What is it called when there is no variation of R-R intervals in an ECG reading?

The term that best describes a situation where there is no variation of R-R intervals in an ECG reading is "absolutely regular." This indicates a scenario where the intervals between heartbeats remain constant, reflecting a uniform rhythm in the electrical activity of the heart. This consistency in R-R intervals suggests that the heart is beating in a steady and predictable manner, which is crucial for assessing the heart's health and rhythm.

In contrast, the other terms do not convey the same specific meaning. For example, while "regular" could imply a consistent rhythm, it does not explicitly indicate the lack of any variations. "Irregular" clearly denotes variability in the intervals, which is the opposite of what is being described. The term "consistent" could suggest steadiness in some contexts but lacks the precision to define the exact nature of R-R intervals being discussed. Thus, "absolutely regular" sharply captures the absence of variation in R-R intervals, making it the most accurate choice.