Which event is characterized by a narrower than normal PR interval due to a premature P wave?

The event characterized by a narrower than normal PR interval due to a premature P wave is a premature atrial contraction, commonly referred to as a PAC. In this scenario, the P wave appears earlier than expected and can appear abnormal in shape, resulting in a shorter PR interval. This early contraction occurs when an ectopic focus in the atria fires before the sinus node can initiate the next normal impulse.

Typically, PACs do not have a significant effect on the heart's overall rhythm, but they can disrupt the regularity. The narrow PR interval is significant because it indicates that the conduction through the AV node is occurring rapidly, allowing for a quick transition to the ventricular response following the early P wave.

The other choices involve different types of rhythms or may not necessarily present with the distinct combination of a premature P wave and a shortened PR interval that is characteristic of PACs. Thus, identifying the PAC is crucial for understanding this specific arrhythmia behavior.