Background and aims of the study: The mitral annulus shows dynamic changes in shape and size during the cardiac cycle. A smaller size in end-diastole is attributed to the sphincteric action of atrial systole, and this may be important for functional integrity of the mitral valve. However, the effect of atrial fibrillation (AF) on dynamic changes in mitral annular size in humans is not known.
Methods: Mitral annular diameters in apical four- and two-chamber views were measured using echocardiography in 25 patients in atrial fibrillation, and in 37 subjects in normal sinus rhythm at mid-diastole, end-diastole and end-systole. Mitral annular area was computed assuming elliptical geometry.
Results: Patients in sinus rhythm showed a significant increase in mitral annular area of 25.9 +/- 12.8% with ventricular systole compared to its area in end-diastole (p < 0.0001), and a 10.5 +/- 8.4% reduction with atrial systole compared to mid-diastole (p < 0.001). Patients in AF had larger mitral annuli which showed non-significant changes in size between these three phases of the cardiac cycle. Percent reduction in mitral annular area in the latter half of diastole correlated significantly with left atrial (LA) diameter (r = -0.54, p < 0.0001), LA volume (r = -0.50, p < 0.0001), left ventricular (LV) fractional shortening (r = 0.37, p = 0.0036), mitral annular area in mid-diastole (r = -0.41, p = 0.0011) and mitral annular area in end-diastole (r = -0.64, p < 0.0001). That is, atrial sphincteric action on the mitral annulus was less in the presence of larger left atrium or the mitral annulus. Stepwise multiple regression analysis showed rhythm and mitral annular size to be independent predictors of dynamic changes in mitral annular area.
Conclusion: It is concluded that AF blunts or eliminates the phasic changes in mitral annular size during the cardiac cycle with loss of its presystolic sphincteric action; this may have implications in the genesis and surgical correction of mitral regurgitation.