Human left main coronary artery blood flow: noninvasive Doppler echocardiography with sample volume tracking.

We developed sample volume tracking units that controlled the pulsed ultrasonic Doppler sample volume location in relation with the anterior-posterior movement of the human left main coronary artery (LMCA). Combined with noninvasive Doppler echocardiographic mechanical sector scanners (DS), the trackers controlled the axial location of the sample volume by range gate control. The Doppler angle was minimized with the long axis of the imaged LMCA. Both stored waveform, memory-driven (MD) and real-time (RT) trackers were developed. These devices were used to measure blood velocity spectral waveforms and lumen diameters, which were used to calculate flow. Using the RT tracker, we compared DS measurements with known flows (0-1000 ml/min) in a moving 4 mm tygon tubing phantom (r = 0.92, SEE = 32 ml/min). Using the MD tracker, we compared the DS with simultaneous invasive flow measurements in 11 patients with angiographically normal coronaries and ventricular function during cardiac catheterization. Using the RT tracker, we compared the DS measurements with subsequent nonsimultaneous, invasive flow data in 8 similar patients. Invasively determined flows were calculated from angiographic diameters and blood velocities which were obtained with a Doppler velocimeter catheter. Regression coefficients (r) were: (Table: see text). V = maximum velocity, D = diameter, Q = mean flow, *p less than .05 Interoperator and intraoperator variabilities in vivo of DS measurements with RT tracking were 21% and 15%, respectively. We conclude that Doppler echocardiography with either MD or RT sample volume tracking may be of limited clinical usefulness in the noninvasive measurement of phasic left main coronary artery blood flow in unselected patients.