Stenosis, ischemia and heart failure | Miscellaneous | Heatlh & Medicine | Khan Academy

Stenosis, ischemia and heart failure | Miscellaneous | Heatlh & Medicine | Khan Academy

August 28, 2019 44 By Bertrand Dibbert


As someone who’s married to a
doctor, in the medical field, I think it’s pretty important
to have a precise understanding of what the words mean, just
so that you can understand what people are talking about if
either you are a health care professional or if some health
care professional is talking to you, as my wife does
when, well, sometimes does, when she comes home from work. So let’s get a little bit more
precise with some of the words we’ve been talking about,
especially relative to heart disease and heart failure
and all of the rest. So let’s say this is an artery. The blood is flowing
in that direction. I’ll show the artery
branching off. It thins as it goes
farther and farther along. So this right here is an artery. And let me draw a
plaque in that artery. And we’ve been
studying these plaques in arteries since the
video on heart attacks. So let’s say that this is a
bunch of white blood cells and lipid material. So it’s cholesterol and
fats and all the rest. Now a word that you might hear
in kind of a medical context is stenosis. And the word “stenosis” just
refers to the narrowing, usually of a blood vessel. So this right here, this blood
vessel has been narrowed. So this right over
here is stenosis. It’s been narrowed
by this plaque. It can also refer
to the narrowing of kind of any type
of tubular structure. So if you have any type of kind
of pipe in a biological system and it gets narrow, they
might refer to stenosis there. But usually they’re talking
about a blood vessel. In this example that I’ve
drawn here it’s an artery. So the stenosis is
just the narrowing. Now once the blood
vessel is narrowed, that restricts the blood supply. So you aren’t able to get
as much blood through it. So the blood supply
is restricted. So restricted blood supply. Put the I there. Restricted blood supply. This restriction
of a blood supply that usually leads
to some type of loss of function, that’s called– so
this restricted blood supply– this is called ischemia. Another fancy word,
but it literally just means restricted blood supply. Ischemia. Now if you have stenosis in one
of your blood vessels, in one of your arteries, and it
restricts your blood supply. So it leads to ischemia. Let’s say let me draw a
muscle cell farther over here. Let’s say this is a coronary
artery that we’re dealing with. The muscle cells over here
are going to get less oxygen. So this guy– let me draw
this cell right over here. And I’m just drawing an
oversimplified diagram. I’m not going to imply
that muscle cells really look like that. And actually, they
won’t be– well, I won’t go into
the details here. But this guy’s not going
to get not enough oxygen. So you can imagine
that if we’re really zoomed in on the
surface of the heart, we’re looking at the heart
muscle tissue right here. If whoever’s heart this was,
if they started to go jogging or whatever, and this
cell needed more oxygen, probably wouldn’t be able
to get that oxygen because of the stenosis which
caused ischemia. And because of that, it
doesn’t have enough oxygen so it won’t be able to
help the heart pump. Remember, this is just one of
the muscles in the heart that’s going to help it pump
the blood properly. So it’s going to lead
to heart failure. And once again, the
word heart failure sounds more dramatic
than maybe it really is. It sounds like cardiac
arrest, where the heart stops. But heart failure is not saying
that the heart is completely failed. It’s just saying that the
heart is failing its ability to kind of properly
do its function. So when this guy goes
jogging, because he has a restricted blood
supply, because the heart is experiencing ischemia
downstream from this stenosis, that’s why there’s
heart failure. So not able to deliver. Now this heart failure, which
is due to the ischemia which is due to the stenosis, you
would call this heart failure due to coronary artery disease. Let me write it. We talked about
that two videos ago. Coronary artery disease. Which is really just kind of
an impairing of the heart’s function because of
reduced blood supply, because of a narrowing
in a blood vessel restricts the blood
supply ischemia, that is coronary artery disease. And because of coronary
artery disease, when this muscle
cell in the heart really needs to pump hard–
maybe because someone’s going up a hill or
climbing stairs– it’s not able to do it because
it’s not getting enough oxygen. And that inability to
properly, for the heart, not just the cell, but for the
whole heart, this is just one of many cells that maybe won’t
be able to pump properly, for the entire heart to not do
its job, that is heart failure. Now you’ve also probably
heard the term coronary heart disease. Or maybe just heart disease. These three things are
all the same thing. These are all the same. They all imply some type
of narrowing or stenosis of arteries that leads to
ischemia, reduced blood flow, so that the heart can’t function
as well as it otherwise could. Now the last thing
I want to focus on, and I talked a little bit
about it in the last video, is the idea of an
infarct or an infarction. These are kind of
funny words to say. I’ll write it over here. So infarct or infarction. So in the example I’ve drawn
so far, this cell, for example, maybe does not
get enough oxygen, especially once the
person is going upstairs and all of that, to properly
contract and help the heart actually pump. But it’s not dead. It’s still getting
some base level oxygen. Less because of the
stenosis and the ischemia, but it still gets some oxygen. And we saw in the video
on myocardial infarction or the video on heart
attacks that sometimes one of these plaques might become
unstable and they break off and then you have
a complete blocking of a vessel, a complete blocking
of an artery right here. And we saw in the
last video, we call this blocking what’s
called an embolism. And an embolism is the
general term for something that floated around and then
eventually blocks a vessel. And if it was due to kind of
a released plaque that also had clotting factors around
it after it got released, then we would call
this a thromboembolism. This would reduce the
blood flow so much, maybe a little bit might
be able to leak around, but it reduces it so much that
the cells downstream from this actually die. So you actually have
the cell right over here and this cell will die. It might get very little
blood or no blood at all, so it’s not getting enough
oxygen to actually survive. And when you have dead tissue
that’s due to a loss of oxygen, this is an infarct, dead
tissue due to a loss of oxygen. The process of it becoming dead
tissue due a loss of oxygen is an infarction. And this infarction, this
dead tissue due to loss of oxygen, in the myocardium, in
the muscle tissue of the heart. So now all of a sudden
you have muscle tissue in the heart that’s
beginning to die. This is a heart attack. This is a myocardial infarction. So hopefully that clarifies
things a little bit.