The normal aortic valve is a trileaflet semilunar valve located at the junction of the left ventricular outflow tract (LVOT) and the ascending aorta. It has three cusps:

• Right coronary cusp (gives off right coronary artery)
• Left coronary cusp (gives off left coronary artery)
• Non-coronary cusp

Each cusp has a sinus of Valsalva behind it. The coronary arteries arise from the right and left coronary sinuses during diastole — this is critically important because coronary filling depends on diastolic aortic pressure.

The LVOT is the region between the body of the left ventricle and the aortic valve. Anatomically, it is bounded by:

• Anteriorly: the interventricular septum
• Posteriorly: the anterior mitral valve leaflet

This is relevant because subvalvar AS involves obstruction within the LVOT (below the valve), while supravalvar AS involves narrowing above the valve in the ascending aorta.

• During systole, the valve opens to allow ejection of blood from LV → aorta
• During diastole, the valve closes, and the sinuses of Valsalva create vortices that fill the coronary arteries
• Normal aortic valve area in adults is 3–4 cm²; in children it is proportionally smaller and is normalised to body surface area (BSA)

Congenital AS can occur at different levels ^[2]:

• Unicuspid valve: Most severe form, typically presents as critical AS in neonates with a pinhole opening. The valve has no real commissures — just a tiny central orifice. This causes near-total obstruction.
• Bicuspid aortic valve (BAV): The most common form in older infants and children. Two cusps instead of three, often with a raphe (fibrous ridge) representing the fused commissure. Even if not significantly stenotic at birth, BAV is inherently abnormal and undergoes progressive fibrosis, calcification, and stiffening over decades.
• Dysplastic valve: Thickened, myxomatous cusps that do not open well; may be seen in association with other syndromes.

• Due to fibrous membrane, fibromuscular ridge, or asymmetric septal hypertrophy (in HOCM) ^[2]
• Discrete membrane is the most common type — a thin crescent-shaped or circumferential fibrous membrane just below the aortic valve
• Tunnel-type: long segment of muscular narrowing of the LVOT (more severe, harder to treat)
• Important: subvalvar AS is often not present at birth but develops in early childhood (suggesting a flow-related aetiology with shear stress causing fibrous tissue formation)
• Almost always progressive — the turbulent jet damages the aortic valve, leading to progressive AR ^[2]

• Least common type
• Usually in Williams syndrome ^[2]
• Williams syndrome (7q11.23 microdeletion including the elastin gene, ELN) → deficient elastin → thick, non-compliant arterial walls → narrowing of ascending aorta just above the sinuses of Valsalva
• Progressive stenosis in Williams syndrome ^[2]
• Can also be autosomal dominant familial form without Williams syndrome

According to age ^[3][4]:

The fundamental problem in congenital AS is obstruction to LV outflow → the LV must generate higher systolic pressures to eject blood past the narrowed orifice → LV pressure overload.

Gradient develops across the aortic valve, obstructing aortic outflow → PRESSURE OVERLOAD ^[3]

Compensatory LVH (no cavity dilatation until HF develops) ^[3][4]

Let's trace the pathophysiology step by step:

When the LV faces chronically elevated afterload, it responds by laying down more sarcomeres in parallel (as opposed to in series, which would cause dilatation). This produces concentric hypertrophy — the wall gets thicker but the cavity size remains normal or even shrinks.

• Why concentric? The law of Laplace: Wall stress (σ) = (Pressure × Radius) / (2 × Wall thickness). By increasing wall thickness, the LV normalises wall stress despite higher intraventricular pressures.
• LV pressure overload → LVH — usually preserved systolic function in children ^[2]. This is a key paediatric point: children can maintain normal ejection fraction for a long time despite severe stenosis.

