Hypoplastic Left Heart Syndrome (HLHS)

HLHS is characterized by a very small left ventricle, with mitral and/or aortic atresia. Blood flow to the head is supplied by retrograde flow through the ductus arteriosus.

Fig 1

Incidence: 1 in 3000 births, accounting for 10-15% of neonatal deaths from cardiac causes.

Sonographic findings:

Fig 2, Fig 3

  • Small left ventricle on the FCV.
  • Hypoplasia of the mitral and aortic valves.
  • Ascending aorta is often hypoplastic.
  • The movement of the mitral valve is severely impaired.
  • Atrial septal defect.
  • Retrograde flow within the ascending aorta and aortic arch, from ductus arteriosus.
  • Abnormal Doppler pattern of pulmonary venous flow which appears to be a reliable predictor of restriction of the atrial septum in the neonate.
  • Congestive heart failure and hydrops fetalis can occur in cases with tricuspid regurgitation.
  • Increased nuchal translucency thickness at 10-14 weeks of gestation.
  • Pitfalls:
    • Mild hypoplastic left heart often occurs with aortic coarctation of aorta.
    • The left side of the heart can be nearly normal in size in the early second trimester and become severely hypoplastic in late pregnancy.
    • Functional aortic stenosis may show retrograde flow in the aortic arch like HLHS.
  • Usually diagnosed in the second half of pregnancy, though possible as early as 13 weeks (with a persistent reversed flow of ductus venosus during atrial contraction).

Fig 1:  Schematic drawing of hypoplastic left heart syndrome (LA = left atrium, LV = left ventricle, RA = right atrium, RV = right ventricle)

Fig 1:  Hypoplastic left heart syndrome  Very small left ventricle (*)

Fig 3:  Hypoplastic left heart syndrome   Short axis view: markedly small aortic root (arrow) (solid circle = right atrium)

Video clips of Hypoplastic left heart syndrome 

HLHS / Arrhythmias :  Four-chamber view: very small left heart with thickened ventricular wall with irregular heart beats, arrow = flap of foramen ovale, * = pericar-dial effusion, arrowhead = spine

Hypoplastic left heart syndrome :  Four-chamber view: single ventricle (right) (*),arrowhead = spine

Hypoplastic left heart syndrome:  Arch view: enlarged ductal arch (arrow) and small aortic arch (*), arrowhead = spine

Hypoplastic left heart syndrome :
– Long-axis view: small aortic root (*) arising from small left ventricle (arrowhead = spine)
– Arch view: small aortic arch (*), compared to large ductal arch (arrowhead = spine)

Hypoplastic left heart syndrome :  Four-chamber view: small left ventricle (*), compared to right ventricle (arrowhead = spine)

Associations: Coarctation of aorta, with chromosome abnormalities seen in 12-25% of cases, especially microdeletion 22q11, trisomy 18 or Turner syndrome.

Management: Careful prenatal and postnatal search for associated anomalies is required as well as chromosome study. Termination of pregnancy should be offered before viability. In continuing pregnancy, delivery should occur where immediate pediatric cardiology and surgery support are available. Vaginal delivery can be allowed. The proportion of infants with HLHS treated with staged surgical palliation and infant heart transplant has increased, resulting in major improvements in survival and quality-of-life outcomes.

Prognosis: Very poor, but better with staged reconstruction surgery in selected cases (survival rate of 25-40%).

Recurrence risk: About 2%, but higher in rare autosomal recessive cases.