Which ECG finding is characteristic of Atrial Fibrillation?

• A. No P waves
• B. Regular rhythm with P waves preceding each QRS
• C. Sawtooth pattern
• D. Wide QRS complexes

Answer: (A)

In atrial fibrillation the atrial electrical activity becomes chaotic, so there are no discrete atrial depolarizations visible on the ECG. That means you don’t see distinct P waves; instead, there may be irregular, fibrillatory activity in the baseline and an irregularly irregular ventricular rate as the AV node conducts impulses at variable intervals. This combination—no clear P waves with an irregular rhythm—is the hallmark feature of AF.

Knowing what the other patterns represent helps: a regular rhythm with P waves before each QRS is normal sinus rhythm, a sawtooth pattern points to atrial flutter, and wide QRS complexes suggest a ventricular conduction problem or a wide complex rhythm rather than AF.