Comparison of phasic blood flow velocity characteristics of arterial and venous coronary artery bypass conduits

Background. Coronary artery bypass conduits derived from internal mammary arteries show relative resistance to atherosclerosis and significantly improved long-term patency compared with saphenous vein grafts. Atherothrombotic occlusion of venous conduits has previously been correlated with lower flow rates measured intraoperatively. To quantitate coronary bypass conduit flow velocity, we examined the phasic blood flow velocity patterns by intravascular Doppler spectral analysis in patients during cardiac catheterization to test the hypothesis that resting systolic and diastolic phasic blood flow velocity patterns differ significantly between arterial and venous bypass conduits. Methods and Results. Spectral phasic blood flow velocity was measured using an intravascular Doppler-tipped angioplasty guidewire in the proximal, mid, and distal segments of 18 internal mammary artery conduits and 11 saphenous vein grafts in 27 patients at a mean of 4 years (range, 1 to 11) postoperatively. In situ internal mammary artery conduits demonstrated a gradual longitudinal transition in the phasic flow pattern from predominantly systolic velocity proximally (diastolic/systolic peak velocity ratio, 0.6±0.2) to predominantly diastolic velocity distally (diastolic/systolic peak velocity ratio, 1.4±0.3; P<.001). Saphenous vein graft flow velocity pattern, however, showed a consistently diastolic predominance, both proximally and distally (diastolic/systolic peak ratios, 1.4±0.6 and 1.5±0.7, respectively; P=NS). Mean flow velocities, total velocity integral, and calculated maximal shear rates were significantly higher in all segments of internal mammary arteries compared with values in saphenous vein grafts. Conclusions. Patterns of resting phasic blood flow, as well as mean velocity and total velocity integral, differ significantly between internal mammary artery and saphenous vein bypass conduits. These differences may have implications regarding blood-vessel wall interactions, the development of degenerative graft disease, and long-term conduit patency.