Hypoplastic Left Heart Syndrome (HLHS)

What is HLHS?

In order to fully understand this congenital heart defect, it is helpful to know how a healthy heart works. The human heart has four chambers—the right atria and ventricle, and the left atria and ventricle. The atria are the upper chambers, and the ventricles are the lower chambers. In a healthy heart, the right and left sides of the heart work together. The right side sends blood to the lungs, where it picks up oxygen. The blood returns to the left side of the heart, where it is pumped into the aorta and circulates through the entire body.

In babies with HLHS, the left atria, mitral valve, left ventricle, aortic valve and the aorta are so poorly formed that the left side of the heart cannot do its job of pumping blood to the body. This means the right side of the heart must also perform the work of the left side to ensure blood reaches both the lungs and the body. While the heart may function this way for a short time (days), it cannot sustain this workload forever.

During fetal development, two connections exist between the right and left sides of the heart. These openings are the ductus arteriosus (a small vessel that connects the pulmonary artery to the aorta) and the foramen ovale (PFO) or atrial septal defect (ASD) - a hole between the right and left atrium. During the first hours and days of life, oxygen-rich blood can mix through these openings in a child born with HLHS. However, when these holes close naturally in the days after birth, it becomes difficult for oxygenated blood to reach the body, and the baby will begin to show symptoms.

When a baby does not have a PFO or ASD, the effects of HLHS are more serious. In these cases, deliveries must be carefully planned because infants require immediate attention by expert cardiologists or surgeons at birth. Maternal fetal medicine specialists, pediatric heart surgeons and pediatric cardiologists at Riley at IU Health work as a team to coordinate care for mothers and babies in an advanced facility that places operating rooms side-by-side with delivery rooms.

What causes HLHS?

Researchers have not yet discovered the cause of HLHS. Families that have one child with HLHS also have a higher risk of having another child with the same condition. Given the genetic link to this condition, some families choose to better understand their risk through genetic counseling. Expert doctors and genetic counselors in our Cardiovascular Genetics Program can work with your whole family to evaluate and screen for inherited cardiovascular disease.

What are the signs and symptoms of HLHS?

Babies with HLHS show signs or symptoms at birth or shortly after. Doctors and parents may notice:

• Lethargy, drowsiness or inactivity
• Cold extremities
• Respiratory distress, such as rapid or difficult breathing
• Poor ability to feed
• Pounding heart
• Blue or gray coloring (cyanosis)

Key Points to Remember

• HLHS is a congenital heart defect that occurs when the main structures on the left side of the heart fail to develop.
• Because of this defect, the right side of the heart must do double-duty for blood to circulate all through the body.
• There is no cure for HLHS, but a series of three operations, performed between birth and 3 years of age, can improve the heart’s function.
• Children with HLHS may continue to experience problems that require management by a cardiologist who specializes in congenital heart disease. Once they reach adulthood, they should seek care from a cardiologist who specializes in caring for adults with congenital heart disease.