58 PAEDIATRIC CARDIAC SURGERY
PAEDIATRIC CARDIAC SURGERY
Congenital heart disease (CHD) affects roughly 8 in 1,000 live births and is the commonest group of birth defects. For MRCS Part A you are not expected to operate on these children, but you are expected to know the embryology, recognise the classic lesions, understand the shunt physiology, and link each syndrome to its associated defect.
The single most useful framework is this: acyanotic = left-to-right shunt (blood recirculates through the lungs, baby is pink but breathless), cyanotic = right-to-left shunt (deoxygenated blood bypasses the lungs and reaches the systemic circulation). Almost every exam question hangs off that distinction.
Fetal circulation — the three shunts
In utero the lungs are collapsed, fluid-filled and high-resistance. Oxygen comes from the placenta, not the alveoli. The fetal circulation therefore exists to deliver placental blood to the systemic circulation while bypassing the lungs. Three shunts make this possible.
➡ Ductus venosus — shunts oxygenated blood from the umbilical vein directly into the IVC, bypassing the hepatic sinusoids.
➡ Foramen ovale — a flap valve in the interatrial septum. Blood entering the right atrium is preferentially streamed across into the left atrium, bypassing the right ventricle and pulmonary circulation.
➡ Ductus arteriosus — connects the pulmonary trunk to the descending aorta. Blood that does enter the right ventricle and pulmonary artery is shunted away from the high-resistance fetal lungs and into the systemic circulation.
The flow path you must be able to recite: placenta → umbilical vein → ductus venosus → IVC → right atrium → foramen ovale → left atrium → left ventricle → aorta → fetal tissues → umbilical arteries → placenta. A smaller stream goes RA → RV → pulmonary artery → ductus arteriosus → descending aorta.
At birth the first breath drops pulmonary vascular resistance, the placenta is removed and systemic vascular resistance rises. Left atrial pressure now exceeds right and the foramen ovale slams shut. Rising arterial oxygen tension and falling prostaglandins close the ductus arteriosus within 24–72 hours.
──────────────────────────────
Adult remnants of fetal structures
A favourite SBA stem: "this ligament is the remnant of…". Memorise the table.
| Fetal structure | Adult remnant |
|---|---|
| Umbilical vein | Ligamentum teres (in the falciform ligament) |
| Ductus venosus | Ligamentum venosum |
| Foramen ovale | Fossa ovalis |
| Ductus arteriosus | Ligamentum arteriosum |
| Umbilical arteries (distal) | Medial umbilical ligaments |
| Urachus (allantois) | Median umbilical ligament |
👩⚕️ Easy trap: the median umbilical ligament is a midline urachal remnant; the medial ligaments are the paired umbilical artery remnants. Singular vs paired, urinary vs vascular.
Classification of congenital heart disease
| Acyanotic (L→R shunt) | Cyanotic (R→L shunt) | |
|---|---|---|
| Physiology | Recirculation through lungs; pulmonary overcirculation | Deoxygenated blood bypasses lungs |
| Presentation | Breathlessness, failure to thrive, recurrent chest infections | Central cyanosis, clubbing, hypoxic spells |
| Examples | VSD, ASD, PDA, AS, PS, coarctation | Tetralogy of Fallot, TGA, truncus arteriosus, TAPVR, tricuspid atresia |
Acyanotic lesions
Ventricular septal defect (VSD) is the commonest congenital cardiac defect, accounting for ~30% of all CHD. A small VSD produces a loud pansystolic murmur at the lower left sternal edge — paradoxically, the smaller the hole, the louder the murmur. Many close spontaneously.
Atrial septal defect (ASD) — ostium secundum is by far the commonest type. Ostium primum ASDs are part of the atrioventricular septal defect spectrum and are strongly associated with Down's syndrome. Classic sign: fixed splitting of the second heart sound.
