EFFECTS OF HIGH-DOSE INTRACORONARY IRRADIATION ON VASOMOTOR FUNCTION AND SMOOTH-MUSCLE HISTOPATHOLOGY

A significant component of restenosis after coronary angioplasty is du e to medial proliferation. Targeted ablation of the proliferating cell s by ionizing radiation may prevent restenosis. We delivered high-dose intracoronary gamma-irradiation in porcine coronary arteries and asse ssed vasomotor function acutely and at 32 days, with pathological anal ysis at 32 days. Changes in luminal area were assessed by intravascula r ultrasound. Irradiated segments acutely displayed vasoconstriction t o acetylcholine, with loss of smooth muscle response to nitroglycerin. Restudy revealed restoration of normal vasodilatory response to acety lcholine but persistent loss of response to nitroglycerin. Histopathol ogy at 32 days revealed minor neointima formation without luminal comp romise and diffuse fibrosis of the smooth muscle layer. The surroundin g myocardium was normal. Focal medial fibrosis without significant end othelial or myocardial damage can be achieved via this technique; intr acoronary irradiation, therefore, may be an effective way of impairing the restenosis process.