Cardiac magnetic resonance in primary prevention of sudden cardiac death

Sudden death accounts for 400,000 deaths annually in the United States. Most sudden deaths are cardiac and are related to arrhythmias secondary to structural heart disease or primary electrical abnormalities of the heart. Implantable cardioverter defibrillator significantly improves survival in patients at increased risk of life-threatening arrhythmias, but better selection of eligible patients is required to avoid unnecessary implantation and identify those patients who may benefit most from this therapy. Left ventricular (LV) ejection fraction (EF) measured by echocardiography has been considered the most reliable parameter for long-term outcome in many cardiac diseases. However, LVEF is an inaccurate parameter for arrhythmic risk assessment as patients with normal or mildly reduced LV systolic function could experience sudden cardiac death (SCD). Among other tools for arrhythmic stratification, magnetic resonance (CMR) provides the most comprehensive cardiac evaluation including in vivo tissue characterization and significantly aids in the identification of patients at higher SCD risk. Most of the evidence are related to late gadolinium enhancement (LGE), which was proven to detect cardiac fibrosis. LGE has been reported to add incremental value for prognostic stratification and SCD prediction across a wide range of cardiac diseases, including both ischemic and nonischemic cardiomyopathies. In addition, T1, T2 mapping and extracellular volume assessment were reported to add incremental value for arrhythmic assessment despite suffering from several technical limitations. CMR should be part of a multiparametric approach for patients' evaluation, and it will play a pivotal role in prognostic stratification according to the current evidence.