Hypoplastic Left Heart Syndrome (HLHS) is one of the most complex cardiac defects seen in the newborn and remains probably the most challenging to manage of all congenital heart defects.

In a child with HLHS, all of the structures on the left side of the heart (the side which receives oxygen-rich blood from the lungs and pumps it out to the body) are severely underdeveloped. The mitral and aortic valves are either completely closed, or they are very small. The left ventricle itself is tiny, and the first part of the aorta is very small, often only a few millimeters in diameter. This results in a situation where the left side of the heart is completely unable to support the circulation needed by the body’s organs, though the right side of the heart (the side that delivers blood to the lungs) is typically normally developed.

Blood returning from the lungs to the left atrium must pass through an atrial septal defect (ASD) to the right side of the heart. The right ventricle must then do a “double duty” of pumping blood both to the lungs (via the pulmonary artery) and out to the body (via a patent ductus arteriosus).

The patent ductus arteriosus, a normal structure in the fetus, is often the only pathway through which blood can reach the body from the heart. When the ductus arteriosus begins to close, as it typically does in the first days of life, the blood flow to the body will severely diminish resulting in dangerously low blood flow to vital organs and leading to shock. Without treatment, HLHS is fatal, often within the first hours or days of life.

Newborns with HLHS will typically have lower-than-normal oxygen saturations because all of the blood from the lungs (the oxygenated “red” blood) mixes together in the single right ventricle before being pumped out of the lungs and body. Cyanosis, therefore, may be the first clue to the presence of a serious underlying cardiac condition. Respiratory distress (difficult or fast breathing) is often present because the lungs will tend to receive an excessively large amount of blood flow. There is often no or just a faint murmur present in newborns with Hypoplastic Left Heart Syndrome.

The pulses may be very weak in all extremities on examination depending on flow through the ductus arteriosus. Lethargy, poor feeding, and worsening respiratory distress may be seen as the ducturs arteriosus closes. Ultimately, severe shock resulting in seizures, renal failure, liver failure, and worsening cardiac function may develop. Whether these problems are reversible depends on both the severity and the duration of shock.

This heart defect is one of the most readily diagnosed on fetal echocardiograms and is one of the most common cardiac defects picked up on screening obstetrical ultrasounds. Such early diagnosis of the anomaly allows for prompt intervention for stabilization at the time of birth so that severe shock may be avoided. Planning to deliver such an infant at a hospital capable of aggressive newborn resuscitation is important in improving the chances for a good outcome.

If the fetus has been diagnosed before delivery, stabilization measures are started immediately so the newborn does not become unstable. In newborns that are delivered and then suspected of having HLHS, stabilization begins even while diagnostic tests are going on. The rapid stabilization of these infants must begin as soon as the diagnosis is suspected.

Catheters are placed to allow medications to be given and blood to be obtained for testing. An infusion of prostaglandin, a medication that prevents the patent ductus arteriosus from closing, is begun, thus maintaining the pathway for blood to reach the body from the right ventricle.

Manipulations of medications and respiratory treatments (including possible mechanical ventilation) are performed to optimally balance the flow of blood to the body and the flow of blood to the lungs.

Treatment options for children with Hypoplastic Left Heart Syndrome include:

• Cardiac transplantation in the newborn period is performed as primary treatment for Hypoplastic Left Heart Syndrome. While transplantation has the advantage of replacing the very abnormal heart of a child with HLHS with one of normal structure, this treatment is limited by the scarcity of newborn organs available for transplantation and the life-long need for anti-rejection therapy. Although outcomes for transplantation continue to improve, and the incidence of rejection is lowest in patients transplanted as newborns, the average life span of the transplanted heart is currently less than 15 years.
• “Staged reconstruction” is the most commonly pursued treatment for HLHS. It involves a series of operations, usually three, to reconfigure the child’s cardiovascular system to be as efficient as possible despite the lack of an adequate left ventricle. These surgeries do not correct the lesion, and are instead considered “palliative”.The first operation in the staged approach is known as the Norwood operation and is typically performed in the first week of life. With the Norwood operation, the right ventricle becomes the systemic or main ventricle pumping to the body. A “new” or “neo” aorta is made from part of the pulmonary artery and the original, tiny aorta, which is reconstructed/enlarged to provide blood flow to the body. Finally, to provide blood flow to the lungs, a small tube graft is placed either from an artery to the lung vessels or from the right ventricle to the lung vessels. Because of the extensive reconstruction of the aorta that must be done, this operation is one of the most challenging heart surgeries in pediatrics.The subsequent operations in the staged reconstruction plan are the bi-directional Glenn procedure, typically done at 3 to 6 months of age, and the Fontan operation, typically done in children older than 2 or 3 years.

Almost all children with Hypoplastic Left Heart Syndrome will continue to need some cardiac medications to maximize the efficient function of their heart, and all will require regular periodic follow-up visits with their cardiologist to evaluate their cardiac function and detect late complications such as arrhythmias.