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1. Development of the Heart
and Great Vessels
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2. Development of the Heart

3. When does the heart begin to develop?

Towards the end of the 3rd week
of gestation.

4. How does the development of the heart
begin?


A pair of endothelial
tubes fuse to
become the
primitive heart tube.
This develops within
the pericardial
cavity, suspended
from its dorsal wall by
a dorsal
mesocardium.

5. Development of the heart

Grooves develop in the primitive heart tube to
divide it into 5 regions:
ANTERIOR
POSTERIOR

7. Development of the heart

The arterial and venous ends of the tube
are surrounded by a layer of visceral
pericardium.

8. Development of the heart
The primitive heart tube then elongates within
the pericardial cavity.
 As the bulbus cordis and ventricle grow more
rapidly than the attachments at either end, the
heart first takes a U-shape and later an S-shape.


9. Development of the heart
At the same time the heart
rotates slightly anticlockwise
and twists so that the right
ventricle lies anteriorly and the
left atrium and ventricle
posteriorly.
 Despite this, and an increase in
the number of vessels entering
and leaving, they still continue
to be enclosed together in this
single tube of pericardium.


10. Development of the heart

As the tube develops,
› the sinus venosus becomes
incorporated into the atrium
› the bulbus cordis becomes
incorporated into the ventricle.

11. Development of the heart
Endocardial cushions
develop between
the primitive atrium
and ventricle.
 An interventricular
septum develops
from the apex up
towards the
endocardial
cushions.


12. Development of the heart

The division of the atrium is
slightly more complicated.
› The septum primum grows down
to fuse with the endocardial
cushions, but leaves a hole in
the upper part which is termed
the foramen ovale.
› The septum secundum
develops just to the right of the
septum primum and foramen
ovale.
› Thus a valve-like structure
develops which allows blood to
go from the right to the left side
of the heart in the fetus.

13. Development of the heart
At birth, when there is an
increased blood flow
through the lungs and a
rise in the left atrial
pressure, the septum
primum is pushed across
to close the foramen
ovale.
 Usually the septa fuse,
obliterating the foramen
ovale and leaving a small
residual dimple (the fossa
ovalis).


14. Development of the heart

The sinus venosus joins the atria,
becoming the 2 venae cavae on the
right and the 4 pulmonary veins on the
left.

15. The Aortic Arches

16. Development of the aortic arches

A common arterial trunk (the truncus
arteriosus), continues from the bulbus
cordis and gives off 6 pairs of aortic
arches.

18. Development of the aortic arches
The aortic arches
The aortic arches
curve around the
pharynx to join to
dorsal aortae which
join together lower
down as the
descending aorta.
 These arches are
equivalent to those
supplying the gill
clefts of a fish.


19. Development of the aortic arches
1st and 2nd arches:
disappear early.
 3rd arch: remains as
the carotid artery.


20. Development of the aortic arches

4th arch:
› On the right:
becomes the
subclavian artery
› On the left:
becomes the arch
of the aorta, giving
off the left
subclavian.

5th arch disappears
early.

21. Development of the aortic arches

Ventral part of 6th
arch:
› becomes the right
and left
pulmonary artery
› The connection to
the dorsal aortae
disappears on the
right but
continuing as the
ductus arteriosus
on the left
connecting with
the aortic arch.

22. The aortic arches and
their derivatives

24. Development of the aortic arches


In the early fetus the larynx is at
the level of 6th aortic arch, and
the vagus gives off its nerve to it
below the 6th arch.
As the neck elongates and the
heart migrates caudally, the
recurrent nerves become
dragged down by the aortic
arches.
› On the right: the 5th and 6th
absorb leaving the nerve to
hook round the 4th (subclavian)
in the adult.
› On the left: the nerve remains
hooked around the 6th arch (the
ligamentum arteriosum) of the
adult.

25. Congenital Anomalies of
the Heart and Great
Vessels

26. Malposition

This includes:
› Dextrocardia: a mirror image of the normal
anatomy
› Situs inversus: inversion of all the viscera.
 Appendicitis may present as left iliac fossa
pain in this condition.

In pure dextrocardia there is no
intracardiac shunting and cardiac
function is normal.

27. Malposition

Very rare in normal life, but
slightly more common in exams!

