EFFECT OF EXTERNAL BEAM IRRADIATION ON NEOINTIMAL HYPERPLASIA AFTER EXPERIMENTAL CORONARY-ARTERY INJURY

Human coronary artery restenosis after percutaneous revascularization is a response to mechanical injury. Smooth muscle cell proliferation i s a major component of restenosis, resulting in obstructive neointimal hyperplasia. Because ionizing radiation inhibits cellular proliferati on, this study tested in a porcine coronary injury model the hypothesi s that the hyperplastic response to coronary artery injury would be at tenuated by X-irradiation. Deep arterial injury was produced in 37 por cine left anterior descending coronary artery segments with overexpand ed, percutaneously delivered tantalum wire coils. Three groups of pigs were irradiated with 300-kV X-rays after coil injury: Group I (n = 10 ), 400 cGy at 1 day; Group II (n = 10), 400 cGy at 1 day and 400 cGy a t 4 days and Group III (n = 9), 800 cGy at 1 day. Eight pigs in the co ntrol group underwent identical injury but received no radiation. Trea tment efficacy was histologically assessed by measuring neointimal thi ckness and percent area stenosis. Mean neointimal thickness in all irr adiated groups was significantly higher than in the control groups and thickness was proportional to X-ray dose. X-irradiation delivered at these doses and times did not inhibit proliferative neointima. Rather, it accentuated the neointimal response to acute arterial injury and m ay have potentiated that injury.