Modification of the thrombogenicity of a self-expanding vascular stent

When placed in the iliac arteries of normal healthy animals, the Wall-stent self-expanding endovascular prosthesis exhibits minimal thrombogenicity, measured by 111In-labeled platelet uptake. Preliminary clinical reports suggest a greater thrombogenicity in diseased human arteries. When evaluated in an ex vivo shunt, these stents exhibit significant thrombogenicity. The ex vivo shunt may therefore provide a model to evaluate strategies to reduce thrombogenicity in the clinical setting. Stents were released into shunts and the uptake of In111-labeled platelets was measured by gamma imaging for 2 h at a flow rate of 100 mL/min. The effect of systemic heparin, 100 U/kg, oral aspirin, 325 mg, and local application of heparin-benzalkonium chloride complex were evaluated. At the end of each study the stents were fixed in situ and evaluated with scanning electron microscopy (SEM). Control stents exhibited a rapid, significant uptake of platelet associated 111In activity, which reached a maximum in approximately 1 h. Twenty-two percent of control stents occluded before 2 h. Aspirin reduced maximum platelet uptake by 46%. Systemic heparin, with a clotting time greater than five times control, reduced maximum platelet uptake by 86%. The benzalkonium-heparin complex coating, with no increase in clotting time, reduced maximum platelet uptake by 84%. No occlusions were observed with the anti-thrombotic regimes. SEM evaluation of the stents supports the results of the isotope uptake studies.