Evaluation of the Right Atrium Using Echocardiography

The right atrium is the least-studied of the four cardiac chambers, but it carries real diagnostic and prognostic weight — RA size and function reflect the cumulative burden of right heart pressure and volume overload, much as the LA does for the left heart. This tutorial covers RA anatomy, sizing, phasic function, and strain, building directly on the Right Ventricle Evaluation tutorial, where RA size already appeared as a supporting parameter for both RV diastolic assessment and pulmonary pressure estimation.

Anatomy and the Three Phases of RA Function

Anatomically, the RA comprises three parts: the appendage (a triangular structure that pumps blood into the RV during atrial systole), the vestibule of the tricuspid valve (smooth-walled myocardium continuous with the tricuspid leaflets), and the venous component, which receives return from the superior and inferior vena cavae and the coronary sinus. The RA also hosts more embryologic remnants and normal variants than any other chamber — the crista terminalis, the Eustachian valve, and Chiari network among them — genuinely common enough to warrant their own differential; see Approach to Cardiac Masses for how to distinguish these from a true RA mass.

Functionally, the RA performs the same three roles across the cardiac cycle that the LA does — a structural and functional parallel worth keeping in mind, since the two chambers are genuinely analogous:

• Reservoir function — storing venous return while the tricuspid valve is closed during RV systole
• Passive conduit function — releasing that stored blood directly into the RV once the tricuspid valve opens, during early diastole
• Active (booster pump) function — atrial contraction in late diastole, completing RV filling

RA function depends substantially on pericardial integrity — the pericardium constrains the thin-walled atria more than the thick-walled ventricles, and after pericardiotomy, RA contractility falls while RA compliance and reservoir function rise. This same thin-walled compliance is why the RA free wall is the first chamber to buckle under elevated intrapericardial pressure — see Pericardial Effusion and Cardiac Tamponade, where RA systolic collapse is one of the earliest and most specific echocardiographic signs. The relationship between RA function and tricuspid regurgitation is severity-dependent in a genuinely interesting way: mild-to-moderate TR actually enhances all three components of RA function, while severe TR specifically reduces the atrial contraction (booster) contribution to RV filling, even as reservoir and passive conduit function increase further to compensate. Atrial fibrillation, unsurprisingly, is associated with loss of the booster function entirely.

RA Size

The RA-Focused View

As with the RV, a dedicated RA-focused apical view improves measurement accuracy over the standard four-chamber window: starting from the RV-focused view, tilt the transducer superiorly (upward) and medially (toward the sternum) to maximize visualization of the entire RA chamber. This atrial-focused approach has been shown to bring 2D area and volume measurements closer to values obtained by 3D echocardiography.

Normal Values

Measurements are taken at end-ventricular-systole, when the RA reaches its largest volume — the RA equivalent of using end-systole for LA sizing. Current guideline-stated thresholds are somewhat stricter than some reference textbook ranges, which is worth knowing when comparing a report against different sources:

Parameter	ASE 2025 (guideline threshold)	EACVI Textbook (reference mean, range)
RA minor (short-axis) diameter	< 4.2 cm	3.6 cm (2.4–4.6 cm)
RA major (long-axis) diameter	< 5.4 cm	4.6 cm (3.2–5.5 cm)
RA area (planimetry)	< 19 cm²	14 cm² (8–20 cm²)
RA volume index, 2D (method of discs)	< 30 mL/m²	22 mL/m² (12–35 mL/m²)
RA volume index, 3D	< 20 mL/m² (end-diastolic)	19 ± 7 mL/m²

The BSE 2020 guideline gives its own sex-specific area threshold — ≤ 22 cm² (men) / ≤ 19 cm² (women) — a further reminder that, as with RV sizing, different current sources don’t converge on one single number, and consistency within a report matters more than chasing the “most correct” figure across sources.

RA volume is a more accurate reflection of true RA size than a single linear diameter, for the same reason this is true of the LA — the chamber can enlarge asymmetrically, and 2D volume methods (single-plane method of discs or area-length) outperform linear dimensions, even though 2D volume itself correlates only modestly with cardiac MRI or 3D echocardiography (partly from foreshortening, partly from the geometric assumptions 2D methods require). 3D-derived RA volume correlates excellently with cardiac MRI and is the most accurate available method where equipment and image quality allow.

A few points on normal variation worth keeping in mind before calling an RA “enlarged”:

• RA size is not significantly influenced by age, in either sex — unlike some other chamber measurements.
• Elite athletes have a larger RA — by area, volume, and indexed volume — than non-athletes, alongside larger RV and IVC dimensions. An enlarged RA in an athlete is not automatically pathological.
• Because of this, RA enlargement should be interpreted in context — alongside RV function, TR severity, and signs of elevated RA pressure — rather than as an isolated abnormal number.

RA Function: Doppler and Tissue Doppler

Tricuspid inflow, recorded by pulsed-wave Doppler at the leaflet tips from the apical four-chamber view, reflects RA passive conduit and booster pump function together, and is best recorded at held end-expiration. Tissue Doppler at the lateral tricuspid annulus (e′ and a′ velocities) is influenced by both RA and RV function. Representative normal reference values:

Parameter	Reference value (range)
Tricuspid E wave	54 cm/s (33–75 cm/s)
Tricuspid A wave	40 cm/s (19–60 cm/s)
Tricuspid E/A ratio	1.4 (0.7–2.2)
Deceleration time	174 ms (105–243 ms)
TDI lateral tricuspid e′	14 cm/s (7–21 cm/s)
TDI lateral tricuspid a′	13 cm/s (7–21 cm/s)
Tricuspid E/e′ ratio	4 (1–7)

These reference ranges are broadly consistent with the RV diastolic function thresholds covered in the Right Ventricle Evaluation tutorial (normal E/A 0.8–2.1, E/e′ < 6.0) — worth cross-checking against that page, since tricuspid inflow reflects RV diastolic filling as much as it reflects the RA itself.

