Pulmonary artery echocardiography

Assessment of pulmonary stenosis

Congenital pulmonary valve defects are most often obstructive in nature. In pulmonary stenosis (Pulmonary Stenosis, PS), right ventricular (RV) pressure increases to overcome the obstruction, leading to compensatory hypertrophy.

Since assessing the actual area of the pulmonary valve orifice is technically difficult, the severity of the defect is determined by the systolic pressure gradient. It is calculated from the transpulmonary flow velocity using the simplified Bernoulli equation ($Gradient = 4 \times velocity^2$).

Classification of severity of isolated valvular stenosis:

• Mild stenosis: peak blood flow velocity < 3 m/s (peak gradient < 36 mm Hg).
• Moderate stenosis: peak velocity 3–4 m/s (peak gradient from 36 to 64 mm Hg).
• Severe stenosis: peak velocity > 4 m/s (peak gradient > 64 mm Hg).

Diagnosis of pulmonary hypertension

EchoCG serves as the primary tool in suspected pulmonary hypertension (PH). The method makes it possible to estimate systolic pulmonary artery pressure by measuring the velocity of the tricuspid regurgitation jet. For instance, a regurgitation velocity of 4 m/s yields an estimated RV systolic pressure of about 64 mm Hg (to which right atrial pressure is added).

In case of a weak signal (if regurgitation is minimal), contrast echocardiography is used to enhance the Doppler signal.

Key objectives of EchoCG in PH:

1. Assessment of the dimensions and systolic/diastolic function of the left heart chambers (to rule out post-capillary PH).
2. Search for intracardiac shunts (ASD, VSD).
3. Assessment of signs of increased pulmonary vascular resistance (systolic flattening of the interventricular septum, notching of the pulmonary artery blood flow curve).

Pulmonary regurgitation

Trace pulmonary regurgitation (Pulmonary Regurgitation, PR) is detected on EchoCG in many patients and is considered a physiological norm. Significant regurgitation, however, is most often iatrogenic in nature (arising after surgical or catheter interventions) or occurs in the rare absent pulmonary valve syndrome.

Significant regurgitation leads to right ventricular volume overload, causing its progressive dilatation and dysfunction. However, the capabilities of standard 2D echocardiography are limited here: it does not allow for accurately calculating the regurgitation volume and adequately assessing the structural and functional changes of the RV. Cardiac magnetic resonance imaging (CMR) is used for these purposes, acting as the gold standard.

Assessment of intracardiac shunts

In ventricular septal defects (VSD) and patent ductus arteriosus (PDA), a left-to-right blood shunt occurs. On EchoCG, the degree of shunting is assessed by measuring the blood flow velocity across the defect:

• Restrictive defects: high-velocity flows are recorded, indicating a preserved pressure gradient between the left and right sides (with normal pulmonary vascular resistance).
• Non-restrictive defects: flows are low-velocity, and ventricular pressures are practically equal.

The exact shunt volume cannot be determined by EchoCG, but the physician can perform a qualitative assessment based on the degree of dilatation of the overloaded heart chambers. In infants, PDA is easily and fully assessed by EchoCG, but in adults, visualization of the ductus may be difficult.

Class and exam questions

What else to study on this topic

• Cardiac MRI (CMR) as the gold standard for assessing pulmonary regurgitation and right ventricular function
• Right heart catheterization for the definitive confirmation of pulmonary hypertension
• Anatomical classification and hemodynamics of ventricular septal defects (VSD)
• Ventilation-perfusion (V/Q) scintigraphy to rule out chronic thromboembolic pulmonary hypertension
• Echocardiographic features of Ebstein's anomaly of the tricuspid valve

Other topics in the «Chest Radiology» section

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