DECREASED-PLATELET ADHERENCE OF POLYMER-COATED TANTALUM STENTS

PURPOSE: To compare the acute thrombogenicity of polyurethane-coated s tents with that of bare tantalum stents. MATERIALS AND METHODS: Thirty stents (15 coated with polyurethane) were balloon expanded in 8-mm x 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) swin e. Platelets were labeled with indium-111 and reinjected for quantitat ive assay. The stented grafts were connected to the arterial and venou s sheaths to create an ex vivo fistula. Each fistula was opened for 5, 10, 30, 60, or 120 minutes, exposing heparinized blood to fully expan ded stents. The fistulas were closed, flushed with saline until clear, and fixed with formalin. Stents were explanted, placed in a radionucl ide well counter, and scanned with electron microscopy. RESULTS: Quant itatively, there were considerably fewer platelets on coated versus un coated stents. At 60 minutes, coated stents averaged 12.93 platelets p er 1,000 mum2 compared with 75.88 platelets per 1,000 mum2 for bare me tallic stents. At 120 minutes, there were 23.22 platelets/1,000 mum2 v ersus 102.31 platelets/1,000 mum2, respectively. Electron microscopy o f 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 exte nsive layering of platelets and fibrin. CONCLUSION: Polyurethane coati ng decreases platelet adhesion, relative to bare tantalum, at all time intervals tested.