This retrospective multicenter cohort will validate an independent association of electrocardiographic (ECG) global electrical heterogeneity (GEH) measures with sustained ventricular tachyarrhythmias and appropriate ICD therapies in systolic heart failure patients with primary prevention ICD, and will validate and re-calibrate GEH ECG risk score for prediction of sustained ventricular tachyarrhythmias and appropriate ICD therapies in systolic heart failure patients with primary prevention ICD.