- [Voiceover] So what you're looking at here
is an ultrasound, or what they call an "echo,"
of the heart, and you can see the four different chambers
and you'll see I've labeled the left ventricle
and the left atrium, and what you'll notice is that
the arrow is pointing to the valve in between
the left ventricle and left atrium,
which is the mitral valve,
and that valve is actually not opening.
When that valve is really tight or doesn't open,
that is what's called mitral stenosis.
So like I said, mitral stenosis is when
you basically have a tight mitral valve.
Now what I'm going to do is I'm going to draw
a little set of lungs here, and kind of briefly
take you through how blood flows
from the right heart through the lungs,
and then from the lungs, and now I'm drawing back
to the left heart, and so those arrows are going
to the pulmonary veins, which go into the left atrium,
which I'm marking off here, LA,
and then the left ventricle, LV.
And that, that I'm circling right now, is the mitral valve.
The progression of blood is left atrium to left ventricle,
out the aorta, and to the rest of the body.
And of course that blood into the left atrium,
like we just said, was from the lungs.
Now if the blood can't get from the left atrium
to the left ventricle, it is going to back up
in the left atrium and the lungs,
everything that was before it.
Let's talk about some of the causes of mitral stenosis.
What causes this valve to be tight?
Well, you can have what's called rheumatic fever,
or more specifically, rheumatic heart disease
when it affects the heart.
So another cause can actually be what's called endocarditis,
and that's really an inflammation or an infection
of the actual valve.
These are are some of the major causes of mitral stenosis.
There are obviously others, but I want
to keep you focused on the major ones.
So what causes rheumatic fever?
It's actually a pretty specific bacteria,
and it's part of a group called "group A streptococcus."
We can actually abbreviate that "GAS,"
Group A Streptococcus, and what we're really talking about
here is a specific bacteria called streptococcus pyogenes.
This bacteria is actually what just causes strep throat.
So what'll happen is someone gets a strep pyogenes
infection, or a pharyngitis, meaning a throat infection,
and two to three weeks later, if it's not treated correctly,
the person can actually present with
some pain in their joints, or arthralgias,
heart problems, like a new heart murmur,
some skin problems,
and a bunch of other symptoms, but for the most part,
the joints, the skin, and for our sake, the heart problems
are what we really want to focus on.
Now the mechanism behind why this infection
by this bacteria actually causes
heart problems is called "molecular mimicry,"
and what happens is here, if you see I draw
this antigen, this green antigen, as a triangle,
and then this red antibody, and so
the antigen is really going to be part of the bacteria
that our body's immune system is going to
respond to with an antibody, but what happens is
some of the antigens that this particular type of bug,
strep pyogenes, puts out are actually very similar
to some of the normal antigens or components
of the tissue of the heart valves.
So what can happen is when you actually form
an antibody response to the particular infection,
those antibodies can actually go ahead and attack the heart.
The reason why you get all the other symptoms
are because those antigens are also found in those parts
of the body, so the joints, the skin, and other things.
Now the early lesion of rheumatic heart disease
is mitral regurgitation, but the late lesion,
meaning when you've had repeated bouts
of this rheumatic heart disease, or of this infection
with strep pyogenes, you actually get mitral stenosis,
which is what we're talking about now.
Mitral stenosis is characteristic
for rheumatic heart disease.
So really what I'm trying to say is that
a strep pyogenes infection itself, the bacteria itself
does not cause the heart problems, it's actually
our body's immune system responding to that infection
that causes the heart problems.
So let's talk about endocarditis now, which we said
is an inflammation or infection of the heart valves.
Now, I'm going to write "infective" here
because there are other rare, more rare,
types of endocarditis, but for the most part,
this is usually infective endocarditis, when it has
something to do with an infection, either by
a bacteria or a fungus or a virus.
So there are kind of different ways that this can happen.
You can get an infection of a completely normal valve
and the way that this happens is you actually have
a bacteria that's really bad, and so it's bad enough
that it can infect a normal valve.
This is something like staph aureus.
Now, you can also have an infection of a previously damaged
valve, so if someone already had some damage
to their valves, a bacteria that's not as bad
may be able to actually cause this problem.
This is often seen with normal flora in the mouth,
or bacteria that normally colonize in the mouth,
such as strep viridans,
and that's actually a class of bacteria,
but these bacteria are just in the mouth,
and so this is actually why some people can get infections
of their valves after having work done at the dentist,
because they actually become bacteremic, or have these
bacteria in their blood after their teeth
and mouth have been manipulated.
The last type is when someone has a prosthesis,
or a prosthetic valve, has had a valve replacement
in the past, and these are characteristically
caused by staph epidermidis, or staph epi.
These like to form little layers on prosthetic valves that
allow them to survive and cause problems, or endocarditis.
In addition, the worst bacteria usually cause
what we call "acute bacterial endocarditis."
The less virulent bacteria usually cause what we call
"sub-acute bacterial endocarditis," and you should
just remember that this infective endocarditis
can be caused by bacteria, viruses, and a little bit
more rare, but can happen, fungi.
Now let's talk about the signs and symptoms
associated with mitral stenosis.
Now granted, these may be based on the mechanism,
or how it was caused, so if you have something like
endocarditis as a result of an infection,
the person may have typical signs of an infection,
like fever, chills, and elevated white blood cell count,
stuff like that, but for signs and symptoms of mitral
stenosis, specifically we're going to talk about signs
and symptoms relating to the heart and cardiac physiology.
If we go back to our drawing of the lungs,
which then return oxygenated blood to the left atrium,
which then goes through the mitral valve to the left
ventricle, and then to the body through the aorta,
we can see that if blood backs up,
you don't have as much output of blood to the body,
so you can get fatigued, you can be short of breath
because blood is backing up into the lungs,
you can have exercise intolerance because you can't
get enough blood to the body to profuse or to adequately
oxygenate your tissues, give you enough oxygen,
or you can have a cough, again, because you're
backing up blood into the lungs.
Some signs that you may be able to see on echo,
or with your physical exam, or maybe on an EKG,
would be signs of left atrial enlargement,
because if blood is backing up into the left atrium.
You can have pulmonary congestion, or edema.
And then you would also have a characteristic
auscultatory finding, or finding that you hear
when you listen with a stethoscope,
and that would be a diastolic rumble.
Now, there's also another characteristic finding
that occurs just before that diastolic rumble.
Do you happen to remember what it is?
It's an opening snap, and if you forget any of these
symptoms, just remember that if you stop bloodflow
from the left atrium to the left ventricle,
it backs up into the lungs, and then you can kind of
regenerate what kind of symptoms and signs
that someone may present with
when they have mitral stenosis.