When it comes to classifying shunts that are present in congenital heart disease,
it's useful to group them into right-to-left and left-to-right shunts.
Right-to-left shunts are gonna be the ones that cause cyanosis most often
because deoxygenated blood from the right side of the heart
is being pushed into the left side of the heart which is then going into systemic circulation.
So this mixture of deoxygenated blood with oxygen in the blood throughout the body
causes the blood to appear more bluish
and the skin and mucous membranes of an affected person
maybe more purplish-blue than someone who's not affected.
So amongst right-to-left shunts we have things like truncus arteriosus
where the blood mixes on its way out of the heart,
transposition of the great vessels because the wrong vessel is receiving blood
from the right ventricle and left ventricle respectively,
tricuspid atresia where blood has to move from the right atrium to the left atrium
and then to the ventricles to get out to the systemic circulation,
Tetralogy of Fallot with a ventricular septal defect
and overriding aorta cause mixing of blood
and lastly, total anomalous pulmonary return.
This is a topic we're going to file away
until after you've seen development of the venous system
because we'll discuss it and its relationship
to how the veins form and drain back to the heart.
Left-to-right shunts tend to be acyanotic because we have oxygenated blood
moving from the left side of the heart to the right
and the oxygenated blood going to the body
remains oxygenated and doesn't cause the bluish tinting.
These will be things like atrial septal defect,
where increased pressures on the left push blood to the right,
ventricular septal defect for the exact same reason,
the right ventricle is under less pressure than the left ventricles
so septal defect there and isolation
will just tend to cause oxygenated blood moving to the right,
patent ductus arteriosus is going to tend to have high pressure blood running through the aorta
to the pulmonary trunk and lastly, atrioventricular canal defect.
This one's a little bit of a misnomer in that a huge atrioventricular canal defect
will definitely cause mixing of the blood travelling to both the aorta and the pulmonary trunk,
but smaller atrioventricular canal defects
probably linked with a ventricular septal or atrial septal defect
will have a net movement of blood from left to right as the pressure in the left side
is greater than the pressure on the right side.
Now things that can happen as a result of these shunts are fairly complicated,
but one very good syndrome to get under your belt is Eisenmenger's syndrome.
If I've got a long standing left-to-right shunt,
I've got blood leaving my left ventricle and moving into my right ventricle.
Over time, that increased volume of blood in the right ventricle causes my right ventricle to enlarge
and get stronger to try to push against that increased pressure.
This hypertension on the right side will eventually cause the right ventricle to get so large
that it becomes stronger than the left ventricle
and we will then reverse and have a right to left shunt.
At this point, we will become cyanotic because deoxygenated blood from the right ventricle
is being pushed much more strongly into the left ventricle and thereafter into circulation,
so that is Eisenmenger's syndrome.
Next stop is Ebstein's anomaly.
In this case, we have the tricuspid valves form in an inappropriate manner
and usually the posterior or septal cusps of the tricuspid valve
are no longer hanging out cleanly between the right atrium and the right ventricle,
they've been displaced into the ventricle.
In effect, this makes the right atrium bigger because it's taking up real estate
that belongs to the right ventricle and the right ventricle is smaller,
so in this condition every time the right ventricle contracts there will be regurgitation of blood
into the right atrium and if there's an atrial septal defect there,
which commonly there is in Ebstein's anomaly,
you will have a net shunting of blood from right to left causing cyanosis.
Thank you very much for your attention and I'll see you on our next talk.