Diagnosing Pulmonary Arterial Hypertension on Echocardiography
Echocardiographic diagnosis of pulmonary arterial hypertension should be based on tricuspid regurgitation velocity measurement combined with additional echocardiographic signs from at least two different categories to assign a probability level of PAH, rather than relying solely on estimated pulmonary artery systolic pressure. 1
Primary Echocardiographic Assessment
Tricuspid Regurgitation Velocity (TRV) Measurement
- Use continuous wave Doppler to measure peak TRV as the main variable for assigning echocardiographic probability of PAH 1
- When TRV is difficult to measure, consider contrast echocardiography (agitated saline IV injection) to improve Doppler signal 1
- Probability classification based on TRV:
- High probability: TRV >3.4 m/s
- Intermediate probability: TRV 2.9-3.4 m/s
- Low probability: TRV ≤2.8 m/s 2
Additional Echocardiographic Signs
Signs from at least two different categories should be present to alter the level of echocardiographic probability of PAH 1:
Ventricle signs:
- Right ventricle/left ventricle basal diameter ratio >1.0
- Flattening of the interventricular septum (left ventricular eccentricity index >1.1 in systole and/or diastole)
Pulmonary artery signs:
- Right ventricular outflow Doppler acceleration time <105 msec and/or midsystolic notching
- Early diastolic pulmonary regurgitation velocity >2.2 m/sec
- Pulmonary artery diameter >25 mm
Inferior vena cava and right atrium signs:
- Inferior vena cava diameter >21 mm with decreased inspiratory collapse (<50% with sniff or <20% with quiet inspiration)
- Right atrial area (end-systole) >18 cm² 1
Important Considerations
Limitations of Echocardiographic Assessment
- Doppler-derived pressure estimation may be inaccurate in individual patients 1
- TRV may be significantly underestimated in patients with severe tricuspid regurgitation 1
- Echocardiography alone is not sufficient to support treatment decisions; right heart catheterization is required for confirmation 2
- Estimation of PAP based solely on Doppler measurements is not suitable for screening mild, asymptomatic PAH 1
Right Atrial Pressure Estimation
- Estimate based on IVC diameter and respiratory variation:
- IVC <2.1 cm with >50% collapse with sniff: normal RA pressure (3 mmHg, range 0-5 mmHg)
- IVC >2.1 cm with <50% collapse with sniff: high RA pressure (15 mmHg, range 10-20 mmHg)
- Intermediate scenarios: use 8 mmHg (range 5-10 mmHg) 1
Additional Echocardiographic Evaluations
- Assess for left ventricular systolic and diastolic dysfunction, left-sided chamber enlargement, or valvular heart disease 1
- Perform contrast echocardiography to look for evidence of intracardiac shunting 1
- Evaluate right ventricular size and function:
- Right atrial enlargement
- Right ventricular enlargement
- Presence of pericardial effusion 1
- Consider 3D echocardiography for better assessment of right ventricular volumes and ejection fraction 1
Next Steps After Echocardiographic Assessment
- For patients with high probability of PAH: proceed to right heart catheterization for definitive diagnosis 2
- For patients with intermediate probability: consider further assessment including right heart catheterization if risk factors for PAH exist 2
- For patients with confirmed PAH: perform V/Q scanning to rule out chronic thromboembolic PH 1
Common Pitfalls to Avoid
- Relying solely on estimated PASP rather than TRV and additional echocardiographic signs 1
- Making treatment decisions based on echocardiography alone without confirmatory right heart catheterization 2
- Failing to consider other causes of elevated pulmonary pressures (left heart disease, lung disease) 1
- Underestimating PAP in patients with severe tricuspid regurgitation 1
- Overestimating PAP in normal subjects 2
Remember that echocardiography is an excellent screening tool for PAH, but right heart catheterization remains the gold standard for definitive diagnosis and classification of pulmonary hypertension 2, 3.