EXTERNAL-BEAM IRRADIATION INHIBITS NEOINTIMAL HYPERPLASIA FOLLOWING BALLOON ANGIOPLASTY

Restenosis is a serious problem limiting the long-term efficacy of per cutaneous transluminal coronary angioplasty. Neointimal smooth muscle proliferation is the major process underlying restenosis. The objectiv e of this study was to investigate the effects of external irradiation on neointimal hyperplasia following balloon angioplasty. We examined the ability of external X-ray irradiation to inhibit intimal hyperplas ia following balloon angioplasty in a nonatherosclerotic rabbit model. Baseline quantitative angiography (day 0) was performed in all rabbit s and balloon angioplasty was performed in the right (control) and the left iliac arteries. Five days after balloon angioplasty, the left il iac in each rabbit was irradiated with either 600 cGy (n = 5) or 1200 cGy (n = 5). Twenty-eight days following angioplasty final angiography was performed. All rabbits were sacrificed, and the iliac arteries we re fixed for morphometric measurements. Comparison of baseline and fin al angiographic measurements revealed a significant decrease in averag e and minimum lumen dimensions for both control and irradiated segment s (600 and 1200 cGy) [average: P (baseline vs. final) 0.008 (control), 0.001 (600 cGy); 0.05 (control), 0.007 (1200 cGy)]. Morphometric anal ysis showed no difference in neointimal cross-sectional area between c ontrol (0.29 +/- 0.05 mm(2)) and 600 cGy irradiated segments (0.32 +/- 0.07 mm(2)) (P = 0.82). However, there was a statistically significan t reduction in neointimal hyperplasia in the 1200 cGy irradiated segme nts (0.09 +/- 0.02 mm(2)) compared to control (0.23 +/- 0.06 mm(2), P = 0.02). There was no significant difference in medial cross-sectional area between control and irradiated segments (600 and 1200 cGy). We c onclude that in this model, external beam X-ray irradiation (1200 cGy) was successful in reducing neointimal proliferation after balloon ang ioplasty. Whether or not this approach can be used successfully to inh ibit restenosis in the clinical setting requires further investigation .