Decreased Platelet Adherence of Polymer-coated Tantalum Stents

To compare the acute thrombogenicity of polyurethane-coated stents with that of bare tantalum stents. Thirty stents (15 coated with polyurethane) were balloon expanded in 8-mm × 80-cm sections of polytetrafluoroethylene grafts (six stents per graft). Under sterile conditions, 8- and 10-F vascular sheaths were placed percutaneously in the femoral artery and vein of a 100-lb (45-kg) swine. Platelets were labeled with indium-111 and reinjected for quantitative assay. The stented grafts were connected to the arterial and venous sheaths to create an ex vivo fistula. Each fistula was opened for 5,10, 30, 60, or 120 minutes, exposing heparinized blood to fully expanded stents. The fistulas were closed, flushed with saline until clear, and fixed with formalin. Stents were explanted, placed in a radionuclide well counter, and scanned with electron microscopy. Quantitatively, there were considerably fewer platelets on coated versus uncoated stents. At 60 minutes, coated stents averaged 12.93 platelets per 1,000 μm 2 compared with 75.88 platelets per 1,000 μm 2 for bare metallic stents. At 120 minutes, there were 23.22 platelets/1,000 μm 2 versus 102.31 platelets/1,000 μm 2, respectively. Electron microscopy of coated stents demonstrated few scattered platelets at 5,10, and 30 minutes. There was a uniform layer of platelets at 60 and 120 minutes. Uncoated stents demonstrated random areas of platelet clumping at 5,10, and 30 minutes. At 60 and 120 minutes, uncoated stents showed extensive layering of platelets and fibrin. Polyurethane coating decreases platelet adhesion, relative to bare tantalum, at all time intervals tested.