Hypoplastic left heart syndrome (HLHS) refers to a range of disorders caused by the underdevelopment or malformation of structures on the left side of the heart. Classic hypoplastic left heart syndrome involves the absence or malformation of the aortic valve and either the absence, malformation, or abnormal narrowing of the mitral valve. The disorders that fall under hypoplastic left heart syndrome include (1) the underdevelopment or incomplete development of the left ventricle wall, (2) the absence or malformation of the aortic or mitral valves, and (3) the underdevelopment or narrowing of the aortic arch. These malformations prevent the proper circulation of blood throughout the heart.
Hypoplastic left heart syndrome is typically diagnosed via ultrasound between 18 and 20 weeks’ gestation, and it has an incidence rate of 1 to 2 per 10,000 live births. Hypoplastic left heart syndrome accounts for 9% of all congenital heart defects, and it affects males two times more often than females.
Further cardiac testing is recommended following a diagnosis of this condition due to the fact that additional heart abnormalities are common. Hypoplastic left heart syndrome is also often associated with anomalies outside of the heart such as agenesis of the corpus callosum, holoprosencephaly, hydrops fetalis, microcephaly, and chromosomal abnormalities like trisomy 13, trisomy 18, trisomy 21 (Down syndrome), and Turner syndrome.
Hypoplastic left heart syndrome has a significant mortality rate, especially when associated with other anomalies, but long-term survival is possible for isolated, surgically-treated cases. The recurrence risk depends on the underlying cause, family history, and associated diagnoses.