Cyanotic Congenital Heart Disease

Cyanotic congenital heart disease (CCHD) is a group of structural cardiac defects in which deoxygenated systemic venous blood reaches the systemic circulation, producing central cyanosis from birth or early infancy. For NEET PG, the high-yield skill is pattern recognition: chest X-ray silhouette, age at presentation, and the "5 Ts" mnemonic — then linking each lesion to its classic management.

Definition and the "5 Ts" Classification

Central cyanosis appears when deoxygenated haemoglobin exceeds 5 g/dL in capillary blood (an absolute value, hence anaemic infants may not look cyanosed despite severe hypoxaemia, while polycythaemic infants cyanose early). CCHD implies a right-to-left shunt or complete mixing of pulmonary and systemic blood.

The classic teaching mnemonic for the cyanotic lesions is the "5 Ts" + a 3 (number of the T corresponds roughly to a numerical clue):

• 1 vessel → Truncus Arteriosus (single arterial trunk)
• 2 vessels transposed → TGA (Transposition of Great Arteries)
• 3 leaflets / Tricuspid → Tricuspid Atresia
• 4 features → Tetralogy of Fallot
• 5 words → TAPVC (Total Anomalous Pulmonary Venous Connection)

Add Ebstein anomaly and Hypoplastic Left Heart Syndrome (HLHS) to complete the commonly-tested list.

High-yield: Cyanosis = >5 g/dL of reduced haemoglobin. It is the absolute amount, not the percentage saturation, that determines visible cyanosis — the single most repeated one-liner from this topic.

A more useful exam classification divides CCHD by pulmonary blood flow, because the chest X-ray reflects this directly:

Pulmonary blood flow	Lesions	CXR lung fields
Decreased	Tetralogy of Fallot, Tricuspid atresia, Pulmonary atresia, Ebstein, severe Ebstein	Oligaemic / dark lungs
Increased	TGA, Truncus, TAPVC, Single ventricle, HLHS	Plethoric lungs

Tetralogy of Fallot (TOF)

TOF is the commonest cyanotic CHD beyond infancy (and overall the commonest cyanotic lesion presenting after the neonatal period). It results from anterocephalad deviation of the infundibular (conal) septum.

The four components (mnemonic PROVe):

1. Pulmonary stenosis (infundibular — the determinant of severity)
2. Right ventricular hypertrophy
3. Overriding aorta
4. VSD (large, non-restrictive, malalignment)

The degree of cyanosis depends on the right ventricular outflow tract (RVOT) obstruction, not the VSD. Severe obstruction → more right-to-left shunt → deeper cyanosis ("pink tet" if mild).

Clinical features

• Cyanosis (often after the neonatal period as PVR falls / infundibular spasm worsens)
• Squatting in older children — increases systemic vascular resistance (SVR), reducing right-to-left shunt and improving pulmonary flow
• Tet spells (hypercyanotic / paroxysmal hypoxic spells) — sudden deep cyanosis, agitation, then limpness; classically on waking/crying/feeding
• Clubbing, single S2 (P2 soft/absent), ejection systolic murmur at left upper sternal border (the murmur is from the PS, not the VSD)

High-yield: During a tet spell the murmur becomes softer or disappears — because flow across the obstructed RVOT falls. A louder murmur during a "spell" argues against TOF.

Investigations and imaging

• CXR: "Boot-shaped heart" (coeur en sabot) — uplifted apex (RVH) + concave pulmonary bay (small main pulmonary artery), oligaemic lung fields. ~25% have a right-sided aortic arch.
• ECG: Right axis deviation + RVH.
• Echocardiography is the investigation of choice — confirms anatomy, VSD, overriding aorta, RVOT gradient.

Management of a tet spell — stepwise

The acute approach is a NEET favourite. Flow:

Knee–chest position → 100% oxygen → Morphine (0.1–0.2 mg/kg SC/IM/IV) → IV fluids (bolus) → Sodium bicarbonate (for acidosis) → if refractory β-blocker (propranolol/esmolol) → Phenylephrine (α-agonist to raise SVR) → Ketamine (raises SVR + sedates).

