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Heart | Hypoplastic left heart syndrome with intact or restrictive atrial septum

The heart is made up of four chambers (two ventricles and two atria, separated by a wall called the septum) and four valves. The foramen ovale is an opening in the septum connecting the right and left atria. The right side of the heart pumps blood to the lungs and the left side pumps blood to the brain and body.  Serious health risks may result from the abnormal development of any of these structures.

Essential Information

  • Hypoplastic left heart syndrome (HLHS) occurs when the left side of the heart is underdeveloped, and therefore unable to pump blood to the body after birth.
  • HLHS is typically detected on ultrasound between 18-22 weeks gestation.
  • If HLHS presents with an intact or restrictive atrial septum, this prevents oxygenated blood from being distributed to the body.
  • For such fetuses, an opening may be made in the septum whilst still in the womb.

Overview

Hypoplastic left heart syndrome (HLHS) occurs when the left side of the heart is severely underdeveloped, and therefore unable to pump blood to the body after birth. If not corrected soon after birth, this can be fatal.

The septum is the wall separating the left atrium and ventricle from the right atrium and ventricle. The foramen ovale is an opening in the inter-atrial septum, which allows oxygenated blood to pass from the right to left atria. Sometimes the atrial septum can be “intact” or “restrictive”.

In newborns with HLHS, the existence of an inter-atrial communication allows oxygenated blood to be distributed to the brain and body, preventing fluid build-up in the lungs. If the atrial septum is intact or restrictive, the outcome for these babies is very poor.

HLHS is typically detected on ultrasound between 18-22 weeks gestation. This diagnosis should be confirmed by a targeted ultrasound of the heart’s structure and function – a fetal echocardiogram. Occasionally, additional imaging with a fetal cardiac MRI may be required.

Fetal Therapy

As the outcome of fetuses with HLHS and an intact or restrictive atrial septum is poor, a procedure to create an opening (septotostomy), or place a stent in the atrial septum may be offered in-utero. This procedure is done under ultrasound-guidance using a fine needle, a catheter and small balloon.

Although urgent surgery will still be required after birth, a fetal intervention may reduce the severity of lung damage and improve the survival rates for affected babies.

Referral Information (for physicians)

Fetal echocardiography will be organized at the Hospital for Sick Children (SickKids). Procedures are done in the Fetal Medicine Unit at Mount Sinai Hospital. Post-operatively, out-of-province patients will be referred back to their local centre with experience in managing high-risk cardiac conditions for ongoing antenatal care and birth. Local patients will have ongoing follow-up at Mount Sinai and SickKids hospitals. 

Please refer patients via the Fetal Cardiac Program at SickKids.