Hypoplastic Left Heart Syndrome

Hypoplastic left heart syndrome (HLHS) is a rare form of congenital heart disease that affects 2 to 3 percent of babies born with congenital heart defects. It is characterized by a combination of defects of the left side of the heart and surrounding blood vessels and occurs when the left side of the heart is not fully formed before birth.

About Hypoplastic Left Heart Syndrome

The term “hypoplastic” refers to underdevelopment of a tissue or organ. In the case of hypoplastic left heart syndrome (HLHS), the left side of a baby’s heart (the side which receives oxygen-rich blood from the lungs and pumps it out to the body) is critically underdeveloped. The mitral and aortic valves are either completely closed or they are very small. The left ventricle itself can be tiny and the first part of the aorta can be very small, often only a few millimeters in diameter. As a result, the left side of the heart is unable to support the circulation needed by the body’s organs. Without a functioning left ventricle, the right side of the heart must perform the action of pumping blood to both the lungs as well as out to the rest of the body. Babies born with hypoplastic left heart syndrome have a bluish appearance known as cyanosis as a result of mixing oxygen-rich and oxygen-poor blood. Without treatment, the condition is fatal.

Two natural communications in the heart and vessels that usually close after birth can help the heart compensate for HLHS. These communications let oxygen-rich and oxygen-poor blood mix in the heart and send some oxygenated blood into the aorta to carry to the body. The baby’s skin, lips, and nails may begin to look blue because the mixed blood doesn’t contain enough oxygen.

One of these natural communications, the ductus arteriosus, connects the pulmonary artery and the aorta. The ductus arteriosus usually closes shortly after a baby is born but a pediatric cardiologist may prescribe medication (prostaglandin) to prevent the vessel from closing (see patent ductus arteriosus) until a baby with HLHS can have surgery. If the ductus arteriosus closes, the baby will get very sick.

Symptoms of Hypoplastic Left Heart Syndrome

HLHS is very serious and requires urgent treatment by a pediatric cardiologist and pediatric heart surgeon. An infant with a hypoplastic left ventricle tends to exhibit symptoms shortly after birth.

Symptoms of HLHS may include:

• Circulatory collapse
• Cold hands and feet
• Enlarged liver
• Gray or blue skin tone
• Irritability
• Poor feeding
• Rapid or troubled breathing
• Tiredness

Diagnosing Hypoplastic Left Heart Syndrome

Your obstetrician may be able to detect hypoplastic left ventricle with fetal echocardiography (ultrasound) before your baby is born. The test can be performed as early as 16 weeks of gestation. Once the baby has been born, your child’s doctor may notice signs of HLHS during a physical examination shortly after birth. To confirm a diagnosis of HLHS, a pediatric cardiologist may perform different tests.

Tests performed when diagnosing HLHS may include:

• Chest X-Ray: A chest X-ray produces an image of the tissue and bones in the heart and lungs and helps your provider assess the shape, size, and structure of the heart and lungs as well as the aeration of or any congestion in the lungs.
• Echocardiogram: An echocardiogram uses ultrasound technology to create a moving image of the heart and its valves, allowing your provider to assess the structure and function of the heart. An echocardiogram also helps provide information about blood flow and how well the heart is pumping blood.
• Electrocardiogram (ECG or EKG): An electrocardiogram uses electrodes that are placed on the body to record the electrical activity taking place in the heart. An ECG/EKG test helps detect abnormal rhythms, such as cardiac arrhythmias, stress on the heart, and damage to the heart muscles.

Treating Hypoplastic Left Heart Syndrome

It’s important that HLHS is treated immediately to save your child’s life. Treatment may begin immediately after birth when babies with HLHS are given intravenous, or IV, medications to stop the ductus arteriosus from closing. Your pediatric cardiologist may also prescribe medication to help dilate blood vessels. Another early treatment may involve using cardiac catheterization to widen one of the communications inside of the heart to allow for better flow.

A child with HLHS will likely need a series of three surgeries between the ages of two weeks and five years old to restore adequate function to the heart. In more severe cases, your pediatric cardiologist may recommend having a heart transplant.

The series of three surgeries related to HLHS include:

• Norwood Procedure: Converts the right ventricle into the main ventricle pumping blood to both the lungs and the body. The main pulmonary artery and the aorta are connected and the main pulmonary artery is cut off from the two branching pulmonary arteries that direct blood to each side of the lungs. Instead, a connection, known as a shunt or conduit, is placed between the pulmonary arteries and either the aorta or the heart to supply blood to the lungs. This procedure typically takes place at birth.
• Glenn Procedure: Diverts half of the blood (the oxygen-poor blood coming back from the upper body) to the lungs. The shunt to the pulmonary arteries is disconnected and the pulmonary arteries are connected directly to the superior vena cava, the vein that brings deoxygenated blood from the upper part of the body to the heart. This sends half of the deoxygenated blood directly to the lungs without going through the ventricle. This procedure typically takes place between 4-6 months of age.
• Fontan Procedure: Connects the inferior vena cava, the blood vessel that drains deoxygenated blood from the lower part of the body into the heart, to the pulmonary artery by creating a channel through or just outside the heart. At this stage, all deoxygenated blood flows passively through the lungs. This typically takes place between 3-4 years of age.

The goal of these procedures is to alter the structures of the heart to allow for the right ventricle to pump blood to the rest of the body while the vessels carrying oxygen-poor blood are redirected into the lungs to oxygenate blood without it having to pass through the heart.

Children with HLHS all need lifelong care from a cardiologist, who can monitor their heart health and prescribe medications to regulate and improve heart function, as well as other specialists. As they grow older, children may need further operations, including, in some cases, a heart transplant. They can also develop problems with other organs, such as the liver, which require ongoing care. Some children with HLHS can lead active lives with few restrictions. Others may need to restrict their activities at the recommendation of their pediatric cardiologist.

Care Team Approach

The Texas Center for Pediatric and Congenital Heart Disease, a clinical partnership between Dell Children’s Medical Center and UT Health Austin, takes a multidisciplinary approach to your child’s care. This means your child and your family will benefit from the expertise of multiple specialists across a variety of disciplines. Your care team will include pediatric cardiologists, cardiothoracic surgeons, interventional cardiologists, critical care specialists, hospitalists, anesthesiologists, perfusionists, nurses, advanced practice providers, social workers, psychologists, child life specialists, dietitians, physical and occupational therapists, pharmacists, and more, who work together to provide unparalleled care for patients every step of the way. We collaborate with our colleagues at the Dell Medical School and The University of Texas at Austin to utilize the latest research, diagnostic, and treatment techniques, allowing us to identify new therapies to improve treatment outcomes. We are committed to communicating and coordinating your child’s care with referring physicians and other partners in the community to ensure that we are providing comprehensive, whole-person care.

Learn More About Your Care Team