Analysis of flow characteristics in poststenotic regions of the human coronary artery during bypass graft surgery.

Poststenotic blood flow velocities were evaluated in nine patients with 75% to 99% stenosis of the left anterior descending coronary artery (LAD) during coronary artery bypass graft surgery. We used the 20 MHz 80-channel pulsed Doppler velocimeter developed in our laboratory. An operator placed a specially designed probe on the native LAD with his fingers. Before induction of extracorporeal circulation, LAD blood velocities were measured at several locations distal to the stenosis. The poststenotic flow velocities were rich in systolic flow component with reduced diastolic component. The velocity configuration in the poststenotic portions was characterized by the presence of reverse flow velocities and/or irregularity of the velocity pattern near the vessel wall, indicating the existence of flow separation and recirculation in the regions. The broadening of the velocity spectrum observed at central axial regions suggested the occurrence of flow disturbances. After grafting, the velocity waveform in the LAD beyond a vein bypass graft changed to a diastolic-predominant pattern with a relatively small systolic component. A transient bypass graft occlusion caused a marked reduction in diastolic flow velocity. The systolic-to-diastolic velocity ratio increased from 0.27 +/- 0.07 to 1.50 +/- 0.50 (p less than .01) by the graft occlusion.