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This Article Full Text Full Text (PDF) All Versions of this Article: JOE-08-0140v1 198/1/253    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by van Noord, C. Articles by Stricker, B. H C. PubMed PubMed Citation Articles by van Noord, C. Articles by Stricker, B. H C.

Departments of¹ Epidemiology and Biostatistics² Internal Medicine³ Medical Informatics, Erasmus Medical Center, PO Box 2040, 3000 CA Rotterdam, The Netherlands⁴ The Inspectorate for Health Care, PO Box 16119, 2500 BC, The Hague, The Netherlands⁵ The Dutch Medicines Evaluation Board, PO Box 16229, 2500 BE, The Hague, The Netherlands

(Correspondence should be addressed to B H Ch Stricker at Department of Epidemiology and Biostatistics, Erasmus Medical Center; Email: b.stricker{at}erasmusmc.nl)

The literature on the effect of excess thyroid hormone on ventricular repolarization is controversial. To study whether free thyroxine (T₄) and TSH are associated with QTc prolongation we conducted population-based cohort study. This study was conducted as part of the Rotterdam Study and included 365 men and 574 women aged 55 years and older with an electrocardiogram, who were randomly sampled for the assessment of thyroid status (free T₄/TSH) at baseline, after exclusion of participants with hypothyroidism, use of antithyroid drugs, thyroid hormones or digoxin, left ventricular hypertrophy, and left and right bundle branch block. Endpoints were the length of the QTc interval and risk of borderline QTc prolongation. The associations were examined by means of linear and logistic regression analysis, adjusted for age and gender, diabetes mellitus, myocardial infarction, hypertension, and heart failure. Overall, there was no significant association between TSH and QTc interval (0.8 ms (95% confidence interval (CI) –3.5, 5.2) in the first quintile compared with the fifth quintile). Subjects in the fifth quintile of free T₄ did not have an increased QTc interval (3.2 ms (95% CI –1.1, 7.6)); stratification on gender showed an increment of 10.9 ms (95% CI 3.4, 18.3) in the fifth quintile in men and 1.1 ms (95% CI –4.2, 6.3) in the fifth quintile of free T₄ in women. When compared with subjects in the first quintile, male subjects in the fifth quintile of free T₄ had a significantly increased risk of a borderline QTc interval and QTc prolongation (odds ratio 2.40 (95% CI 1.20, 4.80)). High levels of free T₄ are associated with substantial QTc prolongation in men of up to 10 ms. The fact that free T₄ is also associated with a significantly increased risk of borderline and prolonged QTc values with its risk of sudden cardiac death, endorses the clinical importance of our findings.