Cardiac magnetic resonance imaging and primary prevention implantable cardioverter defibrillator therapy: current recommendations and future directions

Implantable cardioverter defibrillators (ICDs) have proven to be the most effective preventive therapy of sudden cardiac death (SCD). Based on current guidelines, the indication for prophylactic ICD therapy is primarily based on a left ventricular ejection fraction (LVEF) less than 35%. However, patients with low LVEF may never have an arrhythmic event while patients with normal to moderately reduced LVEF, who are traditionally felt to be at lower risk, can experience SCD. Therefore, LVEF alone is not an ideal risk stratification parameter to determine ICD therapy. The arrhythmic risk depends mainly on myocardial histopathologic features and electrical properties, which are largely not reflected by left ventricular systolic performance. In addition, several studies demonstrated that the presence of myocardial fibrosis represents a substrate for malignant ventricular arrhythmias and SCD. Cardiac MRI with late gadolinium enhancement is a refined technique able to accurately identify and quantify ventricular myocardial fibrosis and numerous studies demonstrated its ability to better stratify arrhythmic risk compared with LVEF. Recently, the combination of conventional clinical risk factors and biomarkers, namely N-terminal pro-B-type natriuretic peptide and high-sensitivity C-reactive protein, with cardiac MRI (CMR) findings is proving to more effectively predict arrhythmic risk. Moreover, the application of strain technique to CMR and new tissue characterization indices such as T1 mapping represents an attractive possibility to predict the occurrence of tachyarrhythmia. The aim of this review is to provide state-of-the-art evidence and future perspectives on the use of CMR for primary prevention ICD therapy.