Does atrial fibrillation (AFib) cause atrial enlargement?

Does Atrial Fibrillation Cause Atrial Enlargement?

Yes, atrial fibrillation directly causes atrial enlargement through a bidirectional relationship where "AF begets AF"—the arrhythmia itself triggers progressive structural remodeling that perpetuates and worsens the condition. 1

The Bidirectional Mechanism

The relationship between AF and atrial enlargement operates as both cause and consequence:

• AF causes atrial dilation through loss of contractility and increased compliance, with stretch-related growth mechanisms and fibrosis increasing the extracellular matrix, especially during prolonged AF episodes 1
• The reduction of atrial contractility during AF enhances atrial dilatation, leading to persistent AF in a self-perpetuating cycle 1
• This creates the principle that "AF begets AF"—the arrhythmia is fundamentally self-perpetuating through structural remodeling 1

Timeline of AF-Induced Atrial Enlargement

The most recent high-quality evidence demonstrates that AF causes measurable atrial enlargement within 6-12 months:

• Patients with AF develop left atrial enlargement at 1.53 times the rate of matched controls without AF (HR 1.53; 95% CI 1.27-1.85; P < .001), with changes typically manifesting within 6-12 months of diagnosis 2
• In patients maintaining persistent AF over 5 years, left atrial volume progressively increases by 14.3% on average, with even greater increases (21.4%) in patients with more severe heart failure symptoms 3
• Mean left atrial volume increases from 45 to 64 cm³ over time in persistent AF, while right atrial volume increases from 49 to 66 cm³ 1

Reversibility Proves Causation

The strongest evidence that AF causes atrial enlargement comes from cardioversion studies showing reversal:

• When sinus rhythm is restored and maintained for 6 months, left atrial volume decreases by 20% (from 72.6±15.1 to 58.5±13.8 cm³, p<0.05) and right atrial volume decreases by 14% 4
• In patients maintaining sinus rhythm for 5 years, anteroposterior LA dimension decreases by 6% (from 49.7±4.5 to 46.8±4.8 mm) and LA volume decreases by 9.2% 3
• In contrast, patients who relapse into AF show no decrease in atrial size—in fact, their atrial dimensions continue to increase 4, 3

This reversibility with rhythm restoration definitively proves AF itself causes the enlargement, not just underlying heart disease.

Pathophysiological Mechanisms

AF causes atrial enlargement through multiple interconnected pathways:

Structural Remodeling

• Myolysis (loss of sarcomeres), perinuclear glycogen accumulation, and loss of sarcoplasmic reticulum occur as protective adaptations to the high metabolic stress of rapid atrial rates 1
• Fibrosis develops through stretch-activated pathways including renin-angiotensin-aldosterone system (RAAS), transforming growth factor-beta1 (TGF-β1), and connective tissue growth factor (CTGF) 1
• Extracellular matrix accumulation and fibrosis become more pronounced once dilation occurs, creating heterogeneous conduction that perpetuates AF 1

Hemodynamic Changes

• Loss of atrial contractility during AF increases atrial compliance, allowing progressive chamber dilation 1
• Reduced atrial contractility may markedly decrease cardiac output, particularly when diastolic ventricular filling is already impaired 1

Electrical Remodeling

• Progressive shortening of effective refractory periods occurs with increasing AF episode duration, making the arrhythmia more sustained 1
• Conduction abnormalities, effective refractory period dispersion, and ectopic activity develop as consequences of tachycardia-related remodeling 1

Critical Clinical Implications

The AF-induced atrial enlargement has major prognostic significance:

• Atrial enlargement is associated with increased risk for embolic stroke in AF patients 4
• Greater atrial enlargement hampers long-term maintenance of sinus rhythm after cardioversion, making early intervention more successful 4
• Patients with low-voltage areas (<0.5 mV) on electroanatomic mapping have higher post-ablation recurrence rates, reflecting advanced structural remodeling 5

Common Pitfall to Avoid

Do not assume atrial enlargement in AF patients is solely due to underlying heart disease (hypertension, valvular disease, heart failure). While these conditions contribute to atrial enlargement, the AF itself independently causes progressive atrial dilation through the mechanisms described above 1. The reversibility with cardioversion proves AF's direct causal role 4, 3.

The key clinical takeaway: Early rhythm control may prevent or reverse AF-induced atrial enlargement, whereas allowing AF to persist leads to progressive structural remodeling that makes the arrhythmia increasingly difficult to treat 1, 2, 3.