How to estimate pulmonary artery pressure (PAP) from RVOT acceleration time (AT) on echocardiography

At PSAX View Aortic Valve Level : Apply PW Doppler at RVOT to get Acceleration Time. Measure the time it takes to reach peak as shown with white lines

To estimate pulmonary artery pressure (PAP) from RVOT acceleration time (AT) on echocardiography, you use the RVOT AT–PASP relationship, which is based on the inverse correlation between AT and pulmonary pressures.

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📌 How to Measure RVOT Acceleration Time (AT)

1. Use PW Doppler in the RV outflow tract just proximal to the pulmonary valve.

2. Align the Doppler cursor parallel to flow in the RVOT (usually PLAX RVOT or PSAX at the AV level).

3. Measure AT from:

Start of systolic flow upstroke

→ to

Peak velocity of the RVOT waveform.

This is the RVOT acceleration time (AT).

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📌 How RVOT AT Estimates Pulmonary Artery Pressure

1. If RVOT AT ≥ 120 ms → Normal PAP

A long acceleration time indicates normal pulmonary pressures.

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2. If RVOT AT < 120 ms → Elevated PAP

General Formula for PASP (if no PS or RVOT obstruction):

➡️ PASP ≈ 79 – (0.45 × RVOT AT)

Or in short 80 - 1/2 RVOT AT

(AT in milliseconds)

Example:

RVOT AT = 80 ms

PASP = 79 – (0.45 × 80)

= 79 – 36

= 43 mmHg

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📌 Alternate Categorization (Used in many labs)

RVOT AT > 130 ms

→ Normal PA pressure

RVOT AT 100–130 ms

→ Mild pulmonary hypertension

RVOT AT 60–100 ms

→ Moderate pulmonary hypertension

RVOT AT < 60 ms

→ Severe pulmonary hypertension

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📌 Important Notes

Not valid when:

Pulmonary stenosis

RVOT obstruction

Tachycardia (AT shortens falsely)

Poor Doppler alignment

RVOT AT is especially useful when TR jet is not satisfactory for estimating RVSP.