When you assess pulmonary hypertension by echocardiography, start with a complete tricuspid regurgitation (TR) continuous-wave envelope, assign right atrial pressure (RAP) from the inferior vena cava (IVC), and then look for supporting signs of right ventricular (RV) pressure overload. Echo estimates the probability of pulmonary hypertension and shows how the right heart is coping. It does not replace right heart catheterization when a definitive hemodynamic diagnosis is required. The sequence below is a practical guide for the scanner and the reading room: views, measurements, commonly cited cutoff ranges, and the pitfalls that lead to over- or underestimation.
How to Measure Pulmonary Hypertension by Echocardiography
Peak TR velocity is the primary number. Use color flow to align continuous-wave Doppler with the jet, and record from more than one window. The apical four-chamber view is standard, but parasternal RV inflow, parasternal short-axis at the aortic valve, subcostal four-chamber, and occasionally a high parasternal or suprasternal window may yield a higher, more complete envelope. Report the highest well-defined modal velocity, not the peak of faint noise.
If the envelope is incomplete, do not force a value. Agitated saline or an ultrasound enhancing agent can opacify a weak TR jet. Technique for enhancing agents is reviewed in IAME's course on contrast-enhanced echocardiography.
Convert TR velocity to RVSP and PASP
Use the simplified Bernoulli equation: RVSP (mmHg) = 4 x (peak TR velocity in m/s) squared + RAP. In the absence of pulmonary stenosis or RV outflow obstruction, RVSP is used as an estimate of PASP. If obstruction is present, RVSP exceeds PASP and the TR-based number no longer represents pulmonary pressure.
Society guidance treats echocardiography as a probability test rather than a yes-or-no diagnosis. Commonly cited TR velocity thresholds are:
- 2.8 m/s or less: not suggestive by itself
- 2.9 to 3.4 m/s: intermediate
- Greater than 3.4 m/s: high probability
A PASP normal range on echo is often cited as below about 35 to 40 mmHg at rest, which roughly matches a TR velocity of 2.8 m/s plus a low RAP. Upper reference values rise with age and with high-output states. Some laboratories still grade estimated RVSP as mild (about 35 to 45 mmHg), moderate (about 46 to 60 mmHg), or severe (above 60 mmHg). That grading is a reporting convention, not a hemodynamic classification, and it should not replace the probability method or catheterization when management depends on precise pressures.
Assign RAP from the IVC
Measure IVC diameter just caudal to the hepatic vein inlet in a subcostal long-axis view, and assess inspiratory collapse with a sniff. A widely used assignment is:
- IVC diameter 2.1 cm or less and collapse greater than 50%: RAP about 3 mmHg (range 0 to 5)
- IVC diameter greater than 2.1 cm and collapse less than 50%: RAP about 15 mmHg (range 10 to 20)
- Intermediate combinations: RAP about 8 mmHg (range 5 to 10)
Sources differ in whether they use 3/8/15 or 5/10/15 mmHg. Use one internally consistent method, state it in the report, and do not pair a high TR velocity with an assumed RAP of 0 mmHg simply to keep PASP looking normal. If TR is absent or uninterpretable, you cannot calculate RVSP. Use acceleration time, pulmonary regurgitation, chamber morphology, and IVC findings rather than calling pressures normal by default.
Echo Signs That Raise the Probability of Pulmonary Hypertension
Combine TR velocity with additional signs rather than hanging the entire interpretation on one Doppler value. Probability rises when velocity is intermediate or high and supporting signs are present. Catheterization is still required when a definitive diagnosis will change therapy.
Ventricular signs of pressure overload
- RV/LV basal diameter ratio greater than 1.0 on an RV-focused apical four-chamber view
- Systolic flattening of the interventricular septum with a D-shaped left ventricle in parasternal short axis (left ventricular eccentricity index greater than 1.1 is a published threshold)
- Reduced TAPSE/sPAP ratio (a commonly cited cutoff is less than 0.55 mm/mmHg)
Systolic septal flattening points to pressure overload. Diastolic flattening is more consistent with RV volume overload, as in severe TR or an atrial-level shunt. Mixed physiology is common. Describe the pattern you see.
