Novel Mechanistic Insights Into Atrial Functional Mitral Regurgitation　- 3-Dimensional Echocardiographic Study.

BACKGROUND Left atrial remodeling caused by persistent atrial fibrillation (AF) causes atrial functional mitral regurgitation (MR), even though left ventricular (LV) remodeling and organic changes of the mitral leaflets are lacking. The detailed mechanism of atrial functional MR has not been fully investigated. METHODSANDRESULTS Of 1,167 patients with AF who underwent 3D transesophageal echocardiography, 75 patients were retrospectively selected who developed no, mild, or moderate-to-severe atrial functional MR (n=25 in each group) despite an LV ejection fraction ≥50% and LV volumes within the normal range. Mitral valve morphology and dynamics were analyzed. Patients with moderate-to-severe MR had a larger mitral annulus (MA) area, smaller MA area fraction, and greater nonplanarity angle and tethering angle of the posterior mitral leaflet (PML) compared with other groups (all P<0.001). In the multiple regression analysis, the MA area, MA area fraction, nonplanarity angle, and PML angle were independent determinants of the effective regurgitant orifice area of MR after adjusting for LV parameters (adjusted R(2)=0.725, P<0.001). The PML angle and MA area had a higher standardized regression coefficient (β=0.403, P<0.001, β=0.404, P<0.001, respectively) than the other variables. CONCLUSIONS Functional atrial MR in persistent AF is caused by not only MA dilatation, but also by multiple factors including the MA contractile dysfunction, disruption of the annular saddle shape, and atriogenic PML tethering. (Circ J 2016; 80: 2240-2248).