welcome to EKG explained clearly by the end of this course you'll have all the
skills needed to confidently interpret EKGs in a systematic way you'll
understand the electrical activity represented on EKG paper that allows
this process to happen the heart to beat and cycle blood through our lungs and
bodies this is the final product whether or not you have experience with EKG
interpretation I think you'll find this series of videos very useful if you
understand the key foundations of how the heart works it'll be much easier to
learn and remember the nuances involved with the EKG that we'll cover later in
this course so we'll start with the anatomy and physiology of the heart
depolarization repolarization and then on to leads and specifics about EKG
paper and how a tracing is captured next are specifics on EKG tracing the P wave
the QRS complexes the QT interval the r2r interval etc we'll cover the impact
of our nervous system and neurotransmitters on the heart then on
to rate rhythm axis escape rhythms PVC bigeminy tachyarrhythmias ventricular
tachycardia and the key differences between ventricular tachycardia and
paroxysmal supraventricular tachycardia with aberrancy the QT c and the
potentially life-threatening Prasad's the points atrial fibrillation and
flutter widened QRS complexes and the various types of heart blocks using
precordial leads to hone in on certain areas of the heart atrial enlargement
and ventricular hypertrophy acute coronary syndromes myocardial infarction
and pericarditis we'll talk about T waves ST segment and T wave changes that
we see with ischemia bundle branch blocks and vesicular blocks and then at
the end we'll put it all together and teach you how to systematically read an
EKG we'll go through a normal one first and then on to a variety of abnormal
EKGs liked sinus tachycardia atrial fibrillation multifocal atrial
tachycardia first second and third-degree heart blocks h'lo largeman
tricular hypertrophy x' hyperkalemia rare anomalies and many many more
abnormal EKGs so let's begin with anatomy this is
a animation here of the heart beating and there's a number of things that I
want you to see so you'll understand this when we talk about the conduction
system of the heart and the EKG so the EKG as you know is a way of looking at
the electrical activity of the heart and it's really the electrical activity of
the heart that is responsible for what we're seeing here right now just for
those that don't know the anatomy of the heart we've got the right ventricle here
on this side we've got the left ventricle here on this side and these
areas up here are the atria so this is the right atrium here and the left
atrium is over here interestingly here what we've got is the tricuspid valve
this is a valve that allows blood to flow in from the right atrium into the
right ventricle and then gets pumped out through the pulmonic artery and this is
the pulmonic valve here the semilunar valves as you can see and then what you
can't really see very well is the aortic valve which is here at the top and this
is where the left ventricle is pumping out into there now one of the things
that I want you to notice first off is if you look carefully you'll see that
the right atrium here beats before the right ventricle right atrium right
before the right ventricle and you'll also notice similarly that the left
atrium beats right before the left ventricle now this is because of the
anatomy of the conduction system there is an electronic conduction system in
the heart that is not made up of nerves but instead of modified specialized
myocardial sites okay up here is the sinoatrial node which because of its
relatively quick activity is the pacemaker for the whole heart it then
goes to the atrial ventricular node which is here and then goes down this
conduction system here called the hiss Purkinje system and as you can see it
goes up and it basically conducts the electric signal to the myocardium
now we're gonna talk more about this in detail but I wanted you to notice that
it's this conduction system that basically makes this movement that we're
seeing right here like a perfectly well timed Symphony depends on the analogy
that you want to use there are several different analogies that you can use the
conductor that is conducting a symphony and you want to make sure that the
violins and the cellos and the flutes and the viola and the timpani they're
all acting all at the same time so you get the maximum effect in other words
everything is working in concert the other way of looking at it is a little
bit more destructive you know that if people are trying to demolish a building
they will have certain areas of the building that are drilled out and
weakened with sticks of dynamite and when they activate that dynamite it has
to be activated in just the right order in just the right fashion so that the
building comes down right on top of its footprint well this is kind of what's
going on here with the heart this electric conduction system the
sinoatrial the atrioventricular and the hiss Purkinje system is activated in
such a way that the electrical conduction goes and stimulates the heart
in concert so the electrical conduction starts up here and then goes to the
ventricle the reason for that is so that the atria contract right before the
ventricle the purpose of that is to get the blood from the atria down into the
ventricle to increase the size of the ventricle right before the ventricles
contract that causes an increase in freeload and allows your cardiac output
to be improved that's happening on both sides so you can see that the atria are
contracting first and then the signal is placed down here to the history Kinji
system it travels down very quickly down this hiss Purkinje system and then up
here into the myocardium so the effect is is that essentially the myocardium is
contracting all at the same time and you want that to happen
instead of having contraction occurring from the top down you want contraction
occurring all at the same time because of this very unique conduction system
this is going to look very unusual or look very unique I should say on an
EKG what is an EKG it's a way of measuring current you know that when you
take a battery and you place it on a voltmeter if you put the positive end to
the positive meter and the negative end to the negative meter you're going to
move the dial up so that you see that there is a difference in the voltage
