Transposition Of The Great Arteries- A Congenital Heart Defect.

Transposition of the great arteries is a serious but rare congenital heart defect present in which the two main arteries leaving the heart are reversed (transposed). Transposition of the great vessels is a cyanotic heart defect. This means there is decreased oxygen in the blood that is pumped from the heart to the rest of the body. It is usually detected either prenatally or within the first hours to weeks of life.

Pathophysiology: In normal hearts, blood that returns from the body goes through the right side of the heart and pulmonary artery to the lungs to get oxygen. The blood then comes back to the left side of the heart and travels out the aorta to the body.

In transposition of the great vessels, the blood goes to the lungs, picks up oxygen, returns to the heart, and then flows right back to the lungs without ever going to the body. Blood from the body returns to the heart and goes back to the body without ever picking up oxygen in the lungs.

Clinical Features: Symptoms of Transposition of the great arteries  include:

• Blue color of the skin (cyanosis)
• Shortness of breath
• Lack of appetite
• Poor weight gain

Risk Factors: Etiology for transposition of the great arteries is unknown and is presumed to be multifactorial. Some of the risk factors include: 

• A history of German measles (rubella) or another viral illness in the mother during pregnancy
• Poor nutrition during pregnancy
• Drinking alcohol during pregnancy
• A mother older than age 40
• A mother who has poorly controlled diabetes
• Down syndrome in the baby

Diagnosis: 

1. Chest X ray: (See picture above) On chest X-ray, transposition of the great vessels typically shows a cardio-mediastinal silhouette appearing as an "egg on a string", wherein in which the enlarged heart represents an egg on its side and the narrowed, atrophic thymus of the superior mediastinum represents the string.

2. Other tests include: 

• Cardiac catheterization
• ECG
• Echocardiogram (if done before birth, it is called a fetal echocardiogram)
• Pulse oximetry (to check blood oxygen level)

Management

1. Maintaining the Ductal Patency: Initial treatment consists of maintaining ductal patency with continuous intravenous (IV) prostaglandin E1 infusion to promote pulmonary blood flow, increase left atrial pressure, and promote left-to-right intercirculatory mixing at the atrial level. This is particularly important in patients with severe left ventricular outflow tract stenosis or atresia. Prostaglandin therapy may or may not benefit the patient with simple transposition of the great arteries (TGA) and an intact ventricular septum without left ventricular outflow tract obstruction.

2. Supportive Care: For the ill neonate, metabolic acidosis should be corrected with fluid replacement and bicarbonate administration.
Mechanical ventilation may be necessary if pulmonary edema develops in concert with severe hypoxemia.
Ultimately, the patient requires surgical repair or palliation early in life.

3. Surgery: Surgical approach depends on the age of the patient at presentation, the presence of associated congenital cardiac lesions, and the experience of the cardiothoracic surgeon with a given surgical technique. Most full-term neonates with uncomplicated transposition of the great arteries can undergo an arterial switch procedure in one operation, with minimal mortality.

A surgery called an arterial switch procedure is used to permanently correct the problem within the baby’s first week of life. This surgery switches the great arteries back to the normal position and keeps the coronary arteries attached to the aorta.

Prognosis: The child’s symptoms will improve after surgery to correct the defect. Most infants who undergo arterial switch do not have symptoms after surgery and live normal lives. If corrective surgery is not performed, the life expectancy is only a few months.