00:00
So, here are the four heart valves. The ones
in blue are the right sided ones of course,
and the ones in red are the left sided ones.
Let’s take the one at top of the diagram
because that’s the front of the heart and
that’s the tricuspid valve. Tricuspid means
three cusps, three components and you can
see that, right? You can see that there are
three parts to the tricuspid valve. So, the
blood is now passing through the tricuspid
valve into the right ventricle and then there
is going to be ven-… right ventricular contraction,
squeeze and the blood is going out the pulmonary
artery. Look at the blue valve to the left-
that’s the pulmonary artery valve and you
will notice it’s open because the right
ventricle is squeezing blood through it. That
blood goes to the lungs as we talked about,
gets oxygenated, get… picks up oxygen, comes
back through the pulmonary veins to the left
atrium and then passes through the valve-
the red circled valve on the right hand side
of the diagram. Notice that valve only has
two cusps. So, it is the only valve with two
cusps. The other three valves have three cusps
- the tricuspid valve, the pulmona-… pulmonic
or pulmonary valve, the aortic valve, all
have three cusps. But the mitral valve, which
is between the left atrium and the left ventricle,
has only two cusps. In fact, it resembles
its name for the Bishop’s mitre which is
the crown that the Bishop wears in the Catholic
Church which basically has just two sides
to it, resembling a little bit the mitral valve.
01:36
Once the blood is in the left ventricle, the
left ventricle contracts and the blood goes
out the aortic valve- that’s the one you
see right in the center and you will notice
it’s also open. So, what we are seeing here
is right and left ventricular systole- that
is squeeze, systole is squeeze and you see
that the pulmonary valve, pulmonic valve and
the aortic valve are open and blood is flowing
respectively into the pulmonary artery through
the pulmonic valve and into the aorta through
the aortic valve.
02:05
Now, I mentioned before that the heart has
an electrical system. Indeed it’s the electrical
system which is the trigger for mechanical
contraction. Without the electrical system,
the heart muscle will not contract. It’s
each… heart cell responds to the electrical
activity by contracting. So, where does this
electrical activity start? It starts at the
top of the atrium, there is a pacemaker- an
automatic pacemaker which can be influenced
by adrenaline circulating or by nerves from
the brain, it can accelerate or it can decelerate
depending upon a variety of conditions which
we will be talking about later. But, in any
case, the impulse starts spontaneously, passes
through a number of little fibers in the atrium
into what you see that little bulb there,
that’s the AV node, it pauses there for
a little bit. Why does it pause? Of course,
you can’t have the atria and the ventricle
contracting at the same time. And if the impulse
traveled rapidly through, you would have them
contracting at the same time and the blood
wouldn’t be going anywhere. So, there is
a certain pause while the atria finish their
mechanical contraction, and then the electrical
activity passes down from that AV node, also
called the Bundle of His, down into the branches
that are in the ventricle and at that point,
the ventricular muscle contracts. You can
see below it a… a diagram of the electrocardiogram.
The first wave is called the P wave- that’s
atrial contraction and the big deflection
is called the QRS- that’s the ventricular
contraction and you can even see the heart
sounds in there with atrial contraction and
ventricular contraction, you can see the first
and second heart sounds. In fact, we record
the electrical impulse passing through the
heart with something called the electrocardiogram.
03:56
I think most of you are well aware of this.
I am going to talk a lot more about this when
we come to the diagnostic lecture, but in
any case, here is a diagram that shows you
six electrocardiographic leads, they are taken
in the frontal plane, that is this plane right
here, but they are taken from different angles.
They are a little electrical biopsy from different
angles around the heart. And we put all of
this information together, as we will talk
about later, it helps us to diagnose specific
forms of heart disease, it also tells us a
lot about how well the wave of depolarization
is passing through the heart- are there abnormalities
in the electrical conduction system? Or are
there abnormalities in some of the minerals
in the blood, for example, potassium?