Evaluation of arteriovenous fistulas of obtuse anastomosis in reducing thrombosis using computational fluid dynamics

Arteriovenous fistula (AVF) failure in hemodialysis patients is strongly influenced by local hemodynamic factors such as elevated wall shear stress, flow separation, and vortex formation. In this study, computational fluid dynamics (CFD) simulations are performed to investigate the influence of anastomosis angle and blood rheology on AVF hemodynamics. Three non-Newtonian blood models (Carreau, power-law, and Casson) are first evaluated at 45°, 90°, and 135° anastomosis angles and validated against available experimental data. Based on shear stress prediction accuracy, the Carreau model is demonstrated as the best agreement and is selected for further simulations. Subsequently, AVFs with 45°, 90°, 110°, 120°, 135°, 145°, and 160° anastomosis angles are analyzed under maximum, medium, and minimum pulsatile flow conditions. Hemodynamic parameters including velocity patterns, wall shear stress distribution, vortex formation, and pressure drop between the proximal artery and vein are evaluated. Results indicate that increasing the anastomosis angle significantly reduces maximum wall shear stress, high-shear regions, vortex intensity, and pressure drop. Compared with the 45° configuration, the 160° angle reduced maximum shear stress by ~78% under peak flow conditions. Overall, obtuse anastomosis angles demonstrated improved hemodynamic performance, suggesting that larger angles may reduce thrombosis risk and cardiovascular burden in hemodialysis patients. Considering both hemodynamic performance and surgical feasibility, the 120° configuration is proposed as a clinically practical and effective option.