In a young woman with known Wolff–Parkinson–White syndrome presenting with palpitations, wide‑complex atrial fibrillation and tachycardia, what is the most appropriate intravenous medication?

Amiodarone is the Most Appropriate Intravenous Medication

In this young woman with WPW syndrome presenting with wide-complex atrial fibrillation at 200 bpm, intravenous amiodarone (option C) is the correct answer among the choices provided, though it is important to understand this is a second-line option when first-line agents are unavailable.

Critical Understanding of WPW with Pre-Excited AF

The wide QRS complexes indicate pre-excitation—conduction is occurring through the accessory pathway rather than the AV node. This is a potentially life-threatening situation because:

• AV nodal blocking agents are absolutely contraindicated (Class III recommendation) in pre-excited AF, as they block the AV node while leaving the accessory pathway unopposed, potentially accelerating ventricular rates and precipitating ventricular fibrillation 1, 2, 3

Why Each Option is Right or Wrong

Options A, B, and D are Contraindicated (Class III - Harmful)

• Metoprolol (beta-blocker): Explicitly contraindicated—can promote preferential conduction through the accessory pathway, leading to life-threatening ventricular arrhythmias 1, 2, 3, 4

• Digoxin: Contraindicated—decreases the effective refractory period of the accessory pathway, increasing ventricular rate and risk of ventricular fibrillation 1, 2, 3, 5

• Diltiazem (calcium channel blocker): Contraindicated—selectively blocks the AV node without affecting the accessory pathway, potentially precipitating ventricular fibrillation 1, 2, 3, 4

Option C: Amiodarone - The Correct Answer (with Important Caveats)

Amiodarone is acceptable as a Class IIb recommendation when first-line agents (procainamide or ibutilide) are unavailable 1, 3. Among the four options provided, it is the only non-contraindicated choice.

The Ideal Management Algorithm (Beyond the Question Options)

Step 1: Assess Hemodynamic Stability

• If hemodynamically unstable: Immediate electrical cardioversion (Class I recommendation) 1, 3
• If stable: Proceed to pharmacologic therapy 1, 3

Step 2: First-Line Pharmacologic Therapy (Not in Options)

• IV procainamide or IV ibutilide are the Class I recommended first-line agents for stable patients with pre-excited AF and wide QRS complexes 1, 3
• Procainamide causes complete or incomplete block in the accessory pathway and significantly reduces ventricular rate 5, 6
• Dosing: Procainamide 100 mg IV every 5 minutes until arrhythmia suppresses (maximum 500-600 mg initially, up to 1 gram total), or loading infusion of 20 mg/mL at 1 mL/min for 25-30 minutes 7

Step 3: Second-Line Option When First-Line Unavailable

• IV amiodarone may be considered (Class IIb) only when procainamide or ibutilide are unavailable 1, 3
• This is the situation presented in your question—amiodarone is the only acceptable option among the choices given

Critical Pitfalls to Avoid

• Never administer AV nodal blockers (beta-blockers, calcium channel blockers, digoxin, adenosine) in pre-excited AF—this is a Class III contraindication with Level of Evidence B 1, 2, 3
• The wide QRS complexes are the key ECG finding indicating pre-excitation and accessory pathway conduction 1, 3
• Even though vital signs are not mentioned, assume stability for pharmacologic therapy; if any signs of instability develop, immediately cardiovert 1, 3

Definitive Long-Term Management

• Catheter ablation of the accessory pathway is the definitive treatment for symptomatic WPW patients, with success rates >95% (Class I recommendation) 1, 2, 3
• This should be strongly considered for this patient after acute management 3