Myocardial 99m Tc-Tetrofosmin Uptake During Adenosine-Induced Vasodilatation With Either a Critical or Mild Coronary Stenosis

Author:

Glover David K.1,Ruiz Mirta1,Yang Joo Y.1,Smith William H.1,Watson Denny D.1,Beller George A.1

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

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