Importance The characteristics and treatment strategies of atrial functional mitral regurgitation (AFMR) are poorly understood. Objective To investigate the prevalence, clinical characteristics, and outcomes of mitral valve (MV) surgery in AFMR. Design, Setting, and Participants This retrospective cohort study, called the Real-World Observational Study for Investigating the Prevalence and Therapeutic Options for Atrial Functional Mitral Regurgitation (REVEAL-AFMR), was conducted across 26 Japanese centers (17 university hospitals, 1 national center, 3 public hospitals, and 5 private hospitals). All transthoracic echocardiography procedures performed from January 1 to December 31, 2019, were reviewed to enroll adult patients (aged ≥20 years) with moderate or severe AFMR, defined by preserved left ventricular function, a dilated left atrium, and an absence of degenerative valvular changes. Data were analyzed from May 8, 2023, to May 16, 2024. Exposures Mitral valve surgery, with or without tricuspid valve intervention. Main Outcomes and Measures The primary composite outcome included heart failure hospitalization and all-cause mortality. Results In 177 235 patients who underwent echocardiography, 8867 had moderate or severe MR. Within this group, 1007 (11.4%) were diagnosed with AFMR (mean [SD] age, 77.8 [9.5] years; 55.7% female), of whom 807 (80.1%) had atrial fibrillation. Of these patients, 113 underwent MV surgery, with 92 (81.4%) receiving concurrent tricuspid valve surgery. Patients who underwent surgery were younger but had more severe MR (57.5% [n = 65] vs 9.4% [n = 84]; P &amp;amp;lt; .001), a larger mean (SD) left atrial volume index (152.5 [97.8] mL/m 2 vs 87.7 [53.1] mL/m 2 ; P &amp;amp;lt; .001), and a higher prevalence of heart failure (according to the New York Heart Association class III [marked limitation of physical activity] or class IV [symptoms of heart failure at rest], 26.5% [n = 30] vs 9.3% [n = 83]; P &amp;amp;lt; .001) than those who remained under medical therapy. During a median follow-up of 1050 days (IQR, 741-1188 days), 286 patients (28.4%) experienced the primary outcome. Despite a more severe disease status, only the surgical group showed a decrease in natriuretic peptide levels at follow-up and had a significantly lower rate of the primary outcome (3-year event rates were 18.3% vs 33.3%; log-rank, P = .03). Statistical adjustments did not alter these findings. Conclusions and Relevance The findings of this cohort study suggest that in patients with AFMR, who were typically older and predominantly had atrial fibrillation, MV surgery was associated with lower rates of adverse clinical outcomes. Future studies are warranted to investigate a possible causal relationship to better regulate cardiovascular medicine.

Clinical Outcomes of Mitral Valve Surgery in Atrial Functional Mitral Regurgitation in the REVEAL-AFMR Registry