Redistribution of 99mTc-sestamibi and 201Tl in the presence of a severe coronary artery stenosis

• Published in: Circulation (New York, N.Y.) N.Y.), 1994-05, Vol.89 (5), p.2332-2341
• Main Authors: Sinusas, A J, Bergin, J D, Edwards, N C, Watson, D D, Ruiz, M, Makuch, R W, Smith, W H, Beller, G A
• Format: Article
• Language: English
• Subjects: Animals; Constriction, Pathologic - diagnostic imaging; Constriction, Pathologic - pathology; Coronary Circulation - physiology; Coronary Vessels - pathology; Dogs; Heart - diagnostic imaging; Image Processing, Computer-Assisted; Myocardial Ischemia - diagnostic imaging; Myocardial Ischemia - pathology; Myocardium - pathology; Radionuclide Imaging; Technetium Tc 99m Sestamibi; Thallium Radioisotopes; Time Factors
• ISSN: 0009-7322; 1524-4539
• DOI: 10.1161/01.CIR.89.5.2332

99mTc-labeled methoxyisobutyl isonitrile (99mTc-sestamibi) is a myocardial perfusion agent that clears slowly from the myocardium. This study evaluates the early and late myocardial distributions of 99mTc-sestamibi and 201Tl in the presence of low-flow ischemia to determine whether 99mTc-sestamibi demonstrates rest "redistribution." Low-flow ischemia was produced in 18 anesthetized, open-chest dogs by partial occlusion of the left anterior descending coronary artery. Dogs were injected intravenously with 99mTc-sestamibi, 301Tl, and radiolabeled microspheres during sustained low-flow ischemia. The hearts were excised either 20 minutes (group 1, 10 dogs) or 2.5 hours (group 2, 8 dogs) after injection for gamma well counting to evaluate the early and late myocardial distributions of these radiotracers, relative to microsphere flow. The early myocardial distributions of 99mTc-sestamibi and 201Tl were comparable and correlated with the flow deficit (group 1). We observed a significant difference in myocardial 201Tl (P = .005) and 99mTc-sestamibi (P < .0001) activities between groups 1 and 2 dogs relative to flow, suggesting some redistribution of both tracers. Myocardial slices were imaged postmortem with a gamma camera, and 99mTc-sestamibi defect intensity was quantified. There was excellent correlation (r = .97) between the early relative 99mTc-sestamibi defect intensity on postmortem images and the flow deficit (group 1). Among group 2 dogs, the correlation was good (r = .87), but the 99mTc-sestamibi defect was less severe than the flow deficit, again suggesting redistribution. The myocardial distributions of 99mTc-sestamibi and 201Tl early after injection are comparable and proportional to flow. Under conditions of sustained low flow, there was detectable rest "redistribution" of 99mTc-sestamibi verified by both gamma well counting and high-resolution postmortem imaging of myocardial slices. Whether this degree of 99mTc-sestamibi rest redistribution will be detectable by serial clinical imaging remains uncertain. Nevertheless, these data suggest that imaging should be delayed after the resting injection of 99mTc-sestamibi when assessing myocardial viability in the presence of a critical stenosis.