Quantification of myocardial infarction: A comparison of single photon-emission computed tomography with pyrophosphate to serial plasma MB-creatine kinase measurements

Single photon-emission computed tomography (SPECT) with ^99mTc-pyrophosphate (PPi) has been shown to estimate size of myocardial infarction accurately in animals. We tested the hypothesis that SPECT with ^99mTc-PPi and blood pool subtraction can provide prompt and accurate estimates of size of myocardial infarction in patients. SPECT estimates are potentially available early after the onset of infarction and should correlate with estimates of infarct size calculated from serial measurements of plasma MB-creatine kinase (CK) activity. Thirty-three patients with acute myocardial infarction and 16 control patients without acute myocardial infarction were studied. Eleven of the patients had transmural anterior myocardial infarction, 16 had transmural inferior myocardial infarction, and six had nontransmural myocardial infarction. SPECT was performed with a commercially available rotating gamma camera. Identical projection images of the distribution of ^99mTc-PPi and the ungated cardiac blood pool were acquired sequentially over 180 degrees. Reconstructed sections were color coded and superimposed for purposes of localization of infarct. Areas of increased PPi uptake within myocardial infarcts were thresholded at 65% of peak activity. The blood pool was thresholded at 50% and subtracted to determine the endocardial border for the left ventricle. Myocardial infarcts ranged in size from 1 to 126 gram equivalents (geq) MB-CK. The correlation of MB-CK estimates of size of infarct with size determined by SPECT (both in geq) was good (r = .89 with a regression line of y = 13.1 + 1.5x). Close correlations were found between values in patients with anterior transmural infarction (r = .93), those with inferior transmural infarction (r = .85), and those with nontransmural myocardial infarction (r = .91). We conclude that the estimation of size of infarction with SPECT and ^99mTc-PPi in patients is accurate and that the results correlate well with MB-CK estimates of size of infarction.