Refining risk stratification for primary prevention ICD therapy: Insights from cardiac MRI in the DO-IT registry.

Background: Implantable cardioverter-defibrillators (ICDs) are recommended for the primary prevention of sudden cardiac death in patients with reduced left ventricular ejection fraction (LVEF). However, reliance on LVEF alone may inadequately identify patients at the highest risk. Objective: This study aimed to evaluate the prognostic value of cardiac magnetic resonance imaging (CMR), particularly late gadolinium enhancement (LGE), in patients with ischemic cardiomyopathy (ICM) and nonischemic dilated cardiomyopathy (NIDCM). Methods: This multicenter substudy of the Dutch Outcome in ICD Therapy registry included 252 patients with a reduced LVEF (≤35%) who underwent CMR before primary prevention ICD implantation. NIDCM was the underlying etiology in 52% and cardiac resynchronization therapy (CRT) was present in 38%. The median follow-up was 4.3 years. Outcomes were appropriate device therapy (ADT) and all-cause mortality. Results: LGE was present in 70% and was significantly more extensive in patients with ICM than in those with NIDCM. During follow-up, ADT occurred in 15%, and 19% died, with similar rates between the ICM and NIDCM groups. LGE presence and extent were not associated with ADT or mortality, in the overall cohort nor in subgroup analyses stratified by etiology or non-CRT status. In contrast, right ventricular dysfunction and increased left ventricular end-diastolic volume were associated with outcomes. Conclusion: LGE on CMR was not associated with ADT or mortality in patients with ICM or NIDCM, nor in the non-CRT subgroup, suggesting a limited role in guiding ICD therapy. In contrast, markers of biventricular dysfunction and adverse remodeling exhibited a prognostic value, highlighting their potential to refine risk stratification beyond traditional LVEF-based criteria.