The thickened, stiff LV wall does not relax properly during diastole:

• Impaired relaxation → reduced early diastolic filling
• The atrium must contract more forcefully to fill the stiff LV → S4 gallop (audible fourth heart sound) in older children
• Elevated LV end-diastolic pressure (LVEDP) → transmitted back to LA → pulmonary veins → pulmonary congestion

This is a critical concept for exams:

↓ Coronary perfusion due to severe AS + ↑ LV EDP (stretched myocardium) ^[2] ↑ Myocardial O₂ consumption due to ↑ LV systolic BP → ↑ afterload ^[2]

Increased demand:

• LVH → more muscle mass requiring more oxygen
• Higher wall stress during systole → more work per contraction
• ↑ LV systolic BP → ↑ afterload ^[2]

Decreased supply:

• Coronary arteries fill during diastole; in severe AS, the elevated LVEDP reduces the coronary perfusion gradient (coronary perfusion pressure = aortic diastolic pressure − LVEDP)
• Prolonged systolic ejection time (the LV takes longer to empty through a narrow orifice) → shortened diastole → less time for coronary filling
• Subendocardial compression: the high intracavitary pressures compress the innermost layer of myocardium, which is furthest from epicardial coronary supply

Eventually, these result in myocardial fibrosis → LV failure ^[2]

Aortic stenosis causes LVH → larger heart muscle wall, perfusion is not sufficient. Aortic stenosis causes LVOT blockage → less blood going into coronary cusps, and coronary arteries during the diastolic phase ^[5]

Inadequate increase in CO during exercise ^[3][4]

In a normal heart, exercise causes:

• Increased heart rate
• Increased contractility (via sympathetic drive)
• Peripheral vasodilation (in exercising muscles)

In congenital AS:

• The fixed obstruction limits the ability to increase stroke volume
• Peripheral vasodilation drops the SVR, but the LV cannot compensate with increased CO
• Exercise-induced peripheral vasodilation in the presence of an obstruction with fixed CO results in hypotension → decreased mean arterial pressure and thus decreased cerebral perfusion ^[6]
• This explains exertional syncope and even sudden cardiac death during exercise

Neonatal HF with shock if critical AS → duct-dependent systemic circulation ^[2]

This is the most severe end of the spectrum:

• In critical (very severe) valvar AS, the LV cannot generate adequate systemic output
• The systemic circulation becomes dependent on the patent ductus arteriosus (PDA): the RV ejects blood into the PA → through PDA → descending aorta
• When the ductus arteriosus closes (usually day 1–3 of life), there is catastrophic loss of systemic circulation → acute heart failure with shock, metabolic acidosis, renal failure, and death

Complete obstruction → no blood flow to descending aorta → bowel ischaemia / necrotising enterocolitis, renal failure, poor perfusion resulting in metabolic acidosis ^[1] Can guarantee baby will be dead in next few days if not discovered and treated ^[1]

Stenosis at all levels are progressive in nature ^[2]:

• Valvar AS: AV often undergoes degeneration / calcification — even bicuspid valves that are mildly stenotic in childhood will progressively calcify
• Subvalvar AS: turbulent jet → AV damage → progressive AR — the high-velocity jet from the subvalvar narrowing strikes the aortic valve cusps, causing endothelial damage, fibrosis, and progressive aortic regurgitation
• Supravalvar AS: progressive stenosis in Williams syndrome — ongoing elastin deficiency leads to progressive arterial wall thickening

Severity is primarily assessed by echocardiographic Doppler:

Severe AS = AV area < 1 cm² and/or Mean pressure gradient > 50 mmHg (lower in HF) ^[3][4]

Note: In neonates and infants, valve area is better indexed to BSA. "Critical AS" specifically refers to neonates with duct-dependent systemic circulation — this is a clinical definition, not purely a gradient number, because when the LV is failing, the gradient paradoxically drops (low flow → low gradient despite severe stenosis).

• In mild-to-moderate AS, growth and development are typically normal
• In severe/critical AS, failure to thrive, feeding difficulties, and poor weight gain may be present due to chronic heart failure and increased metabolic demand
• Exercise restriction is important in moderate-to-severe AS to prevent exertional syncope and SCD — this affects the child's participation in sports and physical education

• Parents must be counselled about the progressive nature of all forms of congenital AS
• Activity restriction in moderate/severe AS must be discussed sensitively — the child may feel isolated from peers
• Genetic counselling: Turner syndrome (valvar AS), Williams syndrome (supravalvar AS), familial BAV
• Long-term follow-up with serial echocardiography is essential — even "mild" AS can progress

