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Limitations of Dobutamine for Enhancing Flow Heterogeneity in the Presence of Single Coronary Stenosis: Implications for Technetium-99m-Sestamibi Imaging

Experimental Nuclear Cardiology Laboratory, Division of Cardiovascular Medicine, Departments of Internal Medicine and Diagnostic Radiology, Yale University, School of Medicine, New Haven, Connecticut

Correspondence: For correspondence or reprints contact: Albert J. Sinusas, MD, Experimental Nuclear Cardiology Laboratory, Yale University, School of Medicine, P.O. Box 208042, 333 Cedar Street, TE-2, New Haven, CT 06520-8042.

ABSTRACT

Dobutamine is used as an alternative to exercise in conjunction with ^99mTc-sestamibi SPECT perfusion imaging for detection of coronary artery disease. However, the use of quantitative dobutamine ^99mTc-sestamibi SPECT imaging for enhanced detection of coronary stenosis has not been established. The goal of this study is to examine the effects of dobutamine stress on regional myocardial blood flow and relative myocardial ^99mTc-sestamibi activity in the presence of a single-vessel stenosis. Methods: In six open-chest dogs with left circumflex artery stenosis, radiolabeled microspheres were injected during baseline, severe stenosis and peak dobutamine stress (10 µg/kg/min). Technetium-99m-sestamibi was injected intravenously at peak dobutamine. Hearts were excised 20 min after ^99mTc-sestamibi injection for SPECT imaging and postmortem gamma-well counting. Results: Dobutamine significantly increased heart rate, rate-pressure product and the first derivative of left ventricular pressure. Ischemic zone (left circumflex) myocardial blood flows (in ml/min/g)were: baseline, 0.92 ± 0.15; stenosis, 0.65 ± 0.16; and dobutamine, 1.19 ± 0.38. Nonischemic zone myocardial blood flows were: baseline, 0.99 ± 0.18; stenosis, 1.01 ± 0.12; and dobutamine, 1.94 ± 0.32 (p < 0.01 versus stenosis). Ischemic flows, expressed as percentages of nonischemic flows, were: baseline, 94% ± 2%; stenosis, 63% ± 11%(p < 0.05 versus baseline) and dobutamine, 60% ± 12% (p was not significant versus stenosis). Technetium-99m-sestamibi activity in the ischemic zone (75% ± 6% nonischemic) underestimated the relative flow deficit produced during dobutamine stress (p = 0.056). Myocardial ^99mTc-sestamibi activity correlated with flow when flow was less than 1.0 ml/min/g. At higher flow ranges (1.0 ml/min/g-3.5 ml/min/g), ^99mTc-sestamibi did not track flow. Conclusion: In a canine model of flow-limiting, single-vessel stenosis, dobutamine (10 µg/kg/min) did not augment flow heterogeneity. In addition, relative myocardial ^99mTc-sestamibi activity underestimated microsphere flow at higher flows induced by dobutamine, leading to underestimation of ischemia. These findings suggest that dobut amine stress ^99mTc-sestamibi scintigraphy may underestimate the relative flow deficit.

Key Words: dobutamine • technetium-99m-sestamibi scintigraphy • stress perfusion imaging • blood flow • coronary artery disease

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