Electrocardiographic effect of thyroid hormones

• Published in: Journal of electrocardiology Vol. 57; pp. S108 - S109
• Main Authors: Isaksen, Jonas L., Graff, Claus, Ellervik, Christina, Kanters, Jorgen K.
• Format: Journal Article
• Language: English
• Published: New York Elsevier Inc 01.11.2019; Elsevier Science Ltd
• Subjects: Cardiac arrhythmia; Electrocardiography; Heart rate; Hyperthyroidism
• ISSN: 0022-0736; 1532-8430
• DOI: 10.1016/j.jelectrocard.2019.08.043

Background: Clinical hyperthyroidism has been associated with tachycardia, QT-prolongation, and atrial fibrillation, and hypothyroidism with bradycardia, QT-prolongation, increased PR interval, and changes to T-wave morphology. Even within the euthyroid range, thyroid hormones have been associated with atrial fibrillation, heart failure, and mortality. However, the electrocardiographic (ECG) effect of thyroid hormones in euthyroid patients, has been only sparsely studied, so we aimed to characterize ECG changes associated with variation in thyroid hormones in euthyroid participants. Method: The Danish General Suburban Population Study (GESUS) consists of 20,852 people aged ≠10.1016/j.jelectrocard.2019.08.043 20 years. We defined the euthyroid range as a thyrotropin (TSH) measurement within 0.4-3.8 mU/L. We excluded people with diagnosed hyper- or hypothyroidism or a TSH outside the euthyroid range, leaving 17,734 participants. A resting 12lead ECG was recorded from which automated measurements of heart rate, QT interval, QRS duration, PR interval, P wave duration, T-wave asymmetry, T-wave flatness, and the presence of notches on the T-wave were extracted. Levels of TSH, total triiodothyronine (T3), and free thyroxine (T4) were correlated with ECG measurements. All models were adjusted for sex, age, smoking, potassium, and heart rate (except heart rate model). A p-value < 0.05 was considered significant. Results are reported per standard deviation (SD) of hormone level. Results: Within the euthyroid range, decreasing levels of TSH was associated with more flattened and asymmetric T waves. Higher levels of total T3 were positively associated with heart rate (2.2 bpm/SD) and Fridericia-correcetd QTc (0.3 ms/SD), and negatively associated with PR interval (-0.5 ms/SD) and QRS duration (-0.3 ms/SD). Increasing levels of free T4 were positively associated with heart rate (0.6 bpm/SD) and risk of having notches on the T-wave (odds ratio 1.4/SD). Conclusions: Thyroid hormone levels in euthyroid people affect heart rate, QTc interval, PR interval, QRS duration, and T-wave morphology.