Hypoplastic Left Heart Syndrome (HLHS)

This page is dedicated to those affected by HLHS and my friend’s son Thomas David Moore
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The heart consists of four chambers: the two upper chambers, called atria, where blood enters the heart; and the two lower chambers, called ventricles, where blood is pumped out of the heart. The flow between the chambers is controlled by a set of valves that act as one-way doors.

…in a healthy heart, oxygen-poor (blue) blood returns to the right atrium from the body, travels to the right ventricle, then is pumped through the pulmonary artery into the lungs where it receives oxygen. Oxygen-rich (red) blood returns to the left atrium from the lungs, passes into the left ventricle, and then is pumped out to the body through the aorta.

With Hypoplastic Left Heart Syndrome, the left side of the heart (the part that pumps oxygenated blood to the rest of the body) is underdeveloped. The degree of underdevelopment differs from child to child.

The structures affected usually include the following:

Mitral valve - The valve that controls blood flow between the left atrium and left ventricle in the heart.

Left ventricle - The lower left-hand chamber of the heart. It receives oxygen-rich (red) blood from the left atrium and pumps it into the aorta, which takes the blood to the body. The left ventricle must be strong and muscular in order to pump enough blood to the body to meet its requirements. When the chamber is small and poorly developed, it will not function effectively and cannot provide enough blood flow to meet the body’s needs.

Aortic valve - The valve that regulates blood flow from the heart into the aorta.

Aorta - The largest artery in the body and the primary blood vessel leading from the heart to the body.

Hypoplastic left heart syndrome occurs in up to four out of every 10,000 live births. The syndrome comprises 8 percent of all cases of congenital heart disease. It is one of the top three heart abnormalities to cause problems in the newborn. HLHS occurs slightly more often in boys (55% -70%) than in girls. In many children, HLHS occurs by chance, with no clear reason evident for the underdevelopment. However, the rate of occurance is increased in patients with Turner, Noonan, Smith-Lemli-Opitz or Holt-Oram Syndromes. Certain chromosomal duplications, translocations and deletions have been associated with HLHS, but not in most cases.

Babies with this condition may appear normal at birth. Fetuses are nourished by oxygen-rich blood from their mothers so they don’t breathe and don’t use their lungs. Babies with hypoplastic left heart syndrome may seem normal at birth because the patent ductus arteriosus (a blood vessel that connects the pulmonary artery to the aorta, thereby bypassing the lungs and the defective left side of the heart.) is still open, allowing blood to continue circulating directly into the aorta and out to the rest of the body. Once the ductus closes a few days after birth, blood flows to the lungs and then to the left side of the heart where it is blocked and can’t circulate through the rest of the body. It is at this time that these babies show symptoms.

The following are the most common symptoms of hypoplastic left heart syndrome:

  • cyanosis (blue color of the skin, lips and nailbeds)
  • pale skin
  • sweaty or clammy skin
  • cool skin
  • heavy and/or rapid breathing
  • fast heart rate
  • difficulty feeding

(As these symptoms may resemble other medical conditions and heart problems. Always consult your child’s physician for a diagnosis.)

How is hypoplastic left heart syndrome diagnosed?

Your child’s physician may have heard a heart murmur during a physical examination and referred your child to a pediatric cardiologist for a diagnosis. A heart murmur is simply a noise caused by the turbulence of blood flowing through a narrow region. Symptoms your child experiences also will help with the diagnosis.

A pediatric cardiologist specializes in the diagnosis and medical management of congenital heart defects, as well as heart problems that may develop later in childhood. The cardiologist will perform a physical examination, listening to the heart and lungs, and make other observations that help in the diagnosis. Other tests are needed to help with the diagnosis.

Chest X-ray — A diagnostic test which uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film.

Electrocardiogram (ECG or EKG) — A test that records the electrical activity of the heart, shows abnormal rhythms (arrhythmias or dysrhythmias) and detects heart muscle damage.

Echocardiogram (echo) — A procedure that evaluates the structure and function of the heart by using sound waves, recorded on an electronic sensor, that produce a moving picture of the heart and heart valves.

Cardiac Catheterization — A procedure that gives function and information about the structure inside the heart. Under sedation, a small, thin, flexible tube (catheter) is inserted into a blood vessel in the groin and guided to the inside of the heart. Blood pressure and oxygen measurements are taken in the four chambers of the heart, as well as in the pulmonary artery and aorta. Contrast dye also is injected to more clearly visualize the structures inside the heart.

Cardiac Magnetic Resonance Imaging (MRI) — A non-invasive test that uses magnets and radio waves to make pictures of structures and blood flow inside the body.

