Intracoronary Low-Dose β-Irradiation Inhibits Neointima Formation After Coronary Artery Balloon Injury in the Swine Restenosis Model

Abstract

Background Neointima formation contributing to recurrent stenosis remains a major limitation of percutaneous transluminal angioplasty. Endovascular low-dose γ-irradiation has been shown to reduce intimal thickening (hyperplasia) after balloon overstretch injury in pig coronary arteries, a model of restenosis. The objective of this study was to determine whether the use of a β-emitting radioisotope for this application would have similar effects and to examine the dose-response relations with this approach. Methods and Results Normal domestic pigs underwent balloon overstretch injury in the left anterior descending and left circumflex and coronary arteries. A flexible catheter was introduced by random assignment into one of these arteries and was afterloaded with a 2.5-cm ribbon of encapsulated ⁹⁰ Strontium/ ⁹⁰ Yttrium sources ( ⁹⁰ Sr/Y, a pure β-emitter). It was left in place for a period of time sufficient to deliver one of four doses: 7, 14, 28, or 56 Gy, to a depth of 2 mm. Animals were killed 14 days after balloon injury, the coronary vasculature was pressure-perfusion fixed, and histomorphometric analysis of arterial cross sections was performed. All arteries treated with radiation demonstrated significantly decreased neointima formation compared with control arteries. The ratio of intimal area to medial fracture length was inversely correlated with increasing radiation dose: control (no radiation), 0.47; 7 Gy, 0.34; 14 Gy, 0.20; 28 Gy, 0.08; and 56 Gy, 0.02 ( r =−.78, P <.000001). Scanning electron microscopy demonstrated a confluent layer of endothelium-like cells both in control and in 14 Gy–irradiated arteries. There was neither evidence of significant necrosis nor excess fibrosis in the media, adventitia, or perivascular space of the coronary arteries or adjacent myocardium in the irradiated groups. Furthermore, the exposure to the staff and the total body exposure to the pig with the β source was a small fraction of the dose previously measured and calculated with ¹⁹² Ir, a γ-emitting radioisotope. Conclusions Administration of endovascular β-radiation to the site of coronary arterial overstretch balloon injury in pigs with ⁹⁰ Sr/Y is technically feasible and safe. Radiation doses between 7 and 56 Gy showed evidence of inhibition of neointima formation. A dose-response relation was demonstrated, but no further inhibitory effect was seen beyond 28 Gy. These data suggest that intracoronary β-irradiation is practical and feasible and may aid in preventing clinical restenosis.