Signs and Symptoms of Transposition
Transposition of the great arteries can be diagnosed by a fetal ultrasound. But this requires special diligence and therefore, at times, can be missed on a routine fetal ultrasound. Sometimes, a fetal echocardiogram performed by specialists is required to make a diagnosis of transposition in a fetus.
After birth, 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 arteriosus 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.
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 that a baby has 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 or cardiac MRI may be performed to clarify some of the details of the defect.
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 may provide adequate mixing by itself.
A procedure called a "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 balloon atrial septostomy 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 ductus arteriosus is no longer necessary and prostaglandin infusion can therefore 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 is 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 operation is not recommended. These cases often involve complex decision making on a case-by-case basis to determine the best options and operative plan.
Results of Treatment
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 sites where the aorta and pulmonary artery are reattached to the proper ventricle. 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.
Sometimes, the aorta becomes enlarged in its portion immediately after it arises from the left ventricle.
Rarely, there may be problems with flow through the coronary arteries.
Patients (after arterial switch operation) usually have normal ventricular function and no heart rhythm abnormalities.
In later years, patients with the arterial switch operation have good quality of life and usually can participate in physical activity and sports without any difficulty or restrictions. Even though patients are expected to do well after the 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. Although repeat operations are not expected, patients may rarely need repeat surgery in later years to correct narrowing of the great arteries or enlargement of the aorta.
Prior to the mid-1980s, most pediatric heart centers performed either the Mustard or Senning operation to manage transposition. These procedures, also known as atrial switch operations, create a physiologically normal heart (oxygen-poor blood goes to the lungs and oxygen-rich blood to the body) but maintains the right ventricle in a position of the systemic ventricle (i.e., the ventricle pumping blood to the body), a situation which may sometimes cause it to develop poorer function in later years. The atrial switch operation also requires a complex "baffle" within the atria that also requires a large amount of suturing. Although these operations generally yielded good results, there is a high incidence of late complications including ventricular failure, baffle obstruction, and rhythm disturbances.
Adult and Adolescent Management
All patients with transposition of the great arteries require lifelong surveillance by a congenital heart expert.
If they have had a Mustard or Senning procedure, the issues have to do with slow heart rates, abnormally fast heart rates, pumping chamber weakness, leaky valves, and technical issues related to the surgical repair. A certain proportion of these patients require pacemakers. Expert assessment is usually recommended on an annual basis.
If they have had an arterial switch procedure, chances are that they will do better over time than do the Mustard and Senning patients. Nonetheless, some of these patients will have problems with their reimplanted coronary arteries, with leaky valves, or with enlarged arteries. Expert surveillance is again recommended.
If they have had a Rastelli repair, they have a tube, called a “valved conduit,” connecting their right ventricle to their pulmonary artery. The conduit may malfunction over time. In the past, conduit problems required reoperation. In the present day, many conduit problems can be fixed in the heart catheterization laboratory using stents and/or tissue valves implanted without opening the chest.
Learn more about the Adolescent and Adult Congenital Heart Disease Program.