Quantification of infarct size by ²⁰¹Tl single-photon emission computed tomography during acute myocardial infarction in humans: Comparison with enzymatic estimates

We prospectively investigated whether ²⁰¹Tl single-photon emission computed tomography (SPECT) could accurately diagnose the presence and quantify the extent of acute myocardial infarction when compared with infarct size assessed by plasma MB-creatine kinase activity. Thirty patients with enzymatic evidence of infarction were imaged within 12-36 hours of chest pain (mean, 23.4 hours). No patient had a previous infarction, and none underwent intervention seeking to restore coronary patency. Infarct size was quantified with computer-generated polar maps of the myocardial radioactivity and expressed as a percentage of the total left ventricular volume. To assess left and right ventricular performance, blood-pool gated radionuclide angiography was performed immediately after SPECT. All 30 patients had perfusion defects consistent with myocardial infarction. Scintigraphic and enzymatic estimates of infarct size correlated well for the group as a whole (r = 0.78, p < 0.001, SEE = 91) but especially for those patients with anterior infarction (r = 0.91, p < 0.001, SEE = 7.9). The poor correlation observed in patients with inferior infarction (r = 0.50, p < 0.05, SEE = 10.0) was believed to be related to the frequent occurrence of right ventricular involvement because SPECT assessed only left ventricular damage, whereas the enzymatic method estimated the myocardial injury in both ventricles. A quantitative index of right ventricular infarct size, derived from the relation between the scintigraphic and enzymatic estimates, had a strong inverse correlation with right ventricular ejection fraction (r = -0.89, p < 0.001, SEE = 3.6). Therefore, ²⁰¹Tl SPECT is highly sensitive for detecting the myocardial perfusion deficit during acute infarction in humans and can accurately quantify left ventricular infarct size. The comparison of infarct size by SPECT to the enzymatic estimate may provide a means to assess the extent of right ventricular involvement in patients with inferior infarction.