Pigs, Dogs, Baboons, and Man: Lessons for Stenting from Animal Studies

A new era in interventional cardiology has arrived with the widespread use of intracoronary stents. These devices have not only markedly improved the safety of dilatation, but have also limited restenosis through achievement of a larger postprocedure lumen. Much work remains in furthering this technology, since two major limitations are thrombosis and neointimal hyperplasia that still cause restenosis. Stent placement in animals provides insight into both of these areas. The volume of neointima is directly proportional to the depth of injury induced by the stent in at least three species: the pig, baboon, and dog. Across each species, a numerically different slope exists for the injury-neointimal thickness regression. Treatments to limit hyperplasia within a species do not change this slope, but instead alter the y-intercept. Stent thrombosis in animal models consists principally of platelet-rich thrombi. The time course of thrombus appears to differ across pigs and baboons. Antiplatelet agents limit, but do not eliminate the problem in animals, suggesting that newer and more potent antiplatelet agents may improve scent thrombosis in clinical trials. The future of stent technology lies in developing an antithrombotic device that also eliminates neointimal hyperplasia. Intense studies of animal models and improved understanding of their pathophysiology will facilitate this progress.