Hypoplastic left heart syndrome (HLHS) is a very serious disease present at birth (congenital heart disease) in which the chambers, valves and related blood vessels on the left side of the heart are so malformed that they cannot efficiently pump blood to the rest of the body. This condition is also frequently referred to as left heart hypoplasia by physicians.

HLHS can manifest in a variety of malformations, including an overly muscular wall between the right and left side of the heart (septum) that pushes into the left heart; abnormal aortic and mitral valves on the left side of the heart; and a abnormally constricted aorta. The most common abnormality is aortic valve atresia, with or without mitral valve atresia.

Infants born with HLHS also have additional heart defects, such as hole in the septum (e.g., a ventricular septal defect). There may also be other abnormalities not associated with the heart. For example, in one review, about 30 percent of infants born with HLHS also suffered from major abnormalities in the central nervous system, and about 30 percent had genetic disorders.

The diagnosis and treatment of HLHS has made great advances in recent decades. In the 1970s, HLHS was invariably fatal. Today, however, physicians can diagnose the disease with a standard fetal ultrasound at 16 to 18 weeks into pregnancy. This extra time allows for physicians to counsel and prepare the parents as well as review the various options available to them and the possible modes of therapy.

After the baby is born, whether or not he or she has already been diagnosed, the question of when to perform surgery depends on the severity of the defects. In general, surgery will be performed a quickly as possible. Today's open-heart surgeries offer new hope for a longer life, though researchers do not yet know if surgery allows HLHS patients to mature past early adulthood.

The open-heart surgeries currently available are initially heart transplant surgery or a Norwood procedure, followed by a series of surgeries, each done at a different age, ranging from infancy through the toddler years. Both heart transplantation and the Norwood procedure carry risks and should only be done by a fully qualified pediatric heart surgeon.  

Hypoplastic left heart syndrome (HLHS) is a very serious congenital heart disease in which the chambers, valves and related blood vessels on the left side of the heart are so malformed that they cannot efficiently pump blood to the rest of the body. The heart defects that may be associated with HLHS include:

Closure of the fetal communication between the two receiving chambers of the heart (premature closure of the foramen ovale) may result in underdevelopment of the left atrium and left ventricle as well as producing severe, extra workload on the lungs.  This particular form of HLHS may produce symptoms even in the fetus and often carries the worse prognosis because of the damage to the blood vessels in the lungs. Fortunately, this form of HLHS is very rare - aortic atresia and mitral atresia account for the vast majority of HLHS cases.

The diagnosis of HLHS has made great strides with the advent of fetal ultrasound. This common test is able to allow a diagnosis of HLHS at 16 to 18 weeks of gestation. This allows pediatric cardiologists time to review the defects, various options, and outcomes with the parents, and offers them valuable time for counseling and education. Additionally, this will allow the surgical team time for planning and transportation of the mother and baby to a surgical center with experiencing in HLHS. Usually delivery at that site is suggested rather than having the child born at a community hospital and then transporting an ill newborn to the medical center.

If the condition is not diagnosed before birth, it will likely be diagnosed shortly afterward. During fetal growth, oxygen-rich blood is supplied through the ductus arteriosus, a special blood vessel that connects the pulmonary artery to the aorta, allowing blood to bypass the lungs and left side of the heart. Because of this detour, the fetus is protected to a certain extent and usually shows no ill-effects from the disorder.  

If the infant has not been diagnosed before birth with a fetal ultrasound, the baby will likely appear to be normal at birth. Throughout this period, the severity of symptoms depends on the balance of blood flow between the lungs and the ductus arteriosus. If there is a good balance, the condition may not manifest itself immediately. If the balance is less than optimal, the child may appear slightly blue, or cyanotic, because of a lack of oxygen-rich blood. However, when the ductus arteriosus closes, which usually occurs in the first few days of life, the child will go into shock and cardiovascular failure. Surgery is required in most cases of HLHS for survival.  

