• Genetic / chromosomal abnormalities: Trisomy 21 (Down syndrome — often AVSD but VSD also common), Trisomy 13, Trisomy 18, 22q11.2 deletion (DiGeorge syndrome — conotruncal defects including VSD)
• Family history of CHD: first-degree relative with CHD increases risk ~3-fold
• Single-gene disorders: Holt-Oram syndrome (TBX5 mutations — ASD/VSD + upper limb anomalies), Noonan syndrome

• Maternal diabetes mellitus (pre-gestational > gestational): increases risk of CHD including VSD
• Maternal rubella infection (first trimester): classic association with PDA but also VSD
• Teratogenic drug exposure: alcohol (fetal alcohol spectrum disorder — VSD/ASD), phenytoin, lithium, isotretinoin, thalidomide
• Maternal obesity, advanced maternal age

• Anterior myocardial infarction (rupture of necrotic interventricular septum) — not relevant in children
• Trauma, post-cardiac surgery (iatrogenic)

The interventricular septum separates the left ventricle (high-pressure, systemic pump) from the right ventricle (low-pressure, pulmonary pump). It is composed of:

1. Membranous septum (small, thin, fibrous portion)

   • Located superiorly, just below the aortic valve
   • Continuous with the aortic root and the central fibrous body
   • Very thin — hence most vulnerable to defects

2. Muscular septum (large, thick, muscular portion)

   • Divided into:
     • Inlet septum: beneath the AV valves (tricuspid/mitral)
     • Trabecular (central muscular) septum: main body, heavily trabeculated on RV side
     • Outlet (infundibular/conal) septum: below the semilunar valves (aortic/pulmonary)

The septum normally maintains the pressure differential: LV systolic pressure ~100 mmHg vs RV systolic pressure ~25 mmHg. Any defect allows blood to flow along this pressure gradient (left → right in normal physiology).

In utero, the right and left ventricular pressures are essentially equal because the high pulmonary vascular resistance (PVR) means the RV pumps against systemic-level resistance (blood shunts across the ductus arteriosus and foramen ovale). Therefore, a VSD in utero causes minimal haemodynamic disturbance — there is little net shunting across the defect ^[1][2].

• Most common type (~70% in Western literature; ~60% overall) ^[1][2]
• Most common cause of clinically significant VSD ^[2]
• Located in the membranous septum, just beneath the aortic valve, adjacent to the septal leaflet of the tricuspid valve and the conduction bundle (bundle of His)
• Why is it the most common? The membranous septum is the thinnest and last portion of the septum to close during embryological development (formed by fusion of the endocardial cushions, muscular septum, and aorticopulmonary septum). Any failure or delay in this fusion results in a perimembranous VSD.
• Spontaneous closure mechanism: The septal leaflet of the tricuspid valve can adhere to ("cover") the defect, forming a "tricuspid valve tissue aneurysm" (also called ventricular septal aneurysm). This is a benign finding and represents partial or complete spontaneous closure ^[1][2].
• Associated risk: Proximity to the bundle of His → risk of conduction abnormalities (RBBB, rarely complete heart block) post-surgically

• Central muscular type is more likely to spontaneously close ^[1][2]
• Located entirely within the muscular septum
• Can be inlet, trabecular (central), or outlet muscular
• May be multiple ("Swiss cheese" septum) — more challenging surgically
• Spontaneous closure: highest rate among all VSD types because muscular septum contracts and hypertrophies, physically closing the defect
• Most small muscular VSDs close by age 2 years

• ~5% of VSDs ^[1][2]
• More common in Asian populations (up to 15–30% in East Asian/Japanese series) — highly relevant for Hong Kong exams
• Located in the outlet septum, just below both semilunar valves (aortic and pulmonary)
• Key clinical significance:
  • Associated with coronary (usually right coronary) cusp prolapse and aortic regurgitation (AR) ^[1][2]
  • The defect lacks muscular support superiorly — the right coronary cusp of the aortic valve can prolapse into the defect due to the Venturi effect (high-velocity jet through VSD creates low pressure that sucks the cusp downwards)
  • Does NOT spontaneously close ^[1][2] — the lack of surrounding muscle means there is no mechanism for spontaneous closure
  • Early surgical repair is recommended even for small subarterial VSDs to prevent progressive AR

• ~5–8% of VSDs
• Located beneath the AV valves in the inlet septum
• Strongly associated with Down syndrome (Trisomy 21) and complete/partial atrioventricular septal defects (AVSD)
• Close to the AV node — risk of conduction disturbances

• Isolated VSD: Most common presentation. Usually sporadic (multifactorial inheritance). Recurrence risk for siblings ~3%.
• VSD as part of complex CHD ^[3][4]:
  • Tetralogy of Fallot (large malalignment VSD with overriding aorta, RVOT obstruction, RVH)
  • Transposition of the great arteries (TGA) with VSD
  • Complete atrioventricular septal defect (AVSD) — inlet VSD with primum ASD and common AV valve
  • Double-outlet right ventricle (DORV)
  • Truncus arteriosus
  • Interrupted aortic arch — type B especially associated with posterior malalignment VSD
• Syndromic associations:
  • Trisomy 21 (Down syndrome): AVSD, VSD
  • Trisomy 13 (Patau): VSD, PDA
  • Trisomy 18 (Edwards): VSD, polyvalvular disease
  • 22q11.2 deletion (DiGeorge/velocardiofacial): conotruncal defects including VSD
  • VACTERL association
  • Holt-Oram syndrome: ASD, VSD

• Post-myocardial infarction (anterior MI → septal rupture) — adult context ^[1]
• Post-cardiac surgery (residual/iatrogenic VSD)
• Traumatic

Blood flows from high pressure to low pressure. In normal postnatal physiology:

• LV systolic pressure ≈ 100 mmHg (systemic)
• RV systolic pressure ≈ 25 mmHg (pulmonary)

Therefore, a VSD allows left-to-right (L→R) shunting — oxygenated blood from the LV crosses into the RV and re-enters the pulmonary circulation. This is NOT cyanotic (initially) because the systemic circulation still receives oxygenated blood; the problem is volume overload of the pulmonary circulation and left heart.

