ventricular tachycardia in patients with unexplained syncope: Relation to clinical variables in a multivariate analysis

Objectives. The purpose of this study was to determine the predictors of electrically induced ventricular tachycardia in a large sample of patients with unexplained syncope and to examine the value of the signal-averaged electrocardiogram (ECG) in those patient subsets with varying pretest probability of ventricular tachycardia. Background. In patients with unexplained syncope, electrophysiologic study can provide important diagnostic information, such as inducibility of ventricular tachycardia. The signal-averaged ECG can predict inducible ventricular tachycardia, but its utility has not been prospectively studied in a large group of patients with unexplained syncope. Methods. At six hospitals, 189 consecutive patients with unexplained syncope underwent signal-averaged ECG and electrophysiologic studies. Results. Ventricular tachycardia was induced in 28 patients (15%). Univariate predictors of ventricular tachycardia included history of previous myocardial infarction, reduced left ventricular ejection fraction and abnormal signal-averaged ECG results. The signal-averaged ECG was the most sensitive test but had poor specificity. By multivariate analysis, the signal-averaged ECG and history of previous myocardial infarction were independently predictive. The risk of ventricular tachycardia increased 17-fold in patients with a previous myocardial infarction who also had an abnormal signal-averaged ECG. In patients with no history of previous myocardial infarction, no additional testing was useful in identifying those at risk for inducible ventricular tachycardia. Conclusions. The signal-averaged ECG was the most sensitive noninvasive test available to predict sustained ventricular tachy-cardia at electrophysiologic study but was false positive in many patients. A history of previous myocardial infarction followed by the signal-averaged ECG was the most efficient screening process for predicting electrically induced ventricular tachycardia.