Late Effect of Mechanical Mitral Valve Diameter on Left Ventricular Function

Abstract

During left ventricular ejection, the minor (transverse) axis of the inner wall shortens by 27% to 37%, while the major axis shortens by 9%. Therefore, shortening of the minor axis accounts for 85% to 90% of the stroke volume and the mitral annulus area alters to assist left ventricular contraction. Mitral valve prostheses with large diameters are preferred but these may lead to systolic malfunction by restricting minor-axis shortening. We studied echocardiographic data of patients who has received mechanical mitral valves with the same inner diameter and opening angle but with different outer diameters (29 mm or 31 mm). Although there was no difference preoperatively in ejection fractions in the two groups, the postoperative ejection fraction was significantly higher in patients with the smaller valve. This finding indicates that mitral valve replacement with a prosthesis of large external diameter caused a deterioration in left ventricular function.