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Circulation, Vol 71, 378-386, Copyright © 1985 by American Heart Association

ARTICLES

Intrinsic washout rates of thallium-201 in normal and ischemic myocardium after dipyridamole-induced vasodilation

GA Beller, HH Holzgrefe and DD Watson

Infusion of dipyridamole has been suggested as an alternative to exercise stress for myocardial perfusion imaging for detection of ischemia, but the mechanism and significance of thallium-201 (201Tl) redistribution after administration of dipyridamole are uncertain. If disparate intrinsic cellular efflux rates of 201Tl from normal and relatively underperfused myocardium in response to dipyridamole-induced vasodilation were observed, this could explain delayed 201Tl redistribution. We investigated eht effect of an intravenous infusion of 0.15 mg/kg dipyridamole on the intrinsic myocardial washout rate of 201Tl as measured with a gamma-detector probe after intracoronary injection (50 muCi) of the radionuclide in open-chested anesthetized dogs. In six normal dogs the t 1/2 for intrinsic 201Tl washout from the myocardium was 89 +/- 11 min (SE) at control conditions and became more rapid at 59 +/- 10 min (p = .0001) after dipyridamole. This corresponded to a significant increase in microsphere-determined epicardial (0.95 +/- 0.11 to 2.23 +/- 0.46 ml/min/g; p = .01) and endocardial (0.86 +/- 0.10 to 1.53 +/- 0.27; p = .029) flows. In 12 dogs with a critical coronary stenosis, the 201Tl intrinsic washout rate slowed from 70 +/- 5 to 104 +/- 6 min (p = .0001) after production of the stenosis and slowed even further to 169 +/- 21 min (p = .003) after dipyridamole.(ABSTRACT TRUNCATED AT 250 WORDS)

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