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Summary Table

Feature	Detail
Risk Factors	Male sex (4:1 ratio), bicuspid aortic valve (most common congenital valve anomaly), Turner syndrome, Williams syndrome (supravalvular type), family history of left-sided obstructive lesions
Etiology	Congenital malformation of the aortic valve (bicuspid or unicuspid morphology), subaortic fibrous membrane, or supravalvular aortic narrowing
Patient Presentation	Often asymptomatic with incidental murmur in childhood; severe cases present with exertional dyspnea, chest pain, syncope on exertion, or heart failure in neonates (critical AS)
Classic Physical Exam	Harsh crescendo-decrescendo systolic ejection murmur at the right upper sternal border radiating to the carotids, systolic ejection click (valvular type only), parvus et tardus pulse, narrowed pulse pressure, precordial thrill at the suprasternal notch
Key Diagnostic Results	Echocardiography showing reduced valve orifice area with elevated transvalvular gradient; ECG with LVH and strain pattern; chest X-ray with post-stenotic dilation of the ascending aorta
Management	Observation for mild AS; balloon valvuloplasty for symptomatic or severe valvular AS in children; surgical repair (Ross procedure or valve replacement) when valvuloplasty fails or anatomy is unsuitable; prostaglandin E1 (PGE1) for critical neonatal AS to maintain ductal patency
Keywords	"Systolic ejection click," "crescendo-decrescendo murmur at RUSB," "syncope on exertion in a child," "bicuspid aortic valve," "post-stenotic dilation," "parvus et tardus," "elfin facies" (supravalvular)

1. Pathophysiology

The aortic valve normally has three cusps (tricuspid morphology). In pediatric aortic stenosis, the valve is most commonly bicuspid, meaning two cusps are fused, creating a functionally narrowed orifice. Less commonly, the valve may be unicuspid (often presenting in neonates with critical obstruction). Unlike the degenerative calcific process seen in elderly adults, pediatric AS is driven by abnormal embryologic valve development.

The narrowed valve creates obstruction to left ventricular outflow. To maintain cardiac output across this fixed obstruction, the left ventricle must generate higher systolic pressures. Over time, this chronic pressure overload triggers concentric left ventricular hypertrophy (LVH), where the ventricular wall thickens inward without chamber dilation. This is a compensatory response, but it comes at a cost: the thickened myocardium has increased oxygen demand while simultaneously compressing intramural coronary vessels, reducing subendocardial perfusion. This mismatch between supply and demand explains why patients experience exertional chest pain and syncope, as the hypertrophied ventricle cannot augment output during exercise, and coronary flow reserve is diminished.

In the neonate with critical aortic stenosis, the obstruction is so severe that the left ventricle cannot generate adequate systemic output. These neonates are ductal-dependent for systemic circulation, meaning blood reaches the systemic circulation via right-to-left shunting through a patent ductus arteriosus. When the ductus closes in the first days of life, the neonate rapidly develops cardiogenic shock with poor perfusion, metabolic acidosis, and cardiovascular collapse.

The systolic ejection click heard in valvular AS is produced by the sudden tensing of the abnormal but still mobile valve cusps at the onset of ejection. This click is absent in subvalvular and supravalvular types because the valve leaflets themselves are structurally normal. The post-stenotic dilation of the ascending aorta seen on chest X-ray occurs because the high-velocity jet emerging from the stenotic valve creates turbulent flow that batters the aortic wall, causing localized dilation.

2. Classification and Clinical Manifestation

By Anatomic Level of Obstruction

Type	Anatomic Lesion	Association	Distinguishing Features
Valvular (most common, ~70%)	Bicuspid or unicuspid aortic valve with commissural fusion	Coarctation of the aorta, Turner syndrome	Systolic ejection click present; post-stenotic dilation of ascending aorta on CXR
Subvalvular (Subaortic) (~20%)	Discrete fibrous membrane or fibromuscular ridge below the aortic valve in the LVOT	Often develops progressively; may cause secondary aortic regurgitation from jet lesion on the valve	No ejection click; aortic regurgitation murmur frequently coexists; no post-stenotic aortic dilation
Supravalvular (~10%)	Narrowing of the ascending aorta above the sinotubular junction	Williams syndrome (elastin gene deletion on chromosome 7)	Elfin facies, hypercalcemia, developmental delay, gregarious personality; no ejection click; blood pressure higher in right arm than left (Coanda effect); coronary ostia exposed to high pressure (risk of coronary ischemia)

