Hypoplastic left heart syndrome occurs when parts of the left side of the heart (mitral valve, left ventricle, aortic valve, and aorta) do not develop completely. The condition is present at birth (congenital).
Causes, incidence, and risk factors
Hypoplastic left heart is a rare type of congenital heart disease. It is more common in males than in females.
As with most congenital heart defects, there is no known cause. About 10% of patients with hypoplastic left heart syndrome also have other birth defects.
The problem develops before birth when the left ventricle and other structures do not grow properly, including the:
- Aorta — the blood vessel that carries oxygen-rich blood from the left ventricle to the entire body
- Entrance and exit of the ventricle
- Mitral and aortic valves
This causes the left ventricle and aorta to be poorly developed, or hypoplastic. In most cases, the left ventricle and aorta are much smaller than normal.
In patients with this condition, the left side of the heart is unable to send enough blood to the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. The right ventricle can support the circulation to both the lungs and the body for a while, but this extra workload eventually causes the right side of the heart to fail.
The only possibility of survival is a connection between the right and the left side of the heart, or between the arteries and pulmonary arteries (the blood vessels that carry blood to the lungs). Babies are normally born with two of these connections:
- Foramen ovale (a hole between the right and left atrium)
- Ductus arteriosus (a small blood vesel that connects the aorta to the pulmonary artery)
Both of these connections normally close on their own a few days after birth.
In babies with hypoplastic left heart syndrome, blood from the right side of the heart travels through the ductus arteriosus. This is the only way for blood to get to the body. If the ductus arteriosus is allowed to close in a baby with hypoplastic left heart syndrome, the patient may quickly die because no blood will be pumped to the body. Babies with known hypoplastic left heart syndrome are usually started on a medicine to keep the ductus arteriosus open.
Because there is little or no flow out of the left heart, blood returning to the heart from the lungs needs to pass through the foramen ovale or an atrial septal defect (a hole connecting the collecting chambers on the left and right sides of the heart) back to the right side of the heart. If there is no foramen ovale, or if it is too small, the baby could die. Patients with this problem have the hole between their atria opened, either with surgery or using a thin, flexible tube (heart catheterization).
At first, a newborn with hypoplastic left heart may appear normal. Symptoms usually occur in the first few hours of life, although it may take up to a few days to develop symptoms. These symptoms may include:
- Bluish (cyanosis) or poor skin color
- Cold hands and feet (extremities)
- Poor pulse
- Poor suckling and feeding
- Pounding heart
- Rapid breathing
- Shortness of breath
In healthy newborns, bluish color in the hands and feet is a response to cold (this reaction is called peripheral cyanosis).
However, a bluish color in the chest or abdomen, lips, and tongue is abnormal (called central cyanosis). It is a sign that there is not enough oxygen in the blood. Central cyanosis often increases with crying.
Signs and tests
A physical exam may show signs of heart failure:
- Faster than normal heart rate
- Liver enlargement
- Rapid breathing
Also, the pulse at various locations (wrist, groin, and others) may be very weak. There are usually (but not always) abnormal heart sounds when listening to the chest.
Tests may include:
- Cardiac catheterization
- X-ray of the chest
Once the diagnosis of hypoplastic left heart is made, the baby will be admitted to the neonatal intensive care unit. A breathing machine (ventilator) may be needed to help the baby breathe. A medicine called prostaglandin E1 is used to keep blood circulating to the body by keeping the ductus arteriosus open.
These measures do not solve the problem. The condition always requires surgery.
The first surgery, called the Norwood operation, occurs within the baby’s first few days of life. Stage I of the Norwood procedure consists of building a new aorta by:
- Using the pulmonary valve and artery
- Connecting the hypoplastic old aorta and coronary arteries to the new aorta
- Removing the wall between the atria (atrial septum)
- Making an artificial connection from either the right ventricle or a body-wide artery to the pulmonary artery to maintain blood flow to the lungs (called a shunt)
Afterwards, the baby usually goes home. The child will need to take daily medicines and be closely followed by a pediatric cardiologist, who will determine when the second stage of surgery should be done.
Stage II of the operation is called the Glenn shunt or hemi-Fontan procedure. This procedure connects the major vein carrying blue blood from the top half of the body (the superior vena cava) directly to blood vessels to the lungs (pulmonary arteries) to get oxygen. The surgery is usually done when the child is 4 to 6 months of age.
During stages I and II, the child may still appear somewhat blue (cyanotic).
Stage III, the final step, is called the Fontan procedure. The rest of the veins that carry blue blood from the body (the inferior vena cava) are connected directly to the blood vessels to the lungs. The right ventricle now serves only as the pumping chamber for the body (no longer the lungs and the body). This surgery is usually performed when the baby is 18 months – 3 years old. After this final step, the baby is no longer blue.
Some patients may need more surgeries in their 20s or 30s if they develop hard to control arrhythmias or other complications of the Fontan procedure.
In some hospitals, heart transplantation is considered a better choice than the three-step surgery process. However, there are few donated hearts available for small infants.
If left untreated, hypoplastic left heart syndrome is fatal. Survival rates for the staged repair continue to rise as surgery techniques and care after surgery improve. Survival after the first stage is more than 75%.
The child’s outcome after surgery depends on the size and function of the right ventricle.
Blockage of the artificial shunt
Chronic diarrhea (from a disease called protein losing enteropathy)
Fluid in the abdomen (ascites) and in the lungs (pleural effusion)
Irregular, fast heart rhythms (arrhythmias)
Strokes and other nervous system complications
Calling your health care provider
Contact your health care provider immediately if your infant:
- Eats less (decreased feeding)
- Has blue (cyanotic) skin
- Has new changes in breathing patterns
There is no known prevention for hypoplastic left heart syndrome. As with many congenital diseases, the causes of hypoplastic left heart syndrome are uncertain and have not been linked to a mother’s disease or behavior.