- Let's look at how your heart will typically heal up
after a myocardial infarct, after a heart attack.
So to do this we're going to zoom in
on this bit of heart muscle here,
part of the left ventricle.
So I'll draw in these cardiomyocytes,
these heart muscle cells here.
And these are the striations that they have
because of their contractile proteins,
and here are their nuclei.
So we'll start off with this non-infarcted heart here,
with nice intact muscle.
So remember, a clot is going to develop upstream
in the coronary artery that serves this area, right?
And that clot will stick around for over 20 minutes,
to cause irreversible damage in this heart muscle, right?
Depriving this area of oxygen.
And so, without oxygen the environment here becomes
not very hospitable, and all of this area
starts to die off after about four hours.
So up until about four hours,
these cells are just struggling.
They're using up all of their energy stores,
and they're really trying their hardest to survive.
So after about four hours,
their membranes start to become leaky,
and enzymes start denaturing or breaking down
the structural proteins of these cardiomyocytes,
and other proteins inside the heart muscle cell
begin to unravel and die off as well.
But as you can see in this little picture here,
the relative architecture of these dead cardiomyocytes
is basically preserved for a few days after they die.
So this process of the cardiomyocytes dying
but still having their architecture preserved
is called coagulative necrosis,
necrosis referring to the death of your cells
and coagulative referring to
this sort of jelly-like substance
that the denatured proteins form after they break down.
So in this drawing I'm showing that protein
is leaking out of your cardiomyocyte,
but, of course, a lot of them stay in there as well.
And so, they start to become a part of coagulative necrosis.
As they denature, they form this
sort of jelly-like substance.
And you might also get some bleeding into this area
from tiny little blood vessels
that surround the infarcted area that have become damaged.
And so, after about 12 hours, 12 to 24 hours actually,
these special white blood cells called neutrophils
begin to enter the area of infarction.
One of the things they love to do
is to clean things up.
So they'll realize that there's dead muscle everywhere
that needs cleaning up, and they'll start to.
A, they'll start to clean up,
and B, they'll start to call for help,
call in other neutrophils to come in and help them.
So I say clean up, but what exactly do I mean?
Well, here are our neutrophils.
They sort of come in, and they break down
the dead cardiomyocytes even more.
They sort of release these enzymes into the cardiomyocytes
and into the area and cause the heart muscle cells
to break down even more.
So what does that mean?
It means that their nuclei will start to degenerate,
and their striations will also start to degenerate,
and everything sort of just begins to
fragment and come apart.
So now a little bit later, between about one to three days,
the cavalry arrives.
There's lots of neutrophils around now.
So you've got your cardiomyocytes still degenerating.
Their nuclei are going away.
Their striations are disappearing,
and your neutrophils are just everywhere.
They're just taking apart or lysing the dead cardiomyocytes.
So now, between four and seven days,
the neutrophils start to die off,
because they're really just overworking themselves,
trying to clear everything up.
So, luckily, new reinforcements arrive, the macrophages.
And macrophages are another type of
white blood cell of the immune system,
and they're really good at cleaning up debris
and cleaning up dead tissue.
So here they begin to remove all the necrotic debris,
including the dead neutrophils,
our hardworking fallen friends here.
So they begin to phagocytose all the debris.
They ingest it all, and they break it down.
That's what phagocytosis is.
So all this area here, all this necrotic area
is being phagocytosed.
And our focus here is to just look at
the healing of an infarct, not really the complications,
but I should quickly mention that this time,
between four and seven days,
is probably the most dangerous period
for a rupture of your myocardium, of your heart muscle,
because of all the work the macrophages are doing here
to sort of clear out and really, therefore,
thin out the infarcted area.
So what happens next?
Well, between seven to 10 days,
the necrotic area is still being cleared up
by our trusty macrophages,
but at this point something really interesting
starts to happen.
You start to get this ingrowth
of these really thin blood vessels into the area,
and that's great because it provides
all these working cells the oxygen that they need
to get your heart repaired.
So now that there's an oxygen source in place,
we can start to think about laying down
a sort of scaffold for rebuilding this wall again.
So, we actually do get that.
We get these cells called fibroblasts
laying down these thin, sort of spindly
strands of structural protein, called type III collagen.
So all of this, these new little blood vessels
and this new collagen
is collectively called granulation tissue.
And actually, healing by granulation tissue
is the same sort of thing that happens after most injuries.
So even if you get a skinned knee, right?
Let's say you're, oh I don't know,
let's say you're rollerblading
and you get attacked by bats
and fall and scrape up your knees.
That actually happened to me a few years ago.
It was terrible.
Your scrapes, your wounds will actually heal up
by the same granulation tissue-mediated process.
So it's a tried and true sort of healing technique
used by our bodies.
What's next?
Well, after about a month, month-and-a-half,
the type III collagen and the granulation tissue
will be completely replaced by a way stronger
type of collagen, called type I collagen,
and that's actually what we know as scar tissue.
So if you have a scar anywhere,
you know what scar tissue is.
It's the same thing here in the heart.
So there's two little points about this scar tissue.
So the first thing is that it's not as strong as
normal heart muscle, but it is pretty strong.
So the hope is that it won't tear
or allow any blood to leak out of the heart.
The second thing is that it's noncontractile,
and I think by now we can all appreciate
that if you want your heart to be able to do one thing,
it's contract properly.
So having scar formation in your heart muscle
would predispose you to weaker contractions
and possibly heart failure down the line,
because remember, heart failure is essentially
a reflection of your heart's inability to
sort of pump out enough blood to meet
the metabolic needs of your body tissues, right?
So you can imagine that if you have
scar tissue in your heart,
and your heart isn't really that contractile,
then that means that your heart won't be able to
sort of muster up the contractions
to pump enough blood out,
and that's essentially heart failure.
So that's a bit about the physical healing
after a myocardial infarct,
but that's really only half the story.
We kind of have to talk about mental healing too,
because there are some really big psychological effects
of having had a heart attack
that need managing and coping with.
For example, for some people it might be a bit of a shock
to the system when they go from taking
maybe no medications on a daily basis
to this new cocktail of maybe
four or five medications daily.
Also, we know that some people are at risk of
depression after a heart attack.
So that needs looking after as well.
And finally, it's important to remember
that when a person has a heart attack,
it doesn't just affect that person.
It likely would also affect their loved ones,
their family and their friends
on a psychological level as well,
and dealing with that is part of
the healing process as well.