Transposition of the Great Arteries
Signs, Symptoms, Diagnosis, Treatments and Results
Explanation | Signs and Symptoms | Diagnosis | Treatments | Treatment Results
What is Transposition of the Great Arteries?
The "great arteries" in this anomaly refer to the Aorta and the Pulmonary Artery, the two major arteries carrying blood away from the heart.
In cases of Transposition of the Great Arteries, these vessels arise from the wrong ventricle. They are "transposed" from their normal position so that the aorta arises from the right ventricle and the pulmonary artery from the left ventricle.
Other heart defects may occur along with Transposition of the Great Arteries. About 25 percent of children with Transposition will also have a ventricular septal defect (VSD). In nearly a third, the branching pattern of the coronary arteries as they leave the transposed aorta is unusual. Infants may also have narrowing below the pulmonary valve which blocks blood flow from the left ventricle to the lungs.
Transposition creates a situation where the systemic (to the body) and pulmonary (to the lungs) circulations are in parallel rather than in series.
This means the oxygen-poor ("blue") blood returning from the body to the right atrium and right ventricle is pumped out to the aorta and to the body, while the oxygen-rich ("red") blood returning from the lungs to the left atrium and ventricle is sent back to the lungs via the pulmonary artery.
Unless there is some place in the circulation where the oxygenated and unoxygenated blood can mix, all of the organs of the body will be deprived of necessary oxygen.
Thus, in order to survive prior to surgery, the blood must mix somewhere in the heart or the body. If present, a ventricular septal defect (VSD) will allow some mixing, but often this does not allow enough mixing. Other places that mixing may occur are through an atrial septal defect (ASD) or a patent ductus arteriosus (PDA). Techniques used to improve mixing before surgery are described below.
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Transposition signs and symptoms
Transposition is almost always diagnosed in the first hours or days of life due to cyanosis or low oxygen levels. All babies have a patent ductus arteriosus (PDA) at birth that may allow enough mixing to prevent severe cyanosis initially, but as the ductus arteriousus closes, as it typically will in the first hours or days of life, cyanosis becomes more severe.
Rapid breathing in response to the low oxygen levels is seen, but the infants are typically described as being "comfortably tachypneic," or not working excessively hard to accomplish this rapid breathing.
Even in the presence of a ventricular septal defect, a heart murmur is often absent in the first days or weeks of life. If there is a site where blood mixing allows for safe oxygen levels, children will often develop signs and symptoms of congestive heart failure over the course of the first weeks or months of life.
Untreated, over 50 percent of infants with transposition will die in the first month of life, 90 percent in the first year.
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Diagnosing Transposition of the Great Arteries
When a newborn with significant cyanosis is first seen, they are often placed in supplemental oxygen. In cases of lung disease this often will improve the oxygen levels, but in cardiac problems such as transposition there will be little effect on the child's oxygen levels.
Failure of this "hyperoxia test" is often the first clue to suspect a cardiac defect such as transposition. Echocardiography can rapidly and accurately demonstrate the abnormal connections of the great arteries as well as other important features of the cardiac anatomy such as the presence and size of an atrial or ventricular septal defect and the branching patterns of the coronary arteries.
If questions about the anatomy, such as the coronary artery pattern remain, cardiac catheterization may be performed to clarify some of the details of the defect.
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Transposition of the Great Arteries treatment
The immediate management of an infant with transposition focuses on establishing safe oxygen levels and stable cardiac and pulmonary function.
A continuous infusion of prostaglandin, a medication that will keep the ductus arteriosus open, is usually initiated when the diagnosis is suspected or confirmed. This will allow some mixing of oxygen-rich blood with oxygen-poor blood but will not usually provide adequate mixing by itself.
A procedure called "balloon atrial septostomy" is often performed once the diagnosis is confirmed. Before birth, all babies have a connection between the right atrium and the left atrium (called a foramen ovale). After birth, this normal connection may allow some mixing of blood to occur but may not provide enough mixing. The foramen ovale may be enlarged or stretched with a balloon which will markedly improve mixing. This procedure is performed by passing a special balloon-tipped catheter into the heart from either a vessel in the umbilicus or a vessel in the groin. Often, the procedure is performed at the bedside, with guidance from an echocardiogram. Occasionally, the procedure will be performed in the catheterization laboratory.
A large atrial septal defect is thus created and typically allows excellent mixing of oxygen-rich and oxygen-poor blood so that the body's oxygen saturation will remain in a safe range, often in the 80 percent range. Following this procedure, the prostaglandin infusion is sometimes able to be discontinued.
Although babies can be stabilized temporarily, surgical correction of the defect is always necessary. In most cases, corrective surgery is typically performed in the first week of life, once an infant has recovered from any instability that occurred during the initial presentation. In more complex cases, such as those with narrowing below the pulmonary valve (pulmonary stenosis), surgical timing is variable.
In most cases of Transposition, an arterial switch operation is performed. The arterial switch operation involves cutting off the aorta and pulmonary arteries just above the point where they leave the heart, and reconnecting them to the proper ventricle. The valve stays attached to the ventricle, so what was once the pulmonary valve is now the aortic valve and vice versa.
Since the coronary arteries must stay with the aorta, they must be taken off the area above the valve and reimplanted separately above the new aortic valve. This is often the most technically challenging part of the operation, particularly if there is unusual branching of these arteries. Closure of ventricular septal defects (if present) and atrial septal defects are also performed as part of the operation.
Occasionally, in more complex cases of Transposition such as in those narrowing below the pulmonary valve, the arterial switch operations is not recommended. These cases often involve complex decision making on a case-by-case basis to determine the best options and operative pain.
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Transposition of the Great Arteries treatment results
The survival of children with Transposition has improved dramatically over recent decades. When there are no unusual risk factors identified, over 95 percent of infants successfully undergo surgery in the newborn period.
Since the arterial switch operation reconstructs the heart to a normal situation both anatomically and functionally, long-term cardiac function should be excellent.
In a small percentage of children, narrowing (stenosis) may occur at the site that the pulmonary artery was reattached. The narrowing may occur months or years following surgery and may require intervention. Options for treating this narrowing include cardiac catheterization with balloon dilation of the narrowed area or reoperation, depending on the characteristics of the narrowing.
Patients (after arterial switch operation) usually have normal ventricular function and no heart rhythm abnormalities.
Prior to the mid-1980s, most pediatric heart centers performed either the Mustard and Senning operations to manage Transposition. These procedures, also known as atrial switch operations, create a physiologically normal heart (deoxygenated blood goes to the lungs and oxygenated blood to the body) but leave the right ventricle as the systemic ventricle. They also require a complex "baffle" within the atrium with a large amount of suturing necessary. Although these operations generally yielded good results, there is a high incidence of late complications including ventricular failure, baffle obstruction, and rhythm disturbances.
Even though patients are expected to do well after arterial switch operation, long-term follow-up with the cardiologist is important to detect problems early. This follow-up often consists of regular cardiac physical exams, periodic echocardiography, and perhaps an exercise stress test when a child is old enough to perform this test.
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Rev. 9/06
