SELF-EXPANDING NITINOL STENTS IN CANINE VERTEBRAL ARTERIES - HEMODYNAMICS AND TISSUE-RESPONSE

PURPOSE: To evaluate the hemodynamics and tissue response associated w ith stent placement in low-now-velocity arteries. METHODS: Six self-ex panding nitinol stents (5.5 mm caliber) were implanted transfemorally within the proximal segments of vertebral arteries (2.5 mm diameter) i n six adult dogs during anticoagulative protection. RESULTS: Control a ngiograms demonstrated patency and 20% dilatation of all stented arter ies. One artery was partially thrombosed 1 week later and subsequently showed a 50% stenosis. Throughout the observation period (4 to 9 mont hs after stenting), the other five arteries remained patent without si gnificant narrowing (less than or equal to 15%). Small cervical muscle branches originating from the vertebral arteries within the stented s egments remained patent. No major branch occlusions of the vertebrobas ilar system were detected. Stent migration or kinking did not occur. M R studies of the brain 4 months after implantation revealed no infarct ed areas. These findings were confirmed with brain sections. Stented a rtery specimens showed delayed stent dilatation. A comparison of the t otal mean thickness of intima covering the five 30- to 40-mm stents re moved at 4, 6, and 9 months showed no significant difference (338, 332 , and 389 mu m, respectively). Histologic findings verified the macros copic impression of a thicker intima at the inner curve of the stented artery segments and at the junctions of the stent filaments. The shor test (10 mm) stent had the thinnest neointimal growth (155 mu m). Sten ted vessels showed compression of the media with atrophy, but without necrosis or perforation. Scanning electron photomicrographs revealed i ntact endothelial cell linings with typical elongated cells. CONCLUSIO NS: No significant risk of thromboembolic events exists after implanti ng these nitinol stents in nonatherosclerotic vertebral arteries in do gs. Thicker neointimal growth after stenting may result from either lo w wall shear stress with possible flow separation or from changes in t he shape and size of the stent, or both.