Species Selection for Vascular Graft Evaluation

Abstract

Similarities and differences between human and several other mammalian species are reviewed with respect to hematologic parameters and the histologic response to implanted prosthetic vascular grafts. No species is clearly more similar to man than any other with regard to all aspects reviewed. For this reason it is suggested that species selection for vascular graft evaluation be based on practical considerations such as ease of handling and of surgical and anesthetic technique and the cost of purchase and maintenance of the animal. Based on these criteria, the dog appears to be the species of choice. In vitro tests of platelet deposition and fibrinogen adsorption to expanded polytetrafluoroethylene (EPTFE) and woven Dacron® during simulated arterial flow was predictive of results reported following implantation of these materials as small diameter vascular grafts in animals and man. These methods may therefore be useful as in vitro screens of new prosthetic vascular materials. With five materials tested, ranking of the intensity of the blood-material response in vitro was the same or similar among three species—human, canine, and porcine—despite the major pathophysiological differences among these species. These observations suggest that, for in vitro hemocompatibility testing, species selection based on apparent similarity to man is neither necessary nor likely to yield more clinically relevant data. There is no compelling evidence at present that data derived from vascular implant studies with the baboon are more relevant to human use than data obtained from studies with the dog. Following vascular graft implantation, thromboembolism was seen more often in the dog while calcification was observed with greater frequency in the pig. Because of such species specificities in the nature of the response, it may be advisable to evaluate grafts in more than one species, specifically the dog and pig. It may also be useful to study the effect on vascular graft patency and other responses, of diseases in the host that simulate those that commonly exist in human candidates for graft implantation.