Risk Stratification and Outcomes of Right Atrial Phasic Function in Arrhythmogenic Right Ventricular Cardiomyopathy: A Cardiac Magnetic Resonance Study

Background Advanced arrhythmogenic right ventricular cardiomyopathy is associated with a high risk of malignant ventricular arrhythmias (MVA) and end‐stage heart failure (HF). However, the prognostic role of right atrial (RA) mechanics, as quantified by cardiac magnetic resonance imaging (CMR), remains largely unexplored. Methods Consecutive patients with arrhythmogenic right ventricular cardiomyopathy undergoing CMR between 2014 and 2021 were retrospectively included. Demographics, clinical history, and strain parameters were collected. The primary clinical end points were end‐stage HF and MVA. Results A total of 316 patients (mean age 38±15 years; 66.1% men) were included. Over a median follow‐up of 5.3 years, 49 developed end‐stage HF and 103 experienced MVA outcomes. Multivariable Cox and Fine‐Gray models showed that impaired RA reservoir strain was an independent predictor of end‐stage HF (hazard ratio [HR] 0.92, 95% CI 0.89–0.96, P <0.001) and MVA outcomes (subdistribution hazard ratio (sHR) 0.98, 95% CI 0.96–0.99, P =0.025), with added prognostic value beyond clinical and imaging variables, improving the C‐statistic to 0.84 and 0.70, respectively. Kaplan–Meier survival curves indicated that RA reservoir strain <18.6% was associated with higher end‐stage HF risk, consistent across subgroups regardless of left ventricular involvement (both log‐rank P <0.05). The association between RA reservoir strain <23.0% and MVA was significant in the overall cohort ( P <0.001) and in patients without left ventricular involvement ( P =0.002), but not in those with left ventricular involvement ( P =0.08). Conclusions Lower cardiac magnetic resonance‐derived RA reservoir strain was independently associated with end‐stage HF and MVA in arrhythmogenic right ventricular cardiomyopathy and provided incremental prognostic value beyond conventional risk markers. These findings support RA mechanics as a potential complementary component of multichamber CMR risk assessment, pending external validation.