A novel duplex ultrasound-based classification of outflow stenosis in native arterio-venous fistulas for hemodialysis

Background: Stenoses of the outflow tract can compromise the function of arteriovenous fistulas (AVFs) used for haemodialysis. Limited data exists to differentiate stenosis types and understand their underlying causes. This study aims to develop a new classification system for AVF stenoses based on the morphology and location of the lesions as assessed by duplex ultrasound (DUS). Materials and methods: A multicenter, cross-sectional cohort study was conducted in four hospitals from October 2017 to February 2024. After exclusions, 1122 patients with dysfunctional AVFs were evaluated. The DUS variables studied were intimal-media thickness (IMT), venous valve calcifications (VVC), and stenosis location. The stenosis location was classified as follows: juxta/post anastomotic tract; middle tract; proximal tract; arm cephalic vein tract; cephalic arch; and arm basilic vein tract. Results: Intimal hyperplasia (corresponding to IMT ≥ 0.4 mm) was present in 718 AVFs (64%; 95% CI 0.61-0.67), with an average thickness of 0.72 ± 0.14 mm (95% CI 0.71-0.73); no intimal hyperplasia (corresponding to IMT < ≥≥0.4 mm) in 354 AVFs (32%; 95% CI 0.29-0.34), and valve calcification in 50 AVFs (4%; 95% CI 3-6). Stenoses were classified in 4 types: Type A, dominant IMT with thickness ≥ 0.6 mm; Type B, IMT 0.4 mm to 0.6 mm; Type C, IMT < 0.4 mm; and Type D, with calcifications of the venous valves. Most of the stenosis fell within Type A and C (79.5%). Type A stenosis was in 80% found in the juxta/post-anastomotic segments. The middle and proximal tract segments showed a similar distribution of all four types of stenosis. Type C and D stenosis were prevalent in the distal segments. Conclusion: DUS reveals distinct characteristics of AVF stenoses, suggesting different underlying causes. This classification system may facilitate the development of targeted interventions for preventing and treating AVF stenosis.