This is a classic exam question ^[12]:

↓ Preload by Valsalva manoeuvre or from squatting to standing will ↑ intensity of HOCM but will ↓ intensity of AS ^[12]

Severe AS = AV area < 1 cm² and/or Mean pressure gradient > 50 mmHg (Lower in HF) ^[3][4]

In paediatrics, the commonly used gradient thresholds are:

Indications of haemodynamic significance (for deciding on intervention) ^[2]:

• Resting systolic pressure gradient > 60 mmHg
• LV systolic dysfunction
• ST/T changes suggestive of LV strain or ischaemia at rest
• Abnormal BP response (no ↑sBP on exercise) or new ST/T changes on exercise

These are not "diagnostic criteria" per se, but rather the thresholds used to decide that the congenital AS is significant enough to warrant intervention — which in practice is how we define "clinically important" disease.

The CXR is a first-line, readily available investigation. In paediatrics, AP films are standard in infants (cannot stand for PA), while older children can have PA and lateral films.

CXR findings in congenital AS ^[2]:

Key paediatric CXR points:

• In neonates, cardiomegaly on CXR is defined as a cardiothoracic ratio (CTR) > 0.6 (normal for neonates is up to 0.6; for older children it is > 0.5 as in adults)
• The thymus can obscure the superior mediastinum in infants — be careful not to confuse a prominent thymus with cardiomegaly or mediastinal widening
• A "boot-shaped" heart is TOF, not AS — don't mix these up

The ECG is essential for detecting LVH and ischaemic changes. Remember that paediatric ECG normal values are age-dependent — what would be "RVH" in an adult may be normal in a neonate (physiological right ventricular dominance at birth).

ECG findings in congenital AS ^[2]:

ECG findings in AS (adult context for reference) ^[7]: LVH, LV strain, left axis deviation, conduction block (LBBB). The conduction block from calcification is essentially an adult phenomenon — calcification of the conduction system is rare in paediatric AS.

Cardiac catheterisation is not routinely required for diagnosis of congenital AS in children (echocardiography is sufficient), but it has two important roles:

1. Therapeutic: Transcatheter balloon aortic valvuloplasty (BAV) — the first-line intervention for critical and severe valvar AS in neonates and children (see management section)
2. Diagnostic (selected cases):
   • When echo is inconclusive or discordant with clinical findings
   • Assessment of haemodynamics: direct measurement of LV pressure, aortic pressure, and the peak-to-peak gradient (note: this is not the same as the echo-derived peak instantaneous gradient — the catheter gradient is typically lower)
   • Coronary anatomy assessment (especially in supravalvar AS where coronary ostial stenosis may coexist in Williams syndrome)
   • Assessment of associated lesions (e.g., coarctation anatomy)

Exercise restriction for moderate/severe AS (> 50–60 mmHg) ^[2]

Exercise testing has a specific and important role in paediatric congenital AS:

• NOT required if the child is symptomatic — symptoms already indicate significant disease and exercise testing would be dangerous
• Useful in asymptomatic children with moderate-to-severe AS to unmask:
  • Abnormal BP response (no ↑ sBP on exercise) ^[2] — failure to augment systolic BP by ≥ 20 mmHg with exercise is abnormal and indicates the LV cannot increase CO; this is ominous
  • New ST/T changes on exercise ^[2] — exercise-induced ischaemia
  • Exercise-induced arrhythmias
  • Symptom provocation — the child may not have noticed subtle exercise limitation

Cardiac MRI is an adjunct investigation in selected paediatric cases:

Paediatric considerations: Young children (typically < 7 years) may require general anaesthesia or deep sedation for MRI due to the long scan time and need to remain still. This limits its use as a first-line investigation but makes it valuable for specific questions that echo cannot fully answer.

Rarely used as first-line in paediatric congenital AS (radiation exposure is a significant concern in children). However, it may be useful for:

• Coronary anatomy assessment (especially pre-Ross procedure or in Williams syndrome where coronary ostial stenosis is a concern)
• Complex anatomy where echo and MRI are insufficient
• Post-operative assessment in selected cases

Urgent PGE₁ + neonatal balloon valvuloplasty in critical AS ^[2]

Why is BAV first-line in neonates?

