In atrial fibrillation, which ECG finding replaces P waves on the surface ECG?

In atrial fibrillation, which ECG finding replaces P waves on the surface ECG?

• A. The presence of fibrillatory (F) waves instead of P waves
• B. A normal rate with clear P waves
• C. A consistent P:QRS ratio
• D. A wide, peaked T wave

Answer: (A)

In atrial fibrillation, the atria fire chaotically rather than sending organized atrial depolarizations. This means discrete P waves do not appear on the surface ECG. Instead, the atrial activity shows as fibrillatory waves—rapid, irregular baseline oscillations that replace the distinct P waves. The ventricular rhythm becomes irregularly irregular because the AV node conducts these impulses in a highly variable fashion, leading to an unpredictable timing between QRS complexes. That’s why the presence of fibrillatory waves is the best descriptor here. A normal rate with clear P waves would indicate sinus rhythm, not AF. A consistent P:QRS ratio isn’t present in AF due to the variable conduction of impulses to the ventricles. A wide, peaked T wave points to a different issue entirely, such as electrolyte disturbance, not atrial fibrillation.

In atrial fibrillation, the atria fire chaotically rather than sending organized atrial depolarizations. This means discrete P waves do not appear on the surface ECG. Instead, the atrial activity shows as fibrillatory waves—rapid, irregular baseline oscillations that replace the distinct P waves. The ventricular rhythm becomes irregularly irregular because the AV node conducts these impulses in a highly variable fashion, leading to an unpredictable timing between QRS complexes.

That’s why the presence of fibrillatory waves is the best descriptor here. A normal rate with clear P waves would indicate sinus rhythm, not AF. A consistent P:QRS ratio isn’t present in AF due to the variable conduction of impulses to the ventricles. A wide, peaked T wave points to a different issue entirely, such as electrolyte disturbance, not atrial fibrillation.