The effect of endovascular irradiation on platelet recruitment at sites ofballoon angioplasty in pig coronary arteries

Background-Endovascular irradiation (EI) inhibits balloon-induced neointima formation in animals and is now in clinical trials for restenosis preventi on. However, little is known of the effect of EI on vessel thrombogenicity due to delayed arterial healing. We investigated EI effects on platelet rec ruitment-in pig coronary arteries. Methods and Results-EI was performed using Sr-90/Y at 0 Gray(Gy), 15Gy, or 30Gy at 2 mm after balloon overstretch injury. At 1 day, 1 week, and 1 mont h, platelet recruitment and thrombus formation were assessed using autologo us In-111-oxine-platelet labeling and light and scanning electron microscop y. In balloon-injured nonirradiated vessels, there was complete reendotheli alization at 1 month, and platelet recruitment was similar to normal uninju red arteries. In irradiated vessels, scanning electron microscopy showed in complete reendothelialization at 1 month, and these areas demonstrated atta chment of activated platelets. Light microscopy: of irradiated coronaries s howed adherent partially organized thrombi and incomplete resolution of int ramural hemorrhages. There was a significant increase in platelet recruitme nt at 1 month in arteries receiving EI at 15Gy (5.1 +/- 2.8x10(6), P=0.02) or 30Gy (12.5 +/- 9.9x10(6), P=0.005) compared with nonirradiated controls (2.7 +/- 1.5x10(6)); 30Gy was also higher than 15Gy (P=0.05). Platelet recr uitment was also increased for 30Gy compared with control at 1 day. Conclusions-Endovascular irradiation at 15Gy or 30Gy after balloon angiopla sty results in incomplete endothelial recovery, impaired resolution of intr amural hemorrhage, and a-dose-dependent increase in platelet recruitment at 1 month.