Dipyridamole Infusion in Normal Canine Myocardium and in Myocardium Distal to a Stenosis

to define myocardial and blood thallium-201 (Tl-201) kinetics after infusion of dipyridamole in normal canine myocardium and in myocardium distal to a coronary artery stenosis. Miniature radiation detector probes were implanted in the left ventricle in 39 openchest dogs. A balloon constrictor was placed around the proximal left circumflex coronary artery. Electromagnetic flow probes were positioned proximally around both the left circumflex and left anterior descending coronary arteries. In five control dogs (group 1) the balloon occluder was not inflated; in 12 dogs (group 2) a mild stenosis was created such that resting flow was not reduced, yet the hyperemic response after 10 s of total occlusion was partially attenuated; in nine dogs (group 3) a moderate stenosis was created such that resting flow was not reduced, yet the hyperemic response was completely eliminated; and in 13 dogs (group 4) a severe stenosis was created such that resting flow was reduced. After intravenous dipyridamole (0.08 mg/kg. min- ' X 4 min), 1.5 mCi TI-201 was injected intravenously and probe counts were collected continuously for 4 h. The mean 4-h fractional myocardial T1-201 clearance for nonstenotic zones was 0.35, 0.27 for group 2 stenotic zones, 0.19 for group 3 stenotic zones, and 0.05 for group 4 stenotic zones (P < 0.0001). After reaching peak activity, myocardial TI-201 activity cleared biexponentially with a final decay constant X2 = 0.0017±0.0001 min- ' (SE) for nonstenotic zones, 0.0011±0.0001 min- ' for group 2 stenotic zones, and 0.0006±0.0001 min- ' for group 3 stenotic zones (P < 0.01). Group 4 stenotic zone Tl-201 clearances were negligible (decay constant essen