Clinical meaning
Congenital heart defects (CHDs) are classified by hemodynamic effect: acyanotic (left-to-right shunts increasing pulmonary blood flow) and cyanotic (right-to-left shunts or mixing lesions causing systemic desaturation). Acyanotic defects include VSD (most common CHD), ASD, and PDA; blood shunts from high-pressure left heart to low-pressure right heart, causing volume overload and eventual pulmonary hypertension. If untreated, chronic left-to-right shunting causes irreversible pulmonary vascular remodeling (Eisenmenger syndrome), where pulmonary resistance exceeds systemic resistance and the shunt REVERSES to right-to-left, causing cyanosis. Cyanotic defects include Tetralogy of Fallot (most common cyanotic CHD: VSD + overriding aorta + RV outflow tract obstruction + RV hypertrophy) and transposition of the great arteries (TGA: aorta from RV, pulmonary artery from LV -- incompatible with life without mixing).
Diagnosis & workup
Diagnostics & workup: - Pulse oximetry screening: mandatory in all US newborn nurseries; pre- and post-ductal SpO2 within 24 hours; positive screen if <95% or >3% difference between pre/post-ductal - Echocardiography: primary diagnostic tool; defines anatomy, hemodynamics, shunt direction and volume, valve function - ECG: RVH pattern in right-sided lesions (Tetralogy, pulmonary stenosis); LVH in left-sided (aortic stenosis, coarctation) - Chest X-ray: increased pulmonary vascularity (left-to-right shunts), decreased vascularity (right-to-left shunts), boot-shaped heart (Tetralogy of Fallot), egg-on-string (TGA), snowman sign (TAPVR) - Cardiac catheterization: definitive hemodynamic assessment; measures pressures and oxygen saturations; interventional procedures (balloon valvuloplasty, coil occlusion of PDA, device closure of ASD) - Cardiac MRI: detailed anatomical assessment for complex defects - Prenatal screening: fetal echocardiography at 18-22 weeks for high-risk pregnancies