What is a common characteristic of premature atrial contractions (PACs)?

Premature atrial contractions (PACs) are characterized by an early depolarization of the atria, resulting in an irregular rhythm with the presence of an early P wave. This early P wave occurs before the next expected sinus P wave, which disrupts the regularity of the heart rhythm. This irregularity is a key feature of PACs and is what distinguishes them from normal sinus rhythm.

In PACs, while there may still be P waves present, their timing is not consistent with the normal pacing of the heart's electrical conduction system, which leads to the characteristic irregularity. Other options describing the PACs either suggest an incorrect regularity or imply a consistent nature that does not align with the inherent nature of PACs. Thus, the identification of PACs is fundamentally tied to their irregular rhythm stemming from these early atrial contractions.