Risk Stratification of Sudden Cardiac Death in Nonischemic Dilated Cardiomyopathy: Arrhythmogenic Substrate Assessment in Cardiac MRI

Background MRI-derived arrhythmogenic substrate, including late gadolinium enhancement (LGE) and extracellular volume fraction (ECV), is indicative of sudden cardiac death (SCD) risk in nonischemic dilated cardiomyopathy (DCM). The relative prognostic value of LGE and ECV remains unclear. Purpose To evaluate the performance of LGE and T1 mapping in predicting SCD in patients with DCM and to explore clinical implementation. Materials and Methods This study enrolled 1105 patients with DCM who underwent cardiac MRI at four centers. The data were analyzed in a development cohort (<i>n</i> = 837, single center) and an external validation cohort (<i>n</i> = 268, multicenter). The primary end point comprised SCD, appropriate implantable cardioverter-defibrillator shock, and resuscitated cardiac arrest. The secondary end point comprised heart failure-related death, heart transplant, and left ventricle (LV) assist device implantation. Risk algorithms and a clinical workflow for SCD risk assessment were developed based on validated MRI predictors. Results In the development cohort, 78 patients reached the primary end point and 120 reached the secondary end point over a median follow-up of 58.3 months. In the adjusted analysis, LGE of at least 7.2% of the LV mass (hazard ratio [HR], 4.75 [95% CI: 2.91, 7.74]; <i>P</i> < .001), an ECV of at least 31.8% (HR, 2.91 [95% CI: 1.63, 5.22]; <i>P</i> = .001), and a native T1 <i>z</i> score of at least 2.1 (HR, 1.69 [95% CI: 1.04, 2.74]; <i>P</i> = .04) were associated with SCD-related events. Patients with an ECV of at least 31.8% and no LGE were at a higher risk of SCD events compared with those with an ECV less than 31.8% and presence of LGE of less than 7.2% or midwall and/or focal LGE. Patients with an LV ejection fraction greater than 35%, LGE less than 7.2%, and an ECV less than 31.8% exhibited a low risk of SCD, with an annual event rate of 0.2%. Patients with LGE of at least 7.2% exhibited a high risk of SCD-related events (annual event rate, 4.65%) irrespective of ECV and native T1 value and LGE distribution and/or pattern. Conclusion In nonischemic DCM, LGE of at least 7.2% was strongly predictive of SCD risk irrespective of distribution and pattern. ECV significantly enhanced risk stratification, particularly in patients with negative or focal and/or midwall LGE. © RSNA, 2025 <i>Supplemental material is available for this article.</i> See also the editorial by Sakuma in this issue.