Pulmonary Regurgitation CW Doppler

This image is teaching pulmonary regurgitation CW Doppler as a way to estimate pulmonary artery pressures, especially when TR Vmax is absent, incomplete, unreliable, or discordant.

The strong teaching message is:

TR Doppler estimates systolic PA pressure

PR Doppler can estimate mean and diastolic PA pressure

Together with RVOT acceleration time/notching, PR gives a deeper picture of pulmonary vascular load

The left panel shows colour Doppler in the RVOT with a pulmonary regurgitation jet returning from the pulmonary artery towards the RV during diastole

The right panel shows the CW Doppler PR envelope. This is diastolic flow, because pulmonary regurgitation happens after pulmonary valve closure, when blood leaks from the pulmonary artery back into the RV

The important visual label is 'Flat PR slope'. That matters because in significant pulmonary hypertension, the pulmonary artery pressure remains high throughout diastole. The pressure gradient between the pulmonary artery and RV does not collapse quickly, so the PR signal can remain relatively high and sustained, giving a flatter, more prolonged Doppler slope:

A steeply decelerating PR signal suggests the PA–RV diastolic gradient falls quickly

A flatter PR slope suggests persistently elevated pulmonary artery diastolic pressure

Key formulas:

mPAP = 4 × PR max velocity² + RAP

PADP = 4 × PR end-diastolic velocity² + RAP

The principle: velocity tells us pressure gradient

For pulmonary regurgitation, the gradient is between the pulmonary artery and the RV during diastole

Because RV diastolic pressure is difficult to measure directly by echo, we commonly use estimated right atrial pressure as a practical surrogate, especially near end-diastole when RV diastolic pressure approximates RA pressure in the absence of major tricuspid inflow obstruction or unusual RV diastolic pathology. So:

Early PR velocity reflects the early diastolic PA–RV gradient → used to estimate mean PAP

End-diastolic PR velocity reflects the late diastolic PA–RV gradient → used to estimate pulmonary artery diastolic pressure

In the second image, the PR CW trace appears broad and sustained with a flat deceleration slope

That means the PR velocity does not rapidly fall back to baseline. The PA-to-RV gradient is being maintained through diastole

So the logic is:

Persistent PR velocity throughout diastole → persistent PA–RV pressure gradient → elevated pulmonary artery diastolic pressure → supportive evidence of raised pulmonary artery pressure

The BSE pulmonary hypertension protocol uses echo to assess the probability of pulmonary hypertension, not to make a definitive diagnosis. It emphasises that echo-derived pressure estimates can be inaccurate in individual patients and that confirmation, where clinically required, is by right heart catheterisation

In the BSE framework, PR Doppler appears as one of the supportive pulmonary artery signs. Specifically, an early diastolic pulmonary regurgitation velocity >2.2 m/s is listed as an additional echocardiographic sign suggesting pulmonary hypertension. BSE also includes RVOT acceleration time <105 ms and/or mid-systolic notching in the same pulmonary artery category

RVOT PW: abnormal forward systolic ejection into high afterload

PR CW: abnormal backward diastolic gradient from a pressurised pulmonary artery

A flat PR slope can support elevated pulmonary pressure, but interpretation becomes weaker if there is poor Doppler alignment, significant pulmonary valve disease, severe RV diastolic dysfunction, marked tachycardia, irregular rhythm, congenital/post-operative RVOT anatomy, or poor envelope definition

Also, estimated RAP is a major source of error. If RAP is guessed badly, both mPAP and PADP estimates become misleading.