Intimal hyperplasia in vascular anastomosis

Abstract

Background. The study was performed to examine the healing process of a vascular prosthesis implanted into the arterial system and the formation of neointima.
Materials and methods. The study was conducted on 16 dogs in which PTFE prostheses of 6 mm diameter had been implanted in the aortofemoral region. The animals underwent autopsy after 6 months. The prosthesis together with the aorta and the femoral artery was explanted in order to perform tests of the proximal and distal anastomosis area under the light and the transmission electron microscopes.
Results. It was confirmed that the inner membrane (intima) of the distal anastomosis was thicker. The results were highly statistically significant (p = 0.0000000002824). Contrary to the proximal anastomosis, the area of the distal anastomosis revealed the presence of macrophages and granulocytes, being the markers of the active inflammatory reaction. Additionally, there were more myofibroblasts in this area and collagen deposits were bigger.
Conclusions. The differences between the proximal and distal anastomosis are the result of haemodynamic processes. Tangential stress, appearing parallel to the blood flow, is much more prominent in the distal anastomosis area as opposed to the shear stress, appearing perpendicular to the vessel. Therefore, neointimal thickening in the area of distal anastomosis is caused by haemodynamic factors and the biological incompatibility of the prosthesis and the artery (compliance mismatch). Prolonged stimulation of the inflammatory process causes the formation of neointima as well as the increased collagen production, hypertrophy and thickening of the inner membrane. All of these result in haemodynamic disturbances, the increase of the vascular resistance and the turbulent blood flow. They, in turn, may become the cause of clinical complications such as thrombosis of the prosthesis, late prosthesis infection and formation of the aneurysm in the area of anastomosis.