SUBACUTE THROMBOSIS AND VASCULAR INJURY RESULTING FROM SLOTTED-TUBE NITINOL AND STAINLESS-STEEL STENTS IN A RABBIT CAROTID-ARTERY MODEL

Background Our objectives were to quantify the thrombogenicity and ext ent of vascular injury created by slotted-tube geometry stainless stee l and nitinol coronary stents in a rabbit carotid artery model. Method s and Results Stents were implanted in rabbit right carotid arteries w ithout antiplatelet therapy. Stainless steel stents were implanted for 4 days while nitinol stents were placed for 4 and 14 days (n=8, 8, an d 6, respectively). Stent thrombosis was assessed by thrombus weight, grading thrombus encroachment of the lumen, and by blood flow in the s tented and contralateral arteries. Stainless steel stents at 4 days co ntained more thrombus than 4- and 14-day nitinol stents (20.0+/-5.9 ve rsus 2.5+/-0.6 and 2.7+/-0.3 mg, respectively; P<.000001). Stainless s teel stents were more often occluded by thrombus (6 of 8) or contained more subocclusive thrombus (2 of 8) than nitinol stents (0 of 14, P<. 002). Resting blood flow was reduced in arteries with stainless steel stents compared with 4- and 14-day nitinol stents (1.5+/-2.8 versus 24 .0+/-2.0 and 25.5+/-1.9 mL/min, respectively, P<.000001). Stainless st eel stents were less uniformly expanded, had deeper strut penetration into the vascular wall, and were associated with more extensive medial smooth muscle cell necrosis. There were strong correlations (r=.77 to .95) between variables of thrombosis extent (thrombus weight and grad e) and histologically determined vascular injury (strut penetration an d medial necrosis). Conclusions Slotted-tube stainless steel stents we re more thrombogenic and created more extensive vascular injury than n itinol stents in a rabbit carotid artery model. The mechanisms underly ing these differences probably are related to metallurgic and design g eometry properties of the two stent types.