Leaflet Morphology Is More Strongly Associated with Atrial Functional Mitral Regurgitation Severity than Annular Dilation: A Three-Dimensional Transesophageal Echocardiographic Study

Background: Atrial functional mitral regurgitation (AFMR) results from left atrial (LA) remodeling and mitral annular dilation in patients with atrial fibrillation and preserved left ventricular function. While annular dilation is considered the primary mechanism, the role of leaflet morphology in determining regurgitation severity remains incompletely characterized. We hypothesized that leaflet morphology, rather than annular dilation alone, is more strongly correlated with AFMR severity. Methods: We prospectively studied 113 consecutive patients with persistent atrial fibrillation and AFMR who underwent comprehensive three-dimensional transesophageal echocardiography (3D TEE). Mitral valve geometry was analyzed using dedicated software (EchoPAC v.206, 3D MVQ Analysis). Patients were classified according to MR severity: non-significant (grade 0–1) versus moderate or severe (grade 2–3). Logistic regression identified predictors of moderate or severe AFMR. Results: Moderate or severe MR was present in 57 patients (50.4%). Compared with patients with non-significant MR, those with moderate or severe regurgitation exhibited larger annular dimensions (3D annular area 12.7 vs. 11.4 cm2, p = 0.005), reduced non-planar angle (145° vs. 149°, p = 0.027), greater leaflet areas, and increased tethering parameters. Anterior leaflet length was markedly greater in the moderate/severe group (2.7 vs. 2.4 cm, p = 0.001). In different multivariable analyses models adjusting for age, sex, LA diameter, and 3D annular area, anterior leaflet length (OR 3.16 per SD, 95% CI 1.65–6.61, p = 0.001), anterior leaflet area (OR 3.42 per SD, 95% CI 1.48–8.74, p = 0.006), and posterior leaflet length (OR 0.39 per SD, 95% CI 0.15–0.86, p = 0.043) remained independently associated with moderate or severe AFMR. ROC analysis demonstrated good discriminative ability for anterior leaflet length (AUC 0.746, with an optimal threshold of 2.55 cm, sensitivity 75%, specificity 68%), and anterior leaflet area (AUC 0.680, and an optimal cut-off value of 5.75 cm2, sensitivity 70.2%, specificity of 64.3%). Conclusions: In patients with AFMR, anterior leaflet dimensions assessed by 3D TEE are the strongest independent predictors of moderate or severe regurgitation, outperforming annular parameters. These measurements may represent practical tools for risk stratification and patient selection for intervention.