Systolic heart failure pathophysiology | Circulatory System and Disease | NCLEX-RN | Khan Academy
Systolic heart failure pathophysiology | Circulatory System and Disease | NCLEX-RN | Khan Academy
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Content
2.183 -> - [Voiceover] So systolic heart failure,
3.72 -> your heart can't pump
as hard as it used to
5.741 -> and so it doesn't
squeeze as much blood out
8.017 -> and it doesn't meet the body's demands.
10.082 -> It's called systolic heart failure
11.639 -> because we're talking about systole,
13.055 -> which is the phase of the cardiac cycle
14.715 -> where the heart contracts and ejects blood
17.132 -> to either the body or the lungs.
19.22 -> You can sort of think of it
like squeezing a water bottle
21.553 -> and squeezing the water out.
22.714 -> It's the same sort of
thing except with the heart
24.676 -> it's actually squeezing blood instead.
27.363 -> So systolic heart failure,
this force of contraction,
30.876 -> or this squeezing force is a lot lower.
33.547 -> And sometimes we say
that has lowered inotropy
36.141 -> which just means the force
of muscle contraction.
39.36 -> And we're just going to talk
about the ventricular inotropy,
41.939 -> which is the strength of these ventricles
43.797 -> or these bigger chambers.
45.532 -> So now think about
squeezing that same bottle,
47.505 -> but just pinching it
instead with two fingers.
50.632 -> You can imagine it's
going to be a lot harder
51.88 -> to squeeze the water out, right?
53.822 -> Well it's the same thing
with weakened muscles.
55.557 -> If they're smaller and weaker,
56.637 -> it's going to be way
harder to squeeze blood out
58.85 -> and your stroke volume
is going to be reduced
60.491 -> and your body's not going
to get as much blood
61.919 -> as it used to.
63.471 -> And this is all due to
this weakened heart muscle.
67.431 -> But how does that muscle get weakened.
69.278 -> Well it's usually caused by
some kind of underlying disease
72.556 -> that causes the death
of cardiac muscle cells
75.131 -> or cardiomyocytes.
78.823 -> So I'm going to draw a few
of these cardiomyocytes
80.59 -> and basically they're
kind of holding hands,
82.491 -> so when they contract they
end up pulling on each other.
86.007 -> And when they pull on each
other they get a little smaller
88.04 -> and this is what causes
that squeezing motion,
90.965 -> but what if a couple of these cells died?
93.441 -> I mean, obviously they're
not going to pull as hard
95.156 -> and you're not going to get
as good of a squeezing motion
97.456 -> and your heart's not going
to eject as much blood
99.232 -> as it used to.
101.333 -> So if you just look at
this heart and compare it
102.958 -> to a healthy heart, you'll
see that these walls
105.548 -> are way thinner and these
ventricles are way bigger.
108.949 -> These are classic signs of a heart
110.272 -> with systolic heart failure.
113.671 -> So what are some of these
underlying diseases?
116.208 -> Well you've essentially
got four categories.
119.112 -> And the first category
is heart muscle diseases
121.949 -> and a lot of times we're just going
122.914 -> to call those cardiomyopathies.
125.191 -> You can essentially break
that down into cardio
127.408 -> which means heart, myo which is muscle,
129.614 -> and pathy which means disease.
131.956 -> But typically with these, the
cause is going to be unknown,
135.32 -> but in general they tend
to weaken the heart muscle
137.937 -> and make it harder to pump blood.
141.206 -> The second category isn't
as straight forward.
143.313 -> It's going to be reduced blood supply,
145.53 -> but I'm not talking about
the blood supply to the body,
147.771 -> I'm actually talking
about to the heart itself.
151.578 -> And so coronary artery
disease is a huge cause
154.191 -> of systolic heart failure
because the coronaries
156.74 -> are what supply your heart with blood.
160.082 -> So let's get some of
this stuff out of the way
161.574 -> and move these guys over here
164.511 -> and then I'm going to draw some vessels
165.951 -> going to the heart muscle cells.
167.693 -> These are going to be
our coronary arteries,
169.631 -> well I guess there's just one,
171.034 -> so it's a coronary artery.
173.897 -> So usually you have blood coming down
175.273 -> and giving oxygen to these muscle cells,
178.664 -> but with coronary artery
disease you have this narrowing
180.73 -> of the vessel because
of a buildup of plaque
183.605 -> and that buildup reduces the blood supply
185.701 -> to the muscle cells and
those cells start to die off
188.608 -> and as we're well aware,
this is not a good thing
190.82 -> because when muscle cells die off
192.792 -> your muscle gets weaker and
makes it harder to pump blood.
197.674 -> If we go one step further and
that plaque builds up so much
200.489 -> that it completely obstructs
or blocks that vessel
204.292 -> then none of those cells
get any oxygen at all
206.853 -> and really they all end up dying off.
