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


RESULTS
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.


CONCLUSIONS
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.
Sinusas
A J
AJ
Division of Cardiovascular Medicine, Yale University, School of Medicine, New Haven, Conn 06520-8042.
Bergin
J D
JD
Edwards
N C
NC
Watson
D D
DD
Ruiz
M
M
Makuch
R W
RW
Smith
W H
WH
Beller
G A
GA
D000818:Animals; D003251:Constriction, Pathologic / Q000000981:diagnostic imaging / Q000473:pathology; D003326:Coronary Circulation / Q000502:physiology; D003331:Coronary Vessels / Q000473:pathology; D004285:Dogs; D006321:Heart / Q000000981:diagnostic imaging*; D007091:Image Processing, Computer-Assisted; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000473:pathology; D009206:Myocardium / Q000473:pathology; D011877:Radionuclide Imaging; D017256:Technetium Tc 99m Sestamibi; D013794:Thallium Radioisotopes; D013997:Time Factors
D013794:Thallium Radioisotopes; D017256:Technetium Tc 99m Sestamibi