Congenital Heart Defects Flashcards
What is dextrocardia?
A rare condition in which the apex of the heart points towards the right side of the chest
In what 2 ways may dextrocardia arise?
- as a result of abnormal cardiac looping
2. it may be induced during gastrulation (week 3)
How may dextrocardia result from abnormal cardiac looping?
Normal looping involves a bend to the RHS, ventrally and caudally
In dextrocardia, it bends to the left
How may dextrocardia occur during gastrulation?
Cilia sweep cells to the correct sides of the body
In Kartagener syndrome, the cilia may sweep cells to the wrong side of the body
What is isolated dextrocardia?
This is when only the heart is on the opposite side of the body
Why does isolated dextrocardia not usually cause problems?
As long as the major vessels connect to the correct structures, there are no issues
What other structural defects is isolated dextrocardia associated with?
Abnormal connections with veins and arteries
Abnormal septation of the heart
What happens in dextrocardia if the vessels transpose?
Serious complications
e.g. oxygenated blood will be sent to the lungs
What is the role of the ductus arteriosus in the foetus?
It joins the aorta to the pulmonary trunk
It is used for blood to pass from the PT into the aorta and bypass the lungs
Why does the ductus arteriosus close at birth?
It closes due to increasing oxygen tension and a decrease in circulating prostaglandins
What does the ductus arteriosus become in the adult?
Ligamentum arteriosum
What happens in patent ductus arteriosus?
The ductus arteriosus remains open after birth
This causes shunting of blood from the aorta to the pulmonary artery
What is the result of having a patent ductus arteriosus in an adult?
Oxygenated blood travels back to the lungs, and then returns to the heart to be pumped out again
This increases the workload of the heart
Why does the blood flow through the ductus arteriosus in the opposite direction to the foetus?
In a foetus, blood moves from pulmonary trunk to aorta
In an adult, blood moves from the aorta to the pulmonary artery
Blood moves down a pressure gradient
What are the 3 main conditions that patent ductus arteriosus can lead to?
- pulmonary hypertension
- ventricular hypertrophy
- heart failure
Why does patent ductus arteriosus lead to pulmonary hypertension?
there is increased pressure going towards the lungs
What is ventricular hypertrophy?
Why is it necessary in patent ductus arteriosus?
The muscle of the ventricle increases in thickness
This is needed to allow the ventricle to work against the extra pressure
In what cardiac defect is a patent ductus arteriosus essential for life?
Coarctation of the aorta
How is patent ductus arteriosus treated?
Why?
Prostaglandin inhibitors
Prostaglandins keep the ductus arteriosus open
As the septum primum reaches full septation, what happens?
There is cell apoptosis to develop a small opening
This allows blood to pass from one side of the heart to the other
How does blood flow through the septa in a foetus and why?
Blood must pass through the foramen primum before the foramen secundum
This is due to the holes in the 2 septa being misaligned
After birth, why does the septum primum push against the septum secundum and fuse?
There is an increased amount of blood entering the left atrium
this pushes the septum primum against the septum secundum
What happens if the septum primum and septum secundum fail to fuse after birth?
This leads to probe patent foramen ovale
How common is probe patent foramen ovale?
Very common and occurs in 1 in 4 people
Why is probe patent foramen ovale usually asymptomatic?
The higher pressure in the left atrium pushes the septum primum against the septum secundum
This mechanically shuts the valve
When will a probe patent foramen ovale become symptomatic?
If there is a higher pressure in the right atrium, this pushes the flimsy septum primum open
What happens if the flimsy septum primum is pushed open?
Blood can shunt from right to left
What is the primum/secundum atrial septal defect caused by?
Malformations in the septum primum or septum secundum
They do not overlap fully, and therefore leave a gap
What is the result of a primum/secundum atrial septal defect?
An opening in the septum means that blood can pass from one atrium to the other
In which septum do defects usually occur ?
Septum secundum
What type of defect will excessive apoptosis in the septum primum lead to?
An ostium secundum defect
This is because the hole is too large to fill
How else may an ostium secundum defect be caused?
Inadequate development of the septum secundum
This can lead to the formaen ovale and ostium (foramen) secundum overlapping
What is the result of a ostium secundum defect?
Blood is shunted from left to right
This can cause enlargement of the right atrium and ventricle
How are ostium secundum defects treated?
Small defects < 5mm are usually asymptomatic as there is not much mixing of blood
Larger defects require surgical repair
What is cor triloculare biventriculare?
It is also called common atrium
It is a rare cardiac defect with complete absence of the atrial septum
What causes cor triloculare biventriculare?
Failure of development of the septum primum and septum secundum
This leads to formation of one common chamber
What is the major consequence of cor triloculare biventriculare?
Mixing of oxygenated and deoxygenated blood
What is ‘premature closure of the foramen ovale’?
This occurs when the foramen ovale closes during prenatal life
How does premature closure of the foramen ovale affect the right and left sides of the heart?
It results in hypertrophy of the right side of the heart
And underdevelopment of the left side of the heart
Why does premature closure of the foramen ovale lead to underdevelopment of the left side of the heart?
Blood cannot go from the right to the left side of the heart
The left side does not receive as much blood, so cannot develop properly
Why does premature closure of the foramen ovale lead to hypertrophy of the right side of the heart?
The right ventricle becomes thicker and more muscular to deal with the increased volume of blood
Why does premature closure of the foramen ovale usually result in death after birth?
