VasQ and Hemodynamic Conditions in AVFs

End-stage renal disease (ESRD) is a growing global health problem, strictly connected with progressive ageing population and longer survival of patients living on renal replacement therapy. The majority of ESRD patients is on hemodialysis (HD) treatment. A successful HD procedure requires a functional vascular access (VA) to provide safe and long-lasting way to connect patient circulation to the artificial kidney. To date, VA dysfunction is the major cause of morbidity and hospitalisation in HD patients, and the major limitation of HD treatment. The current recommendation for VA is the native artero-venous fistula (AVF), surgically created in the forearm, but is still affected by high non-maturation and early failure rates. The most common cause of AVF early-failure is vascular stenosis due to neointimal hyperplasia (NH). Despite the exact mechanisms underlying stenosis development remain tentative, there is general consensus that hemodynamic conditions play a key role in the formation of NH. Previous computational fluid dynamics (CFD) investigations inside patient-specific AVF models conducted by our group revealed transitional laminar-to-turbulent flow in the juxta-anastomotic vein.

Various vascular access devices have been designed to incorporate features to regularize the hemodynamics and favour spiral flow development in the venous segment of the AVF. The VasQ external support device (Laminate Medical Technologies, Israel) is a novel Nitinol implant, externally surrounding and supporting the vein and "hugging" the artery near the junction site, without being in contact with the blood flow.

VasQ attempts at constraining and shaping geometrical parameters of the AVF, as well as reinforcing the vulnerable perianastomotic vein against high pressure, wall tension and flow levels. A prospective single-centre study demonstrated the safety of the VasQ external support device, but the effect of its use on hemodynamic conditions and the advantages in terms of flow regularization in patient-specific AVFs still need to be investigated.

A detailed analysis of the local blood flow field in patient-specific AVFs can be obtained coupling non contrast-enhanced MRI (NCE-MRI) and high-resolution CFD simulations, using a NCE-MRI protocol recently optimized by our group. Our MRI sequence has the advantage of providing high-quality images in a short acquisition time of 5-10 minutes compared to other MRI protocols that require more than 45 minutes for a single acquisition. Combined with high-resolution CFD, our MRI-to-CFD pipeline allowed us to characterize morphological and hemodynamic changes in the AVF of one patient at two timepoints, immediately after AVF surgery and at AVF maturation. Therefore, it seems to be a promising approach to perform morphological and hemodynamic analysis also in AVF created using the VasQ device and can be used to elucidate the effects of VasQ device on hemodynamic conditions, as compared to hemodynamic conditions present in AVFs created using conventional surgery without the use of any device.