Objectives: This study examined the effects of intracoronary irradiation on neointimal proliferation after overstretch balloon angioplasty in a normolipemic swine model of restenosis.
Background: Restenosis after percutaneous transluminal coronary angioplasty represents, in part, a proliferative response of vascular smooth muscle at the site of injury. We have previously shown that ionizing radiation, delivered by means of an intracoronary source, causes focal medial fibrosis. We therefore hypothesized that intracoronary irradiation delivered at the time of balloon angioplasty might impair the restenosis process.
Methods: Nineteen juvenile swine underwent coronary angiography; a segment of the coronary artery was chosen as a target for balloon injury. In 10 swine, a ribbon of iridium-192 was positioned at the target segment, and 2,000 cGy was delivered at the vessel wall. Subsequently, overdilation balloon angioplasty was performed at the irradiated segment. In nine control swine, overdilation balloon angioplasty was performed without previous irradiation. Eighteen animals survived and were killed at 30 days. Histopathologic analysis was performed by a pathologist in blinded manner. The area of maximal lumen compromise within the target segment was analyzed by computer-assisted planimetry.
Results: In the control group, mean (+/- SD) neointimal area was 0.84 +/- 0.60 mm2 compared with that in the irradiated group, 0.24 +/- 0.13 mm2 (p = 0.01). In the control group, mean percent area stenosis was 47.6 +/- 20.7%, whereas that in the irradiated group was 17.6 +/- 10.5% (p = 0.001). This represents a 71.4% reduction in neointimal area and a 63.0% reduction in percent area stenosis in the irradiated group. Adjacent coronary segments and surrounding myocardium were unaffected.
Conclusions: Intracoronary irradiation (2,000 cGy) delivered to a target porcine coronary segment before balloon overdilation markedly reduces neointima formation at 30 days and thus significantly impairs the restenosis process.