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 vascular response to placement of a novel balloon-expandable stent in swine with experimentally induced atherosclerosis. BACKGROUND: The Multi-Link stent is a balloon-expandable stainless steel stent with an interconnected ring structure designed to provide a high degree of compressive resistance while preserving longitudinal flexibility. The placement characteristics and vascular response to this stent in atherosclerotic coronary arteries have not been characterized. METHODS: We tested the delivery characteristics and vascular response to the Multi-Link stent in 19 miniature swine with experimentally induced coronary atherosclerosis created in 37 coronary artery segments by overstretch balloon injury and high cholesterol diet. Quantitative coronary angiography was used to define stent performance characteristics, such as lesion dilation and compressive resistance. Pathologic assessment of the stented arteries was used to evaluate the immediate and long-term vascular response to stent placement. RESULTS: Nineteen (95%) of 20 stents were successfully implanted in the left anterior descending (n = 11), left circumflex (n = 7) or right (n = 1) coronary artery. The baseline angiographic minimal lumen diameter of the stented coronary segment was 2.48 +/- 0.09 mm (reference diameter 2.87 +/- 0.06 mm, mean +/- SE) and increased to 2.82 +/- 0.05 mm (p < 0.001) after stent placement. The balloon-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 filling defects or side branch occlusion. At 56 days, mean neointimal thickness was significantly greater at the stent wire sites in the region of the plaque where the media was absent than the stent wire sites, where 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 nonstented atherosclerotic lesions, after 56 days the stented vessels had a mildly reduced lumen area when normalized to the proximal reference vessel (2.81 +/- 0.27 vs. 2.68 +/- 0.30 mm2, p = 0.07). The mean change in the area within the external elastic lamina relative to a normal proximal reference segment was significantly greater in stented vessels (1.45 +/- 0.34 mm2) than nonstented atherosclerotic vessels (0.44 +/- 0.28 mm2, p = 0.033). CONCLUSIONS: Morphologic data confirm that the principal beneficial effect of stent placement is vessel expansion and attenuation of constrictive remodeling. In vessels with eccentric atherosclerotic fibrocellular plaques, the presence of normal media underlying the stent determines the degree of neointimal formation. These data may be useful in understanding the mechanism of stent restenosis in patients with prior percutaneous transluminal coronary angioplasty.

Inhibition of neointimal proliferation with low-dose irradiation from a beta-particle-emitting stent.

BACKGROUND: Restenosis after successful percutaneous transluminal coronary angioplasty is the major factor limiting the long-term effectiveness of this procedure. Neointimal proliferation in response to arterial injury is an important contributor to restenosis. The use of radiation for the treatment of malignant and benign proliferative conditions has been well established. External beam irradiation and endovascular irradiation by use of an after-loading technique have been shown to inhibit neointimal proliferation in experimental models of restenosis. The objective of this study was to investigate whether low-dose irradiation from a beta-particle-emitting stent would inhibit neointimal proliferation after placement in porcine iliac arteries. METHODS AND RESULTS: Fourteen titanium-mesh stents were implanted in the iliac arteries of nine NIH miniature swine. There were seven beta-particle-emitting radioisotope stents (32P, activity level 0.14 microCi) and seven control stents (31P, nonradioactive). Treatment effect was assessed by angiography and histomorphological examination of the stented iliac segments 28 days after implantation. There was a significant reduction in neointimal area (1.76 +/- 0.37 mm2 versus 2.81 +/- 1.22 mm2, P = .05) and percent area stenosis (24.6 +/- 2.9% versus 36.0 +/- 10.7%, P = .02) within the beta-particle-emitting stents compared with the control stents. Neointimal thickness, which was assessed at each wire site, was also significantly less within the treatment stents (0.26 +/- 0.04 mm versus 0.38 +/- 0.10 mm, P = .012). Scanning electron microscopy was performed on sections from four stents. This demonstrated endothelialization of both the treatment and control stents. There was no excess inflammatory reaction or fibrosis in the media, adventitia, or perivascular space of vessels treated with the beta-particle-emitting stent compared with control vessels. At 28 days, there was no difference in smooth muscle cell proliferation as measured by the proliferating cell nuclear antigen index. CONCLUSIONS: A local, continuous source of low-dose endovascular irradiation via a beta-particle-emitting stent inhibits neointimal formation in porcine arteries. This low dose of local irradiation did not prevent endothelialization of the stents. This novel technique offers promise for the prevention of restenosis and warrants further investigation.

Side-branch occlusion with directional coronary atherectomy: incidence and risk factors.

Side-branch occlusion is a recognized complication of directional coronary atherectomy (DCA). To evaluate the incidence, risk factors, and clinical outcome of side-branch compromise, we analyzed our first 100 consecutive atherectomies of native coronary arteries. Seventy-eight patients had 122 side branches at risk, 21 (17%) of which demonstrated compromised flow after DCA. Origin of the side branch from the culprit atheroma and preexisting side-branch ostial stenosis were highly predictive of this complication in 20 of 55 (p < 0.05) and 14 of 31 (p < 0.05) lesions, respectively. There was one non-Q-wave myocardial infarction, no emergency surgeries, and no deaths. In conclusion, side-branch loss after DCA occurs with a frequency similar to balloon angioplasty and was well tolerated in our patient population. Side branches that originate directly from culprit lesions or that have significant ostial narrowing have a higher incidence of this complication.

Placement and angiographic patency of the Strecker coronary stent.

The Strecker stent is a newer, balloon-expandable vascular prosthesis consisting of a single tantalum filament knitted into a flexible mesh tube. To test the placement characteristics and patency of this device, we implanted 29 stents in the coronary arteries of 24 juvenile Yorkshire swine. Seventeen stents were placed in the left anterior descending artery, and 12 were placed in the left circumflex system. All stents were deployed successfully. Four animals died within the first 24 hr of anesthesia-related complications. The remaining animals were sacrificed at 24 hr, 1 week, 2 weeks, or 4 weeks. Follow-up angiography demonstrated the patency of all stents. There were no episodes of stent migration or side branch occlusion. The Strecker stent has several favorable characteristics, including its unique delivery system, ease of deployment, flexibility, radiopacity, and radial strength. There was 100% patency at up to 4 weeks in this animal model. Further studies are required to define whether the knitted mesh design offers any advantage over previous models.