Levels of troponin release can aid in the early exclusion of stress-induced (takotsubo) cardiomyopathy

Background: Stress-induced cardiomyopathy is usually associated with an increased level of cardiac enzymes, leading to difficulties in differentiating this condition from acute coronary syndrome. The final diagnosis is usually made based on angiographic findings revealing normal coronary arteries. It was hypothesized that maximal cardiac enzyme elevation in these patients should have an upper limit. In the present study, reported cases of stress cardiomyopathy were compared with documented cardiac enzyme levels to evaluate the upper cut-off point of troponin in this population. Method: All of the articles published in PubMed and MEDLINE from November 2007 to July 2008, on takotsubo or stress-induced cardiomyopathy, were identified. Only the cases that reported the absolute or mean level of cardiac enzymes were included. The level of various enzymes were correlated with cardiac function, and the upper limit of enzyme elevation was calculated in these patients. Results: A total of 114 patients (mean [± SD] age 63.5±14-5 years) were included in the study. Seventy-one per cent of the patients were older than 50 years of age and 86% were female. Mean values for troponin I, troponin T, creatine kinase (CK) and CK-MB were 6.5 ng/mL, 3.6 ng/mL, 556 U/L and 32.9 U/L, respectively. All of the patients with takotsubo cardiomyopathy had a troponin T level of 6 ng/mL or less and troponin I level of 15 ng/mL or less. Troponin T showed a significant inverse correlation with initial ejection fraction (R²=0.6), which was not seen with the levels of troponin I, CK and CK-MB. Takotsubo cardiomyopathy was classified as classic (66.7%), mid-cavitary (10%), reverse (23.3%) or local (0%). Conclusion: Among patients with takotsubo cardiomyopathy, troponin T level correlated with initial ejection fraction. Furthermore, the diagnosis of takotsubo cardiomyopathy appears to be unlikely in patients with troponin T greater than 6 ng/mL or troponin I greater than 15 ng/ mL.