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all right we're gonna switch gears a
little bit now and talk about pulseless
electrical activity and this is one of
my favorite rhythms to think about
because it's physiologically much more
complex and interesting than v-fib and
v-tach and there's a broad differential
that you're gonna learn about so what is
PE a PE a again stands for pulseless
electrical activity and what that means
is that there is organized electrical
conduction on the monitor normal-looking
QRS complexes with P waves and T waves
and all the things you expect from a
cardiac rhythm however there is
clinically no pulse
so normal looking activity on the
monitor but no pulse when you actually
palpate the neck what is the single most
important intervention for PE a it's a
little bit of a trick question
the most important intervention is to
figure out what caused it and fix that
so unlike v-fib and v-tach where we do
the same thing for everybody across the
board regardless of the cause in the
case of PE a we're only going to be able
to make our patient better if we can
figure out the cause and treat it now of
course we're gonna provide supportive
care in the mean time but ultimately our
goal is going to be to make a diagnosis
there's two major mechanisms of PE a
that I'd like you to be aware of one is
the empty heart and the other is EMD or
electromechanical dissociation and we're
going to compare and contrast these a
little bit so in the case of an empty
heart the heart is conducting normally
there's nothing wrong with the hearts
conduction system you know if I were to
get shot right now in the aorta and all
of my blood volume were to pour out on
the floor there's nothing wrong with my
heart it's gonna conduct perfectly
normally in the case of
electromechanical dissociation the heart
is also conducting normally electrical
activity in the heart is preserved
however when the heart is empty again if
I get shot in the aorta and all of my
Bloods on the floor there's nothing
wrong with my heart itself so at least
in the short term it's going to keep
Contracting just as hard and fast as it
can to try to perfuse my body so
contraction occurs and it's normal
however that contraction ultimately is
ineffective right because no matter how
hard the heart squeezes if there's
nothing inside of it if my blood is on
the floor and not inside the heart the
heart's not going to fill it's not going
to send blood out to the body by
contrast an electromechanical
dissociation there are normal cardiac
action potentials that yield the pretty
spikes that we see on the cardiac
monitor
however these action potentials do not
yield cardiac contraction so the heart's
conduction is normal but the contraction
is either absent or so impaired that it
doesn't produce a pulse ultimately empty
heart peña is caused either by
hypovolemia as I mentioned with the
example of all of my blood volume being
on the floor or it can be caused by some
kind of obstructive process that
prevents the heart from filling so
examples of those are things like
cardiac tamponade you've got a big
collection of blood around the heart it
physically compresses the heart the
heart can't fill normally so it can't
send blood out to the body normally same
with tension pneumothorax right you have
a huge high pressure air collection in
the chest it's going to mechanically
squish the heart and prevent normal
filling these are all empty heart forms
of peña by contrast
electromechanical dissociation is going
to be caused by systemic Arrangements in
the body so these are going to be things
that affect energy metabolism such that
the heart is able to produce the energy
to maintain normal conduction but it's
not able to maintain the energy to
enable mechanical contraction and as you
can imagine contraction requires a lot
more metabolic energy than conduction so
it's going to be the thing to go in the
setting of severe derangements of
metabolism in the body so what's your
differential diagnosis of peña there's a
common mnemonic that's used which is the
HS and the t's and I'm going to tell you
a secret I don't love this because it
doesn't force you to think about it
physiologically but a lot of students
find it useful so we'll go through them
hypovolemia like we already mentioned if
you don't have any blood volume your
heart's gonna be empty not your heart's
not gonna have good output hypoxia well
how do we make energy in the body we
make it out of oxygen and glucose so if
you're hypoxic you're aerobic metabolism
is going to be ineffective and you're
not going to be able to produce the
normal amount of energy to drive cardiac
contraction so it's potentially a cause
of PE a acidosis or hydrogen ion because
you know we had to make it start with an
H in that kind of situation you know
there's different Optima for every
process in the body there's pH optimum
temperature optimum and physiologic
processes just don't work right when you
have extreme arrangements of those
Optima so in the case of profound
acidosis the heart actually can't
squeeze normally so even though
conduction is intact the cardiac
contraction is not hyper or hypokalemia
it has to be pretty profound but severe
derangements of potassium can actually
precipitate PE a hypothermia like I
mentioned for the same reason as
acidosis if the body's really really
cold the heart's not going to be able to
contract normally we talked about
tension pneumothorax as a cause of empty
heart PE a and the same for tamponade
there's a number of toxins that can
potentially produce PE a by uncoupling
energy metabolism from normal cardiac
contraction massive m eyes can cause
such profound reduction in cardiac
squeeze that you can't actually
clinically detect a pulse and massive PE
s can cause such severe obstruction of
normal pulmonary blood flow that they
basically cause empty heart PE a the
same way any other obstructive cause
would so with PE a it's even more
important than with other types of
cardiac arrest to understand the
underlying cause and to identify what's
going on so you want to get as much
information as you can about the
circumstances that led up to the arrest
what was the patient doing when it
happened did the patient have any
symptoms beforehand
they suddenly clutch their chests and
complain of pain or were they gasping
for breath did they turn blue did they
attempt suicide was there some type of
trauma all of these things will help you
narrow the differential for peña and
treat the patient accordingly for
physical exam it's especially important
if you don't have a good history which
in many cases of cardiac arrest you
won't but if the patient has any signs
of physical trauma when you look at them
maybe you're gonna think more about
hemorrhage as a potential cause of PE a
or tension pneumothorax if the patient's
pregnant that should make you think
about pulmonary embolism if they have a
dialysis catheter hanging out of the
chest that's going to make you think
about hyperkalemia etc so physical
findings can potentially give you clues
that will help narrow your differential
and prioritize your treatments so that
you can help the patient with PE a
another nice adjunct we have nowadays is
bedside ultrasound so ultrasound is a
great extension of physical exam it
allows us to look inside the body in
ways that we couldn't before and
identify in real time is there a
pericardial effusion present or signs of
tamponade is there evidence of a
pneumothorax which is seen by absence of
lung sliding on ultrasound is there an
abnormal cardiac ejection fraction maybe
the heart's just barely beating maybe
the IVC is really distended suggesting
that the patient is volume overloaded or
maybe it's really collapsible in tiny
suggesting that they're dehydrated so
ultrasound is especially good for
cardiac tamponade and pericardial
effusion
this is an example of a cardiac
ultrasound where you can see some of the
chambers labeled but most importantly
you see a large pericardial effusion
which is outlined here on the screen and
that's big enough that you would
certainly want to perform a
pericardiocentesis and get rid of that
to see if that helps the heart beat more
effectively and improves your cardiac
output there's also the inferior vena
cava which is a great overall indicator
of your patient's volume status so like
I mentioned before patients who are
really volume depleted either from
dehydration may be from a diarrhea
illness or hemorrhage blood loss
the
patience will have very very skinny
collapsible inferior vena cavas so if
your vena cavas tiny or if it collapses
down to nothing when you breathe in
deeply that suggests a patient in need
of volume whereas if your IVC is normal
in calibre and it doesn't collapse down
to nothing or maybe it's even distended
that suggests that your euvolemic or
potentially even volume overloaded so
this can help kind of guide your
thinking a little bit about the patient
and particularly for patients who have
evidence of intravascular volume
depletion by giving them fluids or blood
you can potentially reverse their PE a I
didn't have an image to show you here
but I'll also just mention ultrasound is
very commonly used to evaluate for
tension pneumothorax there's a number of
tests that that you can do that'll help
you quickly identify that at the bedside
without moving the patient
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