Investigation of triiodothyronine, thyroxine, and thyroid-stimulating hormone levels’ influence on atrial myocardial electrical instability in experimental hypothyroidism

BACKGROUND: Identifying the association between thyroid dysfunction and the development of nonvalvular atrial fibrillation (AF) remains one of the complex and pressing issue in contemporary cardiology. To date, only a limited number of studies have examined the relationship between AF and the hypothalamic-pituitary-thyroid (HPT) axis, and the available findings are often contradictory. Few papers have explored the association between AF and HPT axis in experimental conditions. AIM: The work aimed to evaluate the association between AF and the HPT axis in experimental models of hypothyroidism, euthyroidism, and thyrotoxicosis in rats. METHODS: The study included 146 outbred rats. Group 1 comprised 42 rats with euthyroidism. Group 2 included 15 rats with overt thyrotoxicosis. Group 3 included 22 rats with subclinical thyrotoxicosis. Group 4 comprised 67 rats with euthyroid sick syndrome. The methods included electrocardiographic monitoring and measurement of thyroid hormone concentrations. RESULTS: The frequency of AF paroxysms was found to depend on thyroid hormone levels: under euthyroid conditions, on thyroid-stimulating hormone (β = −0.250; p 0.001) and thyroxine (β = 0.838; p = 0.012); in overt thyrotoxicosis, on thyroxine (β = 0.732; p = 0.00008) and triiodothyronine (β = 0.352; p = 0.043); and in subclinical thyrotoxicosis, on thyroxine (β = 2.1; p = 0.0002) and triiodothyronine (β = −0.970; p = 0.019). Threshold values of thyroid hormones were determined for euthyroid, subclinical, and overt thyrotoxic states. CONCLUSION: A relationship between atrial fibrillation and thyroid functional status was established.