Evaluation of a stented polyurethane mitral valve prosthesis.

In the search for the perfect valve prosthesis, polyurethane has been used for its excellent physical properties, but thrombosis and embolism have been real problems. The authors investigated the performance and durability of a 23 mm vacuum formed polyurethane Tricuspid Semilunar Valve, in the mitral position. The valve was implanted in eight sheep using standard cardiopulmonary bypass and intermittent aortic cross clamping. Two early failures were due to valve tears. After modification of the manufacturing process, six further valves were implanted in six sheep. All were anticoagulated with warfarin. The valves were calcified on echocardiography and had increasing transvalvular gradients beginning 3 months postoperatively. All six survived and were killed 1-2.5 years after implantation. Despite gross calcification of the leaflets, medium-term function was good. Careful serial sections of brain showed no evidence of thromboembolism. Both kidneys contained small calcium emboli, but no evidence of infarction. Despite calcification, with good medium-term function and no cerebral emboli, this valve may find application in temporary cardiac assist devices.