What force can the myocardium generate on a prosthetic mitral valve ring? An animal experimental study.

Data on the magnitude of forces which can be generated by the myocardium on a prosthetic heart valve ring are not available from the literature. Therefore, we implanted strain gauge mounted 29 mm original specification Edwards-Duromedics mitral valve prostheses in 13 pigs. The valves were implanted in both anatomic and anti-anatomic orientation. In order to estimate the forces on the valve ring, acute in vivo measurements of the dynamic deformation of the valve ring were performed and correlated with the stiffness of the same valves measured in vitro. In the post cardioplegic heart of the anesthetized pigs there was a maximum force developed by the myocardium of 6-8 N on the valve ring with a resulting maximum deformation of 40 microns with valves mounted in the anatomic position. These findings have implications for design of future mechanical mitral valves and for mitral rings used for mitral valvuloplasty. These data can also be used as reference for evaluation of safety limits in existing valves in terms of their physical properties. Based on the direction of the maximum myocardial force acting on the mitral valve ring and the difference in compliance of the valve ring along the pivotal or orthogonal axis, it is indicated from that these acute porcine studies that bileaflet valves in the mitral position are subjected to less deformation when implanted 60 degrees counter-clockwise to the native mitral intercommisural line.