Dextro-transposition of the great arteries (or d-Transposition of the great arteries; abbreviated dextro-TGA or d-TGA) is a potentially life-threatening birth defect in the large arteries of the heart. The primary arteries (the aorta and the pulmonary artery) are transposed.
It is called a cyanotic congenital heart defect (CHD) because the newborn infant turns blue from lack of oxygen. In segmental analysis, this condition is described as ventriculoarterial discordance with atrioventricular concordance, or just ventriculoarterial discordance. d-TGA is often referred to simply as transposition of the great arteries (TGA); however, TGA is a more general term which may also refer to levo-transposition of the great arteries (l-TGA). Another term commonly used to refer to both d-TGA and l-TGA is transposition of the great vessels (TGV), although this term might have an even broader meaning than TGA.
Prenatally, a baby with d-TGA experiences no symptoms as the lungs will not be used until after birth, and oxygen is provided by the mother via the placenta and umbilical cord; in order for the red blood to bypass the lungs in utero, the fetal heart has two shunts that begin to close when the newborn starts breathing; these are the foramen ovale and the ductus arteriosus. The foramen ovale is a hole in the atrial septum which allows blood from the right atrium to flow into the left atrium; after birth, the left atrium will be filled with blood returning from the lungs and the foramen ovale will close. The ductus arteriosus is a small, artery-like structure which allows blood to flow from the trunk of the pulmonary artery into the aorta; after birth, the blood in the pulmonary artery will flow into the lungs and the ductus arteriosus will close. Sometimes these shunts will fail to close after birth; these defects are called patent foramen ovale and patent ductus arteriosus, and either may occur independently, or in combination with one another, or with d-TGA or other heart and/or general defects.
Symptoms and signs
Due to the low oxygen saturation of the blood, cyanosis will appear in peripheral areas: around the mouth and lips, fingertips, and toes; these areas are furthest from the heart, and since the circulated blood is not fully oxygenated to begin with, very little oxygen reaches the peripheral arteries. A d-TGA baby will exhibit indrawing beneath the ribcage and "comfortable tachypnea" (rapid breathing); this is likely a homeostatic reflex of the autonomic nervous system in response to hypoxic hypoxia. The infant will be easily fatigued and may experience weakness, particularly during feeding or playing; this interruption to feeding combined with hypoxia can cause failure to thrive. If d-TGA is not diagnosed and corrected early on, the infant may eventually experience syncopic episodes and develop clubbing of the fingers and toes.
Diagnosis d-TGA can sometimes be diagnosed in utero with an ultrasound after 18 weeks gestation. However, if it is not diagnosed in utero, cyanosis of the newborn (blue baby) should immediately indicate that there is a problem with the cardiovascular system. Normally, the lungs are examined first, then the heart is examined if there are no apparent problems with the lungs. These examinations are typically performed using ultrasound, known as an echocardiogram when performed on the heart. Chest x-rays and electrocardiograms may also be used in reaching or confirming a diagnosis; however, an x-ray may appear normal immediately following birth. If d-TGA is accompanied by both a VSD and pulmonary stenosis, a systolic murmur will be present.
On the rare occasion (when there is a large VSD with no significant left ventricular outflow tract obstruction), initial symptoms may go unnoticed, resulting in the infant being discharged without treatment in the event of a hospital or birthing center birth, or a delay in bringing the infant for diagnosis in the event of a home birth. On these occasions, a layperson is likely not to recognize symptoms until the infant is experiencing moderate to serious congestive heart failure (CHF) as a result of the heart working harder in a futile attempt to increase oxygen flow to the body; this overworking of the heart muscle eventually leads to hypertrophy and may result in cardiac arrest if left untreated.
Description In a normal heart, oxygen-depleted ("blue") blood is pumped from the right side of the heart, through the pulmonary artery, to the lungs where it is oxygenated. The oxygen-rich ("red") blood then returns to the left heart, via the pulmonary veins, and is pumped through the aorta to the rest of the body, including the heart muscle itself.
With d-TGA, deoxygenated blood from the right heart is pumped immediately through the aorta and circulated to the body and the heart itself, bypassing the lungs altogether, while the left heart pumps oxygenated blood continuously back into the lungs through the pulmonary artery. In effect, two separate "circular" (parallel) circulatory systems are created, rather than the "figure 8" (in series) circulation of a normal cardio-pulmonary system.
Variations and similar defects
Arterial spatial relationships Differences in the shape of the atrial septum and/or ventricular outflow tracts affect the relative positions of the aorta and pulmonary artery. In the majority of d-TGA cases, the aorta is anterior and to the right of the pulmonary artery, but it can also be directly anterior or anterior and to the left. The aorta and pulmonary artery can also be side by side, with aorta on either side. This is a less common variant, and with this arrangement, an unusual coronary artery pattern is common. There are also some cases with aorta to the right and posterior to the pulmonary artery.Valdes-Cruz LM and Cayre RO: Chapter 24 in Echocardiographic diagnosis of congenital heart disease. Philadelphia 1998.
