Pulmonary stenosis is a congenital heart defect, most commonly diagnosed in neonates and children, characterized by narrowing of the pulmonary valve or adjacent structures that obstructs right ventricular outflow and impedes blood flow to the lungs.

Pulmonary Stenosis (PS) in Paediatrics

Pulmonary stenosis (PS) refers to obstruction of the right ventricular outflow tract (RVOT), most commonly at the level of the pulmonary valve. The name itself is instructive: "pulmonary" = relating to the lungs/pulmonary artery, "stenosis" (Greek stenos = narrow) = an abnormal narrowing. In the paediatric context, PS is overwhelmingly congenital in origin and represents an important cause of RV pressure overload.

PS is the second most common congenital heart disease (CHD), accounting for 7.5–12% of all CHD, with an incidence of approximately 0.6–0.8 per 1,000 live births ^[1]^[2]. It is associated with Noonan syndrome (thick and dysplastic leaflets) ^[1].

Why Is PS Under-Recognised?

Mild PS is frequently under-reported because it is often asymptomatic and therefore not picked up ^[1]. Many children with mild PS are only detected incidentally on echocardiography performed for other reasons or during evaluation of a murmur heard on routine examination.

Factor	Detail
Prevalence among CHD	7.5–12% of all CHD (second most common after VSD) ^[1]^[2]
Incidence	0.6–0.8 per 1,000 live births ^[1]
Sex ratio	Approximately equal M:F, though some series report slight female preponderance
Genetic associations	Noonan syndrome (autosomal dominant RAS-MAPK pathway mutation; ~50% have PS with thick, dysplastic pulmonary valve leaflets) ^[1]
Other associations	Congenital rubella syndrome (peripheral/supravalvular PS), Williams syndrome (supravalvular AS ± peripheral PS), Alagille syndrome (peripheral PS + bile duct paucity), LEOPARD syndrome, 22q11.2 deletion (more commonly TOF but can have isolated PS)
Isolated vs combined	Often isolated; but PS is also a critical component of Tetralogy of Fallot (TOF), where it is the main haemodynamic determinant ^[3]

Hong Kong Context

Congenital heart disease affects approximately 8–10 per 1,000 live births in Hong Kong
Noonan syndrome is the most clinically important syndromic association to recognise in HK paediatric cardiology clinics because it changes management: dysplastic pulmonary valves do not respond to balloon valvuloplasty and require surgical valvotomy ^[1]
Universal newborn pulse oximetry screening in HK helps pick up critical PS presenting with cyanosis

Anatomy and Function

The pulmonary valve is a semilunar valve situated at the junction of the right ventricular outflow tract (RVOT) and the main pulmonary artery (MPA). It normally has three thin, pliable cusps (anterior, right, and left) that open fully during RV systole to allow unobstructed flow into the pulmonary arteries and close during diastole to prevent regurgitation.

The RVOT itself can be divided into three regions relevant to obstruction:

Subvalvular (infundibular): the muscular infundibulum below the valve
Valvular: the valve leaflets and annulus themselves
Supravalvular: the main pulmonary artery above the valve, including branch pulmonary arteries

The normal RV is a thin-walled, compliant, crescent-shaped chamber designed to pump blood through the low-resistance pulmonary vascular bed
Normal RV systolic pressure in a child is approximately 15–30 mmHg (roughly one-quarter to one-fifth of systemic systolic pressure)
The normal pressure gradient across the pulmonary valve is trivial ( < 10 mmHg)
In the fetus, PVR is high and relatively little blood traverses the lungs; most RV output passes through the ductus arteriosus (DA) into the descending aorta. After birth, PVR falls dramatically as the lungs expand, and the DA closes

Aetiology (Focus on Hong Kong)

The site of RVOT obstruction determines clinical features, investigation findings, and management ^[1]^[2]^[4]:

Level	Relative Frequency	Key Features
Valvular (most common, ~90% of isolated PS)	Most common	Thickened, domed leaflets with restricted opening; commissural fusion; post-stenotic dilation of MPA
Subvalvular (infundibular)	Less common as isolated; common in TOF	Muscular hypertrophy of the RV infundibulum narrowing the outflow; no ejection click (because the click arises from the valve itself)
Supravalvular	Uncommon	Narrowing of the MPA or branch pulmonary arteries; associated with congenital rubella, Williams syndrome, Alagille syndrome
Peripheral/branch PA stenosis	Uncommon	Narrowing of one or both branch PAs; may be physiological in neonates (resolves by 6 months) vs. pathological (Alagille, rubella, post-surgical)

Congenital (overwhelmingly the most common in paediatrics)
- Isolated valvular PS
- Part of a complex CHD: Tetralogy of Fallot, univentricular heart, double-outlet right ventricle
- Syndromic: Noonan, Alagille, Williams, LEOPARD, congenital rubella
Acquired (rare in children)
- Rheumatic heart disease (extremely rare for pulmonary valve; rheumatic disease typically affects left-sided valves)
- Carcinoid syndrome (serotonin-mediated fibrosis of right-sided valves; essentially unheard of in children)
- External compression (e.g., mediastinal tumour)

Pathophysiology

This is the key to understanding every clinical feature, investigation finding, and management decision. Let us build it from first principles:

The stenotic pulmonary valve has reduced effective orifice area → blood must be ejected at higher velocity to maintain cardiac output across the narrowed valve → a systolic pressure gradient develops between the RV and the pulmonary artery.

Bernoulli equation: ΔP = 4V² (where V is peak velocity in m/s, and ΔP is the pressure gradient in mmHg). This is the formula used on Doppler echocardiography to estimate the gradient.

Severity	Peak Gradient	Peak Velocity	RV Pressure
Trivial	< 25 mmHg	< 2.5 m/s	Near normal
Mild	25–39 mmHg	2.5–3.0 m/s	Mildly elevated
Moderate	40–59 mmHg	3.0–4.0 m/s	Moderately elevated
Severe	≥ 60 mmHg	≥ 4.0 m/s	May equal or exceed systemic pressure
Critical	Pinhole opening	Very high or low if flow is duct-dependent	Suprasystemic

RV pressure overload is the principal haemodynamic consequence ^[1].

The RV must generate higher systolic pressure to overcome the obstruction → concentric RVH develops as a compensatory mechanism
RV systolic pressure may even exceed that of the LV in severe PS ^[1]
Why does this matter? The thickened, stiff RV has impaired diastolic relaxation (diastolic dysfunction) → RV end-diastolic pressure (RVEDP) rises → this is transmitted retrograde to the RA

RAH (right atrial hypertrophy) with ↑RVEDP → back pressure ^[1].

Elevated RVEDP impairs RA emptying → RA dilates and hypertrophies
If RA pressure rises sufficiently and a PFO or ASD is present → right-to-left shunting occurs → cyanosis
This explains why critical PS with a pinhole opening plus PFO or ASD is cyanotic: ↑↑↑RA pressure → right-to-left shunting via PFO or ASD ^[1]

Post-stenotic dilation of the pulmonary trunk occurs due to turbulent blood flow ^[1].

The high-velocity jet emerging from the stenotic valve strikes the wall of the main pulmonary artery
This causes localised endothelial injury and elastic fibre degeneration → the vessel wall dilates
This produces the characteristic prominent pulmonary knob on CXR
Post-stenotic dilation is NOT present in infundibular or supravalvular PS ^[1] — because in those cases the jet does not impact the same segment of the PA

Duct-dependent pulmonary circulation occurs in critical PS without PFO/ASD ^[1].

In critical PS, the RV can barely eject any blood through the almost completely obstructed valve
Pulmonary blood flow depends on the patent ductus arteriosus (PDA) to supply blood from the aorta to the pulmonary arteries
When the ductus closes (typically within the first 24–72 hours of life), the infant becomes profoundly cyanotic and may rapidly deteriorate
This is a neonatal emergency requiring prostaglandin E₁ (PGE₁) infusion to keep the ductus open

Critical PS vs. Severe PS

A common student mistake is conflating "severe" and "critical" PS. Severe PS means a high gradient ( ≥ 60 mmHg) but the RV can still eject blood forward. Critical PS means the valve is virtually atretic ("pinhole opening") and the neonate is duct-dependent for pulmonary blood flow — this is a life-threatening emergency.

Classification

Type	Description	Key Distinguishing Point
Valvular	Thickened, domed cusps with commissural fusion or dysplasia	Ejection click present (because the click is produced by abrupt tensing of the domed valve leaflets); post-stenotic MPA dilation on CXR
Subvalvular (infundibular)	Muscular hypertrophy of RVOT below the valve	No ejection click; no post-stenotic dilation; associated with TOF
Supravalvular	Narrowing at or above the sinotubular junction of MPA	No ejection click; no post-stenotic dilation; associated with Williams, Noonan, Alagille, rubella
Peripheral/branch PA	Stenosis of LPA and/or RPA	Continuous murmur radiating to back and axillae; physiological in neonates

Severity	Peak Instantaneous Gradient	Management Implication
Mild	< 40 mmHg	Observe; benign prognosis
Moderate	40–59 mmHg	Monitor; intervention may be needed if progressive
Severe	≥ 60 mmHg	Balloon pulmonary valvuloplasty (BPV) indicated ^[1]
Critical (neonatal)	Near-atretic	Urgent PGE₁ + neonatal balloon valvuloplasty ^[1]

Morphology	Features	Clinical Significance
Typical (non-dysplastic)	Thin leaflets with commissural fusion, dome-shaped in systole	Excellent response to balloon valvuloplasty
Dysplastic	Thick and dysplastic leaflets (classically Noonan syndrome)	Do not respond to BPV → require surgical valvotomy ^[1]

Clinical Features

The clinical presentation of PS depends critically on the severity of obstruction and the age at presentation. The majority of patients with PS are asymptomatic, even with moderate or severe PS ^[1]. Symptoms and signs become apparent as obstruction worsens.

Symptom	Pathophysiological Basis	When It Occurs
Asymptomatic	Majority of children, even with moderate/severe PS ^[1]. The RV compensates well via concentric hypertrophy for a prolonged period.	Mild to moderate PS; many with severe PS
Exertional dyspnoea / exercise intolerance	The RV cannot adequately augment cardiac output during exercise because of fixed obstruction → inadequate pulmonary blood flow → reduced left-sided filling → reduced systemic CO	Moderate to severe PS, typically in older children
Fatigue	Same mechanism as above — reduced ability to increase CO	Moderate to severe PS
Cyanosis	Occurs in critical PS: ↑↑↑RA pressure → right-to-left shunting via PFO or ASD ^[1]. Deoxygenated blood bypasses the lungs and enters the systemic circulation.	Critical PS in neonates
Neonatal distress / collapse	In critical PS, closure of the ductus arteriosus removes the only source of pulmonary blood flow → acute profound hypoxaemia	Critical PS, typically within first 24–72 hours of life
Poor feeding / failure to thrive	Inadequate systemic oxygen delivery + increased metabolic demand of cardiac work; sweating on feeding due to sympathetic activation	Severe/critical PS in infants
Right heart failure symptoms (in late/untreated disease)	Chronic RV pressure overload → RV dysfunction → elevated systemic venous pressure → hepatomegaly, peripheral oedema, ascites	Rare in modern practice due to early intervention; seen in untreated severe PS

Key Clinical Pearl

Unlike left-to-right shunts (e.g., large VSD) which present with heart failure symptoms at 1–2 months as PVR falls, isolated PS presents based on the fixed severity of obstruction. Mild/moderate PS children run, play, and grow normally. The crucial exception is critical PS, which presents in the neonatal period as a duct-dependent lesion.

