A short PR interval with a delta wave on electrocardiogram is diagnostic of which condition?

• A. Wolff-Parkinson-White syndrome
• B. Second-degree AV block
• C. Sick sinus syndrome
• D. Long QT syndrome

Answer: (A)

This ECG pattern shows preexcitation of the ventricles from an accessory conduction pathway, which is classic for Wolff-Parkinson-White syndrome. The accessory pathway bypasses part of the normal AV nodal conduction, so impulses reach the ventricles early, causing a slurred upstroke at the start of the QRS (the delta wave) and a shortened PR interval. The QRS becomes wider because part of the ventricles is depolarized early via the accessory pathway while the rest are activated through the normal His-Purkinje system. This preexcitation explains why WPW is associated with reentrant tachyarrhythmias such as AV reciprocating tachycardia. Other conditions produce different ECG patterns: for example, AV block would show dropped beats with variable PR intervals, sick sinus syndrome presents with bradycardia or pauses, and long QT shows a prolonged QT interval.