So what we have here, quickly is an EKG. I
am going to show you what components of this
EKG would be the most important so that you
can interpret it properly right. Ready? Now we can
the X-axis and Y-axis. X-axis is what we are
going to paying attention to. Is that clear?
The X-axis represents or will show you the
different types of waves, either positive
deflection and negative deflection. Before
we go on, I wish for you to take a look at
a little bit of math up above so that you
clearly see as to the difference between a
little box and a big box okay.
A little box is 1mm. It represents
0.040 memorize that if haven't already. You see that little
box right there. The little box represents
0.04. So from henceforth, whenever I talk
about little box, I am talking about 0.04.
Is that clear? A big box is five little boxes.
It cannot be any more dramatic. So if you
take five of those little boxes, what is your
time it took? Take a look. 0.020 seconds, is that clear?
That you want to memorize. So so far, a little box
0.04, a big box is 0.2, why is that important? I want you to
take that math that we just did please and I want you
to come down and do you see where is this
PR interval? I need you to memorize if you
haven’t already, that that PR interval, the maximum
amount of time normally speaking that PR
interval should exist is 0.020 seconds maximum.
What is the minimum? 0.120 okay. So if you
take a look at the PR interval. What is the
PR interval? The PR interval are the beginnings.
"What does that mean Dr. Raj?" The PR intervals
are the beginning of the P wave to the beginning
of the QRS complex, is that clear? The PR
interval represents what in your head? The
PR interval you are thinking represents the
time that requires an impulse to begin at the
SA node making its way down to the AV node.
Is that clear? Why is that important? Well,
we could talk about how if your time of your
PR interval is greater than how much? 0.2 seconds,
which is the maximum time. You got
a problem. Is that WPW or is that going to
be AV nodal blocks. You see how we have taken
the math that at some point maybe frustrated
you and thought you so "Why do I need to know
this?" I am telling you why right here. Clinical
application. If you find you 0.2 seconds to be
greater for PR interval and that is obviously
AV nodal block because things are slowing
down. And then we will talk about that upcoming.
Whereas if it is less than 0.120 seconds, that
brings us to a very well important diagnosis
known as WPW. Now that's only one component,
but do you see as to how that time becomes
very important to us and how the little box
and the big box will play huge roles? Let
us continue on our X-axis, the P wave we all know
means originating ever SA node, the electrical
activity. You tell me when you mention this
a bunch of times, what goes through the heart
first? Electrical activity followed by the
mechanical activity. What does the P wave
represent? For mechanical activity. The A
wave. Are you seeing it? Take a second. Okay.
You saw it. In your head, P wave represents
A wave. A wave represents atrial kick. Correct.
That is the mechanical activity. What is that
part of again? One more time, late diastole
good. Let us continue. So now we have our
QRS complex. We just discussed PR interval.
The QRS complex represents only the ventricular
depolarization. All it represents is ventricular
depolarization. Now, if you talk about ventricular
depolarization, then what are we referring
to? It's the fact that we have, remember an actual
potential way back basic concepts of physiology
for cardiology. It is a fact that you have 0, 1, 2, 3, 4 okay.
You tell me, with phases 0, 1, 2, 3, 4,
which one of those represents ventricular
depolarization? It is obviously phase 0 right.
What does phase 0 mean to you? So I am really
having you review your basics right now. So
that phase 0 and how important is this? Really
important. I say if you are not good with
this, I highly recommend that you go back
and take a look at your actual potentials
for the heart and here specifically I am doing
my mechanical activity okay. Why is this important?
In a little bit in a lecture series we are going
to antiarrhythmias and if you haven't understood
this, things will get complicated. I don't
want you to get frustrated. It is about really
building upon your information okay. So that
voltage-gated sodium channel is what that
is? That phase 0 is a voltage-gated sodium
channel, isn't it? And you have an ... gate
giving more detail. Stuffs that you already
should know. So that phase 0 is your
voltage-gated sodium channel. It represents
ventricular depolarization. How does that
represent it on EKG? QRS complex. We will
go as far as that right now. We will go into
further detail as we go into phase 1, phase
2, which is plateau and phase 3. Right now
we are focusing upon phase 0, voltage-gated
sodium channel that has an activation gate,
inactivation gate that is represented on your
EKG by the QRS complex, ventricular depolarization.
Let us move on to next portion. The all important
ST segment. So ST segment bunch of things
that we have talked about. If I told non-STEMI,
non-ST elevation myocardial infarction, give
me some differentials, please. If all that
you see in a standard board question or an attending tells you, "Son
or daughter, tell me about non-STEMIs." You
are going to step up to the plate and you
are going to tell them what? You are going
to say maybe this is subendocardial type of
myocardial infarction. What kind? Subendocardial
myocardial infarction or this was a angina.
Correct? "What kind of angina?" Is the attending asking
you. You are not going to tell the patient,
or you are not going to tell the attending that it
is vasospastic angina. More likely
you are referring to stable or perhaps unstable
angina, right. And there you had ST depressions.
Those were your non-STEMIs,
is that clear? What if it was ST elevations?
With ST elevation, the differentials would
be transmural type of myocardial infarction
or maybe vasospastic. Now, the attending or licensing exam
is asking you, well how can you distinguish, how
can you confirm? You're looking for cardiac enzymes.
Cardiac enzymes are present, then you know
your patient for sure had some type of myocardial
infarction. If not, then your differentials
are a little bit more.
So, ST segment, we have spent a lot of time
there. You know that normally it should be
isoelectrical and then we have the T wave.
Tell me about that T wave. Well that T-wave represents
ventricular repolarization. So ventricular
repolarization, now you tell me, if you are
referring to actual potential, this could
be a tricky question, if you haven't properly
studied, if you haven't properly understood
your pathophysiology. The T wave represents
ventricular repolarization. If it is actual
potential of mechanical type that I am referring
to meaning phase 0, 1, 2, 3, 4, you tell me what phase
of your actual potential is represented by
your T wave? Phase 0, we already talked about
was QRS depolarization. Phase 2 is plateau,
that's your calcium influx and that actually is
your ST segment, is that clear? How can you
remember that? Plateau phase 2, ST segment
flat. Here is phase 3. Have you ever put that
into context? I hope you have because you
know this is a beautiful thing. So if that
potassium is effluxing during phase 3, isn't
that repolarization? Of course, it is. So
that is your T wave. Wonderful. Finally, we
have our QT. That is important, isn't it? Why?
I just got them talking to you about torsades
de pointes. What did I say was the predisposing
factor to torsades de pointes. It was a prolonged
QT interval. So if that QT interval is prolonged,
what caused it? Maybe drugs more commonly,
antiarrhythmic such as your sodium-channel
blockers class I, maybe you use antibiotics,
maybe antipsychotics so on and so forth. Then
also inherent such as romano-ward, Lange-Nielsen
and such. Well, if you have a prolonged QT interval,
you are predisposed to torsades de pointes.
These are some of the most important points
of this EKG. You are paying attention to X-axis,
everything that I just went through here
is just give you clinical application in the
subsequent lecture series, we would dive into
details further, further and further, but
it all begins with knowing the foundation.