BACKGROUND: Stratifiers of sudden and total mortality risk are needed to optimally target preventive therapies in patients with coronary artery disease and impaired ventricular function. We assessed the prognostic significance of ECG markers of conduction abnormalities and left ventricular hypertrophy in the Multicenter Unsustained Tachycardia Trial (MUSTT). METHODS AND RESULTS: We analyzed the ECGs of 1638 patients from MUSTT who did not receive antiarrhythmic therapy (antiarrhythmic medication or implantable cardioverter-defibrillator). After adjustment for other significant factors, left bundle-branch block and intraventricular conduction delay were associated with a 50% increase in the risk of both arrhythmic and total mortality. Right bundle-branch block was not associated with arrhythmic or total mortality. Left ventricular hypertrophy was the only ECG predictor of arrhythmic (hazard ratio, 1.35; 95% CI, 1.08 to 1.69) but not total mortality. CONCLUSIONS: In patients with coronary artery disease, depressed left ventricular function, and nonsustained ventricular tachycardia, QRS prolongation resulting from left bundle-branch block or intraventricular conduction delay but not right bundle-branch block provided prognostic information about the risk of arrhythmic and total mortality independently of electrophysiological evaluation and ejection fraction. Left ventricular hypertrophy was associated with increased arrhythmic but not total mortality.