Tc-99m-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 Tc-99m-m ethoxyisobutylisonitrile (sestamibi) retention in humans during pharmacolog ic vasodilation. Methods: For calculation of the increase in Tc-99m-sestami bi retention during hyperemia, baseline and adenosine triphosphate (ATP)-in duced hyperemic stress sestamibi studies were performed using a same-day re st-stress protocol. On the injection of sestamibi, left ventricular dynamic data were obtained for 90 s. The increase in sestamibi retention from base line to hyperemia was calculated by the formula Cm-h(t) integral (t)(0) Cb-b(tau )d tau /Cm-b(t) integral (t)(0) Cb-b(tau ) d tau, where CMh(t) and CMb(t) are myocardial counts on the tomographic image, and Cb-b(tau) and Cb-h(tau) are the left ventricular blood-pool counts during the first transit of sestamibi at baseline and during hyperemia, respective ly. 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 inc reased as coronary flow velocity increased but plateaued at >2.5-3 times ba seline flow velocity. The relationship between the increase in sestamibi re tention (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 Tc-9 9m-sestamibi myocardial retention underestimates coronary flow reserve, par ticularly at high flow rates. Knowledge of these tracer retention character istics will contribute to a more comprehensive understanding of the manner and interpretation of stress sestamibi imaging.