Assessment of Myocardial Viability With 99m Tc Sestamibi in Patients Undergoing Cardiac Transplantation

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Abstract
Background99mTc sestamibi and 201Tl are tracers that allow equivalent detection of myocardial infarction. However, because sestamibi does not undergo as much time-dependent redistribution as does 201Tl, it has been considered suboptimal for the detection of myocardial viability. Methods and Results Fifteen consecutive patients with ischemic cardiomyopathy who underwent orthotopic cardiac transplantation received an intravenous injection of 99mTc sestamibi at 1 to 6 hours before transplantation. Rotational tomography of the excised, intact, native hearts was performed to quantify the extent of myocardial hypoperfusion. The hearts were then sliced and reimaged on a gamma camera, followed by pathological quantification of the extent and severity of scarred and normal myocardium. Samples of normally and abnormally perfused myocardium underwent gamma well counting to determine tissue radioactivity and were examined under light microscopy for delineation of myocardial structure after trichrome staining. The mean extent of scintigraphic scar quantified through the use of rotational tomography was 45±14% of the left ventricle and correlated closely with pathological scar size (r=.89), despite a slight overestimation. Scintigraphic scar size determined with planar imaging of the individual myocardial slices also correlated closely with pathological scar size (r=.88). A good correlation existed between tissue 99mTc sestamibi activity determined through well counting and histological evidence of myocardial viability (r=.89). Most hypokinetic and 40% of akinetic/dyskinetic myocardial segments contained scintigraphically and histologically normal myocardium. Conclusions99mTc sestamibi scintigraphy can be used to accurately quantify the extent of myocardial scarring. Furthermore, the relative sestamibi activity in perfusion defects, measured several hours after administration, is a good indicator of myocardial viability determined with microscopy.

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