Which of the following is an electrical activity that can be detected in patients with atrial fibrillation?

In patients with atrial fibrillation, the characteristic finding is an irregularly irregular rhythm. This term describes the nature of the heart's electrical activity during atrial fibrillation, where instead of having a consistent pattern of electrical impulses that lead to regular heartbeats, the impulses are chaotic and lead to an unpredictable and uneven rhythm. This irregularity is a hallmark of the condition, as it contrasts with normal heart rhythms, which can either be regular or sinus in nature.

Other options, like sinus rhythm and regular rhythm, indicate more stable and predictable electrical activity, which is not present in atrial fibrillation. A flatline indicates a complete cessation of electrical activity, which is not consistent with the oscillating activity seen in atrial fibrillation. Thus, recognizing the irregularly irregular rhythm is crucial for diagnosing and managing atrial fibrillation effectively.