Myocardial 99mTc-tetrofosmin uptake during adenosine-induced vasodilatation with either a critical or mild coronary stenosis: comparison with 201Tl and regional myocardial blood flow.
BACKGROUND
Clinical studies have shown a comparable coronary stenosis detection rate between 99mTc-tetrofosmin and 201Tl but with smaller defect magnitudes for 99mTc-tetrofosmin. The goals of this study were to measure the first-pass extraction fraction (EF) of 99mTc-tetrofosmin in canine myocardium and to compare 99mTc-tetrofosmin with 201Tl uptake during adenosine-induced vasodilatation in dogs with various degrees of coronary stenosis.


RESULTS
EF was calculated in 4 anesthetized, open-chest dogs after intracoronary administration of 125I-labeled albumin and 99mTc-tetrofosmin. In another 16 dogs with either critical (n=6) or mild (n= 10) left anterior descending coronary artery (LAD) stenoses, 201Tl and 99mTc-tetrofosmin were administered during adenosine infusion (250 microg x kg(-1) x min(-1)). Dogs were killed 5 minutes later, and tracer activities were determined by ex vivo imaging of heart slices and by well counting. Mean 99mTc-tetrofosmin EF was 54.0+/-3.7%. In the 6 critical-stenosis dogs, the LAD-to-left circumflex artery (LCx) microsphere flow ratio was 0.22+/-0.02 with adenosine. The LAD-to-LCx activity ratios were 0.37+/-0.04 for 201Tl and 0.67+/-0.05 for 99mTc-tetrofosmin (P<.01). For the 10 mild-stenosis dogs, the LAD-to-LCx flow ratio was 0.44+/-0.05. The 201Tl activity ratio was 0.58+/-0.04, compared with 0.81+/-0.04 for 99mTc-tetrofosmin (P<.01). Thus, in both groups, 99mTc-tetrofosmin uptake underestimated the flow disparity more than 201Tl. Similarly, magnitudes of ex vivo image defects were significantly greater for 201Tl than for 99mTc-tetrofosmin in both groups.


CONCLUSIONS
In this canine model, relative underperfusion with adenosine stress is better resolved with 201Tl than with 99mTc-tetrofosmin and may be explained by the lower EF for 99mTc tetrofosmin. With clinical imaging, greater 201Tl attenuation and redistribution may lessen this advantage.
Glover
D K
DK
Department of Medicine, University of Virginia, Charlottesville 22908, USA. dglover@virginia.edu
Ruiz
M
M
Yang
J Y
JY
Smith
W H
WH
Watson
D D
DD
Beller
G A
GA
D000241:Adenosine / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport; D003326:Coronary Circulation / Q000187:drug effects / Q000502:physiology*; D003327:Coronary Disease / Q000000981:diagnostic imaging* / Q000503:physiopathology*; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging*; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism; D009943:Organophosphorus Compounds / Q000493:pharmacokinetics*; D015609:Organotechnetium Compounds / Q000493:pharmacokinetics*; D011877:Radionuclide Imaging; D012016:Reference Values; D012039:Regional Blood Flow; D013794:Thallium Radioisotopes / Q000493:pharmacokinetics*; D014018:Tissue Distribution; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D009943:Organophosphorus Compounds; D015609:Organotechnetium Compounds; D013794:Thallium Radioisotopes; C078700:technetium tc-99m tetrofosmin; D000241:Adenosine