99mTc-Sestamibi Retention Characteristics During Pharmacologic Hyperemia in Human Myocardium: Comparison with Coronary Flow Reserve Measured by Doppler Flowire

The aim of the study was to investigate the increase in myocardial 99m Tc-methoxyisobutylisonitrile (sestamibi) retention in humans during pharmacologic vasodilation. Methods: For calculation of the increase in 99m Tc-sestamibi retention during hyperemia, baseline and adenosine triphosphate (ATP)-induced hyperemic stress sestamibi studies were performed using a same-day rest-stress protocol. On the injection of sestamibi, left ventricular dynamic data were obtained for 90 s. The increase in sestamibi retention from baseline to hyperemia was calculated by the formula Cm b (t) ∫ 0 1 Cb b (τ)dτ/Cm b (t) ∫ 0 1 Cb b (τ)dτ, where Cm h (t) and Cm b (t) are myocardial counts on the tomographic image, and Cb b (T) and Cb h (T) are the left ventricular blood-pool counts during the first transit of sestamibi at baseline and during hyperemia, respectively. Coronary flow increase during intravenous ATP stress was measured using intracoronary Doppler flow guide wire and compared with the scintigraphic results of 28 measurements in 22 patients. Results: Sestamibi retention increased as coronary flow velocity increased but plateaued at >2.5-3 times baseline flow velocity. The relationship between the increase in sestamibi retention (Y) and the increase in flow (X) is expressed as follows: Y = 0.44 + 0.60X - 0.068X 2 (r = 0.82). Conclusion: In humans, the increase in 99m Tc-sestamibi myocardial retention underestimates coronary flow reserve, particularly at high flow rates. Knowledge of these tracer retention characteristics will contribute to a more comprehensive understanding of the manner and interpretation of stress sestamibi imaging.