ABC | Volume 112, Nº6, June 2019

758 Original Article Subclinical Thyroid Dysfunction was not Associated with Cardiac Arrhythmias in a Cross-Sectional Analysis of the ELSA-Brasil Study Kamilla Maria Araújo Brandão Rajão, 1 A ntônio Luiz Pinho Ribeiro, 2, 3 Valéria Maria Azeredo Passos, 2 Isabela Judith Martins Benseñor , 4 P edro Guatimosim Vidigal , 5 C leber Pinto Camacho, 6 Maria de Fátima Haueisen Sander Diniz 1 ,2 Serviço de Endocrinologia e Metabologia do Hospital das Clínicas da Universidade Federal de Minas Gerais (UFMG), 1 Belo Horizonte, MG – Brazil Departamento de Clínica Médica da Faculdade de Medicina da Universidade Federal de Minas Gerais (FM-UFMG), 2 Belo Horizonte, MG – Brazil Serviço de Cardiologia e Cirurgia Cardiovascular - Hospital das Clínicas da Universidade Federal de Minas Gerais (UFMG), 3 Belo Horizonte, MG – Brazil Centro de Pesquisa Clínica e Epidemiológica da Universidade de São Paulo (USP), 4 São Paulo, SP – Brazil Departamento de Propedêutica da Faculdade de Medicina da Universidade Federal de Minas Gerais (UFMG), 5 Belo Horizonte, MG – Brazil Universidade Nove de Julho (UNINOVE), 6 São Paulo, SP – Brazil Mailing Address: Kamilla Maria Araújo Brandão Rajão • Rua Rubens Carvalho de Andrade, 60/502. Postal Code 30575-810, Buritis, Belo Horizonte, MG – Brazil E-mail: kamillarajao@gmail.com Manuscript received May 27, 2018, revised manuscript October 17, 2018, accepted October 17, 2018 DOI: 10.5935/abc.20190037 Abstract Background: The association of subclinical thyroid dysfunction (STD) with cardiac arrhythmias remains controversial, particularly in the non-elderly population. Objective: To investigate whether STD was associated with cardiac arrhythmias in a cohort of middle-aged and older adults. Methods: Baseline data of the Longitudinal Study of Adult Health, ELSA–Brasil (35–74 years) were collected from 2008 to 2010. After exclusion of clinical hypothyroidism and hyperthyroidism, participants were categorized as euthyroidism (TSH = 0.4–4.0 µU/mL), subclinical hypothyroidism (TSH > 4.0 µU/mL; FT4 = 0.8–1.9 ng/dL), and subclinical hyperthyroidism (TSH < 0.4 µU/mL; FT4 = 0.8–1.9 ng/dL). The prevalence rates of tachycardia (HR > 100) and bradycardia (HR < 60), atrial fibrillation/flutter, conduction disorders, extrasystoles, low QRS voltage, prolonged QT intervals, and persistent supraventricular rhythms were compared between groups after adjusting for age, sex, comorbidities, lifestyle, body mass index and medications. Results: TheHRdataof 13,341participants (52%female;medianage, 51years) and theelectrocardiogramreadingsof 11,795were analyzed; 698 participants (5.23%) were classified as subclinical hypothyroidism, 193 (1.45%) as subclinical hyperthyroidism, and 12,450 (93.32%) as euthyroidism. The prevalence of rhythm and conduction disorders was similar, as were HR medians, even in the subgroups with TSH < 0.01 UI/mL or > 10.0 UI/mL or in older adults. Conduction disorders were less prevalent in older adults with subclinical hypothyroidism (adjusted OR = 0.44; 95% CI 0.24 to 0.80). Conclusion: In this large, multicenter and cross-sectional study, STD was not associated with cardiac arrhythmias, but a longitudinal assessment is necessary. (Arq Bras Cardiol. 2019; 112(6):758-766) Keywords: Thyroid Diseases/complications; Pathologic Processes; Thyroropin (TSH); Arrhythmias, Cardiac; Adults. Introduction Subclinical thyroid dysfunctions (STD), which include subclinical hypothyroidism (SCHypoTh) and subclinical hyperthyroidism (SCHyperTh), are characterized by elevated or suppressed thyroid-stimulating hormone (TSH), without clinical alterations or abnormalities in thyroid hormone levels. 1 Diagnosis of STD has been increasing with the dissemination of ultrasensitive TSH assays; however, the clinical repercussions of STD and the benefits associated with thyroid dysfunction screening are still the object of scientific debate, and further research is needed. The prevalence of SCHyperTh ranges from 1% to 16% in large population-based studies, while that of SCHypoTh varies from 4% to 20%. 1,2 Those prevalence rates can vary according to sex, age, degree of iodine sufficiency, and the TSH reference values adopted in each study. 3 In Brazil, population-based studies have shown prevalence rates of SCHyperTh ranging from 2.4% in older adults 4 to 6.2% in Japanese Brazilians aged > 30 years, 5 while SCHypoTh varied from 6.5% among older adults 4 to 12.3% in women aged > 35 years. 6 There is no consistent evidence of the clinical relevance of STD, particularly regarding the cardiovascular system. Although some meta-analyses and population-based cohort studies have indicated a higher cardiovascular risk and mortality associated with STD, 5,7 other studies do not corroborate those results. 8-10 Regarding arrhythmias, SCHyperTh has been associated with a two- to three-fold risk of tachyarrhythmias, especially sinus tachycardia, atrial fibrillation (AF) and atrial flutter, extrasystoles, supraventricular and ventricular arrhythmias, 11-17 and prolonged QT intervals (QTi). 18 Fewer studies have explored the relationship between