What is the next best step for a patient with atrial fibrillation and a variable ventricular response who remains symptomatic on metoprolol 100 mg twice daily and flecainide 100 mg twice daily?

Management of Symptomatic Atrial Fibrillation with Variable Ventricular Response Despite Current Therapy

For a patient with atrial fibrillation and variable ventricular response who remains symptomatic despite metoprolol 100 mg twice daily and flecainide 100 mg twice daily, the next best step is to increase the flecainide dose to 150 mg twice daily.

Current Treatment Assessment

The patient is currently on:

• Metoprolol 100 mg twice daily (beta-blocker for rate control)
• Flecainide 100 mg twice daily (Class IC antiarrhythmic for rhythm control)

Despite this combination therapy, the patient remains symptomatic with a variable ventricular response, indicating inadequate control of the arrhythmia.

Rationale for Flecainide Dose Adjustment

According to the FDA labeling for flecainide, the medication can be titrated upward in increments of 50 mg twice daily every four days until efficacy is achieved 1. The maximum recommended dose for patients with paroxysmal supraventricular arrhythmias is 300 mg/day.

The ACC/AHA/ESC guidelines support this approach, noting that flecainide is effective in postponing recurrences of AF and reducing overall time spent in AF 2. For patients with atrial fibrillation without structural heart disease, flecainide doses can range from 200-300 mg daily 2.

Evidence Supporting Combination Therapy

Research has shown that the combination of flecainide and metoprolol is more effective than flecainide alone in reducing AF recurrences. A randomized trial demonstrated that this combination significantly reduced recurrences at 1-year follow-up compared to flecainide monotherapy (66.7% vs. 46.8%; P < 0.001), particularly in patients with persistent AF 3. This combination also improved quality of life compared to flecainide alone.

Monitoring Recommendations

When increasing the flecainide dose:

• Monitor for QRS widening (should not exceed 150% of pretreatment QRS duration) 2
• Watch for signs of proarrhythmia, though this is rare in patients without structural heart disease 2
• Consider exercise testing to detect QRS widening that may occur only at rapid heart rates 4
• Ensure the patient has no contraindications such as structural heart disease, recent MI, or significant ventricular dysfunction 4

Alternative Options if Flecainide Dose Adjustment Fails

If increasing the flecainide dose does not provide adequate symptom control, consider these alternatives:

1. Switch to another antiarrhythmic drug:

   • Dofetilide: Effective for maintaining sinus rhythm after cardioversion 2
   • Propafenone: Alternative Class IC agent with similar efficacy to flecainide 2
   • Sotalol: Particularly if the patient has structural heart disease 2
   • Amiodarone: Reserved for patients who have failed other therapies due to its significant long-term toxicity 4

2. Consider catheter ablation: Highly effective definitive treatment with success rates of 93-95% for SVT management 4

3. Electrical cardioversion with continued antiarrhythmic therapy: Reasonable to perform repeated cardioversions if sinus rhythm can be maintained for clinically meaningful periods between procedures 2

Cautions and Contraindications

• Flecainide should not be used in patients with structural heart disease, coronary artery disease, or left ventricular dysfunction 2, 4
• Monitor for rare but serious side effects such as QT prolongation 5
• Avoid rapid dose escalation, as this has been associated with increased incidence of proarrhythmic events 1

Conclusion

Increasing flecainide to 150 mg twice daily is the most appropriate next step for this patient who remains symptomatic on the current regimen. This approach is supported by guidelines and FDA labeling, with evidence showing that the combination of flecainide and metoprolol is particularly effective for controlling symptomatic atrial fibrillation.