HLHS is relatively common among congenital heart defects, affecting between 4 percent and 9 percent of all children with congenital heart disease. An estimated 1,000 babies are born every year in the United States with HLHS. Before the advent of modern treatments, HLHS was responsible for 25 percent of all infant deaths related to congenital heart disease.

A hypoplastic left heart syndrome (HLHS) baby tends to be born well developed, despite the serious defects on the left side of the heart. The reason for this healthy in–utero development is that the normal fetal circulatory system has an open ductus arteriosus, or connection between the pulmonary artery and the aorta that allows blood to bypass the lungs.

In an HLHS fetus, this in-utero system allows blood to circulate normally before the baby is born, despite the fact that the left ventricle is not helping to pump blood to the rest of the body. However, the ductus arteriosus normally closes soon after the baby takes its first breath, closing off the connection between the right ventricle and the aorta. As a result, the malformed left ventricle becomes solely responsible for pumping blood to the body, and the signs of HLHS quickly begin to appear.

Most infants with HLHS will manifest signs of their condition within 48 hours of birth, while still in the nursery. In some cases, however, an infant will be discharged and develop serious complications because the ductus closes spontaneously. In this case, the child may go into serious shock and experience multiorgan failure, seizures, kidney failure and other complications. The severity of these complications, and any long-term damage, depends on how long it takes to reach a hospital and how severe the resulting injuries are. When this happens, the emergency medical team will first seek to establish blood flow to the infant, then stabilize and regain function in his or her noncardiac internal organs.

Fortunately, with the advent of modern fetal ultrasound, HLHS is frequently diagnosed before birth, thus allowing physicians and parents time to develop a treatment plan immediately after birth.

Infants may appear healthy at birth, but signs of hypoplastic left heart syndrome (HLHS) soon become apparent after the ductus arteriosus closes. These signs include:

The sooner hypoplastic left heart syndrome (HLHS) is diagnosed, the more likely treatment will be successful. An HLHS diagnosis may be made either before or after birth. If the diagnosis is made while in-utero, a fetal echocardiogram may be used. Commonly referred to as an ultrasound, an echocardiogram allows the physician to see images of the developing fetus and its various organs and systems, including the heart and cardiovascular system.

If diagnosis is made before birth, parents will likely be offered the option of a medical termination of pregnancy (MTP), also referred to as a “therapeutic abortion.” This is a difficult and personal decision. If they choose to take the pregnancy to term, this period after diagnosis and before birth offers time for counseling and education and transfer of mother and baby to a center experienced in pediatric heart surgery.

After birth, diagnosis is made by any of the following methods:

The first surgeries to correct HLHS were developed in the early 1980s. Since then, these surgeries have been constantly refined and improved, and more and more children are able to survive the rigorous series of open-heart surgeries that are required to establish adequate circulation. Today, parents have new hope that their HLHS baby will be able to live a longer life. Open-heart surgeries are currently available to treat HLHS: heart transplant surgery and the Norwood procedure (followed by a series of three surgeries, each done at a different age, ranging from infancy through the toddler years). Both heart transplant and the Norwood procedure carry risks and are only performed by specialized pediatric heart surgeons.

Before surgery is performed, therapy for HLHS babies begins with an intravenous infusion of a drug called prostaglandin. If the child has been diagnosed before birth, prostaglandin administration will begin immediately after birth. This hormone-like substance will help keep the ductus arteriosus open, thus allowing oxygen-rich blood to reach the tissues of the body. Babies may also be put on a ventilator to assist breathing if necessary.

Heart transplants and HLHS

A heart transplant involves replacing the baby’s defective heart with a donated healthy heart (a relatively new procedure in newborns). The baby’s eligibility for a transplant is determined by the results of blood tests and other specific factors relating to the baby's health and potential for survival. Once that determination is made, he or she is entered into a computerized national waiting list.

