With pericarditis, "peri" means "around," card means "the heart", and itis means
"inflamed".
So pericarditis means the pericardial layer of tissue that covers the heart has inflammation.
Acute pericarditis generally lasts just a few weeks, whereas chronic pericarditis lasts
longer, usually more than 6 months.
People who develop pericarditis are also at risk of also developing a pericardial effusion
- that's when the inflammation causes fluid to accumulate around the heart.
The pericardium is a pouch or cavity that the heart sits inside of.
The outer layer of this pouch is the fibrous pericardium and it helps keep the heart in
place within the chest cavity.
The inner layer of the pouch is the serous pericardium that includes the pericardial
cavity, and is filled with a small amount of fluid that lets the heart slip around as
it beats.
The cells of the serous pericardium secrete and reabsorb the fluid, so usually there's
no more than 50 milliliters of fluid in the pericardial cavity at one time - that's
about as much as a shot glass.
Now, the cause of acute pericarditis is usually idiopathic, meaning that we don't know what
causes it.
When the cause is identified, it's usually a viral infection, like Coxsackie B virus.
Another cause is Dressler syndrome which occurs several weeks after a myocardial infarction,
or heart attack.
Basically, when heart cells die in a myocardial infarction, it leads to massive inflammation
that also involves the serous pericardium.
Another cause of pericarditis, called uremic pericarditis, is when blood levels of urea,
a nitrogen waste product, get really high usually due to kidney problems.
The high levels of urea irritate the serous pericardium, making it secrete a thick pericardial
fluid that's full of fibrin strands and white blood cells.
This gives the wall of the serous pericardium a "buttered bread" appearance.
Pericarditis can also be seen in autoimmune diseases, like rheumatoid arthritis, scleroderma,
or systemic lupus erythematosus, because the immune system attacks its own tissues, including
the pericardium.
Other causes of pericarditis include cancer, radiation therapy in the chest, and even medications
like penicillin, and certain anticonvulsants.
Regardless of the cause, inflammation in the pericardium means that fluid as well as immune
cells start moving from tiny blood vessels in the fibrous and serous pericardium into
the tissue or interstitium of those layers, making the layer itself a bit thicker and
more boggy - think of how a piece of dry flat pasta gets cooked and thickens up as it soaks
up fluid.
Now, a pericardial effusion can also develop.
That's when pericardial fluid begins to pool in the pericardial space, because the
serous pericardium can't remove it as quickly as it comes in.
If a lot of fluid starts to collect in the pericardial space - in other words, if that
pericardial effusion gets really big, then it can start putting pressure on the heart
itself, preventing it from fully stretching out or relaxing between contractions.
This can lead to tamponade physiology which is where the cardiac chambers can't fill
with blood properly, causing a decrease in cardiac output - which can be a medical emergency.
When the inflammation persists for weeks to months, the process is called chronic pericarditis.
In chronic pericarditis, immune cells initiate fibrosis of the serous pericardium which can
produce a inelastic shell around the heart making it hard for the ventricles to expand
-it's like the heart is wrapped by a boa constrictor.
Over time, it becomes harder for the heart to relax or expand, and the stroke volume
- the amount of blood the heart squirts out with each heartbeat goes down, and to compensate
the heart rate goes up.
This is similar to tamponade physiology but happens more gradually and is a result of
a change in the composition of the serous pericardium, rather than a fluid collection
around the serous pericardium.
The main symptom of pericarditis is fever and chest pain that worsens with deep breathing,
but improves with sitting up and leaning forward.
Larger pericardial effusions, those over 100ml of fluid, can cause diminished heart sounds,
and can even diminish cardiac output leading to shortness of breath, low blood pressure,
and lightheadedness.
There are a few ways to diagnose pericarditis and pericardial effusions.
First, when the thickened layers of the pericardium rub up against each other - it creates a friction
rub which can be heard on auscultation.
It sounds like two pieces of leather rubbing against each other.
Next, on an electrocardiogram, there are a few changes that you can expect to see.
In the first couple days to weeks, there can be ST segment elevations and PR segment depressions.
After that, the T waves tend to flatten and then becomes inverted over a few weeks, and
then eventually the ECG returns back to normal.
On an ECG, pericardial effusions, especially large ones, can show low QRS complex voltage
or electrical alternans, which is where the QRS complexes have different heights, as a
result of the heart swinging back and forth in a pool of pericardial fluid.
On an X-ray of a heart with a large pericardial effusion, you can see a silhouette that pools
to the bottom of the heart and gives a classic "water bottle" sign.
On an echocardiogram, a pericardial effusion makes the heart looks like it's dancing
within the pericardium, whereas chronic pericarditis shows the stiff serous pericardium restricting
the heart's movement.
In terms of treatment, the main goal is to relieve pain with analgesic medication, and
to treat the underlying cause of inflammation.
If there's a severe pericardial effusion, a pericardiocentesis can be done by inserting
a needle into the pericardial cavity and draining the excess fluid.
Okay, let's recap - acute pericarditis is usually caused by a idiopathic causes, but
can be caused by viruses or after a myocardial infarction.
It usually results in a friction rub, as well as ECG changes like ST elevation and PR depression,
followed by T wave flattening and inversion.
Pericardial effusions typically lead to low QRS voltages or electrical alternans, and
can be seen on an echocardiograph.
Chronic pericarditis typically results from fibrin deposition in the serous pericardium
and it prevents the heart from fully relaxing.
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