Quinidine for pharmacological cardioversion of atrial fibrillation: A retrospective analysis in 501 consecutive patients

Background: Although quinidine has been used to terminate atrial fibrillation (AFib) for a long time, it has been recently classified to be used as a third-line-drug for cardioversion. However, these recommendations are based on a few small studies, and there are no data available of a larger modern patient population undergoing pharmacological cardioversion of AFib. Therefore, we evaluated the safety of quinidine for cardioversion of paroxysmal AFib in patients after cardiac surgery and coronary intervention. Methods: In 501 consecutive patients (66 ± 9 years, 32% women), 200-400 mg of quinidine were administered every 6 hours until cardioversion or for a maximum of 48 hours. Patients were included with QT interval ≤450 ms, ejection fraction (EF) ≥35%, and plasma potassium >4.3 mEq/L. Exclusion criteria were: unstable angina, myocardial infarction <3 months, and advanced congestive heart failure. Patients received verapamil, beta-blockers, or digitalis to slow down ventricular rate <100 bpm. Results: Quinidine therapy did not have to be stopped due to adverse drug reactions (ADR), and no significant QTc interval prolongation (Bazett and Fridericia correction) and no life-threatening ventricular arrhythmia occurred. Mean quinidine dose was 617 ± 520 mg and 92% of the patients received verapamil or beta-blocker to decrease ventricular rate. Cardioversion was successful in 84% of patients. All ADRs were minor and transient. Multivariate analysis revealed female gender (OR 2.62, CI 1.61-4.26, P < 0.001) and EF 45-54% (OR 1.97, CI 1.15-3.36, P = 0.013) as independent risk factors for ADRs. Conclusions: Quinidine for pharmacological cardioversion of AFib is safe and well tolerated in this subset of patients.