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

Dobutamine is used as an alternative to exercise in conjunction with 99m Tc-sestamibi SPECT perfusion imaging for detection of coronary artery disease. However, the use of quantitative dobutamine 99m Tc-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 99m Tc-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 99m Tc-sestamibi injection for SPECT imaging and post-mortem 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 175% ± 6% nonischemic) underestimated the relative flow deficit produced during dobutamine stress (p = 0.056). Myocardial 99m Tc-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), 99m Tc-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 99m Tc-sestamibi activity underestimated microsphere flow at higher flows induced by dobutamine, leading to underestimation of ischemia. These findings suggest that dobutamine stress 99m Tc-sestamibi scintigraphy may underestimate the relative flow deficit.