THE IMPORTANCE OF THYROID HORMONE LEVELS AFTER HEART SURGERY – PRELIMINARY STUDY

Introduction Thyroid hormone level suppression after serious operations as coronary artery bypass graft (CABG) surgery, and aortic valve replacement (AVR) is a quite common phenomenon. It is called the nonthyroidal illness syndrome. This appears with a decrease in triiodothyronine (T3) and tetra iodothyronine (T4) serum levels with no thyroid disorders in the medical history. Our aim was to investigate the relationship among thyroid hormone levels and postoperative complications after CABG and AVR. Methods This single center retrospective, observational study approved by the IRB (65/2017). 49 patients, who underwent CABG or AVR, were enrolled in our study between the 1st of January 2019 and the 16th of February 2021. Demographic parameters, Euroscore, thyroid disorders, T3, T4 levels in the first postoperative week, the perioperative thyroxine supplementation and the vasopressor- inotropic needs were summarized in our database. Our primary outcome was 1-year mortality, secondary outcome was the length of stay in the intensive care unit (ICU). Spearman's correlation and Cox-regression analysis were used for the statistical analysis. Results Final analysis included 49 patients, 9 (18.4%) were female. The median survival time was 584 days (IQR25-75: 571-614). Five of the 49 patients (10.2%) died until the 16th of February 2021. Seven patients (14.3%) stayed in ICU for more than 72 hours. Four patients (8.2%) were treated with thyroxine in the postoperative period whom did not have preoperative thyroid dysfunction. None of the patients had hypothyroidism nor hyperthyroidism in their medical history. 17 patients (34.7%) had low T3 levels while, none of the patients had low T4 levels on the 1st or 2nd postoperative day. Association was found between the lengths of stay in the ICU and low T4 levels (p=0.048) using nonparametric test. The actual change in T4 levels between the first and the second sample during first postoperative week showed a significant association with 1-year mortality (OR: 1.17; 95%CI: 1.04-1.31; p=0.007). Discussion Our results highlight the role of thyroid function in the postoperative period. The decrease of T4 levels have independent relationship with adverse outcomes as 1-year mortality and the lengths of ICU stay. Thyroid function monitoring could be a beneficial after CABG and AVR operations.