High Wall Shear Stress and Its Gradient Indicates Intimal Hyperplasia in Vascular Bypass Graft End-to-Side Distal Anastomosis

Simulation of three-dimensional (3D) blood flow in a distal end-to-side anastomosis for two total graft flowrate redistributions was performed. For the same total blood flow, the distal end-to-end anastomosis was analyzed. The aim was to analyze the applicability of two hypotheses for intimal hyperplasia (IH) formation in a distal anastomosis of bypass graft: (i) high WSS combined with high WSS gradient and (ii) low wall shear stress (WSS) combined with high stress oscillations. A newly proposed endothelial stretching index (ESI), related to the first hypothesis, and the Relative retention time (RRT), related to the second hypothesis, were calculated over the graft and artery wall, and compared in the considered cases. High ESI regions within end-to-side distal anastomosis correlate very well with regions that were observed to develop IH in vivo. In such anastomosis, the stagnation point in the velocity field travels significantly along the artery floor within a heart period, resulting with highly oscillatory wall shear stress and its high gradient, and predisposing for the IH formation. In end-to-end anastomosis, the obtained values of these two indices are low, which correlates well with low predisposition for IH formation in this type of anastomosis. In the region close to the suture line the high value of ESI indicates IH formation, offering an additional explanation for IH initiation. When planning surgery, it is better to choose an end-to-end distal anastomosis configuration when possible. One possible solution for reducing IH in the end-to-side distal anastomosis is replacing the part of the native artery subjected to high-oscillatory wall shear stress with a prefabricated prosthetic graft.