Hypoplastic left heart syndrome (HLHS) is a birth defect that affects normal blood flow through the heart. As the baby develops during pregnancy, the left side of the heart does not develop and grow appropriately. Hypoplastic left heart syndrome is one type of congenital heart defect. Congenital means present at birth. Because a baby with this defect needs surgery or other procedures soon after birth, HLHS is considered a critical congenital heart defect (CCHD).

In hypoplastic left heart syndrome, the poor growth of the left-sided heart structures results in the following:

• The left ventricle is underdeveloped and too small.
• The mitral valve is not formed or is very small.
• The aortic valve is not formed or is very small.
• The initial part of the aorta is underdeveloped or is too small.
• Often, babies with hypoplastic left heart syndrome also have an atrial septal defect, which is a hole between the left and right upper chambers (atria) of the heart.

In a baby without a congenital heart defect, the right side of the heart pumps oxygen-poor blood from the heart to the lungs. The left side of the heart pumps oxygen-rich blood to the rest of the body. When a baby is growing in a mother’s womb during pregnancy, there are two small openings between the left and right sides of the heart: the patent ductus arteriosus and the patent foramen ovale. Normally, these openings will close a few days after birth.

In babies with hypoplastic left heart syndrome, the left side of the heart cannot pump oxygen-rich blood to the body properly. During the first few days of life for a baby with hypoplastic left heart syndrome, the oxygen-rich blood bypasses the poorly functioning left side of the heart through the patent ductus arteriosus and the patent foramen ovale. In order to survive, the right side of the heart has to “double the work” and needs to pump blood to both the lungs and the rest of the body. However, among babies with hypoplastic left heart syndrome, when these openings close, it becomes hard for oxygen-rich blood to get to the rest of the body.

Occurrence                   

The Centers for Disease Control and Prevention (CDC) estimates that each year about 1,025 babies in the United States are born with hypoplastic left heart syndrome. In other words, about 1 out of every 3,841 babies born in the USA each year is born with hypoplastic left heart syndrome.

Causes and Risk Factors

As with many congenital diseases, the causes of HLHS are uncertain and have not been linked to a mother’s disease or behavior. We believe that the cause of heart defects may be multifactorial in other words a combination of risk factors such as environmental exposures (certain drugs, alcohol, chemicals etc.), chromosome anomalies, nutritional deficiencies etc. Women can take steps before and during pregnancy to reduce the risk of having a baby born with birth defects. Such steps include taking a daily multivitamin with folic acid (400 micrograms) and not smoking,

Diagnosis

Hypoplastic left heart syndrome may be diagnosed during pregnancy or soon after the baby is born.

Prenatal care

“We are now able to diagnose these conditions with a fetal echocardiogram (ultrasound of the babies heart) that allows us time to counsel the family with regards to the heart condition and also allows us to plan timing and mode of delivery as well as to coordinate care regarding the delivery with the neonatology team at a level 3 neonatal intensive care unit, where the neonatal team are experienced in managing complex patients,” said Neill Videlefsky, M.D., of Sibley Heart Center Cardiology. “The mother’s womb is the best intensive care unit for these babies, and if possible, we do not encourage early delivery as the more mature and developed the organ systems, the better the chance for survival.”

After-birth care

Babies with hypoplastic left heart syndrome might not have trouble for the first few days of life while the patent ductus arteriosus and the patent foramen ovale (the normal openings in the heart) are open, but quickly develop signs after these openings are closed, including:

• Problems breathing
• Poor feeding
• Lethargy
• Weak pulse
• Ashen or bluish skin color

During a physical examination, a doctor may detect a heart murmur (an abnormal whooshing sound caused by blood not flowing properly) or other signs of heart disease and may request one or more tests to make a diagnosis, the most common being an echocardiogram. Echocardiography also is useful for helping the health care provider follow the child’s health over time.