The undeveloped left heart cannot pump sufficient amounts of blood around the body after birth
What are the most common congenital heart defects?
Ventricular septal defects
Which part of the heart may be affected by a ventricular septal defect?
Either the muscular or membranous part of the interventricular septum
How do defects of the muscular part of the interventricular septum resolve themselves?
They resolve themselves as the child grows
As they grow, the muscles get bigger and the gap decreases in size until it eventually fuses
What is the result of having a ventricular septal defect on blood flow?
It allows left to right shunting of blood
This leads to an increased amount of blood in the right heart
What can ventricular septal defects cause?
Pulmonary hypertension
Hypertrophy of the right ventricle
Why does a ventricular septal defect lead to pulmonary hypertension?
There is an increased amount of blood and increased pressure going to the lungs
What does formation of the conotruncal septum rely on?
The conotruncal swellings that form the conotruncal septum rely on the migration of neural crest cells from the neural tube
What does abnormal neural crest cell development or migration lead to?
Defects in septation of the truncus arteriosus into the pulmonary trunk and the aorta
What type of septation does the common outflow tract rely on?
Spiral septation
The spiral must develop in an even format to develop into a pulmonary trunk and aorta
What will transposition of the great vessels lead to?
The aorta will lead to the lungs
The pulmonary trunk will lead to the rest of the body
What is the state of the conotruncal septum in persistent truncus arteriosus?
The conotruncal septum is completely absent
It cannot fuse with the interventricular septum
What happens in persistent truncus arteriosus?
The undivided truncus arteriosus is in communication with both ventricles
It receives both oxygenated and deoxygenated blood
What are symptoms of persistent truncus arteriosus?
- cyanosis at birth
- lethargy
- breathlessness
- delayed growth
What happens if persistent truncus arteriosus is not fixed surgically?
It results in heart failure and death within 2 years
What is the state of the conotruncal septum that leads to transposition of the great vessels?
The conotruncal septum does not form in a spiral
It runs straight down
In which situations is transposition of the great vessels compatible with life?
It is incompatible with life unless a shunt exists
This may be:
- ventricular septal defect
- patent foramen ovale
- patent ductus arteriosus
What happens in transposition of the great vessels?
The aorta arises from the RV
The pulmonary artery arises from the LV
Oxygenated blood is going to the lungs, and deoxygenated blood is travelling around the body
What is tetralogy of Fallot?
A collection of 4 abnormalities caused by the same primary defect
What causes the abnormalities in tetralogy of Fallot?
Anterior displacement of the aorticopulmonary septum causes unequal division of the truncus arteriosus
What are the 4 cardiac defects present in tetralogy of Fallot?
- pulmonary stenosis
- ventricular septal defect
- overriding aorta
- right ventricular hypertrophy
What is pulmonary stenosis?
Narrowing of the pulmonary trunk
What is the ventricular septal defect present in tetralogy of Fallot?
the last section of the conotruncal septum cannot form properly
This is where the membranous part of the ventricular septum attaches to
What is overriding aorta?
Rightward displacement of the aorta
And the aorta is larger than usual
What causes right ventricular hypertrophy?
The higher pressure on the right side of the heart
What is the consequence of tetralogy of Fallot?
Poor oxygenation of the body leading to cyanosis
How many births are affected by Tetralogy of Fallot?
1 in 1000 births
It is not fatal
What is coarctation of the aorta?
Narrowing of the aorta that occurs near the ductus arteriosus
What is the consequence of coarctation of the aorta?
Not enough blood can pass through the systemic circulation
What is the cause of coarctation of the aorta?
The cause is unknown but is may be due to abnormal migration of cells from the ductus arteriosus
How is coarctation of the aorta classified?
In relation to the ductus arteriosus
It is either preductal or postductal
What is the difference between preductal and postductal coarctation of the aorta?
Preductal - the narrowing occurs before the ductus arteriosus
Postductal - the narrowing occurs after the ductus arteriosus
What happens to the ductus arteriosus after birth if coarctation is preductal?
It usually remains open
It acts as a shunt to bypass the coarctation
What happens to an infant with preductal coarctation, if the ductus arteriosus is obliterated?
It causes rapid decline of the infant with hypoperfusion of the lower body
This leads to differential cyanosis
What is meant by differential cyanosis in preductal coarctation?
The upper body and head are well perfused
The lower body is cyantotic
How is preductal coarctation of the aorta treated?
Why is postductal coarctation not treated this way?
Administering prostaglandins to keep the ductus arteriosus open
If the coarctation occurs after the ductus arteriosus, there is no point in keeping it open
Which type of coarctation of the aorta is more common?
Postductal coarctation
What happens during development in postductal coarctation of the aorta?
A collateral circulation is established to bypass the narrowing
What is the first part of the collateral circulation?
Blood passes from the arch of the aorta into the subclavian arteries
What do the subclavian arteries join to in the collateral circulation?
The subclavian arteries lead to the internal thoracic arteries
How does blood pass from the internal thoracic arteries into the descending aorta in collateral circulation?
The internal thoracic arteries lead to anterior intercostal arteries
The anterior intercostal arteries anastomose with the posterior intercostal arteries
Blood leads from the posterior intercostal arteries into the descending aorta
As a result of coarctation of the aorta, what happens to the internal thoracic and intercostal arteries?
They enlarge in order to carry greater blood flow
