A 35-year-old man with a known history of Wolff-Parkinson-White (WPW) syndrome presents to the emergency department with palpitations and chest discomfort. His wife reports he collapsed briefly during the episode. Vital signs: HR 220 bpm (irregular), BP 80/50 mmHg, RR 22/min, SpO₂ 92% on room air. 12-lead ECG shows a wide complex tachycardia with a rate of 220 bpm and an irregular rhythm. The QRS duration is 140 ms. Which is the most appropriate immediate management?

Explanation

## Management of Unstable Atrial Fibrillation with Pre-excitation (WPW Syndrome) ### Clinical Context **Key Point:** This patient has hemodynamic instability (BP 80/50, syncope, altered mental status signs) with a wide complex irregular tachycardia in the setting of known WPW syndrome. The irregular rhythm with variable QRS morphology and rate suggests **atrial fibrillation conducting over an accessory pathway** (AF with pre-excitation). ### Why This Is Dangerous **High-Yield:** In WPW syndrome, the accessory pathway (AP) has a shorter refractory period than the AV node. During atrial fibrillation: - The AV node conducts some impulses (slower, longer refractory period) - The accessory pathway conducts others (faster, shorter refractory period) - Result: **very rapid ventricular rates** (often >250 bpm) that can degenerate into ventricular fibrillation ### ECG Features in This Case - **Wide complex tachycardia** (QRS 140 ms) — indicates conduction over the accessory pathway - **Irregular rhythm** — confirms atrial fibrillation - **Rate 220 bpm** — rapid but not the fastest possible (can reach 300+ bpm) ### Hemodynamic Instability **Clinical Pearl:** The patient is: - Hypotensive (80/50) - Tachypneic (RR 22) - Hypoxic (SpO₂ 92%) - Had syncope These are **absolute indications for immediate synchronized DC cardioversion**. ### Why NOT Adenosine or Verapamil? ```mermaid flowchart TD A[AF with WPW + Hemodynamic Instability]:::urgent --> B{Drug or Shock?}:::decision B -->|Adenosine/Verapamil| C[CONTRAINDICATED]:::urgent C --> D[Blocks AV node only]:::action D --> E[AP remains patent]:::action E --> F[Increased conduction via AP]:::urgent F --> G[Faster ventricular rate]:::urgent G --> H[Risk of VF]:::urgent B -->|Synchronized DC Cardioversion| I[CORRECT]:::action I --> J[Immediate rhythm conversion]:::outcome ``` **Warning:** Adenosine and verapamil block the AV node but have NO effect on the accessory pathway. By blocking the AV node, they preferentially shunt conduction to the faster accessory pathway, **paradoxically increasing the ventricular rate and risking ventricular fibrillation**. These drugs are **absolutely contraindicated** in AF with pre-excitation. ### Management Algorithm for WPW-Related SVT | Clinical State | Rhythm | Management | |---|---|---| | **Hemodynamically stable** | AVNRT/AVRT | Adenosine or verapamil | | **Hemodynamically stable** | AF with WPW | IV procainamide or amiodarone (slows AP conduction) | | **Hemodynamically unstable** | Any SVT/AF | **Synchronized DC cardioversion** | | **Hemodynamically unstable** | AF with WPW | **Synchronized DC cardioversion** (do NOT use adenosine/verapamil) | ### Correct Management: Synchronized DC Cardioversion 1. **Immediate action:** Synchronized DC cardioversion at 100 J (or biphasic equivalent) 2. **Rationale:** Converts the arrhythmia directly, restoring normal sinus rhythm and AV nodal conduction 3. **Expected outcome:** Restoration of sinus rhythm, improved blood pressure, resolution of symptoms 4. **Post-conversion:** Admit for monitoring; consider radiofrequency ablation of the accessory pathway (definitive treatment) **High-Yield:** In any hemodynamically unstable patient with SVT (regardless of mechanism), synchronized DC cardioversion is the fastest and most reliable treatment. ### Why Amiodarone Is Second-Line Here While IV amiodarone (150 mg over 10 minutes) is appropriate for stable AF with WPW (it slows both AV nodal and AP conduction), it takes time to work. In a **hemodynamically unstable patient**, waiting for drug effect is unsafe — immediate cardioversion is indicated. [cite:Harrison 21e Ch 297]