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Biology of Disease CH0576

Developmental Defects of Cardiovascular System

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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:-

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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

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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 by-passed.

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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.

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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

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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.

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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.

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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

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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!

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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 still-born infants.

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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

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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.

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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

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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.

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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.

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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.