HLHS is a defect that also can be detected with newborn pulse oximetry screening. Pulse oximetry is a simple bedside test to determine the amount of oxygen in a baby’s blood. Low levels of oxygen in the blood can be a sign of a CCHD. Newborn screening using pulse oximetry can identify some infants with a CCHD, like HLHS, before they show any symptoms.

Management

Medication:

Medication to help keep the patent ductus arteriosus prior to the first surgery as well as other medications to help heart function and help the body get rid of extra fluid.

Nutrition:

Some babies with hypoplastic left heart syndrome become tired while feeding and do not eat enough to gain weight. To make sure babies have a healthy weight gain, a special high-calorie formula might be prescribed. Some babies become extremely tired while feeding and might need to be fed through a feeding tube.

Surgery:

The surgical management of HLHS consists of a series of three operations do not cure hypoplastic left heart syndrome but are designed to improve blood and oxygen supply to the rest of the body.

1. Norwood Procedure
   This surgery usually is done within the first 2 weeks of a baby’s life. Surgeons create a “new” aorta and connect it to the right ventricle. They also place a tube from either the aorta or the right ventricle to the vessels supplying the lungs (pulmonary arteries). Thus, the right ventricle can pump blood to both the lungs and the rest of the body. This is the most technically challenging of the surgeries and has a survival rate greater than 90 percent at centers of excellence such as the Sibley Heart Center. After this procedure, an infant’s skin still might look bluish because oxygen-rich and oxygen-poor blood still mix in the heart.
2. Bi-directional Glenn Shunt Procedure
   This usually is performed when an infant is 4 to 6 months of age. This procedure creates a direct connection between the pulmonary artery and the vessel (the superior vena cava) returning oxygen-poor blood from the upper part of the body to the heart. This reduces the work of the right ventricle by allowing blood returning from the body to flow directly to the lungs.
3. Fontan Procedure
   This procedure usually is performed between 18 months and 5 years of age. The surgeon connects the pulmonary artery and the vessel (the inferior vena cava) returning oxygen-poor blood from the lower part of the body to the heart, allowing the rest of the blood coming back from the body to go to the lungs. Once this procedure is complete, oxygen-rich and oxygen-poor blood no longer mix in the heart and an infant’s skin will no longer look bluish.

Children with HLHS can lead a relatively normal life, attending school and participating in regular physical activities, although they may tire sooner than their peers with more strenuous activities. Infants with hypoplastic left heart syndrome may have lifelong complications. They will need regular follow-up visits with a cardiologist to monitor their progress.

“As the right ventricle is not designed to do the work of the left ventricle, it may weaken significantly with time and more surgeries or procedures may be needed to control arrhythmia, liver complications, gastrointestinal malabsorption and other complications of the Fontan procedure,” Dr. Videlefsky said. “Unfortunately, surgery at this time is not curative, and many of these patients will eventually require heart transplantation. However, the field of congenital heart disease is rapidly advancing, and the outlook continues to improve.”

Progress

Sibley Children’s Heart Center Cardiology has developed:

• Fetal cardiology program
  • Family-centered care
  • Resources for counseling and educating families
  • Detailed information to help families understand the diagnosis
  • Assistance in birth planning and postnatal management of the newborn
• Single ventricle program – strives to balance the need for close attention to clinical condition with the need for families to assume some level of normalization of life at home. As with all our patients, the single ventricle families are given access to phone support 24 hours a day, and our electronic health record allows all providers easy access to the most up-to-date clinical information when families call after hours. We have some of the highest interstage survival rates in the country during this time.
• Emory Adult Congenital Heart Clinic – Children transitioned to clinic with specialized expertise directed to adults with congenital heart disease
• Ongoing research including stem cell study
• Collaboration with Georgia Tech with new insights into understanding flow dynamics and putting into practice these new insights in certain surgical techniques
• Collaboration and participating in research projects with institutions throughout the USA

Resources to learn more about HLHS include the Sibley website, the American Heart Association, and Centers for Disease Control and Prevention, National Center on Birth Defects and Developmental Disabilities.

For more information about Sibley Heart Center Cardiology and our pediatric cardiology specialists, click here.