Hypoplastic Left Heart Syndrome, also known as HLHS, is a rare congenital heart defect in which the left side of the heart is severely underdeveloped. It is one of the most complex cardiac defects seen in newborns and remains probably the most challenging to manage of all congenital heart defects. It is very rare, diagnosed in only 600-800 births annually. In these babies with Hypoplastic Left Heart Syndrome, 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 "atretic" (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 (PDA)). 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, Hypoplastic Left Heart Syndrome is uniformly fatal, often within the first hours or days of life.
What is the treatment of HLHS?
The management of the newborn with Hypoplastic Left Heart Syndrome can be divided into the initial stabilization period and the operative / post-operative period. Even while diagnostic tests may be going on, the rapid stabilization of infants with Hypoplastic Left Heart Syndrome must begin as soon as the diagnosis is suspected. Catheters are placed, usually in the umbilical blood vessels, which 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. Even though the infant may have low oxygen saturations, supplemental oxygen is avoided since it tends to promote more blood flow to the lungs which may steal blood flow from the body and place excessive demands on the already stressed single 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. Close monitoring is essential to detect any organ dysfunction and maintain cardiopulmonary stability because infants with this anomaly may be very unpredictable and undergo quite sudden changes. There are essentially three treatment options that have been proposed for children with Hypoplastic Left Heart Syndrome. In the past, due to poor outcomes with available treatments at that time, no treatment was often recommended. Today it is rare that a family may choose not to treat a child with Hypoplastic Left Heart Syndrome, though in cases when the infant is unable to be satisfactorily stabilized no treatment may be advised.
Cardiac transplantation in the newborn period is performed as primary treatment for Hypoplastic Left Heart Syndrome at some centers in this country. While transplantation has the advantage of replacing the very abnormal heart of a child with Hypoplastic Left Heart Syndrome 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. Additionally, 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 limited (currently less than 15 years). The most commonly pursued treatment for Hypoplastic Left Heart Syndrome is "staged reconstruction" in which a series of operations, usually three, are performed 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 become 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 (called a modified Blalock-Taussig shunt) or from the right ventricle to the lung vessels (called a Sano modification). 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. These operations are described in more detail in the Heart Encyclopedia chapter on "Single Ventricle Cardiac Anomalies."
The Norwood operation is the most complex and highest risk procedure in the sequence of staged reconstruction for Hypoplastic Left Heart Syndrome. Current management at major pediatric heart centers has resulted in survival rates of 75 percent or better. The recovery period in the hospital following the Norwood operation is often unpredictable and complicated, averaging about 3 to 4 weeks. A small percentage of patients who leave the hospital may continue to experience significant problems in the first months of life. Occasionally, the right ventricle does not function well following the Norwood operation and in some case, cardiac transplantation may need to be considered.
If a child with Hypoplastic Left Heart Syndrome reaches the time for the second stage (about 4 to 6 months of age) without major complications, the survival through the Glenn and Fontan operations are much better, exceeding 90 percent with current methods. 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.
While the prognosis for the series of surgeries has greatly improved over the past 20 years, HLHS children still have a long road ahead. Life expectancy to date is unknown, but there are many early patients already in their mid 20's and enjoying life.