Systematic Approach to Cardiovascular Examination in PS

The clinical findings in PS vary predictably with severity. Below is the systematic approach:

1. General Inspection

Finding	Pathophysiological Basis
Cyanosis (central — lips, tongue)	Critical PS with right-to-left shunt through PFO/ASD ^[1]
Well-appearing child	Mild/moderate PS — RV compensates fully
Signs of RV failure (hepatomegaly, oedema)	Late decompensation in untreated severe PS
Features of Noonan syndrome	Short stature, webbed neck, hypertelorism, low-set ears, pectus deformity, undescended testes — associated with dysplastic PS ^[1]

2. Pulse

Usually normal in isolated PS (the left heart is not directly affected)
In critical PS with duct-dependent circulation: pulses may be weak if systemic output is compromised

3. JVP (in older children/adolescents)

Prominent 'a' wave: forceful RA contraction against a stiff, hypertrophied RV
JVP elevation in RV failure

4. Precordial Palpation

Finding	Pathophysiological Basis
RV impulse (left parasternal heave)	RV pressure overload → RV hypertrophy ^[1]. The hypertrophied RV pushes anteriorly against the chest wall.
Suprasternal pulsation/thrill	Turbulent flow in the pulmonary artery in severe PS ^[1]
Systolic thrill at LUSB	Palpable vibration from turbulent flow across the stenotic valve

5. Auscultation — The Most Important Part

Signs depend on severity of obstruction ^[1]:

Finding	Mechanism	Mild PS	Moderate PS	Severe PS	Critical PS
Ejection click	Produced by sudden tensing of the domed, fused valve cusps at the onset of RV ejection. The presence of an ejection click suggests that the stenosis is at the valvar level ^[1]. The click is best heard at the LUSB and characteristically decreases with inspiration (because increased venous return partially opens the valve during diastole, so there is less "snapping" open in systole).	✓ (loud, well-separated from S1)	✓ (moves closer to S1)	✓ (very close to S1 or absent)	Often absent
Ejection systolic murmur (ESM) at LUSB	Turbulent blood flow across the narrowed pulmonary valve. The murmur increases in intensity and duration as stenosis worsens. In mild PS: ESM at LUSB ^[1].	Short, soft, early-peaking	Longer, louder, later-peaking	Long, loud, late-peaking	May be soft/short (very reduced flow through near-atretic valve)
Radiation	The murmur radiates towards the left lung (following the direction of the MPA and LPA) and to the back	Minimal	±	To back/axillae	Variable
S1	Normal	Normal	Normal	Normal	Normal
P2 (pulmonary component of S2)	In PS, the pulmonary valve closes later (because RV ejection time is prolonged) and with less force (low PA pressure distal to the stenosis).	Normal or slightly soft	Soft, widely split S2	Delayed/soft/absent P2 ^[1] → wide splitting of S2	Absent P2
S4	Forceful RA contraction against stiff RV	Absent	Rare	May be present	May be present

High Yield – Ejection Click in PS

The ejection click is pathognomonic for VALVULAR PS ^[1]. It is:

Present in valvular PS (due to abrupt doming of fused cusps)
Absent in subvalvular (infundibular) and supravalvular PS
Decreases with inspiration — a unique feature that distinguishes it from the ejection click of aortic stenosis (which does not change with respiration). The mechanism: increased venous return during inspiration partially pre-opens the stenotic PV during diastole, so there is less "snapping" in the subsequent systole.
Moves closer to S1 as severity increases (the valve opens earlier because RV pressure rises faster)
In very severe PS, the click may merge with S1 and become inaudible

Why Does the ESM Get Louder and Later-Peaking with Increasing Severity?

In mild PS, the RV generates a modest pressure gradient quickly → ejection is completed early → short, early-peaking murmur. In severe PS, the RV must generate a much higher pressure to overcome the obstruction → ejection takes longer and peak flow occurs later in systole → longer, louder, later-peaking murmur. In critical PS, paradoxically the murmur may be soft or absent because there is so little flow across the almost-atretic valve — don't be fooled into thinking "no murmur = no problem."

Differentiating PS Murmur from Other LUSB Murmurs

Common exam trap: both PS and ASD produce murmurs at the LUSB. However:

PS: Ejection systolic murmur with ejection click, single/soft P2, RV heave
ASD: Ejection systolic murmur (due to increased flow across the PV, NOT across the defect) with fixed wide splitting of S2 (P2 is normal or loud because pulmonary flow is increased)

Also distinguish from innocent pulmonary flow murmur in children: soft, short ESM at LUSB, grade ≤ 2/6, no click, normal S2, no thrill, asymptomatic, normal ECG/CXR.

Feature	Mild	Moderate	Severe	Critical (Neonatal)
Symptoms	Asymptomatic	Usually asymptomatic	Dyspnoea on exertion; may be asymptomatic	Cyanosis, collapse when ductus closes
Growth	Normal	Normal	± Reduced exercise tolerance	Failure to thrive
Cyanosis	No	No	No (unless PFO/ASD)	Yes (R→L shunt via PFO/ASD)
Ejection click	Yes (well-separated from S1)	Yes (closer to S1)	Merged with S1 or absent	Often absent
ESM at LUSB	Short, soft	Longer, louder	Long, loud, late-peaking	May be paradoxically soft
P2	Normal	Soft	Delayed/soft/absent	Absent
S2 splitting	Normal or slight	Wider	Wide	Single (absent P2)
RV heave	No	±	Yes	Yes
Thrill	No	±	Yes (LUSB, suprasternal)	±

Age Group	Typical Presentation
Neonate (0–28 days)	Critical PS: cyanosis within hours of birth as ductus closes; duct-dependent pulmonary circulation; neonatal emergency. Absent P2, soft murmur, cyanosis
Infant (1–12 months)	Usually asymptomatic murmur detected at well-baby check; occasionally dyspnoea with feeds if severe
Child (1–12 years)	Incidental murmur at school medical; exercise intolerance if severe; ejection click + ESM at LUSB is the classic finding
Adolescent	As for child; may present with exertional symptoms if previously undiagnosed moderate-severe PS; prominent 'a' wave in JVP

Condition	What to Check	Why
Noonan syndrome	Dysmorphic features (short stature, webbed neck, hypertelorism, low-set ears, ptosis, pectus excavatum, cryptorchidism)	Thick, dysplastic PV → poor response to balloon valvuloplasty ^[1]
PFO/ASD	SpO₂, echocardiography	Presence allows right-to-left shunting → cyanosis in severe/critical PS
TOF	Full echo assessment	PS is a component of TOF; if PS + VSD + overriding aorta + RVH → diagnosis is TOF, not isolated PS
Congenital rubella	Maternal history, rubella IgM, cataracts, deafness	Peripheral PS
Alagille syndrome	Cholestasis, butterfly vertebrae, posterior embryotoxon	Peripheral PS

Scenario: A 3-day-old neonate born at term presents with progressive cyanosis. SpO₂ is 65% on room air. On examination, there is central cyanosis, a soft systolic murmur at the LUSB, and an absent P2. CXR shows oligaemic lung fields with a normal-sized heart.

Reasoning from first principles:

Cyanosis at day 3 → timing suggests ductus closure is removing the source of pulmonary blood flow
Oligaemic lung fields → reduced pulmonary blood flow → obstruction to pulmonary flow (PS, pulmonary atresia, or TOF)
Soft murmur → very little blood is crossing the stenotic valve (paradox of critical PS)
Absent P2 → the pulmonary valve is not closing with any force (because PA pressure is very low distal to the obstruction, and the valve is severely diseased)
Normal heart size → the RV has not had time to dilate; it is pressure-overloaded but not yet volume-overloaded

This is critical PS with duct-dependent pulmonary circulation → immediate PGE₁ infusion ^[1].

The combination of an oligaemic lung field on CXR in a cyanotic neonate supports cyanotic congenital heart disease rather than respiratory disease as the cause of cyanosis ^[5].

High Yield Summary

Pulmonary Stenosis — Key Points for Exams:

Second most common CHD (7.5–12%), incidence 0.6–0.8/1,000 live births ^[1]
Associated with Noonan syndrome (dysplastic valve leaflets) — does NOT respond to balloon valvuloplasty → needs surgical valvotomy ^[1]
Valvular PS is the most common type (~90%) — characterised by presence of an ejection click ^[1]
RV pressure overload is the principal haemodynamic consequence → RVH → ↑RVEDP → RAH ^[1]
Post-stenotic dilation of MPA (present only in valvular PS, NOT in infundibular/supravalvular) ^[1]
Critical PS = duct-dependent pulmonary circulation → PGE₁ + neonatal balloon valvuloplasty ^[1]
Cyanosis in PS requires the combination of critical obstruction + PFO/ASD for R→L shunt ^[1]
Majority of children are asymptomatic, even with moderate/severe PS ^[1]
Key auscultatory findings in severe PS: ejection click, ESM at LUSB, delayed/soft/absent P2, RV impulse, suprasternal pulsation/thrill ^[1]
BPV (balloon pulmonary valvuloplasty) indicated when peak gradient ≥ 60 mmHg ^[1]
Oligaemic lung fields on CXR in a cyanotic neonate → think cyanotic CHD with reduced pulmonary blood flow (critical PS, pulmonary atresia, severe TOF) ^[5]

Active Recall - Pulmonary Stenosis (Definition to Clinical Features)

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 206 — Isolated RVOT Obstruction: Valvular PS) ^[2] Senior notes: Ryan Ho Cardiology.pdf (p. 187 — Tetralogy of Fallot; p. 193 — VSD; context for PS within CHD) ^[3] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 270 — TOF clinical features; p. 242–254 — CHD pathophysiology) ^[4] Lecture slides: GC 147. Heart failure and cyanosis in children acyanotic and cyanotic congenital heart disease - Part 1.pdf; Part 2.pdf ^[5] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supports cyanotic CHD) ^[6] Lecture slides: Block C - Heart failure and cyanosis in children: acyanotic and cyanotic congenital heart disease.pdf ^[7] Senior notes: Maksim Medicine Notes.pdf (p. 35 — Valvular heart disease overview; p. 290 — Pulmonary hypertension classification)

Differential Diagnosis of Pulmonary Stenosis

The differential diagnosis of pulmonary stenosis (PS) in paediatrics is best approached from the clinical presentation rather than the pathology itself. A child with PS may present in several distinct ways depending on severity and age. Below we systematically consider the DDx for each major presenting scenario.

Before listing differentials, recall that PS can present as:

An asymptomatic murmur (the majority — mild/moderate PS detected incidentally)
Neonatal cyanosis with duct-dependent pulmonary circulation (critical PS)
Exercise intolerance / exertional dyspnoea (older child with moderate-severe PS)
Right heart failure (late, untreated severe PS — rare in modern practice)

Each presentation has its own differential "basket."

This is the most common scenario: an ESM at the LUSB is heard at a well-child check.

Differential	Key Distinguishing Features	Why It Mimics PS
Innocent pulmonary flow murmur	Grade ≤ 2/6, soft, short, no click, normal S2, no thrill, asymptomatic, normal ECG/CXR. Very common in children.	ESM at LUSB, vibratory or blowing quality; the turbulence is simply from normal flow in a thin-chested child
Atrial septal defect (ASD)	Fixed wide splitting of S2 (pathognomonic); normal or loud P2 (because pulmonary flow is increased); no ejection click; mid-diastolic rumble at LLSB if large shunt (increased tricuspid flow)	ESM at LUSB from increased flow across a normal PV (not valve stenosis itself). The murmur is due to relative pulmonary stenosis from increased volume flow, NOT a structural valve lesion ^[1]^[3]
Peripheral pulmonary artery stenosis (physiological)	Common in neonates, resolves by ~6 months; soft ESM radiating to back and axillae bilaterally; normal S2	Turbulence in branch PAs that are relatively small compared to the MPA in early infancy
Pathological branch PA stenosis	Associated with Alagille, Williams, rubella syndromes; continuous murmur radiating to back/axillae; does NOT resolve	Obstruction at branch PA level rather than valve level
Tetralogy of Fallot (TOF)	ESM at LUSB from RVOT obstruction + cyanosis ± clubbing + single S2 (soft/absent P2) + boot-shaped heart on CXR + murmur related to PS, NOT VSD ^[3]^[8]	TOF includes PS as a component; the ESM arises from the same mechanism (RVOT obstruction). Key difference: TOF has a VSD + overriding aorta → cyanosis from R-to-L shunting
Supravalvular pulmonary stenosis	Associated with Williams syndrome (elfin facies, supravalvular AS, hypercalcaemia), Noonan, rubella; NO ejection click; NO post-stenotic dilation on CXR	Obstruction above the valve produces a similar ESM at LUSB
Subvalvular (infundibular) PS	Usually part of TOF; NO ejection click; NO post-stenotic dilation; progressive muscular hypertrophy	ESM at LUSB from infundibular narrowing
Aortic stenosis (valvular)	ESM best at RUSB (aortic area) radiating to neck; ejection click does NOT vary with respiration (unlike PS click); slow-rising pulse; may have S4	Both produce ESMs; location and radiation differ
Hypertrophic cardiomyopathy (HCM) / HOCM	ESM at LLSB that increases with Valsalva and standing; may have MR murmur; family history of sudden death	Can mimic PS murmur, but location is more towards LLSB and the dynamic response to manoeuvres is characteristic

High Yield Exam Pearl — ASD vs PS

The crucial distinguishing feature between ASD and valvular PS at the LUSB is the S2:

ASD: Fixed wide splitting of S2 with normal/loud P2 (because pulmonary flow is increased → increased PA pressure)
PS: Wide BUT physiological splitting (widens with inspiration) with SOFT/ABSENT P2 (because PA pressure is LOW distal to the obstruction and RV ejection is prolonged)
Both have ESM at LUSB, but ASD has no ejection click.

