Download Atrial Defects

Biology of Disease CH0576
Developmental Defects of
Cardiovascular System
CH0576/RHY
Congenital Defects
• Given that the embryological and
foetal development of the heart and
the CVS is so complex, it may be
assumed that there would be a vast
range of congenital abnormalities.
• In actual fact around 90% of the
congenital defects can be grouped
together under 4 main headings:CH0576/RHY
Congenital Defects
• The four major headings being:–
–
–
–
Septal defects
Patent Ductus Arteriosus
Pulmonary or Aortic Stenosis
Misplacement of Major Vessels, or
Transposition.
• Most cardiac malformations are
evident at or shortly after birth.
CH0576/RHY
Congenital Defects
• They may well become evident due to
some symptom of cardiac failure or
impairment of function:–
–
–
–
Cyanosis
Breathlessness
Feeding difficulties
Failure to thrive in neonatal period.
CH0576/RHY
Congenital Defects
• In some instances (the vast minority)
the malformations are attributed to
maternal factors:– maternal rubella infection
– chronic alcohol abuse
• In the majority of cases there are no
clear links with any known teratogenic
factors.
CH0576/RHY
Congenital Defects
• The main cardiac abnormalities can be
functionally divided into two major
groups:– Those which cause an abnormal ‘shunting’
of blood between the two sides of the
heart.
– Those which are associated with an
obstruction to blood flow from the
heart.
CH0576/RHY
Congenital Defects
• The abnormal ‘shunting’ is usually a
movement from left to right hand side
of the heart.
– Due to Left > Right, in terms of pressure.
– These defects are not (at least initially)
associated with cyanosis.
CH0576/RHY
Congenital Defects
• If there is some obstruction to blood
flow from the right hand side of the
heart, there will tend to be a right to
left shunt.
– As a consequence the lungs will largely
be bypassed.
– As de-oxygenated blood passes into the
systemic circulation, cyanosis will
develop.
CH0576/RHY
Septal Defects
• Defects within the septa or walls of
the heart can occur in either the
atria or the ventricles.
• Atrial Defects:
• These are the most common of the
septal defects.
– Lesion is usually at the level of the
foramen ovale, from foetal circulation.
CH0576/RHY
Atrial Septal Defect
• After birth the
pressure in Lt > Rt.
• Blood passes via
the lesion from left
to right.
• The right side of
the heart receives
more blood than
usual.
CH0576/RHY
Atrial Septal Defect
• Rt ventricle, in
response to increased
functional demand,
undergoes hypertrophy.
• The pulmonary artery
also responds to the
over-distension by
enlarging.
– Pulmonary arterial
hypertrophy
CH0576/RHY
Atrial Septal Defect
• The presence of an audible murmur on
routine physical examination occurring
at systole, over the second intercostal
space, indicates a likely defect.
• Catheterisation of the heart indicates
that the oxygen content of the right
atrial blood is > that of the superior or
inferior vena cavae.
CH0576/RHY
Atrial Septal Defect
• Should the infant’s condition warrant
treatment, the defect can readily be
closed surgically.
• The surgical procedure nowadays
carrying a very low mortality rate.
CH0576/RHY
Ventricular Septal Defect
• These defects are more serious than
the atrial septal defects.
– Largely due to the much higher pressures
involved.
• The major problem being that the child
with such a defect can develop a rapidly
progressing pulmonary hypertension.
CH0576/RHY
Ventricular Septal Defect
• Initially the symptoms
are of a left to right
shunt with a systolic
murmur.
• With the continuation
of the situation there
will be an pulmonary
resistance to flow, due
to  pulmonary arterial
pressure
CH0576/RHY
Ventricular Septal Defect
• Eventually RVP>LVP
and hence the shunt
will be reversed.
• Blood will pass
through the lesion
from Rt to Lt.
• As a consequence the
lungs are largely bypassed.
CH0576/RHY
Ventricular Septal Defect
• As a result of bypassing the high
resistance pulmonary circuit:– Cyanosis in the tissues.
– 2º Polcythaemia.
– Finger clubbing, may develop as a result
of  pO2 in the peripheral blood.
• It is essential that ventricular septal
defects are diagnosed and treated as
early as possible.
CH0576/RHY
Patent Ductus Arteriosus
• DA is the channel by
which blood passes
from the right heart
into the aorta in foetal
life.
• Deflated lungs are
bypassed and blood is
passed to the placenta
for oxygenation
CH0576/RHY
Patent Ductus Arteriosus
• This duct often
remains open as the
result of a range of
congenital defects.
• Patency of the duct
is more common in
females (2x).
• A recognised link
with maternal rubella
infection.
CH0576/RHY
Patent Ductus Arteriosus
• Blood continually passes into the
pulmonary circuit from the aorta (as,
unlike in foetus) aortic pressure >
pulmonary artery pressure.
• This causes a characteristic ‘machinery
murmur’, reaching a crescendo in
systole, when the aortic pressure
reaches around 125mm Hg.
CH0576/RHY
Patent Ductus Arteriosus
• Eventually a pulmonary hypertension
would result, due to the increase in
pulmonary blood flow  continuous
over - distension of the pulmonary
artery.
