What is a characteristic feature of an ECG in atrial fibrillation?

In atrial fibrillation, one of the hallmark characteristics on an ECG is the presence of a wavy baseline, often referred to as "fib waves," along with the absence of identifiable P waves. This occurs because the chaotic electrical signals in the atria lead to rapid and irregular contractions that do not produce distinct P waves. Instead, you see a baseline that appears undulating due to the numerous, overlapping electrical impulses that the atria generate, reflecting the disorganized nature of this arrhythmia.

This fundamental ECG finding helps clinicians to differentiate atrial fibrillation from other arrhythmias, as the presence of recognizable P waves is typical in normal sinus rhythm and other atrial arrhythmias such as atrial flutter. In atrial flutter, you would typically observe recurring P wave patterns (often referred to as "sawtooth" patterns), distinguishing it from the chaotic, wave-like appearance seen in atrial fibrillation. The absence of organized P waves is a direct result of the disorganized atrial electrical activity, confirming the diagnosis of this specific arrhythmia.