Comparison of Blood-Flow Velocity Waveforms

Characteristics of blood-flow velocities were investigated at different sites in two types of coronary artery bypass grafts, sequential saphenous vein grafts (SSVG) and internal mammary artery grafts (IMAG). The latter appear to have the longest life span. The patency rate of the side-to-side anastomosis of the SSVG is better than that of the end-to-side anastomosis. The SSVG was anastomosed to the major diagonal branch by side-to-side anastomosis and to the left anterior descending coronary artery (LAD) by end-to-side anastomosis in 13 patients who had 75-100% and 75-90% stenoses in the LAD and major diagonal branch, respectively. IMAG anastomoses were performed to the LAD in 10 patients with 75-100% stenoses of the artery. The blood-flow velocities were measured by the 20-MHz, eighty-channel ultrasound pulsed Doppler method during surgery. In six patients in the SSVG group, we investigated the configuration of velocity profiles at the region just proximal to the side-to-side anastomosis and at the bridge portion between the side-to-side and end-to-side anastomosis. In the other seven patients, we measured the blood-flow velocity at several centimeters proximal to the side-to-side anastomosis and compared it with that in the IMAG. At the region just proximal to the side-to-side anastomosis, the velocity profile skewed toward the anastomosis side wall in all patients, and the flow velocity near the wall opposite to the side-to-side anastomosis was reversed in five of six patients. In the bridge portion, directional changes in skewing of the velocity profile were recognized, that is, a skewed pattern toward the wall opposite to the anastomosis (four patients) or a symmetric pattern (two patients). The peak diastolic velocity in the region was 25.4 + 5.8 cm/sec, significantly lower than that (46.6 ± 12.3 cm/sec) just proximal to the side-to-side anastomosis. The velocity profile across the IMAG several centimeters proximal to the graft-coronary anastomosis showed a parabolic configuration with a narrow spectrum. The velocity profile in eight of 10 patients was statistically parabolic. In the SSVG, however, only two of seven patients were parabolic at the region several centimeters proximal to the side-to-side anastomosis. The peak diastolic velocity in the IMAG (26.6 + 2.0 cm/sec) was almost the same as that in the SSVG (26.3 ± 5.5 cm/sec), but the estimated graft diameter of the IMAG (2.3 ± 0.2 mm) was significantly smaller than that of the SSVG (3.4 ± 0.5 mm), indicating a relatively high shear rate in the IMAG. These findings may provide insight into the underlying mechanisms of graft viability because the patterns of blood flow seem to be a contributory factor in determining the fate of the graft. (Circulation 1988;78:1210-1217)