Now here the fibrous pericardium and the underlying
parietal serous pericardium have been cut
along the margins that we see here. So we?ll
follow the outline of the cut margins at the
fibrous pericardium and the inner lining of
the fibrous pericardium ? the parietal.
We cannot really distinguish or discern the
adherent component deep to the fibrous pericardium
but it would be in this general area. It would
be shiny when you open up the fibrous pericardium.
And then here at the level of the great vessels,
superior vena cava. Here?s your aorta. Here?s
your pulmonary trunk. What will happen is
there will be a reflexion of the parietal
pericardium onto the surface of the heart.
So everything we see here on the surface of
the heart represents the visceral pericardium,
also known as the epicardium.
So when you?re in the dissection lab, if
you?re looking at the heart and you see
the vessels and you see the adipose tissue
and you see the muscle fibres, those are lying
deep to the visceral pericardium.
The space or potential space that lies between
the visceral and the parietal pericardium
is known as the pericardial cavity. The best
way to appreciate the pericardial cavity is
through an axial section.
So here?s an axial section through the thoracic
cavity and we can see the heart situated within
the middle mediastinum. We see the pericardial
components here in green. The outer most layer
here would be your fibrous pericardium and
then, adherent to that, would be the parietal
pericardium. And, again, we cannot discern
or distinguish those two pericardial components.
And then, adherent to the surface of the heart,
is the visceral pericardium. And then the
potential space that lies between the visceral
and the parietal pericardium
is your pericardial cavity.
The pericardial cavity is a potential space.
However, there is a clinical condition called
cardiac tamponade. And one cause of cardiac
tamponade is a result of a myocardial infarction
leading to cell death of a portion of the
left ventricular wall. This causes the left
ventricular wall to become greatly weakened.
And, if it?s greatly weakened, it can then
result in an aneurysm ? so a portion of
the left ventricular wall is bulging outwards.
And at some point that aneurysm can rupture.
And if that aneurysm ruptures, you?ll have
blood loss into the pericardial cavity and
blood will start to accumulate in the pericardial
cavity. And, as it does so, it will compress
the heart. The heart will beat again, force
more blood into the pericardial cavity resulting
in further compression of the heart. And now
you?re in a vicious cycle. And at some point
there can be so much fluid loss into the pericardial
cavity that the heart is too compressed to
function normally. And death could then ensue.
The blood that?s accumulated in the pericardial
cavity can be removed as this is an emergent
condition. A needle can be inserted into the
pericardial cavity and then the blood withdrawn.
And certainly another aspect clinically of
this situation would be
to try to repair the aneurysm.
There are some unique aspects of the pericardium.
These result from the complex development
of the heart. And as a result, if we take
a look here, we?re looking at the inner
lining of the fibrous pericardium. And so
this is the parietal pericardium that?s
shiny in through here. These are the cut ends
of the pulmonary veins that would empty into
the left atrium. And, if we take a look, we
can see a reflexion of the pericardium here
and we also have the fibrous pericardium here
as well. And, if you were to put your fingers
there up and under the heart toward the left
atrium further, the pulmonary veins
empty into them, you would reach this limit
and you could push your fingers no further.
This is a pericardial sinus. This is called
the oblique pericardial sinus. We have another
pericardial sinus running right in through
here. And the entryway here is to run your
fingers over anterior to the superior vena
cava, which is this vessel here. Run them
over and behind the aorta. And then all of
a sudden your fingers are in this transverse
pericardial sinus. And they will then run
behind or posterior to the aorta and to the
pulmonary trunk. For someone undergoing coronary
bypass surgery, the cardiac surgeon will need
to cross-clamp the aorta, for example, in
the pulmonary trunk. And this is a way to
identify and place the clamp.