The left side of the heart is underdeveloped in patients who have hypoplastic left heart syndrome (HLHS). The left side of the heart is made up of the left atrium, the left ventricle, the aorta, and the mitral and aortic valves. Blood is pumped to the body by these structures. In HLHS, the left ventricle is too small or absent, the aorta is too narrow or blocked, and the mitral and aortic valves are too small or closed. Therefore, the left side of the heart cannot pump enough blood to the body, and the right side has to work harder.
The exact cause of HLHS is unknown, but it is believed to be a combination of genetic and environmental factors. Some possible risk factors include:
Family history of congenital heart defects
Maternal infections, such as rubella, cytomegalovirus, or toxoplasmosis, during pregnancy
Maternal exposure to certain medications, such as anti-seizure drugs, retinoic acid, or nonsteroidal anti-inflammatory drugs, during pregnancy
Maternal exposure to certain substances, such as alcohol, tobacco, or cocaine, during pregnancy
Maternal diabetes, obesity, or lupus, during pregnancy
In most cases, HLHS is detected before birth using fetal ultrasounds, or after birth using physical examinations and echocardiograms. The symptoms of HLHS can vary depending on the severity of the condition and other defects present, but some common symptoms are listed below.
Bluish or pale skin, lips, or nails (cyanosis)
Rapid or difficulty breathing
Poor feeding or growth
Lethargy or irritability
Cold hands or feet
Weak pulse or low blood pressure
Sweating or clamminess
HLHS can be diagnosed by various tests that evaluate the structure and function of the heart, such as:
Fetal ultrasound, which uses sound waves to create images of the unborn baby’s heart and detect any abnormalities
Echocardiogram, which uses sound waves to create images of the heart and measure its size, shape, and blood flow
Electrocardiogram (EKG), which records the electrical activity of the heart and detects any arrhythmias or abnormal rhythms
Chest X-ray, which uses radiation to create images of the chest and lungs and detect any enlargement of the heart or fluid in the lungs
Cardiac catheterization, which involves inserting a thin tube through a blood vessel into the heart and injecting a dye to visualize the blood vessels and measure the blood pressure and oxygen levels
The main goal of treatment for HLHS is to improve blood flow to the body and reduce the workload of the right side of the heart. Treatment may include:
Blood bypasses the left side of the heart with the help of prostaglandins, which keep the ductus arteriosus (a blood vessel connecting the pulmonary artery and the aorta) open
Surgery, which involves a series of three operations to reconstruct the heart and redirect the blood flow. A Norwood procedure is usually performed within the first week of life, and involves creating a new aorta from the pulmonary artery and connecting it to the right pulmonary artery through a shunt (a small tube). In order to reduce pressure on the right side of the heart, the second operation, called the Glenn procedure, is usually performed between 3 and 6 months of age and involves connecting the superior vena cava to the right pulmonary artery. Thirdly, the Fontan procedure involves connecting the inferior vena cava (a large vein that transports blood from the lower body) to the right pulmonary artery to complete the blood flow redirection.
Heart transplant, which involves replacing the defective heart with a healthy donor heart. This is usually considered as a last resort when the other treatments fail or are not suitable.
HLHS cannot be prevented, but some steps can be taken to reduce the risk of having a baby with HLHS, such as:
Getting regular prenatal care and screening tests, such as fetal ultrasound, to detect any heart defects early and plan for the best treatment options
Avoiding infections, medications, substances, or conditions that may harm the baby’s heart development during pregnancy
Taking folic acid supplements before and during pregnancy to prevent neural tube defects that may affect the heart
Seeking genetic counseling or testing if there is a family history of congenital heart defects or other genetic disorders that may increase the risk of HLHS
By following the doctor's advice and following the treatment plan, and getting support from family, friends, and health care professionals, one can cope with HLHS challenges and complications.