Simple and complex d-TGA d-TGA is often accompanied by other heart defects, the most common type being intracardiac shunts such as atrial septal defect (ASD) including patent foramen ovale (PFO), ventricular septal defect (VSD), and patent ductus arteriosus (PDA). Stenosis of valves or vessels may also be present.
When no other heart defects are present it is called 'simple' d-TGA; when other defects are present it is called 'complex' d-TGA.
Although it may seem counterintuitive, complex d-TGA presents better chance of survival and less developmental risks than simple d-TGA, as well as usually requiring fewer invasive palliative procedures. This is because the left-to-right and bidirectional shunting caused by the defects common to complex d-TGA allow a higher amount of oxygen-rich blood to enter the systemic circulation. However, complex d-TGA may cause a very slight increase to length and risk of the corrective surgery, as most or all other heart defects will normally be repaired at the same time, and the heart becomes "irritated" the more it is manipulated.
Treatment
Life-saving heart surgery is always required. If the diagnosis is made in a standard hospital or other clinical facility, the baby will be transferred to a children's hospital, if such facilities are available, for specialized paediatric treatment and equipment.
The patient will require constant monitoring and care in an intensive care unit (ICU).
Palliative Palliative treatment is normally administered prior to corrective surgery in order to reduce the symptoms of d-TGA (and any other complications), giving the newborn or infant a better chance of surviving the surgery. Treatment may include any combination of:
Surgery
Minor Cardiac catheterization Rashkind balloon atrial septostomy Balloon angioplasty Endovascular stenting Angiography
Cardiac catheterization is a minimally invasive procedure which provides a means of performing a number of other procedures.
A balloon atrial septostomy is performed with a balloon catheter, which is inserted into a patent foramen ovale (PFO), or atrial septal defect (ASD) and inflated to enlarge the opening in the atrial septum; this creates a shunt which allows a larger amount of oxygenated ("red") blood to enter the systemic circulation.
Angioplasty also requires a balloon catheter, which is used to stretch open a stenotic vessel; this relieves restricted blood flow, which could otherwise lead to congestive heart failure (CHF).
An endovascular stent is sometimes placed in a stenotic vessel immediately following a balloon angioplasty to maintain the widened passage.
Angiography involves using the catheter to release a contrast medium into the chambers and/or vessels of the heart; this process facilitates examining the flow of blood through the chambers during an echocardiogram, or shows the vessels clearly on a chest x-ray, MRI, or CT scan - this is of particular importance, as the coronary arteries must be carefully examined and "mapped out" prior to the corrective surgery.
It is commonplace for any of these palliations to be performed on a d-TGA patient.
Moderate Left anterior thoracotomy Isolated pulmonary artery banding (PAB) Left lateral thoracotomy PAB (when coarctation or aortic arch repair also required) Right lateral thoracotomy Blalock-Hanlon atrial septectomy
Each of these procedures is performed through an incision between the ribs and visualized by echocardiogram; these are far less common than heart cath procedures.
Pulmonary artery banding is used in a small number of cases of d-TGA, usually when the corrective surgery needs to be delayed, to create an artificial stenosis in order to control pulmonary blood pressure; PAB involves placing a band around the pulmonary trunk, this band can then be quickly and easily adjusted when necessary.
An atrial septectomy is the surgical removal of the atrial septum; this is performed when a patent foramen ovale (PFO), or atrial septal defect (ASD) are not present and additional shunting is required to raise the oxygen saturation of the blood flowing eventually into the aorta.
Major Median sternotomy PAB (when intracardiac procedures also required) Concomitant atrial septectomy
In recent years, it is quite rare for palliative procedures to be done via median sternotomy. However, if a sternotomy is required for a different procedure, in most cases all procedures that are immediately required will be performed at the same time.
Monitoring and maintenance
Nasogastric tube (NG tube or simply NG) Intubation, oxygen mask, or nasal cannula Intravenous drip (IV) Arterial line Central venous catheter Fingerprick Sphygmomanometer Pulse oximeter EKG
An NG tube is used to deliver nourishment, and occasionally medication, to the patient. Since the tube extends right into the stomach, it can also be used to monitor how well the patient is digesting their "food". Paediatric units normally provide facilities and equipment for mothers of infant patients to pump their breastmilk, which can then be fed to the infant through the NG tube, and/or stored for later use.
Oxygen therapy is commonplace for hospitalized d-TGA patients. This may range from an oxygen mask resting on the bed nearby their head to intubation. In some cases, patients are intubated as a precaution; the machine can monitor breathing and supplement the patient as much or as little as they need.
IV's are used to deliver medication, blood products, or other fluids to the patient. Arterial lines provide a constant monitor of blood pressure, as well as a method of obtaining samples for blood gas tests; central lines can also monitor blood pressure and provide blood samples, as well as provide a means to deliver medication and nourishment; fingerpricks (or heelpricks on small babies) are used to obtain blood samples for certain tests.
A sphygmomanometer may be used for intermittent blood pressure monitoring even if a patient is being otherwise monitored using a central or arterial line.