Congenital Heart Disease & Syndrome Associations — USMLE Step 2 CK Notes

Right-to-left shunts — the cyanotic "5 T's"

• Truncus arteriosus (1 vessel): the aorticopulmonary septum fails to form, so a single arterial trunk overrides a VSD — mixed blood gives early cyanosis and heart failure.
• Transposition of the great arteries (2 vessels swapped): failure of the septum to spiral — aorta arises from the RV and pulmonary artery from the LV, creating two parallel circuits. Incompatible with life unless a shunt exists (PFO, VSD, PDA): give prostaglandin E1 and perform balloon atrial septostomy, then arterial switch. Associated with maternal diabetes.
• Tricuspid atresia (3): absent tricuspid valve with a hypoplastic right ventricle; needs both an ASD and a VSD to survive.
• Tetralogy of Fallot (4): from anterosuperior displacement of the infundibular septum — Pulmonary stenosis (determines severity), Right ventricular hypertrophy, Overriding aorta, VSD (PROVe). Boot-shaped heart; "tet spells" of cyanosis relieved by squatting (raises systemic resistance and reduces right-to-left shunting).
• Total anomalous pulmonary venous return (5 words): pulmonary veins drain into the systemic circulation (right atrium/SVC) instead of the left atrium; requires an ASD/PFO to survive. "Snowman" sign on X-ray.
• Ebstein anomaly: downward displacement of the tricuspid leaflets into the right ventricle → "atrialised" RV, severe tricuspid regurgitation, right heart failure and arrhythmias (often with WPW). Classically linked to maternal lithium exposure.

Left-to-right shunts (acyanotic) — "the 3 D's"

• VSD (commonest congenital defect): harsh holosystolic murmur at the left lower sternal border; smaller defects are louder. Many close spontaneously; large ones cause failure to thrive and pulmonary overcirculation.
• ASD: fixed split S2 with a soft pulmonary flow murmur; ostium secundum is commonest (ostium primum occurs in Down syndrome). Risk of paradoxical emboli.
• PDA: continuous machine-like murmur below the left clavicle with a wide pulse pressure and bounding pulses; associated with prematurity and congenital rubella. Close with indometacin; keep open with prostaglandin E1.

Eisenmenger syndrome

• An uncorrected left-to-right shunt (VSD, ASD, PDA) causes chronic pulmonary overcirculation → pulmonary vascular remodelling and irreversible pulmonary hypertension → right ventricular hypertrophy → the shunt reverses to right-to-left.
• Result: late cyanosis, clubbing and polycythaemia. Once established it is irreversible and contraindicates shunt closure; treat with pulmonary vasodilators or transplantation.

Coarctation of the aorta

• Narrowing near the ligamentum arteriosum. Upper-limb hypertension with weak, delayed femoral pulses (radio-femoral delay) and a blood-pressure difference between arms and legs.
• Complications: left ventricular hypertrophy, heart failure, rib notching from collateral intercostal vessels, berry aneurysm rupture, aortic dissection.
• Associations: bicuspid aortic valve and Turner syndrome. Treat by surgical or catheter repair.

Persistent pulmonary hypertension of the newborn

• Pulmonary vascular resistance fails to fall after birth, so the circulation stays "fetal" with right-to-left shunting through the foramen ovale and ductus arteriosus.
• Presents with severe cyanosis and hypoxaemia refractory to oxygen, often with a pre-ductal/post-ductal saturation gradient. Risk factors: meconium aspiration, sepsis, congenital diaphragmatic hernia, birth asphyxia, maternal NSAID use.
• Treat with oxygen, ventilation and inhaled nitric oxide (a selective pulmonary vasodilator); ECMO if refractory.

Congenital defects & their associations

• Fetal alcohol syndrome: VSD and ASD (plus smooth philtrum, small palpebral fissures, growth restriction).
• Congenital rubella: PDA and pulmonary artery stenosis (with cataracts and deafness).
• Down syndrome: AV septal (endocardial cushion) defect, ostium primum ASD, VSD.
• Marfan syndrome: aortic root dilatation and dissection, mitral valve prolapse.
• Prenatal lithium exposure: Ebstein anomaly.
• Turner syndrome: bicuspid aortic valve and coarctation.
• Williams syndrome: supravalvular aortic stenosis (elastin deletion, chromosome 7).
• 22q11 deletion (DiGeorge): conotruncal anomalies — truncus arteriosus and tetralogy of Fallot.
• Maternal diabetes: transposition of the great arteries and hypertrophic cardiomyopathy of the newborn.

High-yield revision notes; verify against a primary source before clinical use.