Mechanism logic to remember:

• Knee–chest / squatting → ↑ SVR + ↓ venous return of desaturated blood → ↑ pulmonary flow
• Morphine → abolishes hyperpnoea and calms the infant, relaxes infundibular spasm
• Propranolol → relieves infundibular spasm (also used as oral prophylaxis between spells)
• Phenylephrine / ketamine → ↑ SVR
• AVOID agents that drop SVR (e.g. digoxin/inotropes that worsen infundibular contraction are contraindicated; do NOT give vasodilators)

Manoeuvre / drug	Action	Why it helps
Knee–chest	↑ SVR, ↓ venous return	Pushes shunt left→right
Oxygen	Pulmonary vasodilation	↑ oxygenation
Morphine	Sedation, ↓ hyperpnoea	Breaks the spell cycle
Propranolol	↓ infundibular spasm, ↓ HR	Relieves dynamic RVOT obstruction
Phenylephrine	α-agonist, ↑ SVR	↓ right-to-left shunt
Sodium bicarbonate	Corrects acidosis	↓ pulmonary vasoconstriction

High-yield: Knee–chest position + morphine is the first-line answer for an acute tet spell. Propranolol is the agent for prevention of spells while awaiting surgery.

Definitive treatment: complete intracardiac repair (VSD closure + RVOT relief), ideally in infancy. Palliation when too small/anatomy unfavourable: Modified Blalock–Taussig–Thomas shunt (subclavian-to-pulmonary artery via Gore-Tex graft) to augment pulmonary flow.

Transposition of the Great Arteries (TGA)

In d-TGA the aorta arises from the RV and the pulmonary artery from the LV (ventriculo-arterial discordance) — two parallel circulations. Survival depends on mixing through a PDA, PFO/ASD or VSD.

• Commonest cyanotic CHD presenting in the immediate newborn period and the commonest cause of cyanosis on day 1 of life.
• Associated with infants of diabetic mothers.
• Profound cyanosis unresponsive to oxygen, single loud S2, often minimal murmur.

High-yield: TGA = cyanosis in the first 24 hours of life. TOF more often presents later (toddler), because in TOF cyanosis depends on progressive infundibular obstruction.

Imaging

• CXR: "Egg-on-side / egg-on-a-string" appearance — narrow superior mediastinum (great vessels lie antero-posteriorly) + cardiomegaly + increased pulmonary vascularity.

Management — stepwise

Start prostaglandin E1 (alprostadil) infusion to keep the ductus open → Balloon atrial septostomy (Rashkind procedure) to improve mixing → definitive: Arterial Switch Operation (Jatene), ideally within first 2 weeks while the LV can still handle systemic pressures.

High-yield: In any duct-dependent cyanotic neonate (TGA, pulmonary atresia, severe TOF, HLHS), PGE1 keeps the duct patent and is life-saving — a recurring single-best-answer.

Truncus Arteriosus

A single arterial trunk overrides a large VSD and gives rise to the aorta, pulmonary and coronary arteries. Complete mixing → mild cyanosis + features of heart failure as pulmonary flow rises.

• Strongly associated with DiGeorge syndrome (22q11 deletion) — think hypocalcaemia, absent thymus.
• Bounding pulses (diastolic run-off), single S2, often a truncal valve click.
• Increased pulmonary vascularity on CXR.

Total Anomalous Pulmonary Venous Connection (TAPVC)

All four pulmonary veins drain into the systemic venous circulation instead of the left atrium; survival needs an obligatory ASD/PFO.

Type	Drainage site	Note
Supracardiac (I)	Left vertical vein → innominate → SVC	Commonest; "Snowman / figure-of-8" CXR
Cardiac (II)	Coronary sinus / right atrium	—
Infracardiac (III)	Portal vein / IVC below diaphragm	Almost always obstructed, presents early with severe cyanosis + pulmonary oedema
Mixed (IV)	Combination	Rare

High-yield: Obstructed (infracardiac) TAPVC is a true neonatal surgical emergency — severe cyanosis + respiratory distress + pulmonary venous congestion, and PGE1 may worsen it. The "snowman / figure-of-8" sign belongs to the supracardiac type.

