Right Atrium

Right atrial size reflects chronic right-sided pressure and volume loading. It should be interpreted with RV size and function, tricuspid valve disease, pulmonary pressures, and estimated right atrial pressure.

Acquisition¶

Assess the right atrium from an RA-focused apical four-chamber view at end ventricular systole, when atrial size is maximal.

Begin with an RV-focused apical four-chamber view.
Tilt superiorly and medially to maximize the RA chamber.
Avoid atrial foreshortening.
Trace from one side of the tricuspid annulus to the other.
Exclude the venae cavae, coronary sinus, and right atrial appendage.

The subcostal view is useful for evaluating the interatrial septum, venae cavae, and normal right atrial variants.

Measurements¶

Indexed right atrial volume using the single-plane method of disks is preferred. RA area and linear dimensions remain acceptable when volumetric assessment is unavailable.

Measurement	Normal	Mild enlargement	Moderate enlargement	Severe enlargement
Major dimension	<5.4 cm	5.4–5.8 cm	>5.8–6.3 cm	>6.3 cm
Minor dimension	<4.2 cm	4.2–4.7 cm	>4.7–5.1 cm	>5.1 cm
RA area	<19 cm²	19–22 cm²	>22–24 cm²	>24 cm²
RAVi, method of disks	<30 mL/m²	30–36 mL/m²	>36–41 mL/m²	>41 mL/m²

The normal RAVi threshold using the area-length method is approximately <33 mL/m². Measurements obtained using different methods should not be treated as interchangeable.

Important

The former RA area cutoff of 18 cm² has been superseded. The 2025 ASE guideline defines normal RA area as <19 cm².

Measurement Technique¶

RA area and volume¶

Measure at end systole.
Trace the endocardial border from the lateral to septal tricuspid annulus.
Exclude the venae cavae, coronary sinus, and right atrial appendage.
Index volume to body surface area.

Linear dimensions¶

Minor dimension: lateral wall to interatrial septum at the midatrial level
Major dimension: center of the tricuspid annulus to the center of the superior RA wall

Use linear dimensions when the endocardial border is inadequate for volume measurement.

Causes of RA Enlargement¶

Pulmonary hypertension
Chronic RV pressure or volume overload
Significant tricuspid regurgitation
Tricuspid stenosis
Atrial septal defect
Partial anomalous pulmonary venous return
Chronic lung or thromboembolic disease
Atrial fibrillation or flutter
Restrictive cardiomyopathy
Constrictive pericarditis
Congenital heart disease

RA enlargement is not specific for elevated right atrial pressure and should not be used alone to estimate RAP.

See IVC and Right Atrial Pressure.

Normal Variants and Mimics¶

Normal structures that may resemble a mass include:

Crista terminalis
Eustachian valve
Chiari network
Thebesian valve
Lipomatous hypertrophy of the interatrial septum

Evaluate a suspected mass in multiple planes. TEE, ultrasound-enhancing agents, CT, or CMR may be appropriate when TTE remains inconclusive.

Reporting¶

The right atrium is normal in size.

The right atrium is mildly/moderately/severely dilated.

Indexed right atrial volume is ___ mL/m² by the single-plane
method of disks.

A prominent Eustachian valve/Chiari network is present,
representing a normal anatomic variant.

Pitfalls¶

Measuring at end diastole instead of end systole
Using a foreshortened standard four-chamber view
Including the venae cavae, appendage, or coronary sinus in the trace
Relying on a linear dimension when an adequate volume is available
Applying the obsolete RA area cutoff of 18 cm²
Estimating RAP from RA size alone
Mistaking the crista terminalis, Eustachian valve, or Chiari network for a mass
Comparing serial measurements obtained with different methods

Key Points¶

Measure the RA at end systole.
Use an RA-focused apical four-chamber view.
Prefer indexed RA volume by the single-plane method of disks.
Normal RA area is <19 cm².
Normal RAVi by the method of disks is <30 mL/m².
Interpret RA enlargement with the RV, tricuspid valve, and pulmonary-pressure findings.