Late Changes in Formalin-Treated Porcine Aortic Heterografts Replacing Human Mitral Valves:A Pathological Study

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Abstract
Between March 4, and September 16, 1969, 13 consecutive patients had mitral valve replacement with a formalin-treated pig aortic heterograft mounted on a ring support. There were six deaths, not related to the graft per se, between 0 and 26 months after operation. Graft failure occurred in 6 of the patients, between 9 1/2 and 40 months after implantation. Ten grafts were examined microscopically, seven of them post mortem. the effect of treatment with 4% formalin on the tensile strength of unimplanted heterografts, as well as of two grafts removed at re-operation, was studied. Rupture of one or more commissures caused severe mitral regurgita-tion in a majority of the grafts between 11/2 and 2 years after implantation. Extreme thinning with resulting perforation of the cusps appeared after 3 years or more. the reason for the loss of mechanical resistance in these heterografts is believed to be rejection.

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