Congenital heart disease is estimated to occur in about 7 out of every 1000 children born alive. Double inlet left ventricle (DILV) is a very rare condition in which the heart chambers and valves are malformed. It occurs in about 5-10 of every 100 000 babies born alive.
In DILV, the heart has only one functioning ventricle, the left, instead of the normal two pumping chambers, the right and the left ventricle. The right ventricle in these children is small and may not be fully formed. The left ventricle receives all the venous blood from the body, through the right and left atria. In turn, it pumps blood out through the aorta and the pulmonary trunk, to the body and the lungs respectively.
The blood in the left ventricle is a mixture of deoxygenated blood from the body received through the right atrium, and oxygen-rich blood from the lungs, received through the left atrium. This means that the blood pumped out to the rest of the body is not as rich in oxygen as usual. For this reason, children with DILV are slow to feed and gain weight at a normal rate.
In addition, the pumping of blood through the pulmonary trunk by the left ventricle leads to too much blood reaching the lungs, leading to pulmonary congestion. This may hinder proper oxygen transport into the blood in the alveolar capillary bed, further reducing the blood oxygen content.
DILV is diagnosed before birth in a minority of cases. In most cases, the diagnosis is post-natal and is prompted by the child’s symptoms, including breathlessness, failure to thrive and cyanosis.
Other clinical signs include:
- Signs of heart failure such as edema of the abdomen and the legs, breathlessness and frequent coughing due to the buildup of fluid around the lungs
- Abnormalities of heart rhythm picked up on an ECG (electrocardiogram)
- Heart murmurs or abnormal heart sounds
- Abnormally rapid heartbeat
Diagnosis is made by an echocardiogram. This diagnostic test consists of imaging the heart by ultrasound scanning, and can show the anomalies with accuracy, without exposing the infant to ionizing radiation. Greater sensitivity may be achieved, if required, using MRI (magnetic resonance imaging). Electrocardiography and chest X-rays may also be performed as indicated. In some centers, cardiac catheterization may also be done. This procedure consists of passing a flexible thin tube into the heart to visualize the chambers and valves.
DILV is a serious condition and cannot be corrected. However, in many cases, the symptoms and complications may be reduced or prevented by surgery. The timing of surgery depends on the severity of the anomaly, the presence of other abnormalities, and the general condition of the baby. More than one procedure is usually recommended and several stages of surgery are required.
Initial surgery is aimed at correcting the pulmonary vascular flow. In most cases this is excessive. To correct it, pulmonary artery banding is performed. This will narrow the vessel and reduce the amount of blood flowing to the lungs.
When the blood flow to the lungs is deficient, on the other hand, a shunt operation is performed. In this case, a bypass is created between the aorta and the pulmonary artery to allow more blood to reach the lungs.
In some children, associated anomalies will require early treatment as well.
The Fontan Procedure
The most common procedures to manage DILV include:
- A bidirectional Glenn shunt or Hemi-Fontan procedure at around 4-6 months of life
- A Fontan palliation which improves circulation enough to provide a better quality of life
The Fontan procedure is a staged procedure. The adoption of different stages allows for the infant’s body to adapt to the drastic changes in circulation following each surgery. Other intermediate operations to prepare for the final Fontan circuit may also be performed between the stages.
The first stage involves the creation of a cavopulmonary shunt between the superior vena cava and the right pulmonary artery. This immediately reduces the degree of mixing of deoxygenated blood with oxygenated blood. This is called the bidirectional Glenn shunt or Hemi-Fontan procedure. The child is still cyanotic following this surgery, but symptoms are considerably improved.
At a later stage, the inferior vena cava may also be connected to the right pulmonary artery to further improve pulmonary hemodynamics. This total cavopulmonary shunt achieves the final result, and is called the Fontan procedure. This may be achieved via an artificial extracardiac channel, once the patient is able to accept a prosthesis large enough to handle an adult’s venous blood flow.
Another option is the lateral tunnel technique, which creates a channel within the right atrium with a prosthetic baffle. The tubular channel ensures unobstructed flow of venous blood into the right pulmonary artery with exposure of a small part of the right atrial wall to increased pressures.
It ensures that the baby is not cyanotic and offers a reasonable quality of life in uncomplicated cases, usually performed between 18-36 months of life.
Complications of the Fontan procedure include:
- Mortality, either early or late
- Exercise intolerance
- Cardiac enlargement
- Impaired ventricular function
- Arrhythmias or conduction blocks
- Liver enlargement
- Protein-losing enteropathy following lymphatic disturbances
- Thrombosis of systemic veins
- Edema of the limbs
Other surgeries may be required while the baby is waiting for the Fontan procedure. In addition, the child may need to take multiple medications such as anticoagulants, diuretics, digitalis and ACE inhibitors throughout life, or before and after surgery. In the most severe cases, a heart transplant may be recommended once the patient reaches adulthood.
It is important to realize that the Fontan procedure is evolving over time. The patients treated in this way, remain prone to an increasing incidence of heart failure, heart arrhythmias such as supraventricular arrhythmias, primarily because of right atrial dilatation, and pulmonary hypertension, over longer follow-up periods.