Computational modeling of the cephalic arch predicts hemodynamic profiles in patients with brachiocephalic fistula access receiving hemodialysis

Background The most common configuration for arteriovenous fistula is brachiocephalic which often develop cephalic arch stenosis leading to the need for numerous procedures to maintain access patency. The hemodynamics that contributes to the development of cephalic arch stenosis is incompletely understood given the inability to accurately determine shear stress in the cephalic arch. In the current investigation our aim was to determine pressure, velocity and wall shear stress profiles in the cephalic arch in 3D using computational modeling as tools to understand stenosis. Methods Five subjects with brachiocephalic fistula access had protocol labs, Doppler, venogram and intravascular ultrasound imaging performed at 3 and 12 months. 3D reconstructions of the cephalic arch were generated by combining intravascular ultrasounds and venograms. Standard finite element analysis software was used to simulate time dependent blood flow in the cephalic arch with velocity, pressure and wall shear stress profiles generated. Results Our models generated from imaging and flow measurements at 3 and 12 months offer snapshots of the patient’s cephalic arch at a precise time point, although the remodeling of the vessel downstream of an arteriovenous fistula in patients undergoing regular dialysis is a dynamic process that persists over long periods of time (~ 5 years). The velocity and pressure increase at the cephalic bend cause abnormal hemodynamics most prominent along the inner wall of the terminal cephalic arch. The topology of the cephalic arch is highly variable between subjects and predictive of pathologic stenosis at later time points. Conclusions Low flow velocity and wall pressure along the inner wall of the bend may provide possible nidus of endothelial activation that leads to stenosis and thrombosis. In addition, 3D modelling of the arch can indicate areas of stenosis that may be missed by venograms alone. Computational modeling reconstructed from 3D radiologic imaging and Doppler flow provides important insights into the hemodynamics of blood flow in arteriovenous fistula. This technique could be used in future studies to determine optimal flow to prevent endothelial damage for patients with arteriovenous fistula access.

Feasibility of a 3 mm arteriotomy for brachiocephalic fistula formation

Background: The arteriovenous fistula is the modality of choice for long-term haemodialysis access. We describe the feasibility of routinely fashioning a brachiocephalic fistula utilising a 3 mm long arteriotomy in an attempt to reduce the incidence of symptomatic steal syndrome yet while maintaining satisfactory clinical outcomes. Methods: All patients who underwent brachiocephalic fistula formation using a routine 3 mm long arteriotomy within Hammersmith Hospital between January 2017 and March 2018 were included. Primary outcomes included primary failure, failure of maturation, secondary patency and steal syndrome. Results: Sixty-eight brachiocephalic arteriovenous fistula were fashioned utilising a 3 mm long arteriotomy during the study period. Mean age was 60.5 years with 59% having a history of diabetes mellitus. Mean followup was 368 days. Primary failure occurred in 10 (14.7%) patients. Cannulation was achieved in 67.3% of remaining fistula within 3-months, rising to 87.3% by 6-months. Primary patency at 6 and 12 months was 76% and 69%, respectively. Secondary patency at 6 and 12 months was 94% and 91%, respectively. Dialysis access steal syndrome was clinically apparent in three (4.4%) patients with all cases being managed conservatively. Conclusion: A 3 mm long arteriotomy may be routinely utilised for brachiocephalic fistula creation in an attempt to limit the incidence of steal syndrome yet while maintaining clinical patency outcomes.

A cohort study showing correspondence of low wall shear stress and cephalic arch stenosis in brachiocephalic arteriovenous fistula access

Background: A brachiocephalic fistula is frequently placed for hemodialysis; unfortunately, cephalic arch stenosis commonly develops, leading to failure. We hypothesized that a contribution to brachiocephalic fistula failure is low wall shear stress resulting in neointimal hyperplasia leading to venous stenosis. The objective of this investigation is to determine correspondence of low wall shear stress and the development of cephalic arch stenosis. Methods: Forty subjects receiving hemodialysis with a primary brachiocephalic fistula access were followed from time of placement for 3 years or until cephalic arch stenosis. Venogram, Doppler, and viscosity were performed at time of fistula maturation, annually for 3 years or to time of cephalic arch stenosis. Computational hemodynamics modeling was performed to determine location and percent low wall shear stress in the arch. The relationship between wall shear stress at time of maturation and location of cephalic arch stenosis were estimated by correlating computational modeling and quadrant location of cephalic arch stenosis. Results: In total, 32 subjects developed cephalic arch stenosis with 26 displaying correspondence between location of low wall shear stress at time of maturation and subsequent cephalic arch stenosis, whereas 6 subjects did not (p = 0.0015). Most subjects with correspondence had low wall shear stress areas evident in greater than 20% of the arch (p = 0.0006). Low wall shear stress was associated with a higher risk of cephalic arch stenosis in the 23-to-45 age group (p = 0.0029). Conclusions: The presence and magnitude of low wall shear stress in the cephalic arch is a factor associated with development of cephalic arch stenosis in patients with brachiocephalic fistula. Attenuation of low wall shear stress at time of maturation may help prevent the development of cephalic arch stenosis which is difficult to treat once it develops.

Distal Arterial Embolization from an Abandoned Native Brachio-Cephalic Fistula: A Case Report

Abandoned thrombosed arterivenous fistulas are usually left in place with very rare complications. We describe a case of distal embolization from a thrombosed aneurismatic arteriovenous brachiocephalic fistula in a patient who vigorously used the affected arm for pushing his wheelchair. Vigorous physical activity with the hand bearing arteriovenous fistula (AVF) should probably be discouraged even after AVF thrombosis and especially, if the initial part of fistula vein is aneurysmatic. Antiagregation therapy should be considered in such cases.