How effective is cardioversion at converting atrial fibrillation to a normal sinus rhythm in patients with Wolff-Parkinson-White (WPW) syndrome?

Effectiveness of Cardioversion for Atrial Fibrillation in WPW Syndrome

Immediate electrical cardioversion is highly effective and the first-line treatment for patients with WPW syndrome who develop atrial fibrillation with rapid ventricular response, particularly when associated with hemodynamic instability. 1

Cardioversion Approach in WPW with AF

Hemodynamically Unstable Patients

• Immediate direct-current (DC) cardioversion is recommended as Class I treatment (Level of Evidence: B) for:
  • Patients with severe hemodynamic compromise 1
  • Patients with rapid ventricular response causing instability 1
  • Patients at risk of ventricular fibrillation due to short bypass tract refractory periods 1

Hemodynamically Stable Patients

For stable patients with pre-excited AF:

1. Pharmacological cardioversion options:

   • IV procainamide or ibutilide (Class I, Level of Evidence: C) 1
   • IV quinidine, disopyramide, or amiodarone may be considered (Class IIb, Level of Evidence: B) 1

2. Medications to AVOID (Class III: Harm):

   • AV nodal blocking agents including:
     • Beta-blockers
     • Calcium channel blockers (diltiazem, verapamil)
     • Digoxin
     • Adenosine
     • Amiodarone (in some cases)

   These medications can preferentially block the AV node, allowing faster conduction through the accessory pathway, potentially leading to ventricular fibrillation 1, 2

Efficacy of Cardioversion in WPW with AF

1. Electrical cardioversion:

   • Success rate approaches 100% for restoring sinus rhythm 3
   • Should be performed without delay in unstable patients 2
   • Recommended as first-line therapy for hemodynamically compromised patients 1

2. Pharmacological cardioversion:

   • IV procainamide: Effective first-line agent for stable patients 1
   • IV ibutilide: Alternative effective option 1
   • IV amiodarone: Converted AF to sinus rhythm in 28.9% of patients in one study, but carries risks 3, 4

Long-term Management After Cardioversion

Despite successful cardioversion, the risk of recurrence is high without definitive treatment:

• Catheter ablation is recommended (Class I, Level of Evidence: B) for:

  • Symptomatic patients with WPW and AF 1
  • Patients with syncope due to rapid heart rates 1
  • Those with short bypass tract refractory periods 1

• Success rates for catheter ablation exceed 95% 2

• In one study, all patients except one had immediate successful ablation, with only one recurrence requiring a repeat procedure 3

Risk Factors for Poor Outcomes

Patients with WPW and AF at highest risk for sudden death have:

• Short anterograde bypass tract refractory periods (<250 ms) 1, 2
• Multiple accessory pathways (found in 12.2% of patients in one study) 3
• History of pre-excited atrial fibrillation 2
• Posteriorly located accessory pathways (particularly right posteroseptal) 3

Important Clinical Considerations

1. Always have a defibrillator immediately available when treating patients with WPW and AF 2

2. Continuous cardiac monitoring is essential during and after cardioversion to assess for recurrence 2

3. ECG interpretation is crucial before administering any medication to identify pre-excitation 2

4. Without definitive treatment (ablation), recurrence rates of AF after cardioversion are high (71-84% at 1 year) 5

In summary, electrical cardioversion is highly effective for immediate termination of AF in WPW patients, but catheter ablation offers the most definitive long-term treatment to prevent recurrence and reduce the risk of sudden cardiac death.