B. Differential Diagnosis of Neonatal Cyanosis (Critical PS Presentation)

Critical PS is a cause of cyanotic CHD with decreased pulmonary blood flow ^[3]^[8]. The differential for a cyanotic neonate can be categorised by underlying physiology:

Cyanotic CHD can be categorized according to the underlying physiology: ↓ pulmonary blood flow, ↑ pulmonary blood flow, or severe heart failure ^[3]^[8].

These share the same haemodynamic principle as critical PS: obstruction to pulmonary blood flow → reduced oxygenation → cyanosis. Many are duct-dependent.

Differential	Key Features	Duct-Dependent?
Critical pulmonary stenosis	Pinhole valve opening; ESM may be soft; absent P2; duct-dependent: RA → PFO → LV → Aorta → PDA → PA → Lungs ^[8]	Yes
Tetralogy of Fallot (TOF)	VSD + overriding aorta + RVH + RVOT obstruction; boot-shaped heart on CXR; oligaemic lung fields; ESM at LUSB related to PS, not VSD ^[3]^[8]	Only if severe RVOT obstruction
TOF with pulmonary atresia (TOF/PA)	Most extreme variant; no antegrade pulmonary flow; requires PDA; may develop major aortopulmonary collateral arteries (MAPCAs) ^[8]	Yes
Pulmonary atresia with intact ventricular septum (PA/IVS)	Complete RVOT obstruction with no VSD; varying degrees of RV/TV hypoplasia; requires PDA for pulmonary blood flow ^[8]	Yes
Tricuspid atresia (TA)	No communication between RA and RV → total obligatory atrial R-to-L shunt; requires ASD + VSD or PDA for pulmonary flow ^[8]	Yes/No depending on RVOT
Ebstein's anomaly	Downward displacement of tricuspid valve leaflets → reduced RV functional capacity → functional RVOT obstruction; severe TR → RA enlargement → R-to-L shunt via PFO; "wall-to-wall" heart on CXR ^[8]	Variable
Tricuspid stenosis	Atrial R-to-L shunt; rare as isolated lesion	No

These present with cyanosis but have PLETHORIC lung fields on CXR (opposite to critical PS which has oligaemic fields).

Differential	Key Features	Duct-Dependent?
Transposition of great arteries (TGA)	Aorta from RV, PA from LV → parallel circulations; egg-on-a-string silhouette on CXR; plethoric lung fields; cyanosis within hours of birth	Yes (requires mixing — PDA, ASD, or VSD)
Truncus arteriosus	Single great artery from both ventricles; plethoric lungs; presents with cyanosis + HF	No (no mixing required)
Total anomalous pulmonary venous return (TAPVR)	All pulmonary veins drain anomalously; snowman/figure-of-eight sign on CXR (supracardiac type); plethoric or congested lungs	No (no mixing required)

Differential	Key Features	Duct-Dependent?
Coarctation of aorta	Unequal upper/lower limb BP and pulses; differential cyanosis (pink upper, blue lower); collapse when ductus closes	Yes (critical coarctation)
Interrupted aortic arch	Complete discontinuity of aortic arch; severe HF + shock when ductus closes	Yes
Critical aortic stenosis	LV outflow obstruction; poor systemic output; unicuspid/bicuspid valve in neonates	Yes
Hypoplastic left heart syndrome (HLHS)	Underdeveloped LV, MV, AV; entirely duct-dependent systemic circulation	Yes

How to Distinguish Critical PS from Other Cyanotic CHD at the Bedside

Key bedside clues:

CXR: Oligaemic lung fields support cyanotic CHD rather than respiratory disease ^[5]. Critical PS has oligaemic lungs + normal-to-mildly-enlarged heart (vs. boot-shaped in TOF, egg-on-string in TGA, wall-to-wall in Ebstein's)
Hyperoxia test: SpO₂ fails to rise above 85–90% with 100% FiO₂ in cyanotic CHD (both PS and TGA) → confirms fixed R-to-L shunt. However, in critical PS with duct-dependent flow, PaO₂ may partially improve if PDA is still patent.
ECG: RAD + RVH in critical PS (vs. RVH in TOF; but RAD + RVH can also be seen in many cyanotic CHDs)
Echo: Definitive — will show the thickened stenotic PV, turbulent flow, and estimate the gradient

Differential	Key Distinguishing Features
Moderate-severe PS	ESM at LUSB with ejection click; soft P2; RV heave; ECG shows RVH
ASD (secundum)	ESM at LUSB + fixed split S2; usually well child with history of frequent chest infections; ECG shows incomplete RBBB + RAD
TOF (non-operated or palliated)	Cyanosis ± clubbing; single S2; squatting behaviour; boot-shaped heart
Idiopathic pulmonary arterial hypertension	Progressive SOBOE + syncope; loud P2 (opposite to PS!); RV heave; ECG shows RVH + RV strain pattern ^[11]
Mild aortic stenosis	ESM at RUSB radiating to neck; may be asymptomatic or exertional angina/syncope
HCM	ESM at LLSB; family history; dynamic murmur changes with manoeuvres

Key differentiator: In PS, P2 is SOFT or ABSENT; in pulmonary hypertension, P2 is LOUD. Both cause RV heave and RVH on ECG, but the auscultatory finding of P2 immediately separates them.

When RVH is found incidentally on ECG or a parasternal heave is palpated, the differential includes any cause of RV pressure or volume overload:

Condition	Mechanism of RVH	P2 Character
Pulmonary stenosis	RV pressure overload from fixed obstruction	Soft/absent
Pulmonary hypertension (any cause)	RV pressure overload from elevated PVR	Loud
ASD	RV volume overload from L-to-R shunt	Normal/loud + fixed split
TOF	RV pressure overload from RVOT obstruction	Soft/absent
Eisenmenger syndrome	RV pressure overload from irreversible PVR elevation	Loud (single S2)
Cor pulmonale	RV pressure overload from chronic lung disease	Loud

It is essential not to anchor on cardiac causes alone. Respiratory and other causes must be excluded:

Category	Examples	Key Differentiating Feature
Respiratory	RDS, pneumonia, meconium aspiration, congenital diaphragmatic hernia, pneumothorax	Tachypnoea and subcostal recession are prominent; CXR shows parenchymal/pleural disease; hyperoxia test shows improvement in PaO₂ (unless massive shunt)
Persistent pulmonary hypertension of the newborn (PPHN)	Often post-asphyxia or MAS; pre-post ductal SpO₂ difference > 10%	Differential cyanosis; improves with iNO
Methaemoglobinaemia	Congenital or toxin-induced; chocolate-brown blood; SpO₂ reads ~85% regardless of O₂	Does not respond to supplemental O₂; co-oximetry diagnostic
CNS depression	Birth asphyxia, maternal sedation	Apnoea/hypoventilation rather than structural cardiac/lung disease
Sepsis	GBS, E. coli; poor perfusion, temperature instability	Blood cultures, CRP, responds to antibiotics

An oligaemic lung field on CXR supports cyanotic congenital heart disease rather than respiratory disease as the cause of cyanosis ^[5]. This is because respiratory causes of cyanosis typically show parenchymal opacity, air-trapping, or effusion — not reduced vascular markings.

Hyperoxia Test — The Bedside Discriminator

Administer 100% FiO₂ for 10–15 minutes and measure post-ductal PaO₂:

PaO₂ > 150 mmHg: lung disease likely (O₂ can diffuse across the alveolar-capillary membrane once high FiO₂ overcomes V/Q mismatch)
PaO₂ < 100 mmHg: suggests cyanotic CHD with fixed R-to-L shunt (the shunted blood never passes through the lungs, so giving O₂ cannot oxygenate it)
PaO₂ 100–150 mmHg: equivocal — could be either; echocardiography needed

Feature	Valvular PS	ASD	TOF	Innocent Murmur	Pulmonary HTN
Ejection click	✓	✗	✗	✗	✗
S2 splitting	Wide, varies with respiration	Fixed wide	Narrow/single	Normal	Narrow/single
P2 intensity	Soft/absent	Normal/loud	Soft/absent	Normal	Loud
Cyanosis	Only if critical + PFO/ASD	No (unless Eisenmenger)	Yes (proportional to RVOT obstruction)	No	Late
CXR MPA	Prominent (post-stenotic dilation)	Prominent (↑flow)	Concave (small MPA → boot shape)	Normal	Prominent (dilated)
CXR lung fields	Normal	Plethoric	Oligaemic	Normal	Oligaemic/pruned peripherally
ECG	RAD, RVH	RAD, incomplete RBBB	RAD, RVH	Normal	RAD, RVH, RV strain

High Yield Summary — Differential Diagnosis of Pulmonary Stenosis

Asymptomatic ESM at LUSB: Top differentials are innocent murmur, ASD, and valvular PS. Distinguish by: ejection click (PS only), S2 character (fixed wide split = ASD; soft P2 = PS; normal = innocent).
Neonatal cyanosis: Critical PS is one of several causes of cyanotic CHD with decreased pulmonary blood flow (oligaemic lung fields). The DDx includes TOF, TOF/PA, PA/IVS, tricuspid atresia, and Ebstein's anomaly ^[3]^[8]. All may be duct-dependent.
Separate cyanotic CHD with increased pulmonary blood flow (plethoric lungs): TGA, truncus arteriosus, TAPVR — the "3 Ts" ^[3]^[8].
Always consider non-cardiac causes of neonatal cyanosis: respiratory disease, PPHN, sepsis, methaemoglobinaemia.
Oligaemic lung fields on CXR in a cyanotic neonate strongly supports cyanotic CHD over respiratory disease ^[5].
The hyperoxia test is the bedside discriminator: PaO₂ < 100 mmHg on 100% FiO₂ → cyanotic CHD.
RVH on ECG is shared by PS, TOF, pulmonary HTN, and ASD — differentiate by P2 (soft in PS/TOF vs. loud in pulmonary HTN) and S2 splitting pattern (fixed in ASD).

Active Recall - Differential Diagnosis of Pulmonary Stenosis

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 206 — Isolated RVOT Obstruction: Valvular PS) ^[3] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 270–271 — TOF; p. 280–285 — Cyanotic CHD classification and DDx) ^[5] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supports cyanotic CHD) ^[8] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 593–600 — Cyanotic CHD categorisation, PS, PA/IVS, TOF/PA, Ebstein's) ^[11] Senior notes: Ryan Ho Respiratory.pdf (p. 137–138 — Pulmonary hypertension classification and clinical features)

Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Pulmonary Stenosis

Diagnostic Criteria

Unlike many medical conditions (e.g., rheumatic fever with the Jones criteria, or heart failure with the Framingham criteria), pulmonary stenosis does not have a formal set of "diagnostic criteria" that require a point-scoring system. Instead, the diagnosis is made by integrating clinical findings (the characteristic murmur ± signs of severity) with echocardiographic confirmation, which is the definitive investigation.

However, we can define what constitutes a diagnosis and how severity is graded, because severity grading directly determines management.

The clinical diagnosis is suspected when the following constellation is present:

Feature	What It Indicates
Ejection systolic murmur (ESM) at the left upper sternal border (LUSB) ^[1]	Turbulent flow across the narrowed PV
Ejection click preceding the ESM ^[1]	Pathognomonic for valvar-level stenosis. The click is produced by abrupt tensing of the domed, fused valve cusps. Its presence tells you the obstruction is at the valve (not infundibular or supravalvular)
Soft, delayed, or absent P2 ^[1]	Low PA pressure distal to obstruction + prolonged RV ejection time
RV impulse (parasternal heave) and suprasternal thrill ^[1]	RV pressure overload and transmission of turbulent energy
Cyanosis (neonates)	Critical PS with R-to-L shunt via PFO/ASD

The presence of an ejection click suggests that the stenosis is at the valvar level ^[1]. This is a frequently tested point — if the click is absent, consider subvalvular or supravalvular obstruction.

