BEHAVIOR OF MITRAL ALLOGRAFTS IN THE TRICUSPID POSITION IN THE GROWING SHEEP MODEL

Background. On the basis of a previous experience in a chronic sheep m odel in which partial mitral allografts remained viable and properly f unctioning 12 months after operation, we assessed the results obtained by replacing the tricuspid valve with fresh antibiotic-preserved mitr al allografts. Methods. Twenty 3-month-oId sheep with a mean weight of 23.7 +/- 2.3 kg underwent cardiopulmonary bypass and had a fresh anti biotic-preserved mitral allograft implanted in the tricuspid position with the heart beating under normothermic conditions. The tricuspid va lve apparatus was not excised. After a mean follow-up of 13.2 months, the allograft was evaluated by gross inspection and light and electron microscopy. Results. Nine sheep died of technical causes within the f irst week after operation and 2 at 4 and 6 months of infective endocar ditis of the allograft. The hemodynamic study before heart explantatio n revealed residual tricuspid incompetence in 3 of the 9 survivors. Ma croscopic examination showed flexible valves with no signs of structur al deterioration, calcification, or thrombosis. Under light and scanni ng electron microscopic examination, allografts were almost completely denuded of endothelial cells and showed loosely arranged connective t issue with scarce signs of inflammatory reaction. Despite these findin gs, allografts were free from major structural damage. Conclusions. Th e mitral homograft could be an alternative to replacement of the tricu spid valve with a bioprosthesis or a mechanical prosthesis. (C) 1998 b y The Society of Thoracic Surgeons.