A Novel Approach To Understanding Geometric Remodeling Of Surgically Created Arteriovenous Fistulas

Objectives: Failure of arteriovenous fistulas (AVF) for dialysis access remains a persistent problem. The reason for failure is largely unknown. Computational models of AVF have not been validated in parallel with animal experiments. We propose a computational AVF model that predicts venous geometric remodeling. We hypothesize that remodeling may precede AVF failure. Methods: First, we use a validated murine AVF model to define the parameters and boundary conditions for our computational model. Anesthetized mice undergo laparotomy and aortocaval puncture. Ultrasound confirms AVF patency, flow velocities, and vessel geometry throughout the aorta and inferior vena cava (IVC). In vivo CT angiography scans are segmented using 3D software (Simpleware ScanIP) to establish global geometry. We use this geometry to build a simplified geometric model which is then imported into a fluid dynamics simulation (Xflow) and finite element analysis software (Abaqus). Findings: Segmentations of in vivo CT scans establish the global geometry of the AVF (Fig 1a). A fluid dynamics model replicates flow through the fistula (Fig 1b). The model depicts the wall pressure being highest in the artery and around the fistula connection. A computational dynamics model predicts deformation and venous remodeling after pressurization of the system (Fig 1c). Conclusions: This is the first in vivo-computational model of AVF geometry. Our results indicate elevated wall pressure at the level of the fistula leads to venous deformation as hypothesized. These results can be used to predict how the underlying anastomotic geometry may impact anastomotic stress, stenosis, and injury, and may help define anatomic parameters that could optimize AVF durability. Future experiments involving models using the in vivo geometry itself, higher resolution micro CT images, and histologic staining of the vessel wall will provide insight into the deformation mechanisms around these observed areas of remodeling.