OBJECTIVE: This study evaluated the prognostic value of electrocardiogram (ECG)-based predictors in the primary prevention of sudden cardiac arrest (SCA) among ischemic cardiomyopathy patients with depressed left ventricular ejection fraction (LVEF </=35%). BACKGROUND: The prediction of cause-specific mortality in high-risk patients offers the potential for targeting specific therapies (i.e., implantable cardioverter-defibrillator [ICD]). METHODS: Subjects were recruited from the Prediction of Arrhythmic Events with Positron Emission Tomography (PAREPET) study. Continuous Holter 12-lead ECG recordings were obtained at the start of study and used to compute 15 clinically-important ECG abnormalities (e.g., atrial fibrillation). RESULTS: Among 197 patients (age 67 +/- 11 years, 93% male, mean follow-up 4.1 years) enrolled, 30 (15%) were SCA cases and 35 (18%) cardiac non-sudden deaths (C/NS). In multivariate analysis, only heart-rate-corrected QT interval (QTc) predicted SCA (hazard ratio 2.9 [1.2-7.3]) and only depressed heart rate variability (HRV) predicted C/NS (hazard ratio 5.0 [1.5-17.1]) independent of demographic and clinical parameters. CONCLUSIONS: Among patients with depressed LVEF, prolonged QTc suggests greater potential benefit from ICD therapy to prevent SCA; depressed HRV suggests potential benefit from bi-ventricular pacing to prevent C/NS.