2. Epidemiology
• Complete transposition of the great arteries (D-TGA) is the most
common cyanotic CHD presenting in newborn period and comprises
approximately 5% of all CHDs.
• TGA accounts for 20 percent of cyanotic heart disease.
• Female: male 3:1
3. Embryology
• During cardiac development, the conotruncal septum spirals toward the aortic sac dividing the
truncus into the pulmonary arteries and aorta, respectively. TGA occurs when the conotruncal
septum fails to follow its spiral course and instead forms in a linear orientation. Consequently, the
aorta arises from the right ventricle and the pulmonary trunk arises from the left ventricle.
• d-TGA: A more common variation in which the aorta is positioned to the right and front of the
pulmonary artery, arising from the right ventricle rather than the left.
• l-TGA: A less common variation in which the aorta is positioned to the left and front of the
pulmonary artery. This is due to ventricular inversion due to leftward looping of the primitive heart
tube, resulting in the condition commonly known as congenitally corrected transposition.
4. Pathology
• In this condition, the aorta arises from the right ventricle, and the pulmonary artery
arises from the left ventricle.
• The aorta is anterior to the PA, but the aorta usually remains to the right of the PA.
• The atria and ventricles are in normal relationship. The coronary arteries arise from
the aorta, as in a normal heart.
• Associated defects:
• 50% have PFO or PDA
• 5% have PS
• 30-40% have VSD
• 10% have VSD+PS
5. Pathophysiology
• Desaturated blood returning from the body to the right atrium flows out of the aorta
without being oxygenated in the lungs and then returns to the RA. Therefore, tissues,
including vital organs such as the brain and heart, are perfused by blood with a low oxygen
saturation.
• Conversely, well-oxygenated blood returning to the left atrium (LA) flows out of the PA and
returns to the LA. This results in a complete separation of the two circuits. The two circuits
are said to be in parallel rather than in series, as in normal circulation .
• This defect is incompatible with life unless communication between the two circuits occurs
to provide the necessary oxygen to the body. This communication can occur at the atrial,
ventricular, or ductal level or at any combination of these levels.
6. Pathophysiology
• In the most frequently encountered form of D-TGA, only a small communication exists between the
atria, usually a patent foramen ovale (PFO).
• The newborn is notably cyanotic from birth and has an arterial oxygen saturation of 30% to 50%. The
low arterial Po2, causes an anaerobic glycolysis, with resulting metabolic acidosis.
• The normal decrease in pulmonary vascular resistance results in increased pulmonary blood flow and
volume overload to the LA and LV.
• Severe hypoxia and acidosis and volume overload to the left side of the heart cause CHF during the
first week of life. Unless hypoxia and acidosis are corrected, the condition of these infants deteriorates
rapidly.
• Other metabolic problems encountered are hypoglycemia, which is probably secondary to pancreatic
islet hypertrophy and hyperinsulinism, and a tendency toward hypothermia.
7. Clinical features
• Antenatally, TGA is challenging to diagnose. Screening ultrasounds do not routinely reveal
TGA in-utero.
Postnatal:
• Most patients present with signs and symptoms during the neonatal period.
• Cyanosis: It is dependent on the amount of mixing between the two parallel circuits which
depend on the size and presence of an ASD or VSD.
• Tachypnea: Patients usually have a respiratory rate higher than 60 breaths per minute but
without retractions, grunting, or flaring and appear comfortable.
• The S2 is single, mainly because the pulmonary valve is farther from the chest wall, causing
the P2 to be inaudible.
• Murmurs: murmurs are not typically present unless a small VSD or pulmonic stenosis exists.
8. Investigations
1. Lab:
a. Severe arterial hypoxemia usually with acidosis is present. Hypoxemia does not respond to oxygen
inhalation.
b. Hypoglycemia and hypocalcemia are occasionally present.
