Quantitation of absolute flow in coronary artery bypass grafts using digital subtraction angiography

Coronary angiography defines the location and size of obstructive lesions, but does not assess their physiological significance. To assess a new method to measure the blood-flow waveform, reversed saphenous vein grafts from the left subclavian artery to the left anterior descending coronary artery were placed in five mongrel dogs. Contrast material was injected selectively into the vein graft while obtaining fluoroscopic images from AP and 45 degrees LAO projections. Blood flow was measured under baseline, low-flow, and hyperemic conditions using an electromagnetic flow probe (EM). Seventeen radiographic determinations of mean blood flow (range 18-130 ml/min) were linearly correlated to simultaneous EM measurements (r = 0.91 and 0.88, respectively). Contrast material injections changed EM flow measurements by an average of 35%, which though large, is less than with other radiographic methods. The computed blood-flow waveforms had a time resolution of 1/30 sec and were in good agreement with EM waveforms measured simultaneously. Clinical application of this radiographic method for determining the blood-flow waveform may allow early prediction of coronary artery bypass graft closure.