Quantification of coronary artery bypass flow reserve in dogs using cine-computed tomography

Routine coronary angiographic assessment of bypass graft patency does not allow quantification of bypass graft flow reserve. This study was designed to evaluate the use of cine-computed tomography (cine-CT) to determine relative bypass graft flow velocities and flow reserve. Saphenous vein grafts from the left innominate to the midleft circumflex coronary artery were placed in 5 dogs. The proximal portion of the left circumflex was then ligated. A 20-mHz Doppler probe to assess graft flow velocity, a cuff-type vascular occluder to provide variable graft occlusion, and an infusion line for selective drug administration were placed at the midgraft position. Electrocardiographically triggered scans were performed at levels of the aortic root and cardiac base following bolus inferior vena cava contrast administration. Continuous recordings of Doppler velocity and aortic pressure and intermittent measurements of cardiac output were obtained throughout the studies. Selective increases and decreases in coronary artery bypass graft flow velocity from control were performed using combinations of intragraft adenosine and/or variable graft occlusion. Simultaneous contrast clearance curves were generated from a region of interest in the ascending aorta and in the coronary artery bypass graft. Subsequent determinations of a parameter, delta PT (the time difference between peak opacification in the aorta and the bypass graft), were found to highly correlate with individual values of relative coronary bypass graft flow velocity (r = 0.74-0.97, n = 54). This study suggests that cine-computed tomography can be used to noninvasively quantify relative bypass graft flow velocities in individual dogs and eventually in patients.