Mitral Annular Dilatation: The Contribution of Left Atrial Size

Abstract

Left ventricular size has been thought to be a major factor determining the size of the mitral anulus. In the present study, the contribution of left atrial size to the mitral annular size was explored in 38 cases of lone atrial fibrillation and 39 healthy subjects with a sinus rhythm. A color Doppler flow imaging system was employed. Both the left atrial dimension and the mitral annular diameter were significantly larger in lone atrial fibrillation than in healthy subjects. The left atrial dimension was found to have a significant correlation with the mitral annular diameter (r = 0.7, p < 0 .005). Of 39 healthy subjects, 5 (13%) had mitral regurgitation of which maximum distance of the regurgitant stream was less than 2 cm. The cases with lone atrial fibrillation had a high incidence of mitral regurgitation (23/38, 61%); in 70% of the cases having mitral regurgitation, the maximum distance of the regurgitant stream was 2 cm or more. The site of origin of mitral regurgitation was the center of the orifice in all cases. These results suggest that in lone atrial fibrillation, left atrial dilatation leads to the mitral annular dilatation and then to mitral regurgitation from the center of the orifice. Thus, the left atrial dimension can be regarded as one of the important factors determining the mitral annular diameter.