Congenital heart diseases

1. Concept

Congenital heart diseases (CHD) are abnormalities of the heart/great vessels present at birth, mostly from faulty embryogenesis (weeks 3–8). ~90% have unknown cause; risk factors include congenital rubella, alcohol, smoking, chromosomal abnormalities (trisomies 13/18/21, Turner), and familial forms.

Three functional groups: left-to-right shunt, right-to-left shunt, and obstruction.

2. Left-to-right shunts (late/no cyanosis)

Oxygenated blood recirculates to lungs → volume/pressure overload → pulmonary hypertension → RV hypertrophy. If chronic, pulmonary vascular intimal thickening reverses the shunt → Eisenmenger syndrome (now right-to-left → late cyanosis, incurable). Correct before reversal.

Defect	Key points
ASD	Ostium secundum (90%); risk of paradoxical embolism
VSD	Most common; membranous (90%, “Roger’s disease” if isolated); jet lesions → endocarditis risk
PDA	Ductus fails to close (normally closes via ↑O₂, ↓PGE₂); aorta → pulmonary artery

3. Right-to-left shunts (early cyanosis — “blue babies”)

Deoxygenated blood bypasses lungs → cyanosis at birth; chronic hypoxia → polycythemia, clubbing (hypertrophic osteoarthropathy), paradoxical embolism.

• Tetralogy of Fallot — 4 features: VSD, pulmonary stenosis, overriding aorta, RV hypertrophy. Severity tracks the pulmonary stenosis (“pink” vs “blue”).
• Transposition of great arteries — aorta from RV, pulmonary trunk from LV; incompatible with life without mixing (PDA/foramen ovale/VSD).
• Truncus arteriosus — single great artery + VSD.

4. Obstructive lesions

• Coarctation of aorta (most common): infantile/preductal (lower-body cyanosis, PDA-dependent) vs adult/postductal (upper-limb hypertension, lower-limb hypotension, claudication; risk of stroke, aortic dissection).
• Also aortic/pulmonary valve stenosis; atresia = complete obstruction.

💡 High-yield: L→R shunts (ASD, VSD, PDA) = late/no cyanosis → risk Eisenmenger (shunt reversal → late cyanosis). R→L shunts (Tetralogy of Fallot, TGA, truncus) = early cyanosis “blue baby.” ToF = VSD + pulmonary stenosis + overriding aorta + RVH. Coarctation: preductal (infant) vs postductal (upper-limb HTN). Triggers: rubella, trisomies, Turner.