Pediatric Congenital Heart Disease
A high-yield USMLE lesson on pediatric congenital heart disease built around the acyanotic-vs-cyanotic framework, classic buzzwords, syndrome associations, and next-best-step decisions (hyperoxia test, PGE1, echo). Includes the 5 T's and PROVe mnemonics, TGA and tet-spell vignettes, and comparison tables.
Framework: think acyanotic vs cyanotic first
Congenital heart disease (CHD) is the most common group of birth defects. Boards want you to sort every lesion into one bucket first:
- Acyanotic = left-to-right shunt (VSD, ASD, PDA) or an obstructive lesion (coarctation, aortic stenosis). Blood is still oxygenated, so problems come later — volume overload, CHF, failure to thrive, and eventual pulmonary hypertension.
- Cyanotic = right-to-left shunt delivering deoxygenated blood to the systemic circulation → cyanosis in the newborn that does not correct with oxygen.
Timing is the exam clue. Cyanosis in the first hours-to-days of life points to a ductal-dependent lesion or transposition. A left-to-right shunt murmur often surfaces at a few weeks of age, as pulmonary vascular resistance falls and shunt flow increases. The three testable decisions that recur: the hyperoxia test (distinguish cardiac from pulmonary cyanosis), starting prostaglandin E1 to keep the ductus arteriosus open, and confirming anatomy with echocardiography.
- VSD = most common CHD overall; harsh holosystolic murmur at the left lower sternal border; smaller defect = louder murmur; many close spontaneously
- Tetralogy of Fallot = most common cyanotic lesion overall (typically presents beyond the neonatal period)
- d-Transposition (d-TGA) = most common cyanotic lesion presenting at birth
- ASD = wide, fixed split S2; ostium secundum most common; risk of paradoxical embolism
- PDA = continuous "machinery" murmur; indomethacin/ibuprofen closes it, PGE1 keeps it open
- Coarctation = brachial-femoral pulse delay, upper-extremity hypertension, rib notching; think Turner syndrome
- Eisenmenger syndrome = a chronic L→R shunt drives pulmonary hypertension until the shunt reverses to R→L → late-onset cyanosis and clubbing
5 T's of cyanotic CHD — the number is the clue:
- 1 – Truncus arteriosus (one great vessel)
- 2 – Transposition (two vessels running in parallel)
- 3 – Tricuspid atresia (tri = 3)
- 4 – Tetralogy of Fallot (four features)
- 5 – TAPVR — Total Anomalous Pulmonary Venous Return (5 letters)
Tetralogy of Fallot = "PROVe":
- P — Pulmonary stenosis (its severity drives the degree of cyanosis)
- R — Right ventricular hypertrophy
- O — Overriding aorta
- Ve — Ventricular septal defect
Stem: A term newborn of a diabetic mother develops progressive cyanosis within the first day of life. Cyanosis does not improve with 100% oxygen (failed hyperoxia test — PaO2 stays low → cardiac, not pulmonary, cause). Chest X-ray shows a narrow mediastinum with an "egg on a string" silhouette.
Diagnosis: d-Transposition of the great arteries — the aorta arises from the RV and the pulmonary artery from the LV, creating two parallel circuits that are incompatible with life unless mixing occurs (through a PDA, ASD, or VSD).
Next best step: Start prostaglandin E1 (alprostadil) to maintain a patent ductus arteriosus for mixing, then balloon atrial septostomy if mixing is inadequate. Confirm anatomy with echocardiography; definitive repair is the arterial switch operation.
Stem: An 8-month-old with a known murmur suddenly becomes cyanotic, irritable, and hyperpneic while crying, then squats down, which relieves the episode. Exam reveals a harsh systolic ejection murmur; chest X-ray shows a boot-shaped heart.
Diagnosis: Tetralogy of Fallot with a "tet spell" (hypercyanotic episode) — a fall in systemic vascular resistance (or increased RV outflow obstruction) increases right-to-left shunting across the VSD. Squatting raises SVR, reducing the shunt and pushing blood through the pulmonary outflow.
Next best step (acute spell): Knee-to-chest positioning, supplemental oxygen, morphine, and IV fluids; add a beta-blocker (propranolol) or phenylephrine for refractory spells. TOF is associated with DiGeorge syndrome (22q11.2 deletion).
Syndrome / exposure associations
| Syndrome or exposure | Classic defect |
|---|---|
| Down syndrome (trisomy 21) | Complete AV septal (endocardial cushion) defect |
| Turner syndrome | Coarctation of aorta; bicuspid aortic valve |
| DiGeorge (22q11.2 deletion) | Tetralogy of Fallot; truncus arteriosus; interrupted aortic arch |
| Maternal diabetes | Transposition (d-TGA); VSD |
| Congenital rubella | PDA; pulmonary artery stenosis |
| Maternal lithium | Ebstein anomaly |
| Williams syndrome | Supravalvular aortic stenosis |
| Fetal alcohol syndrome | VSD; ASD |
| Marfan syndrome | Aortic root dilation / dissection |
Murmur & imaging fingerprints
| Lesion | Murmur / exam | Imaging clue |
|---|---|---|
| VSD | Harsh holosystolic, LLSB | Cardiomegaly, increased pulmonary markings |
| ASD | Wide fixed split S2 + systolic flow murmur | Increased pulmonary vascularity |
| PDA | Continuous machinery murmur, infraclavicular | Increased pulmonary markings |
| Tetralogy of Fallot | Harsh systolic ejection (pulmonic); single S2 | Boot-shaped heart |
| d-TGA | Often no murmur; single loud S2 | Egg on a string |
| TAPVR | Fixed split S2 | Snowman / figure-8 |
| Coarctation | Brachial-femoral delay; interscapular murmur | Rib notching, "3" sign |
Ductal-dependent lesions need a patent ductus arteriosus to survive — start PGE1 (alprostadil) empirically in any sick, cyanotic neonate while awaiting echo:
- Ductal-dependent pulmonary blood flow: pulmonary atresia, critical pulmonary stenosis, tricuspid atresia, severe TOF
- Ductal-dependent systemic blood flow: hypoplastic left heart syndrome, critical coarctation, critical aortic stenosis, interrupted aortic arch
Next-best-step pearls:
- Cyanotic neonate → hyperoxia test; if PaO2 fails to rise on 100% O2 → cardiac cause → PGE1 + echocardiography
- PGE1 key side effect = apnea (be ready to support ventilation); also fever and hypotension
- Critical CHD screening: routine newborn pulse-oximetry screening (pre- and post-ductal) catches many ductal-dependent lesions before collapse
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