Congenital heart defects Flashcards
What are the groups of causes of CHDs?
Genetic
Environmental
Maternal infections
What are three genetic conditions that give CHDs? Which CHDs do they each give?
Down’s syndrome - atrioventriclar septal defect
Turner’s syndrome - coarctation of aorta
DiGeorge syndrome - tetralogy of fallot
What are the environmental causes of CHDs?
Teratogens e.g. drugs, alcohol
What are two examples of maternal infections that cause CHDs?
Rubella
Toxoplasmosis
What are the categories of CHDs?
Acyanotic
Cyanotic
What are the defects involved in acyanotic CHDs?
Stenosis, obstruction
Or opening
What is the direction of blood flow across openings in acyanotic CHDs?
Left-to-right shunts
How are left-to-right shunts acyanotic?
Oxygenated blood from lungs is travelling back to the lungs
no deoxygenated blood travelling to body
Why does blood move from the left side of the heart to the right side of the heart in left-to-right shunts?
Left side of heart is at higher pressure than right side
What are seven examples of acyanotic CHDs?
Atrial septal defect
Ventricular septal defect
Patent ductus arteriosus
Aortic stenosis
Coarctation of aorta
Mitral stenosis
Pulmonary stenosis
What is an atrial septal defect (ASD)?
Persistent opening in interatrial septum after birth
What is the most common site of an ASD?
Foreamen ovale
What are ASDs caused by?
Septum primum being resorbed too much
or
Septumum secundum being too short
What does the amount of blood moving through an ASD depend on?
Size of opening
What does the RV experience with ASDs? Why?
Volume overload
due to extra blood entering RA from LA, then RV
How does the RV respond to volume overload?
Dilates
What can dilation of the RV lead to?
Right-sided heart failure
What happens to blood flow in the pulmonary circulation with an ASD?
Increased blood flow through pulmonary circulation
What can increased pulmonary blood flow in an ASD lead to?
Pulmonary hypertension
What are VSDs?
Abnormal opening in ventricular septum
Where are VSDs most common?
Membranous portion of ventricular septum
How does the LV respond to volume overload?
Dilates
What does dilation of the LV lead to?
Left sided heart failure
What does the LV experience with VSDs? Why?
Volume overload
increased blood flow in RV, pulmonary circulation, LA, then LV
What may increased blood flow through the pulmonary circulation with a VSD lead to?
Pulmonary hypertension
What is a patent ductus arteriosus (PDA)?
Ductus arteriosus fails to close after birth
persistent communication between pulmonary artery and descending aorta
What does the pulmonary circulation experience with PDA?
Volume overload
What may volume overload in the pulmonary circulaton with PDA lead to?
Pulmonary hypertension
What is the cause of congenital aortic valve stenosis?
Bicuspid form of valve instead of tricuspid
narrower opening
How does congenital aortic stenosis affect blood flow?
Increases resistance to blood flow out of the LV
In what direction does blood shunt in PDA? Why?
From aorta to pulmonary artery
aorta is at higher pressure than pulmonary artery
What do the LA and LV experience with PDA?
Volume overload
How does pulmonic stenosis affect blood flow?
Increases resistance to blood flow out of RV
What happens to the RV with pulmonic stenosis? Why?
RV has to contract harder to generate higher pressure to push blood through pulmonic stenosis
RV hypertrophies
What is coarctation of the aorta?
Narrowing of aortic lumen
What are the causes of pulmonic stenosis?
Pulmonary valve stenosis
Pulmonary artery narrowing
What happens to the LV with coarctation of aorta? Why?
LV has to contract harder to generate higher pressures to pump blood into aorta
LV hypertrophies
What forms around the aorta with coarctation of aorta? Why?
Collateral arteries
to bypass the narrowing
What type of shunt do cyanotic CHDs involve?
Right-to-left shunts
What do right-to-left shunts require? Why?
Opening - for blood to pass through from right side of heart to left side
Distal obstruction - to give increased resistance to blood flow out of RV, so blood moves from RV to LV instead
Why are right-to-left shunts cyanotic?
Deoxygenated blood from body is entering systemic circulation
instead of to the lungs
What is cyanosis?
Blue-purple discolouration of skin and mucous membranes
What is the cause of cyanosis?
High levels of deoxygenated Hb in the blood
What are five examples of cyanotic CHDs?
Tetralogy of Fallot
Transposition of great arteries
Tricuspid atresia
Pulmonary atresia
Hypoplastic left heart syndrome
What are the four defects in Tetralogy of Fallot?