2. Electrocardiography
a. Right ventricular hypertrophy (RVH) is usually present after the first few days of life.
b. The QRS voltages and the QRS axis may be normal in many newborns with the defect.
c. After 3 days of life, an upright T wave in V1 may be the only abnormality suggestive of RVH.
d. Biventricular hypertrophy (BVH) may be present in infants with large VSD, PDA, or pulmonary vascular
obstructive disease because all of these conditions produce an additional left ventricular hypertrophy
(LVH).
e. Occasionally, right atrial hypertrophy (RAH) is present.
9.
10. Radiography
• Note the cardiomegaly
(cardiothoracic ratio 0.7), “egg-
shaped” heart with narrow
waist, and
• increased pulmonary vascular
markings
11. Echocardiography
• A, In this parasternal long-axis view, the great
arteries are seen in parallel alignment. The
posterior artery is directed posteriorly,
bifurcates into two branches, and is therefore a
pulmonary artery (PA). There is a continuity
between the pulmonary valve and the mitral
valve.
• B, In the parasternal short-axis view, the aorta
(AO) and the PA are seen in cross section as
double circles. The aorta is anterior to and right
of the PA. LV, left ventricle; RV, right ventricle
12. Cath
• Cardiac catheterization is performed only for the purpose of balloon
atrial septostomy to improve mixing at the atrial level.
• Rarely, it is performed to look for associated anomalies such as
abnormal coronary artery, collateral circulation, or a small aortic
isthmus.
13. Natural History
1. Progressive hypoxia, acidosis, and heart failure result in death in the newborn period. Without surgical
intervention, death occurs in 90% of patients before they reach 6 months of age.
2. Infants with an intact ventricular septum are the sickest group but demonstrate the most dramatic
improvement after Rashkind balloon atrial septostomy.
3. Infants with VSD are the least cyanotic group but the most likely to develop CHF and pulmonary vascular
obstructive disease. Many infants with TGA and a large VSD develop moderate pulmonary vascular
obstructive disease by 3 to 4 months of age. Thus, surgical procedures are recommended before that age.
4. Infants with a significant PDA are similar to those with a large VSD in terms of their development of CHF
and pulmonary vascular obstructive disease.
5. The combination of VSD and PS allows considerably longer survival without surgery because the pulmonary
vascular bed is protected from developing pulmonary hypertension, but this combination carries a high
surgical risk for correction.
14. Management
Medical
The following measures should be carried out to stabilize the patient before an
emergency cardiac catheterization (if performed) or a surgical procedure is carried
out:
a. Arterial blood gases and pH should be obtained, and metabolic acidosis should be corrected.
Hypoglycemia and hypocalcemia, if present, should be treated.
b. PGE1 infusion should be started to improve arterial oxygen saturation by reopening the
ductus. This should be continued throughout the cardiac catheterization or until the time of
surgery.
c. Oxygen should be administered for severe hypoxia. Oxygen may help lower pulmonary
vascular resistance (PVR) and increase pulmonary blood flow (PBF), which in turn increases
systemic arterial oxygen saturation.
15. d. Before surgery, cardiac catheterization and a balloon atrial septostomy (i.e., the Rashkind procedure) are
often carried out to have some flexibility in planning surgery.
e. If adequate interatrial communication exists and the anatomic diagnosis of TGA is clear by
echocardiographic examination, the patient may go to surgery without cardiac catheterization or the
balloon atrial septostomy.
f. The need for the balloon septostomy may be determined by inadequate atrial mixing through the PFO
(evidenced with a high Doppler flow velocity of >1 m/sec) or a lack of readiness for surgical intervention.
g. In the balloon atrial septostomy, a balloon-tipped catheter is advanced into the left atrium (LA) through
the PFO. The balloon is inflated with diluted radio-opaque dye and abruptly and forcefully withdrawn to
the right atrium (RA) under fluoroscopic or echocardiographic monitoring. This procedure creates a large
defect in the atrial septum through which an improved intracardiac mixing occurs. An increase in the
oxygen saturation of 10% or more and a minimal interatrial pressure gradient are considered satisfactory
results of the procedure.
h. CHF may be treated with diuretics (and digoxin).
