Clinical Significance of Extreme Left Atrial Enlargement in Atrial Functional Mitral Regurgitation

The left atrium (LA) size varies in patients with atrial functional mitral regurgitation (AFMR) and its clinical impact remains unclear. This study aimed to assess the distribution of LA volume index (LAVI) and the impact of LAVI on clinical outcomes in a large cohort of patients with ≥ moderate AFMR. Patients with AFMR diagnosed by transthoracic echocardiography in 2019 were retrospectively enrolled from the REVEAL-AFMR registry. The endpoint was a composite of cardiovascular death and heart failure hospitalization, compared across the LAVI groups. Of the 877 patients (age 78 ± 9 years, 45% male, 81% with atrial fibrillation), the median LAVI was 75 ml/m². LAVIs of < 50, 50 to 99, 100 to 149, 150 to 199, and ≥ 200 ml/m² were observed in 14%, 55%, 18%, 7%, and 6%, respectively. The prevalence of severe MR increased across these LAVI groups (10%, 19%, 38%, 62%, and 66%; p <0.01 for trend), and the prevalence of symptoms also worsened accordingly (56%, 61%, 62%, 82%, and 96%; p <0.01 for trend). During the median follow up of 2.9 years, LAVIs ≥ 200 and 150 to 199 ml/m² were associated with lower event-free survival compared with LAVI < 50 ml/m². LAVI ≥ 150 ml/m² was associated with the adverse event (adjusted hazard ratio 2.14; 95% CI, 1.30 to 3.52; p <0.01), notably independent of severe mitral regurgitation (MR) and atrial fibrillation. In conclusion, larger LA was associated with severe MR and symptoms in patients with AFMR. Extremely enlarged LA with LAVI ≥ 150 ml/m² was observed in 13% and associated with worse outcomes independent of MR severity and atrial fibrillation.