[Estimation of infarct size with 201Tl by multiprojection analysis].

Since mortality resulting from cardiac arrhythmia has been decreased by an introduction of CCU, power failure has become the major cause of death in patients with acute myocardial infarction. The power failure is assumed to be related to an infarct size. Therefore, noninvasive quantification of the infarct size is required for proper assessment of prognosis and treatment. Recently, a scintigraphic technique using radionuclide thallium-201 has developed, which is accumulated not in myocardial necrosis but in the intact myocardium. In this study, we tested two different parameters expressing the infarct size based on 5-projection myocardial scintigrams. One parameter is the ratio of the defect area to the total myocardium (% area), and the other is the ratio of a count decrease by the defect to total counts (% loss counts) in the planar image. Each parameter was obtained from uni- and multi-projection analysis. Six items were selected in the study including % area of 1-projection analysis, % area of 3-projection analysis, % area of 5-projection analysis, % loss counts of 1-projection analysis, % loss counts of 3-projection analysis, and % loss counts of 5-projection analysis. In 56 patients with the first attack of acute myocardial infarction, these parameters showed a clinically acceptable correlation with ejection fractions obtained by contrast ventriculography performed about 4 weeks later, with pulmonary end-diastolic pressure shortly after the onset, and with peak-CPK and sigma CPK obtained by 4 or 6 hourly measurements. Correlation coefficients between two parameters among 6 items showed no difference from each other. Scintigraphy was performed more than twice in 11 patients and the infarct size of these patients was decreased with the clinical course. Validity for estimates of the infarct size obtained with two parameters (% loss counts and % area) in different projection analysis was examined by a phantom model experiment and the clinical implications were discussed. In conclusion, an infarct size estimated by 201Tl scintigraphy provides useful informations about the size of necrosis and cardiac function in patients with acute myocardial infarction.