Arteriovenous fistula creation with VasQTM device: A feasibility study to reveal hemodynamic implications

Abstract

Background: Arteriovenous fistula (AVF) is the preferred vascular access (VA) for hemodialysis, but it is still affected by high non-maturation and early failure rates due to stenosis development. Increasing evidence suggests that the presence of turbulent-like flow may play a key role, therefore, to stabilize the flow in the venous segment, an external support device (VasQ^TM) has been designed. The aim of this study was to provide preliminary evidence of VasQ^TM impact on AVF hemodynamics as compared to AVFs created with conventional surgery.

Methods: In this pilot single-center prospective randomized study six patients were enrolled, three in the VasQ group and three in the control group. Contrast-free magnetic resonance imaging (MRI) scans were acquired at 3 days, 3 months and 1 year after AVF surgery and were used to generate 3D patient-specific models. Computational fluid dynamic (CFD) simulations were performed using pimpleFoam, imposing patient-specific flow waveforms derived from ultrasound (US) examinations at the inlet of the proximal and distal artery, and a traction-free condition at the venous outflow. Morphologic and hemodynamic changes occurring over time were compared between VasQ and control AVFs.

Results: Our MRI protocol provided high-quality images suitable for reliable segmentation and reconstruction of patient-specific 3D models of AVFs at all three timepoints in four out of six patients. The VasQ^TM device maintained the angle between the artery and the vein almost unchanged over time, with a more stable flow in the AVFs supported by the device. In contrast, one of the AVFs of the control group evolved to an extreme dilatation of the vein and highly disturbed flow, while the other developed a stenosis in the juxta-anastomotic region.

Conclusions: This study demonstrated the feasibility of characterizing the morphological and hemodynamic changes occurring over time in AVFs created using the VasQ^TM device and provided preliminary evidence of the potential hemodynamic benefits of its use.

Keywords: Arteriovenous fistula; computational fluid dynamics; disturbed flow; external support device; longitudinal changes.

Figure 1.

Three dimensional geometrical models and blood flow rates of the two AVFs created using the VasQ device (V1 and V2) and the two control AVFs created by conventional surgery (C1 and C2), at 3 days, 3 weeks and 1 year after surgery. Arrows indicate the main direction of blood flow. The amplitude of the angle between the proximal artery and the vein is also shown for each model.

Figure 2.

Velocity streamlines at the systolic peak in the four AVFs under study, two ones created using the VasQ device - V1 and V2, and two control ones created by conventional surgery - C1 and C2, at 3 days, 3 weeks, and 1 year after surgery.

Figure 3.

Velocity-time traces, normalized by their respective cycle averages, at nine selected feature points along the centerline in the four AVFs under study, two ones created using the VasQ^TM device - V1 and V2, and two control ones created by conventional surgery - C1 and C2, at 3 days, 3 weeks, and 1 year after surgery.

Figure 4.

Oscillatory shear index (OSI) and time averaged wall shear stress (TAWSS) surface maps of the four AVFs under study, two ones created using the VasQ^TM device - V1 and V2, and two control ones created by conventional surgery - C1 and C2, at 3 days, 3 weeks and 1 year after surgery.

Figure 5.

Distribution of (a) the variation of cross sectional areas (CSAs) between different timepoints; (b) Oscillatory shear index (OSI); and time averaged wall shear stress (TAWSS) by AVF group (VasQ vs. control) at the three study timepoints. The thick line denotes the median, the box goes from the first to the third quartile, and the whiskers show the minimum and maximum data.