Hepatic vein flow provides a complementary window onto RA pressure and function: systolic-predominant flow is normal, while increased flow reversal — particularly a prominent reversal following atrial contraction (the A wave) — suggests elevated RA pressure.

RA Strain

Speckle-tracking strain of the RA is technically more demanding than LA strain, largely because the RA free wall is thinner still — in one study, adequate tracking was achievable in only about 64% of segments analyzed, a real feasibility limitation worth acknowledging rather than glossing over.

Normal values: peak (reservoir) longitudinal strain around 48% ± 13%, and peak atrial contraction (booster) strain around 16% ± 6%. Two points of context make these numbers more useful than they’d be in isolation:

• RA reservoir strain runs meaningfully higher than LA reservoir strain in the same person (roughly 48% versus the high-30s to low-40s typically seen for the LA — see the Evaluation of the Left Atrium tutorial). This is a normal RA-versus-LA difference, not a sign that one chamber is underperforming relative to the other.
• RA strain is higher in women than men, and increases from infancy through adulthood — but aging is associated with a shift in the balance of function, not just an overall change: passive (conduit) function tends to decrease with age while active (booster) function tends to increase, even as reservoir strain overall trends upward.
• Elite athletes show the opposite pattern from RA size: despite a larger RA by volume and area, athletes have lower peak reservoir and contraction strain than non-athletes (roughly 41% and 13%, respectively) — a physiological remodeling pattern, not dysfunction. Size and strain don’t always move in the same direction, and this is a clear example of why.
• RA strain is reduced in hypertension, metabolic syndrome, and subclinical hypothyroidism, and — as elsewhere in right heart assessment — reduced RA strain has been shown to predict clinical worsening in pulmonary hypertension independent of RA size alone.

Common Causes of RA Enlargement

Organized by mechanism, the same way RV enlargement is typically categorized:

• Volume overload — tricuspid regurgitation, atrial septal defect (see Atrial Septal Defect for how the resulting RA enlargement is diagnosed and quantified), ventricular septal defect, COPD with cor pulmonale
• Pressure overload — pulmonary hypertension, pulmonary embolism, mitral stenosis (via secondary right heart pressure elevation)
• Arrhythmias — atrial fibrillation and atrial flutter are well-established causes of RA (and LA) enlargement, and the relationship runs both directions: RA enlargement is itself a recognized substrate for developing AF
• Congenital heart disease — Ebstein’s anomaly, tricuspid atresia
• Other — chronic heart failure, constrictive pericarditis

A mechanistic link worth making explicit: RA enlargement can itself cause secondary tricuspid regurgitation, by dilating the tricuspid annulus without any primary leaflet abnormality — this is essentially the mechanism behind atriofunctional TR (AFTR), covered in more detail in the Tricuspid Regurgitation tutorial’s discussion of TR mechanisms. Understanding this bidirectional relationship (RA enlargement causing TR, and TR in turn affecting RA function depending on severity, as above) is more useful than treating RA size and TR severity as independent findings.

Clinical Significance

• Volume and pressure overload — chronic RA dilation typically reflects longstanding pressure or volume overload from pulmonary hypertension, tricuspid regurgitation, or a congenital shunt, and — much like LA enlargement on the left side — functions as a kind of chronic “memory” of sustained hemodynamic stress that a single Doppler measurement can’t capture.
• Arrhythmia risk — an enlarged RA increases the risk of atrial fibrillation and associated thromboembolism, particularly with longstanding volume overload or an atrial septal defect.
• Pulmonary hypertension — RA size and function are integral to PH screening and risk stratification; see the Right Ventricle Evaluation tutorial for how RA area fits into the broader hemodynamic assessment.
• Prognosis — enlarged RA size and reduced RA strain both independently predict adverse outcomes in heart failure, pulmonary hypertension, and congenital heart disease.
• Post-surgical follow-up — RA assessment matters after repair of congenital defects or valve surgery, to monitor for residual shunts, elevated pressures, or persistent dysfunction. See Pediatric Transthoracic Echocardiography for how atrial situs and connections are systematically characterized in this population.

Special Imaging Techniques

• 3D echocardiography — the most accurate RA volume measurement, without the geometric assumptions 2D methods require, and the modality with the strongest correlation to cardiac MRI
• Speckle-tracking strain — evaluates phasic RA function directly, though limited in practice by the technical challenges of tracking the thin RA wall reliably
• Contrast echocardiography (agitated saline) — detects intracardiac shunts, such as a patent foramen ovale or atrial septal defect, via bubble study — see the discussion of agitated saline versus commercial contrast agents in the Echocardiography Basics tutorial for why agitated saline specifically is the correct agent for this application
• Transesophageal echocardiography — the preferred modality for detailed imaging of the RA appendage and thrombus detection, when TTE windows are inadequate