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dextro-Transposition of the great arteries (d-Transposition of the great arteries, dextro-TGA, or d-TGA) is a cyanotic congenital heart defect (CHD) in which the primary arteries (the aorta and the pulmonary artery) are transposed; it is sometimes referred to as complete transposition of the great arteries.
In segmental analysis, this 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 general term which can 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 may have an even broader meaning than TGA.
Overview edit
Description edit
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, blue 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 red blood continuously back into the lungs through the pulmonary artery. In effect, two separate "circular" circulatory systems are created, rather than the "figure 8" circulation of a normal cardio-pulmonary system.
Variations and similar defects edit
Arterial spatial relationships edit
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.[1]
Simple and complex d-TGA edit
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 illogical, complex d-TGA presents better chance of survival and less developmental risks than simple d-TGA, and 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.
Similar defects edit
The following defects also involve abnormal spatial arrangement and/or structure of the great arteries:
- Coarctation of the aorta
- Double outlet right ventricle (DORV)
- Left heart hypoplasia or hypoplastic left heart syndrome (HLHS)
- levo-transposition of the great arteries (l-TGA)
- Overriding aorta
- Patent ductus arteriosus (PDA)
- Taussig-Bing syndrome
- Tetralogy of Fallot (TOF)
- Truncus arteriosus
- Vascular rings
Symptoms and diagnoses edit
Prenatal d-TGA edit
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.
operative).]] 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 edit
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 (EKG) 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, 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.
Prognosis edit
With simple d-TGA, if the foramen ovale and ductus arteriosus are allowed to close naturally, the newborn will likely not survive long enough to receive corrective surgery. With complex d-TGA, the infant will fail to thrive and is unlikely to survive longer than a year if corrective surgery is not performed. In most cases, the patient's condition will deteriorate to the point of inoperability if the defect is not corrected in the first year.
While the foramen ovale and ductus arteriosus are open after birth, some mixing of red and blue blood occurs allowing a small amount of oxygen to be delivered to the body; if ASD, VSD, PFO, and/or PDA are present, this will allow a higher amount of the red and blue blood to be mixed, therefore delivering more oxygen to the body, but can complicate and lengthen the corrective surgery and/or be symptomatic.
Modern repair procedures within the ideal timeframe and without additional complications have a very high success rate.
Treatment edit
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 edit
Corrective edit
Statistics edit
- Heart defects are the most common birth defect, occurring in approximately 1% of live births
- Approximately one million people worldwide are currently living with a CHD
- Having a child with a CHD increases an individual’s chances of having another child with a CHD from 1% to 3%. Subsequent children born with a CHD increase that individual’s chances further.
See also edit
References edit
- ^ Valdes-Cruz LM and Cayre RO: Chapter 24 in Echocardiographic diagnosis of congenital heart disease. Philadelphia 1998.