Optimising haemodynamic performance: Investigating the impact of varying anastomosis angles on blood flow in brachiocephalic fistula

• Lower anastomosis angles increase shear forces and flow disturbances. • Wider angles promote smoother flow, reducing oscillatory shear stress. • The 135-degree angle is optimal for brachiocephalic fistula functionality and longevity. • Lower angles may help reduce thrombosis risk in high-risk patients. • Wider angles lower vascular wall damage, improving long-term patency. This study investigates the effect of anastomosis angle on haemodynamic performance in Brachiocephalic fistulas, using computational fluid dynamics to inform optimal surgical configurations for hemodialysis access. Nine idealized brachiocephalic fistula geometries with anastomosis angles ranging from 15° to 135°, in 15° increments, were simulated under pulsatile flow conditions. Key haemodynamic parameters, including pressure, velocity, time-averaged wall shear stress, oscillatory shear index, high oscillatory low magnitude shear, and relative residence time, were assessed to evaluate flow stability and clinical implications. Results indicate that lower anastomosis angles (15°, 30°) exhibit higher TAWSS values, peaking at 3.8 Pa in the anastomosis zone, and demonstrate concentrated HOLMES and OSI regions, indicating elevated flow disturbance and vascular stress. In contrast, wider angles (120°, 135°) promote smoother, more laminar flow, with up to a 60% reduction in adverse WSS-derived parameters, particularly HOLMES and RRT, when compared to sharper angles. These improvements are especially notable in the venous segment, where lower flow stagnation reduces the risk of thrombus formation. Among all configurations, the 135° angle emerged as the most favourable, balancing shear forces and reducing disturbed flow zones, thereby enhancing long-term AVF patency and function. Clinically, sharper angles may benefit patients with thrombosis risk due to increased shear clearing, while wider angles are better suited for minimising endothelial damage and improving durability. These findings support the need for personalised surgical planning, with anastomosis angle tailored to patient-specific vascular health and clinical priorities.