[Infarct size in patients with acute myocardial infarction estimated by emission computed tomography with technetium-99m pyrophosphate: relation to creatine phosphokinase release].

To evaluate the usefulness of single photon emission computed tomography (SPECT) with technetium-99m-pyrophosphate (99mTc-PYP) for estimating infarct size, we compared SPECT data with maximum creatine phosphokinase values. Background threshold was established in a series of phantom experiments. When a 40% cut-off was applied, the SPECT data most closely approximated actual phantom volumes. Therefore, the 40% cut-off level was used in the present study. In 10 patients with acute myocardial infarction, planar 99mTc-PYP myocardial scintigraphy and SPECT using a rotating gamma camera were performed two days after the initial myocardial infarction episode. The maximum creatine phosphokinase value (CPKmax) was also measured repeatedly following the episode. When the infarct size measured by SPECT using transaxial images and calculated by the pixel counts, it correlated very closely with CPKmax (r = 0.94). Most studies so far have reported that the CPKmax level reflects infarct size. We conclude that the infarct size as measured by 99mTc-PYP SPECT closely approximates the actual infarct size, and that this method is useful to determine the severity of infarcts clinically. Among the 10 patients in this series, three of five with infarcts greater than 60 ml died of pump failure. Therefore, we may be able to predict prognosis after accumulating more such cases and improving the methodology.