title: Intrinsic washout rates of thallium-201 in normal and ischemic myocardium after dipyridamole-induced vasodilation.
abstract: 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)
mesh_terms: D000818:Animals; D003326:Coronary Circulation; D003327:Coronary Disease / Q000000981:diagnostic imaging*; D004176:Dipyridamole / Q000494:pharmacology; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging*; D011868:Radioisotopes / Q000378:metabolism; D011877:Radionuclide Imaging; D013793:Thallium / Q000378:metabolism; D014664:Vasodilation / Q000187:drug effects
chemical_list: D011868:Radioisotopes; D004176:Dipyridamole; D013793:Thallium