Right atrial enlargement

Right atrial enlargement is less common, and harder to delineate on chest radiograph, than left atrial enlargement.

Pathology

Causes

Enlargement of the right atrium can result from a number of conditions, including:

• raised right ventricular pressures
  • pulmonary arterial hypertension
  • cor pulmonale
• valvular disease
  • tricuspid regurgitation
  • tricuspid stenosis
  • Ebstein's anomaly
• atrial septal defect (ASD)
• atrial fibrillation (AF)
• dilated cardiomyopathy

Clinical presentation

ECG

• amplitude of P wave in lead II > 2.5 mm
  • often demonstrate "peaked" morphology
• initial positive deflection of P wave in lead V1 > 1.5 mm

Radiographic features

Plain radiograph

On a frontal view, the right atrium is visible because of its interface with the right middle lobe. Subtle and moderate right atrial enlargement is not accurately determined on plain films because there is normal variability in the shape of the right atrium. Features are non-specific but include ^{2, 3}:

• enlarged, globular heart
• narrow vascular pedicle
• gross enlargement of the right atrial shadow, i.e. increased convexity in the lower half of the right cardiac border
  • right atrial convexity is more than 50% of the cardiovascular height
  • right atrial margin is more than 5.5 cm from the midline

CT/MRI

There are no accepted standard reference measurements, and enlargement is usually determined qualitatively on CT or MRI. RA volume is not routinely recorded on echocardiography. Suggested measurements include ⁵:

• right atrial normal size (measured at end systole on four chamber view)
  • long axis: 3.4-5.3 cm
  • short axis: 2.6-4.4 cm
  • area: 10-18 cm²
    • echocardiography estimates tend to be larger than on CT or MRI