Safety and Efficacy of Intravenous Flecainide Within an Early, Electrophysiologist-Guided Rhythm-Control Strategy for Atrial Fibrillation in the Emergency Department (HEROMEDICUS Study)

Background/Objectives: Atrial fibrillation accounts for approximately 0.5–1% of emergency department visits. Contemporary ESC and ACC/AHA guidelines address acute pharmacological cardioversion, anticoagulation before cardioversion, and delayed “wait-and-see” strategies; however, real-world implementation of an early, specialist-guided pathway in the emergency department remains incompletely described. In the HEROMEDICUS study we implemented a protocol for acute management of patients presenting to the emergency department with atrial fibrillation as their main complaint. The present analysis reports the safety and efficacy of intravenous flecainide within that pathway. Methods: All patients who visited the emergency department from 8 September 2023 to 10 October 2025 with a primary diagnosis of atrial fibrillation, atrial flutter, or atrial tachycardia were screened. Patients with known heart failure (left ventricular ejection fraction < 40%), known coronary artery disease, symptoms of acute heart failure or acute coronary syndrome, or intraventricular conduction delay were excluded. Using tablet computers and an in-house application, on-duty cardiologists obtained contemporaneous electrophysiology consultation. In this institution, frontline emergency department care for arrhythmia presentations is provided by cardiologists rather than emergency-medicine physicians. Patients without prior oral loading with >300 mg propafenone or >200 mg flecainide were eligible for intravenous flecainide 2 mg/kg (maximum 150 mg) infused over 10 minutes. Follow-up at the outpatient atrial fibrillation clinic was scheduled through the application. Results: Of 277 patients screened (15 atrial tachycardia, 28 atrial flutter, 234 atrial fi-brillation - mean age 68.5±12.3 years, heart rates 122.9±25.1 bpm and CHA2DS2-VASc 2.3±1.5 points, 53% females), 85 fulfilled criteria for intravenous flecainide administration; of them, 83 had atrial fibrillation on both the triage and recruitment electrocardiograms and 2 had atrial flutter on the triage but atrial fibrillation on the recruitment electrocar-diogram – thus all patients receiving flecainide effectively had atrial fibrillation. A first-diagnosed episode was recorded in 130 patients. Sinus rhythm was restored with flecainide alone in 61/85 patients (71.8%; 95% CI 61.4–80.2%). Of the remaining 24 patients, 22 were subsequently electrically cardioverted in the emergency department and 2 failed both strategies and were discharged after rate control. Among the 26 successful pharmacological conversions with available timestamps, median time from start of in-fusion to sinus rhythm was 13 minutes. No patient developed ventricular proarrhythmia or atrial flutter with 1:1 atrioventricular conduction, at least during their stay in the emergency department. Also, no thromboembolic events occurred in the same period. None of the 85 flecainide-treated patients was admitted. Conclusions: Intravenous flecainide was safe and effective as the initial pharmacological option within the HEROMEDICUS emergency department pathway for selected patients with atrial fibrillation. Subsequent electrical cardioversion rescued most pharmacological failures. These findings apply to atrial fibrillation; they should not be extrapolated to atrial flutter or atrial tachycardia. In the absence of a control group, we report the observed absence of admissions following implementation of our protocol.