The volume of shunting (Qp:Qs ratio) depends on:

1. Size of the defect (resistance at the defect level)
2. Ratio of PVR to SVR (downstream resistance)

Shunt volume = f(VSD size, PVR:SVR ratio)

• Small VSD: Defect is restrictive → large pressure gradient maintained across VSD → small shunt volume regardless of PVR/SVR → Qp:Qs close to 1:1
• Large VSD: Defect is non-restrictive → ventricular pressures equalise → shunt volume determined entirely by PVR:SVR ratio
  • If PVR ≪ SVR (normal postnatal state): massive L→R shunt, Qp:Qs may be 3:1 or 4:1
  • If PVR = SVR: no net shunt (bidirectional)
  • If PVR > SVR: reversal of shunt → R→L → cyanosis (Eisenmenger syndrome)

An important clinical pitfall: A child with moderate/large VSD may appear to "improve" clinically (fewer HF symptoms) without intervention. This does NOT necessarily mean the VSD is closing. Three mechanisms can cause this apparent improvement ^[1][2]:

1. Coverage of perimembranous defect by tricuspid valve tissue (aneurysm formation) — genuine partial closure, this IS a good sign
2. Development of infundibular (subpulmonary) stenosis — RV outflow tract muscular hypertrophy narrows the RVOT, reducing pulmonary blood flow and the L→R shunt. The VSD + infundibular PS essentially creates "acquired Tetralogy of Fallot physiology." This is NOT benign.
3. Increasing pulmonary vascular resistance — the worst scenario. The apparent improvement in HF symptoms is because the shunt volume is decreasing as PVR rises → the child is developing Eisenmenger physiology

These share the core pathophysiology of VSD (left-to-right shunting → pulmonary overcirculation → heart failure), but the level of the shunt differs.

1. Atrial Septal Defect (ASD)

• Shunt at atrial level rather than ventricular level → RV volume overload (not LV) ^[1][7]
• Why it's different from VSD:
  • ASD causes RV volume overload (blood shunts LA → RA → RV), whereas large VSD and PDA cause LV overload ^[7][8]
  • ASD rarely causes symptomatic heart failure in infancy (because the atrial-level pressure gradient is small, shunting is gradual, and the RV is compliant). HF from isolated ASD typically presents in adulthood.
  • Murmur: ejection systolic murmur at the LUSB (from increased flow across the pulmonary valve — NOT the shunt itself, which is silent) with wide and fixed splitting of S2 ^[1]
  • No thrill, no PSM at LLSB
• When to consider ASD in DDx: Child with ESM at LUSB and fixed split S2 — this is NOT VSD. A VSD gives a PSM at LLSB.

2. Atrioventricular Septal Defect (AVSD)

• Primum ASD + inlet VSD + common AV valve in the complete form ^[1]
• 40–50% associated with Down syndrome ^[1]
• Why it mimics VSD: The inlet VSD component produces a PSM, and the patient may present with early heart failure (at 1–2 months or even earlier if severe mitral regurgitation)
• How to differentiate:
  • Look for Down syndrome phenotype (hypotonia, upslanting palpebral fissures, single palmar crease) ^[5]
  • ECG shows left axis deviation (superior QRS axis, "northwest axis") — this is almost pathognomonic for AVSD and is NOT seen in isolated VSD ^[1]
  • Echo is diagnostic: shows the common AV valve straddling the septum
  • Hemodynamic consequences: both RV and LV volume overload (unlike isolated VSD which causes predominantly LV overload) ^[1]
• Clinical presentation: infantile HF at 1–2 months (or earlier if severe MR) in infants with large VSD component; relatively asymptomatic in partial AVSD ^[1]

3. Patent Ductus Arteriosus (PDA)

• Persistent patency of the ductus arteriosus (connects aorta to PA, normally closes within 24–72 hours of birth)
• L→R shunt at great vessel level (aorta → PA) → pulmonary overcirculation → LV volume overload (similar to VSD)
• Why it mimics VSD: Both cause left heart volume overload, pulmonary plethora, and heart failure in infancy
• How to differentiate:
  • Continuous ("machinery") murmur best heard at the left infraclavicular area / upper left sternal border — NOT a PSM. The murmur is continuous because the aorto-pulmonary pressure gradient persists throughout both systole and diastole (aortic pressure > PA pressure at all times)
  • Bounding pulses and wide pulse pressure — because blood runs off from the aorta into the PA during diastole, aortic diastolic pressure drops → wide pulse pressure → the pulses feel "bounding" or "collapsing"
  • VSD: PSM at LLSB, normal pulse pressure
  • More common in preterm infants and associated with maternal rubella

4. Aortopulmonary Window

• Rare defect: direct communication between the ascending aorta and main pulmonary artery (NOT through the ductus)
• Presents similarly to large PDA or VSD with massive pulmonary overcirculation
• Distinguished by echocardiography

When you hear a PSM at the left sternal edge in a child, VSD is the first thought. But consider:

5. Mitral Regurgitation (MR)

• PSM best heard at the apex, radiating to the axilla (not to the right sternal edge) ^[9]
• In children, MR may be caused by:
  • Rheumatic heart disease (increasingly uncommon in Hong Kong, but still seen)
  • Mitral valve prolapse
  • Dilated cardiomyopathy with secondary MR (mitral annular dilatation)
  • Cleft mitral valve (especially in partial AVSD)
• How to differentiate from VSD: Location and radiation of the murmur. VSD = PSM at LLSB radiating widely. MR = PSM at apex radiating to axilla. Echo is definitive.

