Relationship between preoperative FT3 levels and new-onset atrial fibrillation after off-pump coronary artery bypass grafting

Background: Postoperative atrial fibrillation (POAF) is the most common arrhythmia after cardiac surgery. While thyroid dysfunction can predict POAF, the association between preoperative serum free triiodothyronine (FT3) levels and POAF in patients undergoing off-pump coronary artery bypass (OPCAB) grafting remains unclear. This study aimed to investigate the relationship between preoperative FT3 levels and POAF in OPCAB patients. Methods: This prospective observational study included patients with sinus rhythm and no history of atrial fibrillation or thyroid disease who underwent OPCAB and FT3 testing at the Tianjin Chest Hospital from June 2021 to March 2023. The relationship between FT3 level and POAF was evaluated using restricted cubic spline. Cox proportional hazards regression models were used to analyze the associations between FT3 concentration categories [low T3 syndrome (LT3S) (FT3 below the normal range), low normal FT3 (3.10-4.59 pmol/L), high normal FT3 (4.60-6.80 pmol/L)] and POAF, adjusting for potential confounders. Stratified analyses were performed to assess effect modification by gender and age (<60 vs. >= 60 years old). Results: Among 875 patients, 259 (29.6%) developed POAF within 2 days after surgery. Restricted cubic spline analysis showed an S-shaped association between FT3 concentration and POAF risk. Compared to the low normal FT3 group, LT3S was associated with an increased risk of POAF [hazard ratio (HR), 1.41; 95% confidence interval (CI): 1.90-2.19], while high normal FT3 was associated with a decreased risk (HR, 0.72; 95% CI: 0.51-0.99). The association between FT3 and increased POAF risk was more pronounced in patients aged >= 60 years (HR, 1.41; 95% CI: 1.89-2.22) Conclusions: Preoperative FT3 levels most likely could predict POAF risk after OPCAB, especially in patients aged 60 years and older. Measuring FT3 preoperatively may identify high-risk patients benefiting from close monitoring and prophylactic treatment. Further investigation of thyroid hormone replacement therapy for LT3S is warranted.