00:00
Welcome back. We’re going to talk about structures that are
just very slightly outside
of the heart, that is to say the pericardium, and diseases
mostly inflammatory and
some infectious diseases and how they impact myocardial
cardiac function. The normal
pericardium is a very thin layer of mesothelial cells that
sit on a basement membrane.
00:25
As a higher power blowup, what we’re looking at here we have
the endocardium that
faces to the inside of the ventricle, that’s where the blood
is going to be, that’s going to
be endothelial cells. And then we have the myocardium, a
combination of cardiac
myocytes, fibroblasts, endothelial cells being formed in
capillaries, etc. and then a few
inflammatory cells. And then we get into the visceral
pericardium. So, there are
actually 2 layers of the pericardium. We have a pericardial
layer where the mesothelial
cells are sitting on the basement membrane and fibrous
connective tissue that’s tightly
applied to the heart, that’s the visceral pericardium. And
then it folds over and around,
that’s going to form the parietal pericardium. There is a
virtual space between the
visceral and the parietal pericardium that normally contains
5 to 10 cc of serous fluid.
01:17
That’s normal. And the thought is that little bit of fluid
allows some lubrication of the heart
in the pericardial sac. Inflammation of the pericardium,
basically is pericarditis, that’s the
definition. And we’re going to inflame that lining, and it
can be involved just the visceral
pericardium, the parietal pericardium or, in most cases,
both layers. We will see dilated
and leaky vessels. So we will see accumulated fluid because
that’s the nature of acute
inflammation. And we will see inflammatory cells. And,
depending on the tempo and
how long the pericarditis has been around, we may see
predominantly neutrophils
or we may see predominantly mononuclear inflammatory cells
like lymphocytes and
macrophages where we may see some combination thereof. The
etiologies of pericarditis,
in many cases, we don’t know. It’s idiopathic. But we do
have some other causes that
we are well aware of that are causally associated in many
cases. So, viral pericarditis is
is actually reasonably common particularly in certain
seasons where their viruses are
spreading around, Coxsackie B virus, influenza virus, HIV in
the appropriate individual
and echovirus are all causes of a viral pericarditis and can
be probably the more common
causes of pericarditis. We can also have bacterial causes.
If we’re going to look at
bacterial causes of pericarditis, the most common worldwide
is going to be tuberculosis.
02:52
In developed countries, industrialized countries, that’s a
relatively rare cause. And
other bacterial causes include pseudomonas in the
appropriate immunocompromised
host, staphylococcus species, streptococcus species,
mycoplasma kind of atypical
pericarditis, Lyme disease. Lyme pericarditis can occur with
spirochetes. And we can also
have fungal pericarditis, Histoplasma, blastomycosis,
Coccidioides immitis and
aspergillus. So, depending on the host, the geographic
location and various other
things, we may have different organisms that we may invoke.
There can also be
autoimmune causes of pericarditis. So, we can have
inflammation that’s specifically or
preferentially involves the pericardium because of the
antigenic differences that
are there. And these include autoimmune diseases such as
lupus erythematosus,
rheumatoid arthritis, sarcoidosis, and various vasculitides
such as Behcet’s disase and
Takayasu’s arteritis. Metabolic causes of pericarditis
include uremia. And when patients
have renal failure, there can be an increased vascular
permeability particularly in the
pericardium with some associated inflammation and we
attribute that to various
non-metabolism of certain things that would normally be
cleared by the kidney.
04:20
Hypothyroidism is also an interesting form of metabolic
pericarditis. The etiology is not
well understood but can be a cause. Perhaps the more common
causes of pericarditis
are non-infectious and include things like chronic
congestive heart failure where you can
have chronic transudation of fluids because of venous
congestion and poor cardiac
function. Dressler’s syndrome is an interesting one that’s
associated with either prior
surgery on the heart or prior myocardial infarction. The
surgery on the heart or the
myocardial infarction elicits certain neoantigens that
aren’t normally seen or responds
to those neoantigens can give rise to a pericarditis, tends
to be transient, tends to be
very responsive to immunosuppression, steroids or even
aspirin anti-inflammatories.
05:14
That’s Dressler’s syndrome. You can have pericarditis
associated with the aortic
dissection. So if you have retrograde dissection that
involves the pericardial sac,
irritation inflammation there, provided it’s not an
overwhelming dissection with an
overwhelming volume that causes death, can give rise to a
pericarditis.Takotsubo
cardiomyopathy, so-called broken heart syndrome, stress
cardiomyopathy due to
elevated levels of catechols causing focal injury to the
heart, and it’s that inflammation
associated with the focal microscopic infarction of
Takotsubo that will give rise to the
pericarditis. Cancer is an important one. So, cancer is not
confined to any particular
tissue, and if it’s metastatic disease, either solid
malignancy or hematologic malignancy,
it can end up in the pericardium, the inflammation
associated with that cancer or
vasoactive mediators elaborated by that cancer can drive
effusions and can induce
inflammation that will manifest this pericarditis. So,
malignant pericarditis is an important
etiology. There are some drugs that can also manifest with a
pericarditis. It’s idiosyncratic.
06:30
The actual mechanism is not understood although some of the
drugs may act as a
hapten to induce an immune-mediated pericarditis, kind of
like a lupus, for example.
06:41
So, procainamide, hydralazine, isoniazid use to treat
tuberculosis, various
chemotherapies and certainly radiation can all induce injury
inflammation involving
the pericardium.