Myocardial uptake of thallium 201 and technetium 99m-labeled sestamibi after ischemia and reperfusion: comparison by quantitative dual-tracer autoradiography in rabbits.

Abstract

Myocardial scintigraphy with 99mTc-labeled sestamibi (99mTc-sestamibi) or 201Tl is used to assess regional perfusion in acute coronary syndromes associated with metabolic or functional abnormalities, such as acute coronary thrombosis with reperfusion and ischemia at rest. However, the initial uptake of these agents may be affected by a recent ischemic insult because the myocardial retention of these tracers depends on cellular metabolism. Accordingly, 99mTc-sestamibi and 201Tl were injected simultaneously in rabbits after transient brief (10 to 15 minutes, group I) or prolonged (45 to 60 minutes, group II) coronary occlusion. Accumulated subendocardial and subepicardial 99mTc-sestamibi and corresponding 201Tl activity were determined from autoradiographs of 30 microns short-axis slices comounted with serial tissue standards. Circumferential 99mTc-sestamibi and 201Tl activity profiles closely overlapped in both groups. The initial global and segmental myocardial activity per unit blood flow within the ischemic zone did not differ from unity for either tracer regardless of the duration of the ischemic insult. The initial myocardial uptake of both 99mTc-sestamibi and 201Tl after an acute ischemic insult reflected predominantly coronary blood flow, independent of myocardial viability. Thus this study supports the use of both 99mTc-sestamibi and 201Tl as perfusion probes in acute coronary syndromes characterized by acute occlusion and reperfusion.