In ECG terminology, what is defined as absolutely regular?

In ECG terminology, the concept of being "absolutely regular" refers to a rhythm where the intervals between successive heartbeats are constant, specifically measured by the R-R intervals on the ECG tracing. When the R-R intervals are constant, it indicates that the electrical impulses that initiate each heartbeat are firing at a uniform pace, creating a predictable and stable rhythm. This is characteristic of rhythms like normal sinus rhythm, where the heart beats in a regular pattern.

The other options do not meet this criterion. For instance, ventricular fibrillation presents as an extremely irregular and chaotic heart rhythm, making it life-threatening. Complete heart block disrupts the communication between the atria and ventricles, often resulting in varying intervals between beats, while an intermittent heart rhythm implies that there are pauses or irregularities in the rhythm. Therefore, only constant R-R intervals align with the definition of a rhythm that is absolutely regular.