HLHS

Definition

Hypoplastic left heart describes the underdevelopment of the left side of the heart (mitral valve, aortic valve, and aorta). The condition is congenital (present at birth).

Alternative Names

Causes

Hypoplastic left heart is a rare type of congenital heart disease. It affects less than 2 in every 10,000 live births.

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.

As with most congenital heart defects, there is no known cause. Around 10% of patients with hypoplastic left heart syndrome will have other birth defects.

Symptoms

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:

• Lethargy
• 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.

Exams and Tests

A physical exam 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.

Tests may include:

• ECG shows enlargement of the right ventricle of the heart
• X-ray of the chest may show signs of other birth defects
• Echocardiogram
• Cardiac catheterization

Treatment

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 maintain circulation of blood to the body.

These measures are only supportive; they do not solve the problem. The condition always requires surgery.

The first surgery, called the Norwood operation, occurs within the first few days of life. Stage I of the Norwood procedure consists of building a new aorta, and an artificial shunt is inserted to maintain blood flow to the lungs.

Afterwards, the baby usually goes home. The child will need to take one or more 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 Hemifontan procedure. This procedure connects half of the veins carrying blue blood from the body directly to the lungs that get oxygen. The surgery is usually done when the child is between 4 and 6 months of age.

During stage I and II, the child may still appear somewhat blue (cyanotic).

Stage III, the final step, is called the Fontan procedure. The remainder of the veins carrying blue blood from the body is connected directly to the lungs, and the right ventricle now serves as the only pumping chamber for the heart. This surgery is usually performed between the ages of 18 months and 3 years of age. After this final step, the baby is no longer blue (cyanotic).

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 to be a better alternative to the 3-step surgery process, but there are few donated hearts available for small infants.

Outlook (Prognosis)

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.

Possible Complications

Complications include:

• Irregular, fast heart rhythms (arrhythmias)
• Chronic diarrhea
• Heart failure
• Fluid in the abdomen (ascites)
• Blockage of the artificial shunt
• Strokes and other neurological complications
• Sudden death

When to Contact a Medical Professional

If your infant has new changes in breathing patterns, eats less (decreased feeing), or has skin or mucous membranes that are turning blue (cyanotic), contact your health care provider immediately.

Prevention

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.

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