How is pulmonary hypertension assessed using transthoracic echocardiography?

Echocardiographic Assessment of Pulmonary Hypertension

Transthoracic echocardiography should be performed as the initial assessment in all patients with suspected pulmonary hypertension, using tricuspid regurgitation velocity (TRV) combined with multiple secondary echocardiographic signs to assign a probability of PH rather than relying on a single pressure estimate. 1

Primary Assessment: Tricuspid Regurgitation Velocity

The cornerstone of echocardiographic PH assessment is measuring peak TRV using continuous-wave Doppler, which is then used to estimate systolic pulmonary artery pressure (sPAP) via the simplified Bernoulli equation: sPAP = 4(TRV)² + estimated right atrial pressure 1, 2.

Key thresholds:

• TRV >2.8 m/s or estimated sPAP >35 mm Hg suggests possible PH 1
• However, use TRV velocity itself rather than calculated sPAP as the primary variable, as estimation errors are amplified when using derived variables 2

Right Atrial Pressure Estimation

Estimate right atrial pressure based on inferior vena cava (IVC) characteristics 1, 2:

• IVC <2.1 cm with >50% collapse on sniff = 3 mm Hg (range 0-5)
• IVC >2.1 cm with <50% collapse = 15 mm Hg (range 10-20)
• Intermediate scenarios = 8 mm Hg (range 5-10)

Probability Assignment Framework

The 2022 approach assigns PH probability based on TRV plus additional echocardiographic signs across three categories 3, 2:

Three Categories of Secondary Signs:

1. Right ventricular findings: RV/LV basal diameter ratio >1, septal flattening
2. Pulmonary artery findings: PA diameter >25 mm, RV outflow tract acceleration time <105 ms, early diastolic pulmonary regurgitation velocity >2.2 m/s
3. IVC/Right atrial findings: IVC diameter >21 mm with <50% collapse, RA area >18 cm²

Probability Classification 3, 2:

• Low probability: TRV ≤2.8 m/s with no additional signs
• Intermediate probability: TRV ≤2.8 m/s with ≥2 categories positive, OR TRV 2.9-3.4 m/s without additional signs
• High probability: TRV 2.9-3.4 m/s with ≥2 categories positive, OR TRV >3.4 m/s regardless of other signs

Complete Echocardiographic Assessment

Beyond pressure estimation, perform comprehensive evaluation including 1:

For PH Classification (Pre- vs Post-capillary):

Postcapillary indicators:

• Left ventricular hypertrophy
• Systolic or diastolic dysfunction
• Aortic or mitral valvular disease
• Increased indexed left atrial volume 1

Precapillary indicators:

• Severely dilated and remodeled right ventricle
• Notching of RV outflow tract Doppler flow profile
• Absence of left-sided pathology 1

For Prognostic Assessment:

Measure RV systolic function using 1:

• Tricuspid annular plane systolic excursion (TAPSE)
• S' velocity
• RV free wall strain (using 2D speckle tracking—strongest predictor) 1
• RV index of myocardial performance
• Fractional area change

Additional prognostic markers 1:

• Presence/severity of pericardial effusion
• Right atrial area
• Severity of tricuspid regurgitation

Shunt Evaluation:

Perform agitated saline contrast study and/or transesophageal echocardiography routinely when 1:

• Enlarged right heart chambers present
• Significant PH suspected

Critical Limitations and Pitfalls

Echocardiography has important limitations that must be recognized 2, 4:

1. Cannot reliably screen for mild, asymptomatic PH—TRV may be inadequate in trivial tricuspid regurgitation 2
2. Severe tricuspid regurgitation may significantly underestimate TRV 2
3. Discrepancies with right heart catheterization are common, particularly at high pressures, with mean differences ranging 3-38 mm Hg 5
4. Acoustic window limitations in patients with lung disease or body habitus 6
5. A normal echocardiogram does not exclude PH—proceed with right heart catheterization if clinical suspicion remains high 6

When to Proceed to Right Heart Catheterization

Right heart catheterization is mandatory for confirmation before treatment initiation in patients with 6, 3:

• Intermediate or high echocardiographic probability of PH
• Clinical suspicion despite low probability echo when symptoms persist

Technical Standardization

Each laboratory must follow standardized echocardiographic guidelines for imaging and interpretation techniques to minimize variability and improve accuracy 1. Consider using contrast echocardiography (agitated saline) when TRV signal is suboptimal 7, 2.

Emerging Evidence

Recent data suggest that mean PAP estimation using minimal end-diastolic pulmonary regurgitation pressure (mPAPDPmin) demonstrates superior diagnostic accuracy (correlation R=0.92, AUC 0.96) compared to traditional TRV-based methods, with minimal bias and narrow limits of agreement 8. However, this requires adequate pulmonary regurgitation signal and further validation in routine practice.