Congenital Heart Defects Flashcards
What are the 2 possible mechanisms by which dextrocardia can occur?
- it can occur as a result of abnormal cardiac looping
- it can be induced during gastrulation (week 3) when laterality (left / right sides) is determined
What is isolated dextocardia associated with?
- isolated dextrocardia is associated with other structural defects including abnormal connections with veins and arteries or abnormal septation of the heart
What is the consequence of patent ductus arteriosus?
What should happen normally?
- the ductus arteriosus should close soon after birth due to increased oxygen tension and decreased circulating prostaglandins
- a patent ductus arteriosus allows shunting of blood from the aorta into the pulmonary artery
- oxygenated blood travels back to the lungs then returns to the heart to be pumped out again, which increases the workload of the heart
- this can result in pulmonary hypertension, ventricular hypertrophy and heart failure
What is the treatment for patent ductus arteriosus?
- it is treated with prostaglandin inhibitors
- it may occur as an isolated defect or with other cardiac defects
What are the possible mechanisms that can result in atrial septal defects?
- a patent foramen ovale can result from failure of the septum primum and septum secundum to fuse after birth
- malformations in the septum primum or septum secundum can mean that they do not overlap and leave a gap
- malformations in the septum secundum are more common
How common is a patent foramen ovale?
When does it cause symptoms?
- occurs in 1 in 4 people
- it is usually asymptomatic as the higher pressure in the LA pushes the septum primum against the septum secundum to mechanically shut the valve
- if there is higher pressure in the RA (e.g. pulmonary hypertension), this can push the septum primum open and allow a R-L shunt of blood
Why might an ostium secundum defect occur?
What are the consequences of this?
- caused by excessive apoptosis in the septum primum or by inadequate development of the septum secundum
- this causes the foramen ovale and ostium secundum to overlap
- there is a L-R shunt of blood, which can cause enlargement of the RA and RV
- small defects (<5mm) may be asymptomatic, but larger ones may require surgical repair
What happens in cor triloculare biventriculare?
- this condition is also called “common atrium”
- it is a rare cardiac defect in which there is complete absence of the atrial septum
- it occurs due to failure of development of the septum primum and septum secundum
What happens if there is premature closure of the foramen ovale?
- closure of the foramen ovale during prenatal life results in hypertrophy of the right side of the heart and underdevelopment of the left side
- death usually occurs shortly after birth
What is the most common congenital heart defect?
ventricular septal defects
- these are often associated with other congenital malformations e.g. Down’s syndrome
What are the 2 different types of VSD?
What are the clinical consequences of these defects?
- VSDs can either affect the muscular part of the interventricular septum or the membranous part
- VSDs in the muscular part often resolve themselves as the child grows
- VSDs allow for left-to-right shunting of blood
- this can result in pulmonary hypertension and hypertrophy of the RV
What are examples of septation defects of the truncus arteriosus and why do they occur?
- the conotruncal swellings that form the conotruncal septum rely on the migration of neural crest cells from the neural tube
- abnormal neural crest cell development or migration can lead to a number of defects in septation of the truncus arteriosus into the aorta and pulmonary trunk
- examples include:
- persistent truncus arteriosus
- tetralogy of fallot
- transposition of the great vessels
What happens in persistent truncus arteriosus?
What are the symptoms and treatment for this?
- the conotruncal septum is completely absent
- as it is absent, the septum cannot fuse with the interventricular septum, so there is a ventricular septal defect
- the undivided truncus is in communication with both ventricles so receives oxygenated and deoxygenated blood
- symptoms include:
- cyanosis (blue colour) at birth
- lethargy
- breathlessness
- delayed growth
- it must be corrected surgically or else there will be heart failure and death within 2 years
Why does transposition of the great vessels occur?
What must be present for a child with this condition to survive?
- it occurs when the conotruncal septum does not form in a spiral and runs straight down instead
- the aorta arises from the RV and pulmonary trunk from the LV
- it is incompatible with life unless there is an accompanying shunt, such as a VSD, patent foramen ovale or patent ductus arteriosus
What are the 4 features seen in Tetralogy of Fallot and why does this occur?
- pulmonay stenosis
- ventricular septal defect
- overriding aorta (rightward displacement of aorta)
- right ventricular hypertrophy (due to higher pressure on RHS)
- these 4 abnormalities are all caused by the same primary defect
- there is unequal division of the truncus arteriosus caused by anterior displacement of the aorticopulmonary septum
- the result of this is poor oxygenation and cyanosis, but it is not fatal
What is coarctation of the aorta?
Why does it happen and how can it be classified?
- this is narrowing of the aorta that occurs near the ductus arteriosus
- the cause is unknown, but may be due to abnormal migration of cells from the ductus arteriosus
- can be classifed as preductal or postductal in relation to the ductus arteriosus