VSD
Over-riding aorta
Pulmonic stenosis
RV hypertrophy
What is the effect of the over-riding aorta in tetralogy of fallot?
Deoxygenated blood from RV enters aorta
enters systemic circulation
What is the effect of pulmonic stenosis in tetralogy of fallot?
Increased resistance to blood flow out of RV
What causes RV hypertrophy in tetralogy of fallot?
RV has to contract harder to generate higher pressuers to pump blood through pulmonic stenosis
What does the amount of blood shunting from the RV to the LV depend on in tetralogy of fallot?
The size of the VSD
The extent of the pulmonic stenosis
What is transposition of the great arteries?
Aorta arises from RV
Pulmonary artery arises from LV
How does transposition of the great arteries affect blood flow?
Have two separate circuits of blood flow
rather than two circuits in series
What the two separate circuits of blood flow with transposition of the great arteries?
LA - oxygenated blood LV - oxygenated blood Pulmonary artery - oxygenated blood Pulmonary veins - oxygenated blood LA - oxygenated blood
RA - deoxygenated blood RV - deoxygenated blood Aorta - deoxygenated blood Vena cavae - deoxygenated blood RA - deoxygenated blood
Why does a foetus with transposition of the great arteries survive till birth?
Due to the shunts in foetal circulation
- foramen ovale
- ductus arteriosus
Form communication between the two circuits of blood flow
Why is transposition of the great arteries problematic after birth?
Shunts close
loss of communication between two circuits of blood flow
When might transposition of the great arteries not be as much of a problem after birth?
Shunts remain open
e.g. patent foramen ovale
PDA
What is tricuspid atresia?
Complete absence of tricuspid valve
How does tricuspid atresia affect blood flow?
No blood flow into RV
How does tricuspid atresia affect the RV? Why?
RV is hypoplastic - underdeveloped or absent
because it didn’t have any blood to contract against
What is required for a foetus with tricuspid atresia to survive? Why?
ASD
allows blood flow from RA to LA
VSD
allows blood flow from LV to RV to pulmonary artery to lungs to be oxygenated
Why does blood flow from RA to LA with tricuspid atresia?
Blood cannot flow into RV
only route for blood flow is into LA
Why does blood flow from the LV to RV with tricuspid atresia?
RV isn’t receiving any blood from RA
LV is at higher pressure than RV
What is an alternative to the VSD with tricuspid atresia?
PDA
How is tricuspid atresia cyanotic?
Deoxygenated blood moves from RA to LA
to LV
to aorta and systemic circulation, some of it
What is pulmonary atresia?
Sealed pulmonary valve
How does pulmonary atresia affect blood flow?
No blood flow into pulmonary trunk
What is required for a foetus with pulonary atresia to survive? Why?
ASD
Allows blood flow from RA to LA
PDA
Allows blood flow from aorta to pulmonary artery
Why does blood flow from RA to LA with pulmonary atresia?
Increased resistance to blood flow out of RV, into RV
Less resistance to blood flow into LA
Why does blood shunt from the aorta to the pulmonary trunk with pulmonary atresia?
Because pulmonary artery isn’t recieving any blood
aorta is at higher pressure than pulmonary artery
blood flows down the pressure gradient
Why is cyanosis seen with pulmonary atresia?
Because deoxygenated blood is going from RA to LA
to LV
to aorta and systemic circulation, some of it
What is hypoplastic left heart syndrome (HLHS)?
LV and ascending aorta are under-developed
aortic and mitral valves are stenosed or sealed
What is essential for a foetus with HLHS to survive?
ASD
allows blood flow from LA to RA
PDA
allows blood flow from pulmonary trunk to aorta
Why does blood flow from LA to RA with HLHS?
Blood cannot flow into LV
only route for blood flow is into RA
Why does blood flow from pulmonary artery into aorta with HLHS?
Because aorta isn’t receiving any blood
pulmonary artery is at higher pressure than aorta
What is the role of the RV with HLHS?
Support systemic circulation
Why is cyanosis seen with HLHS?
Mixing of oxygenated and deoxygenated blood in RA
oxygenated from LA
deoxygenated from venae cavae
enter RV, pulmonary trunk and aorta
What happens to the LV with congenital aortic stenosis? Why?
LV has to contract harder to generate more pressure to push blood through stenosed valve
LV hypertrophies
How does coarctation of the aorta affect blood flow?
Increases resistance to blood flow in the aorta
increases aortic pressure, afterload