Hypoplastic left heart syndrome (HLHS)

What is hypoplastic left heart syndrome (HLHS)?

Hypoplastic left heart syndrome refers to a congenital condition characterized by a severely underdeveloped (hypoplastic) left ventricle that is not able to function properly and pump sufficient blood volume into the circulatory system. Both left heart valves, the aortic and mitral valves, are either partially or completely closed.

This condition can be associated with other malformations, especially of the cardiovascular system, as well as disorders of placental function. It constitutes around 3% of congenital heart defects, and affects male newborns around 1.5 times as often as female newborns. Nevertheless, it is the cause of one quarter of all heart-related deaths in newborns, and is therefore the most fatal heart disease among this age group. The prognosis has been improving in recent years thanks to specialized care, so that most of the affected patients survive to adulthood.

Cause: How does HLHS develop?

Hypoplastic left heart syndrome is a genetic disease. It may occur in isolation or in the context of higher-level syndromes such as a trisomy, Turner syndrome or Noonan syndrome.

Symptoms: How does HLHS present itself?

The classic symptoms of hypoplastic left heart syndrome include the following:

• Cyanosis (blue discoloration of the skin) particularly on the hands and feet: Once the blood pigment hemoglobin is loaded with oxygen, it is bright red and turns the skin pink. In hypoplastic left heart syndrome, not enough oxygen reaches the periphery, so a large part of the hemoglobin molecules are deprived of oxygen and take on a dark color.

• Dyspnea (difficulty breathing) resulting from fluid build-up in the lungs: In newborns, this is noticeable, for example, by a higher breath rate, loud breathing noises, nasal flaring and retractions between the ribs.

In the fetal blood circulation, there is a connection between the two atria of the heart, known as the foramen ovale, that normally seals within the first few weeks of life. There is also the ductus arteriosus in the fetus, a vascular connection between the pulmonary trunk, which originates from the right ventricle, and the aorta, the main artery, which originates from the left heart. In healthy newborns, the ductus arteriosus closes only hours after birth.

For as long as these two additional connections remain in the circulation, a child with hypoplastic left heart syndrome can survive. This is due to the fact that some of the oxygen-rich blood can pass from the lungs via the foramen ovale into the functioning right heart and from there via the ductus arteriosus into the large circulation, which is usually fed from the left heart.

If the ductus arteriosus closes, the symptoms increase suddenly. Then the following symptoms also occur:

• Weak pulses

• Cold skin

• Decreased urine production

• Lethargy or even coma

Unless the ductus arteriosus is immediately reopened, the result is general organ failure and death.

Diagnosis: How is HLHS diagnosed?

Before birth, hypoplastic left heart syndrome can already be diagnosed using ultrasound.

After birth, the symptoms described above will appear. Furthermore, auscultation results from listening with a stethoscope can provide a clue. The blood gas analysis will show an increased lactate level, since this is a substance that is produced when cells in the body are required to produce energy without oxygen. An X-ray can show fluid build-up in the lungs. The ECG may also show changes. After birth, the diagnosis is also confirmed by an ultrasound examination of the heart.

Therapy and surgery: What are the treatment options?

The little patients require care in the intensive care unit.

To keep the newborn alive, first of all the ductus arteriosus must be kept open. This is done by administering the drug prostaglandin via an intravenous infusion.

Heart surgery must be performed in the medium run. This is generally a three-stage Norwood heart operation. It involves restructuring the heart and circulation so that sufficient supply is then possible via a single-chamber heart. The first step of the operation is performed during the first week of life.

For particularly complicated malformations, a heart transplant is the alternative.

Daily routine and life with HLHS

Following surgery, patients with hypoplastic left heart syndrome have to undergo regular cardiac check-ups for the rest of their lives. After a heart transplant, it is also necessary to continuously take immunosuppressants, which prevent the body from rejecting the donor organ but also weaken the overall immune system, leaving patients more prone to infectious diseases.

A single chamber heart cannot endure the same stress as a healthy heart, meaning that great athletic performance is not possible. The children can, however, live a normal life, can play like healthy children and also engage in light sporting activities. They can easily judge for themselves how much stress they can take. The only thing that should generally be avoided is scuba diving at greater depths, since the increased pressure can dangerously reduce the return flow to the heart.

There is little data for adults, since survival rates have only improved significantly in recent years. Initial studies on a smaller scale suggest that the quality of life is similar to that of the normal population.

Which doctors & clinics specialize in HLHS?

Although the disease can be detected early by gynecologists during routine ultrasound examinations, hypoplastic left heart syndrome represents a pediatric condition which is treated in a neonatal intensive care unit.

The Norwood operation is considered one of the most demanding procedures in cardiac surgery and should only be performed in specialized cardiac surgery centers with the appropriate experience and expertise.