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

Atrial flutter is characterized by a "regularly irregular" pattern due to the repetitive and organized nature of the electrical impulses in the atria, while also exhibiting a predictable pattern of atrial contraction. This rhythm often presents a characteristic "sawtooth" appearance on an electrocardiogram, known as "f-waves," which represents the rapid, organized atrial activity. The rate can be relatively constant but the irregularity comes from the variable conduction through the AV node, resulting in a varying ventricular response.

In contrast, other rhythms may have different characteristics: sinus tachycardia features a regular, but rapid heart rate; ventricular fibrillation is chaotic and irregular without identifiable rhythms; and atrial fibrillation, while also irregular, is often described as "irregularly irregular," lacking any predictable patterns. This is what differentiates atrial flutter as a "regularly irregular" rhythm.