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

Department of Nuclear Medicine, Kanazawa University School of Medicine, Kanazawa; and Department of Cardiology, Fukui Prefectural Hospital, Fukui, Japan

The aim of the study was to investigate the increase in myocardial ^99mTc-methoxyisobutylisonitrile (sestamibi) retention in humans during pharmacologic vasodilation. Methods: For calculation of the increase in ^99mTc-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

where Cm_h(t) and Cm_b(t) are myocardial counts on the tomographic image, and Cb_b() and Cb_h() 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 - 0.068X² (r = 0.82). Conclusion: In humans, the increase in ^99mTc-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.

Key Words: ^99mTc-sestamibi • coronary flow reserve • myocardial tracer retention • pharmacologic hyperemia

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