Short-Term Electrocardiographic and Echocardiographic Effects of Levothyroxine Replacement in Adults with Newly Diagnosed Hypothyroidism

Background and Aims: Thyroid hormones play a key role in modulating the cardiac function and structure. Expectedly, thyroid hormone deficiency in primary hypothyroidism has a profound and clinically relevant effect on the cardiac structure and function manifesting in characteristic electrocardiographic and echocardiographic (ECHO) abnormalities. The aim is to evaluate the effects of levothyroxine replacement therapy on the electrocardiographic (ECG) and ECHO changes in patients with primary hypothyroidism by assessing the changes in ECG and ECHO before and after 6 weeks of optimal levothyroxine (LT4) treatment in adults with newly diagnosed primary hypothyroidism. Methodology: Prospective, observational study conducted in the department of medicine in an armed forces tertiary care teaching hospital from October 2018 to April 2021. We studied newly diagnosed adults with primary hypothyroidism who were treated with optimal LT4 replacement. Descriptive statistics along with Student's t-test and Chi-square test were used to determine the statistical significance. Results: In 152 participants, the mean age was 41.0 +/- 13.2 years and 79% were female. After 6 weeks of LT4 treatment, the proportion of participants with abnormal ECG findings reduced significantly (from 77% to 14.5%, P < 0.0001) with a significant reduction in those having sinus bradycardia (P < 0.0001) and low-voltage complexes (P < 0.0001). On ECHO, there was a significant improvement in left ventricular ejection fraction (P < 0.001), fractional shortening (P < 0.001), and a significant reduction in myocardial thickness parameters. The systolic and diastolic function improved significantly after 6 weeks of treatment. The proportion of patients without pericardial effusion increased from 34.9% to 79.6%. Conclusion: Replacement therapy with LT4 in newly diagnosed primary hypothyroid patients substantially improves cardiac structure, systolic and diastolic function and has a positive impact on underlying pericardial effusion. A large, prospective, trial is necessary to determine the long-term effects after thyroid hormone replacement.