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Hypoplastic Left Heart Syndrome 

What is Hypoplastic Left Heart Syndrome (HLHS)?

Hypoplastic left heart syndrome (HLHS) is a congenital heart defect, where the left side of the baby’s heart is underdeveloped. This means the left side of the heart cannot pump oxygen-rich blood to the rest of body so the right side of the heart takes over this workload.

How is HLHS diagnosed and managed during pregnancy?

If your doctor suspects a fetal heart anomaly after reviewing your routine ultrasound, he or she may request a fetal echocardiogram (echo), an ultrasound of the fetus’s heart. This safe, noninvasive test shows the structure of the heart and how it is functioning, which can help us confirm the diagnosis of HLHS and discuss the best options for treatment during or after delivery. Our Fetal Heart Team will monitor the baby closely for the remainder of the pregnancy.

How does HLHS impact delivery?

Most babies with HLHS can be delivered vaginally, unless there are obstetric indications for another mode of delivery. It is best for these babies to be delivered at a medical center where there is access to a team of pediatric cardiologists and neonatologists, along with an established Neonatal Intensive Care Unit (NICU).

The Fetal Heart Program at the SSM Health St. Louis Fetal Care Institute has the experience, facilities and technology to handle the most medically challenging deliveries. In the most severe cases the team can perform a Cesarean Section at SSM Health Cardinal Glennon Children’s Hospital. If additional intervention is needed, the baby is next door to the pediatric operating room and the pediatric hybrid cardiac catheterization suite.

After delivery, the baby will need prostaglandin (PGE), an intravenous medication that keeps the patent ductus arteriosus (a normal connection present in babies in the womb) open. The patent ductus arteriosus (PDA) will allow the right ventricle to provide blood flow to the body. The baby will also be prepared for the first HLHS surgery, which typically occurs within a week of delivery. In some cases, a cardiac catheterization may be required to perform a balloon atrial septostomy in the first few days of life. This X-ray guided procedure is typically done by placing a thin flexible tube, or catheter, through the umbilical vein (a vessel in the umbilical cord) and does not require an incision. A balloon atrial septostomy creates a larger hole between the top chambers of the heart.

What is the surgery for HLHS, and how does it work?

Within the first week of the baby’s birth, the first of three heart surgeries will be performed unless there are other medical concerns that could delay surgery.

Through these surgeries, the right ventricle becomes the main pumping chamber to the body. The later surgeries direct non-oxygenated blood to the lungs, bypassing the heart. These surgeries are not able to cure HLHS but provide for a functioning heart.

The three-step procedure to treat HLHS

  • Step 1 (Option A) Norwood Procedure
    • This procedure usually occurs within the first week of life. In this surgery, the surgeon uses the pulmonary artery to recreate the aorta and inserts an artificial tube to provide blood flow to the lungs. There is still mixing of oxygen poor and oxygen rich blood.


  • Step 1 (Option B) Hybrid Palliation
    • This procedure usually occurs within the first week of life. In this alternative first stage procedure, a stent is placed in the ductus arteriosus, and bands are placed over the right and left branches of the pulmonary artery to make them smaller. This limits over-circulation to the lungs. There is still mixing of oxygen-poor and oxygen-rich blood.


  • Step 2 Glenn Procedure
    • This procedure typically occurs between four and six months of age. This surgery creates a direct connection between the pulmonary artery and the superior vena cava (vessel returning oxygen-poor blood from the upper part of the body to the heart). This reduces the work the right ventricle has to do by allowing blood returning from the upper body to flow directly to the lungs.


  • Step 3 Fontan Procedure
    • This procedure typically occurs between two and four years of age. This surgery connects the pulmonary artery and the inferior vena cava (vessel returning oxygen-poor blood from the lower part of the body to the heart), allowing the blood coming back from the lower body to go to the lungs. Once this procedure is complete, oxygen-rich and oxygen-poor blood no longer mix in the heart. The surgeon may leave a small connection between the oxygen rich and oxygen poor chambers (a fenestration).

What happens after the surgeries?

After the first surgery the baby may be fragile and have feeding difficulties because the heart is still working very hard. These babies will require a stay in the Neonatal or Pediatric Intensive Care Unit (NICU or PICU) until they overcome any feeding and breathing difficulties. Following these surgeries, these children will need lifelong follow-up visits with a cardiologist to monitor their progress.

What is the long-term prognosis for babies with HLHS?

The three-step procedure for HLHS was only introduced in the 1980’s. Surgical techniques have changed significantly since that time, and continue to improve.

Children with HLHS whose hearts become weak may eventually need heart transplants.

Additional Resources:

Congenital Heart Disease Resource Page
Provided by the Dorothy and Larry Dallas Heart Center at SSM Health Cardinal Glennon Children's Hospital

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