A Nitinol “U-Clip” versus Sutured Arteriovenous Anastomosis: Local Tissue Response and Intimal Hyperplasia Development in a Sheep Model

Abstract

This study sought to compare the local tissue response and subsequent volume of intimal hyperplasia (IH) that develops throughout the maturation of an arteriovenous fistula created using continuous/interrupted polypropylene with that of a novel, metal-alloy, penetrating anastomotic clip device. Forty-six fistulae were created in 23 sheep under a paired design using the nitinol U-Clip (n=23) in one hind limb and continuous (n=20) or interrupted (n=3) polypropylene suture for the other. Animals were killed at 4 (n=3), 14 (n=3), 28 (n=10), 42 (n=3), and 180 (n=4) days. Histological sections were evaluated for quantitative histology and immunohistochemistry. Compared with continuous polypropylene, U-Clip specimens demonstrated less intima-media area per unit length (IMA/L), proliferating cells, and tissue necrosis at all time points (MANOVA, F=9.8-24.1, all p≤.005; observed power >82%). Specifically, values of IMA/L were reduced by 5% (p=.97), 37% (p=.02), 33% (p<.01), 9% (p=.42), and 14% (p=.22) at the time points of 4, 14, 28, 42, and 180 days respectively. Proliferating cells were reduced by 75% (p<.01), 72% (p=.03), 76% (p=.03), 27% (p=.31), and 60% (p=.01) and tissue necrosis by 67% (p<.01), 58% (p=.02), 40% (p=.33), 21% (p=.43), 77% (p=.11). In a 28-day comparison between U-Clip and interrupted polypropylene the U-Clip group demonstrated a 4% (p=.65) reduction in IMA/L, 74% (p<.01) in proliferating cells and 49% (p<.05) in tissue necrosis. These results provide evidence of reduced local tissue necrosis, proliferating cells, and IH, favouring arteriovenous fistulae created using the U-Clip anastomotic device over conventional polypropylene suture techniques most evident over the first 4 weeks.