AOS exam pearl: In the AOS past paper, a child with a displaced apex, murmur at the apex and LLSB, and hepatomegaly 4 cm below the costal margin had cardiomyopathy (with secondary MR) rather than VSD — because VSD is less likely to cause right heart failure at that age and the displaced apex with dilated ventricle points to cardiomyopathy ^[6].

6. Tricuspid Regurgitation (TR)

• PSM at the left lower sternal border — can overlap with VSD location
• Enhanced by inspiration (Carvallo's sign) — because inspiration increases venous return to the right heart, increasing the regurgitant volume
• In children, TR is usually secondary to pulmonary hypertension (which itself may be caused by a large VSD) or Ebstein's anomaly
• Isolated TR in a child without pulmonary hypertension is unusual

This is critically important in paediatrics because the majority of murmurs heard in children are innocent. You must distinguish an innocent murmur from a pathological VSD murmur.

7. Still's Murmur (Vibratory Innocent Murmur)

• The most common innocent murmur in children aged 2–7 years
• Low-pitched, vibratory ("musical," "twanging string"), grade I–III/VI, ejection systolic murmur at the LLSB/between LLSB and apex
• Changes with position (diminishes when upright) and does not radiate
• Why it can mimic VSD: It is heard in a similar location (LLSB)
• How to differentiate:
  • Innocent murmurs are always systolic, never pansystolic (there is a clear gap between the murmur and S2)
  • Never associated with a thrill
  • Normal S1 and S2, no added sounds, no diastolic murmur
  • The child is thriving, asymptomatic, with no other cardiac signs
  • If any doubt, echocardiography will show a structurally normal heart

When a baby presents with heart failure at 1–2 months, VSD is the most common cause, but other conditions must be considered ^[3][4]:

8. Coarctation of the Aorta

• Narrowing of the aorta, typically at the isthmus (just distal to the left subclavian artery, at the site of ductus arteriosus insertion)
• Presents with heart failure in neonates/early infancy if severe (critical coarctation — "duct-dependent" systemic circulation). When the ductus closes, the LV suddenly faces massive afterload → acute LV failure.
• Key differentiating feature: blood pressure discrepancy between upper and lower limbs (higher BP in arms, lower in legs), weak/absent femoral pulses
• 4-limb BP measurement is mandatory in any infant with unexplained heart failure or murmur
• Associated with Turner syndrome (45,X) and bicuspid aortic valve ^[5]

9. Dilated Cardiomyopathy (DCM) / Myocarditis

• Primary myocardial disease causing ventricular dilatation and systolic dysfunction
• In children: viral myocarditis (Coxsackie B, adenovirus, parvovirus B19), inherited DCM, metabolic cardiomyopathies, drug toxicity (anthracyclines)
• How to differentiate from VSD:
  • DCM/myocarditis presents with a globally dilated, poorly contracting LV on echo, often with secondary MR from annular dilatation ^[6][10]
  • No primary structural defect (no VSD seen on echo)
  • ECG may show low voltages, ST-T changes, or arrhythmias
  • History of preceding viral illness (myocarditis), family history (inherited DCM), or chemotherapy exposure

10. Large Arteriovenous Malformation (AVM)

• e.g., Vein of Galen malformation (cerebral AVM) in neonates
• Creates a large left-to-right shunt at the systemic vascular level → high-output cardiac failure in neonates
• Distinguished by cranial bruit, large head circumference, and imaging

If cyanosis is present (or if the murmur has atypical features), consider conditions where VSD is part of a more complex lesion:

11. Tetralogy of Fallot (TOF)

• Large malalignment VSD + overriding aorta + RVOT obstruction (infundibular ± valvular pulmonary stenosis) + RVH ^[4]
• Why it's different from isolated VSD: The RVOT obstruction causes R→L shunting through the VSD → cyanosis (unlike isolated VSD which is acyanotic until Eisenmenger)
• Classic finding: "tet spells" (hypercyanotic spells) — sudden episodes of profound cyanosis, especially during crying, feeding, or straining
• Murmur: ESM at LUSB from RVOT obstruction (NOT a PSM from the VSD — the large malalignment VSD is non-restrictive, so there's little turbulence across it)
• CXR: "boot-shaped heart" (coeur en sabot) from RVH and small main PA segment, with oligaemic lung fields (reduced pulmonary blood flow)

12. Transposition of the Great Arteries (TGA) with VSD

• The aorta arises from the RV and the PA from the LV (ventriculoarterial discordance)
• Without a VSD, there is no mixing → severe cyanosis from birth
• With VSD: some mixing occurs → cyanosis is less severe initially, may present with HF as PVR falls
• Distinguished by echo showing ventriculoarterial discordance

13. Double-Outlet Right Ventricle (DORV)

• Both great arteries arise from the RV; a VSD is the only outlet for the LV
• Clinical presentation varies depending on the VSD location relative to the great arteries and the presence/absence of pulmonary stenosis
• Can mimic TOF or TGA depending on anatomy

14. Truncus Arteriosus

• Single great artery (truncus) arising from both ventricles, with a large VSD
• Massive pulmonary overcirculation → early heart failure + mild cyanosis
• Distinguished by echo showing a single truncal vessel with a truncal valve

15. Pulmonary Atresia with VSD

• Essentially the extreme form of TOF — no antegrade pulmonary blood flow
• Completely duct-dependent pulmonary circulation
• Severe cyanosis from birth

Why order it? CXR provides a quick, non-invasive overview of heart size, pulmonary vascularity, and lung fields. It helps assess the haemodynamic impact of the VSD before echo is available. In paediatrics, CXR is often the first imaging obtained alongside ECG.