Tricuspid Atresia

Absent tricuspid valve → hypoplastic RV; blood must cross an ASD (obligatory) then a VSD/PDA to reach the lungs.

• Only cyanotic CHD with left axis deviation + LVH on ECG (because the LV does all the work) — a near-guaranteed exam point.
• Decreased pulmonary flow; treated along the single-ventricle palliation pathway (BT shunt → Glenn → Fontan).

High-yield: Tricuspid atresia = cyanotic CHD with LEFT axis deviation. Contrast with TOF (right axis deviation).

Ebstein Anomaly

Apical (downward) displacement of the septal/posterior tricuspid leaflets → "atrialised" RV, tricuspid regurgitation, right-to-left shunt via ASD.

• Associated with maternal lithium use.
• Massive cardiomegaly ("wall-to-wall heart", box-shaped) on CXR; associated WPW syndrome / SVT.

Hypoplastic Left Heart Syndrome (HLHS)

Underdevelopment of the LV, mitral/aortic valves and ascending aorta — systemic circulation is duct-dependent. Presents with shock/collapse as the duct closes.

• PGE1 is life-saving initially.
• Staged palliation: Norwood → Glenn → Fontan, or transplant.

Central vs Peripheral Cyanosis & Causes of Central Cyanosis

Feature	Central cyanosis	Peripheral (acrocyanosis)
Site	Tongue, lips, mucosae + extremities	Extremities only; tongue pink
Cause	↓ SaO₂ (cardiac/pulmonary), abnormal Hb	↓ peripheral flow (cold, shock, sluggish circulation)
Warming	No change	Improves
O₂ administration	Cardiac → little change	N/A

Causes of central cyanosis to exclude in a "blue baby":

• Cardiac: the CCHD lesions above
• Respiratory: RDS, meconium aspiration, pneumonia, persistent pulmonary hypertension of newborn (PPHN), pneumothorax
• Haematological: methaemoglobinaemia (chocolate-brown blood, normal PaO₂, low SpO₂, treat with methylene blue), sulfhaemoglobinaemia
• CNS / sepsis: hypoventilation

The Hyperoxia Test (Nitrogen Washout Test)

The bedside method to separate cardiac from respiratory cyanosis. Give 100% oxygen for ~10 minutes and re-measure PaO₂ from a right radial (preductal) arterial sample.

Result (PaO₂ in 100% O₂)	Interpretation
PaO₂ rises > 250 mmHg	Lung disease likely (responds to O₂)
PaO₂ < 100 mmHg (often stays 35–50)	Cyanotic cardiac disease — fixed right-to-left shunt, fails to respond
PaO₂ 100–250 mmHg	Indeterminate (PPHN, mixing lesions)

High-yield: In CCHD the hyperoxia test shows failure of PaO₂ to rise above ~150–250 mmHg despite 100% oxygen, because shunted blood bypasses the alveoli. Methaemoglobinaemia also fails to improve SpO₂ but PaO₂ is normal — a classic discriminator.

Investigation of Choice & Drug/Procedure of Choice — quick map

• Best initial screen in newborn nursery: pulse oximetry screening (pre- and post-ductal; difference >3% or sat <95% is positive).
• Investigation of choice for anatomy: 2D echocardiography with Doppler.
• Gold standard / pre-surgical haemodynamics: cardiac catheterisation (now selective).
• Duct-dependent lesion holding drug: Prostaglandin E1 (alprostadil) — watch for apnoea, fever, hypotension.
• Tet spell first step: knee–chest position.