What are the treatments for hypoplastic left heart syndrome?

HLHS is fatal unless treated. While there are treatments, HLHS is NOT CORRECTABLE!
Specific treatment for hypoplastic left heart syndrome will be determined by your child’s physician based on the following:

  • your child’s age, overall health and medical history
  • extent of the disease
  • your child’s tolerance for specific medications, procedures or therapies
  • how your child’s doctor expects the disease will progress
  • your opinion or preference

Your child most likely will be admitted to the intensive care unit (ICU) or special care nursery once symptoms are noted. Initially, your child may be placed on oxygen, or a ventilator to assist his/her breathing. Intravenous (IV) medications (including prostaglandins which prevent the ductus from closing) may be given to help the heart beat stronger and lungs function more efficiently.

Three options may be presented to you:

Comfort Care - includes the process of relieving pain and suffering, and controlling debilitating symptoms, while not preventing the patient from dying

Surgical Repair - consists of 3 open heart surgeries that will result in the body using one good right ventricle to do the work normally done by 2 ventricles. The goal is to separate blue and red blood circulation. Because blood vessels of the lungs change over the first year of life, the surgery must be performed in stages. A successful Fontan (final stage) requires sufficient and easy blood flow through the lungs so as not to require the force of the missing ventricle to pump the blood. This is not possible in the first months of life and therefore 2 procedures (stages) must be performed until the lungs are matured and ready.

STAGE 1 - Norwood
This surgery is preferrably performed in the first week of life. A repair is made to allow the right ventricle to pump blood to both the lungs and the body. Because blood flow must be forceful for the immature lungs, the surgeon creates a tube from a branch of the aorta to the pulmonary artery known as the modified Blalock-Taussing shunt. The baby will still appear blue (cyanotic) after this surgery.

STAGE 2 - bi-directional Glenn or Hemi-Fontan
This surgery is preferrable performed at about 6 months of life when the blood starts to flow more easily and the vewntricular force is not needed. The surgeon creates a direct connection between the superior vena cava and the pulmonary artery thus diverting half of the blood flow without the assistance of ventricular force. This reduces the work on the right ventricle by allowing it to only pump blood to the body and allowing all blood from the upper body to the lungs.

STAGE 3 - Fontan
This surgery is preferrably performed between 18 - 48 months. The surgeon connects the inferior vena cava to the pulmonary artery. This will allow the remaining blood coming back from the body to go directly to the lungs. The final result will be no mixing of blood in the heart with more oxygen rich blood going to the body. This will significantly improve the child’s health and growth.

Heart Transplant - First an infant must be placed on a transplant list. Then, the infant will remain on prostaglandins to keep the ductus open until a donor heart becomes available. After the successful transplant, the recipient will be required to remain on anti-rejection medications for life.
HLHS requires a life time of follow up care. Most HLHS pateients will require heart medications for life. They are at a high risk of heart valve infection (endocarditis) and require antibiotics before dental work and most surgeries. At this time, life expectancy is relatively unknown. 70% of infants who survive heart transplant or the Fontan will survive to the age of 5.

**Recent studies report neurodevelopmental disabilities in a significant number of HLHS patients (both those with surgical repair and heart transplants)


*In 1979, the first surgical palliation was performed on a newborn.

**HLHS can be easily detected on fetal echocardiography. However, many cases are not diagnosed because the pregnancy is typically uncomplicated and the fetus grows and develops normally because fetal circulation is provided by the mother. As well, little concentration is spent on cardiac anatomy during routine exams.

During cardiac development, adequate blood flow through a structure is responsible for growth of that structure. Because of aortic and mitral valve artresia (narrowing), little or no blood flow goes to the left ventricale and therefore, it does not grow.

Recent research suggests that if the narrowing is discovered early enough, a balloon can be inserted in-utero to allow proper blood flow which will allow the left ventricle to develop. Actually, this procedure has been performed and the baby was indeed born with a functioning left heart! As well, this form of surgical repair leaves little to no scarring. Over 100 of these procedures have been performed. The oldest survivor is 4 years old!

To view an in-utero surgery for HLHS, go to:

***Another theory suggests that HLHS is caused by a premature closure or absence of the foramen ovale. This would eliminate fetal blood flow from the inferior vena cava to the left atrium thus resulting in underdevelopment.

Thanks to Vanessa at CHD Heart Foundation for writing this article.

Disclaimer: The facts and opinions shown in this article are as accurate and up to date as possible, but are provided as general “information resources”, which may not be relevant to individual persons. This article is not a substitute for individual assessment and always take advice from a doctor who is familiar with the particular person..