Vein Contraction and Smooth Muscle Cell Extensions as Causes of Endothelial Damage during Graft Preparation

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Abstract
Meticulous preservation of the endothelial lining of vein grafts harvested during vascular operations is undoubtedly an important factor in determining patency rates following bypass procedures. Destruction of the vein graft's endothelial lining prior to graft implantation results in a more thrombogenic graft which is essentially a collagen-lined tube. This study used light, transmission, and scanning electron microscopy to investigate effects of various methods of vein graft preparation on endothelial and smooth muscle cells of the dog cephalic vein. Veins were removed and stored in one of three heparin-ized solutions at 10 C for either five minutes or one hour: autologous blood, Plasmalyte™ or Plasmalyte™ with 0.6 mg/ml papaverine HCl added. The vein wall was extremely sensitive to dissection, manipulation, or introduction of fixative solutions and reacted to such stimuli with severe contraction which not only diminished the luminal diameter but also resulted in protrusion of endothelial cells into the lumen and formation of cytoplasmic extensions of medial smooth muscle cells. Such cytoplasmic extensions were particularly frequent in the immediate subendothelial area and appeared to be instrumental in elevating, separating, or desquamating the endothelial cell lining. Veins stored in blood alone demonstrated the greatest vessel wall contraction and endothelial cell loss. Veins soaked in Plasmalyte™-papaverine solution had the most relaxed and normal appearance with minimal endothelial cell loss. Papaverine-treated veins which were subjected to brief periods of distension at pressures of 100 mmHg or greater demonstrated large gaps between the endothelial lining cells. The results suggest pretreatment with papaverine greatly reduces vein graft endothelial cell loss due to contraction, although such relaxation may be detrimental if vein grafts are subjected to excessive pressure prior to reversal of relaxation