Severity Grading

Severity	Mean Gradient	Peak Gradient
Mild	< 25 mmHg	< 40 mmHg
Moderate	25 to 49 mmHg	40 to 69 mmHg
Severe	$\geq$ 50 mmHg	$\geq$ 70 mmHg

Clinically, mild aortic stenosis is often discovered incidentally when a murmur is heard during a routine well-child visit. The child is asymptomatic and active without restriction. As severity progresses to moderate or severe, the classic triad of exertional symptoms emerges: dyspnea on exertion, anginal chest pain, and syncope. Any child who presents with syncope during physical activity and a systolic murmur should raise immediate concern for severe outflow obstruction.

3. Diagnostic Workup

Test	Role	Key Findings
Echocardiography	Best initial test AND confirmatory test	Valve morphology (bicuspid vs. tricuspid), transvalvular gradient, valve area, LV function, level of obstruction, associated lesions
ECG	Screening / baseline assessment	LVH with strain pattern (ST depression and T-wave inversion in lateral leads); severe cases show ST-segment changes at rest
Chest X-ray	Adjunctive	Post-stenotic dilation of the ascending aorta (valvular type); cardiomegaly in decompensated cases
Exercise stress testing	Functional severity assessment	Reproduces symptoms, ST-segment changes, or abnormal blood pressure response (failure of BP to rise or frank hypotension with exercise)
Cardiac catheterization	Interventional (therapeutic more than diagnostic)	Direct measurement of peak-to-peak gradient across the valve; simultaneous balloon valvuloplasty can be performed

Echocardiography with Doppler is the cornerstone of both diagnosis and follow-up. It answers every question the clinician needs: What is the valve morphology? Where is the obstruction? How severe is the gradient? Is the LV compensating? Are there associated lesions such as coarctation or mitral valve abnormalities? In pediatric cardiology, echo is both the best initial test and the gold standard for noninvasive assessment.

The ECG is important for detecting LVH and strain. In a vignette, look for tall R waves in V5-V6 with ST depression and T-wave inversion in the lateral leads. The presence of a strain pattern at rest in a child with known AS suggests severe disease and is an indication for intervention even if the child appears asymptomatic.

Exercise stress testing is used in children with moderate AS who claim to be asymptomatic. The test is considered positive (and intervention warranted) if the child develops symptoms, ischemic ECG changes, or an abnormal blood pressure response (defined as failure of systolic BP to increase by at least 20 mmHg, or a drop in BP). This is a high-yield test concept: the question will describe a "asymptomatic" child with moderate AS and ask for the next step, which is exercise testing to unmask latent hemodynamic compromise.

Cardiac catheterization in modern pediatric practice is primarily therapeutic (balloon valvuloplasty) rather than purely diagnostic, since echocardiography provides the needed hemodynamic data noninvasively.

4. Management and Treatment

Clinical Scenario	Management	Details
Critical neonatal AS	PGE1 infusion followed by urgent balloon valvuloplasty	PGE1 (alprostadil) at 0.05 to 0.1 mcg/kg/min IV to maintain ductal patency; stabilize with inotropes and ventilatory support before catheterization
Mild AS (asymptomatic, low gradient)	Observation with serial echocardiography	Echo every 1 to 2 years; restrict from competitive sports if moderate or severe; endocarditis prophylaxis no longer routinely recommended (per AHA guidelines)
Moderate AS, asymptomatic	Exercise stress testing to stratify risk	If normal exercise response, continue surveillance; if abnormal, proceed to intervention
Severe valvular AS or symptomatic moderate AS	Percutaneous balloon aortic valvuloplasty	First-line intervention in children; palliative (does not create a "normal" valve); often produces some degree of aortic regurgitation
Failed valvuloplasty, recurrent stenosis, or significant AR	Surgical intervention	Ross procedure (pulmonary autograft replaces aortic valve + pulmonary homograft in pulmonary position) preferred in growing children; mechanical valve replacement is a last resort due to lifelong anticoagulation and inability to grow with the child
Subvalvular AS	Surgical resection of the membrane	Balloon valvuloplasty is NOT effective (obstruction is below the valve); surgery is the primary treatment
Supravalvular AS	Surgical patch aortoplasty	Address the underlying connective tissue disorder (Williams syndrome workup); balloon dilation is generally ineffective

For the critical neonate, the immediate step before any intervention is prostaglandin E1. This is the answer the exam is looking for whenever a neonate presents with signs of cardiovascular collapse and a suspected ductal-dependent lesion. PGE1 reopens or maintains the ductus arteriosus, restoring systemic perfusion while the team prepares for catheter-based or surgical intervention. Side effects of PGE1 that are commonly tested include apnea (requiring intubation readiness), fever, and hypotension.