Echocardiography with Doppler is the definitive diagnostic modality ^[1]^[3]. It simultaneously confirms the diagnosis and grades severity.

Severity is classified by the peak instantaneous systolic pressure gradient across the pulmonary valve, estimated using Doppler echocardiography ^[1]:

Severity	Peak Gradient (Doppler)	Peak Velocity	Clinical Implication
Trivial / Insignificant	< 25 mmHg	< 2.5 m/s	Normal variant; no follow-up needed
Mild	25–39 mmHg	2.5–3.0 m/s	Observe / no management ^[1]
Moderate	40–59 mmHg	3.0–4.0 m/s	Observe / no management ^[1]; serial follow-up
Severe	≥ 60 mmHg	≥ 4.0 m/s	Balloon pulmonary valvuloplasty (BPV) indicated ^[1]
Critical (neonatal)	Near-atretic (pinhole valve)	Variable (may be low if flow is duct-dependent)	Urgent PGE₁ + neonatal balloon valvuloplasty ^[1]

The gradient is calculated from the modified Bernoulli equation:

ΔP = 4V²

where V = peak transvalvular velocity in m/s measured by continuous-wave (CW) Doppler, and ΔP = peak instantaneous gradient in mmHg.

Why peak instantaneous gradient and not mean gradient? In paediatric PS, peak instantaneous gradient is the standard metric used for grading severity and making intervention decisions. This differs from adult aortic stenosis where mean gradient is more commonly used. The reason is historical convention and because the PS flow profile is well-suited to peak gradient measurement.

High Yield — Intervention Threshold

BPV is indicated when the peak Doppler gradient is ≥ 60 mmHg in valvular PS ^[1]. Below this threshold, the natural history is benign with virtually no risk of sudden death, and most children remain asymptomatic. Above this threshold, progressive RVH and the risk of RV failure or arrhythmias justify intervention even in asymptomatic patients.

Critical PS — Different Diagnostic Paradigm

In critical PS, do not rely on the Doppler gradient alone to judge severity. The gradient may be paradoxically low because there is so little forward flow across the near-atretic valve that velocity is low. The clinical picture (duct-dependent cyanotic neonate) and 2D echo appearance (pinhole valve orifice, hyperdynamic but small RV cavity, PFO with R-to-L shunt) are more important than the gradient number.

The approach to diagnosing PS in paediatrics follows a logical sequence: clinical suspicion → bedside investigations → echocardiographic confirmation.

Investigation Modalities — Detailed Interpretation

When: First-line bedside assessment in any neonate with suspected cyanosis; also part of universal newborn screening in Hong Kong.

What it tells you:

Normal neonatal SpO₂ ≥ 95% by 24 hours of life
SpO₂ < 95% in a neonate warrants investigation for CHD (among other causes)
In critical PS: SpO₂ typically 60–85% depending on PDA patency and degree of R-to-L shunt
Pre-ductal (right hand) vs. post-ductal (foot) SpO₂ difference > 3% suggests differential shunting (more relevant for coarctation/interrupted arch with R-to-L ductal flow; in critical PS the difference is usually minimal because the shunt is at atrial level)

Why it works: Pulse oximetry detects the proportion of oxyhaemoglobin. If deoxygenated blood bypasses the lungs via a R-to-L shunt (critical PS + PFO/ASD), systemic SpO₂ drops.

When: Cyanotic neonate where the cause of cyanosis is uncertain (cardiac vs. respiratory).

How: Administer 100% FiO₂ for 10–15 minutes → measure post-ductal PaO₂ on ABG.

Result	Interpretation	Mechanism
PaO₂ > 150 mmHg	Lung disease likely	O₂ diffuses across alveolar-capillary membrane once high FiO₂ overcomes V/Q mismatch
PaO₂ < 100 mmHg	Cyanotic CHD with fixed R-to-L shunt	Blood that bypasses the lungs never encounters alveolar O₂; no amount of supplemental O₂ can oxygenate it
PaO₂ 100–150 mmHg	Equivocal	Could be either; proceed to echo

A radiograph showing an oligaemic lung field due to reduced pulmonary blood flow supports cyanotic CHD rather than respiratory disease ^[5]. The hyperoxia test confirms this physiologically.

CXR findings in valvular PS ^[1]:

Finding	Pathophysiological Explanation	Present in Valvular PS?
Prominent pulmonary knob (post-stenotic dilation of MPA)	High-velocity jet strikes the MPA wall → endothelial injury → localised dilation	Yes — this is characteristic of valvular PS
Normal heart size	In isolated PS, the RV hypertrophies concentrically without dilating; the LV is normal	Yes (unless decompensated or critical PS with significant TR)
Normal pulmonary vascular markings	In mild-moderate PS, pulmonary blood flow is maintained	Yes in mild/moderate
Oligaemic lung fields	In severe/critical PS, reduced pulmonary blood flow	Only in severe/critical PS

Post-Stenotic Dilation — A Pathognomonic CXR Finding

Post-stenotic dilation of the MPA (prominent pulmonary knob) is NOT present in infundibular or supravalvular PS ^[1]. This is because the turbulent jet in infundibular PS is absorbed before reaching the MPA, and in supravalvular PS the narrowing is beyond the MPA itself. Finding a prominent MPA on CXR in a child with an ESM at the LUSB strongly suggests valvular PS specifically.

Comparison with other conditions on CXR:

Condition	Heart Shape	MPA	Lung Fields
Valvular PS	Normal size	Prominent (post-stenotic dilation)	Normal to oligaemic
TOF	Boot-shaped (uptilted apex + concave MPA segment) ^[3]	Small/concave	Oligaemic
ASD	Mildly enlarged	Prominent (increased flow)	Plethoric
TGA	Egg-on-a-string (narrow mediastinum)	Variable	Plethoric

ECG findings depend on the severity of PS ^[1]:

Severity	ECG Findings	Explanation
Mild PS	Normal ECG ^[1]	The pressure overload is insufficient to produce detectable hypertrophy
Moderate PS	Right axis deviation (RAD); RVH pattern beginning to emerge	Increasing RV mass shifts the mean QRS axis rightward
Moderate-to-Severe PS	Right axis deviation + RV hypertrophy ^[1]	Concentric RVH → tall R wave in V1, deep S wave in V5/V6
Severe PS	RAD + RVH + RA enlargement (P pulmonale) ^[1]	RA hypertrophies due to ↑RVEDP → tall, peaked P waves in lead II ( > 2.5mm) and V1

How to read RVH on paediatric ECG (age-specific — critical in paediatrics):

In neonates, RV dominance is physiological (the RV was the dominant ventricle in utero). Normal R wave in V1 for a neonate is up to 26mm. You must use age-specific normal values.
Beyond ~6 months of age, the LV normally becomes dominant → persistence of RV dominance (tall R in V1, rightward axis) suggests pathological RVH.
In a child beyond infancy: Tall R wave in V1 + deep S wave in V6 + RAD suggests RVH ^[3]
Pure R wave (no S wave) in V1, or qR pattern in V1, in a child suggests significant RV pressure overload (RV systolic pressure approaching systemic)
RV strain pattern (ST depression + T wave inversion in V1–V3) occurs in severe, longstanding RV pressure overload

ECG Feature	What It Represents	In PS Specifically
RAD	Mean QRS axis > +120° in child	RVH shifts axis rightward
Tall R in V1	RV depolarisation dominates anterior leads	Concentric RVH from pressure overload
Deep S in V5/V6	RV forces oppose normal LV forces in lateral leads	RVH
P pulmonale (peaked P in II, tall initial P in V1)	RA enlargement/hypertrophy ^[1]	Elevated RVEDP → RA strain
RV strain pattern (ST↓ + TWI in V1–V3)	Subendocardial ischaemia of hypertrophied RV	Severe PS

ECG in Mild PS — Do Not Be Falsely Reassured

A normal ECG does NOT exclude PS — mild PS has a completely normal ECG ^[1]. The ECG only becomes abnormal when RVH is significant enough to alter the electrical axis and voltage. This is why echocardiography is needed for definitive diagnosis even if the ECG is normal.

5. Echocardiography with Doppler — The Definitive Investigation

Echocardiography is the gold standard for diagnosing and grading PS ^[1]. It provides both anatomical and haemodynamic information.

Finding	What It Shows	Significance
Incomplete opening of PV cusps ^[1]	The valve leaflets dome into the PA during systole rather than opening fully flat	Confirms valvular PS; the leaflets are fused at the commissures
Thickened, dysplastic leaflets	Leaflets are thick, immobile, with poor commissural fusion	Suggests Noonan syndrome-type dysplastic PS → will NOT respond to balloon valvuloplasty ^[1]
Post-stenotic dilatation of MPA ^[1]	Dilated MPA beyond the stenotic valve	Characteristic of valvular PS; confirms valve-level obstruction
RV wall thickness	Increased RV free wall thickness	Concentric RVH from chronic pressure overload
RV cavity size	May be normal or small (in critical PS with RV hypoplasia)	Small RV cavity in critical PS suggests hypoplastic RV — may affect surgical planning
Tricuspid valve morphology	Size and function of TV	TV regurgitation is common in severe PS; TV hypoplasia seen in PA/IVS
Atrial septum	PFO or ASD with direction of shunting	R-to-L shunting via PFO/ASD explains cyanosis in critical PS ^[1]
PDA patency and flow direction	Aorta → PA flow through ductus	Confirms duct-dependent pulmonary circulation in critical PS

Doppler Modality	What It Measures	Application in PS
Continuous-Wave (CW) Doppler	Peak velocity across PV	Estimation of systolic pressure gradient across PV ^[1] using modified Bernoulli: ΔP = 4V². This is the key measurement for severity grading.
Colour Flow Doppler	Direction and pattern of blood flow	Turbulent flow in pulmonary trunk ^[1] — appears as mosaic colour pattern beyond the stenotic valve; also shows direction of shunting at atrial septum
Pulsed-Wave (PW) Doppler	Velocity at a specific sample volume location	Can localise the level of obstruction (subvalvular vs. valvular vs. supravalvular) by placing the sample volume at different points in the RVOT

Parameter	Relevance
TR jet velocity	Allows estimation of RV systolic pressure (RVSP = 4 × TR velocity² + estimated RAP). In severe PS, RVSP may be suprasystemic
RV function (TAPSE, FAC)	Assesses whether RV is compensating or failing
Annular size	Small annulus suggests hypoplasia; important for surgical planning

Echo findings in valvular PS: (1) Incomplete opening of PV cusps, (2) Post-stenotic dilatation, (3) Turbulent flow in pulmonary trunk, (4) Estimation of systolic pressure gradient across PV ^[1]

When: Not routinely needed for diagnosis of isolated PS (echocardiography is sufficient). Reserved for:

Therapeutic balloon pulmonary valvuloplasty (BPV) — catheterisation is both diagnostic and therapeutic in the same procedure ^[1]^[3]
Complex anatomy where echo is insufficient
Assessment of RV-dependent coronary circulation in PA/IVS (not isolated PS, but important differential) ^[1]
Measurement of direct intracardiac pressures when echo estimates are discordant with clinical picture

Catheterisation Measurement	Normal	In PS
RV systolic pressure	15–30 mmHg	Elevated; may equal or exceed LV systolic pressure in severe PS
PA systolic pressure	15–30 mmHg	Low (distal to obstruction)
Systolic pressure gradient (RV – PA)	< 10 mmHg	≥ 60 mmHg indicates severe PS warranting intervention ^[1]
RA mean pressure	< 5 mmHg	Elevated if significant TR or RV diastolic dysfunction
Oxygen saturation sampling	Equal RA and SVC	Drop in arterial saturation confirms R-to-L shunting

When: Rarely needed for isolated valvular PS. More useful in:

Complex RVOT anatomy (e.g., post-surgical re-evaluation)
Quantification of RV volume and function when echo windows are poor (adolescents, post-repair)
Assessment of branch PA stenosis (better visualisation than echo)

What it provides: Accurate RV volume, mass, ejection fraction; flow quantification across the PV; 3D anatomy of the RVOT and branch PAs.

