Which syndrome causes a preexcitation ECG pattern due to an accessory conduction pathway?

• A. Lown-Ganong-Levine syndrome
• B. Sick sinus syndrome
• C. Wolff-Parkinson-White syndrome
• D. Long QT syndrome

Answer: (C)

Preexcitation occurs when an extra conduction pathway connects the atria to the ventricles, bypassing the normal AV nodal delay. Because the ventricle starts to depolarize earlier through this accessory pathway, the ECG shows a delta wave (a slurred upstroke of the initial part of the QRS) and a shortened PR interval, with the QRS complex widened due to premature ventricular activation.

The syndrome that classicly exhibits this pattern due to an accessory pathway is Wolff-Parkinson-White. The delta wave and shortened PR interval together are the hallmark clues that ventricular activation is beginning partly through an abnormal tract rather than solely through the AV node. This pathway predisposes to reentrant tachyarrhythmias, such as AV reentrant tachycardia, and can be risky if atrial fibrillation conducts rapidly down the accessory pathway, sometimes requiring urgent management or definitive treatment with catheter ablation.

Other conditions listed involve different mechanisms: sick sinus syndrome is SA node dysfunction and does not feature preexcitation; long QT syndrome involves prolonged repolarization; and while Lown-Ganong-Levine can cause a short PR interval due to a bypass tract, it typically lacks the delta wave characteristic of WPW.