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← Section IV · Congenital Heart Disease
IV.I

Terminology and Anatomic and Physiologic Basis of CHD

15 cards

Notes

Incidence & epidemiology

  • Congenital heart disease affects 0.5–0.8 % of live births (~32,000 US infants/year).
  • Higher in premature infants if PDA is counted.
  • Most lethal newborn anomaly.
  • Excludes MVP (4–6 % adults) and bicuspid AV (1–2 %).

Frequency (excluding BAV and MVP)

Defect% of CHDM:F
Ventricular septal defect (VSD)18–281:1
Patent ductus arteriosus (PDA)10–181:2–3
Tetralogy of Fallot10–131:1
Atrial septal defect (ASD)7–81:2–4
Pulmonary stenosis7–81:1
Transposition of great arteries4–82–4:1
Coarctation5–72–5:1
AV canal defect2–71:1
Aortic stenosis2–54:1
Truncus arteriosus1–21:1
Tricuspid atresia1–21:1
TAPVR1–21:1

Etiology categories

  1. Heredity / chromosomal - trisomy 21 (AVSD, VSD).
  2. Viral - congenital rubella (PDA).
  3. Chemical - thalidomide (truncus, tetralogy), retinoic acid.
  4. Radiation - VSD.
  5. Multifactorial - most cases; recurrence risk in siblings ~2 % (baseline 0.8 %); 4–6 % if two affected siblings; 6–10 % if the mother is affected.
  • Conotruncal defects (TOF, TGA, truncus) especially heritable.

Syndromic associations

AnomalyIncidence % CHDCommon lesions
Trisomy 2150AVSD, VSD, ASD
Trisomy 1899+VSD, PDA, PS
Trisomy 1390VSD, PDA, dextrocardia
45,X (Turner)35Coarctation, AS, ASD, BAV
Noonan50–80Pulmonic stenosis (dysplastic PV), ASD, HCM
Williams (elastin del 7q11)80Supravalvular AS, supravalvular PS, VSD
Holt-Oram (TBX5)70ASD, VSD (± upper limb anomalies)
Marfan (fibrillin FBN1)50+Aortic root dilation, MVP
DiGeorge / 22q11 deletion80VSD, aortic arch anomalies, TOF, truncus

Fetal circulation

  • Lungs bypassed via foramen ovale and ductus arteriosus.
  • Ductus venosus shunts oxygenated umbilical vein blood past the liver.
  • Fetal ventricular, aortic, and pulmonary pressures all approximately equal at systemic levels.
  • Fetal O₂ saturation ~60 % - compensated by fetal hemoglobin.
  • Ductus-dependent lesions require prostaglandin E1 to maintain patency after birth.

Circulatory transitions at birth

  • First breath → lung expansion → drop in PVR.
  • Umbilical cord clamping → increased SVR.
  • Foramen ovale closes functionally within hours (anatomically over weeks-months).
  • Ductus arteriosus constricts within 10–15 hours (functional close), anatomically by day 2–3.

Terminology - segmental approach (Van Praagh)

  1. Situs - arrangement of atria:
    • Situs solitus (normal, S).
    • Situs inversus (mirror image, I).
    • Situs ambiguus / heterotaxy.
  2. Ventricular looping:
    • D-loop (right-handed) - normal (RV on right).
    • L-loop (left-handed) - RV on left (as in cctga).
  3. Great-artery relationships:
    • Normal (solitus): aorta posterior-right, PA anterior.
    • D-TGA: aorta anterior-right, arises from RV.
    • L-TGA (cctga): aorta anterior-left, arises from morphologic LV.

Cards

  • clozeIV.I-001
    Approximate incidence of congenital heart disease in live births: 0.5–0.8%.
  • basicIV.I-002
    Which is the most common congenital heart defect overall (excluding BAV and MVP)?
    → Ventricular septal defect (VSD), accounting for ~25% of CHD.
  • basicIV.I-003
    Which congenital heart defects are associated with Trisomy 21?
    → Atrioventricular septal defect (AVSD) — most characteristic — followed by VSD and ASD.
  • basicIV.I-004
    Which congenital heart lesion is characteristic of Turner syndrome (45,X)?
    → Coarctation of the aorta (35% of Turner patients). Also bicuspid aortic valve, AS, and secundum ASD.
  • basicIV.I-005
    Which congenital heart lesion is characteristic of Noonan syndrome?
    → Dysplastic pulmonic valve stenosis (thickened, immobile, non-doming leaflets — resistant to balloon valvuloplasty). Also HCM and ASD.
  • basicIV.I-006
    Cardiac lesions of Williams syndrome?
    → Supravalvular aortic stenosis (elastin gene deletion, chromosome 7q11), peripheral pulmonic stenosis, and supravalvular PS. Can also have systemic arterial narrowings.
  • basicIV.I-007
    What cardiac lesions are associated with DiGeorge / 22q11 deletion?
    → Conotruncal defects: tetralogy of Fallot, truncus arteriosus, interrupted aortic arch, VSD. Present in ~80% of affected patients.
  • basicIV.I-008
    What is Holt-Oram syndrome?
    → Autosomal dominant TBX5 mutation. Cardiac: ASD (secundum), VSD, conduction abnormalities. Extracardiac: upper limb anomalies (thumb aplasia, hypoplasia).
  • basicIV.I-009
    Cardiac manifestations of Marfan syndrome?
    → Aortic root dilation (sinus of Valsalva), aortic dissection risk, mitral valve prolapse (typically Barlow's disease).
  • basicIV.I-010
    Recurrence risk of CHD in a family with one previously affected child?
    → ~2% (up from baseline 0.8%). If two affected siblings: 4–6%. If the mother is the affected individual: 6–10%. Conotruncal defects (TOF, TGA, truncus) have higher heritability.
  • basicIV.I-011
    Which structures bypass the fetal lungs?
    → Foramen ovale (right-to-left atrial shunt) and ductus arteriosus (PA to descending aorta). The ductus venosus additionally bypasses the fetal liver.
  • basicIV.I-012
    Approximate fetal oxygen saturation? Compensating mechanism?
    → Fetal SaO₂ ~60%. Compensated by fetal hemoglobin (HbF), which has a higher oxygen affinity and enhances extraction at low O₂ tensions.
  • basicIV.I-013
    Which pharmacologic agent is used to maintain a patent ductus arteriosus in ductal-dependent lesions?
    → Prostaglandin E1 (alprostadil) continuous infusion.
  • basicIV.I-014
    Give three examples of ductal-dependent congenital lesions.
    → Any lesion with critical obstruction to systemic or pulmonary flow: hypoplastic left heart syndrome, critical aortic stenosis, critical coarctation, pulmonary atresia, critical pulmonic stenosis, tricuspid atresia, transposition (for mixing).
  • basicIV.I-015
    Define situs solitus vs situs inversus.
    → Situs solitus: normal atrial arrangement — morphologic RA on the right, morphologic LA on the left. Situs inversus: mirror-image arrangement.