Scanning electron-microscopic study of the anastomosed vein of arteriovenous fistulae.

A scanning electron-microscopic study of experimentally-induced arteriovenous fistulae in rabbits was conducted to investigate the haemodynamically-induced endothelial changes caused by the shunt. Animals were examined from 5 to 696 days postoperatively. The initial endothelial denudation in the vicinity of the anastomosis was rapidly repaired and by 15-20 days re-endotheliazation was complete. Severe surface changes were found in the region of greatest turbulence, opposite the shunt. Changes characteristically consisted of craters, scallops, mounds and ridges, fused together to give a moonscape-like appearance. This area, termed the "jet lesion", was covered with polygonal endothelial cells with thickened, distorted and often highly-crenated margins. The margin of the fistula, where shear stress was expected to be high, exhibited flattened, elongated, generally fusiform endothelial cells with serrated margins. They were aligned parallel to the blood flow, whereas those in the "jet lesion"were polygonal and randomly orientated. These profound changes in the endothelium and the underlying connective tissues, observed as early as 15 days postoperatively, revealed the extent and severity of the effect of haemodynamics on the wall.