Vascular remodelling due to haemodynamics, in an arteriovenous fistula

Abstract

Arteriovenous fistula creation is the preferred vascular access for haemodialysis therapy, but has a large failure rate in the maturation period. This period generally lasts six to eight weeks after surgical creation, in which the vein and artery undergo extensive vascular remodelling, largely due to the haemodynamics. The primary aim of this thesis was to develop a fundamental understanding of the arteriovenous fistula maturation and the associated vascular remodelling.

Previous research, considering the remodelling mechanisms and risks associated with failure-to-mature patients through the use of computational fluid dynamics, has been limited by obtaining the patient-specific boundary conditions at only a few points in the patient history. Here, a non-invasive imaging system was specifically developed to reconstruct the three-dimensional vasculature and use computational fluid dynamics to analyse the haemodynamics.

An initial investigation with six patients demonstrated that each patient had unique vasculature which altered the maturation process. Wall shear stress metrics used to describe disturbed flow were calculated for both successful and unsuccessful maturations. While no clear correlation could determine the cause of failure, high multi-directional wall shear stress was present in the patient before failure and could be an indicator for disease development. The results from this study also showed that vascular remodelling was not complete by six weeks, and therefore another patient was recruited for long-term analysis with high temporal data.

The extended analysis revealed evidence of a control mechanism, which adjusted the lumen diameter to keep the wall shear stress near constant in the proximal regions of the vein and artery. Additionally, the vein and artery were shown to remodel at different growth rates, but the growth rates were also dependent on proximity to the anastomosis.

Finally, the key factors that influenced the maturation were identified from the patient data set. High blood flow rates immediately after creation were found to have positive contribution on successful outward remodelling. Current clinical surveillance was shown to be inadequate for identifying a failing arteriovenous fistula, and highlighted the need for early and regular surveillance of the haemodynamics.