Normal Right Atrial Pressure on Echocardiography
Normal right atrial pressure (RAP) on echocardiography is 3 mm Hg (range 0-5 mm Hg), estimated when the inferior vena cava (IVC) diameter is < 2.1 cm and collapses > 50% with a sniff. 1
Echocardiographic Estimation of RAP
The American Society of Echocardiography and European Association of Cardiovascular Imaging recommend using specific values rather than ranges for uniformity in reporting RAP 1:
IVC-Based RAP Estimation Algorithm
Normal RAP = 3 mm Hg (range 0-5 mm Hg): IVC diameter < 2.1 cm with > 50% collapse during sniff 1, 2
Intermediate RAP = 8 mm Hg (range 5-10 mm Hg): When IVC diameter and collapse do not fit the normal or elevated paradigm 1, 2
Elevated RAP = 15 mm Hg (range 10-20 mm Hg): IVC diameter > 2.1 cm with < 50% collapse during sniff 1, 2
Technical Measurement Details
The IVC should be measured from the subcostal view at 1.0 to 2.0 cm from the junction with the right atrium, using the long-axis view, perpendicular to the IVC long axis 1. The inspiratory response assessment often requires a brief sniff, as normal inspiration may not elicit adequate collapse 1.
Additional Echocardiographic Parameters for RAP Assessment
When IVC measurements are equivocal or intermediate, other indices should be integrated to refine the RAP estimate 1:
Hepatic vein flow patterns: In normal elderly subjects without cardiac disease, predominant forward flow occurs during systole; as RAP increases, flow shifts to predominantly diastolic 1
Hepatic vein atrial reversal (Ar): Increases in amplitude and duration with increasing RAP 1
Tricuspid E/E' ratio: Shows strong correlation with RAP (r = 0.84), with E/E' ≥ 4.5 providing 89% sensitivity and 100% specificity for detecting elevated RAP > 10 mm Hg 3
3D right atrial volume index (3D-RAVi): Values ≥ 35 ml/m² combined with IVC ≥ 2 cm have 88% accuracy for identifying RAP > 10 mm Hg 4
Important Clinical Caveats
Normal young athletes may have dilated IVC in the presence of normal pressure, which can lead to overestimation of RAP 1. This represents a common pitfall where the IVC size alone would suggest elevated RAP, but the clinical context indicates otherwise.
When hepatic venous flow shows predominant diastolic flow with increased atrial reversal, this pattern is consistent with elevated RAP in the 10-15 mm Hg range 1. This finding can help upgrade an intermediate IVC assessment to the elevated category.
The collapsibility index (percentage decrease in IVC diameter during inspiration) correlates inversely with RAP (r = -0.76), and values > 45% predict RAP ≤ 8 mm Hg with high accuracy 5.
Clinical Significance
Elevated RAP > 10 mm Hg is an independent risk factor for mortality in patients with pulmonary arterial hypertension and heart failure 6. Echocardiographic RAP > 15 mm Hg carries a hazard ratio of 2.28 for mortality in PAH patients 6.
The mean RAP measured invasively in patients with cardiac disease averages 9.1 ± 4.3 mm Hg (range 3-20 mm Hg), demonstrating that many cardiac patients have RAP values above the normal range 5.