Stenosis Pulmonal

01Pathophysiology

Pulmonary stenosis refers to obstruction of right ventricular outflow at or near the pulmonic valve. The overwhelming majority of cases are congenital in origin, with the valve leaflets being thickened, fused at the commissures, and forming a dome-shaped structure that restricts opening during systole. This creates a fixed obstruction that the right ventricle must pump against.

Because the RV faces a chronically elevated afterload, it undergoes concentric hypertrophy as a compensatory response. In mild-to-moderate disease, this hypertrophy is sufficient to maintain cardiac output at rest, which is why most patients remain asymptomatic for years. The murmur is often discovered incidentally during a routine physical examination.

As the stenosis progresses or when the RV can no longer compensate, right ventricular failure develops. The failing RV cannot adequately fill the pulmonary vasculature, leading to decreased pulmonary blood flow and therefore reduced left-sided preload. This explains the exertional dyspnea and fatigue. Simultaneously, elevated RV end-diastolic pressure transmits backward into the right atrium and systemic venous system, producing jugular venous distension, hepatomegaly, peripheral edema, and a prominent "a" wave on JVP tracings (reflecting the atrium contracting against a stiff, hypertrophied RV).

The wide splitting of S2 is a direct hemodynamic consequence: the stenotic valve delays RV ejection, so the pulmonic valve closes later than normal. The more severe the stenosis, the later P2 occurs. In critical stenosis, P2 may become inaudible entirely because the valve is so rigid it no longer produces an audible closure sound.

The ejection click in pulmonary stenosis has a unique behavior compared to aortic stenosis. It decreases with inspiration. During inspiration, increased venous return to the right heart partially opens the domed pulmonic valve before systole begins, so when the RV contracts, there is less abrupt tensing of the valve and thus a softer or absent click. This is the only right-sided auscultatory finding that decreases with inspiration, making it a classic exam discriminator.

Acquired causes are far less common. Carcinoid syndrome produces serotonin and other vasoactive substances that cause fibrous plaque deposition on right-sided valve endocardium (because the lung metabolizes serotonin before it reaches the left heart). This leads to pulmonic stenosis and tricuspid regurgitation.

02Classification and Clinical Manifestation

Classification by Anatomy

Classification by Severity (Doppler Echocardiography)

Syndrome Associations

03Diagnostic Workup

Echocardiography is the cornerstone of evaluation. It confirms the diagnosis, defines the anatomy (valvular vs. subvalvular vs. supravalvular), and quantifies severity through Doppler-derived pressure gradients. A peak instantaneous gradient above 64 mmHg or a mean gradient above 40 mmHg indicates severe stenosis requiring intervention. TTE also assesses RV size and function, the degree of tricuspid regurgitation (which reflects RV pressure overload), and whether the interatrial septum is intact or has a PFO/ASD that could permit right-to-left shunting.

ECG is not diagnostic on its own but provides supporting evidence of chronicity. In mild PS, the ECG may be entirely normal. As severity increases, you expect to see right axis deviation and RV hypertrophy pattern (dominant R wave in V1, deep S wave in V5-V6). Right atrial enlargement manifests as peaked P waves (P pulmonale) in the inferior leads.

Chest X-ray classically shows post-stenotic dilatation of the main pulmonary artery. This occurs because the high-velocity jet through the stenotic valve creates turbulence that dilates the PA segment just beyond the valve. The heart size may be normal in compensated disease or enlarged if RV failure has developed. Notably, post-stenotic dilatation is seen with valvular PS but typically not with subvalvular or supravalvular stenosis (because the jet hits a different anatomical segment).

Cardiac catheterization is reserved for cases where intervention is planned or when noninvasive data is inconclusive. It provides direct measurement of the pressure gradient between the RV and pulmonary artery and is performed simultaneously with balloon valvuloplasty when treatment is indicated.

04Management and Treatment

Percutaneous balloon valvuloplasty is the definitive treatment for typical congenital valvular PS. The procedure involves threading a balloon catheter across the stenotic valve and inflating it to split the fused commissures. Success rates exceed 90%, with low complication rates and durable long-term results. The procedure is indicated when the peak catheterization gradient exceeds 60 mmHg (or Doppler peak gradient >64 mmHg), or at lower gradients if the patient is symptomatic.

A critical distinction for exam purposes: balloon valvuloplasty works well for domed valves with fused commissures but is ineffective for dysplastic valves. In Noonan syndrome, the pulmonic valve leaflets are thickened, myxomatous, and immobile, without true commissural fusion. Inflating a balloon across such a valve does not relieve obstruction because there are no commissures to split. These patients require surgical valvotomy or valve replacement.

For neonatal critical PS, the clinical picture is a cyanotic newborn with duct-dependent pulmonary blood flow. The immediate stabilization step is prostaglandin E1 infusion to prevent ductal closure, followed by urgent balloon valvuloplasty. This is analogous to any duct-dependent right-sided lesion (e.g., pulmonary atresia, critical PS, severe Tetralogy of Fallot in neonates).

After successful balloon valvuloplasty, patients generally have excellent long-term outcomes. Follow-up echocardiography monitors for residual stenosis and the development of pulmonic regurgitation (the most common post-procedure sequela, usually mild and well tolerated). Endocarditis prophylaxis is not routinely recommended for isolated PS after successful treatment, unless there is a prosthetic valve or prior endocarditis history.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The single most tested concept in pulmonary stenosis is the behavior of the ejection click. Students commonly apply the rule that all right-sided heart sounds increase with inspiration and mark the wrong answer. The ejection click of PS is the notable exception: it decreases with inspiration because the increased venous return pre-opens the domed valve, eliminating the abrupt snap. If a vignette describes a systolic click at the left upper sternal border that becomes softer when the patient takes a deep breath, that is pulmonary stenosis until proven otherwise.

The second common trap involves confusing PS with ASD. Both can present as an asymptomatic murmur at the pulmonic area with widened S2 splitting. The distinguishing feature is whether the split is fixed (ASD) or variable (PS). Test-writers rely on this distinction heavily, and a single word in the stem ("fixed" vs. "wide") changes the correct answer entirely.

A third pitfall is the management of dysplastic valves. Students who memorize "balloon valvuloplasty for pulmonic stenosis" without nuance will select the wrong treatment for a patient with Noonan syndrome features. When the vignette describes short stature, a webbed neck, and a dysplastic pulmonic valve on echocardiography, the correct answer shifts to surgical intervention.

Finally, for neonatal critical PS, the tested competency is recognizing a duct-dependent lesion. Any cyanotic neonate who worsens as the ductus closes should trigger the reflex to start prostaglandin E1 infusion as the immediate stabilization step, before any definitive repair.

The core skill being assessed across all PS questions is the ability to integrate auscultatory findings (murmur location, click behavior, S2 splitting pattern) with hemodynamic reasoning to arrive at the correct diagnosis and appropriate next step.