What is the role of transthoracic echocardiogram (TTE) in diagnosing pulmonary hypertension in patients with a history of heart disease, lung disease, or connective tissue disease?

Diagnosis of Pulmonary Hypertension Through Transthoracic Echocardiography

Primary Recommendation

Transthoracic echocardiography (TTE) should be performed as the first-line non-invasive diagnostic investigation in all patients with suspected pulmonary hypertension, but it serves as a screening tool only—right heart catheterization remains mandatory for definitive diagnosis before initiating PH-specific therapy. 1, 2

Diagnostic Algorithm Using TTE

Step 1: Measure Tricuspid Regurgitation Velocity (TRV)

Use the peak TRV measurement (not estimated pulmonary artery systolic pressure) as your primary variable for assigning echocardiographic probability of PH. 1, 2

• PH unlikely: TRV ≤2.8 m/s (corresponding to PA systolic pressure ≤36 mmHg) 2
• PH possible: TRV 2.9-3.4 m/s (PA systolic pressure 37-50 mmHg) 2
• PH likely: TRV >3.4 m/s (PA systolic pressure >50 mmHg) 2

Step 2: Assess Additional Echocardiographic Signs

Signs from at least two different categories must be present to alter the echocardiographic probability of PH. 1, 2

Category A (Right Ventricular Signs):

• RV/LV basal diameter ratio >1.0 1, 2
• Flattening of the interventricular septum (leftward septal bowing) 1, 2

Category B (Pulmonary Artery Signs):

• PA diameter >25 mm 1, 2
• RV outflow tract acceleration time <105 ms 1, 2
• Early diastolic pulmonary regurgitation velocity >2.2 m/s 1, 2

Category C (Right Atrium/IVC Signs):

• IVC diameter >21 mm with <50% collapse with inspiration 1, 2
• Right atrial area >18 cm² 1, 2

Step 3: Clinical Management Based on TTE Probability

For symptomatic patients with low probability TTE (TRV ≤2.8 m/s, no additional signs):

• Pursue alternative diagnoses 1, 2
• Consider echocardiographic follow-up if risk factors for PAH/CTEPH are present (connective tissue disease, congenital heart disease, portal hypertension, HIV, history of stimulant use, thromboembolic disease) 2

For intermediate probability TTE (TRV 2.9-3.4 m/s with <2 categories of signs, or TRV ≤2.8 m/s with ≥2 categories):

• Pursue alternative diagnoses and arrange echocardiographic follow-up 1
• Consider right heart catheterization if risk factors/associated conditions are present 2

For high probability TTE (TRV >3.4 m/s with ≥2 categories of signs, or TRV 2.9-3.4 m/s with ≥2 categories):

• Proceed with comprehensive PH workup including pulmonary function tests, high-resolution CT chest, ventilation/perfusion scan, and right heart catheterization 1, 2

Critical Technical Considerations

Optimizing TRV Measurement

Image from multiple acoustic windows to maximize diagnostic accuracy—using five different views increases sensitivity to 87% and specificity to 91% compared to a single apical view. 3

• Standard views: parasternal short axis, RV modified apical four-chamber, apical four-chamber, subcostal, and suprasternal 3
• If TRV is difficult to measure due to trivial tricuspid regurgitation, use agitated saline contrast to enhance the Doppler signal 1
• A multi-view approach changes the echocardiographic diagnosis in 11% of patients compared to single-view imaging 3

Estimating Right Atrial Pressure

Do not use fixed values of 5 or 10 mmHg for RAP estimation—base your estimate on IVC diameter and respiratory variation. 1, 2

• IVC <2.1 cm with >50% collapse on sniff: RAP = 3 mmHg (range 0-5 mmHg) 1
• IVC >2.1 cm with <50% collapse on sniff: RAP = 15 mmHg (range 10-20 mmHg) 1
• Intermediate scenarios: RAP = 8 mmHg (range 5-10 mmHg) 1

Identifying Underlying Causes of PH

TTE helps determine the etiology of PH, particularly distinguishing left heart disease (Group 2 PH) from other causes. 1

• Assess left ventricular systolic and diastolic function to identify Group 2 PH 1
• Evaluate for valvular heart disease (mitral stenosis, mitral regurgitation, aortic stenosis) 1
• Use agitated saline contrast to detect intracardiac shunts (atrial septal defect, patent foramen ovale) suggesting congenital heart disease 1
• Doppler patterns can distinguish pre-capillary from post-capillary PH 1

Important Limitations and Pitfalls

Accuracy Concerns

TTE measurements of pulmonary artery pressure show significant disagreement with right heart catheterization—only 33% of echocardiographic sPAP estimates fall within 10 mmHg of invasive measurements. 4

• Correlation between TRV and invasive systolic PA pressure is good (r=0.83), but individual measurements may be inaccurate 3, 4
• In severe tricuspid regurgitation, TRV may be significantly underestimated and cannot exclude PH 1, 2
• Overestimation can also occur, leading to unnecessary invasive testing 1

What TTE Cannot Do

Never initiate PH-specific therapy based on echocardiography alone—right heart catheterization is mandatory for treatment decisions. 1

• TTE is insensitive for detecting mild PH 1
• A normal TTE does not exclude PH, particularly in patients with risk factors 2
• Assessment of RV size and function by TTE is less accurate than cardiac MRI 1

Contraindicated Practices

Do not use exercise Doppler echocardiography for PH screening—it lacks validated criteria and prospective confirmatory data. 2

Role in Patients with Heart Disease, Lung Disease, or Connective Tissue Disease

Heart Disease Patients

In patients with established left heart disease and unexplained deterioration, TTE is necessary to detect complicating PH and right ventricular dysfunction. 1

• TTE distinguishes whether PH is due to left heart disease (elevated left atrial pressure, diastolic dysfunction) or a superimposed pulmonary vascular process 1

Lung Disease Patients

The role of TTE in primary lung disease is unclear except when PE or PH is specifically suspected. 1

• In established lung disease with unexplained deterioration (COPD, sleep apnea), TTE detects complicating heart failure or PH 1
• Perform pulmonary function tests and high-resolution CT to assess severity of underlying lung disease before attributing symptoms to PH 1

Connective Tissue Disease Patients

Echocardiographic screening for PH is recommended in symptomatic patients with scleroderma spectrum diseases and should be considered in symptomatic patients with all other connective tissue diseases. 1

• Right heart catheterization is indicated in all cases of suspected PAH associated with CTD if specific drug therapy is considered 1
• Consider periodic screening in asymptomatic patients with scleroderma spectrum disease 1

Prognostic Value

Beyond diagnosis, TTE provides important prognostic information through assessment of right ventricular function, which predicts outcomes and guides therapy escalation. 5, 6

• Persistence of RV dysfunction at hospital discharge predicts recurrence of pulmonary embolism 1
• Serial TTE examinations monitor treatment response and identify patients requiring therapy escalation 5, 7