EMBRYOLOGY,MORPHOLOGY AND NATURAL HISTORY OF TGA

1. DR RAKESH KUMAR
MCH CTVS,AIIMS,NEW DELHI

2. • TGA like tetralogy and DORV is an anomaly of
conotruncal development.
• Two basic theories that attempt to explain the
development of conotruncal anomalies.

3. • Conotruncus which will ultimately form the aorta
and pulmonary artery formed as a single tube.
• A process of spiral septation divides the
conotruncus into the two great vessels which
should wrap around each other.
• If the septum does not ‘spiral’ in the usual fashion
at all, the great vessels will be parallel to each
other and there will be transposition of the great
arteries.

4.  Usually the aortic, tricuspid and mitral valves are
in fibrous continuity, united by the fibrous skeleton
of the heart.
 Only the pulmonary valve is separate, being lifted
superiorly from the other three valves by the
subpulmonary conus (infundibulum)

5. • Van Praagh suggested that there is no
subpulmonary conus and the aorta comes to
lie anterior to the pulmonary artery.
• There is a fibrous continuity between the
pulmonary and mitral valves rather than
the usual continuity between the aortic
and mitral valves.
• Only the aortic valve is separate from the other
three valves.

6. NORMAL HEART TGA HEART

7. • RIGHT VENTRICLE
• LEFT VENTRICLE
• VENTRICULAR WALL THICKNESS, CAVITY
SHAPE & FUNCTION
• ATRIA
• CONDUCTION SYSTEM
• GREAT ARTERIES
• CORONARY ARTERIES
• PULMONARY VASCULAR DISEASE
• CO-EXISTING CARDIAC ANOMALIES

8.  Normally positioned, hypertrophied, and large in
TGA.
 In about 90% of cases:
◦ Subaortic conus is seen,
◦ Aorta is rightward and anterior and ascends
parallel to the posterior and leftward
pulmonary trunk.

10. INFUNDIBULAR
SEPTUM JOINING
NORMALLY WITH
THE
VENTRICULAR
SEPTUM
BETWEEN THE
LIMBS OF THE
TSM
HYPERTROPHIED RV

11.  Less wedging of the pulmonary trunk between the
mitral and tricuspid valves in TGA than of the
aorta in normal hearts.
 Larger area of contiguity exists between the mitral
and tricuspid valves than normally.

12.  These atrioventricular (AV) valves may be at
virtually the same level, and the AV septum and
membranous interventricular septum are then
smaller than usual or (rarely) absent.
 The right fibrous trigone is abnormally shaped and
attenuated.

13. • Infrequently
contains a
conus
typically
pulmonary
mitral fibrous
continuity
exists,
comparable
with aortic
mitral
continuity in
the normal
heart.
MITRAL
VALVE
PULMONARY
VALVE

14.  In about 8% of hearts with TGA, and most often in
those with a VSD, a subpulmonary conus is
present in the LV.
 The subpulmonary conus is frequently stenotic.

15.  RV wall is considerably thicker than normal at
birth and increases in thickness with age.
 LV wall is of normal thickness at birth.
 Wall thickness remains static, however, leading to
less-than-normal thickness within a few weeks of
birth and a relatively thin wall by age 2 to 4
months.

17.  LV cavity is the usual ellipsoid in shape at
birth but soon becomes banana shaped.
 RV function is usually normal in TGA in the
perinatal period.

18.  Thereafter, when the ventricular septum is intact,
RV end-diastolic volume is increased and RV
ejection fraction decreased.
 Depressed RV function results from relative
myocardial hypoxia or the geometry of the
chamber & unlikely by increased afterload or
decreased preload.

19.  Are normally formed in TGA.
 Right atrial size is usually larger than normal,
particularly when the ventricular septum is intact.

20. • AV node and bundle of His lie in a normal
position.
• The left bundle branch originates more distally
from the bundle of His than usual and arises as a
single cord rather than a sheath.

21.  Damage to the bifurcation of the bundle at VSD
closure is more likely to produce complete heart
block than in the normally structured heart.

22. • The aorta is most often directed anterior or slightly
to the right.
• In 13% to 30% of patients with TGA, aortic and
pulmonary commissures are not precisely aligned
because of malalignment of either the aortic or
mitral valve.
• Recognition of commissural malalignment
is important in planning the coronary
transfer as well as preventing neoaortic
valve regurgitation.

23.  Usually arise from the aortic sinuses that face the
pulmonary trunk, regardless of the inter-
relationships of the great arteries.
 Thus, the noncoronary sinus is usually the anterior
one.

24. • A more universally applicable scheme is the
Leiden convention
– proposed by the anatomists Gittenberger-DeGroot and
Sauer who were working in Leiden, Holland.

25. • According to Leiden convention
 Using the perspective of an individual looking
from the aorta to the pulmonary artery:
 sinus 1 – adjacent to the pulmonary artery on
the right-handside of the observer
 sinus 2 – adjacent to the pulmonary artery on
the left handside of the observer
 sinus 1 Usually gives rise to the anterior
descending and circumflex coronary arteries.
 sinus 2 usually gives rise to the right coronary
artery.
 This can be abbreviated as (1AD,CX; 2R)

27.  Originally described
by Yacoub and
Radley-Smith in
1978.

29.  Usually the arteries all arise from a single ostium
in the center of the sinus.
 Alternatively, they may arise from a double
barreled ostium consisting of two ostia
immediately adjacent to each other and
constituting essentially a single ostium.

