Heparin reduces the intimal hyperplasia seen in microvascular vein grafts

The influence of heparin on microvascular vein graft intimal hyperplasia was studied in a rat model. The iliolumbar vein was grafted into the iliac artery in 80 rats. Heparin was delivered via a subcutaneous miniosmotic pump, starting either 2 days before grafting (early heparin group, n = 20) or immediately after grafting (heparin group, n = 30). Saline-containing pumps were placed in the control group (n = 30). Heparin activity was measured at 24 h, and again 3 weeks later when the animals were sacrificed. The grafts were harvested and prepared for histological examination. The intimal thickness was measured at the anastomoses and in the mid-graft region using an eye-piece graticule set at right angles to the graft internal elastic lamina. Heparin significantly reduced the intimal thickness at the anastomoses, from a median of 38 microns (range: 10-100 microns) in the control group to a median of 20 microns (range: 10-150 microns) in the heparin group. A similar reduction was seen in the mid-graft region. Although intimal thickening was reduced in the early heparin group, this reduction failed to reach statistical significance. The possible clinical application is discussed.