• Avoids sternotomy and cardiopulmonary bypass in a critically ill neonate
• Can be performed urgently in the catheterisation lab
• The neonatal valve is pliable and non-calcified → balloon inflation effectively splits fused commissures
• If the result is suboptimal, surgical valvotomy can still be performed as a backup

There is no medical therapy that can reduce or reverse the obstruction in congenital AS. Unlike adult degenerative AS where there is interest in statin therapy (which has not been proven effective), in congenital AS the problem is a structural malformation, not degeneration.

Medical management is therefore supportive and preventive:

Severe aortic stenosis, drug contraindications ^[15]:

• Beta-blockers → negative inotropes ^[15] — In severe AS, the LV is already working maximally against the fixed afterload. Reducing contractility with beta-blockers removes the compensatory mechanism and can precipitate acute heart failure. (Note: beta-blockers are used cautiously in mild-moderate AS in some settings, but contraindicated in severe/decompensated AS.)
• Non-dihydropyridine CCBs (verapamil, diltiazem), cardiac selective → negative inotropes ^[15] — Same reasoning as beta-blockers: reducing contractility in an afterload-dependent ventricle is dangerous.
• Nitrates → compromises preload ^[15] — In AS, the stiff, hypertrophied LV is preload-dependent. Nitrates cause venodilation → ↓ venous return → ↓ preload → ↓ LV filling → ↓ CO → hypotension and syncope. The LV cannot compensate by increasing stroke volume because of the fixed obstruction.

Surgical intervention for selected individuals ^[2]:

Indications: either symptomatic or asymptomatic but haemodynamically significant as indicated by ^[2]:

• Resting systolic pressure gradient > 60 mmHg
• LV systolic dysfunction
• ST/T changes suggestive of LV strain or ischaemia at rest
• Abnormal BP response (no ↑ sBP on exercise) or new ST/T changes on exercise

Transcatheter balloon aortic valvotomy (BAV): usually 1st line for valvar AS (less calcific) ^[2]

Surgical valvotomy: alternative to BAV, outcome equivalent or superior to BAV ^[2]

Resection of subaortic membrane/fibromuscular ridge for subvalvar AS ^[2]

Patch repair for supravalvar AS ^[2]

All initial procedures (BAV, surgical valvotomy) are temporising measures. Over time:

Recurrent obstruction or post-procedure AR ^[2]:

• Re-BAV: often effective ^[2] — can be repeated if re-stenosis occurs and valve morphology remains suitable
• AV replacement: if develop severe AR or degenerative AS in which BAV is less effective ^[2]

The Ross procedure is unique to paediatric/young adult AS management and deserves special discussion.

Principle: Replace the diseased aortic valve with the patient's own normal pulmonary valve (autograft). Then replace the pulmonary valve position with a homograft (cadaveric) or bioprosthetic valve.

Steps ^[2]:

1. Aortic root autograft: The entire pulmonary root (including the pulmonary valve) is excised and transplanted into the aortic position
2. Coronary artery re-implantation: The coronary arteries are detached from the native aortic root and re-implanted into the neo-aortic root (pulmonary autograft)
3. Pulmonary root homograft: A cadaveric pulmonary root with valve is implanted in the pulmonary position (right ventricle to pulmonary artery conduit)

Advantages:

• Avoid lifelong anticoagulation in AVR ^[2] — the autograft is living tissue, not thrombogenic
• The pulmonary autograft grows with the child — this is the key advantage in paediatrics; a living valve grows as the child grows, unlike mechanical/bioprosthetic valves
• Excellent haemodynamics (normal valve physiology)
• Lower risk of endocarditis compared to prosthetic valves

Disadvantages:

• High rates of failure with progressive autograft aortic root degeneration ^[2] — the pulmonary valve is not designed to withstand systemic pressures; over time, the autograft neo-aortic root dilates (the thin pulmonary artery wall stretches under systemic pressure), leading to progressive neo-aortic regurgitation
• Turns a "one-valve disease" into a "two-valve disease" — now both the aortic position (autograft) and pulmonary position (homograft) need surveillance and potential re-intervention
• The pulmonary homograft has limited lifespan (10–15 years) and will need replacement (can be done percutaneously via Melody valve or surgical conduit revision)
• Complex operation with longer bypass time

This is the final common pathway of all forms of congenital AS if left untreated.

