WPW syndrome

**Pathophysiology:** Failure of normal separation of atria and ventricles during development leaves an accessory pathway (bundle of Kent) of working myocardium. Unlike the AV node, it has no decremental conduction, so impulses reach the ventricle early (pre-excitation) and cause the delta wave. Normal conduction through the AV node/His-Purkinje system fuses with the early activation, giving a fusion complex: short PR, delta wave, wide QRS, and secondary ST-T changes.

**ECG:** Short PR (<120 ms), delta wave, QRS >110 ms. Pseudo-infarct Q waves may appear. Pathway location can be estimated from delta wave polarity (e.g., a negative delta wave in V1 suggests a right-sided pathway).

**Arrhythmias:** - **Orthodromic AVRT (~95%):** Anterograde conduction through the AV node and retrograde through the accessory pathway. It is a narrow-complex regular tachycardia, and the delta wave is absent during tachycardia. - **Antidromic AVRT (~5%):** Anterograde conduction through the accessory pathway and retrograde through the AV node. It is a wide-complex regular tachycardia. - **Atrial fibrillation with pre-excitation:** This is the dangerous presentation. It appears as an irregularly irregular, wide-complex tachycardia with variable QRS morphology. The accessory pathway conducts rapidly and can degenerate into ventricular fibrillation and sudden cardiac death.

**Management:** - **Stable orthodromic AVRT:** Vagal maneuvers, then adenosine. Alternatives are verapamil or diltiazem, or synchronized cardioversion if unstable. - **AF with WPW or antidromic AVRT:** Give procainamide or ibutilide. If unstable, give synchronized DC cardioversion. **Avoid AV nodal blockers** (β-blockers, calcium channel blockers, digoxin, adenosine, amiodarone). They block the AV node and favor conduction down the accessory pathway, which can precipitate VF. - **Definitive therapy:** Catheter radiofrequency ablation of the accessory pathway, which has a high cure rate. It is indicated for symptomatic patients, high-risk occupations or athletes, and those with AF and pre-excitation.

**Associations:** Ebstein anomaly (often right-sided pathways; maternal lithium exposure), hypertrophic cardiomyopathy, mitral valve prolapse, and familial forms (PRKAG2 mutation). **WPW pattern** means ECG findings alone; **WPW syndrome** means pre-excitation plus symptomatic tachyarrhythmias.

**Board pearls:** The question stem often gives a young patient with palpitations and a delta wave. If it shows AF with a wide, irregular tachycardia, the answer is procainamide (or cardioversion), not diltiazem, digoxin, or a β-blocker.