What rhythm is characterized by a "regularly irregular" pattern?

The rhythm described as "regularly irregular" is typically characterized by a recurring pattern of disruption in normal heart rhythm, and premature atrial contractions (PACs) exemplify this phenomenon effectively. In this rhythm, the heart beats normally but is interrupted occasionally by an early heartbeat originating from the atria. This creates a pattern where the normal sinus rhythm is occasionally interrupted in a systematic way, making it identifiable and predictable, hence "regularly irregular."

In essence, you can recognize PACs because they often appear at consistent intervals following a regular heartbeat, leading to an underlying pattern that deviates from the norm but still maintains a rhythm that can be tracked. This predictable manner distinguishes PACs from other dysrhythmias, such as fibrillation, which is chaotic and irregular without any discernible pattern.