Longitudinal Geometry of Pig Arteriovenous Fistula (AVF)
Background: Hemodynamics has been postulated to be an important factor contributing to successful versus failed AVF maturation. In general, the hemodynamic features of pigs are similar to those in humans making them an attractive animal model for investigating the mechanisms underlying AVF maturation. Previous small clinical studies found associations between AVF geometry and maturation. Since geometry is a critical determinant of hemodynamics, we investigated the geometry of pig AVFs using magnetic resonance imaging (MRI) technology. Methods: Carotid-jugular AVFs were created in domestic pigs. Black-blood MRIs were obtained at 1,2 and 6-10 weeks post-AVF creation (n=3 per time point) and used to reconstruct AVF lumen geometries. Lumen area, anastomosis angle, venous tortuosity, and nonplanarity angle were quantified. Results: The AVF vein lumen area significantly (p=0.0370) increased from 25.3 +/- 11.1 mm^2 in wk 1, to 32.3 +/- 4.3 mm^2 in wk 2, then to 62.7 +/- 21.3 mm^2 in wks 6-10 suggesting that our pig AVF is a model for successful AVF maturation. We also observed an increasing trend in the lumen areas from wk 1 to wks 6-10 of the proximal artery (24.0 +/- 17.3 mm^2 vs 28.0+/- 8.60 mm^2) and the distal artery (24.5 +/- 16.1 mm^2 vs 34.8 +/- 13.9 mm^2). Overall, the anastomosis angles decreased over time while venous tortuosity and the non-planarity angles increased over time. Conclusion: This is the first serial and detailed study of pig AVF geometric parameters. The anastomosis angles of our pig AVFs were in line with human radiocepahlic AVFs in the literature (~30-60°). Our study sets the stage for examining the role of geometry in alterations in hemodynamic forces and in AVF maturation processes.