Abstract and Introduction
Abstract
Background Early failure of the vascular access for haemodialysis (HD) after the surgical creation of a radial-cephalic arteriovenous fistula (AVF) occurs mainly due to a juxta-anastomotic stenosis. Even if elevated blood flow induces high wall shear stress, we have recently shown that disturbed flow, characterized by low and reciprocating flow, may develop in zones of the AVF where it can provide a good indication of the sites of future stenoses. The present study was aimed at investigating whether the anastomosis angle influences disturbed flow in radial-cephalic 'side-to-end' AVF.
Methods By means of a parametric AVF model we created four equivalent meshes with anastomosis angles of 30°, 45°, 60° and 90°, respectively. We then performed transient, non-Newtonian computational fluid dynamics simulations using, as boundary conditions, previously measured blood volume flow and division ratio in subjects requiring primary access. The relative residence time (RRT), a robust indicator of disturbed flow, was calculated for the overall wall surface and disturbed flow was localized as areas having RRT > 1. Quantitative characterization and statistical tests were employed to assess the difference in RRT medians between the four anastomosis angle cases.
Results Disturbed flow was located in all AVF models in the same areas where flow recirculation and stagnation occurred, on the inner wall of the swing segment (SS) and on the arterial wall at the anastomosis floor (AF). A smaller angle AVF had smaller disturbed flow areas with lower RRT peak values, either on the venous or the arterial limb. There were significant differences in the RRT medians on the SS and on the AF between sharper (30° and 45°) and wider (60° or 90°) angles.
Conclusions We have found that in 'side-to-end' radial-cephalic AVFs for HD, the anastomosis angle does impact on the local disturbed flow patterns. Among the four geometries we considered in this study, the smaller angle (30°) would be the preferred choice that minimizes the development of neointima. Clinicians should consider this at the time of AVF creation because the anastomosis angle is in part amenable to surgical manipulation.
Introduction
Distal radial-cephalic arteriovenous fistula (AVF) is the best choice for achieving vascular access (VA) for haemodialysis (HD), but even this type of AVF has relatively high rates of early failure. Early failure of radial-cephalic AVF is defined as the impossible use of the VA for dialysis or total failure within the first 3 months and is usually due to a juxta-anastomotic stenosis. Maturation of the AVF or its early failure is closely related to the response of both feeding artery and draining vein to the increase in haemodynamic forces that occurs after the surgical creation of the anastomosis. Low haemodynamic shear contributes to the pathophysiology of VA failure due to thrombosis secondary to stenosis formation as well as VA re-occlusion after percutaneous interventions.
Observations on whether or not anastomosis angle influences the blood flow field and consequently the pathological response of the vessel wall has previously been reported in 'end-to-side' arterial bypass anastomoses. The artery-side-to-vein-end, briefly 'side-to-end', anastomoses used in VA are geometrically similar to the distal bypass anastomoses, but their different blood volume flow and blood pathways (see Figure 1 for a schematic illustration) will result in diverse wall shear stress (WSS) levels and spatial distributions. Furthermore, the effect of the anastomosis angle on the disturbed flow patterns in AVF has not yet been investigated.
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Figure 1.
Illustration of typical anastomoses and blood flow pathways. (1) 'End-to-side' (distal) anastomosis of a bypass graft with a stenosed host artery. (2) Radial-cephalic 'side-to-end' AVF used as VA for HD: (A) AVF with retrograde blood flow in the DA; (B) AVF with antegrade flow in the DA. V, vein; PA, proximal artery; DA, distal artery. The exact description of the anastomosis (e.g. 'end-to-side' or 'side-to-end') is done by taking into account the direction of blood flow.[9]