Assessment of perfused left ventricular mass in normal, ischemic, and reperfused myocardium by means of single-photon emission computed tomography of technetium-99m isonitrile.

To test the hypothesis that single-photon emission tomography of technetium (Tc) 99m hexakis 2-methoxyisobutyl isonitrile (Tc-MIBI) can accurately measure perfused left ventricular (LV) mass in nonischemic, ischemic, and reperfused myocardium, we acquired Tc-MIBI tomographic images in canines with normally perfused hearts (n = 33) after occlusion of the left anterior descending coronary artery (n = 15), after reperfusion (n = 13), and with subsequent second injection of Tc-MIBI (15 to 18 mCi; n = 12). In all ischemic studies the initial dose of Tc-MIBI (5 to 6 mCi) was injected after coronary artery occlusion but before reflow. Scintigraphic perfused LV mass was calculated from the total voxels demonstrating Tc-MIBI uptake x voxel volume (cm3) x specific gravity of myocardium (1.05 gm/cm3). After being imaged the animals were killed, the left ventricle was weighed, and the risk area was determined by dual perfusion with phthalocyanine blue dye and triphenyltetrazolium chloride (TTC). Perfused LV mass was defined as total LV mass minus the risk area mass. There was good correlation between scintigraphic and morphologic determinations of perfused left ventricular mass in nonischemic hearts (Tc-MIBI left ventricular distribution = 0.84 x left ventricular weight + .20.4, n = 33, r = 0.93, p = 0.0001) and ischemic hearts (Tc-MIBI left ventricular distribution = 0.51 x left ventricular weight + 37.9, n = 15, r = 0.83, p = 0.0001). In animals imaged both before and after reperfusion, scintigraphic determinations of the nonischemic region correlated closely (after-reflow Tc-MIBI distribution = 1.07 x before-reflow Tc-MIBI distribution--8.0, n = 13, r = 0.88, p = 0.0001), indicating that Tc-MIBI does not significantly redistribute into the ischemic zone after reperfusion. After injection of the second dose of Tc-MIBI in acutely reperfused canines, there was good correlation between the distribution mass of Tc-MIBI and the mass of viable myocardium by TTC staining (Tc-MIBI distribution = 0.61 x viable LV mass + 34.2, n = 12, r = 0.77, p = 0.0001). Furthermore, the apparent redistribution of myocardial Tc-MIBI from before and after second injection images correlated with the degree of myocardial salvage by histochemical staining (r = 0.72, p = 0.0082). In conclusion, single-photon emission computed tomography of Tc-MIBI can measure perfused LV mass accurately in both ischemic and nonischemic canine preparations.(ABSTRACT TRUNCATED AT 400 WORDS)