Hypoplastic Left Heart Syndrome

Overview

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 isn’t 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’re 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, in certain circumstances, 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 Centers for Disease Control and Prevention, 1 out of every 3,841 babies born in the U.S. each year is born with HLHS.¹ 

Progression and possible complications

If HLHS in a child is not recognized and treated, the child will become severely ill. Without medical intervention, the child will become progressively weaker, with death possibly occurring in a matter of days or weeks.

Treatment

Once HLHS is discovered, the patent ductus arteriosus can be stimulated to remain open with a medication called prostaglandin that is given via an IV line. Keeping the blood vessel open can allow adequate blood flow to the baby's body. Once the blood flow to the body is reestablished through the patent ductus arteriosus, one of the following three options may be pursued:

• Staged surgeries – One strategy for treating HLHS is a series of surgeries that address the different heart defects.
• Heart transplant – Another choice for children with HLHS 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, often in conjunction with surgically placed pulmonary artery bands to balance the blood flow to the lungs. 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 and the limited longevity of the transplanted heart, this route is less often chosen for babies with HLHS. Following a heart transplant, the child must take many medications to suppress the immune system for the rest of the child’s life. This is necessary to prevent the body from rejecting the new heart.
• Comfort care – A third option, which continues to be offered to parents of a child with such a severe heart defect, is comfort care, which is essentially doing nothing. This may appear odd in view of surgical options available today; however, HLHS 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 perfectly reasonable. Parents of children who are found to have HLHS or other forms of single ventricle congenital heart disease (CHD) should have an honest discussion with their child’s cardiologist about the available treatments and outcomes of pursuing surgery, both in the short term and in the longer term.

References

1. Centers for Disease Control and Prevention (CDC)