A 28-year-old man presents to the emergency department with acute-onset palpitations and irregular rapid heartbeat. His 12-lead ECG shows an irregularly irregular rhythm with wide QRS complexes (>120 ms) of varying morphology, and a ventricular rate of 280 bpm. The structure marked **A** in the diagram demonstrates the characteristic pre-excitation pattern. Which of the following is the MOST appropriate acute management for this patient?

Explanation

## Why Intravenous procainamide or synchronized cardioversion is right The clinical presentation describes **pre-excited atrial fibrillation** (FBI pattern: Fast, Broad, Irregular) — the most dangerous arrhythmia in WPW syndrome. The structure marked **A** (delta wave + short PR + wide QRS) indicates an accessory atrioventricular pathway (Bundle of Kent) that conducts impulses FASTER than the normal AV node, bypassing the protective nodal delay. During atrial fibrillation, rapid atrial impulses conduct directly through the accessory pathway, producing irregular wide-complex tachycardia with varying QRS morphology and dangerously fast ventricular rates (often >250 bpm). The pathophysiology is that the accessory pathway has NO decremental conduction property, so it conducts every atrial impulse rapidly to the ventricle. Management of pre-excited AF requires either **immediate synchronized cardioversion** (preferred for hemodynamic instability or high-risk features) or **IV procainamide/ibutilide** (which block the accessory pathway directly). Both approaches are correct; procainamide is the classic antiarrhythmic choice because it slows conduction through the accessory pathway and can terminate the arrhythmia or slow the ventricular rate to allow safer conversion. (Harrison's 21e, Chapter 246; 2015 ACC/AHA/HRS SVT Guideline) ## Why each distractor is wrong - **Intravenous adenosine 6 mg bolus**: Adenosine blocks the AV node but NOT the accessory pathway. In pre-excited AF, blocking the AV node forces MORE impulses to conduct through the unblocked accessory pathway, potentially ACCELERATING the ventricular rate and precipitating ventricular fibrillation — a critical error. Adenosine is safe only in orthodromic AVRT (narrow QRS), not pre-excited AF. - **Oral verapamil 120 mg followed by beta-blocker therapy**: Verapamil and beta-blockers are AV nodal blockers. Like adenosine, they block the AV node but enhance conduction through the accessory pathway, worsening the arrhythmia and risking VF degeneration. These drugs are contraindicated in pre-excited AF. Additionally, oral dosing is too slow for acute management of a hemodynamically significant arrhythmia. - **Intravenous digoxin loading dose**: Digoxin is an AV nodal blocker and is absolutely contraindicated in pre-excited AF for the same reason as verapamil and beta-blockers — it enhances accessory pathway conduction and can precipitate VF. Digoxin has no role in acute WPW arrhythmia management. **High-Yield:** In WPW pre-excited AF, AVOID all AV nodal blockers (adenosine, beta-blockers, calcium channel blockers, digoxin, amiodarone) — they accelerate conduction through the accessory pathway and risk sudden cardiac death. Use procainamide, ibutilide, or cardioversion instead. [cite: Harrison's Principles of Internal Medicine 21e, Chapter 246 (Tachyarrhythmias); 2015 ACC/AHA/HRS Guideline for the Management of Adult Patients with SVT]