CVS S3 - Foetal Heart Development & Congenital Heart Defects Flashcards Preview

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Flashcards in CVS S3 - Foetal Heart Development & Congenital Heart Defects Deck (27)
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What are the most common congenital heart defects?

Ventricular septal defects (VSD) are the most common, followed by atrial septal defects (ASD)


What are "acyanotic" heart defects?

Heart defects which do not result in a lower than normal blood oxygen concentration
(So babies aren't blue)


What occurs after looping of the primitive heart tube?



Describe septation

The junction between the ventricle and atrium narrows and the atrioventricular canal is formed, providing framework for septation
Endocardial cushions form and grow superiorly/inferiorly to form the septa
This divides the heart into right and left channels


Describe atrial septation

The septum primum grows down towards the fused endocardial cushions
The ostium primum is the hole just before the septum primum fuses with the endocardial cushions
Before this hole closes, a second hole, the ostium secundum, forms above by apoptosis
A crescent shaped second septum then forms, the septum secundum, which has a hole called the foramen ovale


Why is atrial septation so complex?

There need to be two septa and two holes so that:
a) Blood can flow through both holes from one side of the heart to the other before birth
b) After birth, the different pressures in the atria cause the septa to come together, meaning blood can no longer pass between the left and right sides of the heart


What about the foramen ovale and ostium secundum allows blood flow between left and right atria to stop after birth?

Holes are slightly offset, so that when increased pressure in the left ventricle occurs when the first breath is taken and the septa are forced closed, there is essentially no longer a hole for the blood to pass through


What is the adult remnant of the foramen ovale?

The fossa ovalis


Describe the muscular component of ventricular septation

Has muscular and membranous components
Muscular component forms most of the septa and grows upwards towards the fused endocardial cushions
Leaves a hole at the top called the primary inter ventricular foramen


Describe the ductus venosus and explain why it is necessary

Allows oxygenated blood from the umbilical vein to bypass the liver and go straight to the inferior vena cava
It's necessary because if the blood went to the heart via the liver, much of the oxygen and nutrients would be removed, meaning there is not enough for the brain and the rest of the body


Describe the ductus arteriosus and explain why it's necessary

Shunt between the pulmonary trunk and the aorta
Necessary to bypass foetal non functional lungs


Describe the membranous component of ventricular septation

'Fills the gap' of the primary interventricular foramen
Derived from the spiral septum which divides the truncus arteriosus into the main outflow vessels


Why is the foramen ovale necessary?

Foetal lungs are non functional and to develop correctly, it's important they don't receive much blood, which could damage them


What are some important foetal shunts which allow different blood flow before and after birth?

Ductus venosus
Foramen ovale
Ductus arteriosus


How common are congenital heart defects?

About 6-8 per 1000 births


Give some examples of acyanotic heart defects

Atrial septal defect
Patent foramen ovale
Ventral septal defect
Patent ductus arteriosus
Coarction of the aorta


Describe atrial septal defects (ASD)

An opening in the septa between the atria which persists after birth
~67 in 100 000 live births
Usually due to failure of the foramen ovale to close
However because LA pressure>RA pressure, blood flows left to right so very little/no deoxygenated blood ends up in atrial circulations


Describe patent foramen ovale

Not true ASD
Generally clinically silent due to pressure LA>RA
Can be a route for venous emboli to migrate into systemic circulation (aka paradoxical embolism) if transient RA pressure increase


Describe ventricular septal defects

Hole/defect in the ventricular septum
Most commonly occurs in membranous section
Pressure in LA>RA so blood moves from left to right


Describe patent ductus arteriosus

Failure of ductus arteriosus (foetal shunt between aorta and pulmonary trunk) to close after birth
Blood moves from aorta to pulmonary trunk
A constant mechanical murmur may be heard
If untreated may result in remodelling of pulmonary circulation and increased pulmonary resistance
This may cause blood flow in the ductus arteriosus in the opposite direction (Eisenmenger Syndrome)


What happens to the foetal shunts after birth?

Foramen ovale: closes when RA pressureDuctus arteriosus: contracts & becomes ligamentum arteriosus
Ductus venosus: no blood coming in via umbilical vein so closes & becomes ligamentum venosus
Umbilical vein: becomes ligamentum teres


Describe coarctation of the aorta

Narrowing of the aortic lumen near the ligamentum arteriosum
This increases the after load on the left ventricle
May cause left ventricular hypertrophy
Delayed femoral pulse and reduced blood flow to lower body
In severe cases may present as heart failure in babies
In mild cases, may only be detected in adult life


Give some examples of cyan optic heart defects

Tetralogy of fallot
Tricuspid atresia
Transposition of the great arteries
Hypoplastic left heart


Describe tetralogy of fallot

Overriding aorta
Pulmonary stenosis
Right ventricular hypertrophy
Occurs as a result of outflow tract of interventricular septum too far in the anterior and cephalad direction


Describe tricuspid atresia

Lack of development of tricuspid valve
Must be:
-Complete right to left shunting of blood returning to RA (by ASD or PFO)
-PDA or VSD to allow blood flow to lungs


Describe transposition of the great arteries

Results in two unconnected parallel circulations instead of two in series
LV connected to pulmonary trunk and RV connected to aorta
Incompatible with life after birth unless shunt exists eg ductus arteriosus or ASD


Describe hypoplastic left heart

LV and aorta fail to develop properly
PFO or ASD also present with systemic circulation via PDA
Incompatible with life after birth without surgical correction