Congenital Heart Disease and Fetal Cardiac Pathology
Fetal congenital heart disease is best approached by sequential segmental analysis: situs, venous connections, atrioventricular connections, ventricular morphology, ventriculoarterial connections, and arch/ductal arrangement. Major categories include septal defects (VSD, ASD, AVSD), conotruncal anomalies (tetralogy of Fallot, transposition of the great arteries, truncus arteriosus, double-outlet right ventricle), left-sided obstructive lesions (hypoplastic left heart, aortic stenosis, coarctation, interrupted aortic arch), right-sided obstructive lesions (pulmonary stenosis/atresia, tricuspid atresia, Ebstein anomaly), and anomalous pulmonary venous return. Fetal circulation can mask severity: a ductal-dependent lesion may look compensated before birth, and ventricular size discrepancy may be subtle early. Traps include overdiagnosing a small muscular VSD, mislabeling normal right-heart dominance as hypoplasia, and missing coarctation because the four-chamber view is normal. Color and pulsed Doppler, arch views, and the three-vessel trachea view are essential adjuncts; do not rely only on the four-chamber view. Worked example: a four-chamber view with a large VSD and an aorta overriding the septum, plus a small pulmonary artery, suggests tetralogy of Fallot with pulmonary stenosis; if pulmonary forward flow is absent and the ductus arteriosus supplies the lungs, consider pulmonary atresia. Another rule of thumb: when one ventricle is small, assess the corresponding AV valve, outflow, and arch before labeling hypoplasia; asymmetry alone is not a diagnosis. Document all findings and arrange fetal cardiology referral and postnatal planning.