In situ bypass hemodynamics. The effect of residual A-V fistulae

The effect of arteriovenous fistulae on in situ saphenous vein bypass hemodynamics and patency rates has been of great concern to some. It is our practice to ligate only those fistulae which conduct enough dye upon completion angiography to visualize the deep femoral venous system. We have prospectively studied 216 such bypasses using duplex ultrasound scanning to assess overall hemodynamic function over periods from 1 to 156 months postoperatively. Volumetric blood flow was measured in proximal and distal portions of the bypass choosing a region of uniform diameter with laminar flow. Mean fistula flow was derived by subtracting distal bypass flow from proximal bypass flow. Distal flow decreased significantly (p less than 0.01 paired t-test) from 68 +/- 4.6 ml/min (mean +/- SEM) at 2 months postoperatively to 51 +/- 4.8 ml/min at 12 months postoperatively. There was an overall decrease in fistula flow from 256 +/- 26.9 ml/min at 2 months to 86 +/- 22.6 ml/min at 12 months. In 14 of the 216 bypasses (6.5%), arteriovenous fistulae were ligated during the first postoperative year. This was necessitated by persistent increased fistula flow with or without edema and indication from PVR or segmental pressure of decreased resting flow or pressure. Following fistula ligation, fistula flow decreased and distal bypass flow improved. Within this select group of patients with reduced flow capacity, i.e., a proximal stenosis or small vein size, high fistula flow is poorly tolerated with a significant redistribution of flow resulting in reduced distal perfusion. However, for the majority of patients (95%), fistula flow does not deleteriously affect distal bypass flow.