What characteristic of WPW syndrome is typically observed in an ECG?

In Wolff-Parkinson-White (WPW) syndrome, the characteristic features observed on an electrocardiogram (ECG) include a short PR interval and the presence of delta waves. The short PR interval occurs due to the presence of an accessory pathway, which allows for premature conduction from the atria to the ventricles. This bypass results in a faster depolarization and subsequently a shorter interval between the atrial and ventricular contraction.

The delta wave is a distinctive finding in WPW syndrome. It represents the slurred upstroke of the QRS complex that results from the early activation of the ventricles through the accessory pathway. This phenomenon is typically seen alongside a broad QRS complex due to the altered conduction through both the normal conduction system and the accessory pathway. Therefore, the presence of these two features – the short PR interval and delta waves – is what makes option A the correct choice in identifying the hallmark characteristics of WPW syndrome on an ECG.