CORONARY STENTING WITH A NOVEL STAINLESS-STEEL BALLOON-EXPANDABLE STENT - DETERMINANTS OF NEOINTIMAL FORMATION AND CHANGES IN ARTERIAL GEOMETRY AFTER PLACEMENT IN AN ATHEROSCLEROTIC MODEL

Objectives. This study evaluated the delivery characteristics and vasc ular response to placement of a novel balloon-expandable stent in swin e with experimentally induced atherosclerosis. Background. The Multi-L ink stent is a balloon expandable stainless steel stent with an interc onnected ring structure designed to provide a high degree of compressi ve resistance while preserving longitudinal flexibility. The placement characteristics and vascular response to this stent in atheroscleroti c coronary arteries have not been characterized. Methods. We tested th e delivery characteristics and vascular response to the Multi Link ste nt in 19 miniature swine with experimentally induced coronary atherosc lerosis created in 37 coronary artery segments by overstretch balloon injury and high cholesterol diet. Quantitative coronary angiography wa s used to define stent performance characteristics, such as lesion dil ation and compressive resistance. Pathologic assessment of the stented arteries was used to evaluate the immediate and long-term vascular re sponse to stent placement. Results. Nineteen (95%) of 20 stents were s uccessfully implanted in the left anterior descending (n = 11), left c ircumflex (n = 7) or right (n = 1) coronary artery. The baseline angio graphic minimal lumen diameter of the stented coronary segment was 2.4 8 +/- 0.09 mm (reference diameter 2.87 +/- 0.06 mm, mean +/- SE) and i ncreased to 2.82 +/- 0.05 mm (p < 0.001) after stent placement. The ba lloon-inflated stent diameter was 2.98 +/- 0.06 mm with minimal recoil to a final minimal lumen diameter of 2.82 +/- 0.06 mm at 15 min after implantation (p = 0.001). Angiographic and histologic follow-up at 72 h (n = 7), 14 days (n = 4) and 56 days (n = 8) demonstrated that all stents were patent, without evidence of migration, intraluminal fillin g defects or side branch occlusion, At 56 days, mean neointimal thickn ess was significantly greater at the stent sire sites in the region of the plaque where the media was absent than the stent wire sites, wher e the internal elastic lamina was intact with underlying normal media (0.48 +/- 0.01 vs. 0.27 +/- 0.02 mm, p < 0.0001). Compared with the no nstented atherosclerotic lesions, after 56 days the stented vessels ha d a mildly reduced lumen area when normalized to the proximal referenc e vessel (2.81 +/- 0.27 vs. 2.68 +/- 0.30 mm(2), p = 0.07). The mean c hange in the area within the external elastic lamina relative to a nor mal proximal reference segment was significantly greater in stented ve ssels (1.45 +/- 0.34 mm(2)) than nonstented atherosclerotic vessels (0 .44 +/- 0.28 mm(2), p = 0.033). Conclusions. Morphologic data confirm that the principal beneficial effect of stent placement is vessel expa nsion and attenuation of constrictive remodeling. In vessels with ecce ntric atherosclerotic fibrocellular plaques, the presence of normal me dia underlying the stent determines the degree of neointimal formation . These data may be useful in understanding the mechanism of stent res tenosis in patients with prior percutaneous transluminal coronary angi oplasty.