Early Fistula Failure: Back to Basics

Eccentric venous neointimal hyperplasia at the juxta-anastomotic site of an arteriovenous (AV) fistula may occur at regions of low or oscillating wall shear stress and lead to failed fistula maturation. These regions of altered wall shear stress typically occur at the “heel” of the AV anastomosis as well as at the arterial wall opposite the opening of the fistula. The thickened neointima is composed of a variety of cells, including myofibroblasts (MyoFb), vascular smooth muscle cells (VSMC), endothelial cells involved in neovascularization, and inflammatory cells (the latter two are not shown), as well as extracellular matrix. Denuded areas of endothelium may also be seen. Myofibroblasts, a principal component of the neointima, are specialized synthetic and contractile cells involved in wound healing. Ultrastructurally, these cells contain α-smooth muscle actin coupled to extracellular fibronectin by a fibronexus junction that helps to provide support for injured tissue while the tissue is remodeled and new matrix formed. Myofibroblasts may originate from several sources including differentiation and migration of adventitial fibroblasts (AFb), dedifferentiation and migration of VSMC within the media, transdifferentiation from endothelial cells or possibly infiltration from circulating bone marrow-derived fibrocytes (FC). Regulating myofibroblast formation, proliferation, and migration may be key for controlling the eccentric neointimal hyperplasia that leads to fistula failure.