Introduction
The cardiovascular system comprises the heart and blood vessels (arteries and veins). In normal circulation, blood that is low in oxygen returns from the body in veins to the right side of the heart. It is pumped from the right ventricle (right lower chamber) to the lungs through the pulmonary artery. Blood gets oxygenated in the lungs and returns to the heart. Once blood reaches the heart, it is pumped from the left ventricle (left lower chamber) to the body through the aorta, the largest blood vessel. The right side controls pulmonary circulation in a normal healthy heart, whereas the left controls systemic circulation.
What Is ‘Transposition of the Great Vessels’ (TGA)?
The aorta and pulmonary arteries are referred to as the great arteries. Shortly after leaving the heart, the aorta gives off two offshoots called the coronary arteries. These coronary arteries supply the heart with blood. In the transposition of the great arteries, the blood vessels aorta and the pulmonary artery are atypically connected to the heart. This means that the blood returning from the body (which is low in oxygen) is pumped out of the right ventricle to the aorta and back to supply the body. At the same time, blood from the lungs rich in oxygen (oxygenated blood) is pumped from the left ventricle (left lower heart chamber) to the pulmonary artery and then goes back to the lungs. It is a congenital birth defect (defect present at birth). The consequence of transposition of the great arteries is that oxygen cannot be delivered to the body adequately, and unless treated quickly, the infant is unlikely to survive. Transposition of the great vessels (TGA) accounts for three percent of all congenital heart diseases. It affects males more than females (3:1) and is also associated with DiGeorge syndrome, which is usually caused by the deletion of chromosome 22q11.
What Are the Different Types of Transposition of Great Arteries (TGA)?
There are two ways in which the great arteries can be transposed. They are:
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Dextro-Transposition of the Great Arteries (D-TGA): Also known as complete transposition of the great arteries, it is the most common form and elicits symptoms right at birth. Unless treated immediately, the infant is unlikely to survive.
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Levo-Transposition of the Great Arteries (L-TGA): Also referred to as ‘congenitally corrected transposition, it is a less common condition and does not always elicit symptoms right at birth. Treatment varies, and targeted measures are taken depending on the heart defect present at birth.
What Are the Symptoms Elicited by D-Transposition of the Great Vessels (D-TGA)?
Most symptoms are typically seen within the first 30 days of life (neonatal period). The telltale sign and symptoms seen in an infant born with this defect are as follows:
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Severe Cyanosis: It is the bluish skin discoloration that occurs due to a decrease in the oxygen supply and does not resolve on its own. Cyanosis can vary, depending on the presence or absence of other additional heart defects. The infant also has cold extremities.
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Tachypnea: Increased respiratory rate to compensate for the decreased oxygen in the blood circulation.
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Tachycardia: Increased heart rate to compensate for the decreased oxygen in the blood circulation.
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Murmurs: These are heart sounds that can be heard only when additional defects like ventricular septal defect (VSD) and pulmonary stenosis exist.
What Are Other Heart Conditions Seen in Individuals Diagnosed With D- Transposition of the Great Vessels (D-TGA)?
Several other cardiac conditions are associated with the transposition of the great arteries, such as:
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Ventricular Septal Defect (VSD): A common congenital birth defect that occurs when a hole forms in the ventricular septum. The ventricular septum separates the lower heart chambers from each other (left and right ventricles). This defect alters blood flow and shunts blood from the left side of the heart to the right side, leading to an increased blood flow to the lungs. Minor defects usually close up soon, but intervention is needed for large defects.
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Atrial Septal Defect (ASD): A congenital heart defect characterized by an atrial septum opening. The atrial septum separates the upper two chambers from each other (the right and left atrium, respectively). It accounts for 10 to 15 percent of all heart defects.
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Patent Ductus Arteriosus (PDA): It is a congenital heart defect in which the ductus arteriosus does not close after birth, resulting in an increased pulmonary blood flow. Ductus arteriosus refers to an artery that connects the pulmonary artery to the aorta.
Typically, these defects can lead to severe complications. Still, for individuals diagnosed with D- transposition of the great vessels (D-TGA), these defects tend to be beneficial to a certain extent as they allow oxygenated blood to flow through the body until surgical intervention is done to restore proper blood flow.
How Is D-Transposition of the Great Vessels (D-TGA) Diagnosed?
There are several methods of diagnosing D-transposition of the great vessels (D-TGA), such as:
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Electrocardiogram (ECG or EKG): With the help of numerous electrodes (electrodes are tiny sensors that are adhered to different parts of the body), it records the electrical signals from the heart, which helps in identifying the extra or irregular heartbeats and helps locate the origin of the extra heartbeat as well. It is a rapid and painless test.
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Chest Radiography Chest X-Ray: It records black and white images of the lungs, heart, and airways using special beams of radiation called the x-ray beam.
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Cardiac Catheterization: Conventional angiography or cardiac catheterization has always been the go-to procedure for the analysis of the human heart and its associated conditions. It is an invasive technique that involves the use of a slender, flexible tube called a catheter. The catheter is inserted into the blood vessel for visualization of the structures of concern. Occasionally, the physician may advise a contrast angiography. Contrast angiography uses a special dye which is used to amplify the images.
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Echocardiogram: A test that employs the use of ultrasonography to inspect the abnormalities of the heart and its supporting tissues.
What Is the Treatment for D-Transposition of the Great Vessels (D-TGA)?
Restoring blood flow is the fundamental goal of the treatment so that the body can receive oxygenated blood. The following surgical procedures are performed sequentially-
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Balloon Atrial Septostomy: This procedure is performed immediately once a baby is born with this defect to increase the oxygen saturation in the blood and is done by enlarging the foramen ovale. The foramen ovale is a natural hole between two collecting chambers of the heart (right and left atrium). This surgery is not a permanent solution and helps buy time until the infant is ready for major heart surgery.
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Arterial Switch Operation (ASO): This surgical procedure aims at switching the positions of the great arteries (both the pulmonary artery and the aorta) to their anatomically correct positions. This procedure is done in patients who do not have severe pulmonary stenosis. If the patient has other heart defects, such as the ventricular septal defect (VSD), they are also repaired in this surgery.
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Rastelli Procedure: This surgery is advised for patients with significant ventricular septal defect (VSD) and severe pulmonary stenosis. A baffle (tunnel) is created between the right and left atria, which improves the oxygen saturation in the blood.
Conclusion
D-transposition of the great vessels, also referred to as D-TGA, is a critical congenital heart defect in which the aorta and pulmonary artery swap positions, which leads to a decrease in oxygen saturation. The prognosis in such individuals is excellent following surgical correction (the survival rates are greater than 90 percent).
