Tetralogy of Fallot (TOF): a defect consisting of four related lesions: ventricular septal defect, obstruction of the right ventricular outflow tract, override of the ventricular septum by the aortic root, and right ventricular hypertrophy. The magnitude of pulmonary blood flow obstruction determines the onset and severity of symptoms, with a greater obstruction associated with more severe illness.3

Total anomalous pulmonary venous return (TAPVR): a malformation characterized by the absence of any connection between the pulmonary veins and left atrium; instead, the pulmonary veins empty into the right atrium or systemic veins, resulting in a mix of oxygenated and unoxygenated blood entering the systemic circulation.3

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Transposition of the great arteries (TGA): a family of malformations characterized by two discordant circulatory tracks, whereby unoxygenated blood is circulated to the body via the aorta, and oxygenated blood is recirculated between the lungs and the pulmonary artery. 

Tricuspid atresia: a defect where the tricuspid valve fails to develop, leading to a range of symptoms including cyanosis, dyspnea, tachypnea, and metabolic acidosis. Tricuspid atresia commonly occurs with other cardiac defects that also contribute to cyanosis.3

Truncus arteriosus: a malformation characterized by the presence of a single great artery that arises from both ventricles and thereby supplies both oxygenated and unoxygenated blood to the pulmonary, coronary, and systemic circulations.3

Table 1 summarizes the epidemiology, clinical features, and natural history of each subtype of CCHD. Many defects are ductal-dependent, meaning that the diagnosis may be delayed in cases when the ductus arteriosus closes after the newborn is discharged from the hospital nursery. The 
common finding of hypoxemia, however, has important implications for CCHD screening.

Table 1. Types and natural history of critical congenital heart disease
Cardiac Defect Hypoxemia Ductal Dependent Prevalence Age at Symptom Onset Natural History
HLHS All All Up to 7 in 10,000 live births Immediately, or within first two months of life Universally fatal without surgery
Pulmonary artresia with intact septum All All 1% of all congenital cardiac defects Immediately When the ductus closes, the newborn becomes severely ill, leading to death if not urgently treated
TOF Most Uncommon 3 in 10,000 live births Neonatal period Onset and severity of  symptoms depend on amount of pulmonary blood flow obstruction
TAPVR All None 1%-3% of all congenital cardiac defects Immediately, or within first two months of life Survival unlikely if the obstruction is left untreated
TGA All Uncommon Up to 3 in 10,000 live births Immediately Onset and severity of symptoms depend on anatomic and functional variants with inadequate blood flow, the newborn will die
Tricuspid artresia All Some 1% to 3% of all congenital cardiac defects Immediately, or within first month of life Cyanotic newborns with a ductal-dependant defect are critically ill
Truncus arteriosus All None 2% to 4% of all congenital cardiac defects Within the first two months of life Fewer than 25% will survive past the first year of life without surgical intervention
CCHD = critical congenital heart disease; HLHS = hypoplastic left heart syndrome; TOF = tetralolgy of Fallot; TAPVR = total anamolous pulmonary venous return; TGA = transposition of the great arteries.

Source: Knapp AA, et al. Maternal and Child Health Bureau, U.S. Department of Health and Human Services. 2010.