Patient-specific computational haemodynamics associated with the surgical creation of an arteriovenous fistula.

Despite arteriovenous fistulae (AVF) being the preferred vascular access for haemodialysis, high primary failure rates (30-70%) and low one-year patency rates (40-70%) hamper their use. Furthermore, AVF creation has been associated with haemodynamic changes causing maladaptive cardiac remodelling leading to cardiovascular (CV) complications. In this study, we present a new workflow for characterising the haemodynamic profile prior to and following surgical creation of a successful left radiocephalic AVF in a 20-year-old end-stage kidney disease patient. The reconstructed vasculature was generated using multiple ferumoxytol-enhanced magnetic resonance angiography (FeMRA) datasets. Computational fluid dynamics (CFD) simulations utilising a scale-resolving turbulence model were completed to investigate the changes in the proximal haemodynamics following AVF creation, in addition to the post-AVF juxta-anastomosis flow patterns, which is impractical to obtain in-vivo. Following AVF creation, a significant 2-3-fold increase in blood flow rate was induced downstream of the left subclavian artery. This was validated through comparison with post-AVF patient-specific phase-contrast data. Proximal to the anastomosis, the increased flow rate yielded an increase in time-averaged wall shear stress (WSS), which is a key marker of adaptive vascular remodelling. In the juxta-anastomosis region, the success of the AVF was discussed with respect to the National Kidney Foundation's vascular access guidelines, where the patient-specific AVF met the flow rate and geometry criterion. The AVF venous diameter exceeded 6mm and the venous flow rate surpassed 600mL/min. This workflow may potentially be significant clinically when applied to multi-patient cohorts, with population-wide patient-specific conclusions being ascertained for the haemodynamic assessment of AVFs and improved surgical planning.

Early Cannulation ePTFE Arteriovenous Access Grafts are Associated with a Low Incidence of Pseudoaneurysm Formation.

BACKGROUND: Pseudoaneurysm formation is common in standard thin-walled polytetrafluoroethylene (sPTFE) grafts, occurring in up to 10% of grafts, and is reported as the most common cause of graft loss for grafts more than 2 years old. The Gore® Acuseal™ graft is an early cannulation graft, needled before incorporation, and thus may be especially prone to pseudoaneurysm formation. In addition, as this is a relatively new product, there are limited data on long-term outcomes such as pseudoaneurysm. We report one center's experience of the incidence and etiological factors associated with pseudoaneurysm formation over 5 years and 265 grafts. METHODS: A total of 265 Acuseal grafts were placed in the last 5 years. All patients had prospective data entered into an electronic searchable patient record. Surveillance was performed with 3 monthly imaging (digital subtraction angiography or ultrasound), clinical examination, and hemodynamic performance. Data examined included the incidence, causative factors, and outcomes of pseudoaneurysm. RESULTS: Eleven grafts (4.15%) developed a pseudoaneurysm, with 2 patients developing significant hemorrhage. The median time to development of a pseudoaneurysm was 25 months interquartile range (IQR, 20-28 months). Several common etiological factors were identified. All but one patient had overuse of needling sites (n = 10; 90.9%). Other factors associated with pseudoaneurysm formation were inadequate surveillance (n = 9; 81.8%), venous outflow stenosis (n = 9; 81.8%), and anticoagulation/dual antiplatelet therapy (n = 7; 63.6%). Management included observation and needle rotation (n = 5; 45.5%), stent grafting (n = 3; 27.3%), or excision (n = 1; 9.1%) of the pseudoaneurysm. Surgical or endovascular augmentation of the venous outflow was required in 9 patients (81.8%). Graft ligation and explantation were required in 5 patients (45.5%) with graft preservation achieved in 6/11 patients (54.5%). CONCLUSIONS: Pseudoaneurysm formation occurs less frequently in Acuseal grafts compared with historical data for standard PTFE grafts. Pseudoaneurysm formation did not occur in any graft within the first 13 months after implantation, suggesting early cannulation before incorporation is not by itself a risk factor for pseudoaneurysm development. Poor needling, venous stenosis, inadequate surveillance, and anticoagulation/dual antiplatelet therapy are remediable factors, and graft preservation is possible. Acuseal is a robust graft with lower rates of pseudoaneurysm formation on long-term follow-up than standard PTFE grafts.