Patent ductus arteriosus (PDA) — failure of the ductus to close. Produces a continuous "machinery" murmur at the left upper sternal edge, with a wide pulse pressure and bounding pulses. Pharmacology is high-yield:
➡ Indomethacin (a prostaglandin synthesis inhibitor) closes a PDA — used in preterm infants with a haemodynamically significant duct.
➡ Prostaglandin E1 (alprostadil) keeps the duct open — life-saving in duct-dependent lesions such as transposition of the great arteries, critical coarctation and pulmonary atresia, where systemic or pulmonary flow depends on ductal patency.
Coarctation of the aorta — narrowing typically just distal to the left subclavian artery, opposite the ligamentum arteriosum. Classic signs: radio-femoral delay, upper-limb hypertension, weak femoral pulses, and rib notching on CXR from collateral intercostal arteries. Strong association with Turner's syndrome and bicuspid aortic valve.
Cyanotic lesions — the "5 Ts"
| Defect | |
|---|---|
| Tetralogy of Fallot | Commonest cyanotic CHD |
| Transposition of the great arteries | Commonest cyanotic lesion presenting in the first day of life |
| Truncus arteriosus | Single great vessel |
| Total anomalous pulmonary venous return | Pulmonary veins drain into systemic venous system |
| Tricuspid atresia | No tricuspid valve; obligatory ASD/VSD |
Tetralogy of Fallot is the commonest cyanotic CHD overall (~10% of CHD). The four components — remember PROVe:
➡ Pulmonary stenosis (the degree of which determines severity)
➡ Right ventricular hypertrophy
➡ Overriding aorta
➡ VSD
The pulmonary stenosis raises right ventricular pressure above left, driving a right-to-left shunt across the VSD. Children get "tet spells" — episodes of severe cyanosis on crying or feeding, classically relieved by squatting, which increases systemic vascular resistance and reduces the right-to-left shunt. CXR shows a boot-shaped heart (coeur en sabot) from RVH and a concave pulmonary bay.
Transposition of the great arteries (TGA) — the aorta arises from the right ventricle and the pulmonary artery from the left ventricle. The result is two parallel circulations that do not mix; survival depends on a duct, ASD or VSD allowing mixing. Prostaglandin E1 is started immediately to maintain ductal patency until surgical correction (arterial switch). CXR shows the classic "egg on a string" appearance from a narrow mediastinum.
Eisenmenger syndrome
A long-standing untreated left-to-right shunt (VSD, ASD or PDA) drives chronic pulmonary overcirculation. Pulmonary vascular resistance progressively rises until it exceeds systemic — at which point the shunt reverses to right-to-left and the previously acyanotic child becomes cyanotic. This is Eisenmenger syndrome, and once established it is irreversible — the only definitive treatment is heart-lung transplantation. The lesson: close significant left-to-right shunts before pulmonary hypertension becomes fixed.
👩⚕️ In a PDA with established Eisenmenger physiology you get differential cyanosis — deoxygenated blood from the pulmonary artery enters the descending aorta distal to the left subclavian, so the lower limbs and left arm are cyanosed and clubbed but the right arm and head are pink.
Syndromic associations
| Syndrome | Cardiac defect | Mnemonic |
|---|---|---|
| Down's (trisomy 21) | AVSD / ostium primum ASD, VSD | "Down's = endocardial cushion" |
| Turner's (45,XO) | Coarctation, bicuspid aortic valve | Webbed neck, weak femorals |
| William's | Supravalvular aortic stenosis | "Elfin face, loves music" |
| DiGeorge (22q11 deletion) | Truncus arteriosus, TOF, interrupted aortic arch | CATCH-22 |
| Marfan | Aortic root dilatation, dissection, MV prolapse | Tall, arachnodactyly |
| Noonan | Pulmonary stenosis, HOCM | "Male Turner" phenotype |
Examination and investigation
➡ Radio-femoral delay → coarctation of the aorta.
➡ Differential cyanosis (pink upper, blue lower) → PDA with Eisenmenger reversal.
➡ Reverse differential cyanosis (blue upper, pink lower) → TGA with PDA.
➡ Fixed split S2 → ASD.
