When the two main arteries arising from the heart, the pulmonary artery and the aorta, are switched, causing unoxygenated blood to be pumped back out through the aorta into the circulation. The normal heart at far right is shown here for comparison.
skin is a bluish color, they are sometimes referred to as "blue babies." In some cases of transposition of the great arteries, there also may be other heart defects, such as ventricular septal defect.
Infants suffering from transposition are usually quite cyanotic, and if it is not corrected, they will probably not survive their first year of life. Before the advent of the heart-lung machine, there were some palliative operations developed, but these procedures were not cures. In fact, even today many infants with transposition undergo a procedure to make or enlarge a hole in the atrial septum shortly after birth. This procedure is done in the cardiac catheterization laboratory with a special catheter threaded up through a blood vessel in the groin. The hole in the atrial septum allows mixing of blood and temporarily improves the infant's condition until a surgical repair can be made.
Currently there are a number of ways this defect can be repaired surgically. One technique involves switching the pulmonary artery back to the right ventricle and the aorta back to the left ventricle. This procedure is technically challenging because the coronary arteries that come off the aorta are quite small, particularly in infants. These tiny coronary arteries have to be moved and reconnected to the aorta in its new location.
With current surgical techniques, the chances of surviving the surgical procedure, depending on the complexity of the transposition malformation, are between 90 and 95 percent. The long-term survival is good for most patients.
This complicated condition is actually four different congenital defects occurring simultaneously in the same heart. Tetralogy, in fact, means "set of four," and Fallot was a French physician who was one of the first to describe the condition.
In this defect (Fig. 7.7), 1) there is a ventricular septal defect; 2) blood flow from the right ventricle to the pulmonary arteries is obstructed (the obstruction can be at the pulmonary valve or in the right ventricular outflow tract leading to the valve and/or in the pulmonary arteries themselves); 3) the aortic valve overrides the ventricular septal defect; and 4) the right ventricle is abnormally thickened.
Superior Vena Cava
Pulmonary s\ VJ'1 Aorta /Artery
Inferior Vena Cava
Ventricular Septal Defect
Pulmonary Valve Fig. 7.7
Because of the location of the ventricular septal defect in relation to the aortic valve and the obstruction of blood flow through the pulmonary arteries to the lungs, unoxygenated blood returning from the body is shunted from the right ventricle to the left ventricle. It mixes with the oxygenated blood returning from the lungs, which results in blueness or cyanosis. In some forms of tetralogy of Fallot, the defects are more severe, particularly in terms of the amount of un-oxygenated blood flowing from the right ventricle across to the left ventricle. The more severe the obstruction, the more cyanotic the patient. In some cases, new-borns will suffer from severe cyanosis and may have to undergo urgent surgery.
In most cases, doctors recommend that the defect be corrected sooner rather than later, usually within the first six months of life. The surgical repair includes closing the ventricular septal defect and relieving the obstruction of blood flow to the pulmonary arteries. In some special circumstances, however, palliative shunting procedures are recommended before a complete repair is made.
Because of the cyanosis associated with this defect, patients used to be called
"blue babies," and the early surgical shunts, like the Blalock-Taussig shunt, that were performed were known as "blue baby operations." These operations would alleviate a good deal of the cyanosis and restore the children to a more normal color.
The chance of surviving a primary surgical repair is greater than 90 percent. Long-term survival in most of the patients whose defect is repaired is good.
If the defect is not repaired, serious complications can develop, including progressive cyanosis, strokes and infections of the brain, pulmonary hemorrhage, and severe hypoxic spells related to a lack of oxygen. Without surgical intervention, most patients with tetralogy of Fallot will not survive until their twentieth birthday.
Pulmonary valve stenosis is a narrowing of the heart valve located between the right ventricle and the pulmonary artery (Fig. 7.8). When the valve is very narrow, the patient may have substantial symptoms while still an infant, including a bluish tinge to the skin. This defect can be life threatening. In older children, symp-
Narrowed Pulmonary Valve
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