Affiliation:
1. From the Experimental Cardiology Laboratory, Cardiovascular Division, Department of Medicine, University of Virginia, Charlottesville.
Abstract
Background
Clinical studies have shown a comparable coronary stenosis detection rate between
99m
Tc-tetrofosmin and
201
Tl but with smaller defect magnitudes for
99m
Tc-tetrofosmin. The goals of this study were to measure the first-pass extraction fraction (EF) of
99m
Tc-tetrofosmin in canine myocardium and to compare
99m
Tc-tetrofosmin with
201
Tl uptake during adenosine-induced vasodilatation in dogs with various degrees of coronary stenosis.
Methods and Results
EF was calculated in 4 anesthetized, open-chest dogs after intracoronary administration of
125
I-labeled albumin and
99m
Tc-tetrofosmin. In another 16 dogs with either critical (n=6) or mild (n=10) left anterior descending coronary artery (LAD) stenoses,
201
Tl and
99m
Tc-tetrofosmin were administered during adenosine infusion (250 μg · kg
−1
· 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
99m
Tc-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
201
Tl and 0.67±0.05 for
99m
Tc-tetrofosmin (
P
<.01). For the 10 mild-stenosis dogs, the LAD-to-LCx flow ratio was 0.44±0.05. The
201
Tl activity ratio was 0.58±0.04, compared with 0.81±0.04 for
99m
Tc-tetrofosmin (
P
<.01). Thus, in both groups,
99m
Tc-tetrofosmin uptake underestimated the flow disparity more than
201
Tl. Similarly, magnitudes of ex vivo image defects were significantly greater for
201
Tl than for
99m
Tc-tetrofosmin in both groups.
Conclusions
In this canine model, relative underperfusion with adenosine stress is better resolved with
201
Tl than with
99m
Tc-tetrofosmin and may be explained by the lower EF for
99m
Tc tetrofosmin. With clinical imaging, greater
201
Tl attenuation and redistribution may lessen this advantage.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Physiology (medical),Cardiology and Cardiovascular Medicine
Cited by
49 articles.
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