Morphology of healing in vascular prostheses.

Vascular grafts differ in shape and size, material, mode of construction, and porosity. The latter was found to be of great importance with respect to tissue response of the host to the graft. The first reaction of the host after implantation represents the phase of exsudation. An aggregate of platelets and fibrin will cover most of the luminal and external surface of the graft, which is also seen between the interstices. The following phase of resorption develops within 2 weeks. It is characterized by replacement of the fibrinous material on the outer surface and between the interstices by capillaries, histiocytes, and myofibroblasts. Organisation of the outer capsule will then occur, and is also seen inside the transprosthetic bridges within one month. However, organization of the luminal lining remains very slow and is almost never completed. Healing depends on blood flow and local hemodynamic factors, and a mismatch in mechanical properties between the graft and host vessel may be important. Sources of endothelium in graft healing are anastomotic sites, pluripotent cells growing through the graft wall or deposition of pluripotent cells from the blood. Early failure of a prosthetic vascular graft occurs mainly as a result of separation at its sites of attachment. Late complications may be the result of mechanical failure (anastomotic sites or within the graft), kinking, inadequate or incomplete healing, and infection. The incidence of infectious complications varies from 0.25% to 6.0%, usually associated with high mortality rates.