Cryopreservation of rat aortic valves results in increased structural failure

Background-The cause of valve allograft failure is most likely multifactori al and may include mechanical, immunological, and other factors. Cryopreser vation of these valves is often used to extend storage times. However, ther e has been considerable confusion as to the effects of cryopreservation on valve durability. Our objective was to determine the effects of cryopreserv ation on histopathological changes in rat aortic valve grafts. Methods and Results-Syngeneic rat aortic valve grafts (Lewis to Lewis; n=24 ) and allogeneic rat aortic valve grafts (Brown Norway to Lewis; n=24) were implanted infrarenally, either fresh or after cryopreservation. At 7, 14, and 28 days, the valves were explanted, and histological and immunohistoche mical examinations were performed in a blinded fashion. Fresh syngeneic gra ft leaflets retained their normal structure for the 28-day period of observ ation. Cryopreserved syngeneic grafts showed retrovalvar thrombus formation , with leaflet destruction at 7, 14, and 28 days. Fresh allogeneic graft le aflets showed significant leaflet thickening and progressive destruction at 14 and 28 days. Cryopreserved allogeneic grafts had evidence of retrovalva r thrombus formation with leaflet destruction at 7, 14, and 28 days. Cryopr eserved syngeneic grafts resulted in significant infiltration of mononuclea r (ED1(+)) cells not seen with fresh syngeneic grafts but similar to fresh allogeneic grafts. All allogeneic grafts resulted in significant infiltrati on of T-lymphocytes (CD3(+), CD8(+), CD43(+)). Conclusions-Cryopreservation appears to pre dispose syngeneic and allogenei c rat aortic valve leaflets to accelerated injury and destruction. This mod e of failure resembles that of fresh allogeneic valve grafts.