Hypoplastic left heart syndrome (HLHS) is a rare heart defect where the left side of the heart is underdeveloped and cannot provide effective circulation. For babies born with HLHS to survive, a heart vessel called the ductus arteriosus (1), which normally closes shortly after birth, needs to remain open so that blood can pass from the baby’s heart to the body. To keep the vessel from closing, doctors typically treat the baby with a medication called prostaglandin E1. Babies with HLHS also need to have a hole between the upper chambers of the heart (2) to allow oxygen-rich blood to pass into the heart so it can be pumped to the rest of the body. Babies with HLHS also have an underdeveloped mitral valve (3) and aortic valve (4), resulting in a small left ventricle (5), which cannot provide blood to the body. When Ian McDonagh was born 11 years ago, with hypoplastic left heart syndrome and no hole in his heart, there were almost no treatment options available for him. Watch the story of how his doctors saved Ian’s life and pioneered a new approach to treating HLHS.
This image is reprinted with permission from University of Michigan Congenital Heart Center.
In hypoplastic left heart syndrome (HLHS), the heart’s main pumping chamber (the left ventricle) and left-sided valves (mitral, aortic) are poorly developed. Due to its small size, inadequate valves 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 outwardly 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, and the placenta, not the lungs, supply oxygen to the blood of the fetus. This is facilitated by a blood vessel (the patent ductus arteriosus) present in all babies 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 and can lead to sudden, life-threatening shock.
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 a medication called prostaglandin that is given via an IV (intravenous) line. Keeping the blood vessel open can allow adequate blood flow to the baby's body. Once the blood flow to the body is re-established through the patent ductus arteriosus, one of the following three options may be pursued.
One strategy for treating HLHS is a series of surgeries that address the different heart defects. You can learn about all three surgeries here.
Another choice for children with hypoplastic left heart syndrome is primary heart transplantation. In this procedure, the child is kept on prostaglandin to keep the patent ductus arteriosus open or a stent is inserted into the ductus arteriosus to keep it open and allow blood to pass freely from the heart to the aorta. Once a heart becomes available, the child’s heart is removed and the new heart is implanted. Because of the scarcity of donor organs, potentially long wait times as well as the limited longevity of the transplanted heart, this route is less often chosen for babies with HLHS.
Following heart transplant, the child takes many medications to suppress the immune system for the rest of his or her life. This is necessary to prevent the body from rejecting the new heart.
Although a heart transplant is simpler to perform than the Norwood procedure, there are significant continuing issues with living with a transplanted heart. Serious infections can be picked up because the body’s immune system is suppressed by anti-rejection medications. Ongoing surveillance of the transplanted heart, including regularly scheduled sampling of heart tissue (biopies) are necessary.
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 are very challenging and may 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, both in the short term and in the longer term.