BETAFLEC-CHIOS, is a single-center registry that was initiated in the "Skylitseion" General Hospital of Chios in January 2020 and is ongoing. The inclusion criterion is IV flecainide administration for recent-onset AF lasting less than 48 hours. Oral b-blockers are co-administered in all patients. The main exclusion criteria are severe structural or ischemic heart disease and conduction system dysfunction. Continuous monitoring is applied during and after administration of IV flecainide. If no conversion to sinus rhythm is achieved at 2 hours after flecainide infusion, the patient is recorded as "unsuccessful conversion attempt".

Patient population BETAFLEC-CHIOS, is a single-center registry that was initiated in the "Skylitseion" General Hospital of Chios in January 2020 and is ongoing. Patients are included in the registry if presenting with recent-onset atrial fibrillation (AF) (≤48 hours of onset) and lasting ≥30min, documented by a 12-lead ECG and having received intravenous (IV) flecainide on treating physician's discretion. Exclusion criteria are severe structural or ischemic heart disease (previous cardiac surgery, any cardiomyopathy, myocardial infarction at any time), atrial flutter, sick sinus syndrome, high degree atrioventricular block, bifascicular block, abnormal electrolyte levels (especially hypo- or hyperkalemia) or known sensitivity to flecainide. Continuous monitoring is applied during and after administration of IV flecainide. If no conversion to sinus rhythm is achieved at 2 hours after flecainide infusion initiation, the patient is recorded as "unsuccessful conversion attempt" and forwarded for direct current cardioversion (DCC). All patients were anticoagulated according to the current European Society Guidelines (ESC) or the management of AF [ESC Afib 2020].

Flecainide administration Flecainide is given as an IV infusion of 1.5 mg/kg (max 150 mg) in DW 5% over 10 min under continuous monitoring. Concomitant administration of a b-blocker is also applied in all patients. The dose and type of b-blocker are selected according to heart rate during the AF and patient's medical history. "Time to conversion" is calculated as the time interval from the end of the infusion up to when sinus rhythm is observed on the monitor and confirmed subsequently with a 12-lead ECG.

Inclusion Criteria:

1. Informed written consent.
2. Recent-onset atrial fibrillation (AF) (≤48 hours of onset) and lasting ≥30min, documented by a 12-lead ECG
3. Administration of intravenous flecainide
4. Administration of an oral b-blocker

Exclusion Criteria:

1. Age <18 years
2. Severe structural or ischemic heart disease (previous cardiac surgery, any cardiomyopathy, myocardial infarction at any time)
3. Atrial flutter, sick sinus syndrome, high degree atrioventricular block, bifascicular block
4. Abnormal electrolyte levels (especially hypo- or hyperkalemia)
5. Known sensitivity to flecainide

Patients are included in the registry if presenting with recent-onset atrial fibrillation (AF) (≤48 hours of onset) and lasting ≥30min, documented by a 12-lead ECG and having received intravenous (IV) flecainide on treating physician's discretion. Exclusion criteria are severe structural or ischemic heart disease (previous cardiac surgery, any cardiomyopathy, myocardial infarction at any time), atrial flutter, sick sinus syndrome, high degree atrioventricular block, bifascicular block, abnormal electrolyte levels (especially hypo- or hyperkalemia) or known sensitivity to flecainide. Continuous monitoring is applied during and after administration of IV flecainide.