Intimal hyperplasia and hemodynamic factors in arterial bypass and arteriovenous grafts: a review.

Stenosis at the graft-vein junction caused by intimal hyperplasia (IH) is the major cause of failure of vascular access grafts used for hemodialysis. There is a strong relationship between hemodynamic factors and formation of IH. The hemodynamic pattern and the location of IH are different in arterial bypass grafts (ABGs) compared with arteriovenous grafts (AVGs). In an ABG, end-to-side anastomosis of the expanded polytetrafluoroethylene graft and artery produces hemodynamic changes around the junction. IH develops at the arterial floor and the toe and heel of the distal anastomosis. Low shear stress and oscillating shear forces at the arterial floor and the heel plus a high wall sheer stress (WSS) gradient at the toe probably promote IH development. Compliance mismatch between the graft and artery causes turbulence that may contribute to IH formation. The blood flow rate in AVGs is 5-10 times greater than that in ABGs. High flow causes turbulence that injures endothelial cells and eventually results in IH. The peak WSS in AVGs is about 6 N/m(2), much higher than that in ABGs. Excessively high WSS may effect IH formation in AVGs. Several venous cuff or patch anastomotic designs have been used in attempts to regulate hemodynamic factors in grafts. In ABGs, these designs appear to help decrease IH formation. In AVGs, however, they generally have not improved patency rates. In a high-flow system such as an AVG, more drastic changes in anastomotic design may be required.