Effects of Dobutamine Stress on Myocardial Blood Flow, ^99m Tc Sestamibi Uptake, and Systolic Wall Thickening in the Presence of Coronary Artery Stenoses

Abstract

Background Although dobutamine stress is used with both 99m Tc sestamibi (sestamibi) myocardial perfusion imaging and echocardiography for detecting coronary artery stenoses, the impact of stenosis severity on test end points (myocardial sestamibi uptake and systolic thickening, respectively) has not been clearly defined. Methods and Results In 15 open-chest dogs, dobutamine (2.5 to 30 μg · kg −1 · min −1 ) was infused after placement of an LAD stenosis that reduced (n=8) or abolished (n=7) flow reserve. In dogs with reduced flow reserve, the stenotic-to-normal sestamibi activity ratio (0.86±0.03) significantly underestimated the ≈2-to-1 dobutamine-induced flow disparity at the time of sestamibi injection (flow ratio, 0.53±0.04; P <.001). Stenotic-zone thickening increased at low but not at higher doses of dobutamine (2.9±0.4 versus 4.2±0.4 mm in normal zone at peak dobutamine; P =.055) but did not fall below baseline (2.7±0.3 mm). Similarly, in dogs with absent flow reserve, the sestamibi activity ratio (0.78±0.02) underestimated the ≈2.5-to-1 dobutamine-induced flow disparity (flow ratio, 0.41±0.05; P <.001), and failure to increase systolic thickening was observed in the stenotic zone (2.7±0.4 versus 4.6±0.3 mm in the normal zone at peak stress, P <.01). In both groups of dogs, myocardial sestamibi uptake and image defect magnitudes were less than expected for the dobutamine-induced hyperemia, suggesting that dobutamine adversely affects myocardial sestamibi binding. Finally, a significant reduction in stenotic-zone thickening was seen during postdobutamine recovery, consistent with myocardial stunning. Conclusions In the presence of stenoses that reduced or abolished regional flow reserve, (1) myocardial sestamibi uptake significantly underestimated the dobutamine-induced flow heterogeneity, (2) a “failure to increase systolic thickening” rather than a reduction in thickening was observed during dobutamine stress, and (3) myocardial stunning was observed during postdobutamine recovery.