What is the initial drug of choice for Wolff-Parkinson-White (WPW) syndrome?

Initial Drug Management for Wolff-Parkinson-White (WPW) Syndrome

The initial drug of choice depends critically on the type of arrhythmia: for regular narrow-complex supraventricular tachycardia (orthodromic AVRT), use adenosine 6 mg IV push; for pre-excited atrial fibrillation without hemodynamic compromise, use IV procainamide or ibutilide; for hemodynamically unstable patients with any WPW-related arrhythmia, immediate direct-current cardioversion is mandatory—never use AV nodal blocking agents (adenosine, beta-blockers, calcium channel blockers, digoxin, or amiodarone) in pre-excited atrial fibrillation as they can precipitate ventricular fibrillation. 1, 2, 3

Critical First Step: Identify the QRS Complex Width

• Narrow QRS complex (<120 ms) during tachycardia indicates anterograde conduction through the AV node (orthodromic AVRT), which is the most common arrhythmia in WPW syndrome 3

• Wide QRS complex (≥120 ms) during tachycardia indicates anterograde conduction through the accessory pathway (pre-excited AF or antidromic AVRT), which carries risk of degeneration to ventricular fibrillation 1, 3

Treatment Algorithm Based on Arrhythmia Type

For Narrow-Complex Tachycardia (Orthodromic AVRT)

• First-line: Vagal maneuvers (Valsalva or carotid sinus massage) terminate up to 25% of cases 1

• Second-line: Adenosine 6 mg IV push through a large antecubital vein followed immediately by 20 mL saline flush; if no conversion in 1-2 minutes, give 12 mg IV push 1, 3

  • Adenosine terminates approximately 95% of orthodromic AVRT by blocking AV nodal conduction 3
  • Critical safety requirement: A defibrillator must be immediately available when administering adenosine to any patient with known or suspected WPW, as it can trigger atrial fibrillation with rapid ventricular rates through the accessory pathway 1, 3

• Third-line alternatives: If adenosine fails or tachycardia recurs, consider longer-acting AV nodal blocking agents (diltiazem, verapamil, or beta-blockers) only for narrow-complex tachycardia 1

For Wide-Complex Tachycardia (Pre-Excited Atrial Fibrillation)

• Hemodynamically unstable patients: Immediate direct-current cardioversion is the only appropriate intervention 1, 2

• Hemodynamically stable patients: IV procainamide or ibutilide to restore sinus rhythm or slow ventricular rate 1, 2

  • These agents slow conduction through the accessory pathway rather than the AV node 2, 3
  • Flecainide and propafenone are alternative Class IC agents that prolong accessory pathway refractory periods 4, 5

Absolutely Contraindicated Medications in Pre-Excited AF

Never administer the following drugs in patients with WPW who have wide-complex tachycardia or pre-excited atrial fibrillation, as they accelerate conduction through the accessory pathway and can precipitate ventricular fibrillation: 1, 2

• Adenosine (contraindicated in wide-complex WPW tachycardia despite being first-line for narrow-complex) 1, 3
• Digoxin (oral or IV) 1, 2
• Nondihydropyridine calcium channel blockers (verapamil, diltiazem—oral or IV) 1, 2
• Beta-blockers (including metoprolol) can worsen outcomes by accelerating accessory pathway conduction during AF 2
• IV amiodarone 1

The mechanism of harm is that these AV nodal blocking agents slow conduction through the normal AV node but do not affect the accessory pathway, leading to preferential conduction through the bypass tract with potentially fatal rapid ventricular rates 2

Important Clinical Caveats

• Risk stratification matters: Patients with short RR intervals (<250 ms) between pre-excited beats during atrial fibrillation, history of symptomatic tachycardia, or multiple accessory pathways are at highest risk for sudden cardiac death (2.2% annual risk in symptomatic patients vs 0.15-0.2% in general WPW population) 2

• Adenosine dosing adjustments: Reduce initial dose to 3 mg in patients taking dipyridamole or carbamazepine, those with transplanted hearts, or if given by central venous access; larger doses may be required for patients on theophylline or caffeine 1

• Post-conversion monitoring: After successful termination of any WPW-related arrhythmia, monitor closely for recurrence and consider definitive therapy 1

Definitive Management

• Catheter ablation of the accessory pathway is the first-line definitive treatment for symptomatic WPW patients, with success rates >95% and complication rates <1-2% in experienced centers 1, 2

• Ablation is particularly indicated for patients with syncope due to rapid heart rate, short bypass tract refractory period, or recurrent symptomatic arrhythmias 1, 2

• This approach avoids lifelong antiarrhythmic drug therapy and eliminates the risk of sudden cardiac death from the accessory pathway 2