Increased Inlet Blood Flow Velocity Predicts Low Wall Shear Stress in the Cephalic Arch of Patients with Brachiocephalic Fistula Access

<div><p>Background</p><p>An autogenous arteriovenous fistula is the optimal vascular access for hemodialysis. In the case of brachiocephalic fistula, cephalic arch stenosis commonly develops leading to access failure. We have hypothesized that a contribution to fistula failure is low wall shear stress resulting from post-fistula creation hemodynamic changes that occur in the cephalic arch.</p><p>Methods</p><p>Twenty-two subjects with advanced renal failure had brachiocephalic fistulae placed. The following procedures were performed at mapping (pre-operative) and at fistula maturation (8–32 weeks post-operative): venogram, Doppler to measure venous blood flow velocity, and whole blood viscosity. Geometric and computational modeling was performed to determine wall shear stress and other geometric parameters. The relationship between hemodynamic parameters and clinical findings was examined using univariate analysis and linear regression.</p><p>Results</p><p>The percent low wall shear stress was linearly related to the increase in blood flow velocity (<i>p</i> < 0.01). This relationship was more significant in non-diabetic patients (<i>p</i> < 0.01) than diabetic patients. The change in global measures of arch curvature and asymmetry also evolve with time to maturation (<i>p</i> < 0.05).</p><p>Conclusions</p><p>The curvature and hemodynamic changes during fistula maturation increase the percentage of low wall shear stress regions within the cephalic arch. Low wall shear stress may contribute to subsequent neointimal hyperplasia and resultant cephalic arch stenosis. If this hypothesis remains tenable with further studies, ways of protecting the arch through control of blood flow velocity may need to be developed.</p></div

Scatterplot depicting the relationship of blood flow velocity and WSS at maturation.

<p>Maximum blood flow velocity (cm/sec) is shown on the <i>x</i>-axis and percent low wall shear stress is shown on the <i>y</i>-axis. Blood flow velocity is correlated with changes in low wall shear stress (solid line) (<i>p</i> < 0.05). The patients with diabetes are represented by closed circles, the patients without diabetes by open circles with significant correlation in non-diabetics (<i>p</i> < 0.05).</p

Wall shear stress at mapping in 12 subjects.

<p>WSS (log <i>Pa</i>) at mapping for 12 subjects. Within-patient log-transformed wall shear stress values in the upper (dark grey) and lower wall (light grey). Red reference lines show the normal range on the original scale log scale [log(0.076)-log(0.76)].</p

Scatterplots depicting the relationship between weeks since access placement and Global Curvature or Global Asymmetry.

<p>Time since access placement (weeks) is shown on the <i>x</i>-axis and change in Global Curvature and Global Asymmetry are shown on the <i>y</i>-axis. Changes in Global Curvature (left panel) and Global Asymmetry (right panel) increase with time since the fistula was placed (<i>p</i> < 0.05). The relationship did not differ significantly in patients with diabetes (closed circles) compared to those without diabetes (open circles) (<i>p</i> < 0.05).</p

Patient Measured Parameters.

<p>Patient Measured Parameters.</p

Computational flow plot of cephalic arch.

<p>Terminal cephalic arch with inflow from right to left. Critical wall shear regions (< 0.076 Pa) are denoted with bold, red lines and are superimposed on streamlines. Computational flow plot for subject 7 at baseline (Panel A) and 30 weeks (Panel B). Computational flow plot for subject 2 at baseline (Panel C) and 8 weeks (Panel D). Black arrow on Panel D shows tiny area of low wall shear stress.</p

Subject Characteristics.

<p>Subject Characteristics.</p

Schematic of hypothesis.

<p>Arteriovenous fistula (AVF) creation leads to high blood flow velocity (BFV) diverted into the curved cephalic arch (Panel A black arrow shows normal curved cephalic arch). Low wall shear stress (WSS) (bold red on upper and lower wall) causes recirculation areas represented in Panel B (red arrow). Low WSS will eventually cause excessive neointimal hyperplasia (NH) and resultant cephalic arch stenosis (CAS) (Panel B black arrow).</p

Scatterplot depicting relationship of percent low WSS and cycle average percent low WSS.

<p>Percent low WSS in arch is shown on the <i>x</i>-axis with cycle average percent low WSS shown on the <i>y</i>-axis. The percent low WSS are strongly correlated with cycle average percent low WSS (<i>p</i> < 0.001).</p