LV pressure overload → LVH → eventually myocardial fibrosis → LV failure ^[2]

The mechanism traces back to the core pathophysiology covered in Part 1:

• Chronic pressure overload → concentric LVH → diastolic dysfunction (stiff, non-compliant LV)
• ↓ Coronary perfusion due to severe AS + ↑ LV EDP ^[2] → subendocardial ischaemia
• ↑ Myocardial O₂ consumption due to ↑ LV systolic BP → ↑ afterload ^[2]
• Eventually, the myocytes undergo irreversible fibrosis → the LV dilates → systolic dysfunction → decompensated heart failure with pulmonary oedema

Decompensation due to chronic LV pressure overload → rapid deterioration with LV failure (dilated LV) → pulmonary oedema ^[16]

In neonates with critical AS: LV failure is the presenting feature — the neonate is in cardiogenic shock from the outset because the LV simply cannot overcome the near-total obstruction.

In children: LV failure is a late complication of untreated severe AS. Children compensate remarkably well and may remain asymptomatic for years, but once decompensation begins, the deterioration is rapid.

When symptomatic, mortality 50% in 3 years ^[3] — this adult-derived statistic underscores the gravity of symptomatic AS. In paediatrics, prompt intervention before decompensation is the strategy.

Congestive cardiac failure is listed as one of the classic clinical features of AS ^[3]. In the adult literature, the prognosis is: Angina = 5 years; Syncope = 3 years; CHF = 2 years ^[17]. While these exact survival numbers apply to adults with calcific AS, the principle holds: heart failure is the most ominous symptom.

Sudden cardiac death due to ventricular arrhythmias ^[16]

SCD is the most feared complication of congenital AS in the paediatric population. It occurs primarily during or immediately after exertion.

Mechanism from first principles:

1. Severe AS → chronic LVH → disorganised myocardial fibres + fibrosis → creates a substrate for re-entrant ventricular arrhythmias (ventricular tachycardia → ventricular fibrillation)
2. Exertion → increased myocardial O₂ demand + peripheral vasodilation → ↓ coronary perfusion pressure → acute ischaemia → triggers VT/VF
3. Exertion → ↓ BP (inability to ↑ CO through fixed obstruction + peripheral vasodilation) → loss of consciousness → if arrhythmia does not self-terminate → cardiac arrest

Potential cause is activation of ventricular baroreceptors resulting in paradoxical bradycardia, decreased contractility and hypotension ^[17]

This is why exercise restriction for moderate/severe AS (> 50–60 mmHg) ^[2] is so important. Strenuous competitive sport is the typical trigger.

Arrhythmias are a recognised complication of AS ^[7][16]:

In the paediatric context, heart block is primarily a procedural complication (see Section B below) rather than a disease complication, because paediatric valves are not calcified.

Infective endocarditis ^[7][17]

Any abnormal valve — whether bicuspid, unicuspid, or post-interventional — creates turbulent flow across the valve surface. This turbulence damages the endothelium, promoting platelet-fibrin deposition (non-bacterial thrombotic endocarditis, NBTE), which serves as a nidus for bacteraemia to seed and establish vegetations.

In congenital AS specifically:

• Bicuspid aortic valve is one of the most common predisposing lesions for IE in the paediatric and young adult population
• Risk is present even in mild AS — the turbulence is what matters, not the severity of stenosis
• IE can both be a cause and result ^[17] — endocarditis destroys valve tissue, worsening existing stenosis or creating new regurgitation; conversely, the abnormal valve predisposes to IE
• Post-interventional patients (post-BAV, post-valvotomy, post-AVR) are at higher risk due to prosthetic material, sutures, or damaged endothelium

IE prophylaxis in paediatrics (current guidelines):

