for tetralogy a fellow don't worry about
what fellow means that's just the name
of the guy this French physician who
named this disease so we want to focus
on the first word here which is
tetralogy and going back to Latin here
tetra tetralogy the word is telling us
that there are four defects that we care
about that make up this particular heart
disease remember that this is congenital
so people are born with these four
defects in the heart but first let's
quickly review what a normal heart does
so blood from the body that returns to
the heart initially is going to be blue
because it's low and oxygen the muscles
have used up the oxygen so it returns to
the heart into the right atrium the
receiving chamber from there goes to the
right ventricle which pumps it into this
blood vessel which is the pulmonary
artery remember that any vessel that
receives blood going out of the heart is
an artery so even though it's an artery
it's still blue - donated blood from the
lungs red oxygenated blood returns here
via the pulmonary veins into the left
atrium and there goes to the left
ventricle and goes out this big red
structure the aorta to the body so
neutrality the first effect that we
worry about some would argue it's the
defect that governs how this heart
functions is called pulmonary stenosis
so pulmonary you know has to do with the
lungs in this case is referring to the
valve that leads blood to the lungs so
the pulmonary valve is right here
cenotes is a structure and narrowing
so this pulmonary valve here is
thickened see as the right ventricle is
pumping blood into it it is harder to
pass through it because it's literally
just thick and restricting so the degree
of pulmonary stenosis determines how
hard is it to pump blood into the
pulmonary arteries and determines how
severe this heart is functionally
damaged now our second defect is a
direct result of this and also depends
on the degree of stenosis and that is
right ventricular hypertrophy so imagine
trying to pump blood against a narrow
open
day in and day out hypertrophy is when
the muscle is over exercised and
overused and it literally becomes bigger
so the right ventricle this chamber
right here becomes thicker just on the
extra workload that it has for pumping
against this narrow valve so a lot of
times this hypertrophy is enough to
alter the shape of this right ventricle
here so do you see in the way I've drawn
it before has a nice slope so if our
normal heart follows a curvature kind of
like this in technology the shape can
actually look more like this it comes
down here right angle and that's why
some people actually say on x-ray we're
just looking at the growth shape of the
heart can look like a boot so the boot
sign is something that we associate with
tetralogy because of the severe right
ventricle hypertrophy that can happen
all right let's move on to the third one
so usually if there is a hole between
the right and left ventricle the bottom
chambers we draw this whole red here it
can actually be anywhere along this
septum and we call it a VSD which stands
for ventricular that tells you where it
is it's between the ventricles septal
which is the wall the septum between
them defect have a hole okay I'm going
to draw this right here so now in the
machinery of the heart we have a
connection between the left and right
and now for the last defect we have an
overriding aorta
what is the overriding so the aorta is
usually plugged into the left ventricle
but overriding means that it actually
receives blood from both the left and
right now and from the place I've drawn
the VSD right under the aorta I could
almost just leave it like this but just
to drive the point home I want to redraw
this part that the aorta comes over to
the right and it's now this kind of
central structure now from here now it
can receive blood both from the right
and the left so now let's think about if
I'm drop of blood where I want to go in
this new heart with these four defects
so from the right atrium go to the right
ventricle that's normal so from here I
have a choice right I can either
go up this pulmonary artery's through
this very narrow opening in the valve
that's going difficult or I can easily
go into this a Horta with a valve that's
more welcoming that's less restricted
see I draw these two arrows with
different calibers as I'm leading you to
the answer which is that I want to go
this way into the aorta also in general
blood in the right ventricle is going to
be push toward the left because look at
how big the right ventricle is now it's
this huge powerful muscle and it serves
as the motor that drives this right to
left shut and there and you have the
answer for why this is cyanotic disease
because blue blood is being forced to
the left because a it's hard to go
through the pulmonary artery we're
supposed to go and be the right
ventricle is so powerful it's going to
push it across the VSD remember blood
follows the easiest path so the left
ventricle is still pumping and the blood
is basically going to go into the aorta
so now in the aorta going out to the
body we have red blood and we have blue
blood so what actually goes out to
oxygenate our body is this purplish