209.371 -> This is really serious because
you can get whole areas
212.087 -> of cells that die and
also why heart attack
214.978 -> is a major contributor to
systolic heart failure.
219.55 -> Alrighty, so the third class of diseases
221.874 -> are actually valve diseases.
224.451 -> So your heart has four valves.
225.961 -> Two valves that separate
the upper and lower chambers
228.224 -> and then two valves that
separate the lower chambers
231.011 -> from wherever the blood's going to,
232.485 -> either the body or the lungs.
234.726 -> So if we start with the
valves that separate
236.548 -> the two chambers, we
can talk about something
238.51 -> called regurgitation.
240.345 -> And this just means
that the lower chambers
242.26 -> are letting blood go back
into the upper chambers.
245.635 -> So if we just watch this heart beat,
247.511 -> usually those valves close
when the blood's pumped out,
251.048 -> but regurgitation means
that the valves stay open
253.626 -> just a little bit and let
some of the blood go back
256.18 -> into the upper chambers.
258.664 -> Now blood is still pumped out,
260.714 -> but some is allowed to go
into the upper chambers
262.484 -> and so naturally you lose
the blood that's going
265.049 -> into the upper chambers and less blood
266.826 -> is pumped to the body.
268.765 -> If we think about our favorite
water bottle analogy again,
272.164 -> but this time there's this
like hole on the side,
274.943 -> every time you squeeze it,
276.044 -> most of the water goes out,
277.344 -> but some's going to leak out the hole.
280.001 -> And since now we're pumping less blood,
281.663 -> the heart has to work harder to maintain
283.462 -> that same level as it had before
286.035 -> and more work costs more oxygen,
287.978 -> but with heart failure,
that's the whole thing,
289.801 -> we can't supply more oxygen
292.085 -> and more cells die off as a result.
297.975 -> The other valve disease has to do with
299.321 -> these other two valves.
300.563 -> It's called stenosis and
that means that the blood
303.165 -> is being pumped out through
this smaller opening,
305.218 -> which makes it a lot harder to pump blood.
310.498 -> Well I guess, let's look
at our water bottle,
312.409 -> but this time let's have our
nozzle being super small.
315.497 -> Just think about trying
to squeeze it through
316.862 -> that smaller nozzle.
318.058 -> It's going to be a lot harder, right?
320.282 -> Well it turns out it's also a lot harder
321.959 -> for your heart muscles to squeeze blood
323.724 -> through a smaller opening.
325.341 -> And the same way as regurgitation,
327.018 -> now the heart has to
work harder to maintain
328.703 -> the same blood supply
330.433 -> and more work equals more
oxygen that can't be supplied,
333.857 -> so more cells die off.
336.958 -> Alright, last one.
338.279 -> This one's arrhythmias, which
means abnormal heart rhythm.
342.145 -> This could be a rhythm
that's either too slow
344.504 -> or maybe too fast or even uncoordinated.
348.087 -> And uncoordinated, that
just means that the chambers
350.184 -> don't contract at the same time.
352.526 -> Usually they would
contract at the same time,
354.384 -> but maybe now the left
one's going before the right
356.857 -> or the right one's going before the left.
360.063 -> Either way, all these lead
to a serious reduction
362.382 -> in pumping efficiency,
which means less blood
365.076 -> is pumped to the body.
366.973 -> And by kind of the same mechanisms
368.361 -> as we talked about before, the more work
370.962 -> means more oxygen demand
and more cell death.
374.399 -> So we start to see this pattern, right?
376.415 -> Where each one reduces the pumping ability
379.05 -> and this makes it a lot
harder for the heart
380.459 -> to maintain the same supply.
382.641 -> And those cells that work
harder will demand more oxygen,
384.998 -> but the oxygen can't be supplied
386.693 -> and those muscle cells die off.
388.701 -> And when they die off
the heart gets weaker
390.733 -> and your pumping ability
is lowered even more.
395.023 -> So we see that pumping
ability is really important.
397.898 -> And one way we can measure pumping ability
399.556 -> is by the ejection fraction,
401.598 -> which is the percentage of
blood ejected with each beat.
406.85 -> So if we look at our water bottle,
408.486 -> we can take the total volume filled
410.862 -> and then we can also take
the total volume ejected
414.785 -> and then if we divide the volume ejected
416.86 -> by the total volume filled,
418.986 -> and then I guess multiply it
by 100 to get the percent,
421.993 -> you get your ejection fraction.
425.254 -> And usually we just talk
about the ejection fraction
427.259 -> for the left ventricle,
when it is possible to look
429.915 -> at your right ventricle
ejection fraction too.
434.142 -> A normal range is about 55 to 70%
437.411 -> and abnormal range would
be considered anything
439.4 -> between 40 and 55% and then
evidence for heart failure
443.723 -> is anything under 40%.
Source: https://www.youtube.com/watch?v=FL3Q5Q6IdAY