Background: Atrial Fibrillation (AF) is a common complication after open heart surgery and is frequently associated with increased hospital stay, complications, and mortality rates. The effect of β-blockers on prevention of supraventricular arrhythmias has been confirmed in several prospective randomized studies.

Objectives: This clinical trial aimed to compare the preventive effects of carvedilol and metoprolol on occurrence of AF after CABG surgery.

Patients and Methods: This prospective, double-blind, randomized clinical trial was conducted on 150 patients (55 females, 95 males; mean age: 59 ± 10 years) who underwent CABG surgery. The patients with no contraindication for β-blocker use were randomly divided into two groups of carvedilol and metoprolol Tartarate (n = 75). Treatment with β-blocker was started on the first postoperative day (metoprolol, 25 mg BD; carvedilol, 6.25 mg, BD) and the dosage was regulated according to the patients’ hemodynamic response. All the patients were monitored 5 days after the surgery and incidence of AF and other complications was recorded in both groups.

Results: AF was detected in 18 patients in the carvedilol group and 21 patients in the metoprolol group (P = 0.577). The results of Fisher Exact test showed no significant relationship between the type of the drug and the occurrence of AF (P < 0.05). Nevertheless, the prevalence of AF was higher in the renal failure group. AF was mostly recorded on the second and third days after the surgery. The results showed an association between old age and higher occurrence of AF. AF was recorded in 11 patients (14%) in the metoprolol group and 9 ones (12%) in the carvedilol group, with Left Ventricle Ejection Fraction (LVEF) being between 35% and 45% (P = 0.587). However, no significant difference was found between the two groups in this regard.

Conclusions: In the patients with sufficient ejection fraction, no difference was observed in using carvedilol or metoprolol in prevention of post-CABG AF. Yet, given the anti-oxidant and anti- inflammatory effects of carvedilol, it might be more beneficial in comparison to metoprolol, particularly in the patients with lower ejection fractions or heart failure.