• Good dental hygiene is the most important preventive measure for all children with congenital AS
• Antibiotic prophylaxis before dental/invasive procedures: only recommended for the highest-risk category (prosthetic valve, previous IE, unrepaired cyanotic CHD, repaired CHD with residual defects adjacent to prosthetic material)
• Native unrepaired bicuspid AV or mild AS: prophylaxis is not routinely recommended under current AHA/ESC guidelines (though this remains debated)

Syncope or sudden death ^[3]

Exertional syncope in AS results from:

1. Inability to ↑ CO + ↓ SVR due to peripheral vasodilatation → sudden ↓ BP leading to syncope ^[16]
2. Exercise-induced arrhythmia (VT) causing transient loss of output
3. Baroreceptor-mediated paradoxical bradycardia and hypotension ^[17]

Syncope in a child with known AS is an emergency signal — it indicates the stenosis is haemodynamically critical and warrants urgent evaluation for intervention. Any child with AS who experiences syncope should be admitted and should not be discharged without a clear plan.

Aortic stenosis causes LVH → larger heart muscle wall, perfusion is not sufficient. Aortic stenosis causes LVOT blockage → less blood going into coronary cusps, and coronary arteries during the diastolic phase ^[3]

Myocardial ischaemia in congenital AS occurs without coronary artery disease (CAD is extremely rare in children). The mechanism is purely supply-demand mismatch:

Chronic subendocardial ischaemia → myocardial fibrosis → contributes to diastolic dysfunction, systolic dysfunction, and arrhythmic substrate.

Special note for supravalvar AS (Williams syndrome): In supravalvar AS, the coronary arteries are exposed to high pressure (they arise below the supravalvar narrowing, i.e., in the high-pressure zone). Additionally, coronary artery ostial stenosis ^[14] may be present in Williams syndrome. This combination means that children with supravalvar AS can develop true coronary ischaemia from coronary ostial obstruction — not just from supply-demand mismatch. This makes supravalvar AS potentially more dangerous than equivalent-gradient valvar AS.

Heyde's syndrome → Fe deficiency anaemia ^[7]

Acquired vWF disease results from mechanical disruption of von Willebrand multimers during turbulent passage through the narrowed valve and from vWF interaction with platelets that trigger platelet clearance ^[17]

Multisystem disorder characterized by the triad of aortic stenosis (AS), gastrointestinal bleeding, and acquired von Willebrand syndrome (shear stress in blood due to narrowed aortic valve, induce conformational changes and early degradation of vWF) ^[18]

Mechanism from first principles:

• Blood passes through the severely stenotic aortic valve at very high velocity (4–5 m/s)
• This high-velocity, turbulent flow exerts enormous shear stress on plasma proteins
• Von Willebrand factor (vWF) exists as large multimers; these high molecular weight (HMW) multimers are essential for primary haemostasis
• The shear stress unfolds the HMW-vWF multimers, making them susceptible to cleavage by ADAMTS13 (the vWF-cleaving protease)
• Loss of HMW-vWF multimers → acquired type 2A von Willebrand disease
• Clinically: mucocutaneous bleeding, GI bleeding from angiodysplasia (angiodysplasia forms because vWF normally supports angiogenesis regulation; loss of HMW-vWF → aberrant angiogenesis → fragile vessels in the GI mucosa)
• In paediatrics, this is less commonly clinically apparent than in elderly patients with calcific AS, but it can occur in any age group with severe congenital AS
• Key point: Heyde's syndrome reverses after aortic valve replacement or successful relief of obstruction because the shear stress is reduced and vWF multimer processing normalises

Bicuspid aortic valve (BAV) is associated with an intrinsic aortopathy — the ascending aorta has abnormal extracellular matrix (deficient fibrillin-1 and increased matrix metalloproteinase activity) independent of the haemodynamic effects of the stenosis.

Consequences:

• Progressive dilatation of the ascending aorta (aortic root or tubular ascending aorta depending on the BAV morphology and cusp fusion pattern)
• Risk of aortic dissection — rare in childhood but increasingly relevant in adolescence and young adulthood
• Risk of aortic aneurysm
• This aortopathy persists even after successful relief of valve obstruction — meaning a child who has had BAV repaired still needs lifelong surveillance of aortic root dimensions

High rates of failure with progressive autograft aortic root degeneration ^[2]