Mitral Ball-Valve Prosthesis

REPLACEMENT of nonfunctioning valves is a significant recent advancement in the correction of cardiac valvular disease. The most widely used artificial device replacing the mitral valve is the Starr-Edwards ballvalve prosthesis.' Its effectiveness was shown in recent reports by the marked clinical improvement in properly selected patients.2 However, cardiologists and cardiac surgeons are faced with several problems in the use of this valve, which can be answered only by careful studies of the flow dynamics of the ballvalve prosthesis and hemodynamic and clinical evaluation of the patient before and after surgery. Despite the effective correction of the regurgitation by the Starr valve, it is assumed that the resistance to blood flow through this mechanical device is greater than that of the normal mammalian leaflet valve. The normal mitral valve has a diastolic valve area of 3.5 to 5 cm.2 while the presently used Starr-Edwards prosthesis has an opening of 1.8 to 3.1 cm.2 measured at the inner ring of the valve cage. It is assumed that the "effective orifice" is even less, due to changed dynamics of flow during closure and opening of the ball valve. The "stenotic" orifice of the ball-valve prosthesis becomes even more significant during high cardiac outputs of exercise. Studies to determine the "'effective orifice" of the Starr-Edwards valve during the diastolic flow and the dynamics of the flow during closure and opening of the valve are therefore important. It is presumed that the ball-valve prosthesis with the largest "effective orifice" which a