Is there a relationship between thyroid hormone change and postoperative arrhythmia in patients undergoing coronary bypass surgery? A prospective randomized controlled trial

Aim: Several factors are known to be associated with arrhythmias after cardiac surgery. This paper examines the changes in thyroid hormones after cardiac surgery and the relationship with arrhythmias. Material and Methods: A random sample of euthyroid patients scheduled for isolated coronary artery bypass surgery were recruited for a randomized prospective study. Patients were divided into two groups based on developing a new-onset arrhythmia (NOA) or atrial fibrillation (NOAF) after surgery (Group 2, n=18), and patients without NOA or NOAF after surgery were included in Group 1 (n=66). Blood samples for free triiodothyronine (fT3) and free thyroxin (fT4) levels were collected preoperatively and at the time of arrival to intensive care unit (D0), 24th hour (D1), 48th hour (D2), 72nd hour (D3) and 96th hour (D4). Results: Arrhythmia was detected in 21.43% of patients. Twelve patients had NOAF and six patients had ventricular NOA. The postoperative second day was the most common day for arrhythmia. fT3 values were lower than preoperative values in both groups. When intra-group decreases were compared, the fT3 value decrease was more prominent in the arrhythmia group and fT3 regression at the D2 term (p=0.036) was especially significant. Postoperative fT4 values were higher than preoperative values in both groups. When intra-group raises were compared, fT4 values increased in both groups. This raising was more significant in the arrhythmia group and the fT4 rise at D1 term (p=0.022) was especially important. Conclusion: The decrease of fT3 values in the arrhythmia group (Group 2) was greater. This is more prominent on the postoperative second day, which is the most common day for arrhythmia after cardiac surgery. There is a rise in fT4 values and this is higher in the arrhythmia group. These relatively high values may be mimicking hyperthyroidism and may be considered a predisposition for arrhythmia and atrial fibrillation.