Biocompatibility and performance of the wallstent and several covered stents in a sheep iliac artery model

PURPOSE: To compare the biocompatibility and performance of various stent-g rafts to those of a bare stent in an ovine model with a subchronic (3 month s) endpoint. MATERIALS AND METHODS: Three different types of stent-grafts (ePTFE/nitinol , n = 8; polyester/nitinol, n = 8; and polycarbonate urethane/cobalt-alloy, n = 8) and a bare stent as a control (Ni-Co-Ti-steel-alloy, n = 8) were im planted in the iliac arteries in eight female sheep. One type of each stent -graft was implanted per animal, two implants at each side. The implantatio n sites for each type varied from animal to animal. Angiographic control an d intravascular ultrasound (IVUS) imaging were performed before and after i mplantation, after 2 months, and before explantation at 3 months and were u sed to characterize patency and to assess intimal hyperplasia. After 3 mont hs, the implants were retrieved and subjected to histologic evaluation (aft er methacrylate embedding, cutting, and histologic staining) to characteriz e the biologic response. RESULTS: Implantation was technically successful in all procedures. At 2 an d 3 months after implantation, all segments in which stents had been implan ted were patent. Marked neointima formation was found in the polyester-cove red stent-graft that showed significant luminal narrowing of 50%, compared to the ePTFE-covered (24%) and polycarbonate urethane-covered endoprosthese s (22%), as well as the bare stent (Wallstent; 9%; P < .001). A minimal inf lammatory vessel wall reaction was demonstrated for the polyester-covered a nd ePTFE-covered endoprostheses; the polycarbonate urethane-covered stent-g raft's response was demonstrable but not significantly different from that of the Wallstent. At 3 months, the ePTFE-covered stent-graft showed incompl ete (>90%) endothelial coverage; in the other endoprostheses, complete but partially immature endothelialization was found. CONCLUSION: All stent-grafts induced an inflammatory vessel wall reaction w ith neointimal hyperplasia. The polyester-covered endoprosthesis caused a m arked reaction with 50% luminal stenosis. Endothelialization was retarded w ith the ePTFE-covered stent-graft. The bare stent performed best in regard to neointimal formation and caused the least inflammatory response.