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The peak cardiac enzyme (troponin and creatine kinase [CK]) after ST-elevation myocardial infarction (STEMI) correlates strongly with infarct size. It has been reported that hypertrophied cardiomyocytes display an increased troponin concentration. Therefore, we hypothesized that the systemic release of troponin after STEMI will be disproportionally higher than that of CK in patients with a high left ventricular mass index (LVMI).
From January 2007 to August 2013, 480 patients with STEMI were retrospectively reviewed. Of the 480 patients, 203 patients were excluded (30 with history of myocardial infarction, 25 without CK elevation and 148 with missing values) and 277 patients were included in the final analysis. Troponin I and CK levels were measured every 6 hours. The peak troponin I to peak CK ratio (TCR) was calculated and TCR value higher than +1SD (n=35) was defined as high TCR and others were included in controls (n=242). LVMI was calculated according to the guideline from the American Society of Echocardiography. Clinical data, angiographic characteristics, left ventricular ejection fraction (LVEF) and LVMI were assessed for the association with high TCR.
Peak troponin I levels were 284.6±405.4 ng/mL in high TCR group and 94.9±110.5 ng/mL in controls (p=0.01), but there was no significant difference in peak CK value (2984±2571 U/L vs. 2896±2903 U/L, p=0.85). Patients with high TCR were significantly older (68±12 yrs vs. 58±11 yrs, p<0.001) and had higher LVMI (99.2±21.8 g/m2 vs. 89.4±20.2 g/m2, p=0.01), lower estimated glomerular filtration rate (69±23 ml/min/1.73m2 vs. 82±24 ml/min/1.73m2, p=0.003) and lower LVEF (41±16% vs. 48±14%, p=0.01). With multivariate analysis, high TCR was independently associated with an advanced age (odds ratio 1.06; 95% confidence interval, 1.03 to 1.10; p<0.001) and high LVMI (odds ratio 1.02; 95% confidence interval, 1.00 to 1.04; p=0.03), but not with estimated glomerular filtration rate (odds ratio 0.99; 95% confidence interval, 0.97 to 1.01; p=0.22) or LVEF (odds ratio 0.98; 95% confidence interval, 0.95 to 1.00; p=0.10).
A high TCR after STEMI was significantly associated with an advanced age and high LVMI. Therefore, the peak troponin level may overestimate infarct size compared to CK in this population.