Tetralogy of fallot | Circulatory System and Disease | NCLEX-RN | Khan Academy
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Tetralogy of fallot | Circulatory System and Disease | NCLEX-RN | Khan Academy

– For Tetralogy of
Fallot, don’t worry about what Fallot means. That’s just the name of the
guy, this French physician, who named this disease. So we wanna 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. The blood from the body that
returns to the heart initially is gonna be blue because
it’s lower in oxygen. The muscles have used up the oxygen. So it returns to the heart
into the right atrium, the receiving chamber. From there it goes to the right ventricle, which pumps it into this blue 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, de-oxygenated blood. From the lungs, red oxygen
in the blood returns here via the pulmonary veins,
into the left atrium. From there it goes to the left ventricle, and it goes out this big
red structure, the aorta, to the body. So in tetralogy, the first
defect 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, it’s referring to the valve that leads blood to the lungs. So the pulmonary valve is right here. Stenosis is a stricture or narrowing, so this pulmonary valve here is thickened. So 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 opening, day in and day out. Hypertrophy is when the
muscle is over exercised and over used and it
literally becomes bigger. So the right ventricle,
this chamber right here, becomes thicker to assume 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, it has this nice slope. So if our normal heart follows a curvature kind of like this, in tetralogy
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, when just looking at the
growth shape of the heart, that it’ll 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. Alright, let’s move on to the third one. So usually there is a hole between the right and left ventricle,
the bottom chambers. I’m gonna draw this hole right here. It can actually be
anywhere along this septum. And we call it a VSD, which
stands for ventricular. It tells you where it is,
it’s between the ventricles. Septal, which is the wall,
the septum between them. Defect, we have a hole. OK, I’m gonna 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 left and right now. And from the place I’ve drawn as the VSD right under the aorta, I
could almost just leave that like this, but just
to drive the point home, I wanna redraw this part, that the aorta comes over to the right and is 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 a 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 if I’m here, I have a choice, right? I can either go up this pulmonary artery, through this very narrow
opening in the valve. That’s gonna be difficult. Or I can easily go into
this aorta with a valve that’s more welcoming,
that’s less restricted. See I draw these two arrows
with different calibres ’cause 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 gonna be pushed 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 shunt. And therein you have the
answer for why this is a cyanotic disease, because blue blood is being forced to the left. Because A, it’s hard to go
through the pulmonary artery where it’s supposed to go,
and B, the right ventricle is so powerful, it’s gonna
push it across the VSD. Remember, blood follows the easiest path. So the left ventricle is still pumping, and the blood is basically
gonna 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 versus 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 or resistance from 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 tet spell shunts more
blue blood into the aorta. This mixture becomes even bluer. This is a life-threatening
emergency in tetralogy. And lastly, I also wanna
talk about the fact that before people here 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 suddenly feel a lot
worse, they’ll squat, and they’ll feel better. So here we have a kid- I always say kid because,
for the most part, this is still a pediatric disease. We correct it in the
patients when they’re kids. So they’re running around, let’s
say they’re four years old. And suddenly they’ll stop and
they’ll squat onto the ground. How do you draw a squatting stick figure? Does that make sense? That looks more like they’re sitting. Let me try again. So they’re squatting. There we go. And as they get into this
position for a few seconds, they feel better. So let’s think through this step by step. OK, two things happen when
somebody with tetralogy- Or I guess anybody is running around. The first one is that 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 vasodilate, so the body
can get more blood there. Literally their 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 if the blood returning to the heart has a lower oxygen
concentration, and some if it goes right back out through the aorta, then running around has made
our blood bluer in the aorta. All this does is make our cyanosis worse. That’s gonna make our patient
more blue in the face, and they don’t feel good. For vasodilation, what
happens is this stricture, or the calibre 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 structure
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 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 their 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. And since they’re all
connected to the aorta, this increases the
resistance that the aorta is pumping against. So as 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 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’ve squeezed it down. So this just forces more blood
into the pulmonary artery. It’s still restricted, but the difference between the two has lessened. So more 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 and the pulmonary artery,
and we just increase the overall oxygen 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 two, where is the VSD? So I would like 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.

