Fetal circulation and developmental causes of congenital heart disease
THE CONTEXT
Normal fetal blood flow and cardiac development help explain the anatomical defects and maternal associations described in congenital heart disease.
Fetal circulation
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The fetal lungs are collapsed and receive little blood flow because they are not required for gas exchange.
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Oxygenated placental blood passes from the right atrium to the left side of the heart through the foramen ovale, bypassing the lungs.
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Blood also passes from the pulmonary artery into the aorta through the ductus arteriosus.
Developmental mechanisms
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The early embryonic heart develops as a single tube that folds back on itself and divides into two separate circulations.
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Failure of septation can cause some forms of atrial and ventricular septal defect.
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Failure of alignment of the great vessels with the ventricles contributes to transposition of the great arteries, tetralogy of Fallot and truncus arteriosus.
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Failure of ductus arteriosus closure after birth results in a persistent ductus arteriosus.
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Failure of aortic development at the isthmus and the site of ductus attachment can lead to coarctation of the aorta.
Maternal and genetic associations
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Maternal infection and exposure to drugs or toxins are important causes of congenital heart disease.
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Maternal rubella is associated with persistent ductus arteriosus, pulmonary valvular or pulmonary artery stenosis, and atrial septal defect.
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Maternal alcohol misuse is associated with septal defects, while maternal lupus erythematosus is associated with congenital complete heart block.
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Genetic or chromosomal abnormalities, including Down syndrome, may cause septal defects.
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The passage also identifies Marfan syndrome and Turner syndrome, with karyotype XO, among conditions associated with specific abnormalities.