The effects of thyrotropin suppression therapy on cardiac functions in patients with operated differential thyroid cancer

Aim: In this study, it was aimed to evaluate the effect thyrotropin suppression therapy on cardiac functions (heart rate variability (HRV), QT dispersion, rhythm disorders and diastolic function) in differentiated thyroid cancer (DTC) patients who received total thyroidectomy. Methods: This cross-sectional study was carried out in Endocrinology and Metabolism Diseases Out-Patient Department of Uşak Training and Research Hospital between 30 June 2021 and 31 December 2022. The study included 125 patients with DTC who underwent total thyroidectomy and received L-T4 suppression therapy for at least one year. The patients were divided into three groups according to the revised American Thyroid Association Management Guidelines for thyroid nodules and DTC, those with thyroid stimulating hormone (TSH) levels <0.1 mIU/L (i), between 0.1-0.5 mIU/L (ii), and between 0.5-2 mIU/L (iii). The first two groups were defined as the TSH suppression group, and the last group as the TSH replacement (control) group. Results: There were 43 (34%) patients with a TSH value of 0.5-2 mIU/L, 55 (44%) with 0.1-0.5 mIU/L, and 27 (22%) patients with a TSH value below 0.1mIU/L. 90.4% of the cases were women and the mean age was 42±6 years. There is no difference between groups in other demographic data (age, height, body weight, body mass index (BMI). No significant difference was observed between the suppression and replacement groups in terms of the frequency of atrial fibrillation, atrial premature contraction (APC), ventricular premature contraction (VPC) and HRV in the analyzes performed with 24-hour rhythm holter. In echocardiographic evaluation, left ventricular end-diastolic diameter (LV EDD) values of patients with TSH below 0.1 mIU/L were found to be significantly higher than in the replacement group with TSH in the range of 0.5-2 mIU/L (45.35±3, 54 and 42.74±6.08; p=0.016). Early diastolic filling mitral valve velocity (E) value was found to be significantly lower in patients with TSH values between 0.1-0.5 mIU/L than in patients with TSH values between 0.5-2 mIU/L (0.7(0, 6-0.8) and 0.84(0.7-0.98); p=0.010). QT dispersion (QTd) and QTc dispersion (QTcd) times were found to be significantly longer in the suppression groups compared to the replacement group. In multivariate regression analyzes, it was determined that TSH affected QTd (β =-0.299; p=0.002) and QTcd (β =-0.300; p=0.002) values independently from other variables. As the TSH value decreases, the QT and/or QTc dispersion time increases. Conclusion: TSH suppression therapy may have effects on QTd and/or QTcd and diastolic functions in patients with DTC. In clinical practice, the evaluation of QTd and QTcd in patients with DTC may provide clinicians with important clues for determining cardiovascular risk and adjusting TSH suppression intensity. However, it has been shown that there is no significant increase in arrhythmia risk in these patients in the long term. It is important that TSH suppression treatment is carried out according to the risk stratification defined by the ATA guideline and that it is revised according to the ongoing risk reassessments. Keywords: Differentiated thyroid cancer, Thyrotropine suppression therapy, cardiac functions, Heart rate variability, QT dispersion