mixture purple some blue some red and at
any given moment how blue it is or how
red depends on the tug-of-war between
all these factors how restricted is this
pulmonary artery how much resistance is
coming from the lungs
remember the pulmonary arteries are
plugged into the lungs how hard the
right ventricle is pumping blood across
the VSD so these are all factors that
determine how much our purplish mixture
is red vs. blue sometimes kids who have
tetralogy can have a sudden Tet spell
which is when they get acutely worse and
they can't breathe that's because their
pulmonary artery pressure a resistance
when the lungs has suddenly increased
all that does is create more back
pressure in the pulmonary artery it's
already hard to get blood in here and
the Tet spell makes it even worse so a
Texas patients more blue blood into the
aorta this mixture becomes even bluer
this is a life-threatening emergency in
tetralogy and lastly I want to talk
about the fact that before people even
knew what tetralogy was or what the
heart actually looked like
we noticed that kids who have it
or this type of kid would suddenly squat
onto the ground especially when they've
been playing or running around they'll
suddenly feel a lot worse they'll squat
and they'll feel better so here we have
a kid I was a kid because for the most
part this is still a pediatric disease
we correct it in the patients when there
are kids so they're running around let's
say they're four years old and suddenly
they'll stop and they'll squat on to the
ground how do you draw a squatting stick
figure does that make sense that looks
more like they're sitting like and try
again so they're squatting there we go
and as they get into this position for a
few seconds they feel better too let's
think through this step by step okay two
things happen when somebody with
tetralogy or I guess anybody is running
around the first one is at the o2 or
oxygen saturation in their veins drops
because their muscles are working hard
and they're extracting more oxygen from
it so the blood going back to the heart
here and here have a lower oxygen
content and secondly what happens is
that their vessels in their legs or
whatever muscles they're using a lot
they vasodilator
so the body can get more blood they're
literally the vessels in their blood the
diameter goes from this to this it just
gets bigger so let's look at this one at
a time so if the o2 in the veins drop
what happens so the blood returning to
the heart is essentially bluer so the
blood returning to the heart has a lower
oxygen concentration and some of it goes
right back out to the aorta then running
around has made our blood bluer in the
aorta all this does is make our cyanosis
worse that's going to make our patient
more blue in the face and they don't
feel good for vasodilation what happens
is the structure or the caliber of the
vessels determines how much resistance
is pushing back on our aorta
so the vasodilation really lowers the
resistance in the aorta so in the
competition between the right and left
between the blue and the red again this
makes us bluer making this red straw
sure have lower resistance means more of
the blue blood will get into it so again
we're bluer and more cyanotic so now
this child is really not feeling well
and look when they squat both of these
things are reversed first of all they've
stopped running around so the oxygen
content in their veins can go up so here
they've got slightly higher oxygen
content in their veins just by stopping
and trying to take deeper breath and
secondly they're literally taking the
vessels in their legs and squeezing them
which increases their systemic
resistance this is the resistance of all
the arteries in the body systemic
resistance since they're all connected
to the aorta this increases the
resistance that the aorta is pumping
against so ask these two colors of blood
rush at this general area when the
resistance in the aorta increases it
literally just forces more blood into
the pulmonary artery so the competition
is where where is it harder to go and
when this child has squatted it is
harder to go into the aorta at this
point because it's like they've taken
the end of a hose and they squeeze it
down so this just force it's more blood
into the pulmonary artery it's still
restricted but it's not the difference
between the two has lessened so when
blood goes into the pulmonary artery
this child will feel like it's easier to
take some good breaths and this will
also increase the return of oxygenated
blood into the left side of the heart so
the whole effect is that we reverse the
shunt a little bit we get more blood out
to the lungs the pulmonary artery and we
just increase the overall Austrian
content in our mixture a little bit so
when we think of tetralogy the things
that most determine how bad or how
severe a person's symptoms are one the
pulmonary stenosis how severe is it and
to where is the VSD so I would think of
tetralogy overall as a constant fight a
tug-of-war for the heart to pump blood
into either the pulmonary artery or the
aorta and the state of the mixture
between the red and blue blood
determines this person's symptoms
at any given moment