How is pulmonary artery systolic pressure calculated in 2D (two-dimensional) echo (echocardiography)?

Calculation of Pulmonary Artery Systolic Pressure on 2D Echocardiography

Pulmonary artery systolic pressure (PASP) is calculated using the modified Bernoulli equation applied to the peak tricuspid regurgitation velocity, then adding an estimate of right atrial pressure: PASP = 4(TRV)² + RAP. 1

Step-by-Step Calculation Method

Step 1: Measure Peak Tricuspid Regurgitation Velocity (TRV)

• Use continuous-wave Doppler to measure the peak velocity of the tricuspid regurgitation jet 1
• The measurement should capture the maximum velocity of the TR jet throughout systole 2
• TR jets are detectable in approximately 79-89% of patients 1, 2
• If the TR signal is weak or difficult to measure, agitated saline contrast can be administered intravenously to enhance the Doppler signal 1

Step 2: Calculate the Transtricuspid Pressure Gradient

• Apply the simplified Bernoulli equation: Pressure Gradient = 4 × (TRV)² 1
• This calculates the systolic pressure difference between the right ventricle and right atrium 2, 3
• The velocity must be measured in meters per second (m/s) 4

Step 3: Estimate Right Atrial Pressure (RAP)

RAP estimation is based on inferior vena cava (IVC) diameter and respiratory collapse: 1, 5

• Normal RAP = 3 mmHg (range 0-5 mmHg): IVC diameter <2.1 cm with >50% collapse during sniff 1, 5
• Intermediate RAP = 8 mmHg (range 5-10 mmHg): IVC measurements that don't fit normal or elevated criteria 1, 5
• Elevated RAP = 15 mmHg (range 10-20 mmHg): IVC diameter >2.1 cm with <50% collapse during sniff or <20% on quiet inspiration 1, 5

Technical measurement details: 5

• Measure IVC from subcostal view at 1.0-2.0 cm from the junction with the right atrium
• Use long-axis view, perpendicular to the IVC long axis
• Assessment often requires a brief sniff maneuver rather than normal inspiration

Step 4: Calculate Final PASP

• PASP = 4(TRV)² + RAP 1, 4
• Example: If TRV = 3.0 m/s and estimated RAP = 8 mmHg, then PASP = 4(3.0)² + 8 = 36 + 8 = 44 mmHg

Important Clinical Considerations

Interpretation of Values

• Normal PASP: <35 mmHg (upper limit of normal 30-35 mmHg) 4
• Borderline elevated: 35-40 mmHg 4
• Elevated: >40 mmHg suggests pulmonary hypertension 1
• Even PASP >30 mmHg is associated with increased mortality risk, despite being below the traditional 40 mmHg threshold 1, 4

Critical Pitfalls and Limitations

The European Society of Cardiology and European Respiratory Society recommend using peak TRV (not the calculated PASP) as the primary variable for assigning echocardiographic probability of pulmonary hypertension, due to inaccuracies in RAP estimation and amplification of measurement errors. 1

Specific scenarios where PASP calculation may be inaccurate: 1

• Severe tricuspid regurgitation: TRV may be significantly underestimated and cannot exclude pulmonary hypertension
• Trivial or mild TR: Peak TRV may be technically difficult to measure (occurs in 11-23% of patients) 1, 2
• Young athletes: May have dilated IVC despite normal pressure, leading to RAP overestimation 5
• Overestimation can also occur in individual patients despite good correlation in populations 1

When PASP Cannot Be Measured

In patients without measurable TR (13-21% of cases), look for alternative signs of elevated pulmonary pressure: 1, 4

• Short pulmonary acceleration time on pulsed-wave Doppler
• Notching in the Doppler flow recording in the right ventricular outflow tract
• Right ventricular hypertrophy, dilation, or dysfunction
• Absence of a TR jet does not rule out elevated pulmonary artery pressure 1, 4

Additional Supportive Echocardiographic Variables

The 2015 ESC/ERS Guidelines recommend assessing multiple echocardiographic signs beyond TRV to determine probability of pulmonary hypertension: 1

• Right ventricular size and evidence of pressure overload
• Pattern of blood flow velocity from the right ventricle
• Pulmonary artery diameter
• Interventricular septal motion and bowing
• Right atrial size 1

Role of Right Heart Catheterization

Right heart catheterization is necessary for confirmation of pulmonary hypertension before initiating treatment in patients with intermediate or high echocardiographic probability of PH. 1 Echocardiography alone is not sufficient to support treatment decisions when specific pulmonary hypertension therapy is being considered 1.