BACKGROUND: Thyroid hormones within the euthyroid range have been linked to mortality and differences in heart rate. However, some relations between thyroid hormone concentration and various electrocardiographic measurements remain unassessed. We aimed to investigate the association between thyroid hormone concentrations within the euthyroid range and different electrocardiographic markers in people free of thyroid disease.
METHODS: We obtained electrocardiograms (ECG) and blood samples of free T4, total T3, and thyrotropin (TSH) in 20,852 subjects from the general population (the GESUS study). Relations between concentrations of TSH, free T4, and total T3 and heart rate, QTc, QRS duration, PR interval, P-wave duration and T-wave morphology were assessed in a multivariate adjusted linear model stratified by sex.
RESULTS: Roughly half of the 18,046 included participants with thyroid hormone measurements within euthyroid range were men, and the average age was 56 years. Heart rate increased with concentrations of T3 (6.4 bpm/nM, p<0.001 in women and 5.3 bpm/nM, p<0.001 in men) and T4 (3.7 bpm/10pM, p<0.001 in women and 3.1 bpm/10pM, p<0.001 in men). We found no relation between TSH and heart rate. PR interval and QRS duration decreased with higher concentrations of T3 (all p<0.01). QTc increased with higher concentrations of T4 in men (5 ms/10pM), and T waves were flatter, more asymmetric and more often had notches with higher concentrations of T4 (all p≤0.01).
CONCLUSIONS: Thyroid hormone concentrations within the euthyroid range in people free of thyroid disease were associated with changes in the electrocardiogram in a general population.