How long after initiating flecainide therapy can I expect my cardiac rhythm to normalize?

Time to Rhythm Normalization with Flecainide

For recent-onset atrial fibrillation, flecainide typically restores normal sinus rhythm within 1 to 6 hours after administration, with the majority of conversions occurring within the first hour when given intravenously. 1, 2

Intravenous Administration Timeline

When flecainide is given intravenously (2 mg/kg over 10 minutes), most patients who will convert do so within the first hour, with an overall conversion rate of 67-92% achieved by 6 hours. 1

• In one study of 69 patients, the mean time from starting IV flecainide to restoration of sinus rhythm was approximately 5 hours (301 minutes), with a range of 5 minutes to 1,600 minutes 2
• Notably, 33 of these patients (48%) converted to normal rhythm within the first 5 minutes after the IV injection 2
• The conversion rate is highest (79%) when atrial fibrillation has been present for less than 10 days, compared to only 38% for longer-standing arrhythmias 2

Oral Administration Timeline

When flecainide is taken orally (200-400 mg), conversion typically occurs within a few hours, with expected conversion rates between 41-91% in recent-onset atrial fibrillation. 1

• Oral flecainide at doses of 200-300 mg has been shown effective for recent-onset AF, with most conversions occurring within several hours 1
• The "pill-in-the-pocket" approach using oral flecainide (200-300 mg) or propafenone has demonstrated 94% efficacy in converting AF episodes 1

Important Clinical Factors Affecting Conversion Time

Your likelihood of converting quickly and successfully depends on several key factors:

• Duration of atrial fibrillation: Shorter duration (<24 hours, especially <10 days) predicts faster and more successful conversion 1, 2
• Left atrial size: Smaller atria (mean 40 mm) are associated with higher conversion rates compared to larger atria (mean 46 mm) 2
• Route of administration: IV flecainide works faster than oral, with many conversions in the first hour versus several hours for oral 1, 2

Critical Safety Considerations

Flecainide should only be used if you do not have structural heart disease, coronary artery disease, heart failure, or reduced left ventricular function, as these are absolute contraindications. 1, 3

• The drug is most effective and safest in patients with "lone" atrial fibrillation (no underlying heart disease) 1
• If you have underlying heart disease involving abnormal LV function or ischemia, flecainide should be avoided entirely 1
• Initial conversion should ideally be undertaken in a hospital setting to monitor for potential complications, particularly atrial flutter with rapid ventricular conduction 1, 3

What to Expect During Treatment

During the conversion period, you should be monitored with ECG, as flecainide can cause QRS widening and, rarely, may convert atrial fibrillation to atrial flutter with a rapid heart rate. 1, 3

• A QRS duration increase of ≥25% from baseline signals potential proarrhythmia risk and requires dose adjustment or discontinuation 3
• The drug may inadvertently increase ventricular rate due to conversion to atrial flutter with 1:1 conduction to the ventricles 1