Effect of chronic subcutaneous or intramural administration of heparin on femoral artery restenosis after balloon angioplasty in hypercholesterolemic rabbits: A quantitative angiographic and histopathological study

Background. Heparin is known to have antithrombotic, anticoagulant, and antiproliferative effects. We hypothesized that chronic subcutaneous and/or direct intramural administration of heparin would reduce restenosis and inhibit plaque growth after balloon angioplasty. Methods and Results. Focal atherosclerosis was induced bilaterally in the femoral arteries of 59 rabbits by air desiccation intimal injury and a 2% cholesterol diet. After angioplasty, the rabbits were assigned to one of four treatment groups. Control arteries (n=21) received no additional heparin. A second group of 20 arteries was treated with a porous balloon that delivered heparin (1,500 units) directly into the arterial wall. A third group (n=29) received subcutaneous heparin (350 units·kg^-1·day^-1) for 28 days, and a fourth group (n=23) was treated with subcutaneous and intramural heparin. Quantitative angiography showed a modest reduction in restenosis (defined as the change in minimal luminal diameter from immediately after angioplasty to 28 days) with subcutaneous heparin compared with control arteries (0.32±0.18 versus 0.58±034 mm, p<0.01); however, luminal diameter was not improved at 28 days compared with before angioplasty. Intramural delivery of heparin by the porous balloon catheter was confirmed by use of fluoresceinated heparin in one animal. Angiographic restenosis was not reduced in arteries treated with intramural heparin versus controls (0.61±0.54 versus 0.58±0.34 mm, p=NS). Blinded planimetric analysis of histological sections showed no differences in luminal cross-sectional area narrowing by atherosclerotic plaque, in plaque area, or in plaque/media ratio at 28 days among the four treatment groups. Conclusions. Chronic subcutaneous heparin after balloon angioplasty results in a modest reduction in angiographic restenosis in this model; however, the absolute luminal diameter is not improved compared with before angioplasty, and plaque area and percent luminal narrowing by plaque were not different among the four treatment groups. Heparin can be delivered into an atherosclerotic plaque by a porous balloon, but this treatment does not reduce restenosis after angioplasty in this model.