Background

Thyroid dysfunction has a strong association with cardiac arrhythmias. The extent of subclinical and latent hypothyroidism, however, is often neglected in studies. Although there are indications of TSH-dependent cardiac remodeling and prolongation of the repolarization phase. The specific relationship between latent hypothyroidism and the occurrence of atrial fibrillation has not yet been addressed. The aim of the study was to analyze the incidence of cardiac arrhythmias in patients with elevated TSH levels also a multifactorial analysis of risk factors for the occurrence of atrial fibrillation in this patient group.

Methods

The study design is retrospective and monocentric. A total of 3134 patients (from 2007-2020) were retrospective analyzed using the Research Ware House of Cardiology at the University Hospital Heidelberg. Medical records, ECGs and echocardiographies of the Department of Cardiology were used. Inclusion criteria were a patient age over 18 years, a normal level of fT₄, TSH values between 0.4-75 mU/l, an ECG within 7 days of the blood sample and an echocardiography or MRI within 6 months of the blood sample. Exclusion criteria included the failure to meet the inclusion criteria, an inflammatory constellation as the cause of the laboratory changes or a previous drug therapy with catecholamines, methimazole, propylthiouracil, glucocorticoids or lithium. Evaluation and presentation were carried out using descriptive statistics.

Results

For the evaluation, the patients were divided into groups depending on their TSH value. An increased incidence of atrial fibrillation with rising TSH values was found, both between the individual groups, and between the patient groups and representative patient collectives with normal TSH values. In the group of patients with a TSH value of 25-45 mU/l, atrial fibrillation occurred in 39.4% of the cases, in the group of patients with a TSH value of 45-75 mU/l it occurred in 55.6% of the cases.

Conclusion

In summary, the results suggest a connection between high levels of TSH and the occurrence of cardiac arrhythmias, especially atrial fibrillation. This suggests the influence of hypothyroidism on the electrophysiological cardiac activity already in the latent stage. Future Prospective studies with control groups are needed to validate the results.