What is congenital heart disease?
These are the structural and anatomical abnormalities, and the rhythm disturbances, that arise during embryogenesis and the development of the fetal heart. Worldwide, 1,500,000 children are born with some form of congenital heart disease (CHD). CHD accounts for about 8 per 1,000 of the congenital abnormalities seen in live newborns. To give an idea, CHD during fetal life is 6.5 times commoner than chromosomal abnormalities and 4 times commoner than neural tube defects. The most vulnerable period is the first 6 weeks of pregnancy. Four per 1,000 are major forms of CHD, which account for more than 20% of perinatal deaths and more than 50% of deaths in childhood due to a congenital abnormality. Fifty per cent of CHD requires some form of surgery.
Indications: when fetal echocardiography should be done
Maternal or family indications:
- a family history of congenital heart disease — that is, previous children or one of the two parents with cardiac malformations (a 1–4% risk of recurrence)
- inherited diseases with an increased risk of cardiac malformation (the risk of recurrence varies with the type of disease)
- infection during pregnancy, mainly rubella, cytomegalovirus (HCMV) and Coxsackie virus; insulin-dependent diabetes mellitus
- autoimmune disease (anti-Ro and anti-La autoantibodies in systemic lupus erythematosus); the use of drugs with proven teratogenic effects (anticonvulsants, alcohol, lithium, retinoic acid)
Fetal indications:
- suspicion of congenital heart disease during a routine scan
- fetal arrhythmia
- nuchal translucency above the 99th centile (that is, above 3.5 mm)
- early-onset growth restriction (in the second trimester)
- extracardiac abnormalities
- non-immune fetal hydrops (increased fluid in the fetal tissues)
- monochorionic twins
- chromosomal abnormalities.
Why is early examination (at 13–14 weeks of pregnancy) important?
Early confirmation that the cardiac anatomy is normal reassures the parents, while if there is any abnormality there is ample time for decisions to be made. There is likewise enough time for the karyotype to be checked and for the parents to be given proper genetic counselling. The incidence of chromosomal abnormalities present at birth is 0.3–22%, and they account for 15% of fetuses that survive to birth. The chance that a fetus with a chromosomal abnormality will survive depends on the type of abnormality. The risk of an autosomal chromosomal abnormality in a fetus with CHD is about 30%, and many of these fetuses do not survive in utero, so that 6% of live newborns with CHD have a chromosomal abnormality.
Why is cardiac monitoring important throughout the pregnancy?
There are rare cardiac problems that appear late in pregnancy — myocardial hypertrophy, obstruction of the ventricular outflow tracts, endocardial fibroelastosis and the appearance of a cardiac tumour — and these worsen the prognosis. The fetal heart starts to beat at 21–22 days of life, but arrhythmias usually appear after the second trimester, in 1–2% of cases. An arrhythmia conceals underlying CHD in 30–50% of cases of atrioventricular block, in 2–5% of isolated ectopic beats, and in 20–30% of tachycardia and bradycardia. Among the arrhythmias, 5–8% are tachycardias (>180/min), 5–8% bradycardias (<100/min) and 85% isolated ectopic beats. Infections such as chlamydia have been implicated in fetal arrhythmias, as has increased consumption of coffee, cigarettes and medication during pregnancy. Ten per cent of fetuses with an arrhythmia have increased morbidity, since they can develop heart failure, myocardial hypertrophy and fetal hydrops. Bradycardias have the worst prognosis.