Hypoplastic Left Heart Syndrome

Basics

Description

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).

Epidemiology

  • 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

Genetics

  • 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)

Pathophysiology

  • 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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