Incomplete Restoration of Homeostatic Shear Stress Within Arteriovenous Fistulae

Arteriovenous fistulae are created surgically to provide an adequate access for dialysis in patients with End-Stage Renal Disease (ESRD). Producing an autogenous shunt linking an artery and a vein in the peripheral circulation bypasses the high resistance capillary bed in order to provide the necessary flow rates at sites easily accessible for dialysis. In successful fistulae, venous flow rates can easily exceed 1000 mL/min. It has long been recognized that the hemodynamics constitute the primary external influence on the remodeling process [1]; The high flow rate, together with the exposure of the venous tissue to the high arterial pressure, leads to a rapid process of wall remodeling that may end in a mature access or in failure. Recent hemodynamic simulations [2,3] have computed very high viscous wall shear stresses within fistulae; Stresses > 15Pa have been reported which are much greater than what is typically considered normal (i.e. homeostatic, ≈ 1Pa). Both sustained high shear and sustained low shear have been hypothesized to cause pathological venous remodeling (i.e. intimal hyperplasia) which causes stenoses and threatens fistula patency. The role of high vs. low shear stress in effecting patency remains unclear. Given the high failure rate of dialysis access sites (up to 50% require surgical revision within one year [4]), understanding the dynamics of blood flow within the fistula is a necessary step in understanding the remodeling, and ultimately, in improving clinical outcomes.