16. Definitive Repair
1. Atrial baffle operations (Mustard and Senning operations): These procedures reroute pulmonary
and systemic venous returns at the atrial level with resulting physiologic correction. The
pulmonary venous blood eventually goes to the aorta, and the systemic venous blood goes to
the PA.
2. The Mustard operation uses a pericardial or a prosthetic baffle, and the Senning operation uses
the patient’s own atrial septal flap and the RA free wall to redirect the venous returns.
3. Rastelli operation. In patients with VSD and severe PS, redirection of the pulmonary and systemic
venous blood is carried out at the ventricular level. The LV is directed to the aorta by creating an
intraventricular tunnel between the VSD and the aortic valve. A valved conduit or a homograft is
placed between the RV and the PA. Most surgeons prefer to delay this procedure until after the
first year of life. The mortality rate is between 10% and 29%.
17. Atrial baffle operation.
1. The hemodynamic results of the Mustard
and Senning operations are shown.
2. Systemic venous blood (shaded) is
redirected at the atrial level to the anatomic
left atrium (LA) and left ventricle (LV) and
eventually to the pulmonary circulation.
3. Pulmonary venous blood is redirected at
the atrial level to the anatomic right atrium
(RA) and right ventricle (RV) through the
tricuspid valve and to the aorta.
18.
19. Arterial switch operation
1. The ASO is now firmly established as the procedure of choice.
2. The coronary arteries are transplanted to the PA, and the proximal great arteries are
connected to the distal end of the other great artery, resulting in an anatomic correction.
3. This procedure has advantages over the atrial baffle operations because it is an anatomic
(not physiologic) correction, and long-term complications are infrequent. This procedure
is indicated not only for simple TGA but also TGA with other associated anomalies (e.g.,
VSD or PDA) and the Taussig-Bing type of double outlet right ventricle (DORV) with
subpulmonary VSD.
4. The operative mortality rate for neonates with TGA and intact ventricular septum is
down to around 6%.
20. Arterial switch
1) The aorta and pulmonary arteries are cut off
close to the base where they connect to the heart.
The coronary arteries are also detached from the
base of the aorta.
2) The aorta and coronary arteries are attached to
the base of the original pulmonary artery. The
pulmonary artery is moved in front of the new
aorta.
3) The pulmonary artery is then attached to the
base of the original aorta and holes from the
removed coronary arteries are patched.
21. Damus-Kaye-Stansel operation
1. Infants with a large VSD and significant subaortic stenosis may receive the Damus-Kaye-
Stansel operation at 1 to 2 years of age.
2. In this procedure, the coronary arteries are not transferred to a neoaorta. Instead, the
subaortic stenosis is bypassed by connecting the proximal PA trunk to the ascending
aorta. The VSD is closed, and a conduit is placed between the RV and the distal PA.
3. The mortality rate is considerable, ranging from 15% to 30%.
4. The Damus-Kaye-Stansel operation is also applicable in patients with single ventricle and
TGA with an obstructive bulboventricular foramen (BVF) or DORV with subaortic stenosis
22. • A, D-TGA with VSD and subaortic stenosis is
illustrated. The main pulmonary artery (MPA) is
transected near its bifurcation. An appropriately
positioned and sized incision is made in the
ascending aorta (AO).
• B, The proximal MPA is anastomosed end to side to
the ascending aorta using either a Dacron tube or
Gore-Tex. This channel will direct left ventricular
blood to the aorta. The aortic valve is either closed
or left unclosed. The VSD is closed (through a right
ventriculotomy).
• C, A valved conduit is placed between the right
ventricle (RV) and the distal pulmonary artery (PA).
This channel will carry RV blood to the PA. LV, left
ventricle; RA, right atrium.
