Corrected Transposition of the Great Arteries (c-TGA) is a complex and unusual abnormality occurring in fewer than 1 percent of people with congenital (present at birth) heart disease. It occurs in males twice as often as females.

The condition is actually a combination of two heart abnormalities that cancel each other out, resulting in a condition in which the circulation of blood through the body is “correct.” That is, oxygen-poor blood from the body ends up going into the lungs to pick up oxygen and oxygen-rich blood from the lungs goes out to nourish the body.

It seems like a case of two “wrongs” making “right,” and while about 1 percent of people with this condition may go through life with no ill effects, the majority develop associated conditions that require treatment. They must remain under the care of a cardiologist throughout their lives.

In the normal heart, the right ventricle pumps (blue) blood to the pulmonary artery and lungs, and the left ventricle pumps (red) blood to the aorta and the body. The ventricle that pumps blood around the body’s system is called the systemic ventricle. This is the “left” ventricle under normal circulstances. The “right” ventricle has a different structure than the left ventricle. The right ventricle normally pumps blood to the lungs and works at a low pressure (about 25 mmHg). The left ventricle normally pumps blood to the body and therefore pumps at whatever pressure your blood pressure is (about 120 mmHg).

In congenitally corrected transposition, the position of the two ventricles is reversed so that the right atrium connects to the left ventricle and the left atrium connects to the right ventricle. The two great arteries (the aorta and pulmonary artery) therefore arise from the wrong ventricle. In other words, the aorta arises from the right ventricle and sends blood around the body; and the pulmonary artery arises from the left ventricle and takes blood to the lungs. You will note, however, that with this arrangement, while the blood is flowing through the wrong ventricles, it is still going in the correct direction, hence the term “congenitally corrected transposition.”

The medical terms for this arrangement are atrioventricular discordance (since the atria are connected to the opposite ventricles) and ventriculo-arterial discordance (since the ventricles give rise to the opposite artery). It is sometimes called “ventricular inversion.”

Additional problems within the heart are common in people with transposition of the great arteries. For people who have no associated heart defects, the condition may not cause much of a problem except that the chest X-ray or electrocardiogram may look abnormal (because of the unusual position of the ventricles and arteries). With time, since the right ventricle is not built to pump to such a high pressure, the right ventricle may weaken, dilate, and cause fatigue or breathlessness.

Congenitally corrected transposition of the great arteries is usually diagnosed while evaluating other problems associated with this heart defect. Tests may include echocardiogram, electrocardiogram and/or cardiac catheterization.

If there are no other heart abnormalities, people with the condition may not have symptoms throughout life, although this is very rare. Most often, the constant stress on the right ventricle weakens the ventricle and its tricuspid value. Regurgitation (leaking backwards) of the tricuspid valve produces a characteristic heart murmur, and congestive heart failure may develop due to the weakened pumping action of the right ventricle. Corrected transposition of the great arteries is often discovered due to symptoms that accompany other common heart defects present with this condition.

Most babies born with Congenitally Corrected Transposition of the Great Arteries also have other heart defects. Each condition has a treatment option. Depending on how serious each abnormality is, surgery may be necessary anytime from early infancy to adulthood. These defects include:

  • Ventricular Septal Defect (VSD) – This defect allows blood to mix between the two ventricles and may dilate and weaken the ventricles since they work harder because of increased blood volume. It may also allow venous (unoxygenated — blue) blood to mix with arterial (oxygenated — red) blood and give a bluish tinge to the skin, called cyanosis.

  • Pulmonary Stenosis (PS) – This is narrowing of the pulmonary valve. This obstruction makes the left ventricle work harder, but the left ventricle was built to pump at a higher pressure anyway.

  • Tricuspid Valve Regurgitation – The valve that enters the right ventricle (atrioventricular or AV valve) is the tricuspid valve and is a thin and delicate structure. In a normal heart, it functions in the low-pressure pulmonary circulation. In this anomaly, however, since the ventricles are “switched” or transposed, the valve is exposed to high pressure in the right ventricle. This pressure may cause the valve to leak blood backwards (regurgitation).

    As the right ventricle weakens and dilates with time it may pull the cusps of the tricuspid valve apart, causing it to leak even more. This is an added burden for the right ventricle, which has to pump blood to the body, but also has to cope with a leaky valve. The added burden may hasten its deterioration in function.

    Sometimes the systemic valve is intrinsically abnormal. Because this tricuspid valve usually sits in the right ventricle on the other side of the heart, it is called a left-sided or systemic AV valve since it is in the patient’s left chest. This helps avoid confusion when describing the AV valves.

  • Complete Heart Block – Because the ventricles are reversed, the conducting pathways in the heart are thin and fragile and may not conduct the electrical impulses around the heart normally. Thus, there is an increased chance of interruption of the electrical impulses before they reach the bottom chambers. This is called complete heart block and may need to be remedied with a pacemaker.

The standard surgical approach is to treat each condition associated with corrected transposition separately. This approach, however, does not solve the problem of the right ventricle having to do the work that is normally done by a larger, stronger left ventricle — pushing oxygen-rich blood throughout the body. Over time, this extra burden on the right ventricle results in gradual deterioration of function of the right ventricle and can lead to congestive heart failure.

Valve Regurgitation
Surgery to replace the tricuspid valve is considered before the pumping function of the right ventricle is impaired. If the ventricular pumping function is reduced, contraction may not return to normal even after a perfect valve replacement. The valve will need to be replaced before severe symptoms develop since symptoms occur late in the course of decreasing heart function. If the function of the right ventricle has become severely depressed, valve replacement surgery may no longer be possible or recommended. Heart transplantation may be considered.

Pulmonary Stenosis
In some cases, pulmonary or subpulmonary stenosis may occur. A conduit (tube) may be placed between the ventricle and pulmonary artery bypassing the obstruction. In other cases, the obstruction can be surgically removed or, if the obstruction is caused by a narrowed pulmonary valve, replacement or enlargement of the valve is considered.

Ventricular Septal Defect (VSD)
A VSD may occur in patients with corrected transposition. It is usually surgically closed in childhood, occasionally in adulthood.

Double Switch Operation
Today, more patients are being offered a “double switch” operation. At the time the surgeon fixes a defect such as a ventricular septal defect, he or she also reroutes the great arteries so that the ventricles are pumping blood in the direction of a normal heart. This is clearly a much more formidable surgical undertaking, with somewhat greater risk, but if successful, should result in better long-term health of ventricles, especially the over-worked right ventricle.

The best surgical approach to use today in patients with corrected transposition remains controversial, but as surgeons gain greater experience with the “double switch” operation and surgical risk decreases, there is increasing enthusiasm for this approach.

Source: MayoClinic.org