967-20 Reduced Thrombogenicity of Nitinol vs Stainless Steel Slotted-Tube Stents in Rabbit Carotid Arteries

Abstract

The thrombogenicity of slotted-tube stents made of nitinol or stainless steel (Palmaz Schatz) was assessed in a rabbit carotid artery model. Fourteen nitinol and 8 stainless steel stents (7 mm long single segment stents) were deployed in a carotid artery of 22 NZW rabbits with a 3.0 mm balloon inflated twice at 6 atm for 1 min. No antiplatelet or antithrombotic drugs were given. Eight rabbits with nitinol and 8 with stainless steel stents were euthanized after 4 days. The remaining 6 rabbits with nitinol stents were euthanized after 14 days. At sacrifice, both carotids (stented and control) were exposed and resting blood flow measured. The amount of thrombus on each stent was assessed by a semi-quantitative grading scale (I: no lumen encroachment; II: lumen encroachment; III: subocclusive thrombus; and IV: occlusive thrombus) and by the weight of the dry thrombus. All nitinol were patent at 4 and 14 days whereas 6 out of 8 (75%) stainless steel stents had total thrombotic occlusion at 4 days (p < 0.0001). Parameter Stainless Steel 4 day Nitinol 4 day Nitinol 14 day ANOVA p-value n 8 8 6 Carotid flow (ml/min) 1.5 ± 2.8 24.0 ± 2.0 25.5 ± 19 <0.000001 Thrombus grade III = 2, IV = 6 I = 8 I = 6 <0.0001 Thrombus weight (mg) 20.0 ± 5.9 2.5 ± 0.6 2.7 ± 0.3 <0.000001 Histologic examination of stented arterial segments showed that although the depth of strut penetration was similar in all 4 day rabbits, the group with stainless steel stents consistently had evidence of diffuse medial necrosis and thinning (8/8 vs 118; P = 0.0004). Nitinol stents developed significantly less thrombus in comparison to stainless steel stents of similar design as measured by thrombus weight. thrombus grade and degree of blood flow reduction at 4 days in the rabbit carotid artery model. For nitinol stents there was no worsening of these thrombotic parameters at 14 days, compared to 4 days. More severe vascular injury may contribute to the thrombogenicity of stainless steel stents.