Effects of vascular runoff on myointimal hyperplasia after mechanical balloon or thermal laser arterial injury in dogs

Abstract

Background. Clinical evidence suggests that poor vascular runoff reduces the long-term success rate of femoral angioplasty procedures. The purpose of this experimental study was to examine myointimal hyperplasia of dog femoral arteries after balloon denudation, thermal laser arterial injury, or sham operation in normal and reduced vascular runoff conditions. Methods and Results. Before mechanical balloon injury or transluminal heated laser probe motion, the peripheral vascular runoff of dogs was reduced by ligating the femoral artery below its three distal side branches, decreasing the femoral flow rate from 114±9 to 52±5 ml/min (mean±SEM). Endothelial denudation with a predominantly intact elastic internal membrane and circumferential structural changes in the media were noted by light microscopy 1 hour after balloon injury. Focal completely necrotic lesions of intima and media were found 1 hour after thermal laser arterial injury. After 8 weeks, the maximal thickness of neointima plus media of the site of previous intervention was greater after balloon injury (0.45±0.03 mm) and thermal laser injury (0.54±0.03 mm) than after sham operation (0.40±0.01 mm; p<0.001) in normal runoff dogs. Reduced vascular runoff augmented myointimal hyperplasia both in the balloon-injured and thermally damaged arteries; the wall thickness increased from 0.45±0.03 to 0.93±0.10 mm and from 0.54±0.03 to 0.65±0.05 mm, respectively (p<0.001). The neointimal and medial wall area of the balloon-injured arteries contributed 48% to the area encompassed by the external elastic membrane compared with an 81% portion when vascular runoff was reduced (p<0.01). A 47% neointimal and medial wall area was found in thermally injured arteries with normal runoff compared with 63% after runoff reduction (p<0.05). Conclusion. This study suggests that hemodynamic factors associated with poor vascular runoff play an important role in extending myointimal hyperplasia independent of method and severity of the arterial injury during angioplasty.