Mitral valve replacement in the baboon (Papio ursinus) and the human with the University of Stellenbosch mitral valve prosthesis.

To study the problem of thromboembolism that occurs following the use of prosthetic valves, the mitral valve was replaced in 20 Cape Chagma baboons with the University of Stellenbosch (U.S.B.) mitral valve prosthesis. In the absence of anticoagulants massive thrombus invariably formed on the metal portion of the prosthesis when the latter was left uncovered by material that allows for tissue ingrowth. Smooth, fairly well controlled tissue ingrowth occurred when the prosthetic ring was covered by Dacron velour material. Massive thrombus formation was never encountered although small fibrin thrombi, a potential source of emboli, became loosely attached to the Dacron velour covered prosthetic ring during the first eight post-operative weeks. Thereafter the smooth ingrowth of living tissue into the prosthesis appears capable of preventing thromboembolism. The clinical use of anticoagulants during the initial 3-4 post-operative months is recommended in view of our experimental findings and clinical experience of early embolism that occurred in 3 of 10 patients in whom the U.S.B. Dacron velour covered prosthesis was used in the absence of anticoagulants. This is the first reported study in which a sub-human primate was used to study the problem of thromboembolism associated with prosthetic valve replacement. The baboon can be highly recommended for this purpose.