Investigation	Purpose	Key Points for Paediatrics
Arterial blood gas (ABG)	Assess severity of hypoxaemia in critical PS	Low PaO₂, metabolic acidosis (lactic acidosis from poor tissue perfusion)
CBC	Polycythaemia in chronic cyanosis (critical/severe PS with shunting)	Elevated haematocrit as compensatory response to chronic hypoxaemia
Genetic testing	If syndromic features suggest Noonan, Alagille, Williams	Noonan: PTPN11, SOS1, RAF1, KRAS mutations (RAS-MAPK pathway); Alagille: JAG1/NOTCH2
Prenatal echo (fetal echocardiography)	Antenatal detection	Critical PS can be detected on fetal echo → allows delivery planning at a centre with paediatric cardiology and NICU

Investigation	Mild PS	Moderate PS	Severe PS	Critical PS (Neonate)
SpO₂	Normal	Normal	Normal (unless PFO/ASD)	60–85%
CXR heart size	Normal	Normal	Normal	Normal or mildly enlarged
CXR MPA	Prominent (post-stenotic dilation)	Prominent	Prominent	May be less prominent (very little jet)
CXR lung fields	Normal	Normal	Normal to mildly oligaemic	Oligaemic
ECG	Normal ^[1]	RAD ± mild RVH	RAD + RVH + RA enlargement ^[1]	RAD + RVH + P pulmonale
Echo: PV cusps	Incomplete opening ^[1]	Doming, restricted	Severely restricted	Pinhole / near-atretic
Echo: post-stenotic dilation	Present ^[1]	Present	Present	± (minimal flow)
Echo: peak gradient	25–39 mmHg	40–59 mmHg	≥ 60 mmHg ^[1]	May be low (reduced flow)
Echo: turbulent PA flow	Yes ^[1]	Yes	Yes (high velocity)	Minimal
Echo: atrial shunt	None	None	± R-to-L if PFO	R-to-L through PFO/ASD
Echo: PDA	Closed	Closed	Closed	Patent, L-to-R flow (aorta → PA)

Here is how to think about the diagnosis of PS from a first-principles perspective, as you would on a ward round:

You hear an ESM at the LUSB → think RVOT obstruction or increased pulmonary flow
Ejection click present? → Yes = valvular PS (click is from the domed valve)
P2 character? → Soft/absent = PS; loud = pulmonary HTN; fixed wide split = ASD
Get an ECG → normal in mild PS; RVH in severe PS
Get a CXR → prominent MPA (post-stenotic dilation) + normal heart size + normal lung fields = classic valvular PS
Get an echo → confirms diagnosis, grades severity (peak gradient), assesses valve morphology (typical vs dysplastic), looks for associated lesions
If gradient ≥ 60 mmHg or critical PS → proceed to catheterisation for BPV

High Yield Summary — Diagnosis of Pulmonary Stenosis

No formal diagnostic criteria exist — diagnosis is clinical (ESM at LUSB ± ejection click ± soft P2) confirmed by echocardiography.
Echocardiography with Doppler is the definitive investigation ^[1]: shows incomplete PV opening, post-stenotic dilation, turbulent PA flow, and estimates the gradient.
Severity grading is by peak Doppler gradient: mild < 40, moderate 40–59, severe ≥ 60 mmHg ^[1].
BPV threshold: peak gradient ≥ 60 mmHg ^[1].
In critical PS, the gradient may be paradoxically low — use the clinical picture (cyanosis, duct dependence) and 2D echo anatomy.
CXR: prominent pulmonary knob (post-stenotic dilation) with normal heart size and normal lung markings — present only in VALVULAR PS, NOT infundibular/supravalvular ^[1].
ECG: normal in mild PS; RAD + RVH + RA enlargement in moderate/severe PS ^[1]. A normal ECG does NOT exclude PS.
Oligaemic lung fields on CXR in a cyanotic neonate supports cyanotic CHD ^[5].
Hyperoxia test: PaO₂ < 100 mmHg on 100% FiO₂ confirms fixed R-to-L shunt (cyanotic CHD).
Cardiac catheterisation is primarily therapeutic (BPV), not needed purely for diagnosis in isolated PS.

Active Recall - Diagnosis and Investigations of Pulmonary Stenosis

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 206 — Isolated RVOT Obstruction: Valvular PS — investigations and severity grading) ^[3] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 270–271 — TOF diagnosis, ECG, CXR, Echo, catheterisation) ^[5] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supports cyanotic CHD) ^[12] Senior notes: Block A - Cardiology Data Interpretation.pdf (p. 1 — ECG interpretation systematic approach) ^[13] Senior notes: Block A - Introduction to CVS investigations (including ECG).pdf (p. 7 — CXR interpretation in CVS) ^[14] Lecture slides: GC 050. Fever and a murmur.pdf (p. 12 — Echocardiogram and investigation findings in valvular disease)

Management of Pulmonary Stenosis in Paediatrics

The management of pulmonary stenosis (PS) in children follows a remarkably clean, logical framework. Think of it as a decision tree based on two key variables:

Severity — determined by the peak Doppler gradient on echocardiography
Valve morphology — typical (thin, domed, fused commissures) vs. dysplastic (thick, immobile leaflets as in Noonan syndrome)

The beauty of PS management in paediatrics is that it is one of the most gratifying interventions in congenital heart disease: balloon pulmonary valvuloplasty (BPV) is the treatment of choice for typical valvular PS and has excellent long-term outcomes ^[1]. Unlike many other CHDs that require open-heart surgery, most children with significant PS can be treated in the catheterisation lab without a sternotomy.

Scenario 1: Critical PS in the Neonate — Emergency Management

This is a life-threatening emergency. The neonate is duct-dependent for pulmonary blood flow. When the ductus arteriosus closes, the baby dies.

Action	Rationale
IV Prostaglandin E₁ (PGE₁ / alprostadil) infusion ^[1]	PGE₁ relaxes the smooth muscle of the ductus arteriosus, keeping it patent. This is the lifeline — it maintains the only route for blood to reach the lungs (aorta → PDA → PA → lungs). Starting dose: 5–10 ng/kg/min IV; can increase up to 50–100 ng/kg/min if needed
Monitor for PGE₁ side effects	Apnoea (10–12% of neonates — have intubation equipment ready), fever, hypotension, jitteriness, flushing. These are dose-related.
Correct metabolic acidosis	Severe hypoxaemia → lactic acidosis from anaerobic metabolism. Sodium bicarbonate IV if pH < 7.1 and ventilation is adequate. Primarily correct by restoring oxygenation.
Maintain normothermia	Hypothermia increases metabolic demand and worsens acidosis
Minimal handling, keep SpO₂ monitored	Reduce oxygen consumption; continuous pulse oximetry
Avoid high-concentration supplemental O₂ in isolation	O₂ alone cannot fix a fixed R-to-L shunt; the definitive fix is restoring antegrade pulmonary flow

PGE₁ — Know the Drug

PGE₁ (alprostadil): "prostaglandin" = pro-inflammatory lipid mediator; E₁ = specific subtype that acts on EP₄ receptors on ductal smooth muscle to maintain dilation.

Route: IV infusion only (continuous)
Paediatric dose: Start at 5 ng/kg/min; titrate up to 50–100 ng/kg/min
Key side effect: Apnoea (most feared — always have intubation equipment at the bedside; ~10% of neonates)
Other side effects: Fever, hypotension, peripheral vasodilatation (flushing), jitteriness, diarrhoea
When to wean: After successful BPV establishes adequate antegrade pulmonary flow

Urgent PGE₁ + neonatal balloon valvuloplasty in critical PS ^[1].

Aspect	Detail
Procedure	Percutaneous — catheter inserted via femoral vein → advanced through IVC → RA → RV → across the stenotic PV. A balloon catheter is positioned across the PV annulus and inflated to fracture the fused commissures.
Balloon size	Typically 120–140% of the PV annulus diameter. Oversizing is intentional — you need to tear the fused commissures apart.
Success rate	Excellent — > 90% procedural success in typical valvular PS
When it fails	Dysplastic valves, hypoplastic PV annulus, inability to cross the valve (near-atretic)
If BPV fails	Proceed to surgical valvotomy or modified Blalock-Taussig (mBT) shunt as a temporising measure to provide pulmonary blood flow ^[1]

The modified Blalock-Taussig shunt provides extra pulmonary flow for cyanotic heart disease with inadequate pulmonary flow or in frank duct-dependent pulmonary circulation ^[1].

Observe / no management in mild PS ^[1].

Action	Rationale
No intervention	Mild PS (peak gradient < 40 mmHg) is benign. The natural history is excellent — the vast majority of children remain asymptomatic throughout life. Some may even show spontaneous improvement as the child grows and the annulus enlarges.
Reassure family	This is a critical part of family-centred paediatric care. Parents are often anxious when told their child has a "heart problem." Explain: "Your child has a mild narrowing of one of the heart valves. It is not dangerous, does not need treatment, and your child can do all normal activities including sports."
No activity restriction	Children with mild PS have no exercise limitation
Follow-up	Routine review every 2–5 years with clinical assessment ± echocardiography to ensure the gradient has not progressed
Infective endocarditis prophylaxis	NOT routinely recommended for isolated native valvular PS (2007 AHA/2015 ESC guidelines). IE prophylaxis is reserved for high-risk prosthetic valve patients or those with previous IE.

Observe / no management in moderate PS ^[1].

Action	Rationale
Serial follow-up every 1–2 years	Moderate PS (gradient 40–59 mmHg) may remain stable or slowly progress. Regular echocardiography monitors the gradient.
Intervene if: gradient crosses ≥ 60 mmHg threshold, or symptoms develop (exertional dyspnoea, exercise intolerance), or evidence of RV dysfunction on echo	Progression from moderate to severe warrants intervention
No routine activity restriction	Most children with moderate PS tolerate normal activities; competitive strenuous sports may require individualised assessment

Scenario 4: Severe PS — Balloon Pulmonary Valvuloplasty (BPV)

Balloon pulmonary valvuloplasty (BPV) is indicated in severe PS (gradient > 60 mmHg) ^[1].

BPV is one of the landmark achievements of paediatric interventional cardiology. Introduced in 1982 by Jean Kan, it transformed PS from a surgical disease to one manageable in the cath lab.

Step	What Happens	Why
Access	Percutaneous femoral venous access (occasionally internal jugular in neonates)	The venous route provides direct access to the right heart
Catheter advancement	Guidewire → catheter advanced from IVC → RA → TV → RV → across stenotic PV into PA	Follows the normal direction of blood flow
Balloon positioning	Balloon catheter positioned so the balloon straddles the PV annulus (half in RV, half in PA)	The constriction ("waist") on the balloon during initial inflation corresponds to the stenotic valve — this confirms correct positioning
Inflation	Balloon inflated rapidly to high pressure	The mechanical force of the expanding balloon tears open the fused commissures between the valve leaflets. Think of it as surgically "splitting" the valve without a scalpel.
Deflation and withdrawal	Balloon deflated immediately and pulled back	Minimise period of complete RVOT obstruction during inflation
Post-procedure assessment	Pull-back pressure gradient measured: catheter records pressure in PA, then pulled back into RV → the difference is the residual gradient	Success = significant reduction in gradient (usually to < 25–30 mmHg); mild residual PS is acceptable and common

Indication	Evidence
Peak Doppler gradient ≥ 60 mmHg (severe PS) ^[1]	This is the standard threshold regardless of symptoms. Even asymptomatic patients with gradients ≥ 60 mmHg benefit from BPV because of the risk of progressive RVH and late RV dysfunction.
Critical PS in neonates	Urgent neonatal BPV ^[1] after stabilisation with PGE₁
Moderate PS with symptoms or evidence of RV dysfunction	Individualised decision — intervention may be justified if gradient 40–59 mmHg but child is symptomatic

Scenario	Why BPV Won't Work	Alternative
Dysplastic pulmonary valve (e.g., Noonan syndrome)	Thick and dysplastic leaflets do not have fused commissures that can be torn apart by a balloon. The pathology is intrinsic leaflet thickening, not commissural fusion.	Surgical valvotomy ^[1]
Infundibular (subvalvular) PS	Obstruction is muscular, below the valve. Balloon dilation of the valve will not relieve muscular obstruction.	Surgical resection of infundibular muscle (infundibulectomy)
Supravalvular PS / branch PA stenosis	Obstruction is above the valve or in the branch PAs. PV is normal.	Balloon angioplasty of the branch PA ± stenting; surgical patch augmentation
Associated significant pulmonary regurgitation (PR)	If PR is already moderate-severe before BPV, further balloon dilation will worsen PR (you are making the valve even more incompetent)	Surgical valve replacement (bioprosthetic or homograft)

Dysplastic PV (e.g., Noonan syndrome) does not respond to BPV — requires surgical valvotomy ^[1]. This is one of the most important management distinctions to remember.

