Cardiac troponin I release correlates with myocardial infarction size

Cardiac troponin I, creatine kinase, and creatine kinase MB activity were tested in serial blood samples from 15 patients with first-time Q wave acute myocardial infarction (2 anterior and 13 inferior wall infarctions). All patients received intravenous thrombolytic therapy. Cardiac troponin I and creatine kinase MB activity were compared with scintigraphic estimates of myocardial scar (single photon emission computed tomography [SPECT] with 99m Technetium-isonitrile [Tc-sestamibi]) on late images at rest about 5 weeks after myocardial infarction. Scintigraphic defect sizes ranged from 3.2 to 41.2% (median : 27.3%) of left ventricle. Cardiac troponin I increased and peaked in parallel with creatine kinase MB activity, and the peak values correlated with each other (r = 0.76, p = 0.002). Troponin I stayed increased for several days longer than creatine kinase and creatine kinase MB activity. It could be detected at least until the 4th day after admission. Significant correlation coefficients were found between 99m Tc-isonitrile defect sizes and areas under cardiac troponin I curves (r = 0.53, p = 0.042) and between 99m Tc-isonitrile defect sizes and cumulative creatine kinase MB activity release (r = 0.64, p = 0.01). Animal studies have already shown a very close correlation between histologic infarct size and SPECT 99m Tc-isonitrile defect size. Therefore, our results indicate that cardiac troponin I release in patients with acute myocardial infarction is also correlated with infarct size.