Effects of intracoronary radiation on thrombosis after balloon overstretchinjury in the porcine model

Background-The main complications of PTCA remain thrombosis and restenosis. Recent studies have demonstrated reduction in the neointimal hyperplasia a fter intracoronary radiation (IR) with doses of 10 to 25 Gy of ionizing rad iation delivered by either beta- or gamma-emitters to injured vessels. The purpose of this study was to examine the effect of ionizing radiation on th e thrombosis rate (TR) of injured porcine coronary arteries. Methods and Results-Thirty-four juvenile swine (63 coronary arteries) were subjected to overstretch balloon injury followed by IR with doses of 0 to 1 8 Gy of either beta- or gamma-radiation, Two weeks after treatment, tissue sections were perfusion-fixed, stained with hematoxylin-eosin and Verhoeff- van Gieson's stain, and analyzed for presence of a thrombus, thrombus morph ology, and neointima formation by computer-assisted histomorphometry techni ques. Although the overall TR increased dose-dependently from 0 to 18 Gy pr escribed dose, luminal thrombi decreased. Thrombus area also decreased with increasing radiation dose, whether assessed at the prescription point or a t the luminal surface, which corresponded to decreased intimal area. Furthe rmore, luminal thrombi present after TR tended to consist mostly of fibrin and thus were less organized than in controls. Conclusion-These results suggest that LR induces thrombosis but does not ne cessarily compromise the lumen. Strategies for reducing TR may further decr ease intimal area as well as increasing the safety of this therapy.