Prognostic Value of Papillary Muscle Scarring in Patients With Dilated Cardiomyopathy.

Importance Papillary muscle scarring (papSCAR) can occur without epicardial coronary artery disease, likely due to microvascular dysfunction. Dilated cardiomyopathy (DCM) has been associated with microvascular dysfunction; the prevalence and prognostic significance of papSCAR in patients with DCM are unclear. Objective To determine the prevalence of papSCAR in patients with DCM and to evaluate if papSCAR is associated with adverse outcomes. Design, Setting, and Participants This cohort study was conducted among consecutive patients with known or suspected DCM prospectively enrolled at an academic hospital in North Carolina from January 2011 to December 2020. Patients were referred for cardiovascular magnetic resonance (CMR) imaging, and the study protocol included flow-independent dark blood delayed-enhancement (FIDDLE) imaging, which improves the detection of papSCAR. Data were analyzed from January 2022 to December 2022. Main Outcomes and Measures The primary end point was cardiac mortality. Secondary end points included a composite of heart failure events (heart failure death or cardiac transplant) and a composite of arrhythmia events (sudden cardiac death [SCD] or aborted SCD). Results This cohort study included 470 patients (mean [SD] age, 55.3 [14.3] years; 205 female patients [43.6%]). During up to 8 years of follow-up (2082 patient-years), there were 53 cardiac deaths, 49 heart failure events, and 24 arrhythmia events. PapSCAR was present in 137 patients (29.1%), and mean (SD) left ventricular ejection fraction (LVEF) was similar between those with and without papSCAR (30.7% [11.0%] vs 31.4% [10.3%]; P = .52). Patients with papSCAR had a higher rate of cardiac death than those without (19.0% vs 8.1%; hazard ratio [HR], 2.30; 95% CI, 1.34-3.95; P = .002). After adjustment for prespecified variables known to have prognostic value in DCM (age, systolic blood pressure, heart rate, LVEF, and midwall myocardial scar), papSCAR was independently associated with cardiac death (HR, 1.86; 95% CI, 1.07-3.24; P = .03) and provided incremental prognostic value (incremental χ2, 4.68; P = .03). PapSCAR was also independently associated with heart failure events (HR, 2.05; 95% CI, 1.16-3.61; P = .01) and arrhythmia events (HR, 3.41; 95% CI, 1.46-7.94; P = .005). Conclusions and Relevance In this single-center cohort study, papSCAR as detected by dark blood delayed-enhancement CMR was present in approximately one-third of patients with DCM and was independently associated with cardiac death.