What is atrial fibrillation with aberrancy?

Atrial Fibrillation with Aberrancy

Atrial fibrillation with aberrancy is a condition where atrial fibrillation is accompanied by abnormal ventricular conduction, resulting in wide QRS complexes that can be mistaken for ventricular tachycardia. This phenomenon occurs when a relatively short R-R interval follows a long R-R interval during atrial fibrillation, causing the QRS complex to be conducted with aberration (Ashman phenomenon) 1.

Pathophysiology

Atrial fibrillation itself is characterized by:

• Uncoordinated atrial activation with consequent deterioration of atrial mechanical function
• Irregular R-R intervals on ECG
• Absence of distinct P waves, replaced by rapid oscillations or fibrillatory waves
• Irregular ventricular response when AV conduction is intact 1

When aberrant conduction occurs during AF:

• The QRS complexes become wide
• This aberrancy is facilitated by the irregularity of the ventricular response
• Typically follows a pattern where a long interval is followed by a relatively short interval
• The QRS complex that closes the short interval is often aberrantly conducted 1

Mechanism of Aberrancy

The aberrant conduction during AF occurs due to:

1. Ashman Phenomenon: When a relatively short R-R interval follows a long R-R interval, the QRS complex that closes the short interval is conducted with aberration 1

2. Rate-Related Bundle Branch Block: At faster heart rates, one of the bundle branches may not have sufficient time to recover its conductivity, leading to a wide QRS complex 1

3. Fixed Bundle Branch Block: Some patients may have pre-existing bundle branch block that is always present 1

Differential Diagnosis

It's crucial to differentiate atrial fibrillation with aberrancy from:

• Atrial fibrillation with pre-excitation (WPW syndrome): In this condition, conduction occurs over an accessory pathway, which can result in a dangerously rapid ventricular rate 1
• Ventricular tachycardia: A rapid, irregular, sustained, wide-QRS-complex tachycardia strongly suggests AF with aberrant conduction or underlying bundle-branch block 1

Clinical Significance

Understanding AF with aberrancy is important because:

• It can be mistaken for more serious arrhythmias like ventricular tachycardia
• Unlike ventricular tachycardia, AF with aberrancy doesn't typically require immediate cardioversion
• Treatment should focus on managing the underlying atrial fibrillation
• Misdiagnosis can lead to inappropriate therapy

Management Considerations

The management of AF with aberrancy focuses on treating the underlying AF:

• Rate control with beta-blockers or non-dihydropyridine calcium channel blockers 2
• Rhythm control when appropriate based on symptoms and patient factors
• Anticoagulation based on stroke risk assessment
• Caution with certain medications:
  • Digitalis, calcium channel antagonists, and beta-blockers should be used cautiously if there's suspicion of an accessory pathway, as they may enhance conduction over the accessory pathway 1

Important Caveats

• In patients with AF and WPW syndrome, drugs that impair AV nodal conduction (like calcium channel blockers) may paradoxically accelerate the ventricular rate by favoring conduction over the accessory pathway 1
• Regular monitoring of the ECG is important to distinguish between AF with aberrancy and more serious arrhythmias
• The hemodynamic consequences of AF with aberrancy depend on ventricular rate control, loss of atrial contraction, and beat-to-beat variability in ventricular filling 1

Understanding the mechanism of aberrant conduction in AF is essential for proper diagnosis and management, as it helps distinguish this relatively benign conduction abnormality from more serious ventricular arrhythmias that require different treatment approaches.