Outcome	Data
Procedural success rate	> 90–95% for typical valvular PS
Residual gradient	Usually < 25–30 mmHg; mild residual PS is common and acceptable
Pulmonary regurgitation (PR)	Mild-to-moderate PR develops in most patients post-BPV. This is generally well-tolerated in the paediatric age group. Severe PR is uncommon.
Re-intervention rate	5–10% over long-term follow-up; higher in neonates and dysplastic valves
Long-term prognosis	Excellent — most children lead completely normal lives after successful BPV
Complications	Rare: TV damage, RV perforation, cardiac tamponade (all < 1%); transient bradycardia during balloon inflation; femoral vein thrombosis (especially in neonates — use heparin)

Why Does BPV Work So Well in PS?

BPV works well because the pathology of typical valvular PS is commissural fusion — the leaflets are thin and pliable but stuck together at the commissures, creating a dome. The balloon physically rips open these fused commissures, restoring a near-normal orifice. This is analogous to percutaneous mitral balloon commissurotomy (PMBC) in rheumatic mitral stenosis — same principle, different valve. The reason BPV fails in dysplastic PS is that the pathology is different: the leaflets themselves are thick, immobile, and often myxomatous, and there are no fused commissures to split.

Scenario 5: Dysplastic PS — Surgical Valvotomy

Surgical valvotomy is indicated in those with dysplastic PV (e.g., Noonan syndrome) → do not respond to BPV ^[1].

Aspect	Detail
Approach	Open-heart surgery via median sternotomy, on cardiopulmonary bypass
What the surgeon does	Direct incision and excision of the thickened, dysplastic valve tissue (valvectomy); may include partial excision of leaflets to enlarge the orifice. In some cases, a transannular patch is placed to widen the RVOT and PV annulus.
PV competence after surgery	Some degree of pulmonary regurgitation is almost inevitable — accepted as a trade-off for relief of obstruction
When transannular patch is needed	If the PV annulus is hypoplastic (too small), a patch of pericardium or synthetic material is sewn across the annulus to enlarge it. This sacrifices PV competence entirely (free PR), but is necessary for adequate relief of obstruction.

Indication	Explanation
Dysplastic PV not amenable to BPV ^[1]	Primary indication — the thick, immobile leaflets need surgical excision
Failed BPV	If catheter-based intervention is unsuccessful or the gradient remains severely elevated after BPV
Associated infundibular stenosis requiring resection	Muscular infundibular obstruction cannot be relieved by balloon — requires surgical myectomy
PS as part of complex CHD requiring surgical repair	E.g., TOF repair includes relief of RVOT obstruction (infundibular resection ± transannular patch ± PV commissurotomy) as part of the comprehensive repair
Severe PR after prior BPV (late complication)	Pulmonary valve replacement (bioprosthetic or homograft) — this is a separate, later operation

Mortality: < 1% for isolated PS surgery in experienced centres
Long-term: excellent functional outcome; most children are NYHA class I
Main long-term issue: pulmonary regurgitation → may require PV replacement decades later if RV dilates

The modified Blalock-Taussig shunt provides extra pulmonary flow for cyanotic heart disease with inadequate pulmonary flow or in frank duct-dependent pulmonary circulation ^[1].

This is NOT a definitive repair. It is a palliative procedure used as a bridge when:

BPV fails in critical PS
The anatomy is too complex for primary repair in the neonatal period
Buying time for the infant to grow before definitive surgery

Aspect	Detail
Procedure	A Gore-Tex tube graft (typically 3.5–4.0 mm in neonates) is placed between the subclavian artery (or innominate artery) and the ipsilateral pulmonary artery
Effect	Creates a systemic-to-pulmonary arterial shunt → delivers aortic blood (oxygenated) to the lungs → augments pulmonary blood flow → improves oxygenation
Temporary measure	Requires revision or takedown when definitive repair is performed
Indications include ^[1]	Pre-repair TOF with severe cyanosis or uncontrolled Tet spell; PAIVS before Fontan; Univentricular heart with inadequate pulmonary flow; failed BPV in critical PS
Complications	Shunt thrombosis (requires aspirin or heparin), shunt stenosis, pulmonary overcirculation, distortion of PA anatomy

Time Point	Action	Rationale
24–48 hours post-BPV	Repeat echocardiography	Assess residual gradient, degree of PR, RV function, PDA status (in neonates)
1 month	Clinical review + echo	Early detection of restenosis or complications
6 months	Clinical review + echo
12 months	Clinical review + echo + ECG	Assess for RVH regression
Annually for 3–5 years then every 2–5 years	Clinical + echo	Long-term surveillance for: restenosis (gradient increase), progressive PR, RV dilation/dysfunction
Lifelong follow-up	Periodic review in adult congenital heart disease (ACHD) clinic from age 16–18	Late complications may emerge decades later: progressive PR → RV dilation → RV failure → need for PV replacement

What to Watch For in Long-Term Follow-Up

Complication	Mechanism	Management
Restenosis	Scar tissue formation at the valve; incomplete initial commissurotomy	Repeat BPV or surgical valvotomy
Progressive pulmonary regurgitation	Valve leaflets become incompetent after splitting commissures; worse if transannular patch was used	Tolerated for years; PV replacement (surgical or transcatheter) when RV dilates or symptoms develop
RV dysfunction	Chronic volume overload from PR → RV dilation → eventual RV failure	Surveillance with echo/MRI; PV replacement before irreversible RV damage
Arrhythmias	RV scar, dilation, or chronic pressure overload → substrate for re-entrant arrhythmias	Holter monitoring; anti-arrhythmic therapy or ablation if needed
Exercise intolerance	Residual PS, significant PR, or RV dysfunction	Quantify with exercise testing; guide timing of re-intervention
Infective endocarditis	Low but non-zero lifetime risk, especially post-intervention	Routine IE prophylaxis is NOT recommended for native valvular PS or after BPV (2007 AHA/2015 ESC guidelines). Prophylaxis IS indicated for prosthetic valves or prior IE. Educate family on oral hygiene and recognising symptoms of IE.

Special Considerations in Paediatric Management

Aspect	What to Communicate
Mild PS	"Your child has a very mild narrowing. No treatment is needed. They can do everything a normal child does — running, swimming, PE. We will check periodically to make sure it stays the same."
Severe PS / pre-BPV	"The narrowing is significant enough that we recommend a procedure to widen the valve. This is done through a small tube inserted in the leg vein — no open surgery. The success rate is very high, and most children do extremely well afterwards."
Critical PS / neonate	Sensitive conversation with parents in crisis. "Your baby has a very tight narrowing of the heart valve. We have started a medicine to keep an important blood vessel open. We need to do an urgent procedure to open the valve. The team is very experienced in this."
Noonan syndrome	"Because of the type of valve your child has, the catheter procedure may not work well. Surgery may be needed. We will try the catheter approach first if appropriate, but we want you to know that surgery is a safe and effective backup."
Long-term follow-up	"Even after successful treatment, your child will need lifelong heart check-ups, though they will be infrequent and simple. As they grow up, they will transfer to an adult congenital heart disease clinic."

Severity	Activity Guidance
Mild PS or successful BPV with minimal residual	No restriction — full participation in all sports including competitive
Moderate residual PS	Individualised — avoid isometric high-intensity activities (heavy weightlifting); aerobic exercise usually fine
Severe residual PS or significant RV dysfunction	Restrict strenuous competitive sports; encourage light-moderate exercise

Mild-moderate PS: pregnancy usually well tolerated
Severe PS: should be treated (BPV) before pregnancy
Noonan syndrome: genetic counselling regarding autosomal dominant inheritance and recurrence risk ^[15]

Clinical Scenario	Management
Mild PS (gradient < 40 mmHg)	Observe, no intervention, routine follow-up ^[1]
Moderate PS (gradient 40–59 mmHg)	Observe with serial echo every 1–2 years; intervene if progressive or symptomatic ^[1]
Severe PS (gradient ≥ 60 mmHg), typical valve	Balloon pulmonary valvuloplasty (BPV) ^[1]
Severe PS, dysplastic valve (Noonan)	Surgical pulmonary valvotomy ^[1]
Critical PS (neonate, duct-dependent)	Urgent PGE₁ + neonatal BPV ^[1]
Failed BPV	Surgical valvotomy ± modified BT shunt
Infundibular PS	Surgical infundibular resection (BPV not effective for muscular obstruction)
Branch/peripheral PA stenosis	Balloon angioplasty ± stenting of branch PA
Late significant PR post-intervention	Pulmonary valve replacement (surgical or transcatheter Melody/Harmony valve)

High Yield Summary — Management of Pulmonary Stenosis

Mild and moderate PS: observe, no intervention needed ^[1]. Reassure the family; no activity restriction.
Severe PS (peak gradient ≥ 60 mmHg): balloon pulmonary valvuloplasty (BPV) is the treatment of choice ^[1]. Works by mechanically tearing open fused commissures. Success rate > 90%.
Critical PS (neonate): immediate IV PGE₁ (alprostadil) to maintain PDA + urgent neonatal BPV ^[1]. PGE₁ side effects: apnoea (have intubation ready), fever, hypotension.
Dysplastic PV (Noonan syndrome): does NOT respond to BPV → surgical valvotomy ^[1]. The thick, immobile leaflets lack fused commissures.
Modified BT shunt: palliative procedure for duct-dependent pulmonary circulation when BPV fails ^[1].
Long-term: watch for restenosis, progressive PR, and RV dysfunction. Late PV replacement may be needed.
IE prophylaxis is NOT routinely recommended for native PS or post-BPV.
Family-centred communication is essential at every stage — age-appropriate, honest, and reassuring.

Active Recall - Management of Pulmonary Stenosis

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 206 — Isolated RVOT Obstruction: Valvular PS — management: BPV, PGE₁, surgical valvotomy, observation; p. 222 — palliative procedures including modified BT shunt) ^[5] AOS material: AOS - Paeds.pdf (Question 6 — oligaemic lung field supports cyanotic CHD; context for critical PS management) ^[15] Senior notes: Ryan Ho Rheumatology.pdf (p. 172 — Noonan syndrome: associated with pulmonary stenosis and specific facial features)

Complications of Pulmonary Stenosis

Complications of PS can be categorised into two broad groups: (A) complications of the disease itself (untreated or undertreated PS) and (B) complications of treatment (post-BPV or post-surgical). We will also address the important natural-history complications that arise from chronic RV pressure overload, and the unique complications relevant to neonates with critical PS.

Think of it this way: the RV is a thin-walled chamber built for low-pressure work. When you force it to generate systemic-level pressures, bad things happen over time — just as overloading any pump beyond its design capacity eventually causes it to fail.

A. Complications of Untreated / Undertreated Pulmonary Stenosis

Stage	Mechanism	Clinical Consequence
Compensated RVH	Chronic pressure overload → concentric hypertrophy of the RV free wall. The RV generates higher systolic pressure to maintain forward flow across the stenotic valve. This is initially adaptive.	Asymptomatic; detected as RV heave on examination and RVH pattern on ECG
RV diastolic dysfunction	The thickened, stiff RV wall impairs diastolic relaxation → ↑RVEDP → elevated RA pressure	Prominent 'a' wave in JVP; hepatic congestion; may trigger R-to-L shunting if PFO/ASD present
RV systolic failure	Eventually, the hypertrophied RV myocardium becomes ischaemic (supply-demand mismatch — the thickened muscle demands more O₂ but coronary perfusion is limited, especially at suprasystemic RV pressures where myocardial compression impedes coronary flow) → RV dilates and systolic function deteriorates	Tricuspid regurgitation (from annular dilatation), hepatomegaly, peripheral oedema, ascites, exercise intolerance, eventually cardiogenic shock. Progressive right heart failure ^[1]^[16]

RV pressure overload is the principal haemodynamic consequence of PS ^[1]. If left untreated, the compensatory RVH eventually decompensates into RV failure.

Why is this particularly important in paediatrics? In children, the RV can compensate for remarkably long periods — so a child with severe PS may appear deceptively well for years. This makes timely intervention (BPV at gradient ≥ 60 mmHg) so important: you intervene before irreversible RV damage occurs.

