Does atrial fibrillation (afib) have a normal P wave?

Atrial Fibrillation and P Waves

Atrial fibrillation does not have P waves; instead, P waves are replaced by rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing. 1, 2

ECG Characteristics of Atrial Fibrillation

Atrial Activity

• The normal, organized P waves seen in sinus rhythm are absent in atrial fibrillation
• Instead, the ECG shows:
  • Rapid oscillations or fibrillatory waves
  • Variable amplitude, shape, and timing of these waves
  • No clear isoelectric baseline between deflections 1

Ventricular Response

• Irregular ventricular response (irregular R-R intervals) when AV conduction is intact
• Often rapid ventricular rate, though this depends on:
  • Electrophysiological properties of the AV node
  • Vagal and sympathetic tone
  • Presence/absence of accessory pathways
  • Effect of medications 1

Diagnostic Criteria for Atrial Fibrillation

The European Society of Cardiology defines AF by these characteristics 1:

1. "Absolutely" irregular RR intervals (no repetitive pattern)
2. No distinct P waves on the surface ECG
3. Atrial cycle length (when visible) is usually variable and <200 ms (≥300 bpm)

Differentiating from Related Arrhythmias

Atrial Flutter

• Has organized, regular "saw-tooth" pattern (flutter waves)
• Flutter waves are particularly visible in leads II, III, aVF, and V1
• Atrial rate typically 240-320 beats per minute
• Often occurs with 2:1 AV block, producing ventricular rate of 120-160 bpm 1

Other Supraventricular Tachycardias

• Focal atrial tachycardias, AV reentrant tachycardias, and AV nodal reentrant tachycardias show:
  • Distinct P waves separated by an isoelectric baseline
  • P wave morphology that can help localize the origin 1

Clinical Implications

• The absence of P waves and presence of fibrillatory waves reflect uncoordinated atrial activation 1
• This uncoordinated activation results in deterioration of atrial mechanical function, reducing cardiac output by 5-15% 1
• Even short irregular supraventricular tachycardias without P waves are associated with increased risk of future AF diagnosis and ischemic stroke 3

Diagnostic Pitfalls

• Atrial flutter may be misdiagnosed as AF when atrial activity is prominent in more than one ECG lead 1
• In patients with pacemakers, temporary inhibition of the pacemaker may be necessary to expose atrial fibrillatory activity 1
• Regular R-R intervals may occasionally occur in AF when there is AV block or ventricular/junctional tachycardia 1

The absence of P waves is a defining characteristic of atrial fibrillation and reflects the underlying pathophysiology of disorganized atrial electrical activity that distinguishes this arrhythmia from normal sinus rhythm and other supraventricular arrhythmias.