In hypoplastic left heart syndrome (HLHS), the heart’s main pumping chamber (the left ventricle), is poorly developed. Due to its small size and limited ability to function, the left ventricle is not able to deliver enough blood to the body to sustain life. In this condition, other structures of the heart, including the mitral and aortic valves and the first portion of the aorta, are small (hypoplastic).
Babies born with HLHS are well developed, a surprise perhaps in view of their severe heart defect. Until birth, they are able to continue to develop because, before birth, one pumping chamber (in this case, the right ventricle) can adequately maintain proper blood supply (cardiac output) to the body. This is facilitated by a blood vessel (patent ductus arteriosus) present in all children before birth that connects the blood circulation of the body with that of the lungs. Even if the left ventricle is not properly developed, the right ventricle can compensate by pumping blood to the body through the patent ductus arteriosus.
However, when the patent ductus arteriosus naturally closes soon after birth, the amount of blood pumped out to the body is diminished significantly.
According to the American Heart Association, of the thousands of babies born each year with a cardiovascular defect, 4 to 8 percent have hypoplastic left heart syndrome.
Progression and Possible Complications
If hypoplastic left heart syndrome is not recognized and treated, the child will become severely ill. Without medical intervention, he or she will become progressively weaker. Death may occur in a matter of days or weeks.
Once hypoplastic left heart syndrome is discovered, the patent ductus arteriosus can be stimulated to remain open with medication (prostaglandin) given via an IV (intravenous) line. Keeping the vessel open can allow adequate blood flow to the body.
Once the blood flow to the body is re-established through the patent ductus arteriosus, one of three options may be pursued:
- At approximately 1 to 2 weeks of life: The right ventricle is made to pump blood to the body. This is accomplished by converging the blood vessel (pulmonary artery) that comes out of the right ventricle and goes to the lungs with the blood vessel (aorta) that emerges from the left ventricle and carries blood to the body. This step also includes removing the atrial septum (the wall between the heart’s two upper chambers) and placing a prosthetic blood vessel to handle blood flow to the lungs. A shunt is placed between one of the branches of the aorta and one of the pulmonary arteries. As a result, blood returning from the lungs to the left atrium will cross the surgically removed atrial septum and mix with blood coming back from the body in the right atrium. After the blood flows into and fills the right ventricle, it is pumped to both the body and lungs.
- At approximately 3 to 4 months of life: In this stage, the blood vessel that delivers blood from the upper part of the body (head, neck and upper extremities) to the heart is connected directly into the pulmonary artery. The shunt that was previously placed is removed. With this step, blood flow to the lungs comes directly from the upper part of the body without first going to the heart. This lifts some of the load from the heart since it no longer must pump blood to both the lungs and the body.
- At approximately 18 months to 6 years of life: At this stage, which is typically performed when the child reaches about 18 months of age, the vein (inferior vena cava) that brings blood back from the lower part of the body to the heart is also connected directly into the lung circulation, bypassing the heart and saving the heart (and its only functioning ventricle) the work of pumping blood to the lungs. Blood returning from the lungs (now rich in oxygen and pink in color) returns to the heart and is pumped out by the right ventricle into the aorta and to the body. After this stage, there is no pumping chamber connected to the lungs. Blood must flow passively through the lungs at this stage with the single ventricle being used to pump blood to the body.
Children treated with these staged surgeries may suffer from failure of the Norwood cardiovascular circulation (Stage 1). This may be due to any of several factors, including failure of the right side of the heart to pump blood to the entire body, high pressure in the blood vessels of the lungs due to lung disease, or abnormal heart rhythm.
Twenty to 40 percent of children die before or soon after all stages of surgery are performed. Long-term outcomes for this approach are not well known. Currently, the oldest people who have undergone these staged surgeries are in their 20s.
New 'hybrid' treatments are being developed where interventional cardiologists and surgeons work together at the same time to complete some of these procedures.
The other choice for children with hypoplastic left heart syndrome is heart transplantation. In this procedure, the child is kept on prostaglandin to keep the patent ductus arteriosus open. Once a heart becomes available, the child’s heart is removed and the new heart is implanted.
Following heart transplant, the child takes many medications to suppress the immune system for the rest of his or her life to prevent the body from rejecting the new heart.
Heart transplant is simpler to perform than the Norwood procedure – and the child is able to leave the hospital sooner. However, the chance of death from heart transplantation is high. Death can be due to serious infections picked up because the body’s immune system is suppressed. Or it may result from damage to the new heart caused by the immune system’s rejection of it.
A third option, which continues to be offered to parents of a child with such a severe heart defect, is to do nothing. This may appear odd in view of surgical options available today. However, hypoplastic left heart syndrome is severe – and the courses of managing it have limited success. The decision to do nothing and allow the child to pass away naturally is not unreasonable.
Parents of children who are found to have HLHS or other forms of single ventricle congenital heart disease should have an honest discussion with their cardiologist about the available treatments and outcomes of pursuing surgery.