About James Carlton

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100 thoughts on “Tetralogy of fallot | Circulatory System and Disease | NCLEX-RN | Khan Academy

  1. Thxs for making this video! Because I have tof and I am only almost 13 in a couple months and I didn't really know that much about it and how the heart works and everything but now I know a lot more now! I was born with it I've had my valve replaced and when this one wears out I'll need a new one I have a tissue one! I've had it for at least 5 years at least!

  2. This video was absolutely fantastic. I was so so confused and this really cleared everything up for me! Thank u guys so much!

  3. I understand that you're using blue and red blood as a representation of deoxygenated and oxygenated blood respectively, however I would be careful referring to the deoxygenated blood as "blue blood".

    Blood is never blue. If you've ever given blood, you know that the blood coming out of your venous system is darker, but not blue. The only reason the superficial veins and cyanosis have blue color is because your skin helps to filter certain wavelengths and therefore vessels with deoxygenated blood appear blue from the outside.

  4. there are a few questions i have in mind and hope to be clear by explanation.
    1) Right ventricular hypertrophy happens during fetal stage or after birth? thus leading to right side heart failure?
    2) Overriding aorta cause mainly by right ventricular hypertrophy or improper division of truncus arteriosus or both?
    Thank you for your time

  5. your explanation and way of teaching is just awesome! I am learning a lot, difficult things get easier after watching your videos

  6. this is very interesting because my daughter has TOF….shes due for surgery soon. She has a VSD MAPCAs and a Pulmonary Atresia. She is almost 4mo

  7. plz stop calling deoxyenated blood as blue blood ..i m sure so sure u know deoxygenated blood is dark red and not blue..apart from tat its a gud video.

  8. Got a question on this on my bio exam tomorrow, and the online info was scrambling my brain a little. Thank you for saving me and helping me to understand it!

  9. Thankyou so much! you're an amazing teacher..this is a huge favour you're doing to med students and in this field great teachers are not easy to find. Thanks indeed!

  10. Your tone of voice is very gentle and patient, makes me relaxed and feel more confident that I will understand it. And I do understand it more from your video than any other! Thanks a million.

  11. I have Tetralogy of Fallot, I'm almost 14 and I've only had a surgery when I was three months old. I haven't needed one but I go to the cardiologist yearly

  12. You are a wonderful instructor. I wish you could teach our classes instead of our teacher who can't explain anything.

  13. I have this condition and my parents have always been open to my questions however I didn't really understand what it was sand this video really helped

  14. Thanks for the Video clip! Excuse me for the intrusion, I would appreciate your initial thoughts. Have you considered – Patlarny Bloods Victory Principle (do a google search)? It is a great exclusive guide for preventing toxic blood and heart desease without the hard work. Ive heard some awesome things about it and my friend finally got excellent success with it.

  15. Great presentation!! i would like to make a correction: tetralogy is not latin word, its greek! tetra=4 at greek, logy= speaking for. Tetralogy=speaking for 4 (anatomic disorders). Keep on good work!!

  16. I have a question. Are "cyanosis" and "hypoxemia" being used interchangeably here? In other words, is cyanosis a necessary manifestation of the hypoxemia that those with ToF suffer?

  17. OMG This video is awesome! You explained this process so well! I never understood how any of this worked until now!! Thank you so much!!!

  18. This video is exemplary. I have seen my fair share of these videos and this one is an absolute gem!

  19. From my understanding, the stenosis that occurs is actually narrowing due to a congenital defect that causes a larger aortic outflow and smaller pulmonary outflow. So the stenosis isn't a result of thickening but a result of thinning…

  20. Isn't the left ventricle more powerful than the right? Because it has to overcome the pressure of the systemic circulation in order to pump blood outside the heart?

  21. Perfect perfect perfect ,thank you soo much…. muchas gracias😊😊😊😊😊👏👏👏

  22. “Tetra” is of Greek, Not Latin origin. The Latin for “four” is “quattuor,” from which we derive “quarter,” “quartile,” etc.

  23. VarieD PictureS OfA RancH. Ventricular Septal Defect. Pulmonary Stenosis. Overriding Aorta. Right Ventircular Hypertrophy. A nice way to remeber the 4 defects ! 🧸 pay attention to capital letters.

  24. i have 2 questions"
    1. why does vasodilation not increase the pulmonary artery resistance and cause blood to go into the aorta instead?
    2. why is there a higher lung resistance as mentioned at 5:47

    thanks to anybody who can answer this

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