Valvular Pulmonary Stenosis (PS) is a form of right ventricular outflow tract obstruction where the pulmonary valve leaflets are thickened, fused, or dysplastic, impeding blood flow from the right ventricle (RV) to the pulmonary artery.
Pathophysiology
The narrowing of the valve increases the workload on the right ventricle. To maintain adequate cardiac output across the stenotic orifice, the RV must generate higher pressures, leading to:
- Concentric RV Hypertrophy: A compensatory mechanism to handle the pressure overload.
- Post-stenotic Dilation: The high-velocity jet striking the wall of the pulmonary artery and the eddy currents there often causes it to dilate.
- Right Heart Failure: Eventually, the RV may fail, leading to systemic venous congestion.
Clinical Presentation
Most patients with mild-to-moderate PS are asymptomatic for years. Symptoms typically correlate with the severity of the obstruction:
- Mild/Moderate: Often incidentally discovered during a routine exam.
- Severe: Dyspnea on exertion, fatigue, and occasionally chest pain or syncope (similar to aortic stenosis).
- Physical Exam Findings:
- Systolic Ejection Murmur: A harsh crescendo-decrescendo murmur at the left upper sternal border. Longer murmur is heard in severe pulmonary stenosis
- Systolic Ejection Click: Often decreases in intensity during inspiration (a unique feature, as most right-sided sounds increase with inspiration). This phasic ejection click is closer to the first heart sound in severe pulmonary stenosis compared to mild pulmonary stenosis.
- Widely Split S2: Due to prolonged RV ejection time.
Severity Classification
Severity is primarily defined by the peak instantaneous gradient across the valve measured via Doppler echocardiography:
| Severity | Peak Gradient (mmHg) | Peak Velocity (m/s) |
| Mild | < 36 | < 3 |
| Moderate | 36 – 64 | 3 – 4 |
| Severe | > 64 | > 4 |
Diagnostic Evaluation
- Echocardiography: The gold standard. It assesses valve morphology (e.g., doming, dysplasia), measures gradients, and evaluates RV function/size.
- ECG: May show right axis deviation, RV hypertrophy (R > S in V1), or right atrial enlargement (P-pulmonale).
- Cardiac MRI/CT: Useful if echo windows are poor or to precisely quantify RV volumes and the main pulmonary artery anatomy.
- Chest X-ray: Often shows a prominent main pulmonary artery segment due to post-stenotic dilation.
Management & Intervention
Management depends on the pressure gradient and the presence of symptoms.
- Medical Management: Primarily focused on endocarditis prophylaxis (in specific cases) and monitoring.
- Balloon Pulmonary Valvuloplasty (BPV): The treatment of choice for symptomatic patients or those with a peak gradient > 50-60 mmHg. It has excellent long-term results.
- Surgical Valvotomy: Reserved for cases where the valve is severely dysplastic, or there is associated sub-valvular or supra-valvular stenosis that a balloon cannot address.
In the context of valvular pulmonary stenosis (PS), distinguishing between a classic “doming” valve and a “dysplastic” valve is critical because it directly determines whether Balloon Pulmonary Valvuloplasty (BPV) will be successful. Dysplastic pulmonary valve is typically seen in Noonan syndrome.
1. Classic Mobile Valve (Typical PS)
This is the most common form, often seen in isolated congenital PS.
- Echo Appearance: The leaflets are thin and flexible but fused at the commissures. During systole, the valve “domes” into the pulmonary artery.
- Jet Dynamics: You will see a narrow, high-velocity central jet.
- Success Rate: Highly amenable to BPV. The balloon effectively “cracks” the fused commissures, often resulting in a near-normal gradient post-procedure.
2. Dysplastic Pulmonary Valve
Commonly associated with Noonan Syndrome.
- Echo Appearance: The leaflets are markedly thickened, irregular, and redundant. There is often very little commissural fusion; instead, the obstruction is caused by the sheer bulk of the valve tissue and a small valve annulus.
- Mobility: There is minimal to no “doming.” The leaflets move poorly and appear “rubbery.”
- Success Rate: Frequently fails BPV because there are no fused commissures to split. These patients often require surgical intervention (valvotomy or valve replacement).
3. Assessment “Pearls”
- Subcostal View: This is often the best window in pediatric cases to get a clear “en face” view of the valve and the best alignment for CW Doppler.
- The “Infundibulum” Check: Always look for secondary sub-valvular hypertrophy. If the PS is severe, the RVOT (infundibulum) can become dynamically obstructed. If you see a “dagger-shaped” late-peaking spectral Doppler envelope, you are likely picking up this dynamic component.
- PR Evaluation: Check the degree of Pulmonary Regurgitation. If the valve is already significantly regurgitant and stenotic (a “mixed” lesion), BPV may worsen the PR to a point that is clinically poorly tolerated.
- Z-Scores: In pediatric patients, always calculate the Z-score of the pulmonary valve annulus. If the annulus is hypoplastic (Z-score < -2), a balloon alone is unlikely to solve the obstruction.
4. Associated Findings to Document
- RV Strain: Look for flattening of the interventricular septum (D-shaped LV) in short-axis, indicating RV pressure overload.
- Tricuspid Regurgitation (TR): Use the TR jet velocity to estimate the RV systolic pressure (RVSP = 4V2 + RAP). In isolated PS, the RVSP will be significantly higher than the PA pressure.