Arrhythmia	Mechanism	Clinical Significance
Atrial arrhythmias (atrial flutter, atrial tachycardia)	RA dilatation and hypertrophy from chronic elevated RVEDP → atrial myocardial stretch and fibrosis → re-entrant circuits	Can cause haemodynamic compromise (loss of AV synchrony reduces CO); palpitations; risk of thromboembolism
Ventricular arrhythmias (VT, VF)	RV myocardial fibrosis from chronic pressure overload; post-surgical scar tissue (see below)	Risk of sudden cardiac death — rare but devastating; more common in post-operative patients with RV scar, residual PS, or severe PR ^[16]

Arrhythmia is a recognised complication of both untreated PS and post-surgical repair ^[1]^[16]. The substrate is RV fibrosis from chronic pressure or volume overload.

Aspect	Detail
Mechanism	Turbulent flow across the stenotic or abnormal valve damages the endothelial surface → deposition of platelets and fibrin → non-bacterial thrombotic vegetation → colonisation during transient bacteraemia → IE
Risk	Low but non-zero lifetime risk in any structurally abnormal valve. IE can occur regardless of PS severity (even mild PS creates turbulent flow)
Organisms	Viridans group Streptococci (most common in native valve IE), Staphylococcus aureus
Prophylaxis	Routine IE antibiotic prophylaxis is NOT recommended for native PS (2007 AHA / 2015 ESC / 2023 AHA guideline update). Prophylaxis IS indicated for: (1) prosthetic valves, (2) prior IE, (3) specific repaired CHD with residual shunts at or adjacent to prosthetic material. Good oral hygiene is the most important preventive measure.
Presentation	Fever + new/changed murmur + embolic phenomena (splinter haemorrhages, Osler nodes, Janeway lesions, haematuria). In children, IE often presents insidiously with prolonged fever and non-specific symptoms → high index of suspicion needed.

IE Prophylaxis — Common Exam Confusion

Students often assume that ALL congenital heart disease requires IE prophylaxis. This is incorrect. Current guidelines (AHA 2023) restrict prophylaxis to a small high-risk group. Isolated native valvular PS does NOT require routine prophylaxis. However, if the child has had BPV with a residual prosthetic device, or has undergone surgical valve replacement, then prophylaxis IS indicated.

When cyanosis is present (critical PS with PFO/ASD), the chronic hypoxaemia triggers a cascade of systemic complications analogous to those seen in any cyanotic CHD:

Complication	Mechanism	Clinical Relevance
Polycythaemia (reactive erythrocytosis)	Chronic hypoxaemia stimulates EPO production by the kidneys → increased red cell mass	Raised haematocrit → hyperviscosity → risk of thromboembolism, headaches, fatigue. Polycythaemia is a recognised systemic complication ^[1]^[16]
Cerebral abscess	R-to-L shunt allows venous blood (which may contain micro-organisms) to bypass the pulmonary filter → direct access to systemic circulation including cerebral vasculature	Cerebral abscess is a feared complication of cyanotic CHD ^[1]^[16]. Presents with headache, focal neurology, seizures, fever. Risk is proportional to degree and chronicity of R-to-L shunting.
Cerebral thromboembolism / stroke	Paradoxical embolism via R-to-L shunt; polycythaemia-related hyperviscosity	Cerebral embolism ^[1]^[16]
Stunted growth and failure to thrive	Chronic hypoxia → reduced tissue oxygenation → increased metabolic demand + poor caloric intake (tiring easily during feeds)	Stunted growth from hypoxia ^[1]^[16]; measure weight, height, and head circumference at every visit
Iron deficiency	Chronic erythrocytosis depletes iron stores; children have lower iron reserves; relative iron deficiency worsens hyperviscosity (microcytic red cells are less deformable)	Monitor ferritin; iron supplementation improves rheological properties of blood
Hyperuricaemia and gout	Increased red cell turnover → nucleotide breakdown → elevated uric acid	Rare in children; more relevant in adolescents/adults with longstanding cyanosis
Coagulopathy	Polycythaemia → impaired coagulation factor function; thrombocytopenia from sequestration	Bleeding tendency (epistaxis, gum bleeding, excessive surgical bleeding) despite the prothrombotic state — a paradoxical combination

Duct-dependent pulmonary circulation occurs in critical PS ^[1]. When the ductus closes, the consequences are catastrophic:

Complication	Mechanism	Timeline
Severe hypoxaemia	Loss of the only route for pulmonary blood flow (PDA was supplying it) → virtually no oxygenation	Hours after ductal closure (typically day 1–3 of life)
Metabolic acidosis	Profound tissue hypoxia → anaerobic metabolism → lactic acidosis	Rapidly following hypoxaemia
Seizures	Cerebral hypoxia-ischaemia	If not rescued promptly
Cardiogenic shock and cardiac arrest	RV failure from suprasystemic pressures; inadequate systemic oxygen delivery → multiorgan failure → death	Uniformly fatal if untreated — ~50% die within 2 weeks, 85% within 6 months in PA/IVS (most extreme form) ^[1]

B. Complications of Treatment (Post-Intervention)

Complication	Mechanism	Incidence / Management
Pulmonary regurgitation (PR)	Balloon disrupts the valve leaflets → they no longer coapt properly during diastole → PR. This is the most common post-BPV complication and is essentially an expected trade-off.	Mild-moderate PR: almost universal; well-tolerated. Severe PR: uncommon after isolated BPV; more common if transannular patch used (see surgical below)
Restenosis	Scar tissue formation at the valve; incomplete initial commissurotomy; elastic recoil of valve tissue	5–10% over long-term; higher in neonates and dysplastic valves. Management: repeat BPV or surgical valvotomy
Tricuspid valve injury	Balloon catheter passes through the tricuspid valve → can damage TV leaflets or chordae	Rare ( < 2%); may cause new TR
Cardiac perforation / tamponade	Guidewire or catheter perforates the thin-walled RV or PA	Very rare ( < 1%); requires emergency pericardiocentesis ± surgical repair
Femoral vein thrombosis	Catheter insertion through femoral vein → endothelial injury + vessel spasm → thrombosis. Neonates are particularly at risk (small vessels).	Use heparin during procedure; leg elevation; monitor for limb swelling
Transient bradycardia / heart block	Vagal stimulation during balloon inflation in the RVOT	Usually self-resolving; atropine rarely needed
Infundibular spasm (reactive infundibular stenosis)	After relief of valvular obstruction, the hypertrophied infundibulum may spasm → creates a new subvalvular obstruction. This is a paradoxical worsening of the gradient immediately post-BPV.	Usually transient (resolves over days to weeks as the infundibular muscle regresses). Treat with IV fluids (maintain preload) + beta-blockers (reduce infundibular contractility). Do NOT panic and re-intervene — it will resolve.

Reactive Infundibular Stenosis — A Post-BPV Trap

After successful BPV, the echo may show a persistent or even higher gradient at the subvalvular level. This is reactive infundibular spasm, NOT failure of the procedure. The mechanism: the hypertrophied infundibular muscle, previously "held open" by the high RV pressure proximal to the stenotic valve, now contracts vigorously when the valvular obstruction is relieved. Think of it as the RV "squeezing down" on the now-open outflow tract. It resolves spontaneously over weeks as the infundibular hypertrophy regresses. Beta-blockers can help by reducing dynamic obstruction.

2. Post-Surgical Complications

Complication	Mechanism	Management
Bleeding / haemorrhage	Cardiopulmonary bypass-related coagulopathy; surgical site bleeding	Protamine (reverses heparin); blood products; surgical re-exploration if major
Infection (mediastinitis, wound infection)	Any sternotomy carries this risk	IV antibiotics; wound care; surgical drainage if mediastinitis
Low cardiac output syndrome	Post-bypass myocardial stunning; acute RV dysfunction; residual obstruction	Inotropes (milrinone, dobutamine); volume optimisation; ECMO in refractory cases
Heart block	Surgical trauma to conduction tissue (rare in isolated PV surgery; more common in TOF repair where VSD closure is near the bundle of His)	Temporary pacing; permanent pacemaker if persists > 7–10 days
Pericardial effusion	Post-pericardiotomy syndrome (autoimmune inflammatory reaction to surgical pericardial trauma)	NSAIDs ± colchicine; pericardiocentesis if tamponade

Complication	Mechanism	Why It Matters	Management
Pulmonary regurgitation (PR) — the PRINCIPAL late complication	Surgical valvotomy or transannular patch disrupts valve competence → free PR. "Although pulmonary stenosis, many a time after surgery to correct stenosis the patients get pulmonary regurgitation post-op" ^[17]	PR causes chronic RV volume overload → RV dilation → eventual RV systolic failure → exercise intolerance, arrhythmias, heart failure, sudden death ^[16]	Surveillance with echo ± cardiac MRI (MRI is gold standard for RV volume quantification). Pulmonary valve replacement (PVR) indicated when: (1) MRI shows RV dilation + regurgitant fraction > 25%, or (2) symptomatic (RV failure, arrhythmia) ^[16]
RV dilation and dysfunction	Progressive volume overload from PR → the RV stretches and loses contractile efficiency	RV dilation, decreased exercise tolerance, arrhythmia, sudden cardiac death ^[16]	PVR before irreversible RV damage; exercise testing every 3–4 years to quantify functional capacity
Arrhythmias	RV scar from surgery + chronic dilation → substrate for re-entrant ventricular tachycardia; atrial dilatation → atrial flutter/fibrillation	Arrhythmia is a serious late complication; VT can cause sudden cardiac death ^[16]	Holter monitoring; anti-arrhythmic drugs; catheter ablation; ICD in high-risk patients
Restenosis	Fibrosis at the surgical site; re-growth of infundibular muscle; inadequate initial relief	Re-emergence of gradient on follow-up echo	Repeat BPV (if valvular) or re-do surgery
Exercise intolerance	Residual PS, significant PR, RV dysfunction, or chronotropic incompetence	Affects quality of life; limits sporting participation	Quantify with exercise testing; guide timing of re-intervention
Need for re-intervention	Restenosis, progressive PR, branch PA stenosis (distortion from prior surgery or shunt)	Lifelong follow-up is required; transition to ACHD clinic at 16–18 years	Transcatheter PVR (Melody valve or Harmony valve) is increasingly used; surgical PVR if anatomy unsuitable for transcatheter approach

Pulmonary regurgitation is the principal late complication of TOF repair and PS surgery ^[16]^[17]. It causes RV dilation and dysfunction, decreased exercise tolerance, arrhythmia, and sudden cardiac death. Long-term follow-up and exercise testing every 3–4 years is essential ^[16].

For adolescents and young adults with significant PR after prior intervention, transcatheter PVR (e.g., Melody valve, Edwards SAPIEN, Harmony valve) offers a non-surgical option:

Deployed via percutaneous catheter approach through the femoral vein
Requires a suitable "landing zone" (conduit or pre-existing bioprosthetic valve)
Avoids repeat sternotomy
Increasingly used in Hong Kong paediatric/ACHD centres

Noonan Syndrome-Specific Complications

Since Noonan syndrome is the most important syndromic association of PS ^[1], its complications deserve mention:

Complication	Mechanism	Surveillance
HCM (hypertrophic cardiomyopathy)	RAS-MAPK pathway mutations cause myocardial hypertrophy independent of PS	Echocardiographic screening at diagnosis and regularly
Bleeding diathesis	Factor XI deficiency and platelet function defects are common in Noonan syndrome	Pre-procedural coagulation screen; haematology input before BPV or surgery
Lymphatic dysplasia	Chylothorax post-surgery; peripheral lymphoedema	Monitor for pleural effusion post-operatively
Developmental delay	Part of the syndrome	Developmental assessment and early intervention
Cryptorchidism and fertility concerns	Males: undescended testes → risk of infertility and malignancy	Refer to paediatric surgeon/endocrinologist
Short stature	Part of the syndrome; may be eligible for GH therapy	Growth monitoring; endocrine referral

Category	Complications
Cardiac	RV failure, arrhythmias (atrial/ventricular), IE
Pulmonary	PR (post-intervention), pulmonary artery thrombosis (rare, in Eisenmenger context)
Systemic (cyanotic PS only)	Polycythaemia, cerebral embolism/abscess, stunted growth ^[1]^[16]
Neonatal (critical PS)	Hypoxaemia, metabolic acidosis, seizures, shock, death if ductus closes
Post-BPV	PR, restenosis, reactive infundibular stenosis, TV injury, femoral vein thrombosis, perforation
Post-surgical	PR (principal late complication), bleeding, infection, heart block, restenosis, arrhythmias, need for re-intervention
Noonan-specific	HCM, bleeding diathesis, chylothorax, developmental delay

High Yield Summary — Complications of Pulmonary Stenosis

RV pressure overload → compensatory RVH → eventual RV failure — this is the fundamental cardiac complication of untreated PS ^[1].
Arrhythmias (atrial and ventricular) arise from RV myocardial fibrosis and dilatation — risk of sudden cardiac death ^[1]^[16].
Infective endocarditis can occur regardless of PS severity; routine prophylaxis is NOT recommended for native PS ^[1].
Cyanotic complications (critical/severe PS with shunt): polycythaemia, cerebral embolism/abscess, stunted growth, iron deficiency, coagulopathy ^[1]^[16].
Critical PS in neonates: closure of the ductus → severe hypoxaemia → metabolic acidosis → seizures → death if untreated ^[1].
Pulmonary regurgitation is the PRINCIPAL late complication after intervention (BPV or surgery) ^[16]^[17]. Causes RV volume overload → RV dilation → arrhythmias → RV failure.
Reactive infundibular stenosis post-BPV is a transient phenomenon — treat with beta-blockers and fluids, NOT re-intervention.
Lifelong follow-up is mandatory: echo ± cardiac MRI, exercise testing every 3–4 years, eventual transition to ACHD clinic ^[16].
PV replacement (surgical or transcatheter) is indicated for significant PR with RV dilation or symptoms ^[16].
Noonan syndrome adds specific complications: HCM, bleeding diathesis, lymphatic issues, developmental delay.

