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Catalina Poiana1, Raluca Trifanescu1

1 Department of Endocrinology, „C.I.Parhon” Institute, „Carol Davila” University of Medicine and Pharmacy, Bucharest, Romania

The relationship between thyroid hormones and heart diseases was extensively studied1. Subclinical thyroid dysfunction is one of few reversible causes of atrial fibrillation and heart failure; it is very important to diagnose these conditions in order to improve patients’ outcome. The paper published by Gheorghe GS et al. provides important epidemiological data on prevalence of subclinical thyroid dysfunction in Romanian population,  with it’s specific iodine intake. The authors found a prevalence of subclinical hyperthyroidism of 3.44%, similar with that reported by Collet et al – 4.2%2. Prevalence of subclinical hypothyroidism was 2%, lower than 3.8% reported by Aghini-Lombardi et al. in a population with iodine deficiency3. This difference is due to the fact that the paper published by Gheorghe GS et al. consider only cases with TSH >6.5 mIU/L, and the Italian study consider cases with TSH >3.7 mIU/L. Subclinical hyperthyroidism was associated in the literature with a 2-3 fold increase risk of atrial fibrillation in elderly people4,5. In a meta-analysis on five prospective cohort studies (7901 euthyroid and 810 subclinical hyperthyroidism participants), the hazard ratio for incident atrial fibrillation was significantly higher in patients with subclinical hyperthyroidism than in euthyroid ones and in those with grade 2 subclinical
hyperthyroidism (TSH <0.1 mIU/L) than in those with  grade 1 subclinical hyperthyroidism (TSH 0.1-0.44 mIU/L)2. Gheorghe GS et al. found a tendency to a higher
heart rate in atrial fibrillation patients on maximum beta blockers dose in patients with subclinical hyperthyroidism as compared to euthyroid patients. In a recently published paper, subclinical hypothyroidism, but not subclinical hyperthyroidism or low-T3 syndrome, was proved to be an independent predictor of adverse cardiovascular outcomes in patients with acute decompensated heart failure6. In the paper of Gheorghe GS et al, there were no statistically significant differences in left atrial areas between euthyroid patients and patients with subclinical hyper and
hypothyroidism, respectively. In the literature, subclinical hypothyroidism was associated with increased left atrial pressure in AF patients7. A large proportion of patients included in the study
of Gheorghe GS had heart failure. Subclinical hyperthyroidism was associated in the literature with increased all-cause and cardiovascular mortality; the risk of major cardiovascular events was increased in subclinical hyperthyroidism, driven by heart failure8. The paper published by Gheorghe GS et al. has to be continued with larger cardiovascular trials on subclinical thyroid dysfunction in cardiac patients.
Conflict of interest: none declared.
References
1. Jabbar A, Pingitore A, Pearce SH, Zaman A, Iervasi G, Razvi S. Thyroid hormones and cardiovascular disease. Nat Rev Cardiol. 2016 Nov 4. doi: 10.1038/nrcardio.2016.174. [Epub ahead of print]
2. Collet TH, Gussekloo J, Bauer DC, den Elzen WP, Cappola AR, Balmer  P, Iervasi G, Åsvold BO, Sgarbi JA, Völzke H, Gencer B, Maciel RM, Molinaro S, Bremner A, Luben RN, Maisonneuve P, Cornuz J, Newman AB, Khaw KT, Westendorp RG, Franklyn JA, Vittinghoff E, Walsh JP, Rodondi N; Thyroid Studies Collaboration. Subclinical hyperthyroidism and the risk of coronary heart disease and mortality. Arch Intern Med. 2012 May 28;172(10):799-809. doi: 10.1001/  archinternmed.2012.402.
3. Aghini-Lombardi F, Antonangeli L, Martino E, Vitti P, Maccherini D, Leoli F, Rago T, Grasso L, Valeriano R, Balestrieri A, Pinchera A.The spectrum of thyroid disorders in an iodine-defi cient community: the Pescopagano survey. J Clin Endocrinol Metab. 1999 Feb;84(2):561-6.
4. Cappola AR, Fried LP, Arnold AM et al. Thyroid status, cardiovascular risk and mortality in older adults. JAMA. 2006;295:1033-1041.