How is atrial fibrillation (afib) diagnosed?

Diagnosis of Atrial Fibrillation

Atrial fibrillation is definitively diagnosed by electrocardiographic documentation showing irregular R-R intervals, absence of distinct P waves, and irregular atrial activity (fibrillatory waves). 1

ECG Characteristics of Atrial Fibrillation

• AF is characterized by uncoordinated atrial activation with consequent deterioration of atrial mechanical function 1
• On ECG, AF shows replacement of consistent P waves by rapid oscillations or fibrillatory waves that vary in amplitude, shape, and timing 1
• The ventricular response is typically irregular when AV conduction is intact 1
• Regular R-R intervals may occur in the presence of AV block or ventricular/junctional tachycardia 1

Required Diagnostic Testing

• 12-lead ECG during the arrhythmia is the cornerstone for diagnosis 1
• Visual confirmation of the ECG is necessary to confirm the diagnosis 1, 2
• In patients with implanted pacemakers, temporary inhibition of the pacemaker may be needed to expose atrial fibrillatory activity 1

Diagnostic Approach for Suspected AF

Initial Evaluation

• Physical examination may reveal irregular pulse, irregular jugular venous pulsations, and variation in the first heart sound intensity 1
• Physical findings alone are insufficient for definitive diagnosis and require ECG confirmation 3

ECG Documentation Methods

• For patients with persistent AF, a standard 12-lead ECG is usually sufficient 1
• For paroxysmal AF, additional monitoring strategies may be needed 4:
  • 24-hour Holter monitoring (if episodes are frequent) 1
  • Event recorders (if episodes are infrequent) 1
  • Portable ECG recording tools 1
  • Wearable devices with ECG capability 2, 5

Additional Diagnostic Evaluation

Once AF is documented, a minimum evaluation should include:

• Transthoracic echocardiogram to assess 1:

  • Left atrial and right atrial size
  • Left ventricular size and function
  • Valvular heart disease
  • Left ventricular hypertrophy
  • Pericardial disease

• Blood tests 1:

  • Thyroid function tests
  • Renal function
  • Hepatic function

• Chest radiograph (when clinically indicated) to evaluate 1:

  • Lung parenchyma
  • Pulmonary vasculature

Differentiating AF from Related Arrhythmias

• Atrial flutter typically shows a saw-tooth pattern of regular atrial activation (flutter waves) on ECG, particularly visible in leads II, III, aVF, and V1 1
• Atrial tachycardia shows identifiable P waves separated by an isoelectric baseline 1
• Wide-complex tachycardias require careful analysis to distinguish ventricular tachycardia from supraventricular tachycardia with aberrant conduction 3

Common Pitfalls in AF Diagnosis

• Failing to obtain an ECG during symptoms can lead to misdiagnosis 3
• Misdiagnosing AF as atrial flutter when atrial activity is prominent on ECG in more than one lead 1
• In patients with rapid, irregular, wide-QRS-complex tachycardia, consider AF with accessory pathway conduction or AF with underlying bundle-branch block 1
• Extremely rapid rates (over 200 beats/min) suggest the presence of an accessory pathway 1

Special Considerations

• For patients with suspected paroxysmal AF, longer monitoring periods will detect more cases 4
• Post-stroke patients should receive extended cardiac monitoring as a single ECG may miss cases of paroxysmal AF 4
• Consumer wearables with automated AF detection can help diagnose even asymptomatic AF, provided they can record a single-lead ECG rhythm strip 2, 5