Aortic valve grafts in the rat: Evidence for rejection

Objective: The histopathologic changes of fresh rat aortic valve allografts over time and the effect of cryopreservation were examined. Methods: Fifty-six syngeneic and allogeneic rat aortic valves were transplanted, either fresh or after cryopreservation, and then at different time points they were explanted and histologically examined in a blinded fashion. Results: Histopathologic changes in the first week are similar in syngeneic and allogeneic grafts. Fresh syngeneic grafts and leaflets retained normal structure up to 56 days. Allogeneic grafts showed retrovalvular thrombus formation with leaflet ghosts and neointimal proliferation. Cryopreservation did not alter this process. Conclusions: Cardiac allograft valves in the rat model undergo changes that are characteristic of cell-mediated rejection and lead to valve failure.