THE VARIATION IN VEIN GRAFT FLOW VELOCITY WITH LUMINAL DIAMETER AND OUTFLOW LEVEL

Duplex scanning has recently been used to monitor the patency of infrainguinal vein grafts. Empirically derived criteria that have been used for identifying the failing graft have never accounted for the effect of vein graft diameter or varying outflow resistance, despite the fact that they are major determinants of flow. We prospectively examined thc variation in graft peak systolic flow velocity with graft diameter and outflow level in a consecutive series of 68 patients with 72 normally functioning vein grafts returning for routine follow-up. Images were obtained of vein grafts with a duplex scanner throughout their lengths, and the distal peak systolic flow velocity and intraluminal diameters were recorded. There were 15 popliteal, 26 tibial, and 21 inframalleolar grafts. The mean ankle-brachial index of inframalleolar grafts was 1.01 +/- 0.04 and did not differ significantly from tibial (0.96 +/- 0.03) or popliteal (0.93 +/- 0.06) grafts (p = 0.32). Grafts to the three outflow levels differed significantly in diameter, with inframalleolar grafts measuring 3.95 +/- 0.17 mm, tibial grafts 4.78 +/- 0.21 mm, and popliteal grafts 5.65 +/- 0.38 mm (p = 0.0001). In a similar manner inframalleolar grafts had significantly lower peak systolic flow velocities (59.1 +/- 3.4 cm/sec) than tibial (77.2 +/- 5.6 cm/sec) or popliteal (71.0 +/- 7.6 cm/sec) grafts (p = 0.04). Inframalleolar grafts did not demonstrate a significant correlation (r = -0.21,p +/- 0.29) between peak systolic flow velocity and graft diameter. Conversely, both tibial (r = -0.49, p = 0.005) and popliteal (r = -0.73, p = 0.002) grafts demonstrated significant inverse correlations. Furthermore, linear regression analysis revealed that popliteal and tibial grafts shared a similar and predictable inverse relationship between peak systolic flow velocity and graft diameter. We propose that consideration of peak systolic flow velocity independent of graft diameter is a suboptimal indicator of impending graft failure. Comparison of each peak systolic flow velocity with a diameter-specific range of acceptable values should improve the accuracy of duplex scan surveillance studies.