➡ Continuous machinery murmur → PDA.
➡ Ejection systolic murmur with squatting relief → TOF.
Echocardiography is the first-line investigation for any suspected CHD — it defines anatomy, shunt direction and ventricular function. ECG shows chamber hypertrophy patterns. CXR provides the classic silhouettes: boot-shaped heart in TOF, egg-on-string in TGA, snowman / figure-of-8 in TAPVR, rib notching in coarctation.
Hyperoxia test — give 100% oxygen for 10 minutes and recheck arterial PaO₂. If PaO₂ fails to rise above ~15 kPa (~150 mmHg), the cyanosis is cardiac (right-to-left shunt that oxygen cannot bypass) rather than respiratory. This is the bedside test that separates a cyanotic CHD from neonatal pneumonia or RDS.
Test yourself
Which of the following is a component of tetralogy of Fallot?
- ((Patent foramen ovale::Not a component — TOF involves a VSD, not a PFO.))
- ((Transposition of the great vessels::A separate cyanotic lesion — TGA, not TOF.))
- ((Overriding aorta::☑️ One of the four components (PROVe: Pulmonary stenosis, RVH, Overriding aorta, VSD).))
- ((Left ventricular hypertrophy::TOF causes right ventricular hypertrophy from outflow obstruction.))
- ((Atrial septal defect::TOF includes a VSD, not an ASD.))
👩⚕️ Remember PROVe: Pulmonary stenosis, RVH, Overriding aorta, VSD.
A neonate is centrally cyanosed within hours of birth. Which is the most likely diagnosis?
- ((VSD::Acyanotic L→R shunt; presents later with failure to thrive, not day-1 cyanosis.))
- ((ASD::Acyanotic; often asymptomatic in infancy.))
- ((PDA::Acyanotic machinery murmur; cyanosis only if Eisenmenger develops.))
- ((Transposition of the great arteries::☑️ Commonest cyanotic lesion presenting on day 1 — parallel circulations, duct-dependent.))
- ((Mitral regurgitation::Not a typical cause of neonatal central cyanosis.))
👩⚕️ Day-1 cyanosis in an otherwise well term baby = TGA until proven otherwise. Start prostaglandin E1.
A child has a continuous "machinery" murmur at the left upper sternal edge. Which best describes the haemodynamics?
- ((Left-to-right shunt from aorta to pulmonary artery::☑️ Classic PDA — aortic pressure exceeds pulmonary throughout the cycle, hence continuous murmur.))
- ((Right-to-left shunt across a VSD::That is TOF physiology, not PDA.))
- ((Bidirectional shunt across an ASD::ASD gives a fixed split S2, not a machinery murmur.))
- ((Obstruction at the aortic valve::Aortic stenosis gives an ejection systolic murmur, not continuous.))
- ((Obstruction of the pulmonary valve::Pulmonary stenosis is ejection systolic at the upper left sternal edge.))
👩⚕️ Indomethacin closes a PDA; prostaglandin E1 keeps it open in duct-dependent lesions.
A neonate with cyanosis is found to have transposition of the great arteries. Which drug is given to maintain duct patency?
- ((Indomethacin::Closes the duct — the opposite of what you want here.))
- ((Ibuprofen::Like indomethacin, a prostaglandin inhibitor that closes the duct.))
- ((Prostaglandin E1 (alprostadil)::☑️ Maintains ductal patency, allowing mixing of parallel circulations until surgery.))
- ((Adenosine::Used for SVT, not duct patency.))
- ((Furosemide::Diuretic for pulmonary overcirculation, no effect on the duct.))
Which ASD is most strongly associated with Down's syndrome?
- ((Ostium primum / AVSD::☑️ Endocardial cushion defects are the classic Down's association.))
- ((Ostium secundum::Commonest ASD overall but not specifically linked to Down's.))
- ((Sinus venosus::Rare; associated with anomalous pulmonary venous drainage.))
- ((Coronary sinus::Rare ASD variant, no Down's link.))
