Tetralogy of Fallot: Information & Specialists in Tetralogy of Fallot

Tetralogy of Fallot is caused by a malformation of the vascular system during the embryonic period. Up until the fifth week of development, the aorta and the pulmonary artery together form the heart’s outflow tract. After that, a septum (aortopulmonary septum) forms, separating the two arteries.

In tetralogy of Fallot, this septum is displaced. As a result, the pulmonary artery, which originates from the right ventricle, is narrowed.

This displacement results in the anatomical malformations characteristic of tetralogy of Fallot:

• a narrowing of the pulmonary artery with an underdeveloped and consequently narrowed pulmonary valve (pulmonary stenosis)
• a hole in the heart’s septum (ventricular septal defect)
• an aorta positioned above this hole and thus over the right ventricle (transposition of the great arteries)
• a thickening of the muscular walls of the right ventricle. By building up more muscle mass, the heart attempts to pump more blood into the lungs and withstand the increased pressure in the ventricle (right ventricular hypertrophy)

Illustration of a heart affected by tetralogy of Fallot next to a healthy heart © Mariana Ruiz | Wikimedia

Normally, the aorta originates from the left ventricle. It runs downward through the chest and abdomen, supplying the body’s organs with oxygen.

In Tetralogy of Fallot, due to an incomplete separation, the aorta lies above the right ventricle. The aorta essentially “rides” over the hole in the septum. As a result, it also receives blood from the right ventricle.

This blood is supposed to pass through the pulmonary circulation and be oxygenated. It is therefore low in oxygen. In addition, the pulmonary artery is narrowed, so less blood reaches the lungs for oxygenation.

In summary, this means that less oxygen is transported to the body via the blood than normal. The severity of tetralogy—and thus the bluish discoloration of the skin and mucous membranes—depends on

• how much oxygen-poor blood enters the aorta, and
• how severely the pulmonary artery is narrowed and, consequently, how much less blood it transports.

The cause of the underlying malformation of the vascular system is not yet fully understood. About 32 percent of those affected have genetic abnormalities, such as trisomy 21 (Down syndrome). Therefore, a genetic component is assumed. In addition, the risk of recurrence in children of affected parents is reported to be between 1.2 and 8.3 percent.

Symptoms depend largely on the severity of the four characteristic malformations. They can vary greatly from person to person. No two cases of tetralogy are exactly alike.

If the narrowing of the pulmonary artery is only mild to moderate, sufficient oxygen-poor blood reaches the lungs. Affected children generally do not exhibit the typical cyanosis.

If, on the other hand, the narrowing is severe, oxygen deprivation occurs. This also causes the characteristic bluish discoloration of the skin and mucous membranes.

Newborns and infants are usually identified early on by

• a heart murmur caused by the narrowed pulmonary valve, as well as
• by cyanosis of varying severity around the mouth, on the lips, and on the tongue

. The bluish discoloration may become more pronounced, especially when the infant cries.

In addition, shortness of breath and reduced physical capacity become apparent as early as the first year of life. Children also frequently assume a crouching position (knees to the chest). This position improves the body’s oxygen saturation.

During periods of intense agitation or vigorous, prolonged crying, the outflow tract of the right ventricle may close completely. This can lead to an episode (hypoxemia) with

• marked cyanosis,
• shortness of breath, and
• loss of consciousness

. A hypoxemic episode requires emergency medical care. Parents of affected children should, in this case,

• immediately contact emergency medical services and
• place their child in a squatting position (bending the knees toward the chest), and
• try to calm the child down.

In recent years, early surgical correction of the anatomical malformations has become the standard of care.

However, the optimal timing for such a procedure remains a subject of debate. According to comparative studies, the average age for the procedure is between four and twelve months of age.

The goal of the correction is to close the hole in the heart’s septum and correct the malpositioned septum.

This cardiac surgical procedure is performed using a heart-lung machine. The surgeon first closes the hole in the septum. To do this, he uses a patch made of Gore-Tex material or a small piece of the child’s pericardium (patch closure).

Next, the surgeon removes the constricting muscle tissue (myectomy). Finally, the outflow tract is widened below the valve annulus by suturing in another patch.

If the pulmonary artery is also too narrow, it is widened using a patch as well.

If the valve annulus is severely narrowed, it must be cut through, flared open, and enlarged using a large patch. The patch extends from the wall of the ventricle across the opened valve annulus into the pulmonary artery. This procedure is also known as transannular patch enlargement plasty.

In some cases, it is necessary to replace parts of the pulmonary artery and its valve. If such a primary total correction is not possible, palliative measures are indicated. These aim to improve pulmonary blood flow.

Pulmonary blood flow can be improved with medication, surgery, or using a catheter.