Intracoronary beta-radiation exacerbates long-term neointima formation in balloon-injured pig coronary arteries

Background-Long-term biological effects of ionizing radiation on coronary a rteries remain poorly defined. We examined late arterial responses 6 months after balloon angioplasty and beta -radiation in normal pig coronary arter ies. Methods and Results-Coronary arteries of 25 adult pigs were randomized to r eceive 20 Gy (n=8) or 30 Gy (n=9) of Re-186 beta -radiation or sham radiati on (n=8) immediately after balloon angioplasty. Aspirin was given daily dur ing follow-up. The study vessels were analyzed histopathologically at 6 mon ths. beta -Radiation decreased lumen area (20 Gy, 1.55 +/-0.99 mm(2); 30 Gy , 1.03 +/-0.82 mm(2); and 0 Gy, 2.05 +/-0.80 mm(2); P <0.05) but not overal l vessel area. The neointimal area was significantly larger within the inju red segment with beta -radiation (20 Gy, 1.92 +/-1.23 mm(2); 30 Gy, 1.51 +/ -0.97 mm(2); and 0 Gy, 0.89 +/-0.31 mm(2); 0 Gy versus 20 Gy, P <0.05), and a significant increase of edge stenosis was observed with beta -radiation. Irradiated vessels also had larger thrombus areas within the neointima (30 Gy, 0.24 +/-0.61 mm(2); 20 Gy, 0.98 +/-1.57 mm(2); and 0 Gy, 0.00 +/-0.01 mm(2); P <0.05) and larger adventitial areas (20 Gy, 2.25 +/-0.75 mm(2); 30 Gy, 2.38 +/-0.98 mm(2); and 0 Gy, 1.23 +/-0.29 mm(2); 0 Gy versus 20 or 30 Gy, P <0.05) that showed substantial collagen accumulation. Conclusions-Intracoronary beta -radiation did not inhibit neointima formati on in balloon-injured normal pig coronary arteries 6 months after the inter ventional procedure. Unresorbed thrombus contributed to, but was not the so le component of, augmented neointima formation. Irradiated vessels demonstr ated more adventitial thickening and fibrosis. These observations may have relevance for long-term clinical outcomes after intracoronary beta -radiati on.