Key findings in VSD ^[1][2]:

Detailed CXR interpretation in large VSD:

• Cardiomegaly ^[1][2][3]:
  • Cardiothoracic ratio (CTR) ≥ 0.6 in infants, ≥ 0.5 in older children ^[1]
  • Why? LV volume overload → LV dilatation → overall heart enlargement
  • Pitfall in infants: The thymus in infants/young children can simulate cardiomegaly — the thymic shadow can be very prominent, giving a falsely wide mediastinal/cardiac silhouette ^[1]. This is a common trap. The "sail sign" or "wave sign" of the thymus should be distinguished from true cardiomegaly.

• Pulmonary plethora (increased pulmonary vascular markings) ^[1][2]:

  • Why? L→R shunt → increased pulmonary blood flow → the pulmonary arteries and veins appear engorged, extending well into the outer third of the lung fields
  • L-to-R shunt pattern: pulmonary plethora + cardiomegaly (volume overload) ^[1] — this distinguishes it from:
    • Pulmonary venous congestion (e.g., MS): plethora + hazy markings + NO cardiomegaly
    • Pulmonary outflow obstruction (e.g., TOF): pulmonary oligaemia (reduced markings)

• Cardiac contour changes ^[1]:

  • LV enlargement (LVE): apex extends laterally and points downwards ^[1]
  • LA enlargement: small bulge on the left cardiac border below the main PA shadow ("third mogul sign") — from increased pulmonary venous return filling and dilating the LA ^[1]
  • Note: LVH (without dilatation) produces NO CXR abnormalities — you need ECG or echo for that ^[1]

• In Eisenmenger syndrome:

  • Prominent main pulmonary artery segment (dilated MPA)
  • "Pruned" peripheral pulmonary vasculature (central vessels dilated but peripheral vessels attenuated from irreversible pulmonary vascular disease)
  • Heart size may actually normalise (because the shunt volume decreases as PVR rises)

Why order it? ECG is a non-invasive, rapid bedside investigation. While it cannot directly visualise the defect, it reflects the haemodynamic consequences of the VSD on chamber size and pressures. It also helps differentiate VSD from other causes of murmur/heart failure.

ECG is the initial investigation for ALL potential cardiac conditions ^[11]

Key ECG findings in VSD ^[1][2]:

Detailed ECG interpretation:

• Normal axis in small VSD: The axis remains normal (0° to +90° in older children; right axis deviation is normal in neonates due to physiological RV dominance)

• LV hypertrophy (LVH) ^[12]:

  • Tall R waves in left-sided leads (V5, V6, I, aVL)
  • Deep S waves in right-sided leads (V1, V2)
  • Sokolow-Lyon criteria: S in V1 + R in V5/V6 ≥ 35 mm (adult; paediatric values are age-adjusted — use paediatric ECG normal values!)
  • Why LVH? The LV is chronically volume-overloaded from the recirculated shunt blood → compensatory hypertrophy
  • LV volume overload pattern: Tall R waves in V5/V6 with prominent Q waves (representing increased diastolic filling and resultant septal hypertrophy) and peaked T waves

• Biventricular hypertrophy (BVH) ^[1][2]:

  • Features of both LVH AND RVH on the same ECG
  • Large equiphasic (Katz-Wachtel) complexes in mid-precordial leads (V2–V4) — tall R and deep S of similar amplitude
  • Why BVH in large VSD? The LV is volume-overloaded (large shunt), and the RV is pressure-overloaded (developing pulmonary hypertension). Both chambers hypertrophy.

• RV hypertrophy (RVH) ^[12]:

  • Tall R in V1 (R/S > 1 in V1), deep S in V5/V6
  • Right axis deviation
  • Why pure RVH only in Eisenmenger? When PVR exceeds SVR, the shunt reverses (R→L). Now the LV is no longer volume-overloaded (less blood returns from the lungs), but the RV is massively pressure-overloaded.

• P-wave changes:

  • P mitrale (broad, bifid P wave) = LA enlargement — from increased pulmonary venous return ^[10]
  • P pulmonale (tall, peaked P wave) = RA enlargement — from pulmonary hypertension ^[10]

Important paediatric ECG caveat: In neonates and young infants, right axis deviation and RV dominance are physiologically normal (because of the in-utero high PVR state). You must compare against age-appropriate normal values. A tall R wave in V1 is normal in a neonate but abnormal in a 5-year-old.

Echocardiography is the definitive diagnostic modality for VSD. ^{[1][2][3][11]}

Why is echo the gold standard? Because it directly visualises the defect in real-time, measures its size, determines its anatomical location, quantifies the shunt, and assesses all haemodynamic consequences — all non-invasively, with no radiation, and repeatable at the bedside. In paediatrics, transthoracic echocardiography (TTE) is almost always sufficient (children have excellent acoustic windows due to thin chest walls).

Echocardiography can detect shunts including ASD and VSD ^[11]

What echo tells you — systematic assessment:

Colour Doppler — the key to visualisation:

• The VSD jet appears as a mosaic of colours (turbulent flow) crossing the interventricular septum during systole
• Direction: In standard L→R shunt, the jet goes from the LV (high pressure) into the RV
• Multiple jets may indicate multiple VSDs (Swiss cheese septum)

Continuous wave (CW) Doppler — estimating pressure gradient:

• Measures the peak velocity of blood flow across the VSD
• Using the simplified Bernoulli equation: ΔP = 4V²
  • Where ΔP is the pressure gradient between LV and RV, and V is the peak velocity
• Small restrictive VSD: high velocity (e.g., 4–5 m/s → ΔP = 64–100 mmHg) — means LV pressure is much higher than RV → RV pressure is normal → no pulmonary hypertension
• Large non-restrictive VSD: low velocity (e.g., 1–2 m/s → ΔP = 4–16 mmHg) — means pressures are nearly equalised → RV pressure is elevated → pulmonary hypertension

Clinical reasoning from Doppler: If systolic BP is 100 mmHg and VSD gradient is 80 mmHg, then RVSP = 100 – 80 = 20 mmHg (normal). If VSD gradient is only 20 mmHg, then RVSP = 100 – 20 = 80 mmHg (severe pulmonary hypertension). A low-velocity VSD jet is paradoxically more concerning than a high-velocity jet.

