Intense Inflammatory Reaction to Heparin Polymer Coated Intravascular Palmaz Stents in Porcine Arteries Compared to Uncoated Palmaz Stents

The objective of this study was to evaluate the efficacy of heparin-polymer-coated intravascular stents in the reduction of vessel stenosis. Three types of coatings for Palmaz stents were tested: 1) heparin covalently bound to a polyethylene oxide (Hp-PEO) tether; 2) heparin copolymerized with ethylene vinyl acetate (Hp-Elvax) and 3) Elvax alone. Polymer-coated stents and uncoated controls were deployed in the external iliac arteries following endothelial injury in 18 swine. The animals were maintained on an atherogenic diet and examined by angiography at 6 and 12 weeks. The stented segments were then harvested for histopathologic analysis. Both types of heparin-coated stents resulted in increased luminal narrowing as compared to the contralateral uncoated stents. At 6 weeks, average luminal stenosis was 48% for Hp-PEO stents vs 35% for uncoated stents (p < 0.05). At 12 weeks, average luminal stenosis was 36% for Hp-PEO stents vs 26% for uncoated stents (p = NS). For Hp-Elvax stents, the average stenosis was 58% vs 33% for uncoated controls (p < 0.05) at 6 weeks and 47% vs 19% for uncoated controls (p < 0.05) at 12 weeks. There was no significant difference between Hp-Elvax stents and Elvax stents (p = NS). Increased luminal narrowing in coated stents was primarily secondary to a marked inflammatory response. Heparin-polyethylene oxide and heparin-ethylene vinyl acetate-coated stents resulted in increased luminal narrowing as compared with uncoated stents, due to a marked inflammatory response.