Hypoplastic Left Heart Syndrome 101: What You Should Know

The heart is an intricate organ that is vital for life and health. Hypoplasia occurs when any part of the heart doesn’t grow to its full size. When those parts are on the left side, the diagnosis is hypoplastic left heart syndrome (HLHS).

Parts inside the left side of the heart that may not develop properly include:

• Aorta. Considered the heart’s main artery, the aorta transports oxygen-rich blood out of the heart, so it can travel throughout the body.
• Aortic valve. The aortic valve opens to allow blood to move from the left ventricle into the aorta. It then closes to prevent blood from backwashing into the left ventricle.
• Left ventricle. This is the fourth and final heart chamber that blood passes through. Once it leaves the left ventricle, it goes through the aortic valve and aorta to nourish the rest of the body.
• Mitral valve. Situated between the left atrium and left ventricle, this valve regulates blood flow between these two heart chambers.

According to the Centers for Disease Control and Prevention, fewer than 1,000 babies are born with this congenital heart defect each year. Early diagnosis and treatment increase the likelihood of long-term survival.

What Increases the Risk of Hypoplastic Left Heart Syndrome

It’s currently unclear why a baby is born with hypoplastic left heart syndrome. Whatever the cause, something occurs during the fourth and eighth weeks of pregnancy that affects the heart’s development.

While the cause is unknown, certain risk factors seem to increase the likelihood of this congenital heart disease. These include the following:

• Advanced maternal age (35 years or older on due date)
• Baby is a male
• Low folate levels and other nutritional deficiencies while pregnant
• Obesity during pregnancy
• Type 1 or 2 diabetes before conceiving

Additionally, children with hypoplastic left heart syndrome are at higher risk for genetic diseases and other birth defects. They may have Turner syndrome, trisomy 13 and 18 or other conditions.

Symptoms That May Indicate Hypoplastic Issues in the Heart

When hypoplastic left heart syndrome is present, it reduces the amount of blood pumped from the heart, which flows into the body. This can cause several life-threatening symptoms.

These symptoms may arise within a few hours or days of birth. It is vital to recognize them and act immediately.

Symptoms your child may have hypoplastic left heart syndrome include:

• Blue-colored skin
• Breathing problems, such as fast breathing or shortness of breath
• Cold hands and feet
• Difficulty feeding and suckling
• Lethargy
• Weak pulse
• Pounding heartbeat

Diagnosing HLHS During Pregnancy

The sooner hypoplastic left heart syndrome is diagnosed, the better. In some cases, routine screening tests, such as an ultrasound, can help detect the condition. A fetal echocardiogram then confirms the diagnosis.

Undergoing a fetal echocardiogram follows the same process as having a regular ultrasound. Your care provider applies gel to your stomach and then moves a wand around on your belly. Ultrasound waves emitted from the wand help visualize your baby’s body, including the heart.

No preparation is needed for the exam, and it normally takes between 30 and 120 minutes, depending on the position of your baby.

A diagnosis cannot always be made during pregnancy. The small abnormalities in an unborn child’s heart can be difficult to see, even with a fetal echocardiogram. In some of these cases, genetic testing and other screening can help uncover potential problems.

Detecting Hypoplastic Left Heart Syndrome in Infants

When hypoplastic left heart syndrome goes undetected during pregnancy screenings, diagnosis starts with symptoms after your child is born. During a physical exam, your child’s provider may notice an abnormal heart rate, breathing difficulty, or other symptoms.

Based on these symptoms, one or more imaging tests can give a clear view of the heart and detect any heart issues. Imaging tests that may help diagnose a congenital heart defect include:

• Cardiac catheterization. A pediatric interventional cardiologist guides a thin, flexible tube (catheter) through a small incision in your child’s leg or arm to the heart. X-ray technology then helps visualize the heart’s upper chambers, lower chambers, and other parts.
• Chest X-ray. Electromagnetic radiation passes through your child’s body to produce images of various body structures.
• Electrocardiogram (ECG). A member of your child’s care team places several small electrodes on your child’s body. Wires run from these electrodes to a computer system that measures the electrical activity in your child’s heart.
• Echocardiogram. A pediatric specialist moves an ultrasound wand over your child’s chest. As with other ultrasound technologies, the echocardiogram produces moving and still images of your child’s heart.

Treatment and Outlook of HLHS

Though no treatment for hypoplastic left heart syndrome can cure the condition, it prolongs life and improves quality of life. Nutritional supplements can offset deficiencies, and medication can help manage symptoms. However, surgeries are necessary to help the heart pump blood through the body.

The Centers for Disease Control and Prevention state that babies with hypoplastic left heart syndrome typically require three pediatric cardiovascular surgeries in a specific order. Most of the time, the first takes place very soon after birth, and the final occurs by age 3.

• Norwood procedure. The surgeon builds and connects a new aorta to the right ventricle. This allows blood to bypass the abnormal left ventricle and leave the heart to nourish the rest of the body. Additionally, the surgeon places a tube between the right ventricle or aorta and vessels that lead to the lungs, which helps blood reach the lungs. This procedure occurs within the first couple of weeks of a child’s life.
• Bi-directional Glenn Shunt procedure. Blood reaches the lungs through the pulmonary artery. The second surgery for treating hypoplastic left heart syndrome connects this artery to the vessel that transfers blood from the upper body to the heart. This procedure normally takes place between 4 and 6 months of age and helps ease the burden on the right ventricle.
• Fontan procedure. Between 18 months and 3 years of age, children undergo the third and final surgery. This procedure allows blood into the lungs from the body. To achieve this result, the surgeon connects the pulmonary artery to the vessel that brings blood into the heart after it’s finished traveling around the body.

Thanks to advances in care, a growing number of children with HLHS now live decades after their surgeries. Some eventually require a heart transplant, and routine checkups help manage potential complications.

At Driscoll Children’s Hospital, a multidisciplinary team surrounds families whose children have hypoplastic left heart syndrome. We work together to explain the condition and develop an individualized treatment plan to help families through the process. Then we walk by your side every step of the way, from the Neonatal Intensive Care Unit (NICU) to the operating room and beyond, ensuring you remain informed and empowered.

Suspect your child may benefit from expert pediatric cardiology services at Driscoll Children’s Hospital? Find a doctor today or learn more about the Driscoll Children’s Heart Center.