28. Left to right shunts (late cyanosis)
Atrial septal defect (ASD)
Ventricular septal defect (VSD)
Patent ductus arteriosus (PDA)

29. Atrial septal defect (ASD)
This may be from the ostium primum,
secundum or sinus venosus and
represents failure in the primary or
secondary septa.
 Treatment:

› Closure with a pericardial patch
› Catheter-introduced atrial baffles made
of Dacron (more recently)

30. Atrial septal defect (ASD)

Clinical differences between ASD with
intracardiac shunting and a persistent
patent foramen ovale:
› A probe may be passed obliquely
through the septum.
› In PFO, flow of blood does not occur after
birth, because of the higher pressure in
the left atrium.
› This condition is said to occur in 10% of
subjects, but it is not normally of any
significance.

31. Ventricular septal defect (VSD)

VSD is the most
common abnormality.
› Small defects in the
muscular part of the
septum may close.
› Larger ones in the
membranous part just
below the aortic valves
do not close
spontaneously and may
require repair.

32. Patent ductus arteriosus (PDA)



This normal channel in the fetus may
occasionally fail to close after birth.
It should be corrected surgically
because it causes increased load to the
left ventricle and pulmonary
hypertension.
Along with septal defects, PDA may later
cause reverse flow and, therefore, late
cyanosis.

35. Eisenmenger’s syndrome



Pulmonary hypertension may cause
reversed flow (right to left shunting).
This is due to an increased pulmonary
flow resulting from either an ASD, or VSD
or PDA.
When cyanosis occurs from this
mechanism it is known as Eisenmenger’s
syndrome.

36. Right to left shunts (cyanotic)
Fallot’s tetralogy

37. Fallot’s tetralogy

The 4 features of this
abnormality are
› VSD,
› Stenosed pulmonary
outflow tract
› Wide aorta which
overrides both the right
and left ventricles
› Right ventricular
hypertrophy

39. Fallot’s tetralogy

Because there is a
right to left shunt
across the VSD there
is usually cyanosis at
an early stage,
depending mainly on
the severity of the
pulmonary outflow
obstruction.

40. Obstructive non-cyanotic abnormalities
Coarctation of the aorta
Abnormalities of the valves

41. Coarctation of the aorta


This is a narrowing of the
aorta, normally just
distal to the ductus
arteriosus.
Thought to be an
abnormality related to
the obliterative process
of the ductus.

42. Coarctation of the aorta

Clinical sequelae:
› Hypertension in the
upper part of the
body
› Weak delayed
femoral pulses

43. Coarctation of the aorta

Extensive collaterals develop to
try and bring the blood down to
the lower part of the body,
resulting in large vessels around
the scapula, anastomosing with
the intercostal arteries and the
internal mammary and inferior
epigastric arteries.
› These enlarged intercostals
usually cause notching of the
inferior border of the ribs (a
diagnostic feature seen on
chest x-ray).

44. Coarctation of the aorta

Treatment:
› This condition used to require a
major thoracic operation but now
can frequently be treated by
balloon angioplasty.

45. Abnormalities of the valves


Any of these may be imperfectly formed
and tend to cause either stenosis or
complete occlusion (atresia).
The pulmonary and the aortic valves are
more frequently affected than the other
two.

46. Type of Defect
Mechanism
Ventricular Septal Defect (VSD)
There is a defect within the membranous or muscular portions of the
intraventricular septum that produces a left-to-right shunt, more severe with larger
defects
Atrial Septal Defect (ASD)
A hole from a septum secundum or septum primum defect in the interatrial
septum produces a modest left-to-right shunt
Patent Ductus Arteriosus (PDA)
The ductus arteriosus, which normally closes soon after birth, remains open, and
a left-to-right shunt develops
Tetralogy of Fallot
Pulmonic stenosis results in right ventricular hypertrophy and a right-to-left shunt
across a VSD, which also has an overriding aorta
Transposition of Great Vessels
The aorta arises from the right ventricle and the pulmonic trunk from the left
ventricle. A VSD, or ASD with PDA, is needed for extrauterine survival. There is
right-to-left shunting.
Truncus Arteriosus
There is incomplete separation of the aortic and pulmonary outflows, along with
VSD, which allows mixing of oxygenated and deoxygenated blood and right-to-left
shunting
Coarctation of Aorta
Either just proximal (infantile form) or just distal (adult form) to the ductus is a
narrowing of the aortic lumen, leading to outflow obstruction

47. References


Raftery AT (2008): Applied Basic Science
for Basic Surgical Training, 2nd ed. Elsevier,
Edinburgh.
Ellis H (2006): Clinical Anatomy, 11th ed.
Blackwell Publishing