Heterogeneity in the nonplanarity and arterial curvature of arteriovenous fistulas in vivo

Abstract

Objective: Native arteriovenous fistulas (AVFs) for hemodialysis are susceptible to nonmaturation. Adverse features of local blood flow have been implicated in the formation of perianastomotic neointimal hyperplasia that may underpin nonmaturation. Whereas computational fluid dynamic simulations of idealized models highlight the importance of geometry on fluid and vessel wall interactions, little is known in vivo about AVF geometry and its role in adverse clinical outcomes. This study set out to examine the three-dimensional geometry of native AVFs and the geometric correlates of AVF failure. Methods: As part of an observational study between 2013 and 2016, patients underwent creation of an upper limb AVF according to current surgical best practice. Phase-contrast magnetic resonance imaging was performed on the day of surgery to obtain luminal geometry along with ultrasound measurements of flow. Magnetic resonance imaging data sets were segmented and reconstructed for quantitative and qualitative analysis of local geometry. Clinical maturation was evaluated at 6 weeks. Results: There were 60 patients who were successfully imaged on the day of surgery. Radiocephalic (n = 17), brachiocephalic (n = 40), and brachiobasilic (n = 3) fistulas were included in the study. Centerlines extracted from segmented vessel lumen exhibited significant heterogeneity in arterial nonplanarity and curvature. Furthermore, these features are more marked in brachiocephalic than in radiocephalic fistulas. Across the cohort, the projected bifurcation angle was 73 ± 16 degrees (mean ± standard deviation). Geometry was preserved at 2 weeks in 20 patients who underwent repeated imaging. A greater degree of arterial nonplanarity (log odds ratio [logOR], 0.95 per 0.1/vessel diameter; 95% confidence interval [CI], 0.22-1.90; P =.03) and a larger bifurcation angle (logOR, 0.05 per degree; 95% CI, 0.01-0.09; P =.02) are associated with a greater rate of maturation, as is fistula location (upper vs lower arm; logOR, −1.9; 95% CI, −3.2 to 0.7; P =.002). Conclusions: There is significant heterogeneity in the three-dimensional geometry of AVFs, in particular, arterial nonplanarity and curvature. In this largest cohort of AVF geometry to date, the effect of individual geometric correlates on maturation is uncertain but supports the premise that future modeling studies will need to acknowledge the complex geometry of AVFs. Clinical Relevance: Arteriovenous fistulas (AVFs) created for hemodialysis are susceptible to nonmaturation. Vascular geometry influences local blood flow, which in turn is implicated in the development of neointimal hyperplasia, which is central to fistula failure. Whereas AVFs are often considered to be two-dimensional structures created from straight vessels, this work highlights the three-dimensional nature of AVFs in vivo. The study is, to date, the largest using cross-sectional imaging to explore both the geometry of AVFs and the conformation on the day of surgery. Recognition of the complex geometry will be informative to clinical studies addressing AVF nonmaturation.