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

Background-Endovascular irradiation (EI) inhibits balloon-induced neointima formation in animals and is now in clinical trials for restenosis prevention. However, little is known of the effect of EI on vessel thrombogenicity due to delayed arterial healing. We investigated EI effects on platelet recruitment-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 month, platelet recruitment and thrombus formation were assessed using autologous In-111-oxine-platelet labeling and light and scanning electron microscopy. In balloon-injured nonirradiated vessels, there was complete reendothelialization at 1 month, and platelet recruitment was similar to normal uninjured arteries. In irradiated vessels, scanning electron microscopy showed incomplete reendothelialization at 1 month, and these areas demonstrated attachment of activated platelets. Light microscopy: of irradiated coronaries showed adherent partially organized thrombi and incomplete resolution of intramural hemorrhages. There was a significant increase in platelet recruitment 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 recruitment was also increased for 30Gy compared with control at 1 day. Conclusions-Endovascular irradiation at 15Gy or 30Gy after balloon angioplasty results in incomplete endothelial recovery, impaired resolution of intramural hemorrhage, and a-dose-dependent increase in platelet recruitment at 1 month.