Ultrastructural features of progressive intimal hyperplasia at the distal end-to-side anastomosis of vein grafts.

The features of intimal hyperplasia at the distal end-to-side anastomosis of arterially implanted autovein bypass grafts in dogs were examined using light and transmission electron microscopy. The bypass grafting was done under conditions of reduced blood flow with an abnormal flow wave and high peripheral resistance. Anastomotic intimal hyperplasia was evident 14 to 31 days after implantation, then gradually increased, particularly at the toe portion of the anastomosis. From 6 to 12 months after implantation, the intimal hyperplasia was excessively increased and severe luminal stenosis had developed. The hyperplastic neointima consisted of two layers; a laminated superficial layer and a randomly arranged deeper layer. The superficial layer had three to four layers of smooth muscle cells, while the deeper layer was mostly fibrocollagenous tissues. Thus, the intimal hyperplasia at the distal end-to-side anastomosis of the arterially implanted autovein graft developed as a result of infiltration of fibroblast-like cells, presumably tissue-synthesizing mesenchymal cells. The neointima at the distal anastomosis, under conditions of reduced blood flow with high peripheral resistance, remained in an active phase of intimal hyperplasia even 12 months after bypass grafting.