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Background The function of deiodinases – selenoproteins converting thyroid hormones may be disturbed by oxidative stress accompanying heart failure. Selenium (Se) may be used by glutathione peroxidase, leading to a lack of deiodinase and triiodothyronine (T3). The aim of the study was the evaluation of the prevalence and clinical significance of low T3 syndrome in heart failure and the assessment of the association of low fT3 and Se deficiency. Methods The study group consisted of 59 consecutive patients hospitalized due to decompensated HFrEF NYHA III or IV. Exclusion criteria were: thyroid dysfunction, severe systemic disease, treatment with amiodarone, steroids or propranolol. Group A included 9 patients with low free T3 (fT3) concentration below 3.1 pmol/L. Group B consisted of the remaining 50 patients with normal fT3 levels. Results The prevalence of low T3 syndrome was 15.3%. The prevalence of Se deficiency was 74.6%. We demonstrated correlations between fT3 and main clinical variables (i.e. NT-proBNP, LVEF, hsCRP), but we did not find correlation between fT3 and the Se level. Kaplan-Meier survival analysis showed lower survival probability in patients with low fT3 ( p < 0.001). Conclusions Low T3 syndrome is frequently found in patients with HFrEF and is associated with a poor outcome. We did not identify any significant correlation between Se and fT3 level.

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What's new?Nitric oxide synthase (NOS) produces a potent signaling molecule nitric oxide but arginase competes with NOS for the same substrate arginine reducing nitric oxide production. This study demonstrates that during the acute phase of myocardial infarction arginine metabolism is shifted towards arginase over NOS. An enhanced arginase activity in the acute setting is associated with the presence of the features of unstable coronary plaque responsible for acute coronary syndromes expressed as thin-cap fibroatheroma. In turn, a similar residual metabolic shift towards arginase in the chronic phase is correlated with a higher thickness of intima-media in the stable segments of infarct-related artery. The current study provides arguments that arginine metabolites and their derivatives might be considered as the new, non-invasive indicators useful for identification of patients who are more likely to have vulnerable plaque as well as for monitoring of the extent of chronic atherosclerotic lesions.