Tetralogy of Fallot is a combination of four heart defects that can result in a baby turning blue (or cyanotic) because of a lack of oxygen in the blood. It usually is diagnosed in infancy.
Its cause is thought to be due to environmental or genetic factors or a combination. It occurs slightly more often in males than in females.
The heart consists of four chambers: the two upper chambers, called atria, where blood enters the heart; and the two lower chambers, called ventricles, where blood is pumped out of the heart. Valves that act as one-way doors control the flow between the chambers and between the arteries.
The heart also has been pictured as two side-by-side pumps with one side pumping blood into the lungs and the other side pumping blood from the lungs back to the body. Blood is pumped from the right side of the heart up through the pulmonary valve and the pulmonary artery to the lungs, where the blood is filled with oxygen. From the lungs, the blood travels back down to the left atrium and left ventricle and is then pumped through another big blood vessel called the aorta to the rest of the body.
The four defects characteristic of this condition include:
- An abnormal opening in the wall separating the ventricles called a ventricular septal defect (VSD) that allows blood to go directly from the right to left ventricle without going through the lungs
- An overly muscular right ventricle, also called right ventricular hypertrophy
- A displaced aorta, also called overriding aorta or Ao, directly over the abnormal opening between the ventricles
- A narrowing of pulmonary valve or below the valve called pulmonary stenosis that partially blocks blood flow to the lungs
Babies with tetralogy are blue at birth or soon after, and have detectable heart murmurs, an extra sound in the heartbeat. Activity such as crying may exacerbate the condition and babies may have shortness of breath or may faint. Babies also may experience a “tetralogy spell” in which oxygen levels drop suddenly leading to irritability and then sleepiness or unresponsiveness.
Once tetralogy of Fallot is diagnosed, the immediate management focuses on determining whether the child’s oxygen levels are in a safe range. If oxygen levels are critically low soon after birth, a prostaglandin infusion is usually initiated to keep the ductus arteriosus open which will provide additional pulmonary blood flow and increase the child’s oxygen level. These infants will usually require surgical intervention in the neonatal period. Infants with normal oxygen levels or only mild cyanosis are usually able to go home in the first week of life.
Surgical correction of the defect is always necessary. Complete repair is usually done electively when the children are about six months of age, as long as the oxygen levels remain adequate.
The surgery involves:
- Closure of the ventricular septal defect with a synthetic Dacron patch so that the blood can flow normally from the left ventricle to the aorta.
- The narrowing of the pulmonary valve and right ventricular outflow tract is augmented (enlarged) by a combination of cutting away (resecting) obstructive muscle tissue in the right ventricle and by enlarging the outflow pathway with a patch.
- In some babies the coronary arteries will branch across the right ventricular outflow tract where the patch would normally be placed. In these babies an incision in this area to place the patch would damage the coronary artery so this cannot safely be done. When this occurs, a hole is made in the front surface of the right ventricle (avoiding the coronary artery) and a tube is sewn from the right ventricle to the bifurcation of the pulmonary arteries to provide unobstructed blood flow from the right ventricle to the lungs.
Survival of children with tetralogy of Fallot has improved dramatically over recent decades. In the absence of confounding risk factors, more than 95 percent of infants with tetralogy of Fallot successfully undergo surgery in the first year of life.
Most babies are fairly sick in the first few days after surgery, since the right ventricle is “stiff” from the previous hypertrophy (thickness) and because an incision is made into the muscle of the ventricle, making the muscle temporarily weaker. This right ventricular dysfunction usually improves significantly in the days following surgery.
Patients may also have rhythm problems after surgery. An abnormally fast rhythm (called junctional tachycardia) may occur and may require treatment with medication or the use of a temporary pacemaker. This abnormal rhythm is usually temporary and the rhythm generally will return to normal as the right ventricle recovers.
Patients are also at risk for slow heart rates after surgery due to heart block. Heart block may be caused by injury to or inflammation of the conduction system in the heart. In many patients, the conduction improves and normal rhythm returns. Rarely, a permanent pacemaker may be necessary.
Patients who have had repair of tetralogy of Fallot can also redevelop a narrowing at the outflow area or in the branch (left or right) pulmonary arteries, which will cause the right ventricle to pump at abnormally high pressures. If these problems occur, surgical intervention to further widen the outflow tract or pulmonary arteries may be necessary. Narrowing the pulmonary arteries can sometimes be treated without surgery, with balloon dilation of the vessels during cardiac catheterization.
Long-term follow-up with a cardiologist to detect recurrent or new problems as early as possible is essential.
Most adults with tetralogy of Fallot have had surgery during childhood. The adult with unrepaired tetralogy usually has milder cyanosis and a heart murmur or extra heart sound.