EM Advances Use of rate control medication before cardioversion of recent-onset atrial fibrillation or flutter in the emergency department is associated with reduced success rates

Objective: It is believed that when patients present to the emergency department (ED) with recent-onset atrial fibrillation or flutter (RAFF), controlling the ventricular rate before cardioversion improves the success rate. We evaluated the influence of rate control medication and other variables on the success of cardioversion. Methods: This secondary analysis of a medical records review comprised 1,068 patients with RAFF who presented to eight Canadian EDs over 12 months. Univariate analysis was performed to find associations between predictors of conversion to sinus rhythm including use of rate control, rhythm control, and other variables. Predictive variables were incorporated into the multivariate model to calculate adjusted odds ratios (ORs) associated with successful cardioversion. Results: A total of 634 patients underwent attempted cardioversion: 428 electrical, 354 chemical, and 148 both. Adjusted ORs for factors associated with successful electrical cardioversion were use of rate control medication, 0.39 (95% confidence interval [CI] 0.21–0.74); rhythm control medication, 0.28 (95% CI 0.15–0.53); and CHADS2 score . 0, 0.43 (95% CI 0.15–0.83). ORs for factors associated with successful chemical cardioversion were use of rate control medication, 1.29 (95% CI 0.82–2.03); female sex, 2.37 (95% CI 1.50–3.72); and use of procainamide, 2.32 (95% CI 1.43–3.74). Conclusion: We demonstrated reduced successful electrical cardioversion of RAFF when patients were pretreated with either rate or rhythm control medication. Although rate control medication was not associated with increased success of chemical cardioversion, use of procainamide was. Slowing the ventricular rate prior to cardioversion should be avoided.