There is a shortage of heart donors, especially within the newborn population. Each year, only about 300 transplants are performed worldwide on young people under the age of 18. Therefore, transplantation usually involves a long, uncertain waiting period during which the infant is on “standby” for a suitable heart. Some patients’ hearts give out before a suitable donor heart can be found.

Even if a donor heart match is made, transplantation carries a risk of rejection and the early development of conditions such as coronary artery disease or lymphoma – cancer of the lymph nodes. Lifelong use of medication to prevent rejection and infection must be taken, including the use of antibiotics before dental procedures and certain surgeries to prevent endocarditis. Lifelong medical management will be necessary, and the long–term results for newborn transplantations are not yet known.

Most pediatric cardiology surgical centers do not offer transplant as the initial option. The Norwood procedure and its modifications are by far the most frequently pursued approach for newborns with HLHS.

Norwood procedure for HLHS

The Norwood procedure, which was introduced in 1983, as well as other further surgeries that may include a bi-directional Glenn shunt, hemiFontan, and the Fontan procedure, are a series of three open-heart surgeries. Each open-heart surgery is done at a different age, ranging from infancy through the toddler years. The first two surgeries (Stages I and II) are designed to temporarily relieve blood flow problems to and from the lungs. The third surgery (Stage III) is used to permanently establish blood flow to the lungs by bypassing the heart. The three surgeries are done at three different ages, which are as follows:

Initial results from the surgery have been good. Overall, survival at five years is 70 to 75 percent and HLHS children have reached their teenage years. Research has found a higher incidence of learning disabilities, cerebral palsy and mental retardation among children who have undergone the procedure.

It is possible, however, that these complications are a result of different surgical methods than are in use today. Most of the children in these studies underwent their surgeries in the 1990s or late 1980s, when longer periods of circulatory arrest were common. Today, the operations have been refined and move more quickly, thus limiting the children's time on cardiopulmonary bypass. Follow-up studies will help determine if the deficits seen among earlier children are still present, meaning that they are related to HLHS itself rather than the surgical approach. Some modifications in routine child care, schooling, and activity participation may be necessary.

Researchers, however, are still looking for ways to improve the Norwood procedure. One study showed that a mechanical device called a ventricular assist device (VAD) might help infants survive the series of operations. This device helps the heart pump oxygen-rich blood from the heart to the rest of the body. The VAD for infants is still in research stages and there is very limited evidence about its use in humans in general.

It should be remembered that surgical treatment for this condition does not cure HLHS. It corrects most of the circulation problems but specialized medical care and medications to maintain the heart’s efficiency are required throughout life.

A condition even more rare than hypoplastic left heart syndrome (HLHS) is known as hypoplastic right heart syndrome. In this condition, the infant will be born well-developed but with chambers, valves and related blood vessels on the right side of the heart so malformed that they cannot efficiently pump blood to the lungs.

These defects result in severely reduced oxygen-rich blood supply throughout the body, and the baby will have a bluish tint (cyanosis) to the skin, lips, fingernails and other parts of the body. Like HLHS, the treatment options include open-heart surgeries, heart transplant surgery or the Norwood procedure.

Preparing questions in advance can help patients to have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following HLHS-related questions:

1. What centers have the most experience with this condition?
   
   
2. Can you give us the contact information for parental support groups for children with this condition?
   
   
3. Is our case suitable for catheter-based interventions before birth?
   
   
4. Will we need any special equipment at home to care for our infant in between surgeries?
   
   
5. When can we expect our child will achieve developmental milestones such as talking and walking? How will the child's development be affected in the first years of life?
   
   
6. What is the survival rate for children with this condition?
   
   
7. What is the recurrence risk of this condition and how may this impact on family planning?
   
   
8. If we choose to continue with the pregnancy when would we plan on admission to the hospital and would this effect the type of delivery, vaginal or caesarean section?  Also, when and where will the baby be delivered?
   
   
9. What kind of financial burden will this condition place on our family? What resources are available to deal with them?