when that voltage starts to move that is when you have an electric current and so
what an EKG does is it sees how is this depolarization or this movement of
positive charges that's going down the hiss Purkinje system how does it look
from the electric vision if you will in other words if I have an ultrasound
machine I could see if there is fluid or fluid moving on the ultrasound what an
EKG does is it does exactly the same thing except instead of fluid moving and
objects that you could see you're seeing electricity moving and so that is what
we're going to look at today atria contract first then ventricles contract
second but they're contracting in concert and then what happens is
everything resets back to normal and you have the same contraction happening
again the next series that we're going to talk about is we're going to break
things down to the smallest level and then we're going to build it up so that
we can finally see how we get back to this point again
okay so zooming in a little bit more now in terms of where we were
let's pull away all the muscular activity here and let's look
specifically at this conduction system I want to be very clear the thing that
you've got to understand that these are not nerves
okay these are modified myocardial cells that conduct electricity very quickly
and we'll talk about how that happens so the first one that you've got to know is
the sinoatrial node it is at the very top and the reason why it is there and
as the pacemaker is because its intrinsic activity is the fastest and
since it is the fastest it's going to cause depolarization to occur all the
way down and everything else is going to have to be in concert so this is kind of
the conductor of the concert now there are different pathways to get to the AV
node you can see here that the SA node can
to the AV node now the AV node is right here and it kind of holds things up it
kind of delays things we'll talk about that in another lecture so that what you
have here is you have the sinoatrial node saying okay it's time to contract
and we'll talk about how that happens and the atria contract and then the
electrical conduction gets down to here and it holds up what that effectively
allows the heart to do is to pump blood from the atria down into the ventricles
and allows it the time to pump it member this happens so quickly SA node to AV
node then when the blood is in the ventricle the AV node then conducts this
depolarization that's occurring into the Hispano system and it travels down and
around so quickly so very quickly that essentially the entire myocardium that
this innervates okay or that it penetrates basically depolarizes almost
all at the same time so that again is sort of a map of this cardiac conduction
system and really it's this cardiac conduction system that allows the
depolarization to occur in such a nice and timed way now on an EKG when we're
actually looking at the electrical depolarization are we actually seeing
the electrical movement down this conduction system the answer is no this
is such a small amount of electricity that it's almost imperceptible on an EKG
what is it that we're actually measuring what we're measuring is the
depolarization of the muscle the depolarization of the muscle is very
large and amplitude and that is what we are picking up on the EKG kind of like
if we are demolishing a building what do we see on the video do we actually see
the electricity going into the wires to the dynamite no we're actually seeing
the dynamite blow up and the building coming down that's in other words what
we're seeing on the EKG even though there is electrical conduction going
down this what we're seeing electrically on an EKG is the depolarization of the
actual muscle cells so just be aware of that okay so to get
a little bit more of the insight about what's going on let's go down to the
microscopic level and I want to show you a myocyte here now the thing that you
should know about a myocyte is just like any other skeletal or smooth muscle cell
it has a collection in it called the sarcoplasmic reticulum we'll call that
SR and the SR is full of calcium and the reason why it's full of calcium is
because this calcium can be released into the cell upon depolarization of the
cell we'll talk about that and that's gonna cause contraction of the striated
muscle so we'll just put a bunch of muscle cells here it's going to contract
okay and if you were to look histologically at the areas of the
myofibrils that are in cells you'll see how muscle cells work but basically
calcium is what's going to activate them to contract and they're made up of
troponin and all of these other things that we won't get into the key here
though is the sarcoplasmic reticulum causes calcium to be released and that's
what triggers it the question is is what triggers the sarcoplasmic reticulum well
what happens is as you may know on the cell surface of these cells you have a
sodium potassium pump and the purpose of that is to pump sodium out of the cell
and as you know sodium has a plus one charge and at the same time pump in
potassium and potassium has a positive one charge but it pumps out three sodium
for every two potassium and so what ends up happening is is there's a very high
concentration of sodium okay one plus outside the cell and there's a very high
concentration of potassium inside the cell now as it turns out the cell is
very important so sodium stays very high outside of the cell the way of thinking
about it is because three are going out and two are going in there is a negative
charge on the inside of the cell okay negative charge on the in
of the cell and there are positive charges if you will on the outside of
the cell we'll ignore those for now because the outside of the cell is very
very large and the inside of the cell is very very small so as a result of that
there's a far more negative charge that we see here now the other thing that's
important to know is that the cell while it is very important it is very
permeable to potassium and as a result of that potassium leaks out somewhat now
as it leaks out it's losing a positive charge so that even makes it more
negative and as a result you have a very negative resting potential on the inside
of the cell
now with that basis of history let us go forward here in the next lecture and
talk about why this interior negative charge is so important to the electrical
conduction that we're going to talk about here in our EKG course thanks for
joining us