Active Recall - Complications of Pulmonary Stenosis

References

^[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 193 — Eisenmenger complications including cardiac, pulmonary, and systemic; p. 206 — Valvular PS management and pathophysiology; p. 211 — Duct-dependent circulation and its consequences) ^[16] Senior notes: Ryan Ho Cardiology.pdf (p. 186 — Eisenmenger syndrome complications: progressive RHF, arrhythmia, IE, polycythaemia, cerebral embolism/abscess, stunted growth; p. 188 — TOF repair complications including PR as principal late complication, arrhythmias, RV dilation, PV replacement indications) ^[17] Lecture slides: Block C - I am pregnant: medical problems complicating pregnancy.pdf (p. 28 — "Although pulmonary stenosis, many a time in ToF after the surgery to correct stenosis the patients get a pulmonary regurgitation post-op")

High Yield Summary

Pulmonary Stenosis — Key Points for Exams:

Second most common CHD (7.5–12%), incidence 0.6–0.8/1,000 live births ^[1]
Associated with Noonan syndrome (dysplastic valve leaflets) — does NOT respond to balloon valvuloplasty → needs surgical valvotomy ^[1]
Valvular PS is the most common type (~90%) — characterised by presence of an ejection click ^[1]
RV pressure overload is the principal haemodynamic consequence → RVH → ↑RVEDP → RAH ^[1]
Post-stenotic dilation of MPA (present only in valvular PS, NOT in infundibular/supravalvular) ^[1]
Critical PS = duct-dependent pulmonary circulation → PGE₁ + neonatal balloon valvuloplasty ^[1]
Cyanosis in PS requires the combination of critical obstruction + PFO/ASD for R→L shunt ^[1]
Majority of children are asymptomatic, even with moderate/severe PS ^[1]
Key auscultatory findings in severe PS: ejection click, ESM at LUSB, delayed/soft/absent P2, RV impulse, suprasternal pulsation/thrill ^[1]
BPV (balloon pulmonary valvuloplasty) indicated when peak gradient ≥ 60 mmHg ^[1]
Oligaemic lung fields on CXR in a cyanotic neonate → think cyanotic CHD with reduced pulmonary blood flow (critical PS, pulmonary atresia, severe TOF) ^[5]

High Yield Summary — Differential Diagnosis of Pulmonary Stenosis

Asymptomatic ESM at LUSB: Top differentials are innocent murmur, ASD, and valvular PS. Distinguish by: ejection click (PS only), S2 character (fixed wide split = ASD; soft P2 = PS; normal = innocent).
Neonatal cyanosis: Critical PS is one of several causes of cyanotic CHD with decreased pulmonary blood flow (oligaemic lung fields). The DDx includes TOF, TOF/PA, PA/IVS, tricuspid atresia, and Ebstein's anomaly ^[3]^[8]. All may be duct-dependent.
Separate cyanotic CHD with increased pulmonary blood flow (plethoric lungs): TGA, truncus arteriosus, TAPVR — the "3 Ts" ^[3]^[8].
Always consider non-cardiac causes of neonatal cyanosis: respiratory disease, PPHN, sepsis, methaemoglobinaemia.
Oligaemic lung fields on CXR in a cyanotic neonate strongly supports cyanotic CHD over respiratory disease ^[5].
The hyperoxia test is the bedside discriminator: PaO₂ < 100 mmHg on 100% FiO₂ → cyanotic CHD.
RVH on ECG is shared by PS, TOF, pulmonary HTN, and ASD — differentiate by P2 (soft in PS/TOF vs. loud in pulmonary HTN) and S2 splitting pattern (fixed in ASD).

High Yield Summary — Diagnosis of Pulmonary Stenosis

No formal diagnostic criteria exist — diagnosis is clinical (ESM at LUSB ± ejection click ± soft P2) confirmed by echocardiography.
Echocardiography with Doppler is the definitive investigation ^[1]: shows incomplete PV opening, post-stenotic dilation, turbulent PA flow, and estimates the gradient.
Severity grading is by peak Doppler gradient: mild < 40, moderate 40–59, severe ≥ 60 mmHg ^[1].
BPV threshold: peak gradient ≥ 60 mmHg ^[1].
In critical PS, the gradient may be paradoxically low — use the clinical picture (cyanosis, duct dependence) and 2D echo anatomy.
CXR: prominent pulmonary knob (post-stenotic dilation) with normal heart size and normal lung markings — present only in VALVULAR PS, NOT infundibular/supravalvular ^[1].
ECG: normal in mild PS; RAD + RVH + RA enlargement in moderate/severe PS ^[1]. A normal ECG does NOT exclude PS.
Oligaemic lung fields on CXR in a cyanotic neonate supports cyanotic CHD ^[5].
Hyperoxia test: PaO₂ < 100 mmHg on 100% FiO₂ confirms fixed R-to-L shunt (cyanotic CHD).
Cardiac catheterisation is primarily therapeutic (BPV), not needed purely for diagnosis in isolated PS.

High Yield Summary — Management of Pulmonary Stenosis

Mild and moderate PS: observe, no intervention needed ^[1]. Reassure the family; no activity restriction.
Severe PS (peak gradient ≥ 60 mmHg): balloon pulmonary valvuloplasty (BPV) is the treatment of choice ^[1]. Works by mechanically tearing open fused commissures. Success rate > 90%.
Critical PS (neonate): immediate IV PGE₁ (alprostadil) to maintain PDA + urgent neonatal BPV ^[1]. PGE₁ side effects: apnoea (have intubation ready), fever, hypotension.
Dysplastic PV (Noonan syndrome): does NOT respond to BPV → surgical valvotomy ^[1]. The thick, immobile leaflets lack fused commissures.
Modified BT shunt: palliative procedure for duct-dependent pulmonary circulation when BPV fails ^[1].
Long-term: watch for restenosis, progressive PR, and RV dysfunction. Late PV replacement may be needed.
IE prophylaxis is NOT routinely recommended for native PS or post-BPV.
Family-centred communication is essential at every stage — age-appropriate, honest, and reassuring.

High Yield Summary — Complications of Pulmonary Stenosis

RV pressure overload → compensatory RVH → eventual RV failure — this is the fundamental cardiac complication of untreated PS ^[1].
Arrhythmias (atrial and ventricular) arise from RV myocardial fibrosis and dilatation — risk of sudden cardiac death ^[1]^[16].
Infective endocarditis can occur regardless of PS severity; routine prophylaxis is NOT recommended for native PS ^[1].
Cyanotic complications (critical/severe PS with shunt): polycythaemia, cerebral embolism/abscess, stunted growth, iron deficiency, coagulopathy ^[1]^[16].
Critical PS in neonates: closure of the ductus → severe hypoxaemia → metabolic acidosis → seizures → death if untreated ^[1].
Pulmonary regurgitation is the PRINCIPAL late complication after intervention (BPV or surgery) ^[16]^[17]. Causes RV volume overload → RV dilation → arrhythmias → RV failure.
Reactive infundibular stenosis post-BPV is a transient phenomenon — treat with beta-blockers and fluids, NOT re-intervention.
Lifelong follow-up is mandatory: echo ± cardiac MRI, exercise testing every 3–4 years, eventual transition to ACHD clinic ^[16].
PV replacement (surgical or transcatheter) is indicated for significant PR with RV dilation or symptoms ^[16].
Noonan syndrome adds specific complications: HCM, bleeding diathesis, lymphatic issues, developmental delay.

Pulmonary Stenosis

Definition

Epidemiology and Risk Factors

Anatomy and Function

Normal Pulmonary Valve Anatomy

Normal RV Physiology (Age-Specific)

Aetiology (Focus on Hong Kong)

A. By Level of Obstruction

B. By Aetiology

Pathophysiology

Step 1: Obstruction Creates a Pressure Gradient

Step 2: RV Pressure Overload → RV Hypertrophy

Step 3: Right Atrial Hypertension

Step 4: Post-Stenotic Dilation

Step 5: Duct-Dependent Pulmonary Circulation (Critical PS)

Classification

By Level of Obstruction (Anatomical)

By Severity (Haemodynamic — Doppler-Based)

By Valve Morphology

Clinical Features

Overview Principle

Symptoms

Signs

Summary Table: Clinical Features by Severity

Age-Specific Presentation

Associated Conditions to Look For

Integrating Clinical Features with Pathophysiology — A Worked Example

Active Recall - Pulmonary Stenosis (Definition to Clinical Features)

References

Framing the Differential: How Does PS Present?

A. Differential Diagnosis of an Ejection Systolic Murmur at the Left Upper Sternal Border (LUSB) in a Child

B. Differential Diagnosis of Neonatal Cyanosis (Critical PS Presentation)

1. Cyanotic CHD with Decreased Pulmonary Blood Flow (↓Qp)

2. Cyanotic CHD with Increased Pulmonary Blood Flow (↑Qp) — "The 3 Ts"

3. Cyanotic CHD Presenting with Severe Heart Failure

C. Differential Diagnosis of Exercise Intolerance with an LUSB Murmur in an Older Child

D. Differential Diagnosis of RV Heave / RVH on ECG

Differential Diagnosis Decision Algorithm

Non-Cardiac Differentials for the Neonatal Cyanosis Presentation

Summary Table: Key Differentiators for PS vs. Top Mimics

Active Recall - Differential Diagnosis of Pulmonary Stenosis

Diagnostic Criteria

A. Clinical Criteria Suggestive of Valvular PS

B. Echocardiographic Diagnostic Confirmation and Severity Grading

Diagnostic Algorithm

Investigation Modalities — Detailed Interpretation

1. Pulse Oximetry (SpO₂)

2. Hyperoxia Test

3. Chest X-Ray (CXR)

4. Electrocardiogram (ECG)

5. Echocardiography with Doppler — The Definitive Investigation

a. Two-Dimensional (2D) Echocardiography — Anatomy

b. Doppler Echocardiography — Haemodynamics

c. Additional Echo Parameters

6. Cardiac Catheterisation

7. Cardiac MRI

8. Additional Investigations (Supportive, Not Diagnostic)

Summary: Investigation Findings at a Glance by Severity

Putting It All Together: The Diagnostic Thought Process

Active Recall - Diagnosis and Investigations of Pulmonary Stenosis

General Principles

Management Algorithm

Scenario 1: Critical PS in the Neonate — Emergency Management

Step 1: Immediate Stabilisation (Resuscitation Phase)

Step 2: Definitive Intervention — Neonatal Balloon Pulmonary Valvuloplasty

Scenario 2: Mild PS — Observation

Scenario 3: Moderate PS — Watchful Waiting with Follow-Up

Scenario 4: Severe PS — Balloon Pulmonary Valvuloplasty (BPV)

The Definitive Treatment

How BPV Works — From First Principles

Indications for BPV

Contraindications / When BPV Is Not Appropriate

Outcomes of BPV

Scenario 5: Dysplastic PS — Surgical Valvotomy

Procedure

Indications for Surgical Intervention in PS

Surgical Outcomes

Scenario 6: Modified Blalock-Taussig (mBT) Shunt — Palliative

Follow-Up Strategy After Intervention

Special Considerations in Paediatric Management