Pulmonary artery, RA, and IVC signs
- RV outflow tract acceleration time less than 105 ms, with or without mid-systolic notching
- Early diastolic pulmonary regurgitation velocity greater than 2.2 m/s
- Main pulmonary artery diameter greater than 25 mm
- IVC diameter greater than 21 mm with reduced inspiratory collapse (less than 50% with a sniff, or less than 20% during quiet inspiration)
- Right atrial end-systolic area greater than 18 square centimeters
A practical application of pulmonary hypertension echo criteria is:
- Low probability: TR velocity 2.8 m/s or less, or not measurable, and no additional signs
- Intermediate probability: TR velocity 2.8 m/s or less with additional signs, or TR velocity 2.9 to 3.4 m/s without additional signs
- High probability: TR velocity 2.9 to 3.4 m/s with additional signs, or TR velocity greater than 3.4 m/s with or without additional signs
If TR velocity cannot be measured, several supporting findings should still raise concern. A single borderline sign in an otherwise normal study is weaker evidence.
Pulmonary Acceleration Time and Pulmonary Regurgitation
Pulmonary acceleration time is measured with pulsed-wave Doppler in the RVOT, just proximal to the pulmonary valve, usually from the parasternal short-axis view. Measure from the onset of flow to peak velocity. A short time to peak and mid-systolic notching are associated with elevated pulmonary pressure and resistance. A commonly used cutoff is less than 105 ms; other sources use about 100 ms. Heart rate, sample volume position, and high cardiac output all affect the value, so treat it as supportive. Notching is more suggestive of a high-resistance circuit than a mildly shortened time alone.
When pulmonary regurgitation is present, early diastolic velocity converted as 4v squared plus RAP estimates mean pulmonary artery pressure, and end-diastolic velocity estimates pulmonary artery diastolic pressure. These estimates share TR's alignment and gain pitfalls and help most when the TR jet is unreliable.
Mean pulmonary artery pressure on catheterization is the definitional measurement. Older sources often used a resting mean of 25 mmHg or higher. More recent consensus and European society guidance use a mean greater than 20 mmHg, with further subdivision by wedge pressure and pulmonary vascular resistance. Echocardiography does not measure those values directly.
Right Ventricular Size, Septal Motion, and Function
Remodeling matters as much as the pressure estimate. A dilated, hypertrophied, poorly functioning RV supports a chronic process. A small, thin-walled RV with acute septal flattening and a high TR velocity raises the possibility of an acute afterload rise, including pulmonary embolism. Echo cannot assign a clinical group by itself.
- Use an RV-focused apical four-chamber view for basal diameter and RV/LV ratio. A basal RV diameter above about 4.1 cm is a commonly cited enlargement threshold.
- Look for free-wall hypertrophy (thickness greater than 5 mm from a subcostal window is a frequently used cutoff) when chronic disease is suspected.
- Quantify function with more than one method: TAPSE, tricuspid annular s' velocity, fractional area change, and RV free-wall strain when image quality allows. TAPSE below about 1.7 cm and s' below about 9.5 cm/s are widely used flags. They are load dependent.
- Note pericardial effusion. In established pulmonary arterial hypertension, effusion is an adverse prognostic sign, not a diagnosis.
Complete the left heart examination. Post-capillary disease from left ventricular systolic or diastolic dysfunction, mitral valve disease, or aortic stenosis is common. Estimated PASP still describes RV afterload, but the therapeutic target is often the left heart.
Pitfalls That Overestimate or Underestimate Pressure
Most errors in RVSP pulmonary hypertension reporting are technical.
Underestimation occurs with an incomplete TR envelope; severe, dense TR in which a triangular early-peaking jet violates Bernoulli assumptions; an RAP that is too low for the IVC; failure to use a non-apical window that holds a higher velocity; and the assumption that absent TR means normal pressure.