Specific echo findings by VSD type:

When is it needed? Cardiac catheterisation is NOT routine for simple VSD diagnosis — echo is sufficient. It is reserved for specific indications:

Indications for cardiac catheterisation in VSD:

• To assess pulmonary vascular resistance (PVR) when Eisenmenger syndrome is suspected or borderline — determines operability
• To perform vasoreactivity testing (e.g., with inhaled nitric oxide or oxygen) — if PVR drops with vasodilators, the pulmonary vascular disease is still partially reversible → surgery may still be possible
• When non-invasive imaging is inconclusive about haemodynamic significance
• Prior to surgical intervention in complex cases with multiple lesions

What catheterisation provides:

• Direct measurement of pressures: PA pressure, RV pressure, LV pressure, PCWP
• Oximetry data: Step-up in oxygen saturation at the RV level confirms L→R shunt at the ventricular level (the "oxygen saturation step-up" method)
  • Why? Oxygenated blood from the LV enters the RV through the VSD → RV oxygen saturation is higher than RA oxygen saturation
  • Normal RA O₂ sat ≈ 70%; normal RV O₂ sat ≈ 70–75%. A step-up > 7% between RA and RV is significant for a VSD.
• Calculation of Qp:Qs (using the Fick principle):
  • Qp:Qs = (SaO₂ – MvO₂) / (PvO₂ – PaO₂)
  • Where SaO₂ = systemic arterial O₂ sat, MvO₂ = mixed venous O₂ sat, PvO₂ = pulmonary venous O₂ sat, PaO₂ = pulmonary arterial O₂ sat
• PVR calculation: PVR = (mean PA pressure – PCWP) / Qp
  • PVR > 8 Wood units/m² or PVR:SVR > 0.67 generally indicates inoperability (Eisenmenger)

a. Pulse Oximetry (SpO₂)

• Pre- and post-ductal saturations — important in neonates to screen for duct-dependent lesions and cyanotic CHD
• In isolated VSD (acyanotic): SpO₂ is normal (≥ 95% in room air)
• If SpO₂ < 95%, think: Eisenmenger, or VSD is part of complex cyanotic CHD (TOF, TGA, etc.)
• Newborn pulse oximetry screening (performed at 24–48 hours of life in Hong Kong) aims to detect critical CHD. A simple VSD may not be detected by oximetry screening because it is acyanotic.

b. Blood Tests

• Not diagnostic for VSD itself, but important for:
  • FBC: anaemia (worsens HF symptoms by increasing cardiac output demand), polycythaemia (suggests chronic cyanosis in Eisenmenger)
  • BNP / NT-proBNP: elevated in haemodynamically significant VSD with heart failure — correlates with LV volume overload and wall stress. Useful for monitoring response to treatment. Paediatric normal values are age-dependent (neonatal levels are physiologically high).
  • ABG / VBG: metabolic acidosis may be present in severe heart failure or cardiogenic shock
  • Renal function / Electrolytes: baseline before starting diuretics/ACE inhibitors

c. Cardiac MRI (CMR)

• Not first-line for simple VSD
• Useful in complex cases: multiple VSDs, associated lesions, or when echo windows are suboptimal (rare in children, more relevant in older adolescents/adults)
• Can precisely quantify shunt volume (Qp:Qs), ventricular volumes, and myocardial tissue characterisation

d. CT Angiography

• Not routinely used for VSD
• May be helpful for associated vascular anomalies (aortic arch anatomy, coronary artery anatomy pre-surgery)

Patients with small VSD do not require treatment ^[7][8].

Why no treatment?

• The shunt is haemodynamically insignificant — no volume overload, no pulmonary hypertension
• 75% spontaneously close by age 2 years ^[1][2], and the remainder are typically benign
• The risk of surgery (cardiopulmonary bypass in an infant) far outweighs any benefit

What DO you do?

1. Reassurance of parents: explain the benign natural history, high spontaneous closure rate
2. Outpatient follow-up with periodic echocardiography (typically annually or biannually) to:
   • Confirm the defect is not enlarging
   • Monitor for development of aortic regurgitation (especially if close to subarterial position)
   • Document spontaneous closure
3. Infective endocarditis (IE) counselling — the turbulent jet through even a small VSD damages the RV endocardium, creating a nidus for infection. IE risk persists regardless of VSD size ^[1][2].
4. Normal activity — no exercise restriction needed for small VSDs
5. Growth monitoring — should remain on normal centiles

This is extremely high yield. Know these indications cold.

Indications for surgical closure of VSD ^[2][7][8]:

1. Poor medical control of heart failure (refractory HF)
2. Pulmonary hypertension — defined as pulmonary arterial pressure > 50% of systemic pressure ^[2]
3. Failure to thrive despite optimal medical and nutritional management
4. Recurrent chest infections
5. Subarterial defects — even if asymptomatic — to prevent development of aortic insufficiency due to coronary cusp prolapse ^[7][8]
6. Persistent L-to-R shunt with LV dilatation — defined as Qp:Qs > 2:1 ^[2]
7. Unlikely to close spontaneously — e.g., subarterial defect, associated RVOT infundibular stenosis ^[2]

Timing of surgical repair: most patients undergo surgical repair before 6 months of age ^[7][8].

Why before 6 months?

• To prevent irreversible pulmonary vascular disease. The "window of opportunity" for repair is before fixed pulmonary vascular changes develop.
• Large VSDs with significant shunting should ideally be repaired by 3–6 months of age. Waiting beyond 6–12 months significantly increases the risk of permanent pulmonary hypertension.

Contraindications to Surgical Closure [2]

Contraindication: PAP suprasystemic or PVR > 12 Wood units → risk of precipitating acute RV heart failure + ↓LV output ^[2]

• Why is surgery contraindicated in Eisenmenger? If PVR is fixed and suprasystemic, the VSD is serving as a "pop-off valve" — the RV can decompress through the VSD. If you close the VSD, the RV faces the full brunt of the irreversibly elevated PVR with no escape route → acute RV failure → death.
• Caution zone: PAP 75–100% of systemic, PVR 8–12 WU → associated with ↑risk of perioperative complications ^[2] — may still proceed with specialist discussion and careful perioperative management, but risk is significantly higher.

Subarterial defects warrant surgical referral even if asymptomatic, to prevent the development of aortic insufficiency due to coronary cusp prolapse ^[7][8]

• Why early surgery even when asymptomatic? The subarterial VSD sits immediately below the aortic valve. The high-velocity jet creates a Venturi effect that progressively pulls the right coronary cusp (or non-coronary cusp) into the defect → progressive prolapse → progressive AR. Once significant AR is established, it may not fully reverse even after VSD closure. Therefore, prophylactic closure is indicated.
• Subarterial VSDs do NOT close spontaneously ^[1][2]
• Timing: Repair as soon as aortic cusp prolapse or early AR is detected, or prophylactically if the defect is of significant size. In practice, often repaired in early childhood.

When PVR has become fixed and suprasystemic, the VSD is inoperable. Management shifts to palliative care:

• Pulmonary vasodilator therapy:
  • Bosentan (endothelin receptor antagonist): reduces PVR, improves exercise capacity and functional class
  • Sildenafil (phosphodiesterase-5 inhibitor): pulmonary vasodilation via NO-cGMP pathway
  • Iloprost (inhaled prostacyclin analogue): used in severe cases
• Avoid: dehydration, excessive exertion, pregnancy (extremely high maternal mortality), high altitude, general anaesthesia (if avoidable)
• Phlebotomy: if polycythaemia is symptomatic (hyperviscosity — headache, visual disturbance) with Hct > 65%
• Supplemental iron: iron deficiency worsens hyperviscosity (microcytic cells are less deformable)
• Heart-lung transplantation: ultimate option for end-stage Eisenmenger, but donor availability is severely limited

This is important for clinical exams — you will be expected to counsel a parent about their child's VSD.

Key counselling points:

1. Frequency: VSD accounts for 30–40% of all congenital heart disease ^[7][8]
2. Reassurance for small VSD: Benign natural history; spontaneous closure occurs in 60–80% within the first 5 years ^[7][8]
3. Recurrence risk ^[7][8]:
   • Recurrence risk in siblings = 3%
   • Recurrence risk in offspring:
     • Mother affected = 6%
     • Father affected = 2%
4. Growth and development: Most children with small/moderate VSD (repaired or spontaneously closed) have normal growth and development. Those with large VSD requiring surgery should catch up after successful repair.
5. Activity: Small VSD — no restriction. Post-surgical repair with good result — usually return to normal activity after recovery. Eisenmenger — significant restriction.

Unrepaired congenital heart defects belong to the moderate-risk category for IE ^[7][8].

Current guidelines (2023 AHA/ESC, adapted for paediatrics):

Antibiotic prophylaxis for IE is indicated in high-risk groups only:

• Unrepaired cyanotic CHD
• Repaired CHD with prosthetic material/device during the first 6 months after procedure (until endothelialisation occurs)
• Repaired CHD with residual defects at or adjacent to prosthetic material (which prevents endothelialisation)
• Previous history of IE

For isolated, unrepaired VSD (non-cyanotic): The current guidelines are nuanced. The AHA/ESC have shifted away from routine prophylaxis for most moderate-risk conditions. However, HKU/Hong Kong practice may still recommend prophylaxis for unrepaired VSD during dental procedures — check local guidelines. The exam framing from senior notes states: "Unrepaired congenital heart defects belong to the moderate-risk category" ^[7][8], and prophylaxis is mentioned.

If prophylaxis is given (dental procedures):

• Amoxicillin 50 mg/kg PO (max 2 g) single dose, 30–60 minutes before procedure (paediatric dose)
• If penicillin-allergic: Clindamycin 20 mg/kg PO (max 600 mg)

After successful VSD repair with no residual defect: Prophylaxis is needed for the first 6 months post-procedure only, then can be discontinued if the defect is fully closed.

• Applies to: moderate and large VSDs
• Timing: Presents at 1–2 months of age as PVR falls postnatally and L→R shunt volume increases ^[1][2]
• Pathophysiology: ↓PVR → ↑L→R shunt → pulmonary overcirculation → LV volume overload → LV dilatation and failure → backward failure (pulmonary congestion) + forward failure (poor systemic perfusion)
• Clinical manifestation in infants: tachypnoea, feeding difficulty, diaphoresis, failure to thrive, hepatomegaly, gallop rhythm
• Why it matters: Heart failure is the most common early complication and the primary reason for medical therapy and surgical referral in the first 6 months of life. If left untreated, chronic heart failure leads to growth retardation, recurrent chest infections, and ultimately Eisenmenger syndrome.
• Management: Medical therapy (diuretics, ACEI, nutritional support) → surgical closure if refractory (covered in management section)

• Applies to: moderate and large VSDs with significant shunting
• Pathophysiology: The combination of:
  • Inadequate caloric intake — tachypnoea makes feeding exhausting and inefficient; the infant tires before completing a feed
  • Increased caloric expenditure — increased work of breathing, increased cardiac work (the heart is pumping extra volume through the pulmonary circuit), and chronic sympathetic activation all burn calories
  • Recurrent infections — chronic pulmonary congestion predisposes to respiratory infections, which further increase metabolic demand and decrease intake
• Pattern: Weight affected before length/height; head circumference usually spared ^[1] — this reflects that energy is redirected to brain growth (which is metabolically prioritised) while somatic growth suffers
• Clinical significance: Failure to thrive despite optimal nutritional support and medical management is an indication for surgical closure ^[7][8]
• Outcome after surgery: Catch-up growth typically occurs within 6–12 months after successful VSD repair

• Applies to: moderate and large VSDs with persistent significant L→R shunting
• Pathophysiology (build from first principles):
  1. Chronic exposure of the pulmonary vasculature to high flow (increased Qp) and high pressure (transmitted from the LV through the non-restrictive VSD)
  2. Initially, pHTN is reactive/reversible — pulmonary arteriolar vasoconstriction and medial smooth muscle hypertrophy
  3. Over months to years, progressive irreversible pulmonary vascular changes develop ^[1][2]:
     • Intimal hyperplasia → intimal fibrosis → plexiform lesions → arteritis and fibrinoid necrosis
     • These stages are classified by the Heath-Edwards classification (Grade I–VI):
       • Grade I: Medial hypertrophy of pulmonary arterioles
       • Grade II: Intimal cellular proliferation
       • Grade III: Intimal fibrosis with lumen narrowing
       • Grade IV: Plexiform lesions (irreversible beyond this point)
       • Grade V: Angiomatoid lesions
       • Grade VI: Fibrinoid necrosis
  4. Once Grade IV or beyond, changes are irreversible → fixed elevation of PVR
• Why it matters: Progressive pHTN is the mechanism that ultimately leads to Eisenmenger syndrome. This is why surgical repair should be performed before 6 months of age for large VSDs — to close the defect before irreversible pulmonary vascular damage occurs ^[7][8].

This is the most feared long-term complication of an unrepaired large VSD and warrants detailed discussion.

• Eisenmenger syndrome: triad of (1) congenital L-to-R shunt (2) pulmonary arterial disease (3) cyanosis ^[2][14]
• Incidence: up to 80% in large unrepaired VSD and PDA in infancy/early childhood ^[2]
• Pathophysiology: Large unrepaired L→R shunt → progressive destruction of pulmonary arterioles → irreversible pulmonary vascular disease with ↑PVR → eventual equalisation or reversal of pressures → R→L shunt → systemic hypoxia → cyanosis ^[2][14]

Clinical features of Eisenmenger syndrome ^[2][14]:

Symptoms:

• Hypoxaemia: exertional dyspnoea, fatigue, reduced exercise tolerance
  • Why? R→L shunt delivers deoxygenated blood into the systemic circulation
• Reactive erythrocytosis: fatigue, headache, stroke risk
  • Why? Chronic hypoxia stimulates EPO production → secondary polycythaemia → hyperviscosity
• Haemoptysis: from ruptured pulmonary vessels or pulmonary artery thrombosis
  • Why? Hypertensive pulmonary arterioles are fragile; in situ thrombosis is common due to sluggish flow in dilated pulmonary arteries
• Stunted growth if occurring in early childhood ^[2][14]
  • Why? Chronic hypoxia impairs cellular metabolism and growth

Signs:

• Central cyanosis and digital clubbing ^[2]
  • Clubbing develops from chronic hypoxia → proliferation of connective tissue in the distal phalanges (exact mechanism still debated — likely involves platelet-derived growth factor bypassing the pulmonary capillary filter via R→L shunt)
• Left parasternal heave (RVH) ± palpable P2
• Loud and early P2 or single S2 (pulmonary hypertension) ^[2]
• Loss of previous shunt murmur ^[2]
  • Why? When PVR equals SVR, the pressure gradient across the VSD disappears → no flow → no turbulence → no murmur. A "quieter" murmur in an unrepaired large VSD is an ominous sign, not a reassuring one.
• New murmurs of pulmonary regurgitation (PR) or tricuspid regurgitation (TR) may develop from pulmonary arterial and RV dilatation

Complications of Eisenmenger syndrome ^[1][2][14]:

• Prognosis: 30–40% 10-year mortality, with mean age of death at 37 years if transplant not done ^[1][2][14]

• IE risk persists regardless of VSD size ^[1][2] — even tiny, haemodynamically insignificant VSDs carry IE risk

• Pathophysiology from first principles:

  1. The high-velocity jet through the VSD strikes the endocardial surface of the RV side of the septum or the RV free wall
  2. This creates a "jet lesion" — endothelial damage from the shear stress of the turbulent jet
  3. Damaged endothelium exposes subendothelial collagen → platelet and fibrin deposition → forms a non-bacterial thrombotic vegetation (NBTV)
  4. During transient bacteraemia (e.g., dental procedures, skin infections), circulating bacteria adhere to the NBTV → establish infection → IE
  5. Paradoxically, small VSDs may carry higher IE risk than large VSDs because the high-velocity jet in small VSDs creates more endothelial damage than the low-velocity flow in large VSDs

• Common organisms in children: Streptococcus viridans (post-dental), Staphylococcus aureus (skin/soft tissue), HACEK organisms ^[15]

• Clinical features: fever, new/changing murmur, splenomegaly, petechiae, splinter haemorrhages, Osler nodes (painful, fingertips), Janeway lesions (painless, palms/soles), Roth spots (retinal haemorrhages)

• Complications of IE ^[15][16]:

  • Heart failure — valve destruction, abscess formation
  • Stroke — septic emboli from vegetations > 1 cm ^[16]
  • Mycotic aneurysm — persistent bacteraemia causes aneurysm formation in cerebral arteries → risk of haemorrhagic stroke ^[16]
  • Renal involvement — embolic renal infarcts, immune complex-mediated glomerulonephritis

• Prevention: IE prophylaxis with amoxicillin before dental procedures (discussed in management section)

• Subarterial VSD is associated with coronary cusp prolapse and aortic regurgitation ^[1][2]
• Pathophysiology:
  • The subarterial defect lies directly beneath both semilunar valves with no muscular support superiorly
  • The high-velocity L→R jet through the VSD creates a Venturi effect (low pressure zone) just below the aortic valve
  • This sucks the right coronary cusp (most commonly) downward into the defect → progressive prolapse → loss of coaptation → aortic regurgitation
  • AR is progressive and may not fully reverse even after VSD closure if it has been longstanding
• Why it matters: This is the primary reason subarterial VSDs are repaired even when asymptomatic ^[7][8] — to prevent progressive, irreversible AR
• Clinical detection: Early diastolic decrescendo murmur at the left sternal edge (AR murmur) appearing in a child with a known subarterial VSD → urgent surgical referral
• Prevalence in Asian populations: Subarterial VSDs are more common in East Asian populations (up to 15–30%) compared to Western populations (~5%), making AR a particularly relevant complication in Hong Kong practice

• Applies to: large VSDs with longstanding L→R shunting
• Pathophysiology: Chronic exposure of the RV outflow tract to the high-velocity VSD jet causes reactive muscular hypertrophy of the infundibulum (subpulmonary region) → progressive narrowing of the RVOT
• Clinical significance:
  • May cause apparent clinical improvement (the RVOT obstruction reduces pulmonary blood flow and the L→R shunt) — but this is NOT benign ^[1][2]
  • Essentially creates "acquired Tetralogy of Fallot" physiology: VSD + RVOT obstruction
  • If the infundibular stenosis becomes severe, the child may develop cyanosis (R→L shunt through the VSD due to RVOT obstruction)
  • This is an indication for surgical repair even if the VSD itself is moderate in size ^[2]

• Applies to: moderate and large VSDs
• Pathophysiology: Pulmonary overcirculation → pulmonary venous congestion → interstitial oedema → impaired mucociliary clearance + bronchiolar wall oedema → favourable environment for bacterial colonisation → recurrent pneumonia, bronchiolitis
• Additionally, cardiac conditions with pulmonary artery dilation can compress large airways (especially the left main bronchus, which runs between the PA and the aorta) → atelectasis and recurrent infection ^[17]
• Clinical significance: Recurrent chest infections are one of the indications for surgical closure ^[7][8]. Parents often report the child is "always sick."

• Less common in the natural history of uncomplicated VSD compared to other CHD
• LV dilatation from chronic volume overload → substrate for atrial arrhythmias (especially atrial fibrillation/flutter in older children/adults with longstanding VSD)
• Eisenmenger physiology → RV dilatation and fibrosis → ventricular arrhythmias → risk of sudden cardiac death

• Incidence: 1–3% after surgical VSD repair
• Pathophysiology: The bundle of His runs along the posteroinferior rim of a perimembranous VSD. During patch placement, sutures placed near this conduction tissue can damage or transect the bundle → complete AV dissociation
• Clinical features: Bradycardia, haemodynamic compromise, syncope
• Management: Temporary epicardial pacing wires (placed at surgery) → if block persists beyond 7–10 days post-op, a permanent pacemaker is indicated
• Prevention: Meticulous surgical technique, avoiding deep bites near the conduction tissue. Some surgeons place sutures on the RV side of the septum to stay further from the bundle.

• Incidence: Small residual leaks are common (5–10%) immediately post-op; most are haemodynamically insignificant and close spontaneously as the patch endothelialises
• Pathophysiology: Incomplete coverage of the defect margins by the patch, or suture dehiscence
• Clinical significance: A small residual VSD produces a murmur but is usually benign. A large residual VSD with haemodynamic significance may require re-operation or transcatheter closure.
• Detection: Post-operative echocardiography with colour Doppler

• Pathophysiology: The surgical approach to perimembranous VSD is typically through a right atriotomy, working through the tricuspid valve. Retraction, suturing, or chordal damage can cause tricuspid regurgitation.
• Clinical features: New TR murmur post-operatively, signs of right heart failure if severe
• Management: Usually mild and well-tolerated; severe TR may require valve repair

• Particularly relevant in subarterial VSD repair: Even after successful closure, some degree of AR may persist if cusp prolapse was longstanding before repair
• Also possible in perimembranous VSD repair: Sutures near the aortic annulus can distort the aortic valve
• Outcome: Mild AR is usually well-tolerated; progressive AR may eventually require aortic valve repair/replacement years later

• Right bundle branch block (RBBB): Very common after VSD repair (up to 30–50% of patients) due to the surgical approach through the RV or septum. Usually benign and haemodynamically insignificant.
• Late ventricular arrhythmias: Scar tissue from the patch or ventriculotomy (if used) can serve as a substrate for re-entrant ventricular tachycardia years later
• Atrial arrhythmias: Atrial manipulation during surgery → scar-mediated atrial flutter/fibrillation

• Risk during the first 6 months after repair: The prosthetic patch material has not yet fully endothelialised → foreign body serves as nidus for infection
• Risk with residual VSD: If there is a residual leak adjacent to the patch, turbulent flow + foreign material = significant IE risk
• After complete closure with no residual defect: IE risk drops to essentially population baseline after 6 months (once full endothelialisation)
• IE prophylaxis is recommended for the first 6 months post-repair, and indefinitely if residual defect is present