Complications of CCHD

• Hypoxic spells and syncope (TOF)
• Polycythaemia → hyperviscosity, cerebral venous sinus thrombosis and stroke (especially with iron-deficiency micro­cytosis paradoxically increasing risk)
• Brain abscess (right-to-left shunt bypasses pulmonary filter; right-to-left shunt + age >2 yr) — classically TOF
• Infective endocarditis
• Cerebral abscess and paradoxical emboli
• Eisenmenger syndrome (if initially acyanotic L→R shunt reverses) — late, with established pulmonary vascular disease
• Growth failure, clubbing, hyperuricaemia/gout

High-yield: Brain abscess and cerebral thromboembolic stroke are the classic CNS complications of cyanotic CHD (especially TOF). Iron-deficient microcytic polycythaemic children are at highest stroke risk — correct the iron, do not just hydrate.

Key Differentials — How to Tell Them Apart

By CXR silhouette (high-yield single-liners):

• Boot-shaped → TOF
• Egg-on-side / egg-on-a-string → TGA
• Snowman / figure-of-8 → supracardiac TAPVC
• Box-shaped / wall-to-wall → Ebstein
• "Scimitar" sign → partial APVC (Scimitar syndrome) — acyanotic, but loved as a distractor

By ECG axis:

• Right axis + RVH → TOF
• Left axis + LVH → Tricuspid atresia
• Superior axis → also seen in AV canal defects (acyanotic distractor)

By age of cyanosis onset:

• Day 1 → TGA
• First weeks, ductal closure shock → HLHS, severe LVOT/coarctation
• After neonatal period / toddler → TOF

Recently asked / exam angle

• Tet spell management — the single most repeated stem: "infant with TOF turns blue while crying, next step?" → knee–chest position (first), then oxygen and morphine; propranolol for prevention.
• CXR sign matching — boot-shaped (TOF), egg-on-side (TGA), snowman (TAPVC). Direct image-based MCQs.
• Most common cyanotic CHD overall / after infancy = TOF; most common presenting at birth = TGA.
• PGE1 for duct-dependent lesions and its side-effect apnoea.
• Hyperoxia test interpretation — cardiac vs pulmonary cyanosis.
• Tricuspid atresia = LAD + LVH on ECG — frequently tested ECG discriminator.
• TGA association with infant of diabetic mother; Truncus with DiGeorge (22q11); Ebstein with lithium.
• Brain abscess as a complication of right-to-left shunt.
• Determinant of cyanosis severity in TOF = degree of pulmonary/infundibular stenosis, not VSD size.
• Murmur in TOF softens during a spell.

Rapid revision

1. Cyanosis becomes visible when reduced haemoglobin >5 g/dL (absolute value).
2. TOF = commonest cyanotic CHD beyond infancy; four features = PS + RVH + overriding aorta + VSD; boot-shaped heart.
3. Severity of cyanosis in TOF depends on infundibular pulmonary stenosis; murmur softens during a tet spell.
4. Tet spell: knee–chest → O₂ → morphine → fluids → bicarbonate → β-blocker → phenylephrine/ketamine. Propranolol prevents spells.
5. TGA = commonest cyanotic CHD at birth / day 1; egg-on-side CXR; association with diabetic mother.
6. PGE1 (alprostadil) keeps the duct open in duct-dependent lesions — side effect apnoea; balloon atrial septostomy (Rashkind) then arterial switch (Jatene) for TGA.
7. Truncus arteriosus → single arterial trunk, linked to DiGeorge / 22q11.
8. TAPVC: supracardiac = snowman/figure-of-8; infracardiac is obstructed and a surgical emergency.
9. Tricuspid atresia = the cyanotic lesion with left axis deviation + LVH.
10. Ebstein = downward-displaced tricuspid leaflets, lithium, WPW, box-shaped heart.
11. Hyperoxia test: PaO₂ fails to rise (<150–250 mmHg) in cardiac cyanosis; rises markedly in lung disease; normal PaO₂ with low SpO₂ → methaemoglobinaemia (treat with methylene blue).
12. Cyanotic CHD complications: brain abscess, paradoxical embolism/stroke, polycythaemia, infective endocarditis, Eisenmenger; echocardiography is the investigation of choice.