1) Obstructive left heart lesions (hypoplastic left heart syndrome (HLHS), coarctation, critical aortic stenosis)
2) Obstructive right heart lesions (tricuspid/pulmonary atresia, critical pulmonary stenosis, tetralogy of Fallot)
3) Common mixing (transposition of the great arteries)
Although 2) and 3) are classically cyanotic, congestive cardiac failure/pulmonary oedema and shock can result in low saturations in 1). The clue that this is coarctation is the differential pulse volumes which are appreciated after some resuscitation.
Duct dependent congenital heart disease accounts for 10% of infant mortality and is present in 6-8/1000 live births. A common lesion is coarctation.
