How is the regularity of Atrial Flutter best described?

Atrial flutter is characterized by a consistent rapid reentrant circuit within the atria, typically resulting in a distinctive "sawtooth" pattern on an electrocardiogram, specifically in the inferior leads. This reentrant circuit can produce a regular atrial rate, commonly around 240 to 340 beats per minute, which is usually perceived as a regular rhythm.

However, the ventricular response in atrial flutter can vary widely depending on the conduction through the AV node. If there is a fixed AV conduction ratio (for instance, 2:1), the ventricular response will also be regular. On the other hand, if the AV node conducts impulses variably (for example, 1:1 or 3:1), this can lead to an irregular ventricular rate.

Therefore, since both regular and variable patterns can emerge in atrial flutter, describing the regularity as "regular or irregular" accurately encompasses the potential diversity in rhythm presentation, making the selected answer the most appropriate one.