VEIN ADAPTATION TO THE HEMODYNAMIC ENVIRONMENT OF INFRAINGUINAL GRAFTS

Purpose: Although arteries appear to remodel in response to changes in hemodynamic parameters such as shear stress, Little is known about fu nctioning human vein grafts. This study was designed to explore diamet er changes in human saphenous vein grafts after infrainguinal bypass. Methods: We used duplex ultrasonography to measure hemodynamic variabl es that might affect the diameter of 48 in situ saphenous vein grafts during the first year after infrainguinal arterial bypass. Volumetric flow rate, average velocity, peak systolic velocity, and vein diameter in the proximal and distal thirds of these grafts were each measured at 1 week and at 3, 6, and 12 months after operation, Veins were divid ed into three groups based on initial size (1 week after bypass) in th e below-knee segment: small, < 3.5 mm diameter; medium, 3.5 to 4 mm di ameter; and large, > 4 mm diameter. Results: Distal vein diameters at 1 week for small, medium, and large grafts were 2.9 +/- 0.1, 3.7 +/- 0 .1, and 4.3 +/- 0.1 mm, respectively (p < 0.001), but by 12 months the se diameters were 3.6 +/- 0.2, 3.8 +/- 0.2, and 3.9 +/- 0.2 mm, respec tively (p = 0.54). Large veins decreased in diameter, whereas small. v eins increased in diameter, as confirmed by linear regression of perce nt change in diameter versus initial vein graft diameter (r = -0.62, p < 0.001). Volumetric flow rate, peak systolic velocity, and shear str ess also tended to approach uniform values over time. Of the hemodynam ic variables studied, the best predictor of diameter change was shear stress (linear regression of percent change in diameter vs shear stres s, r = 0.67,p < 0.001). Veins with a diameter increase greater than 10 % over time had significantly higher initial shear stress than veins w ith a diameter decrease greater than 10% over time (28.6 +/- 3.8 vs 13 .1 +/- 1.8 dynes/cm(2), p < 0.01), whereas initial volumetric how rate s in these two groups were similar (135 +/- 23 vs 130 +/- 15 ml/min). Conclusions: Infrainguinal in situ vein graft diameter, volume how rat e, peak systolic velocity, and shear stress ah tend to stabilize at un iform values regardless of the initial vein graft diameter. Of the hem odynamic variables studied, shear stress is most strongly associated w ith the change in diameter over time. Thus human saphenous vein appear s to be capable of adapting to its hemodynamic environment after arter ial grafting by modulating diameter to normalize shear stress.