Hypoplastic Left Heart Syndrome

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What is Hypoplastic Left Heart Syndrome?

Hypoplastic left heart syndrome (HLHS) is a rare congenital condition where the left side of the heart is not completely developed. This disrupts the blood flow through the heart and into the body (systemic circulation).

The left side of the heart pumps blood that is rich in oxygen to the rest of the body via the aorta, the largest artery of the body, and its branches. It consists of the upper chamber called the left atrium, the lower chamber called the left ventricle, the valve between the two chambers called the mitral valve and the valve between the left ventricle and the aorta called the aortic valve. In hypoplastic left heart syndrome, either of these structures including the beginning of the aorta could be affected, thus reducing the oxygen-rich blood supply to the rest of the body.

Since the right side of the heart has to take over the function of the left side, it is usually enlarged or thickened.

Other defects that may be present include:
  • Atrial septal defect (a hole in the heart between the left and right atrium).
  • Patent ductus arteriosus. The ductus arteriosus is a communication between the aorta and the pulmonary artery, which carries deoxygenated blood to the right atrium. It usually closes a few days after birth. If it does not, the condition is called patent ductus arteriosus.

    In HLHS, the atrial septal defect and the patent ductus arteriosus are actually beneficial in the initial days prior to the surgery. They allow the blood to move from the left side to the right side of the heart, from where it is taken to the lungs and the rest of the body. The ductus arteriosus is actually kept open and not allowed to close with medications, and an atrial septal defect is sometimes created so that circulation can be maintained till definitive surgery can be undertaken.
  • Coarctation of the aorta (narrowing of a part of the aorta).

What are the Causes & Risk Factors of Hypoplastic Left Heart Syndrome?

HLHS occurs due to a problem during the development of the baby during pregnancy. It affects boys more commonly than girls. Certain genetic syndromes that are associated with HLHS include:
Causes of Hypoplastic Left Heart Syndrome

Some families have a genetic disposition to develop HLHS So far, mutations in genes NOTCH1 and NKX2.5 have been identified in some HLHS cases.

Other risk factors could include:
  • Medications consumed during pregnancy
  • Certain environmental factors that affect the mother during pregnancy
  • Diet of the mother during pregnancy

What are the Symptoms of Hypoplastic Left Heart Syndrome?

The symptoms of HLHS manifest within a few hours or a few days (1 to 3 days) after birth; they typically become prominent once the ductus arteriosus closes. The child may suffer from cardiovascular shock (extremely low blood pressure) and collapse.

The symptoms include:
  • Skin feels cold and clammy
  • Bluish discoloration of the skin called cyanosis
  • Abnormality in breathing
  • Rapid pulse that is weak
  • Poor feeding, as a result of which tube feeding may be required in the initial days
The changes in the systemic circulation could result in metabolic acidosis and death. The average age of death for infants dying in the first 2 weeks is 4.5 days. Certain infants can survive for more than 60 days without any surgery, but mortality is 100% in the absence of surgery.

Symptoms of Hypoplastic Left Heart Syndrome

How Do You Diagnose Hypoplastic Left Heart Syndrome?

HLHS is diagnosed either before birth (prenatal) or post birth (postnatal).

Prenatal diagnosis -

High resolution ultrasonography has a specificity above 95% in identifying HLHS in fetuses. If there is a suspicion that the fetus may have HLHS, the physician may order a fetal echocardiogram to verify the diagnosis.

Fetal Echocardiogram Helps to Diagnose Hypoplastic Left Heart Syndrome

Postnatal diagnosis -

A heart problem may be suspected based on the symptoms of the baby. Additional tests that will be required include the following:

Blood tests: Blood tests may indicate electrolyte disturbances, an altered acid-base status, and reduced liver and kidney function.

Some of the tests used for diagnosis include:
  • ECG, to study the electrical activity of the heart. It helps to identify changes like right heart enlargement
  • Echocardiography, which shows structural changes and the blood flow to the heart. It is a treatment of choice in these patients
  • Chest X-ray, which may show the presence of an enlarged right heart. The chest x-ray is not diagnostic for the condition and is not a preferred test
  • Catheterization of the heart, but this test is usually not necessary for the diagnosis

How Do You Treat Hypoplastic Left Heart Syndrome?

Prostaglandin E1 infusion prevents the closure of the ductus arteriosus, and helps to maintain the circulation for short durations. Some babies may be needed to be put on a ventilator.

Metabolic acidosis, if present, should be corrected with sodium bicarbonate. Drugs to improve the contraction of the heart and reduce edema may also be required.

The baby has to undergo a series of surgery to prevent death. The surgeries do not correct the defects. Following the surgeries, the right side of the heart takes over the function of the left side, that is, pumping oxygen-rich blood to the whole body. In addition, the main arteries and veins are connected in such a way that the oxygen-poor blood does not have to come to the right side of the heart, but bypasses it and is directed directly to the lungs for oxygenation. The surgeries include:

Stage 1 (Norwood procedure): This surgery is performed in the first 2 weeks after birth. In this surgery:
  • The aorta is connected to the right side of the heart. Thus, the right side pumps blood to the body through this connection.
  • A tube is introduced that connects the right side of the heart or the artery to the pulmonary arteries that take the blood to the lungs to get oxygenated.
Despite the surgery, the skin could still appear bluish since oxygen-rich and oxygen-poor blood continue to mix in the right side of the heart

Norwood Procedure Surgery Is Performed to Treat Hypoplastic Left Heart Syndrome

Stages 2 (Hemi-Fontan or Bi-directional Glenn Shunt) and 3 (Fenestrated Fontan):

Stage 2 is performed on children between 4 and 6 months of age. In stage 2, the superior vena cava, the main vein of the upper part of the body and the pulmonary artery, which takes blood to the lungs for oxygenation are connected. As a result, the oxygen-poor blood from the superior vena cava goes directly to the lungs by bypassing the heart. Thus, the work of the heart is reduced.

The stage 3 procedure is performed in children between 18 months and 3 years. Here, the inferior vena cava, which brings oxygen-poor blood from the lower part of the body is connected to the pulmonary artery.

Cardiac transplantation: Cardiac transplantation may be recommended for children who are not candidates for the Norwood procedure, or suffer from complications following surgery. Donor shortage, however, is a limitation.

Comfort management: Some parents choose comfort care or palliative care as an option over surgery if they do not wish multiple surgeries for their baby. The parents should be provided adequate support during the difficult time.

What are the Complications Following HLHS Surgery?

Following HLHS surgery, the children may suffer from complications for the rest of their life. However, the rate of survival increases from a sure death in the absence of surgery to around 75% with surgery.

Complications that may occur following HLHS surgery include:
  • Abnormal heart rhythms
  • Fluid accumulation in lungs and tissues
  • Stroke or pulmonary embolism due to a blood clot in the brain or lungs, respectively
  • Neurological problems
  • Weakening of the heart requiring transplantation
  • Following transplantation, the child could suffer from complications like graft rejection and infections.

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