What is the effectiveness of defibrillation versus adenosine (adenosine) in treating ventricular fibrillation caused by Wolff-Parkinson-White (WPW) syndrome?

Management of Ventricular Fibrillation in WPW Syndrome

Immediate electrical cardioversion is the only effective treatment for ventricular fibrillation in patients with Wolff-Parkinson-White syndrome, while adenosine is contraindicated and potentially harmful in this scenario. 1

Understanding WPW and Ventricular Fibrillation Risk

Wolff-Parkinson-White syndrome is characterized by the presence of accessory pathways that can conduct electrical impulses between the atria and ventricles, bypassing the normal AV node. When atrial fibrillation occurs in WPW patients, it can lead to:

• Extremely rapid conduction through the accessory pathway
• Potential degeneration into ventricular fibrillation
• Risk of sudden cardiac death

Emergency Management Algorithm

For Ventricular Fibrillation in WPW:

1. Immediate direct-current cardioversion (Class I, Level of Evidence: B) 2
   • This is the definitive treatment for ventricular fibrillation
   • No delay should occur for medication administration

For Pre-excited Atrial Fibrillation with Hemodynamic Instability:

1. Immediate direct-current cardioversion (Class I, Level of Evidence: B) 2
   • Required when rapid tachycardias or hemodynamic instability occurs

For Pre-excited Atrial Fibrillation without Hemodynamic Instability:

1. Intravenous procainamide or ibutilide (Class I, Level of Evidence: C) 2

   • First-line pharmacological therapy
   • Goal is to restore sinus rhythm

2. Alternative medications (Class IIb, Level of Evidence: B) 2

   • IV flecainide
   • IV quinidine
   • IV disopyramide
   • IV amiodarone (with caution)

Critical Contraindications

Absolutely Contraindicated in WPW with Pre-excited AF (Class III: Harm):

• Adenosine 1
• Digitalis glycosides 2
• Non-dihydropyridine calcium channel antagonists (diltiazem, verapamil) 2
• Beta-blockers 1

These medications preferentially block the AV node, allowing faster conduction through the accessory pathway, potentially worsening ventricular rates and precipitating ventricular fibrillation 1.

Why Adenosine is Dangerous in WPW with AF/VF

Adenosine can be particularly dangerous in WPW patients with atrial fibrillation or ventricular fibrillation because:

1. It blocks conduction through the AV node
2. This promotes preferential conduction through the accessory pathway
3. Conduction through the accessory pathway can be extremely rapid
4. This can precipitate or worsen ventricular fibrillation
5. It may lead to sudden cardiac death

Long-term Management After Stabilization

After successful cardioversion and stabilization:

1. Catheter ablation of the accessory pathway (Class I, Level of Evidence: B) 2

   • Recommended for symptomatic patients with WPW
   • Particularly important for those with syncope due to rapid heart rate
   • Success rates exceed 95% 1

2. Risk stratification

   • Assess for risk factors for sudden cardiac death:
     • Short refractory period of accessory pathway (<250 ms)
     • Multiple accessory pathways
     • History of pre-excited atrial fibrillation
     • Associated cardiac anomalies 1

Key Clinical Pearls

1. Always have a defibrillator immediately available when treating any patient with suspected WPW 1

2. ECG interpretation is crucial before administering any medication:

   • Wide QRS (≥120 ms) in WPW with AF indicates pre-excitation
   • Avoid AV nodal blocking agents in this scenario 1

3. Long-term follow-up studies show that successful ablation of accessory pathways in resuscitated WPW patients prevents recurrence of cardiac arrest 3