Healing after a heart attack (myocardial infarction) | NCLEX-RN | Khan Academy
Healing after a heart attack (myocardial infarction) | NCLEX-RN | Khan Academy
Created by Vishal Punwani.
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Content
1.389 -> - Let's look at how your
heart will typically heal up
3.421 -> after a myocardial infarct,
after a heart attack.
7.159 -> So to do this we're going to zoom in
8.898 -> on this bit of heart muscle here,
10.67 -> part of the left ventricle.
13.184 -> So I'll draw in these cardiomyocytes,
15.393 -> these heart muscle cells here.
20.006 -> And these are the
striations that they have
21.906 -> because of their contractile proteins,
25.507 -> and here are their nuclei.
27.381 -> So we'll start off with this
non-infarcted heart here,
30.706 -> with nice intact muscle.
32.968 -> So remember, a clot is
going to develop upstream
35.606 -> in the coronary artery that
serves this area, right?
39.006 -> And that clot will stick
around for over 20 minutes,
42.395 -> to cause irreversible damage
in this heart muscle, right?
45.574 -> Depriving this area of oxygen.
48.674 -> And so, without oxygen the
environment here becomes
51.309 -> not very hospitable, and all of this area
53.47 -> starts to die off after about four hours.
56.833 -> So up until about four hours,
58.385 -> these cells are just struggling.
61.318 -> They're using up all
of their energy stores,
63.321 -> and they're really trying
their hardest to survive.
66.489 -> So after about four hours,
68.109 -> their membranes start to become leaky,
70.509 -> and enzymes start
denaturing or breaking down
73.749 -> the structural proteins
of these cardiomyocytes,
76.435 -> and other proteins inside
the heart muscle cell
78.712 -> begin to unravel and die off as well.
81.889 -> But as you can see in
this little picture here,
83.522 -> the relative architecture
of these dead cardiomyocytes
87.389 -> is basically preserved for
a few days after they die.
91.409 -> So this process of the
cardiomyocytes dying
94.378 -> but still having their
architecture preserved
96.919 -> is called coagulative necrosis,
100.029 -> necrosis referring to
the death of your cells
102.79 -> and coagulative referring to
104.475 -> this sort of jelly-like substance
106.469 -> that the denatured proteins
form after they break down.
110.515 -> So in this drawing I'm
showing that protein
112.809 -> is leaking out of your cardiomyocyte,
114.952 -> but, of course, a lot of
them stay in there as well.
117.538 -> And so, they start to become a
part of coagulative necrosis.
120.645 -> As they denature, they form this
122.17 -> sort of jelly-like substance.
124.241 -> And you might also get some
bleeding into this area
126.649 -> from tiny little blood vessels
127.989 -> that surround the infarcted
area that have become damaged.
131.649 -> And so, after about 12 hours,
12 to 24 hours actually,
135.009 -> these special white blood
cells called neutrophils
138.129 -> begin to enter the area of infarction.
141.149 -> One of the things they love to do
143.229 -> is to clean things up.
144.729 -> So they'll realize that
there's dead muscle everywhere
146.853 -> that needs cleaning up,
and they'll start to.
149.664 -> A, they'll start to clean up,
150.881 -> and B, they'll start to call for help,
153.089 -> call in other neutrophils
to come in and help them.
156.613 -> So I say clean up, but
what exactly do I mean?
159.449 -> Well, here are our neutrophils.
161.009 -> They sort of come in, and they break down
163.149 -> the dead cardiomyocytes even more.
165.629 -> They sort of release these
enzymes into the cardiomyocytes
169.029 -> and into the area and cause
the heart muscle cells
171.749 -> to break down even more.
172.798 -> So what does that mean?
173.529 -> It means that their nuclei
will start to degenerate,
176.169 -> and their striations will
also start to degenerate,
179.921 -> and everything sort of just begins to
181.749 -> fragment and come apart.
183.461 -> So now a little bit later,
between about one to three days,
186.749 -> the cavalry arrives.
188.649 -> There's lots of neutrophils around now.
191.18 -> So you've got your cardiomyocytes
still degenerating.
193.809 -> Their nuclei are going away.
195.449 -> Their striations are disappearing,
196.707 -> and your neutrophils are just everywhere.
198.505 -> They're just taking apart or
lysing the dead cardiomyocytes.
203.143 -> So now, between four and seven days,
205.409 -> the neutrophils start to die off,
207.109 -> because they're really just
overworking themselves,
209.489 -> trying to clear everything up.
211.021 -> So, luckily, new reinforcements
arrive, the macrophages.
215.289 -> And macrophages are another type of
217.221 -> white blood cell of the immune system,
219.205 -> and they're really good
at cleaning up debris
221.436 -> and cleaning up dead tissue.
223.449 -> So here they begin to remove
all the necrotic debris,
226.589 -> including the dead neutrophils,
228.189 -> our hardworking fallen friends here.
231.049 -> So they begin to
phagocytose all the debris.
