Wolff-Parkinson-White syndrome (WPW) is a heart condition caused by the presence of an extra electrical pathway between the atria and ventricles, known as an accessory pathway or bundle of Kent. This additional connection bypasses the AV node (which normally acts as a gatekeeper, slowing electrical signals between the upper and lower chambers) and can cause fast heart rhythms (tachycardias), and in rare cases, sudden cardiac arrest.
**The ECG finding: pre-excitation**
Because the accessory pathway conducts faster than the normal AV node pathway, part of the ventricle is activated slightly early (pre-excited). This produces a characteristic pattern on the ECG: a short PR interval and a slurred upstroke on the QRS complex called a delta wave. This pattern may be identified incidentally during a routine ECG.
**Arrhythmias in WPW**
The extra pathway can participate in two main types of tachycardia:
– **Atrioventricular re-entrant tachycardia (AVRT):** the most common arrhythmia in WPW, involving a re-entry circuit that travels down the normal pathway and back up the accessory pathway (or vice versa). This causes a fast but regular heart rhythm, typically 150 to 250 beats per minute.
– **Atrial fibrillation with rapid ventricular response:** in people with WPW, AF can be particularly dangerous because the accessory pathway can conduct impulses to the ventricles very rapidly (bypassing the AV node’s rate-limiting function), potentially causing ventricular fibrillation and sudden cardiac death.
**Treatment**
The definitive treatment for WPW is catheter ablation, which uses radiofrequency energy or cryotherapy to destroy the accessory pathway. This is curative in the majority of cases and eliminates the risk of arrhythmia related to the pathway. Risk stratification is important in deciding who needs ablation urgently.
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