Late Arterial Responses (6 and 12 Months) After 32 P β-Emitting Stent Placement

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Abstract
pick;5248p1-foo;0;;clb/clb>Background —Three-month studies of stent-delivered brachytherapy in the rabbit model show reduced neointimal growth. However, intimal healing is delayed, raising the possibility that intimal inhibition is merely delayed rather than prevented. The purpose of this study was to explore the long-term histological changes after placement of β-emitting radioactive stents in normal rabbit iliac arteries. Methods and Results —Three-millimeter β-emitting 32 P stents (6, 24, and 48 μCi) were placed in normal rabbit iliac arteries with nonradioactive stents as controls. Animals were euthanatized at 6 and 12 months, and histological assessment, morphometry, and analysis of endothelialization were performed. Morphometric measurements demonstrated a >50% reduction in intimal growth and percent lumen stenosis within 24- and 48-μCi stents versus control nonradioactive stents at both 6 and 12 months. However, the 24- and 48-μCi stents also showed delayed healing of the intimal surface, characterized by persistent fibrin thrombus with nonconfluent areas of matrix, incomplete endothelialization, and increased intimal cellular proliferation. Stent edge stenosis was present at 12 months in the 24- and 48-μCi stent groups, characterized by both intimal thickening and negative arterial remodeling. Conclusions —Inhibition of intimal growth is maintained 6 and 12 months after 32 P β-emitting stent placement. However, delayed arterial healing, incomplete endothelialization, and edge effects are present.