ABC | Volume 112, Nº6, June 2019

764 Original Article Rajão et al Subclinical thyroid dysfunction and arrhythmias Arq Bras Cardiol. 2019; 112(6):758-766 1. Vanderpump M, Tunbridge WM, French JM, Appleton D, Bates D, Clark F, et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clin Endocrinol. 1995;43(1):55-68. 2. Canaris GJ, Manowitz NR, Mayor G, Ridgway EC. The Colorado thyroid disease prevalence study. Arch Intern Med. 2000;160(4):526-34. 3. Donangelo I, BraunsteinG. Update on subclinical hyperthyroidism. AmFam Physician. 2011;83(8):933-8. 4. Benseñor IM, Goulart AC, Lotufo PA, Menezes PR, ScazufcaM. Prevalence of thyroid disorders among older people: results from the São Paulo Ageing & Health Study. Cad Saude Publica. 2011;27(1):155-61. 5. Sgarbi JA, Matsumura LK, Kasamatsu TS, Ferreira SR, Maciel RM. STDs are independent risk factors for mortality in a 7.5-year follow-up: the Japanese- Brasilian thyroid study. Eur J Endocrinol. 2010;162(3):569-77. 6. Sichieri R, Baima J, Marante T, de Vasconcellos MT, Moura AS, Vaisman M. Low prevalence of hypothyroidism among black and Mulatto people in a population-based study of Brazilian women. Clin Endocrinol. 2007;66(6):803-7. 7. Selmer C, Olesen JB, Hansen ML, von Kappelgaard LM, Madsen JC, Hansen PR, et al. Subclinical and overt thyroid dysfunction and risk of all- cause mortality and cardiovascular events: a large population study. J Clin Endocrinol Metab. 2014;99(7):2372-82. References In line with previous studies, 1,2,13 SCHypoTh was more frequent than SCHyperTh in the current study (5.23% vs. 1.45%). As expected, SCHypoTh was more frequent with increasing age, female sex, higher BMI, and white skin color. In contrast, SCHypoTh was negatively associated with black skin color and current smoking. 1,2,6 SCHyperTh showed a positive and independent association with increasing age, female sex, and black skin color, which are also consistent with population-based studies. 3,6 The strengths of the present study were the large multicenter samples, the methodological rigor in recruiting and data collection, and the centralized analysis of the laboratory tests and ECGs. The cohort was composed of volunteers, mostly middle-aged individuals, recruited outside of the hospital and evaluated in the absence of any acute illness, which most likely excluded non-thyroid diseases. The limitations of this study include the following: TSH was measured only once; FT4 concentrations were measured only for those participants with abnormal TSH levels, and a single ECG was used for the diagnosis of arrhythmias; and no other laboratory, clinical, or ecographic data were available to assess whether the laboratory test abnormalities indeed correspond to STD. This limitation should be kept inmind, especially considering the TSHmedians that indicated mild STD. Not all of the ECGs were available for analysis, however the mean age of the participants whose ECGs were analyzed was greater than that of the total cohort sample, which might in fact overestimate the overall prevalence of arrhythmias e corroborates the lack of association with STD. Only 33 of the participants had TSH > 10 μU/mL (4.73% of SCHypoTh) while 35 showed TSH < 0.1 μU/mL (18.13% of SCHyperTh). Moreover, some ECG abnormalities were rather uncommon, as rhythm disorders, with a prevalence of less than 1%. Therefore, the statistical power to identify associations between those subgroups and rhythm and conduction alterations may have been insufficient. A longitudinal assessment is needed to determine the incidence of arrhythmias as well as their relative risk for each of the STD groups. Conclusion The present study provides contrary evidence to the association between electrocardiographic changes and STD in a seemingly healthy non-elderly population. Although, given the limitations inherent to a cross-sectional analysis, the lack of this association cannot be definitively excluded at this point, and a longitudinal assessment is needed. Author contributions Conception and design of the research: Ribeiro ALP, Rajão KMAB, Passos VMA, Benseñor IJM, Diniz MFHS; Acquisition of data: Ribeiro ALP, Passos VMA, Benseñor IJM, Vidigal PG; Analysis and interpretation of the data and Critical revision of the manuscript for intellectual content: Ribeiro ALP, Rajão KMAB, Passos VMA, Benseñor IJM, Vidigal PG, Camacho CP, Diniz MFHS; Statistical analysis and Writing of the manuscript: Rajão KMAB, Passos VMA, Camacho CP, Diniz MFHS; Obtaining financing: Passos VMA, Benseñor IJM,. Potential Conflict of Interest No potential conflict of interest relevant to this article was reported. Sources of Funding This study was funded by Departamento de Ciência e Tecnologia do Ministério da Saúde do Brasil (Decit); Ministério da Ciência, Tecnologia e Inovação; CNPq e FINEP. Study Association This article is part of the thesis of master submitted by Kamilla Maria Araújo Brandão, from Universidade Federal de Minas Gerais - UFMG. Ethics approval and consent to participate This study was approved by the Ethics Committee of theFaculdade Federal de Minas Gerais under the protocol number ETIC 186/06. All the procedures in this study were in accordance with the 1975 Helsinki Declaration, updated in 2013. Informed consent was obtained from all participants included in the study.