Balloon aortic valvuloplasty is the preferred first-line intervention for symptomatic valvular AS in children because it avoids open-heart surgery and cardiopulmonary bypass. However, it is palliative rather than curative. The procedure relieves the gradient but almost always induces some degree of aortic regurgitation by tearing the fused commissures. Patients require lifelong follow-up because restenosis and progressive regurgitation will eventually necessitate surgical valve intervention.

The Ross procedure is favored in the pediatric population because the pulmonary autograft is a living tissue valve that grows with the child, eliminating the need for repeat operations due to somatic growth and avoiding lifelong anticoagulation required by mechanical prostheses. The trade-off is that it converts single-valve disease into a two-valve problem, as the pulmonary homograft placed in the pulmonary position will eventually degenerate and require replacement.

Activity restriction is a frequently tested management concept. Children with mild AS can participate in all activities. Those with moderate AS should avoid competitive athletics and isometric exercise (e.g., weightlifting). Children with severe AS are restricted from all strenuous activity due to the risk of sudden cardiac death from exercise-induced arrhythmia in the setting of a hypertrophied, ischemia-prone ventricle.

5. Differential Diagnosis and Distractors

Differential Diagnosis	Why It Looks Similar	Key Discriminator
Hypertrophic cardiomyopathy (HCM)	Systolic murmur, LVH on ECG, exertional syncope in a young patient	HCM murmur increases with Valsalva and standing (decreased preload); AS murmur decreases. HCM has asymmetric septal hypertrophy on echo, no ejection click, and family history of sudden death
Pulmonary stenosis (PS)	Systolic ejection murmur with an ejection click in a child	PS murmur is heard best at the left upper sternal border (not right); the ejection click of PS decreases with inspiration (the only right-sided click to do so); ECG shows RVH rather than LVH
Ventricular septal defect (VSD)	Systolic murmur in a child	VSD produces a holosystolic (pansystolic) murmur at the left lower sternal border, not a crescendo-decrescendo murmur; no ejection click
Coarctation of the aorta	Can coexist with bicuspid aortic valve; presents with LVH and systolic murmur	Coarctation has upper extremity hypertension with diminished femoral pulses (brachial-femoral delay); rib notching on CXR in older children; "figure 3" sign on CXR
Innocent (Still) murmur	Systolic murmur in an asymptomatic child	Still murmur is musical/vibratory, grade I-II, changes with position, no click, no thrill, normal ECG and echo

6. Traps and High-Yield Pearls

The most common way students get questions on pediatric aortic stenosis wrong is by confusing the three anatomic subtypes and applying the wrong intervention. Balloon valvuloplasty is the correct answer only for valvular AS. If the vignette describes a progressive murmur with aortic regurgitation but no ejection click, this is subvalvular (membranous) AS, and the answer is surgical resection, not balloon dilation. Similarly, if the stem describes an child with elfin facies, developmental delay, and a suprasternal murmur with right arm blood pressure higher than left, this is supravalvular AS from Williams syndrome, and balloon dilation is again not the answer.

A second common trap involves the neonatal presentation. When a newborn presents in shock with poor pulses and metabolic acidosis in the first week of life, the next best step is PGE1, not immediate echocardiography or surgery. Students who jump to "get an echo" miss that this is a ductal-dependent emergency requiring pharmacologic stabilization first.

Finally, remember that the ejection click is the single physical exam finding that localizes the obstruction to the valve level. Its presence confirms valvular AS; its absence should make you consider subvalvular or supravalvular pathology. The click is best heard at the apex, does not vary with respiration (unlike the pulmonary ejection click), and disappears as the valve calcifies and loses mobility (more relevant in adults, but occasionally tested).

The core competency being tested across all pediatric AS questions is the ability to localize the level of obstruction based on physical exam and associations, match the correct intervention to the correct subtype, and recognize ductal-dependent physiology in the neonate.

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