Tetralogy of Fallot

Overview

Tetralogy of Fallot (fuh-LOE), a form of congenital heart disease (CHD), affects normal blood flow to the heart. Four things contribute to create tetralogy of Fallot:

• Ventricular septal defect (VSD) – There’s a large hole in the wall between the two lower pumping chambers.
• Overriding aorta – The aorta sits over the hole between the bottom pumping chambers (ventricles).
• Narrowing in the outflow to the lungs – The pathway from the heart to the lungs (infundibulum) is smaller than normal, as are the pulmonary valve and main pulmonary artery.
• Right ventricular hypertrophy – Like any muscle, if the heart has to work harder, it becomes thicker.

Because of the large VSD defect and outflow obstruction, the muscle of the right ventricle becomes thicker. The degree of obstruction of blood to the lungs can vary from minimal to severe. It’s relatively common for the course of the main body artery to be rightward (rather than leftward) in tetralogy of Fallot. This is called right aortic arch.

Once blood comes into the right ventricle, it has two choices for where to go: either to the lungs or through the hole (the VSD) to the aorta and the body. If the right ventricle’s outlet is narrow, some of the blood will be forced across the VSD to the aorta. This oxygen-poor blood (blue blood) mixes with blood that is rich in oxygen (red in color) from the other ventricle and goes out to the body. When blue and red blood mix, the child’s skin coloration may turn bluish (cyanosis), evident mostly in the lips, tongue, and fingernails or toenails. In addition to the bluish discoloration, the heart muscles of the right ventricle will become thicker as it works hard to push blood through the narrow outlet.

According to the Centers for Disease Control and Prevention (CDC), about 1 in every 2,518 babies born in the U.S. each year are born with tetralogy of Fallot.¹ 

Progression and possible complications

Because the narrowing of the right ventricle outlet may not be severe initially, the skin of children born with tetralogy of Fallot typically doesn’t appear bluish right away. However, as the outlet becomes increasingly narrowed over time, more “blue” blood may pass through the VSD and out to the body, increasing the bluish color. Occasionally, the narrowing of the outlet and obstruction of blood flow to the lungs become so severe that the amount of blood flowing to the lungs is suddenly significantly reduced. As a result, since very little blood can reach the lungs, very little blood carrying oxygen returns to the heart. Not only may this lack of oxygen cause the child to faint (syncope), but it also intensifies the discoloration (referred to as a hypercyanotic spell, tetralogy spell, or “tet” spell). This can be a life-threatening medical emergency that requires immediate medical treatment.

If left unrepaired, tetralogy of Fallot will eventually cause the hardworking right ventricle to enlarge, resulting in right heart failure. In addition, blood clots that normally form in veins and are filtered in the lungs may cross the VSD from the right to the left ventricle and into the body, possibly causing damage to organs such as the kidneys or resulting in a stroke. Strokes are rarely seen in the first year of life, however. Children with tetralogy of Fallot, particularly those who undergo surgical treatment for it after age 1, may develop abnormal heart rhythms. This is due to damage to the right heart muscles from their added workload. Also, heart surgery to repair the defect may cause scarring of the heart muscles, which may contribute to abnormal heart rhythms later in life.

Treatment

Traditionally, surgery is performed at about 6 to 9 months of age, although it may be performed earlier if necessary. During the open-heart surgery, the surgeon closes the hole between the two ventricles and widens the right ventricle outlet by removing thickened muscles. A patch may be inserted to enlarge the outflow pathway of the right ventricle to the main pulmonary artery. The valve is typically disrupted in doing this, so no functional tissue remains. This allows there to be no narrowing but also allows leakage of blood from the lungs back into the right side of the heart. However, this is generally been well tolerated for many years.

Abnormalities with the branching pattern of the heart (coronary) arteries may result in placing a valved tube (conduit), rather than a patch, to allow flow from the heart to the lungs during surgical repair. These conduits may become narrow over time and may leak. Children can outgrow these conduits as well, as they don’t grow with the child. With a patch or conduit, significant leakage may develop over time, which will require the placement of a new valve or conduit to prevent blood from leaking back from the lung arteries into the right side of the heart. Special metal mesh tubes (stents) with attached tissue valves have been developed to allow less-invasive placement of new valves in the hospital’s catheterization lab rather than by open-heart surgery.

Follow-up care into adulthood

Regular follow-up care is recommended for people with tetralogy of Fallot. Of particular importance is monitoring the size of the heart’s right ventricle and leakage (or regurgitation) of the valve in the heart that allows blood to flow to the lungs (the pulmonary valve). Many tests may be recommended, including an echocardiogram, electrocardiogram, CT or MRI scan, and angiogram. Problems with an abnormally fast heartbeat may appear years after the heart is surgically repaired. Due to continuing abnormalities with the pulmonary valve and outflow of the heart’s right ventricle to the lungs, those with tetralogy of Fallot may require further surgeries or catheter-based procedures as adults. For some, emerging catheter-based pulmonary valve replacement may be an option to avoid some, but not all, future cardiac surgery. Tell your cardiologist if you develop fatigue, decreased energy that makes it difficult to perform everyday tasks, shortness of breath, palpitations (or feelings of a rapid heart rate or heart “racing” or “fluttering”), dizziness, passing, out or any other symptoms.

In people with congenital heart defects, heart disease acquired later in life can increase the chance of a heart attack, heart failure, sudden death, and stroke. Fortunately, acquired heart disease can be largely prevented by reducing or eliminating lifestyle risk factors such as smoking, poor diet, high blood pressure, high cholesterol, and lack of physical activity. Therefore, a heart-healthy lifestyle is strongly recommended, though be sure to speak with your doctor before starting any new physical activity.

References

1. Centers for Disease Control and Prevention (CDC)