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(Circulation. 1999;100:1653-1659.)
© 1999 American Heart Association, Inc.

Basic Science Reports

Myocardial Uptake of ^99mTc-N-NOET and ²⁰¹Tl During Dobutamine Infusion

Comparison With Adenosine Stress

Dennis A. Calnon, MD; Mirta Ruiz, MD; Gérald Vanzetto, MD, PhD; Denny D. Watson, PhD; George A. Beller, MD; David K. Glover, ME

From the Experimental Cardiology Laboratory, Cardiovascular Division, Department of Medicine, University of Virginia Health Sciences Center, Charlottesville. Dr Calnon is now at MidOhio Cardiology Consultants, Columbus, Ohio.

Background—The myocardial uptake of ^99mTc-sestamibi is attenuated by dobutamine stress, resulting in underestimation of ischemia. N-Ethyl-N-ethoxy-dithiocarbamato-N-^99mTc (^99mTc-N-NOET) is a new ^99mTc-labeled perfusion agent that is highly extracted by the myocardium by a mechanism different from that defined for ^99mTc-sestamibi. We therefore hypothesized that ^99mTc-N-NOET uptake would not be attenuated by dobutamine and that ^99mTc-N-NOET uptake would be comparable to ²⁰¹Tl uptake during dobutamine stress.

Methods and Results—In 28 open-chest dogs, after placement of a stenosis in the left anterior descending coronary artery that reduced flow reserve by >50%, adenosine (300 µg · kg^-1 · min^-1; n=15) or dobutamine (2.5 to 30 µg · kg^-1 · min^-1; n=13) was infused. During adenosine stress, the stenotic-to-normal activity ratio for ^99mTc-N-NOET was 0.55±0.05. The stenotic-to-normal flow ratio was 0.33±0.04 at the time of ^99mTc-N-NOET injection. During dobutamine stress, the stenotic-to-normal ^99mTc-N-NOET activity ratio was 0.63±0.04, comparable to the ²⁰¹Tl activity ratio of 0.59±0.04. The stenotic-to-normal flow ratio was 0.47±0.04 at the time of ^99mTc-N-NOET and ²⁰¹Tl injection. The relationship between ^99mTc-N-NOET uptake and blood flow was comparable for adenosine and dobutamine stress, with no evidence of attenuation of ^99mTc-N-NOET extraction by dobutamine.

Conclusions—In the presence of coronary stenoses that reduced regional flow reserve, the myocardial uptake of ^99mTc-N-NOET and ²⁰¹Tl are closely proportional to blood flow during both adenosine and dobutamine stress, suggesting that the adverse effect of dobutamine on ^99mTc-sestamibi uptake is a tracer-specific phenomenon rather than a generalized effect. The clinical implication of this finding is that ^99mTc-N-NOET might be preferable to ^99mTc-sestamibi when used with dobutamine stress for detection of coronary stenoses.

Key Words: imaging • radioisotopes • inotropic agents • adenosine

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