Scanning Electron Microscopy of the Endothelial Surface of Small Diameter Vein Grafts in Rats Treated With Heparin

Abstract

There are patients with cerebral ischaemia who would benefit from an extracranial-intracranial anastomosis but whose external carotid arteries are blocked and, therefore, do not have scalp arteries available for an anastomosis. In these cases a vein graft would seem to be the obvious choice to carry an extra supply of blood to the brain. However, at the point of anastomosis to the cerebral artery the vein graft would need to have a diameter of about 1 mm, and in rats vein grafts of this size have been shown to have a very poor patency rate (Bannister et al. 1977). The venous internal elastic lamina has a net-like construction, and lies over numerous collagen fibres in the subendothelial layer. Damage and loss of the endothelium during dissection and anastomosis exposes the collagen fibres to the blood stream, platelets and fibrin are deposited on them, and in less than an hour all the experimental grafts were occluded by thrombus. In spite of these findings vein grafts remain an attractive way of carrying blood to the ischaemic brain, and warrant further investigation for means of keeping them patent over long periods of time. Heparin was selected for investigation because of its anti-coagulant and anti-platelet adhesive actions.