Intramural stresses at the distal graft/artery junction following femoral artery bypass surgery

Intimal hyperplasia development in the downstream anastomosis of a peripheral bypass grafts has been the subject of much investigation due to its site specific focal development at specific sites within the junction. Compliance mismatch between the synthetic graft and host artery is seen as a major cause of intimal hyperplasia formation along the suture line of synthetic graft/host artery anastomoses, with wall stress, wall shear stress, and local mass transport also playing an important role in intimal hyperplasia formation. The majority of previously published computational and experimental analyses focus on flow dynamics and the distribution of wall shear stress at distal End-To-Side bypass anastomoses. Studies associated with anastomotic mechanics and associated wall stress have reported abnormal wall stress at graft/artery anastomoses associated over excessive response by arterial tissue to the aforementioned stresses may correlate to intimal hyperplasia formation at anastomotic sites. The aim of this study is to further investigate abnormal wall stresses at the synthetic graft/artery anastomoses and to correlate abnormal wall stresses to sites of intimal hyperplasia formation at the distal End-To-Side anastomosis of the femoropopliteal system. To this end, computational investigation was undertaken to examine mechanical factors affecting the wall stresses of the arterial tissue at anastomoses. These mechanical factors included variations in geometry and compliance mismatch between the graft and host artery. Results show that abnormal wall stresses exist at the suture line of End-To-Side anastomoses, and the geometry of an idealised End-To-Side anastomosis significantly affect these abnormal wall stresses. Peak abnormal equivalent Cauchy stress magnitudes reach a peak are 113 times baseline values along the suture line, with an average deviation of 38 times baseline equivalent Cauchy stress across the suture line of an idealised End-To-Side anastomosis. This large deviation of wall stress deviation correlates to intimal hyperplasia formation at the suture line, which is reportedly induced by compliance mismatch between the graft and host artery. To quantify the affect of compliance mismatch, a compliant graft was employed at an idealised End-To-Side anastomosis. Abnormal equivalent Cauchy stress magnitudes were significantly reduced across the suture line, with the average and peak equivalent Cauchy stress reduced by 46.58% and 32.99%, respectively. But significant abnormal wall stresses are still present at the suture line with a compliance matching graft, with approximately 16 and 46 fold increase for average and peak abnormal equivalent Cauchy stress. The Prolong°R bypass graft was considered as an alternative arterial bypass configuration to the End-To-Side procedure. The analysis included four different configurations of End-To-End anastomoses, including a novel technique for joining synthetic grafts to host arterial tissue, which comes in the form of an S shaped incision (S-cut). Resolved abnormal wall stresses along the suture line for the four different End-To-End configurations were compared to the resolved abnormal wall stresses along the suture line of the End-To-Side anastomosis. It was demonstrated that a percentage reduction for the normalised equivalent Cauchy stress of 85.77%, 78%, 77.77%, and 74.11%, for the Planar, Bevel, S-cut1, and S-cut2 anastomosis configurations was achieved for the Prolong°R graft when compared to the idealised End-To-Side anastomosis. It is common perception that the compliance mismatch between the graft and the host artery is a major cause of graft failure. In the case of the distal End-To-Side nastomosis, this study has shown that it is the geometry that influences the wall stresses the most, and that a compliance matching graft material reduces abnormal wall stress of the arterial tissue, but they still do not approach the idealised healthy case of a healthy arterial vessel.