What pharmacotherapy is indicated for a patient with Wolff-Parkinson-White (WPW) syndrome presenting with worsening palpitations, diaphoresis, and electrocardiogram (ECG) changes?

Management of Wolff-Parkinson-White Syndrome with Worsening Palpitations

Intravenous procainamide is the indicated pharmacotherapy for this patient with Wolff-Parkinson-White syndrome presenting with worsening palpitations and diaphoresis. 1

Rationale for Procainamide Selection

The American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines provide a Class I recommendation (Level of Evidence: C) for intravenous procainamide in patients with pre-excited atrial fibrillation and rapid ventricular response who are not hemodynamically compromised 1. This patient's presentation with worsening palpitations, diaphoresis, and stable blood pressure (108/77) is consistent with pre-excited atrial fibrillation in WPW syndrome that requires immediate intervention.

Why NOT the other options:

1. Diltiazem (Calcium channel blocker) - CONTRAINDICATED

   • The FDA explicitly states that diltiazem "should not be used in patients with atrial fibrillation or atrial flutter associated with an accessory bypass tract such as in Wolff-Parkinson-White (WPW) syndrome" 2
   • Guidelines classify AV nodal blocking agents like calcium channel antagonists as Class III: Harm (potentially dangerous) in WPW with pre-excited AF 1, 3

2. Amiodarone - CONTRAINDICATED

   • Guidelines specifically warn against intravenous amiodarone in patients with WPW syndrome who have pre-excited AF as it can accelerate the ventricular rate and potentially precipitate ventricular fibrillation 1
   • This carries a Class III: Harm recommendation with Level of Evidence: B 1

3. Adenosine - CONTRAINDICATED

   • Like other AV nodal blocking agents, adenosine is contraindicated in WPW with pre-excited AF 1, 3
   • It can accelerate conduction through the accessory pathway, potentially precipitating ventricular fibrillation 3

Pathophysiology and Management Principles

In WPW syndrome with pre-excited atrial fibrillation:

• The accessory pathway can conduct impulses at dangerously high rates
• AV nodal blocking agents (diltiazem, amiodarone, adenosine) block the normal AV node but not the accessory pathway
• This results in preferential conduction through the accessory pathway, which can lead to extremely rapid ventricular rates and potentially ventricular fibrillation

Procainamide works by:

• Directly slowing conduction through the accessory pathway
• Increasing the refractory period of the accessory pathway
• Potentially converting the arrhythmia to sinus rhythm 4

Clinical Algorithm for WPW with Suspected Pre-excited AF

1. Assess hemodynamic stability:

   • If unstable (hypotension, altered mental status, shock): Immediate electrical cardioversion 1, 3
   • If stable (as in this case): Proceed with pharmacotherapy

2. Pharmacotherapy for stable patients:

   • First-line: IV procainamide 1, 3
   • Alternative: IV ibutilide 1

3. Definitive management:

   • Catheter ablation of the accessory pathway (Class I recommendation for symptomatic patients) 1, 3

Important Cautions

• Never administer AV nodal blocking agents (diltiazem, beta-blockers, digoxin, adenosine) to patients with WPW and suspected pre-excited atrial fibrillation
• Have defibrillation equipment immediately available when treating these patients
• Monitor ECG continuously during treatment
• Consider definitive treatment with catheter ablation after the acute episode resolves

The patient should be referred for electrophysiology study and catheter ablation after stabilization, as this provides definitive treatment with success rates exceeding 95% 3.