Mechanism of atrial functional mitral regurgitation in patients with atrial fibrillation: A study using three-dimensional transesophageal echocardiography.

BACKGROUND: Functional mitral regurgitation (MR) can occur in patients with atrial fibrillation (AF) despite having preserved left ventricular (LV) systolic function. This MR is known as atrial functional MR. The aim of this study was to clarify the mechanism of atrial functional MR using real-time three-dimensional transesophageal echocardiography (3DTEE).

METHODS: Sixty patients underwent transthoracic echocardiography and 3DTEE: 16 patients with AF and significant non-organic MR and preserved LV ejection fraction (>50%) constituted the AF-MR group, 20 patients with AF and no significant MR formed the AF-NSMR group, and 24 normal subjects comprised the control group.

RESULTS: The left atrial volume index was significantly larger in the AF-MR group (95±41ml/m2 ) than in the AF-NSMR group (38±13ml/m2 , p<0.05) or the control group (21±7ml/m2 , p<0.05). The 3D annular circumference was significantly longer in the AF-MR group than in the AF-NSMR group. The annular-anterior leaflet coaptation angle was smaller in the AF-MR group than in the AF-NSMR group (11±6° vs. 18±9°, p<0.05). The annular-posterior leaflet coaptation angle was comparable between the two AF groups (26±12° vs. 28±10°), whereas the annular-posterior leaflet tip angle was larger in the AF-MR group than in the AF-NSMR group (59±13° vs. 44±11°, p<0.05). The posterior leaflet bending toward LV cavity was therefore significantly larger in the AF-MR group than in the AF-NSMR group (32±10° vs. 18±15°, p<0.05).

CONCLUSIONS: In patients with AF and significant functional MR occurring despite their preserved LV systolic function, the left atrium and mitral annulus were dilated and the anterior leaflet was flattened along the mitral annular plane, whereas the posterior leaflet was bent toward the LV cavity.