Welcome to EKGs explained clearly. By the end of this course, you'll have all the
skills needed to competently 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 and pitfalls 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 interva,l 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 QTc and the
potentially life-threatening Torsades de Pointes, 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 like sinus tachycardia, atrial fibrillation, multifocal atrial
tachycardia, first, second, and third degree heart blocks, atrial enlargement,
left ventricular hypertrophy, hyperkalemia, rare anomalies, and many many more
abnormal EKGs. So let's begin with anatomy, this is
an 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
myocardiocytes. Up here is the sinoatrial node (SA) 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 His-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. It 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 His-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 preload 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 His-Purkinje
System it travels down very quickly down this His-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 gonna 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 His-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 is 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 His-bundle system and it travels down and around so quickly so
very quickly that essentially the entire myocardium that this innervates 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
okay 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 that'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 gonna 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 a 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 end 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