Local intravascular effects of the nitinol wire blood clot filter

To determine the biocompatibility and thrombogenicity of nitinol blood clot filters, we inserted 27 nitinol wire devices into the venae cavae of 16 dogs and one sheep and studied the results angiographically and at autopsy after periods of one week to four years. Filter shape, location in the vena cava, wire cleaning procedure and wire surface finish were varied. All 18 cleaned nitinol wire filters remained patent by venogram, although some showed small venographic filling defects caused by adherent organized thrombi. Filters in larger veins tended to have less thrombus. Surface polishing and filter shape had no observable effect on thrombogenicity. Histologic study revealed patchy chronic inflammation at the surface of uncleaned filters but only benign fibrous tissue reaction for the cleaned filters. Neointimal tissue overgrowth was observed where nitinol wire contacted the wall of the vena cava. Two filters implanted for four years had no appreciable weight loss caused by corrosion. Platelet adhesion and plasma coagulation effects of nitinol wire were tested in vitro in human blood and found to be similar to those of stainless steel, which is used in comparable devices. These encouraging results suggest that nitinol may be a promising material for human intravascular prosthetic applications.