Influence of mitral valve prosthesis or rigid mitral ring on left ventricular pump function. A study on exposed and isolated blood-perfused porcine hearts.

We have studied the effects on cardiac function of a Björk-Shiley mitral prosthesis or a rigid mitral ring implanted in pigs for as long as 6 weeks. We studied these effects first in the exposed heart and subsequently in the isolated heart. The coronary arteries were cannulated and perfused with fresh whole blood. The left ventricle was filled with an electrolyte solution and was allowed to pump against an artificial load. Studies were completed in 37 of 45 animals (19 controls, 12 with mitral prostheses and six with mitral rings). In the open-thorax situation, surgically treated hearts differed little from controls, apart from a higher pressure drop over the mitral ostium. Compared with controls, isolated hearts with a prosthesis showed a 28% lower peak isovolumic pressure and a 25% lower unloaded maximal stroke volume; hearts with a mitral ring showed 14% and 25% lower values, respectively. Prosthetic valve or ring implantation causes obstruction of the mitral ostium, impedes pressure development, and restricts movement of the basal ventricular wall. Resection of the native valve doubles the loss of contractile function.