233.719 -> They ingest it all,
and they break it down.
235.405 -> That's what phagocytosis is.
237.409 -> So all this area here,
all this necrotic area
240.181 -> is being phagocytosed.
242.109 -> And our focus here is to just look at
244.09 -> the healing of an infarct,
not really the complications,
247.11 -> but I should quickly
mention that this time,
249.831 -> between four and seven days,
251.57 -> is probably the most dangerous period
253.81 -> for a rupture of your
myocardium, of your heart muscle,
256.649 -> because of all the work the
macrophages are doing here
259.288 -> to sort of clear out
and really, therefore,
262.17 -> thin out the infarcted area.
264.23 -> So what happens next?
265.37 -> Well, between seven to 10 days,
268.51 -> the necrotic area is
still being cleared up
271.068 -> by our trusty macrophages,
272.91 -> but at this point something
really interesting
274.63 -> starts to happen.
275.95 -> You start to get this ingrowth
277.85 -> of these really thin blood
vessels into the area,
281.03 -> and that's great because it provides
282.45 -> all these working cells
the oxygen that they need
285.21 -> to get your heart repaired.
286.879 -> So now that there's an
oxygen source in place,
289.25 -> we can start to think about laying down
291.27 -> a sort of scaffold for
rebuilding this wall again.
294.57 -> So, we actually do get that.
296.423 -> We get these cells called fibroblasts
298.87 -> laying down these thin, sort of spindly
301.07 -> strands of structural protein,
called type III collagen.
305.526 -> So all of this, these
new little blood vessels
308.35 -> and this new collagen
309.61 -> is collectively called granulation tissue.
312.95 -> And actually, healing
by granulation tissue
315.506 -> is the same sort of thing that
happens after most injuries.
318.662 -> So even if you get a skinned knee, right?
320.988 -> Let's say you're, oh I don't know,
322.868 -> let's say you're rollerblading
324.31 -> and you get attacked by bats
326.128 -> and fall and scrape up your knees.
328.09 -> That actually happened
to me a few years ago.
330.17 -> It was terrible.
330.93 -> Your scrapes, your wounds
will actually heal up
333.482 -> by the same granulation
tissue-mediated process.
337.09 -> So it's a tried and true
sort of healing technique
339.75 -> used by our bodies.
341.41 -> What's next?
342.41 -> Well, after about a
month, month-and-a-half,
344.55 -> the type III collagen and
the granulation tissue
347.323 -> will be completely
replaced by a way stronger
350.37 -> type of collagen, called type I collagen,
353.23 -> and that's actually what
we know as scar tissue.
355.499 -> So if you have a scar anywhere,
356.77 -> you know what scar tissue is.
358.243 -> It's the same thing here in the heart.
360.17 -> So there's two little points
about this scar tissue.
363.03 -> So the first thing is
that it's not as strong as
365.39 -> normal heart muscle,
but it is pretty strong.
367.81 -> So the hope is that it won't tear
369.77 -> or allow any blood to
leak out of the heart.
372.37 -> The second thing is that
it's noncontractile,
375.522 -> and I think by now we can all appreciate
377.59 -> that if you want your heart
to be able to do one thing,
380.01 -> it's contract properly.
382.43 -> So having scar formation
in your heart muscle
384.79 -> would predispose you
to weaker contractions
387.31 -> and possibly heart failure down the line,
390.014 -> because remember, heart
failure is essentially
392.53 -> a reflection of your heart's inability to
395.37 -> sort of pump out enough blood to meet
398.071 -> the metabolic needs of
your body tissues, right?
402.13 -> So you can imagine that if you have
403.57 -> scar tissue in your heart,
404.548 -> and your heart isn't
really that contractile,
407.45 -> then that means that your
heart won't be able to
409.81 -> sort of muster up the contractions
411.43 -> to pump enough blood out,
413.19 -> and that's essentially heart failure.
416.216 -> So that's a bit about the physical healing
417.999 -> after a myocardial infarct,
419.75 -> but that's really only half the story.
421.95 -> We kind of have to talk
about mental healing too,
424.504 -> because there are some really
big psychological effects
427.097 -> of having had a heart attack
428.71 -> that need managing and coping with.
430.473 -> For example, for some people
it might be a bit of a shock
433.023 -> to the system when they go from taking
434.91 -> maybe no medications on a daily basis
437.31 -> to this new cocktail of maybe
439.23 -> four or five medications daily.
441.47 -> Also, we know that some
people are at risk of
443.71 -> depression after a heart attack.
445.237 -> So that needs looking after as well.
447.61 -> And finally, it's important to remember
448.97 -> that when a person has a heart attack,
450.733 -> it doesn't just affect that person.
453.11 -> It likely would also
affect their loved ones,
455.859 -> their family and their friends
457.174 -> on a psychological level as well,
459.408 -> and dealing with that is part of
460.997 -> the healing process as well.
Source: https://www.youtube.com/watch?v=9lIxelNVmNU