Overestimation occurs when gain is too high and the speckled peak is measured; when mitral regurgitation or outflow tract flow contaminates the TR signal; when RAP is assigned at 15 or 20 mmHg without IVC data; when pulmonary stenosis or a ventricular septal defect jet is mistaken for TR; and when PASP is reported despite RV outflow obstruction.
Average several beats in atrial fibrillation. Anemia, pregnancy, and other high-output states raise velocity with flow, not only with resistance. Resting cutoffs do not apply unchanged during exercise. When unexplained dyspnea persists and resting probability is low or intermediate, stress echocardiography protocols are sometimes used to evaluate exertional TR velocity and RV function. That approach follows a laboratory protocol and is not a substitute for invasive hemodynamics.
If the number and the right heart disagree, for example an estimated PASP of 70 mmHg with a small, thin-walled, normal RV, re-interrogate the Doppler before you lock the interpretation.
What to Include in the Echo Report
A useful report answers three questions: what pressure did you estimate, what is the probability of pulmonary hypertension, and how is the right heart coping?
- Peak TR velocity and the window used
- RAP method and assigned value
- Estimated RVSP or PASP, labeled as an estimate
- Exclusion of pulmonary stenosis
- Supporting signs, listed rather than implied
- RV size and systolic function
- Left heart findings that could explain post-capillary disease
- Image quality and limitations, including incomplete TR or a poorly seen IVC
Avoid language that treats estimated PASP as a catheter equivalent. Prefer intermediate-probability wording plus the raw measurements over an isolated label of moderate pulmonary hypertension when mean pressure has not been measured invasively.
Echocardiography is the right first test for suspected pulmonary hypertension because it is available, repeatable, and rich in ancillary signs. It is the wrong last test when therapy depends on precise hemodynamics. Measure TR velocity carefully, assign RAP consistently, inspect the RV and pulmonary artery, and be explicit about limitations. IAME offers accredited ultrasound CME on pulmonary hypertension for clinicians who want a structured review of scanning technique and interpretation.
Frequently Asked Questions
How accurate is echocardiography for pulmonary hypertension?
Echocardiography is a strong screening and monitoring tool, but estimated PASP can disagree with catheter systolic pressure by a clinically important margin in either direction. Accuracy falls when the TR jet is incomplete, RAP is guessed, or severe TR invalidates the Bernoulli relationship. Treat the study as a probability assessment and use catheterization when a definitive diagnosis or targeted therapy is under consideration.
What numbers on an echo show pulmonary hypertension?
No single echo value diagnoses pulmonary hypertension. Peak TR velocity greater than 3.4 m/s indicates high probability. Velocities of 2.9 to 3.4 m/s are intermediate and become high probability when supporting signs are present. Many laboratories also flag estimated PASP above about 35 to 40 mmHg, but current guidance emphasizes TR velocity plus ancillary signs rather than one PASP cutoff.
What is the most accurate test for pulmonary hypertension?
Right heart catheterization is the reference standard because it measures mean pulmonary artery pressure, wedge pressure, and pulmonary vascular resistance directly. Echocardiography remains the first-line test to decide who needs catheterization, to look for left heart causes, and to follow RV function. Additional lung, vascular, and laboratory testing completes the workup once pulmonary hypertension is confirmed or still strongly suspected.
How do you measure pulmonary hypertension on echo?
Obtain the highest-quality TR continuous-wave envelope from multiple windows, measure peak modal velocity, estimate RAP from IVC size and collapse, and calculate RVSP as 4v squared plus RAP. Then document RVOT acceleration time, septal shape, RV size and function, pulmonary artery size, and RA and IVC findings so the study reports probability, not only a Bernoulli number.
What is a normal PASP range on echo?
A commonly cited resting PASP normal range is below about 35 to 40 mmHg, corresponding roughly to a TR velocity of 2.8 m/s with normal RAP. Upper limits increase with age and flow. Because RAP assignment and Doppler quality vary, it is more reproducible to report TR velocity, RAP, and probability than to treat a single PASP value as strictly normal or abnormal.
