Low-energy gamma-emitting stents inhibit intimal hyperplasia with minimal "edge effects" in a pig coronary artery model.

PURPOSE: The objective of this study was to determine the effects of different doses of gamma-emitting radioactive stents on intimal hyperplasia in a porcine coronary stent model at 28 days. METHODS: Sixty-four bare stents and those coated with palladium-103 [activities of 0 (control), 0.5, 1.0, 2.0, and 4.0 mCi] were implanted in the coronary arteries of 32 pigs. Stented segments were evaluated by histomorphometry at 28 days. RESULTS: There was significantly more intima in the 0.5- and 1-mCi stents than in controls (4.27+/-0.52 and 4.71+/-1.13 vs. 1.71+/-0.61 mm(2); P<.0001). Neointimal formation in 2-mCi stents was similar to that in controls, while that in 4-mCi stents was reduced compared to that in controls (2.34+/-1.61 and 0.82+/-0.25 vs. 1.71+/-0.61 mm(2); P=NS and P<.05, respectively). Stent margin neointimal response was representative of that within the stent body, with nonsignficant modest increases in intimal area at adjacent nonstented segments in radioactive stent groups. There was a dose-dependent increase in inflammation scores. Radioactive stents had lower intimal smooth muscle and higher fibrin scores. There was an increase in adventitial fibrosis in 1- and 2-mCi stents versus controls (1.26+/-0.99, and 2.25+/-1.27 vs. 0.21+/-0.31; P<.001). CONCLUSION: Dose-response inhibition of in-stent hyperplasia with minimal "edge effects" occurs with low-energy gamma-emitting stents. An increased inflammatory response at higher doses in palladium-103 stents indicates that later follow-up studies are necessary.

Late effects of low-energy gamma-emitting stents in a rabbit iliac artery model.

PURPOSE: To determine the long-term dose response of novel low-dose gamma-emitting stents in a rabbit iliac artery model. METHODS AND MATERIALS: Control stents (n=24) and 103Pd stents 1.0 to 4.0 mCi (n=36) were implanted in the iliac arteries of 30 New Zealand rabbits. Stents were evaluated by intravascular ultrasound (immediately post procedure and before killing) and by histomorphometry. RESULTS: At 26 weeks, 28 rabbits were killed, with no evidence of stent thrombosis. In the body of the stent there was a dose-response relationship with 50% inhibition of intimal hyperplasia at the highest activity compared to control stents (p=0.07) and a significant increase in intimal hyperplasia at the lowest activity (p < 0.01). At the stent edges, there was a significant reduction of lumen area at all activity levels compared to control stents, which was most prominent at the proximal stent edge. Higher-activity stents demonstrated incomplete endothelialization and immature neointimal formation. CONCLUSIONS: Continuous low-dose-rate irradiation by gamma-emitting 103Pd stents is feasible with reduction of in-stent hyperplasia in a dose-related manner. However, significant narrowing at the stent edges, increased in-stent hyperplasia at lower activities, and incomplete vascular healing with persistence of immature neointima at higher activities are significant limitations.