Mild: Peak gradient <36 mm Hg
Moderate: Between 36 and 64 mm Hg
Severe stenosis: >64 mm Hg
Critical stenosis: Inadequate anterograde flow through RVOT. Prostaglandin-E1 dependent for pulmonary blood flow.
Reference: https://www.ncbi.nlm.nih.gov/books/NBK560750/ and https://pmc.ncbi.nlm.nih.gov/articles/PMC10320808/
Pulmonary atresia with a VSD and a PDA:
Qp/Qs Example Calculation:
Aortic saturation is 85%, Pulmonary Artery saturation is the same because fed by the left to right PDA (85%)
Assuming a normal systemic A-V difference (oxygen consumption in the systemic compartment) of 30%, then vena cava saturations will be approximately 55% (85-30).
Pulmonary vein saturation is 100% if no V/Q mismatch
Then Qp/Qs = (Aortic Sat - Mixed Venous Sat) / (Pulm Vein Sat - Pulmonary Artery Sat) = (85-55)/(100-85) = 30/15 = 2/1.
Clinical Paradox: Patients can be cyanotic (blue) yet present with symptoms of hyper-flow (e.g., dyspnea) due to elevated pulmonary blood flow by the PDA and high filling pressures. This emphasizes that cyanosis does not directly correlate with low pulmonary blood flow in all congenital heart diseases. ◦
Morphological Consequences: High pulmonary flow can lead to dilated left atrium and left ventricle. The management of oxygen administration in these children is complex since it can further vasodilate the pulmonary vascualture, and requires careful consideration once the diagnosis is established
Pulmonary valve is seen in parasternal long axis view. While it is opening, there is doming of the pulmonary valve, which has thick leaflets.
The ductus arteriosus (tortuous) is seen here and left to right.
Still image with the pulmonary valve closed in parasternal long axis view. The valve is thick and leaflet tips are abnormal.
The left and right pulmonary arteries are of normal caliber. The ductal flow during fetal life allows for appropriate growth of the pulmonary vessels.
Measurement of the left to right PDA. The CW-doppler indicates that the profile is left to right and with a peak gradient in systole of 30 mmHg. Knowing that the systolic blood pressure of the newborn was 60 mmHg, one can assume that the systolic pulmonary arterial pressure is about 30 mmHg. The gradient through the valve was 90 mmHg, indicated that the RV peak systolic pressure was around 120 mmHg. The RV is suprasystemic.
Some flow passing through the pulmonary valve with acceleration via Colour Doppler. The colour box must show flow through the pulmonary valve. In pulmonary atresia, there is no flow through the valve via colour doppler, but flow is seen retrograde from the ductus arteriosus.
Apical view showing the RV outflow tract and the colour flow box indicating that flow is originating below the valve and goes through the stenotic valve with acceleration.
The apical 4 chamber view indicates that there is good function of the right ventricle. There is some hypertrophy of the RV. However, one may miss the presence of RVOT obstruction without the appropriate sweep towards the RVOT and with Colour Doppler. The RV is non-apex forming but tripartite. There is a hypertrabeculated left ventricle, possibly from the increased volume of flow towards the LV during fetal life.
The CW-Doppler indicates a gradient through the valve of 82-92 mmHg. This indicates a significant obstruction.
Visualization of the valve in 2D still frame, with measurements below of the opening (orifice). The measurement is often difficult to make in newborns due to non-homogeneous opening of the valve. The orifice is not circular but irregular in shape.