Hypoplastic Left Heart Syndrome

Hypoplastic Left Heart Syndrome is a topic covered in the Select 5-Minute Pediatrics Topics.

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Hypoplastic left heart syndrome (HLHS) is a continuum of congenital cardiac defects resulting from severe underdevelopment of the structures of the left side of the heart (left atrium, mitral valve, left ventricle, aortic valve, and ascending aorta).


  • 0.16–0.36 per 1,000 live births
  • 8% of congenital heart disease (CHD); 3rd most common cause of critical CHD in the newborn
  • 23% of all neonatal mortality from CHD
  • Male predominance (67%)

Risk Factors


  • Familial inheritance: Sibling recurrence risk ranges from 8% to 21%, with higher recurrence observed when cardiovascular malformations are present in either parent. In addition, rare kinships have a frequency approaching autosomal dominant transmission.

Commonly Associated Conditions

  • Increased mortality when associated with definable genetic disorders, which comprise 10–28% of HLHS patients:
    • Turner syndrome, Noonan syndrome, Smith-Lemli-Opitz syndrome, Holt-Oram syndrome
    • Trisomy 13, 18, 21, or microdeletion syndromes
  • Major extracardiac anomalies (diaphragmatic hernia, omphalocele)


  • The etiology appears multifactorial, most likely resulting from an in utero reduction of left ventricular inflow or outflow (mechanisms postulated include premature closure of the foramen ovale and fetal cardiomyopathy).
  • As a result, the right ventricle (RV) must supply both the pulmonary and systemic circulations (via the ductus arteriosus) before and after birth.
  • The reduction in pulmonary vascular resistance that occurs with lung expansion at birth reduces the proportion of RV output to the systemic circulation. If the ductus arteriosus closes, shock occurs.

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