Causes of Right Atrial Enlargement
Right atrial enlargement results primarily from volume overload due to tricuspid regurgitation, pressure overload from pulmonary hypertension and right ventricular dysfunction, or structural abnormalities including congenital heart defects.
Primary Mechanisms
Volume Overload Conditions
Tricuspid regurgitation is the most common cause of right atrial enlargement, occurring through two distinct pathways 1:
- Secondary (functional) tricuspid regurgitation develops from RV dilation and/or tricuspid annular dilation, which impairs valve coaptation and leads to progressive right atrial enlargement 1
- The underlying causes include left-sided heart valve diseases, pulmonary hypertension, congenital heart defects, and cardiomyopathy 1
- Atrial functional tricuspid regurgitation (AF-TR) represents an underappreciated mechanism where right atrial enlargement itself causes tricuspid regurgitation, most commonly in lone atrial fibrillation but also occurring idiopathically 2
- This creates a vicious cycle: tricuspid regurgitation causes further RV dilation and dysfunction, leading to more right atrial enlargement, increased tricuspid annular dilation and leaflet tethering, which worsens the regurgitation 1
Atrial septal defects cause right atrial enlargement through left-to-right shunting 1, 3:
- The shunt produces RV volume overload and pulmonary overcirculation 1
- Right atrial enlargement occurs with relative preservation of LV chamber size in the presence of significant shunting 1
- Closure is indicated when right atrial and RV enlargement are documented, with or without symptoms 3
Pressure Overload Conditions
Pulmonary hypertension causes right atrial enlargement through RV dysfunction and secondary tricuspid regurgitation 1:
- Elevated pulmonary pressures lead to RV remodeling, which causes tricuspid annular dilation and papillary muscle displacement 1
- Right atrial enlargement in pulmonary arterial hypertension independently predicts clinically significant supraventricular arrhythmias, with a threshold of 21.7 cm²/m² identifying high-risk patients 4
Ebstein's anomaly produces characteristic right atrial enlargement through multiple mechanisms 1, 3:
- Apical displacement of septal and posterior tricuspid leaflets causes atrialization of the RV inflow portion 1
- Redundancy, tethering, and fenestrations of the anterior leaflet result in varying degrees of tricuspid regurgitation 1
- More than 50% have an atrial-level shunt (patent foramen ovale or secundum ASD) 1
- The chest x-ray shows severe right atrial enlargement with a "globular" cardiac contour and clear lung fields 1, 3
Post-Cardiac Transplant
Right atrial enlargement after heart transplantation results from surgical anastomosis technique 1:
- Biatrial anastomosis creates enlargement of the long-axis atrial dimension with a ridge at the anastomosis site 1
- The surgical technique influences tricuspid regurgitation occurrence due to altered right atrial morphology 1
Rare Causes
Idiopathic right atrial aneurysmal dilation represents an uncommon cause characterized by 5, 6:
- Massive disproportionate right atrial enlargement (volumes exceeding 1400 mL reported) without typical associations like Ebstein's anomaly, tricuspid stenosis, or pulmonary hypertension 5
- Wall thinning and focal fibrosis on histology 6
- Risk of thrombus formation within the giant right atrium 6
Critical Clinical Implications
The enlarged right atrium creates hemodynamic and thrombotic complications 1, 3:
- Stasis within the enlarged chamber predisposes to thrombus formation, particularly with atrial fibrillation 1, 3
- Anticoagulation with warfarin is mandatory for patients with right atrial enlargement and history of paradoxical embolus or atrial fibrillation 1, 3
- Electrophysiological symptoms (atrial arrhythmias including atrial flutter, atrial fibrillation, and sick sinus syndrome) are more common than hemodynamic symptoms in adults 1
- Approximately 25% of Ebstein's patients have one or more accessory conduction pathways, increasing atrial tachycardia risk 1
Right atrial enlargement independently predicts adverse outcomes 4: