Acyanotic Congenital Heart Disease

Acyanotic congenital heart disease (CHD) comprises lesions in which there is no right-to-left shunt at rest, so deoxygenated blood does not bypass the lungs and the child is pink. The hallmark is either a left-to-right (L→R) shunt (VSD, ASD, PDA, AVSD) or an obstructive lesion (pulmonary/aortic stenosis, coarctation). This is a recurring NEET PG zone — examiners love the murmur character, ECG axis, chest X-ray clue, and the indomethacin-vs-prostaglandin trap.

Classification

Congenital heart disease is first split by the presence or absence of cyanosis. Acyanotic lesions are then divided by haemodynamics.

Group	Mechanism	Lesions
L→R shunt (volume overload)	Oxygenated blood recirculates to lungs	VSD, ASD, PDA, AVSD, aortopulmonary window
Obstructive (pressure overload)	Outflow obstruction, no shunt	Pulmonary stenosis (PS), aortic stenosis (AS), coarctation of aorta

High-yield: VSD is the commonest CHD overall (≈ 30–40% of all CHD). Bicuspid aortic valve is the commonest congenital cardiac malformation if you count it as a structural anomaly, but for "commonest CHD" in exams the answer is VSD. The commonest cyanotic CHD is Tetralogy of Fallot (do not confuse).

The level of the shunt determines which chambers dilate, which in turn determines the ECG and X-ray:

• Pre-tricuspid shunt (ASD) → right atrial + right ventricular volume overload.
• Post-tricuspid shunt (VSD, PDA) → left atrial + left ventricular volume overload (LV handles the recirculated volume).

Ventricular septal defect (VSD)

The commonest CHD. Classified by location:

• Perimembranous (membranous) — commonest type (~80%), near the membranous septum/AV node.
• Muscular (trabecular) — often multiple ("Swiss-cheese"), frequently close spontaneously.
• Outlet/supracristal (subarterial, doubly committed) — risk of aortic cusp prolapse → aortic regurgitation.
• Inlet (AV-canal type) — associated with Down syndrome.

Clinical features depend on size:

• Small VSD — loud, harsh pansystolic murmur at the left lower sternal border (3rd–4th LICS), often a thrill; paradoxically the smaller the defect the louder the murmur (maladie de Roger). Asymptomatic, normal growth.
• Large VSD — presents at 6–8 weeks as pulmonary vascular resistance falls: tachypnoea, feeding difficulty, sweating, failure to thrive, recurrent chest infections, hepatomegaly. A mid-diastolic rumble at the apex indicates a large shunt (relative mitral stenosis, Qp:Qs > 2:1).

Investigations:

• ECG — biventricular hypertrophy (large VSD); LVH with small/moderate.
• CXR — cardiomegaly, increased pulmonary vascularity, prominent pulmonary artery.
• Echocardiography is the investigation of choice — confirms size, location, shunt direction, and gradient.

High-yield: Most small muscular and perimembranous VSDs close spontaneously, often within the first 1–2 years. Spontaneous closure is least likely in outlet/supracristal and inlet defects.

Management flow: Small VSD → observe + endocarditis hygiene → most close spontaneously. Large VSD → anti-failure therapy (diuretics + ACE inhibitor ± digoxin) + high-calorie feeds → surgical closure if CHF/failure to thrive/pulmonary hypertension persists (typically 3–6 months).

Atrial septal defect (ASD)

A pre-tricuspid L→R shunt. Often silent in childhood and may present in adulthood.

Type	Location	Key associations
Ostium secundum	Mid-septum (fossa ovalis)	Commonest ASD (~70%); right axis deviation + RBBB; isolated
Ostium primum	Lower septum (AV-canal defect)	Left axis deviation; cleft mitral valve → MR; Down syndrome
Sinus venosus	Near SVC/IVC entry	Anomalous pulmonary venous drainage (PAPVC)
Coronary sinus	Unroofed coronary sinus	Rare; persistent left SVC

Clinical hallmark: a wide, fixed split S2 (the split does not vary with respiration because the RV volume is constant across the cycle). There is an ejection systolic murmur at the pulmonary area (increased flow across a normal pulmonary valve, not the ASD itself) and, with large shunts, a tricuspid mid-diastolic flow murmur at the lower left sternal border.

ECG is a classic discriminator:

• Ostium secundum → right axis deviation + incomplete RBBB (rSR′ in V1).
• Ostium primum → left axis deviation (superior axis) + RBBB ± first-degree AV block.

High-yield: Fixed splitting of S2 = ASD until proven otherwise. Left-axis deviation in an ASD points to ostium primum (AV-canal defect, think Down syndrome with a cleft mitral valve).

CXR: cardiomegaly, dilated pulmonary artery, pulmonary plethora; aortic knuckle is small ("small aorta, big pulmonary artery").

Management: Secundum ASDs with significant shunt (RV volume overload, Qp:Qs ≥ 1.5–2:1) are closed, ideally by transcatheter device closure between 2–5 years; primum and sinus venosus defects require surgical repair. Spontaneous closure can occur in small secundum defects < 8 mm.

Patent ductus arteriosus (PDA)

The ductus arteriosus connects the pulmonary artery (just left of the bifurcation) to the descending aorta and normally closes functionally within 24–72 hours of birth and anatomically by 2–3 weeks. Persistence beyond this is a PDA. More common in preterm infants, females, and post-rubella babies, and at high altitude.

Clinical features:

• Continuous "machinery" murmur (Gibson murmur) maximal in the left infraclavicular region / 2nd LICS, peaking at S2.
• Wide pulse pressure → bounding (collapsing/water-hammer) pulses, low diastolic BP.
• Large PDA → CHF, failure to thrive, an apical mid-diastolic rumble.

High-yield: The murmur of PDA is continuous (systole + diastole) because the aortic pressure exceeds pulmonary pressure throughout the cycle. Contrast with the pansystolic murmur of VSD and the fixed split S2 of ASD.

Ductal physiology — the exam's favourite pharmacology pairing:

• Patency is maintained by prostaglandin E2 (PGE2).
• Closure is promoted by inhibiting prostaglandin synthesis with NSAIDs.

Goal	Drug	Clinical setting
Close the ductus	Indomethacin or ibuprofen (paracetamol is an emerging alternative)	Haemodynamically significant PDA in a preterm neonate
Keep open the ductus	Prostaglandin E1 (alprostadil) infusion	Duct-dependent lesions (e.g. TGA, pulmonary atresia, coarctation) until surgery

High-yield: In a preterm infant, a symptomatic PDA is closed medically with indomethacin or ibuprofen. In a term infant or beyond infancy, medical closure usually fails — definitive treatment is transcatheter coil/device occlusion (or surgical ligation). Never give indomethacin to close a duct that the circulation depends on.

Contraindications to indomethacin: active bleeding, necrotising enterocolitis, renal impairment, thrombocytopenia, significant hyperbilirubinaemia.

Atrioventricular septal defect (AVSD / AV canal)

A deficiency of the endocardial cushions producing a common AV junction. Complete AVSD = primum ASD + inlet VSD + a common AV valve.

• Strongly associated with Down syndrome (trisomy 21) — the commonest cardiac lesion in Down syndrome is AVSD/endocardial cushion defect (VSD is the next commonest).
• ECG: superior/left axis deviation with a counter-clockwise frontal loop — a near-pathognomonic clue.
• Presents early with large L→R shunt, CHF, and a high risk of early pulmonary vascular disease, hence early surgical repair (within the first 3–6 months) before irreversible pulmonary hypertension develops.

High-yield: Down syndrome + superior QRS axis on ECG = AVSD (endocardial cushion defect). These children develop Eisenmenger physiology faster than others, so repair is done early.

Pulmonary stenosis (PS)

An obstructive acyanotic lesion (no shunt unless an associated ASD/PFO allows R→L).

• Valvular PS is commonest; the valve is dome-shaped. Associated with Noonan syndrome (dysplastic valve) and Williams syndrome (supravalvular, along with supravalvular AS).
• Murmur: harsh ejection systolic murmur at the left 2nd ICS (pulmonary area), radiating to the back/axilla, with an ejection click (valvular) that decreases with inspiration — the only right-sided sound that softens on inspiration. Widely split S2 with a soft P2.
• ECG: right axis deviation, RVH; CXR: post-stenotic dilatation of the main pulmonary artery with normal/oligaemic lung fields.
• Management: Balloon pulmonary valvuloplasty is the treatment of choice for moderate–severe valvular PS (peak gradient > 40–50 mmHg).

Eisenmenger syndrome

The dreaded endpoint of an uncorrected large L→R shunt. Chronic high pulmonary blood flow → pulmonary arteriolar remodelling → irreversible pulmonary vascular obstructive disease → pulmonary pressure exceeds systemic → the shunt reverses to right-to-left → the previously pink ("acyanotic") child becomes cyanosed and clubbed.

Approach: Large VSD/PDA/ASD → ↑ pulmonary blood flow → pulmonary arteriolar hypertrophy & fibrosis → pulmonary vascular resistance rises → shunt reversal (R→L) → cyanosis + clubbing + erythrocytosis = Eisenmenger.

High-yield: Once Eisenmenger syndrome develops, the defect becomes inoperable — surgical closure removes the "pop-off" and causes acute RV failure. The only definitive option is heart–lung (or lung) transplantation. This is why large shunts are closed early, before fixed pulmonary hypertension sets in.

Clinically: differential cyanosis and clubbing (toes more than fingers) in a PDA-driven Eisenmenger, because the reversed deoxygenated blood enters the aorta distal to the left subclavian.

Murmur quick-reference

Lesion	Murmur	Best heard	S2
VSD	Pansystolic ± thrill	Left lower sternal border	Normal (loud P2 if PHT)
ASD	Ejection systolic (pulmonary flow)	Pulmonary area	Wide fixed split
PDA	Continuous "machinery"	Left infraclavicular	Buried in murmur
PS	Ejection systolic + click	Pulmonary area	Wide split, soft P2
AVSD	Systolic ± MR	LLSB/apex	Variable; superior axis on ECG

Diagnosis & investigation of choice

• Transthoracic echocardiography with colour Doppler is the single investigation of choice for all acyanotic CHD — it defines anatomy, shunt direction, chamber dilatation and gradients, and is non-invasive.
• ECG localises the volume/pressure load (axis is the clue: RAD in secundum ASD, LAD/superior axis in primum ASD and AVSD).
• Chest X-ray shows the grade of shunt (plethora, cardiomegaly) and pulmonary artery size.
• Cardiac catheterisation is reserved for quantifying pulmonary vascular resistance and reversibility testing (with oxygen/nitric oxide) when pulmonary hypertension is suspected and operability is in question.

Complications

• Infective endocarditis — risk with VSD, PDA, bicuspid valve, PS (high-velocity jet lesions). Endocarditis prophylaxis is now reserved for high-risk situations.
• Pulmonary arterial hypertension → Eisenmenger syndrome (large unrepaired shunts).
• Congestive cardiac failure & failure to thrive in infancy (large shunts).
• Arrhythmias — atrial in ASD/AVSD; AV block risk near membranous VSD/AVSD surgery.
• Aortic regurgitation — outlet (supracristal) VSD due to cusp prolapse.
• Paradoxical embolism / stroke in ASD.

Key differentials

• Innocent (Still's) murmur vs small VSD — Still's is soft, vibratory/musical, mid-systolic, varies with posture, with a normal ECG/CXR; VSD is harsh and pansystolic.
• VSD vs MR — both pansystolic; MR radiates to axilla, VSD to right sternal border.
• PDA (continuous murmur) vs venous hum (disappears on lying down/compressing neck), AP window, ruptured sinus of Valsalva.
• ASD vs PS — both give a pulmonary ejection murmur; the fixed split S2 points to ASD, the click softening on inspiration points to PS.
• Acyanotic with later cyanosis — always think Eisenmenger physiology.

Recently asked / exam angle

• "Wide fixed split S2" in a stem → ASD; if left axis deviation is added → ostium primum; if right axis + RBBB → ostium secundum.
• "Continuous machinery murmur + wide pulse pressure + bounding pulses" → PDA; the drug to close it in a preterm is indomethacin/ibuprofen, and PGE1 keeps it open in duct-dependent lesions.
• "Down syndrome + superior/left axis on ECG" → AVSD (endocardial cushion defect).
• Commonest CHD → VSD; commonest ASD → ostium secundum; commonest cyanotic CHD → TOF (distractor).
• Maladie de Roger = small VSD with a loud murmur; smaller defect, louder sound.
• Post-stenotic dilatation of pulmonary artery on CXR → valvular pulmonary stenosis; treatment balloon valvuloplasty.
• Acyanotic CHD turning cyanotic with clubbing → Eisenmenger syndrome, now inoperable (needs heart–lung transplant).
• Differential cyanosis (lower limbs > upper limbs) → Eisenmenger via PDA / interrupted aortic arch.

Rapid revision

1. VSD = commonest CHD; perimembranous is the commonest VSD type; most small/muscular VSDs close spontaneously.
2. VSD murmur = harsh pansystolic at LLSB; an apical diastolic rumble means a large shunt (Qp:Qs > 2:1).
3. ASD = wide FIXED split S2; murmur is pulmonary flow, not the defect itself.
4. Ostium secundum → right axis + RBBB; ostium primum → left axis + cleft MV (Down syndrome).
5. PDA = continuous machinery murmur + bounding pulses + wide pulse pressure.
6. Preterm symptomatic PDA → close with indomethacin/ibuprofen; term/older → device or surgical closure.
7. Duct-dependent lesions → keep duct open with PGE1 (alprostadil) until surgery.
8. Down syndrome → AVSD (endocardial cushion defect); ECG shows superior axis; repair early.
9. Pulmonary stenosis → ejection click softening on inspiration + post-stenotic PA dilatation; balloon valvuloplasty is treatment of choice.
10. Eisenmenger = shunt reversal to R→L → cyanosis + clubbing; defect becomes inoperable, transplant only.
11. Echocardiography with Doppler = investigation of choice for every acyanotic lesion.
12. Pre-tricuspid shunt (ASD) overloads the right heart; post-tricuspid shunts (VSD, PDA) overload the left heart.