- ((Patent foramen ovale::Not a true ASD — normal anatomical variant in ~25% of adults.))
A newborn has weak femoral pulses and radio-femoral delay. Which syndromic association is most likely?
- ((Down's syndrome::Associated with AVSD, not coarctation.))
- ((Turner's syndrome::☑️ Coarctation and bicuspid aortic valve are classic Turner's features.))
- ((William's syndrome::Supravalvular aortic stenosis, not coarctation.))
- ((DiGeorge syndrome::Truncus arteriosus, TOF, interrupted aortic arch.))
- ((Marfan syndrome::Aortic root dilatation and dissection, not coarctation.))
The ligamentum arteriosum is the adult remnant of which fetal structure?
- ((Umbilical vein::Becomes the ligamentum teres in the falciform ligament.))
- ((Ductus venosus::Becomes the ligamentum venosum.))
- ((Foramen ovale::Becomes the fossa ovalis.))
- ((Ductus arteriosus::☑️ Connects pulmonary trunk to descending aorta in utero; closes within 72 hours of birth.))
- ((Umbilical arteries::Become the medial umbilical ligaments.))
👩⚕️ The left recurrent laryngeal nerve hooks under the ligamentum arteriosum — relevant to aortic arch surgery and hoarseness from a left hilar tumour.
A teenager with a long-standing untreated VSD now has central cyanosis and clubbing. What has happened?
- ((Spontaneous closure of the VSD::Would resolve symptoms, not cause new cyanosis.))
- ((Development of tetralogy of Fallot::TOF is congenital, not acquired.))
- ((Eisenmenger syndrome::☑️ Chronic L→R shunt raises pulmonary vascular resistance until the shunt reverses to R→L.))
- ((Infective endocarditis::Causes fever and embolic phenomena, not chronic cyanosis.))
- ((Rheumatic fever::Causes valvular disease, not shunt reversal.))
👩⚕️ Once Eisenmenger is established, the defect can no longer be safely closed — only heart-lung transplantation helps.
Which is the first-line investigation for suspected congenital heart disease?
- ((Chest X-ray::Useful adjunct (boot-shape, egg-on-string) but not diagnostic.))
- ((ECG::Shows chamber hypertrophy but does not define anatomy.))
- ((Echocardiogram::☑️ Defines anatomy, shunt direction and ventricular function non-invasively.))
- ((Cardiac MRI::Reserved for complex anatomy after echo.))
- ((Cardiac catheterisation::Invasive; used for haemodynamic assessment or intervention, not screening.))
Revision summary
➡ Fetal shunts: ductus venosus, foramen ovale, ductus arteriosus — all bypass the high-resistance fetal lungs.
➡ Adult remnants: DV → ligamentum venosum; FO → fossa ovalis; DA → ligamentum arteriosum; umbilical vein → ligamentum teres; umbilical arteries → medial umbilical ligaments.
➡ Acyanotic = L→R shunt: VSD (commonest CHD overall), ASD (secundum commonest; primum = Down's), PDA (machinery murmur), coarctation (Turner's, radio-femoral delay).
➡ Cyanotic = R→L shunt — the 5 Ts: TOF (commonest cyanotic), TGA (day-1 cyanosis), truncus, TAPVR, tricuspid atresia.
➡ TOF = PROVe: Pulmonary stenosis, RVH, Overriding aorta, VSD. Boot-shaped heart. Tet spells relieved by squatting.
➡ TGA: egg-on-string CXR; start prostaglandin E1 to keep duct open.
➡ PDA: indomethacin closes, prostaglandin keeps open.
➡ Eisenmenger: chronic L→R shunt reverses when pulmonary vascular resistance exceeds systemic — close shunts early.
➡ Syndromes: Down's = AVSD; Turner's = coarctation; William's = supravalvular AS; DiGeorge (22q11) = truncus / TOF / interrupted arch.
➡ First-line investigation: echocardiogram. Hyperoxia test distinguishes cardiac from respiratory cyanosis.