Association Between Serum Free Thyroxine Concentration and Atrial Fibrillation

Abstract

Background: Previous studies have suggested that minor changes in thyroid function are associated with risk of atrial fibrillation (AF). Our objective was to determine the relationship between thyroid function and presence of atrial fibrillation (AF) in older subjects. Methods: A population-based study of 5860 subjects 65 years and older, which excluded those being treated for thyroid dysfunction and those with previous hyperthyroidism. Main outcome measures included tests of thyroid function (serum free thyroxine [T 4 ] and thyrotropin [TSH]) and the presence of AF on resting electrocardiogram.Results: Fourteen subjects (0.2%) had previously undiagnosed overt hyperthyroidism and 126 (2.2%), subclinical hyperthyroidism; 5519 (94.4%) were euthyroid; and 167 (2.9%) had subclinical hypothyroidism and 23 (0.4%), overt hypothyroidism. The prevalence of AF in the whole cohort was 6.6% in men and 3.1% in women (odds ratio, 2.23; PϽ.001). After adjusting for sex, logistic regression showed a higher prevalence of AF in those with subclinical hyperthyroidism compared with euthy-roid subjects (9.5% vs 4.7%; adjusted odds ratio, 2.27; P =.01). Median serum free T 4 concentration was higher in those with AF than in those without (1.14 ng/dL; interquartile range [IQR], 1.

High-Normal Thyroid Function and Risk of Recurrence of Atrial Fibrillation After Catheter Ablation

“…In a populationbased study, higher FT4 concentrations were found in those with AF compared with those without AF in a subgroup analysis confined to 5,519 euthyroid subjects. 3 In logistic analysis, serum FT4 was an independent predictor of AF. In the Rotterdam study, the multivariate adjusted level of FT4 showed a graded association with the risk of new onset AF.…”

“…A crosssectional population-based study showed that the serum free thyroxine (FT4) concentration was independently associated with AF, even in euthyroid persons with TSH levels in the normal range. 3 Because most of the AF pathogenic factors present in patients with high levels of FT4 remain even after ablation, it is reasonable to hypothesize that FT4 at a highnormal level increases the risk of recurrence of AF after catheter ablation, so we conducted a prospective study to test this hypothesis.…”

Higher free thyroxine levels are associated with all-cause mortality in euthyroid older men: the Health In Men Study

“…Excessive exposure to thyroid hormones exerts deleterious effects on cardiac rate, rhythm and function (39). In a study of 5860 adults aged R65 years, Gammage et al (12) reported that FT 4 levels were independently associated with the presence of atrial fibrillation even in euthyroid subjects with normal TSH levels. Therefore, atrial fibrillation reflects one adverse cardiac consequence of excess thyroid hormone exposure on the cardiovascular system, which may be shared between people with subclinical hyperthyroidism and those with highnormal FT 4 levels.…”

“…This may reflect reduced sensitivity of the pituitary to T 4 -or liothyronine (T 3 )-mediated suppression of TSH levels, altered TSH bioactivity or reduced thyroid sensitivity to TSH, requiring compensatory elevation of levels to maintain thyroid homeostasis (10). Small differences in thyroid function between euthyroid subjects have been reported to be associated with specific health-related outcomes including atrial fibrillation, reduced bone mineral density and incident dementia (12,13,14). However, the effect of differences in thyroid function in euthyroid older people on the key outcome of mortality remains unclear, with limited available data and inconsistent findings reported (11,15,16,17).…”

Genetic and environmental influence on thyroid gland volume and thickness of thyroid isthmus: a twin study

“…An association between thyroid volume and serum calcitonin has been established (2,8). Studies have investigated the thyroid function on atrial fibrillation and blood pressure as well (13,14).…”