Hemodynamic study: impact of anastomosis floor arterial stenosis on neointimal hyperplasia in hemodialysis arteriovenous fistulas.

Objective: This study aimed to investigate the hemodynamic mechanisms associated with arterial stenosis at the anastomosis floor of arteriovenous fistula (AVF), with a particular focus on characterizing how varying degrees of stenosis affect hemodynamic parameters in downstream venous hyperplastic regions. Methods: Computational fluid dynamics (CFD) simulations were conducted to numerically analyze hemodynamic characteristics in AVF using a standardized idealized AVF model. Key hemodynamic parameters, such as wall shear stress (WSS) and oscillatory shear index (OSI), were quantitatively evaluated. Particular attention was given to the variations and spatial distribution of these parameters in the presence of stenotic lesions within the arterial wall at the anastomosis floor, as well as across varying severities of stenosis. Results: The regions of high wall shear stress in AVF are predominantly located at the anastomosis and along the outer wall of the juxta-anastomotic vein, whereas the low wall shear stress regions are primarily observed on the arterial wall at the floor of the anastomosis and along the inner wall of the swinging segment of the cephalic vein. These regions show partial consistency with the areas of high oscillatory shear index. In this idealized model, when the hyperplastic size of the artery at the anastomosis floor reaches approximately 1.0 mm, the wall shear stress level within the hyperplastic region returns to physiological levels, at which point neointimal hyperplasia ceases. At hyperplastic sizes of 0.5 mm and 1.0 mm in the artery at the anastomosis floor, the area of the high wall shear stress region on the outer wall of the juxta-anastomotic vein was reduced by 3.6% and 9.5%, respectively, compared to the non-hyperplastic state, with corresponding decreases in maximum wall shear stress of 7.0% and 10.2%. Similarly, under these hyperplastic conditions, the area of the low wall shear stress region on the inner wall of the swinging segment of the cephalic vein was reduced by 8.6% and 17.4%, respectively, relative to the non-hyperplastic state. Conclusion: In this idealized AVF model, when neointimal hyperplasia develops in the arterial wall at the anastomosis floor and reaches moderate severity, key hemodynamic parameters are restored toward physiological ranges, which is associated with attenuation of neointimal hyperplasia progression. This hyperplasia-induced moderate stenosis of the radial artery helps reduce the hyperplastic region in the cephalic vein near the anastomosis, thereby lowering the risk of stenosis and occlusion in the cephalic vein's swing segment.