Assessment of coronary artery bypass graft flow by intraoperative Doppler ultrasound technique

A high frequency (10 MHz) Doppler ultrasound pencil probe was used to estimate flow in coronary artery bypass grafts in vitro and during cardiac surgery. In vitro, increasing the angle of the Doppler transducer in relation to flow caused underestimation of the Doppler derived flow, and using the external rather than internal vessel diameter to calculate cross sectional area caused significant overestimation. This overestimation was considerably greater for the internal mammary artery. Accurate flow estimation was obtained in vitro by the Doppler technique, but considerable variation occurred in patients studied during coronary artery bypass surgery. In conclusion, intraoperative Doppler ultrasound provides a qualitative assessment of phasic flow in coronary artery bypass grafts but is less accurate in quantifying absolute flow in these patients.