Heart dysfunctions have been shown to be associated with altered concentrations of thyroid hormones. However, the relation between thyroid hormones and subclinical myocardial injury in those without clinically apparent coronary heart disease is not well-established. We examined the correlation between altered levels of thyrotropin, free thyroxine, and triiodothyronine (T3) and high-sensitivity cardiac troponin T (hs-cTnT) in 250 patients (mean age 60 years; 42% men) with chest pain, who were free of coronary heart disease and heart failure. These patients were examined in the emergency room or outpatient department of the cardiovascular center of Chosun University Hospital. Multivariate logistic regression models were used for statistical analysis. The baseline values of T3 were associated with elevated hs-cTnT levels (r = −0.428, p <0.001), a significantly negative correlation. We did not observe any significant correlation between the thyrotropin or free thyroxine and hs-cTnT levels. When the T3 cutoff was set at 74.6 ng/dl using the receiver operating characteristic curve, the sensitivity and specificity was 70% and 69%, respectively, for differentiating between groups with and without myocardial injury. After adjusting for traditional risk factors, the odds ratio for an elevated hs-cTnT level (≥0.014 ng/ml) for patients with T3 <74.6 ng/dl was 6.95 (95% confidence interval 3.09 to 15.66) compared to patients with T3 ≥74.6 ng/dl. In conclusion, the T3 levels were negatively related to hs-cTnT levels among patients without clinically obvious coronary heart disease.
Among the several biomarkers that permit noninvasive detection of subclinical myocardial injury, cardiac troponin-T has been shown to be related to coronary heart disease (CHD). Cardiac troponin-T is a biomarker recommended for the diagnosis of myocardial infarction and in the situation of an acute coronary syndrome. A new high-sensitivity cardiac troponin-T (hs-cTnT) test allows the recognition of hs-cTnT levels below clinical thresholds or the detection limits of conventional assays. With this new test, troponin levels less than the detection limit of the conventional cardiac troponin-T assay have recently been shown to predict cardiovascular events and mortality in patients with CHD, in those with heart failure, and in the general population. Some investigators have suggested that slightly, but significantly, increased levels of troponin might indicate subclinical cardiac damage, and the hs-cTnT assay can currently allow the detection of previously concealed early stages of myocardial injury. The aim of the present study was to determine the relation between thyroid hormone levels and subclinical myocardial injury in subjects without clinically apparent CHD using the hs-cTnT assay.
Methods
A total of 365 consecutive patients with chest pain, whose thyrotropin (TSH), free thyroxine (FT4), triiodothyronine (T3), and hs-cTnT levels had been measured in the emergency room or outpatient department of the cardiovascular center of Chosun University Hospital from November 2011 to January 2012 were included in the present study. The Chosun University Hospital research ethics committee approved the study (IRB-12E-281). Of these 365 patients, 250 were included in the present analysis, because patients who were diagnosed with CHD or overt hyperthyroidism were excluded.
Venous blood samples were collected in K2-ethylenediaminetetraacetic acid–coated tubes (BD Vacutainer Systems, Franklin Lakes, New Jersey) and serum separator blood-drawing tubes (BD Vacutainer Systems). Immunoradiometric assays and radioimmunoassays were conducted using RIA-gnost FT4, TSH, and T3 kits (CIS Bio International, Gif Sur Yvette, France) to determine the TSH, T3, and FT4 levels (normal range TSH 0.25 to 4 mIU/L, T3 60 to 190 ng/dl, and FT4 0.7 to 1.8 ng/dl), respectively, with the Packard Cobra E 5005 gamma counter (Global Medical Instrumentation Inc., Minnesota). The levels of hs-cTnT were measured using the cobas 6,000 (Roche Diagnostics, Penzberg, Germany) with a lower limit of detection of 0.003 ng/ml. All assays were done within 2 hours after sample collection.
The relation between the thyroid hormone levels and hs-cTnT was evaluated using Pearson’s correlation analysis. Receiver operating characteristic analysis was performed to determine the sensitivity and specificity, with 95% confidence intervals, for the thyroid hormone levels at the cutoff values. All values are expressed as the mean ± SD or numbers and percentages. The baseline characteristics of the groups were compared using the Student t test for continuous variables and the chi-square statistic for noncontinuous variables. In addition, multivariate logistic regression analysis of the factors associated with elevated hs-cTnT levels (≥0.014 ng/ml) was performed using a forward stepwise model, with independent variables possessing a p value of <0.1 on univariate analysis entered into the model. All statistical analyses were performed using SPSS, version 12.0 (SPSS, Chicago, Illinois), and p <0.05 was considered statistically significant.
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