31.  Now that repair of simple TGA is usually
performed in the first few weeks of life, and repair
of TGA with VSD is usually performed in the first
few months of life, pulmonary vascular disease
has almost disappeared.

32.  About 75% of neonates presenting with TGA have
no important coexisting cardiac anomaly other
than a patent foramen ovale or an atrial septal
defect.
 About 25% to 40% have a large or small VSD.
 Only about 5% have associated LVOTO.

33.  Same types of VSD occur with TGA as occur in
hearts with a primary VSD.
 Conoventricular defects of the several different
varieties are most common.

34.  In some hearts with conoventricular VSDs, the
infundibular septum is malaligned and fails to
insert within the Y of the TSM.
 The septum may be displaced leftward, resulting
in a variable degree of LVOTO and or rightward,
tending to result in RV (subaortic) obstruction.

35. • Development of LVOTO, which produces
subpulmonary obstruction, is part of the natural
history of many patients with TGA.
• The obstruction may be dynamic or
anatomic.
• LVOTO occurs in an important way at birth or
within a few days in only 0.7% of patients with
TGA and intact ventricular septum.

36.  Obstruction is present in about 20% of patients
born with TGA and VSD.
 LVOTO may become apparent or develop after
birth in other patients, thus reaching an overall
prevalence of 30% to 35%.

38. RV SIDE LV SIDE
MALALIGNED INFUNDIBULUM
DEVIATED TOWARDS LV
TSM
RV
VSD
PV
MALALIGNED INFUNDIBULAR
SEPTUM MERGING WITH
LV WALL VSD
AORTIC
VALVE

39. PRV>PLV
LEFT WARD
BULGING OF IVS
DYNAMIC
OBSTRUCTI
ON

40.  Particularly likely to occur if the aorta lies anterior
and more to the left than usual, with increased
wedging of the subpulmonary area.

41. • Important structural anomalies of the mitral valve
are present in 20% to 30% of hearts with TGA,
mostly in combination with a VSD,
• But the majority are not functionally important.
• The most important from a surgical standpoint are
those of mitral valve overriding or straddling, in
which the mitral valve leaflet is frequently cleft.

42.  Coexisting aortic obstruction can be discrete
(coarctation or less often, interrupted aortic arch)
or caused by distal arch hypoplasia.
 Rarely, it occurs when the ventricular septum is
essentially intact, but it occurs in 7% to 10% of
patients with TGA and VSD.

43.  In the normal heart the systemic and pulmonary
circulations are in series, in transposition they
function as two separate and parallel circuits.
 After birth, the oxygenated pulmonary venous
blood does not reach the systemic circuit, and the
systemic venous return does not circulate to the
lungs.

46.  This results in severe systemic arterial
desaturation.
 Absence of any communication between the
pulmonary and systemic circulations is
incompatible with life.

49. • Depends upon:
– pulmonary vascular resistance,
– Inter-atrial communication.
• When inter-atrial communication is non-restrictive
&

50. • The presence of a ventricular septal defect can
have a variable influence on the circulation.
• This in part depends on the:
– size of the defect,
– the presence of interatrial mixing, and
– the pulmonary vascular resistance
• A large interventricular communication may lead
to unrestricted flow to the lungs may result in
symptomatic heart failure.

51.  PREVALENCE:
 Common form of congenital heart disease,
occurring in 1 : 2100 to 1 : 4500 births
 Accounts for 7-8% of all congenital heart disease.

52. 2 : 1Male predominance increases to 3.3 : 1 when
the ventricular septum is essentially intact

53. • When patients with all varieties of TGA are
considered:
– 55% survive 1 month,
– 15% survive 6 months, and
– only 10% survive 1 year
• Survival without treatment is different among
subsets.

54. • It is particularly poor in untreated patients with
TGA and essentially intact ventricular septum:
– 80% at 1 week
– 17% at 2 months and
– 4% at 1 year

55. • In patients with TGA and VSD, early survival is
higher:
– 91% at 1 month,
– 43% at 5 months, and
– 32% at 1 year

56.  The combination of large VSD and aortic
obstruction (coarctation, interrupted aortic arch) is
particularly lethal:
all patients die within a few months of
birth with severe heart failure.

57.  In patients with TGA, VSD, and LVOTO, early
survival is still better, reaching
◦ 70% at 1 year and
◦ 29% at 5 years,
 This is because in many patients LVOTO is only
moderate initially.

58.  Poor survival in patients with TGA and essentially
intact ventricular septum is related primarily to
hypoxia.
 Intercurrent pulmonary infections may develop
and are particularly lethal because they reduce
Qep and lead rapidly to increasing hypoxia,
acidemia, and death.

59. • Death in this group may also result from cerebro-
vascular events, usually caused by:
– the polycythemia and
– increased blood viscosity (both secondary to
severe cyanosis)
particularly in association with dehydration.
• Nonfatal cerebrovascular events occur in about
6% of patients treated by BAS and include
cerebral abscess.

60.  Patients with TGA and VSD usually die with heart
failure.
 Hypoxia is the primary cause of morbidity and
mortality in patients with TGA, VSD and LVOTO.