Compliance and diameter mismatch affect the wall shear rate distribution near an end-to-end anastomosis

Abstract

The development of intimal hyperplasia near the anastomosis of a vascular graft to an artery may be related to changes in the wall shear rate distribution. Mismatches in compliance and diameter at the end-to-end anastomosis of a compliant artery and a rigid graft cause shear rate disturbances that may induce intimal hyperplasia and ultimately graft failure. The goal of this study is to determine how compliance mismatch, diameter mismatch, and impedance phase angle affect the wall shear rate distribution in end-to-end anastomosis models under sinusoidal flow conditions. Wall shear rates are obtained through flow visualization using a photochromic dye. In a model with a well-matched graft diameter (6% undersized), the compliance mismatch causes low mean wall shear rates near the distal anastomosis. Considering diameter mismatch, the wall shear rate distributions in 6% undersized, 16% undersized, and 13% oversized graft models are markedly different at similar phase angles. In the two undersized graft models, the minimum mean shear rate occurs near the distal anastomosis, and this minimum is lower in the model with greater diameter mismatch. The oversized graft model has a minimum mean shear rate near the proximal anastomosis. Thus in all three models, the minimum mean wall shear rate is observed at the site of the divergent geometry. The impedance phase angle, which can be altered by disease states and vasoactive drugs, has a minor effect on the wall shear rate amplitude far from the anastomosis but a more pronounced effect closer to the anastomosis. Mean wall shear rates under sinusoidal flow conditions are significantly lower than under steady flow conditions at the same mean flow rate, but they are fairly insensitive to phase angle changes. In order to avoid the divergent geometry that may cause lower wall shear rates, we recommend that compliance mismatch be minimized whenever possible and that graft diameter be chosen to match the arterial diameter at the relevant physiologic pressure, not at the reduced pressure present when the graft is implanted.