- The majority of patients receiving implantable cardioverter-defibrillator (ICD) implantation under current guidelines never develop sustained ventricular arrhythmia; therefore, better markers of risk for sustained ventricular tachycardia and/or ventricular fibrillation (VT/VF) are needed. To identify cardiac magnetic resonance arrhythmic risk predictors for ischemic cardiomyopathy prior to ICD implantation. Forty-three subjects (64.5±11.9 years) with prior myocardial infarction (MI) who were referred for ICD implantation were evaluated by cardiac MRI. The MRI protocol included left ventricular (LV) functional parameter assessment using steady state free precession and LGE-MRI using inversion recovery fast gradient echo. LV functional parameters were measured using cardiac magnetic resonance software. Subjects were followed-up for 6-46 months and the events of appropriate ICD treatments (shocks and anti-tachycardia pacing) were recorded. Twenty-eight patients experienced 46 spontaneous episodes during a median follow up of 30 months. The total MI size (18.05±11.44g versus 38.83±19.87 g, p=0.0006), MI core (11.63±7.14 g versus 24.12±12.73 g, p=0.0002) and infarct gray zone (6.43±4.64g versus 14.71±7.65g, p=0.0004) were significantly larger in subjects who received appropriate ICD therapy compared with those who did not experience an episode of VT/VF. Multivariate regression analyses for infarct gray zone and for MI core, adjusted for NYHA class, diabetes, and etiology (primary or secondary prevention) revealed that the gray zone and MI core were predictors for appropriate ICD therapies (p=0.0018 and p=0.007 respectively). The extent of MI scar may predict which patients would benefit most from ICD implantation. Copyright © 2015. Published by Elsevier Inc.