The Role of Arteriovenous Graft Curvature in Haemodynamics: an Image-Based Approach
About
Vascular access, such as arteriovenous grafts, is crucial for patients undergoing haemodialysis as part of kidney replacement therapy. One of the primary causes of arteriovenous graft failure and loss of patency is disordered blood flow, as the vein is exposed to the arterial environment with high flow rates and shear stress. We hypothesize that secondary flow downstream of the vein-graft anastomosis plays a critical role in generating low shear regions, thereby promoting neointima hyperplasia. The secondary flow highlighted here also promotes high oscillatory shear index regions downstream of the vein-graft anastomosis, further contributing to graft failure. To prolong the overall graft survival and patency, we aim to develop a strategy to optimise graft configurations with reduced levels of disturbed haemodynamics. We developed an image-based approach to build three-dimensional geometries for subsequent computational fluid dynamics (CFD) numerical simulations. This simple, yet accurate, method allowed us to improve the accuracy of geometries, thus facilitating comparisons between different vein-graft anastomotic angles. Our results reveal that overall graft curvature (looped vs. straight) plays a dominant role in characterising the failure metrics. Looped grafts, particularly at moderate vein-graft anastomotic angles (30{\deg}-45{\deg}), exhibited the most favourable metrics, including reduced values of low wall shear stress, high wall shear stress, and high oscillatory shear index. These findings provide critical insights to inform medical professionals about graft areas that are subject to high shear stresses due to the oscillating nature of blood flow as well as the graft geometric configuration when performing surgery. The model developed in this work offers a framework enabling personalised vascular access strategies tailored to individual patient needs.