Metoprolol Versus Amiodarone in the Prevention of Atrial Fibrillation After Cardiac Surgery

BACKGROUND: Current guidelines recommend β-blockers as the first-line preventive treatment of atrial fibrillation (AF) after cardiac surgery. Despite this, 19% of physicians report using amiodarone as first-line prophylaxis of postoperative AF. Data directly comparing the efficacy of these agents in preventing postoperative AF are lacking. OBJECTIVE: To determine whether intravenous metoprolol and amiodarone are equally effective in preventing postoperative AF after cardiac surgery. DESIGN: Randomized, prospective, equivalence, open-label, multicenter study. (ClinicalTrials.gov registration number: NCT00784316) SETTING: 3 cardiac care referral centers in Finland. PATIENTS: 316 consecutive patients who were hemodynamically stable and free of mechanical ventilation and AF within 24 hours after cardiac surgery. INTERVENTION: Patients were randomly assigned to receive 48-hour infusion of metoprolol, 1 to 3 mg/h, according to heart rate, or amiodarone, 15 mg/kg of body weight daily, with a maximum daily dose of 1000 mg, starting 15 to 21 hours after cardiac surgery. MEASUREMENTS: The primary end point was the occurrence of the first AF episode or completion of the 48-hour infusion. RESULTS: Atrial fibrillation occurred in 38 of 159 (23.9%) patients in the metoprolol group and 39 of 157 (24.8%) patients in the amiodarone group (P = 0.85). However, the difference (-0.9 percentage point [90% CI, -8.9 to 7.0 percentage points]) does not meet the prespecified equivalence margin of 5 percentage points. The adjusted hazard ratio of the metoprolol group compared with the amiodarone group was 1.09 (95% CI, 0.67 to 1.76). LIMITATIONS: Caregivers were not blinded to treatment allocation, and the trial evaluated only stable patients who were not at particularly elevated risk for AF. The withdrawal of preoperative β-blocker therapy may have increased the risk for AF in the amiodarone group. CONCLUSION: The occurrence of AF was similar in the metoprolol and amiodarone groups. However, because of the wide range of the CIs, the authors cannot conclude that the 2 treatments were equally effective. PRIMARY FUNDING SOURCE: The Finnish Foundation for Cardiovascular Research and the Kuopio University EVO Foundation.