• This would result in hypertrophy of
the vessel walls.
– This condition should be diagnosed
before this situation arises, surgical
ligation of the PDA is 100% effective
CH0576/RHY
Aortic Coarctation
• This is simply defined as a narrowing, or
stenosis, of the aorta.
• This condition is essentially divided into
two main types:– Infantile
– Adult type.
• These conditions differ in the position
of the stenosis, and in their outcome!
CH0576/RHY
Aortic Coarctation
• Infantile type is associated with the
coarctation being proximal to the DA.
• The DA remains patent.
• In this form of condition a number of
other cardiac abnormalities are
common.
• The infantile type is not consistent
with life, and is generally seen in stillborn infants.
CH0576/RHY
Aortic Coarctation
• In the Adult type the stenosis is at
or just distal to the DA, which is
closed.
• Coarctation of the aorta is associated
with the presence of a loud systolic
murmur, caused by turbulence at the
stenotic site.
• Murmur is generally loudest towards
the base of the heart.
CH0576/RHY
Aortic Coarctation
• Aortic constriction increases the
workload on the left ventricle, triggering
left ventricular hypertrophy ( a poor
prognostic indicator, as previously seen).
• Cardiac output is maintained at normal
levels and the blood flow to the upper
part of the body is normal or increased,
as the pressure proximal to the stenotic
site is higher.
CH0576/RHY
Aortic Coarctation
• The blood makes its way to the lower
part of the body by means of greatly
dilated collateral vessels.
• This collateral circulation fails to
develop in the infantile type, as blood
enters the aorta through the patent
DA, beyond the constriction.
CH0576/RHY
Aortic Coarctation
• The clinical picture of aortic coarctation
is clear and characteristic:– There is arterial hypertension of the upper
part of the body.
– Relative weakness and delay (or lag) in the
pulse in the lower limbs, compared to that of
the upper body and arms.
– Evidence of an anastomotic collateral
circulation.
CH0576/RHY
Aortic Coarctation
• Again, early surgical intervention is ideal.
• In most cases the condition is discovered
after some secondary complication has
arisen.
• Mild coarctations are consistent with a
relatively long life.
• Average life span is greatly diminished.
• Generally few symptoms may be evident
in childhood.
CH0576/RHY
Aortic Coarctation
• Potential hazards which may occur,
include:– Severe hypertension in upper body
resulting in cardiac failure and/or CVAs
– Bacterial endocarditis at the stenotic
site.
– Aneurysm formation immediately above
or below the constriction.
– Aortic rupture.
CH0576/RHY
Aortic Coarctation
• Treatment:
• Aided by the well developed collateral
circulation the surgeon clamps off the
aorta above and beyond the stenosis.
• The aorta is surgically divided, and the
stenotic site removed.
• The divided ends can either be sutured
together or the stenotic area replaced
by a catheter
CH0576/RHY
Aortic Coarctation
• Occasionally the treatment can cause a
further problem:– When the full force of the arterial
pressure hits the wall of the aorta, distal
to the coarctation, the result can be a
widespread necrosis of the branches of
the abdominal aorta.
– Resulting in a widespread gangrene of the
small intestine.
CH0576/RHY
Tetralogy of Fallot
• As the name suggests this
a syndrome with four
major features.
• Probably the most
important congenital lesion
of the heart.
• It is the most common
lesion causing cyanosis.
• About 70% of ‘blue babies’
are examples of this
syndrome.
CH0576/RHY
Tetralogy of Fallot
• It is essentially a VSD
associated with other
cardiac abnormalities.
• The 4 features being:– A high VSD
– Pulmonary stenosis
– Dextraposed over-riding
aorta
– Right ventricular
hypertrophy
CH0576/RHY
Tetralogy of Fallot
• Basic change in this tetralogy
is the dextraposed aorta.
• This causes the pulmonary
artery stenosis.
• The aorta is thick walled and
wide compared with the
stenotic pulmonary artery
• The aorta over-rides the VSD
and so receives blood from
both ventricles.
CH0576/RHY
Tetralogy of Fallot
• If the pulmonary stenosis
is extensive or complete
the DA must remain
patent, to allow blood flow
to the lungs.
• Early closing of the DA in
these circumstances
would result in death.
• Most cases are surgically
treated
CH0576/RHY
Tetralogy of Fallot
• The surgical operation known as the
Blalock-Taussig procedure may be
employed.
• This bypasses the obstruction by
creating an artificial DA, through which
an adequate supply of blood can reach
the lungs.
• The subclavian artery is anastomosed
with the pulmonary artery.
CH0576/RHY
Tetralogy of Fallot
• The increase in blood flow to the
lungs causes an increase in blood flow
to the left heart.
• This raises LVP, and minimises any
right to left shunt.
• Hence the cyanosis is relieved.
CH0576/RHY
Tetralogy of Fallot
• Other surgical procedures which have
been employed include the removal of
and replacement of the pulmonary
valve.
• Resection of the stenotic region of
the pulmonary artery has also been
employed.
• Complications may include bacterial
endocarditis.
CH0576/RHY