What are the typical ECG changes in atrial fibrillation (AFib)?

ECG Changes in Atrial Fibrillation

Atrial fibrillation is characterized on ECG by the replacement of consistent P waves with rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing, associated with an irregular ventricular response when atrioventricular conduction is intact. 1, 2

Key ECG Characteristics of Atrial Fibrillation

• Absence of P waves: Normal P waves are replaced by fibrillatory waves (f waves) that vary in size, shape, and timing 1, 2
• Irregular ventricular response: Completely irregular RR intervals when AV conduction is intact 1
• Fibrillatory waves: Rapid oscillations that can be classified as:
  • Coarse fibrillatory waves: Amplitude ≥0.1 mV 3, 4
  • Fine fibrillatory waves: Amplitude <0.1 mV 3, 4
• Variable ventricular rate: Depends on AV node properties, vagal/sympathetic tone, and medication effects 1

Diagnostic Nuances

• Regular RR intervals may occasionally be seen in AF with:
  • AV block 1, 2
  • Ventricular or junctional tachycardia 1, 2
  • Pacemaker rhythm 1
• Extremely rapid ventricular rates (>200 beats/min) suggest the presence of an accessory pathway 1, 2
• Wide QRS complex with rapid irregular rhythm suggests AF with bundle branch block or conduction over an accessory pathway 1
• In patients with implanted pacemakers, temporary inhibition of the pacemaker may be needed to expose atrial fibrillatory activity 1

Related Arrhythmias and Differential Diagnosis

• Atrial flutter: Often coexists with or transitions to/from AF 1

  • Characterized by regular saw-tooth pattern (flutter waves) particularly visible in leads II, III, aVF, and V1 1, 2
  • Atrial rate typically 240-320 beats/min 1, 2
  • Often presents with 2:1 AV block (ventricular rate 120-160 beats/min) 1, 2
  • May be misdiagnosed as AF when atrial activity is prominent in multiple leads 1, 2

• Other supraventricular tachycardias: Can trigger AF 1

  • Focal atrial tachycardias 1
  • AV reentrant tachycardias 1
  • AV nodal reentrant tachycardias 1

Clinical Significance of Fibrillatory Wave Characteristics

• Coarse fibrillatory waves (≥0.1 mV):

  • Associated with higher success rates of electrical cardioversion 5, 3
  • Better maintenance of sinus rhythm after cardioversion (72% vs 42% at 6 weeks) 3

• Fine fibrillatory waves (<0.1 mV):

  • Associated with larger left atrial diameter and sustained AF 4
  • Independent predictor of heart failure events (HR 1.31,95% CI 1.07-1.61) 4
  • May represent more advanced atrial remodeling 4

Diagnostic Value of Short Episodes

• Even short irregular supraventricular tachycardia episodes without P waves (<70 beats) are associated with:
  • Increased risk of developing sustained AF (HR 4.95% CI 2.06-11.9) 6
  • Higher risk of ischemic stroke 6
  • May represent early stages of AF or atrial myopathy 6

Physiological Factors Affecting Fibrillatory Waves

• Frequency of fibrillatory waves can be modulated by autonomic influences, particularly parasympathetic activity 7
• Spatial and temporal patterns of acetylcholine release affect fibrillatory wave characteristics 7
• These variations may explain some of the dynamic changes seen in f-wave morphology during continuous monitoring 7