The pathology of human aortic valve homografts

Beta-propiolactone sterilized, freeze-dried aortic valve homografts offer a dead framework which is accepted by the host and is capable of immediate and full function. The survival time of such grafts as fully functional units may be limited by physical and chemical alterations produced in the tissues by sterilization and freeze-drying. The organizing reaction of the host in covering the grafts or using them as a scaffolding may also be affected by these processes. It is possible that better long-term results may be achieved by using fresh grafts. There is no difference in host cellular response to fresh and sterilized and/or freeze-dried grafts. There is a possibility that heterogeneous reactions to polypeptides in the graft may occur in some individuals. Organization and covering of the graft by host tissue occurs from host tissues contiguous to the graft. Cells circulating in the bloodstream play no part in this by seeding on the surface. Thrombosis, in the absence of infection, is a rare complication. (Anticoagulants were not used in these patients.) Calcification occurs as only a late complication in persisting `dead' tissue. Unsuspected, and often extensive, myocardial ischaemia occurs frequently under bypass conditions with coronary artery perfusion and substantially contributes to immediate post-operative mortality and morbidity.