- [Voiceover] So systolic heart failure,
your heart can't pump as hard as it used to
and so it doesn't squeeze as much blood out
and it doesn't meet the body's demands.
It's called systolic heart failure
because we're talking about systole,
which is the phase of the cardiac cycle
where the heart contracts and ejects blood
to either the body or the lungs.
You can sort of think of it like squeezing a water bottle
and squeezing the water out.
It's the same sort of thing except with the heart
it's actually squeezing blood instead.
So systolic heart failure, this force of contraction,
or this squeezing force is a lot lower.
And sometimes we say that has lowered inotropy
which just means the force of muscle contraction.
And we're just going to talk about the ventricular inotropy,
which is the strength of these ventricles
or these bigger chambers.
So now think about squeezing that same bottle,
but just pinching it instead with two fingers.
You can imagine it's going to be a lot harder
to squeeze the water out, right?
Well it's the same thing with weakened muscles.
If they're smaller and weaker,
it's going to be way harder to squeeze blood out
and your stroke volume is going to be reduced
and your body's not going to get as much blood
as it used to.
And this is all due to this weakened heart muscle.
But how does that muscle get weakened.
Well it's usually caused by some kind of underlying disease
that causes the death of cardiac muscle cells
or cardiomyocytes.
So I'm going to draw a few of these cardiomyocytes
and basically they're kind of holding hands,
so when they contract they end up pulling on each other.
And when they pull on each other they get a little smaller
and this is what causes that squeezing motion,
but what if a couple of these cells died?
I mean, obviously they're not going to pull as hard
and you're not going to get as good of a squeezing motion
and your heart's not going to eject as much blood
as it used to.
So if you just look at this heart and compare it
to a healthy heart, you'll see that these walls
are way thinner and these ventricles are way bigger.
These are classic signs of a heart
with systolic heart failure.
So what are some of these underlying diseases?
Well you've essentially got four categories.
And the first category is heart muscle diseases
and a lot of times we're just going
to call those cardiomyopathies.
You can essentially break that down into cardio
which means heart, myo which is muscle,
and pathy which means disease.
But typically with these, the cause is going to be unknown,
but in general they tend to weaken the heart muscle
and make it harder to pump blood.
The second category isn't as straight forward.
It's going to be reduced blood supply,
but I'm not talking about the blood supply to the body,
I'm actually talking about to the heart itself.
And so coronary artery disease is a huge cause
of systolic heart failure because the coronaries
are what supply your heart with blood.
So let's get some of this stuff out of the way
and move these guys over here
and then I'm going to draw some vessels
going to the heart muscle cells.
These are going to be our coronary arteries,
well I guess there's just one,
so it's a coronary artery.
So usually you have blood coming down
and giving oxygen to these muscle cells,
but with coronary artery disease you have this narrowing
of the vessel because of a buildup of plaque
and that buildup reduces the blood supply
to the muscle cells and those cells start to die off
and as we're well aware, this is not a good thing
because when muscle cells die off
your muscle gets weaker and makes it harder to pump blood.
If we go one step further and that plaque builds up so much
that it completely obstructs or blocks that vessel
then none of those cells get any oxygen at all
and really they all end up dying off.
This is really serious because you can get whole areas
of cells that die and also why heart attack
is a major contributor to systolic heart failure.
Alrighty, so the third class of diseases
are actually valve diseases.
So your heart has four valves.
Two valves that separate the upper and lower chambers
and then two valves that separate the lower chambers
from wherever the blood's going to,
either the body or the lungs.
So if we start with the valves that separate
the two chambers, we can talk about something
called regurgitation.
And this just means that the lower chambers
are letting blood go back into the upper chambers.
So if we just watch this heart beat,
usually those valves close when the blood's pumped out,
but regurgitation means that the valves stay open
just a little bit and let some of the blood go back
into the upper chambers.
Now blood is still pumped out,
but some is allowed to go into the upper chambers
and so naturally you lose the blood that's going
into the upper chambers and less blood
is pumped to the body.
If we think about our favorite water bottle analogy again,
but this time there's this like hole on the side,
every time you squeeze it,
most of the water goes out,
but some's going to leak out the hole.
And since now we're pumping less blood,
the heart has to work harder to maintain
that same level as it had before
and more work costs more oxygen,
but with heart failure, that's the whole thing,
we can't supply more oxygen
and more cells die off as a result.
The other valve disease has to do with
these other two valves.
It's called stenosis and that means that the blood
is being pumped out through this smaller opening,
which makes it a lot harder to pump blood.
Well I guess, let's look at our water bottle,
but this time let's have our nozzle being super small.
Just think about trying to squeeze it through
that smaller nozzle.
It's going to be a lot harder, right?
Well it turns out it's also a lot harder
for your heart muscles to squeeze blood
through a smaller opening.
And the same way as regurgitation,
now the heart has to work harder to maintain
the same blood supply
and more work equals more oxygen that can't be supplied,
so more cells die off.
Alright, last one.
This one's arrhythmias, which means abnormal heart rhythm.
This could be a rhythm that's either too slow
or maybe too fast or even uncoordinated.
And uncoordinated, that just means that the chambers
don't contract at the same time.
Usually they would contract at the same time,
but maybe now the left one's going before the right
or the right one's going before the left.
Either way, all these lead to a serious reduction
in pumping efficiency, which means less blood
is pumped to the body.
And by kind of the same mechanisms
as we talked about before, the more work
means more oxygen demand and more cell death.
So we start to see this pattern, right?
Where each one reduces the pumping ability
and this makes it a lot harder for the heart
to maintain the same supply.
And those cells that work harder will demand more oxygen,
but the oxygen can't be supplied
and those muscle cells die off.
And when they die off the heart gets weaker
and your pumping ability is lowered even more.
So we see that pumping ability is really important.
And one way we can measure pumping ability
is by the ejection fraction,
which is the percentage of blood ejected with each beat.
So if we look at our water bottle,
we can take the total volume filled
and then we can also take the total volume ejected
and then if we divide the volume ejected
by the total volume filled,
and then I guess multiply it by 100 to get the percent,
you get your ejection fraction.
And usually we just talk about the ejection fraction
for the left ventricle, when it is possible to look
at your right ventricle ejection fraction too.
A normal range is about 55 to 70%
and abnormal range would be considered anything
between 40 and 55% and then evidence for heart failure
is anything under 40%.