Hypoplastic left heart syndrome; HLHS
Hypoplastic left heart describes the underdevelopment of the left side of the heart (left ventricle, aortic valve, and aorta). The condition is congenital (present at birth).
Causes, incidence, and risk factors
Hypoplastic left heart is a rare type of congenital heart disease. The problem develops before birth when there is inadequate growth of the left ventricle and associated structures (aortic and mitral valves that guard the exit and entrance of the ventricle and the aorta which is the blood vessel that carries oxygenated blood from the left ventricle to the entire body).
In patients with this condition, the left side of the heart is unable to maintain blood circulation for the body. As a result, the right side of the heart must maintain the circulation for both the lungs and the body. This extra workload eventually causes the heart to fail.
The only possibility of survival is a connection between the right and the left side of the heart through which blood may pass. This is called a shunt. Babies are normally born with two of these connections (the foramen ovale and the ductus arteriosus), which spontaneously close a few days after birth.
If these structures are allowed to close in a baby with Hypoplastic left heart syndrome, however, the patient will quickly die because no blood will be pumped to the body.
There is no known cause of Hypoplastic left heart syndrome. Up to 40% of patients with this condition have other birth defects.
Initially, 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:
- Poor suckling and feeding
- Shortness of breath
- Rapid breathing
- Cold extremities
- Enlarged liver
- Poor pulse
- Pounding heart
- Bluish or poor skin color
- Sudden death
In healthy newborns, bluish color occurs in hands and feet as a response to cold (this reaction is called peripheral cyanosis).
However, a bluish color observed in the chest or abdomen, lips, and tongue is abnormal (called central cyanosis) because it reflects lack of adequate levels of oxygen in the blood. This is secondary to the heart malformation and circulatory malfunction. Central cyanosis often increases with crying.
Signs and tests
A physical examination usually reveals a blue, critically ill patient who may show signs of congestive heart failure, liver enlargement, rapid breathing, and lethargy. Additionally, the pulse at various locations (wrist, groin, and others) is usually very weak.
- An ECG shows enlargement of the right ventricle of the heart.
- An x-ray of the chest shows heart enlargement.
- An echocardiogram for the definitive diagnosis shows the tiny left ventricle
- A cardiac catheterization may be necessary in some cases to complement the echocardiogram.
Once the diagnosis of hypoplastic left heart is made, a nunber of things are done. First, the patient is put on a ventilator to assist with breathing if necessary. A medicine called prostaglandin E1 is started to prevent a shunt called the ductus arteriosus from closing. Intravenous fluids are started and medicine to help the heart beat stronger is often begun.
These measures are only supportive; they do not solve the problem. The next step is surgery.
There are two surgical approaches to Hypoplastic left heart syndrome. One is to do a heart transplant early in life. This means that a small donor heart, which is very rare, must be available. It also means that the patient will have to take a number of medicines to prevent rejection of the new heart.
The other option is a series of operations done over the first 3 years of life; this option is called the Norwood procedure. Stage I of the Norwood procedure is done within the first few days of life and consists of attaching the functioning right ventricle to the aorta (vessel that delivers blood to the body).
Because the lungs must still receive blood, a surgically created conduit (tunnel) is created to attach the a large artery in the chest to the pulmonary arteries (the vessels that lead to the lungs). This conduit is called a Blalock-Taussig (BT) shunt.
In the stage II operation, called the Glenn or Hemi-Fontan procedure, the superior vena cava (the vessel that removes deoxygenated blood from the head and arms) is attached to the pulmonary arteries and the BT shunt is removed.
During stage III, called the Fontan procedure, the inferior vena cava (the vessel that returns deoxyganted blood from the lower half of the body) is also attached to the pulmonary arteries. This is usually performed between the ages of 2-3 years. After the third stage the patient is no longer blue (cyanotic).
The Norwood procedure is relatively new, but outcomes have been good so far. While it is possible that these patients’ hearts eventually will fail and they will need a heart transplant, it is much easier to transplant an older patient than an infant.
If left untreated, Hypoplastic left heart syndrome is fatal. Survival rates for the staged repair continue to rise as surgical technique and postoperative management improve. Survival after the first stage is more than 75%.
It is important to note that the size and function of the right ventricle are important determinants of outcome after surgery.
If untreated, heart failure continues to worsen and will result in death.
Calling your health care provider
If your infant shows any of the symptoms of Hypoplastic left heart syndrome, contact your health care provider immediately.
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 any maternal diseases or behavior.
by Janet G. Derge, M.D.