Is flecainide contraindicated in Wolff‑Parkinson‑White syndrome, especially in atrial fibrillation or other pre‑excited tachyarrhythmias?

Flecainide in Wolff-Parkinson-White Syndrome

Flecainide is NOT contraindicated in WPW syndrome; in fact, it is specifically recommended as a Class IIa agent for acute management of pre-excited atrial fibrillation and is highly effective for both acute termination and chronic prevention of accessory pathway-mediated tachycardias. 1

Critical Distinction: What IS Contraindicated

The confusion arises because AV nodal blocking agents are absolutely contraindicated in WPW with pre-excited atrial fibrillation, but flecainide works through an entirely different mechanism 1, 2:

• Never use: Digoxin, beta-blockers, non-dihydropyridine calcium channel blockers (diltiazem, verapamil), or adenosine (when QRS ≥120 ms) 1, 2
• These agents are Class III contraindications because they block the AV node while leaving the accessory pathway unaffected, potentially accelerating ventricular rates and precipitating ventricular fibrillation 1, 3

Why Flecainide Works in WPW

Flecainide is a Class Ic antiarrhythmic that directly blocks conduction through the accessory pathway itself, not the AV node 1, 4:

• Blocks anterograde accessory pathway conduction in 40% of cases and prolongs refractoriness in the remainder 4
• Increases the shortest RR interval during pre-excited atrial fibrillation from 218 ms to 320 ms, dramatically slowing dangerous ventricular rates 5
• Converts pre-excited atrial fibrillation to sinus rhythm in the majority of cases 4, 5

Guideline Recommendations for Flecainide in WPW

For acute pre-excited atrial fibrillation with hemodynamic stability:

• Class I recommendation: IV procainamide or IV ibutilide are first-line agents 1, 2, 6
• Class IIa recommendation: IV flecainide is reasonable when very rapid ventricular rates occur 1
• Class IIb recommendation: Flecainide may be considered as an alternative 1

For chronic prevention of tachycardia:

• Oral flecainide prevents clinical recurrences in >60% of cases 1, 4
• Efficacy increases to >90% when combined with a beta-blocker 1
• Long-term success is predicted by abolition of accessory pathway conduction or prevention of tachycardia induction during electrophysiologic testing 4

Clinical Algorithm for WPW with Tachyarrhythmia

Step 1: Assess hemodynamic stability

• If unstable → immediate DC cardioversion 1, 2, 6

Step 2: If stable, identify QRS morphology

• Wide QRS (≥120 ms) = pre-excited atrial fibrillation → use procainamide, ibutilide, or flecainide 1, 2, 6
• Narrow QRS = likely AVRT → adenosine is safe, or use flecainide/procainamide 1

Step 3: Pharmacologic management

• First-line: IV procainamide or IV ibutilide 1, 2, 6
• Alternative: IV flecainide (Class IIa) 1
• Never use AV nodal blockers 1, 2, 3

Step 4: Definitive therapy

• Catheter ablation is first-line definitive treatment with >95% success rate 1, 2, 6

Important Caveats

Proarrhythmic risk: Serious ventricular proarrhythmia with flecainide occurs almost exclusively in patients with structural heart disease 4. Screen for coronary disease, cardiomyopathy, or heart failure before use.

Incessant tachycardia: Oral flecainide may occasionally cause incessant tachycardia, requiring discontinuation 4.

Atrial flutter risk: When using flecainide for chronic suppression, always co-administer an AV nodal blocker to prevent 1:1 conduction during atrial flutter—but this applies only to non-pre-excited rhythms 1. In pre-excited atrial fibrillation, use flecainide alone.

Post-ablation monitoring: Even after successful ablation, atrial fibrillation may recur, especially in older patients, and additional therapy may be needed 2.