Pulmonary Valvular Stenosis

Severity

• Mild: Peak Doppler gradient < 36 mmHg (mean < 20 mmHg) 

• Moderate: Peak Doppler gradient 36–64 mmHg (mean ~20–40 mmHg) 

• Severe: Peak Doppler gradient ≥ 64 mmHg (mean > 40 mmHg)

• Critical stenosis: Inadequate anterograde flow through RVOT. Prostaglandin-E1 dependent for pulmonary blood flow. Defined less by absolute gradient and more by ductal-dependency for pulmonary blood flow. In neonates with poor RV output, the gradient may be deceptively low (low-flow, low-gradient physiology), yet the lesion is life-threatening. These infants often require prostaglandin to maintain ductal patency and urgent balloon valvuloplasty.

• A hypertrophied, noncompliant RV may lead to high right atrial pressures and a right-to-left shunt at the foramen ovale, even if the measured gradient is not extreme. Clinical cyanosis in this setting should be considered equivalent to severe/critical PS.

• The end-spectrum of pulmonary stenosis is pulmonary atresia (complete obstruction). 

• The gradient through the pulmonary valve must be taking into account that the patient may have downstream low flow and a low gradient may not mean that the obstruction is not severe. The numbers must be interpreted in context of right ventricular (RV) function, RV compliance, and ductal shunting. A patent ductus arteriosus can mask the true hemodynamic severity by providing an alternate route for pulmonary blood flow.

• Reference: https://www.ncbi.nlm.nih.gov/books/NBK560750/ and https://pmc.ncbi.nlm.nih.gov/articles/PMC10320808/ 

Cyanosis after balloon valvuloplasty - Why?

Even after successful relief of right ventricular outflow tract (RVOT) obstruction, infants may remain cyanotic due to persistence of a right-to-left atrial shunt. Cyanosis in this context reflects admixture of deoxygenated blood from the right atrium with oxygenated pulmonary venous return entering the systemic circulation. In conditions such as severe RVOT obstruction (e.g., critical pulmonary stenosis, pulmonary atresia with a restrictive ventricular septal defect [VSD], or pulmonary atresia with intact ventricular septum), there is little or no antegrade flow from the right ventricle (RV) to the pulmonary arteries. When obstruction develops in utero, the RV is chronically exposed to elevated afterload, leading to maladaptive changes: hypertrophy, poor compliance, and in some cases reduced cavity size. This process of RV hypertrophy and remodelling is also seen in antenatal ductal closure due to the increased RV afterload being exposed to high PVR. Importantly, for this maladaptation to occur, afterload must rise. Another factor is RV cavity size. In some infants, hypertrophy itself “fills in” the chamber, reducing its effective volume and compliance; in others, there may be true RV hypoplasia. In the latter scenario, compliance does not improve because remodeling cannot enlarge the underdeveloped ventricle. By contrast, in an adequately sized RV with marked hypertrophy, decompression after relief of obstruction allows gradual remodeling. However, this process takes time—days to weeks—before the RV wall thins, compliance improves, and right-to-left shunting decreases. Therefore, even with a technically successful RVOT intervention (e.g., valvotomy, balloon dilation, or surgical relief of obstruction), cyanosis may persist until RV remodeling occurs. During this transitional period, maintaining ductal patency with prostaglandin may be necessary to ensure adequate pulmonary blood flow and pulmonary venous return to the left atrium, thereby supporting systemic oxygenation. It is often attempted to wean the PGE after the intervention and see the tolerance in terms of saturations.

After relief of RVOT obstruction, the ductus is no longer required once antegrade pulmonary blood flow is sufficient to maintain stable systemic saturations without prostaglandin support. In the immediate post-intervention period, saturations of 80–85% are generally considered acceptable, while values persistently below 75% suggest inadequate pulmonary blood flow or excessive right-to-left atrial shunting, in which case the duct should remain open. Higher saturations above 90% are reassuring, but not strictly necessary once antegrade flow is established. The key determinants are hemodynamic: Doppler evidence of forward flow into the pulmonary arteries, absence of ductal dependency, adequate pulmonary venous return to the left atrium, and right ventricular function that is sufficient to sustain pulmonary circulation. Because a hypertrophied and poorly compliant right ventricle may still generate significant atrial shunting, the duct may need to remain open until remodeling improves filling. In practice, prostaglandin is continued if saturations fall below 75–80% or if systemic perfusion is compromised, and it can be weaned once saturations remain consistently above 80–85% on room air or minimal oxygen with evidence of stable pulmonary blood flow. Closure of the duct is therefore acceptable when the infant maintains adequate systemic saturations, shows no signs of acidosis or hypoperfusion, and has demonstrable antegrade pulmonary blood flow on echocardiography.

Quick Review - Tetralogy of Falot with Pulmonary Atresia - Pulmonary Atresia with VSD (PA-VSD)

Pulmonary atresia with ventricular septal defect (PA-VSD) represents the most severe form of pulmonary stenosis. In the French literature it is often referred to as APSO (atrésie pulmonaire à septum ouvert), though this terminology is imprecise and best avoided, as some patients may present with pulmonary atresia and a VSD outside the tetralogy of Fallot (TOF) spectrum—for example, in association with a double inlet left ventricle. Clinically and embryologically, PA-VSD is considered an “extreme” variant of TOF and is usually classified as TOF with pulmonary atresia, given the shared genetic and developmental background. In fetal life, the physiology mirrors that of TOF when the VSD is non-restrictive: both ventricles preload identically, face the same afterload, and maintain preserved intrinsic properties of diastolic filling and systolic contractility. Because the pulmonary artery is atretic, all antegrade output must traverse the ascending aorta. Despite this, fetal perfusion remains normal, and coarctation does not occur, since the left ventricular outflow tract and ascending aorta provide adequate forward flow to the cerebral and coronary circulations, continuing through the isthmus into the descending aorta. The defining hemodynamic feature is the role of the ductus arteriosus, which becomes the sole source of pulmonary perfusion. Blood flows retrograde from the aorta into the pulmonary arteries, and this reversal of flow profoundly alters ductal morphology. Instead of forming a smooth second arch, the ductus often arises from the undersurface of the aortic arch and develops a tortuous, angulated, or looped course. This illustrates how flow not only governs vessel caliber but also sculpts its form. Clinically, these morphological changes pose significant challenges for catheter-based interventions, making ductal stenting technically demanding and often necessitating alternative access routes, such as via the carotid or innominate artery, rather than the standard femoral approach.

Echocardiography indicating pulmonary valvular stenosis

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. 

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. 

Balloon dilatation of the pulmonary valves by catheterism

Presentation by Dr Shiran Moore and Mrs Laila Wazneh on pulmonary valvular stenosis