Cardiac tamponade can be broken down: “tamponade” refers to pressure which obstructs blood flow,
and “cardiac” refers to the heart.
So in cardiac tamponade there’s a buildup of fluid in the pericardium, and that fluid
puts pressure on the outside of the heart.
As a result, the heart is unable to pump normally and blood flow is obstructed.
Normally, the heart sits inside the pericardium which is a pouch or cavity with two layers.
The outer layer 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, and 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 then reabsorb the fluid, so usually there’s
no more than 50 milliliters of fluid in the pericardial cavity at any time - that’s
about as much as a big shot glass.
A pericardial effusion is when the fluid begins to pool in the pericardial space, and it can
develop into cardiac tamponade depending on how much fluid there is and how quickly it
accumulates.
A rapid accumulation of fluid can happen as a result of trauma to the chest.
For example, a stab wound can puncture a blood vessel and fill the pericardium with blood.
Even blunt trauma, like a steering wheel getting pushed into your chest during a car crash
can lead to tamponade, because the force of the impact causes the rupture of lots of small
blood vessels.
Cardiac tamponade can classically happen a few days after a myocardial infarction, because
the weak, infarcted ventricular wall ruptures when it’s exposed to the high ventricular
pressures.
A rare cause is heart surgery, where, once again a weakened muscle can rupture and cause
cardiac tamponade days after the operation.
Yet another cause is aortic dissection, which is when blood pools in the actual wall of
the aorta.
If the aortic dissection ruptures through the wall of the aorta and through the fibrous
pericardium, blood can spill right into the pericardial cavity, leading to cardiac tamponade.
In these rapid situations, even a small volume - as little as 150 ml - can lead to tamponade,
because the pericardium doesn’t have time to stretch and accommodate it.
Other causes of cardiac tamponade typically happen over long periods of time, and in these
cases the fluid comes from a chronically inflamed serous pericardium that can’t resorb pericardial
fluid as quickly as it builds up.
This includes cancers that have spread to the pericardium, often from the lung and the
breast.
Another cause is uremic pericarditis, where blood levels of urea, a nitrogen waste product,
get really high usually due to a kidney problem.
The high levels of urea irritate the serous pericardium.
More rarely, cardiac tamponade can happen because of hypothyroidism or because of chronic
inflammation from a connective tissue disease.
In these situations, when fluid accumulates gradually, the pericardium can hold as much
as 1.5 L of fluid before tamponade sets in.
So tamponade means that fluid puts pressure on the heart itself, preventing it from fully
stretching out or relaxing between contractions.
This means that cardiac chambers can’t fill with blood properly, causing a decrease in
cardiac output or a lower amount of blood being squeezed out with each heartbeat, which
leads to hypotension.
Less blood leaving the heart also means less blood reaching the organs and tissues, and
the heart tries to compensate for its low output by beating faster.
When a person suffering from cardiac tamponade inhales, the systolic blood pressure sometimes
drops.
Normally, breathing in creates a tiny bit of negative pressure which pulls blood into
the heart, momentarily increasing systemic venous return.
When that happens, the right heart volumes increases, and the right ventricle expands
a bit into the pericardial space, so it doesn’t affect the left heart volume at all.
In cardiac tamponade, during inspiration, the right ventricle can’t move into the
pericardial space, so the extra volume pushes the interventricular septum toward the left.
This leads to a reduction in left ventricular diastolic volume, a lower stroke volume, and
a drop in systolic blood pressure during inspiration.
A decrease in the systolic pressure of greater than 10 mm mercury is called pulsus paradoxus,
and it’s a classic sign of cardiac tamponade.
In tamponade, there’s also trouble in the upper heart chambers: the atria can’t distend
enough to accommodate the venous blood returning to the heart.
That blood will have nowhere to go but back into the veins.
That’s why you’ll typically see distended jugular veins when you look at the neck of
a person with cardiac tamponade.
This sign is actually part of a triad of symptoms called Beck’s triad: distended neck veins,
hypotension, and distant heart sounds on auscultation.
Although not part of the triad, tachycardia, as well as coughing can also develop.
People with tamponade will also dyspnea, or difficulty breathing, as well as weakness
and lightheadedness.
If it gets severe enough, the heart can ultimately start getting ischemic, or low on blood, which
causes it to stop beating: this situation requires immediate drainage of pericardial
fluid.
A diagnosis of cardiac tamponade often starts with an ECG.
Classic findings include tachycardia, a low QRS complex voltage, and electrical alternans,
which is when the QRS complexes have different heights.
Echocardiography can show the excess pericardial fluid, as well as the heart “swinging”
inside the pericardial cavity.
Cardiac catheterization measures the pressure inside the cardiac chambers—in the case
of tamponade, the pressure in all four chambers is equal.
Treatment of cardiac tamponade in the acute setting is a pericardiocentesis.
That’s where a needle is inserted into the pericardium to drain the excess pericardial
fluid.
After that, the underlying disease needs addressed.
All right, as a quick recap – cardiac tamponade is a collection of fluid inside the pericardium
that puts pressure on the heart, affecting its function.
It frequently presents with Beck’s triad – hypotension, distended neck veins and
distant heart sounds on auscultation.
Treatment of cardiac tamponade requires an immediate pericardiocentesis, as well as management
of the underlying condition.