What is the role of adenosine in Wolff-Parkinson-White (WPW) syndrome?

Role of Adenosine in Wolff-Parkinson-White (WPW) Syndrome

Primary Recommendation

Adenosine should be used with extreme caution in WPW syndrome and is contraindicated in patients with pre-excited atrial fibrillation, as it can precipitate life-threatening ventricular fibrillation by triggering atrial fibrillation with rapid ventricular rates through the accessory pathway. 1

When Adenosine May Be Used

Narrow-Complex Tachycardia (Orthodromic AVRT)

• Adenosine is the preferred agent for acute termination of regular, narrow-complex supraventricular tachycardia in hemodynamically stable WPW patients, as this indicates anterograde conduction is occurring through the AV node rather than the accessory pathway 1, 2
• The narrow QRS complex (less than 120 ms duration) during tachycardia confirms safe use because the accessory pathway is not conducting anterograde 1
• Adenosine terminates approximately 95% of orthodromic AVRT cases by blocking AV nodal conduction 2
• Administer 6 mg IV push via large proximal vein followed immediately by 20 mL saline flush; if no conversion in 1-2 minutes, give 12 mg IV push 2

Diagnostic Utility

• Adenosine can serve as a diagnostic tool to unmask WPW pattern by temporarily blocking AV nodal conduction and revealing increased pre-excitation 3
• In pediatric patients, blocked accessory pathway conduction with adenosine has 100% specificity and positive predictive value for identifying non-rapid baseline accessory pathway conduction (cycle length >250 ms), which indicates lower risk 3
• Adenosine-sensitive accessory pathways demonstrate longer local AV intervals (median 40.5 ms vs 32.0 ms) and are less likely to support rapid conduction 4

Critical Contraindications

Pre-Excited (Wide-Complex) Tachycardia

• Adenosine is contraindicated when the QRS complex is wide (≥120 ms) during tachycardia, as this indicates anterograde conduction through the accessory pathway 1
• In antidromic AVRT or pre-excited atrial fibrillation, adenosine can trigger atrial fibrillation in 1-15% of cases, potentially leading to ventricular fibrillation and sudden death 1
• For wide-complex tachycardia in WPW, use procainamide, ibutilide, or flecainide instead, which slow conduction through the accessory pathway 1

Pre-Excited Atrial Fibrillation

• Immediate electrical cardioversion is mandatory for pre-excited AF with hemodynamic instability rather than any pharmacologic agent 1, 5
• For hemodynamically stable pre-excited AF, use intravenous procainamide or ibutilide, not adenosine 1, 5

Safety Precautions

Essential Monitoring

• A defibrillator must be immediately available when administering adenosine to any patient with known or suspected WPW due to the risk of precipitating rapid atrial fibrillation 2
• Continuous ECG recording during administration aids diagnosis and distinguishes drug failure from successful termination with immediate reinitiation 2

Dose Modifications

• Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access 2
• Larger doses may be required for patients with significant blood levels of theophylline, caffeine, or theobromine 2
• Adenosine should not be given to patients with asthma due to risk of bronchospasm 2

Clinical Algorithm for Adenosine Use in WPW

1. Assess QRS width during tachycardia:

   • Narrow (<120 ms) → Adenosine is appropriate 1
   • Wide (≥120 ms) → Adenosine is contraindicated; use procainamide/ibutilide 1

2. Assess hemodynamic stability:

   • Unstable → Immediate DC cardioversion regardless of QRS width 1, 5
   • Stable with narrow QRS → Proceed with adenosine 1, 2

3. Ensure defibrillator availability before administration 2

4. Monitor for post-conversion recurrence and treat with repeat adenosine or longer-acting AV nodal blocker (diltiazem or beta-blocker) if narrow-complex tachycardia recurs 2, 6

Key Pitfalls to Avoid

• Never use adenosine, beta-blockers, calcium channel blockers, or digoxin in pre-excited atrial fibrillation, as these AV nodal blocking agents can paradoxically accelerate conduction through the accessory pathway and precipitate ventricular fibrillation 1, 5
• Do not assume all WPW tachycardias are safe for adenosine; always verify narrow QRS complex first 1
• Adenosine's ultra-short half-life means it can trigger atrial fibrillation that outlasts its therapeutic effect, leaving the patient vulnerable to rapid conduction through the accessory pathway 1

Definitive Management

• Catheter ablation remains the first-line definitive treatment for symptomatic WPW patients, with success rates exceeding 95% and complication rates under 1-2% in experienced centers 5, 7
• Ablation is particularly indicated for patients with syncope, short bypass tract refractory period (<250 ms), or documented rapid pre-excited atrial fibrillation 1, 5