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Hypoplastic left heart syndrome
Hypoplastic left heart syndrome (HLHS) refers to the abnormal development of the left-sided cardiac structures, resulting in obstruction to blood flow from the left ventricular outflow tract. In addition, the syndrome includes underdevelopment of the left ventricle, aorta, and aortic arch, as well as mitral atresia or stenosis.
HLHS has been reported to occur in 1-2 in 6250 live births.
Newborn infants with the condition are generally born at full term and initially appear healthy. As the arterial duct closes, systemic perfusion decreases, resulting in hypoxemia, acidosis, and cardiogenic shock. Usually, no heart murmur (or a non-specific heart murmur) is detected. The second heart sound is loud and single because of aortic atresia. Often the liver is enlarged secondary to congestive heart failure.
The embryologic cause of the disease, as in the case of most congenital cardiac defects, is not fully known.
The most useful diagnostic modality is the echocardiogram.
Differential diagnosis includes other left-sided obstructive lesions where the systemic circulation is dependent on ductal flow (critical aortic stenosis, coarctation of the aorta, interrupted aortic arch: see these terms).
The syndrome can be diagnosed by fetal echocardiography between 18 and 22 weeks of gestation.
Management and treatment
Children with the syndrome require neonatal surgery, as they have duct-dependent systemic circulation. Currently, there are two major modalities, primary cardiac transplantation or a series of staged functionally univentricular palliations. The treatment chosen is dependent on the preference of the institution and its experience.
Although survival following initial surgical intervention has improved significantly over the last 20 years, significant mortality and morbidity are associated with both surgical strategies. As a result, pediatric cardiologists continue to be challenged by discussions with families regarding the initial decision relative to the treatment and long-term prognosis, particularly as information on long-term survival and quality of life for those born with the syndrome is limited.
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