ECG Basics | How to Read & Interpret ECGs: Updated Lecture

0:14What's up Ninja Nerds? In this video

0:16today, we're going to be talking about

0:17the basics of EKGs. Let's go ahead and

0:20get started. Hi Ninja Nerds. So, when we

0:22talk about EKGs, we obviously have to

0:26start with the basics. Understanding the

0:28physics, understanding the physiology

0:30before we actually start going through

0:31and reading 12-lead EKG cases and

0:34determining what's going on.

0:35So, what I want to do is is I want us to

0:38take us a stroll really quick through

0:40some basic physics and physiology, which

0:42will really prepare us when we start

0:44going through a systematic approach of

0:45EKGs. In order for us to under to under

0:48understand that and to start this

0:49process, what I want us to do is I want

0:51you to imagine. Imagine I have this

0:53ventricular myocardium here, and I'm

0:55just going to take and cut like a chunk

0:57of tissue out and place those chunks of

0:59tissue here in this box layer, okay?

1:02Then what I'm going to do is I'm going

1:03to get a little evil

1:05and I'm going to put some electrodes on

1:07each end

1:08of this tissue, right? I'm going to put

1:10a positive electrode on that side, a

1:11negative electrode on that side.

1:13Then what I'm going to do

1:15is I'm going to stimulate. I'm going to

1:17come at this end of this tissue and I'm

1:19going to stimulate. I'm going to provide

1:20some electrical stimulus.

1:22When this tissue becomes stimulated, it

1:24actually, you know, cells they undergo

1:26depolarization, right? Positive ions

1:28like calcium and sodium ions will flood

1:31into these cells, cause them to flip,

1:34become positive, depolarize them, right?

1:36And you know, there's little junctions,

1:38right? If I had like a little hole

1:39between this cell and this cell, there's

1:40little gap junctions. And so, those

1:42sodium ions and calcium ions can move

1:44through those gap junctions from cell to

1:45cell to cell to cell, creating kind of

1:47this electrical signal that's being

1:49propagated

1:51from this end of the tissue to this end

1:53of the tissue. And what kind of charge

1:55is being propagated? Well, remember,

1:57this cell was resting. So, originally

1:59it's kind of slightly negative, right?

2:01Then it becomes positive, positive,

2:02positive, positive. So, there's a flow

2:04of positive charges moving in which

2:06direction if I go ahead and apply a

2:08stimulus at this end. There's going to

2:10be a flow

2:12of positive charge moving towards this

2:15positive electrode.

2:17Now,

2:18why is that important? If I take the

2:20positive electrode and I hook it up to

2:22an EKG machine, it should cause a

2:25particular type of deflection, right?

2:26When you look at EKGs, all they look

2:27like is you see upward deflections,

2:29downward deflections, you see flat

2:30lines.

2:31What does that mean?

2:33I'll tell you what it means. If a

2:35particular tissue is generating action

2:37potentials, depolarizing waves that are

2:40moving towards a positive electrode,

2:42it'll get read from that electrode, send

2:44it to the EKG machine, and produce a

2:46positive deflection that shows up on the

2:48EKG. So, I want you to remember that. A

2:51flow of positive charges moving towards

2:54the positive electrode of any kind of

2:56lead of the 12-lead system should

2:58produce a

2:59upward deflection, okay?

3:03Let's take the opposite scenario.

3:05Let's say I take and I put a negative

3:06electrode here on that same side, a

3:08positive electrode on this side. But

3:10now,

3:11what I want to do

3:12is I want to stimulate this end of the

3:14tissue, okay? So, I'm going to go ahead

3:16and stimulate this end of the tissue,

3:18stimulate it, it'll depolarize, positive

3:20charges will then flow from this cell to

3:21this cell to this cell to this cell via

3:23the gap junctions, right? And it'll move

3:25in which direction? Towards the negative

3:27electrode or what we like to say is away

3:30from the positive electrode, right? And

3:32again, what kind of charge is flowing

3:34here? Positive charges.

3:36Whenever this flow of positive charges

3:38is moving away, very, very important,

3:41away from the positive electrode, it'll

3:43then get picked up by the electrode,

3:45send it to the EKG machine, and produce

3:47a downward deflection. So, again,

3:50downward deflection.

3:52All right. so to quickly recap,

3:54positive charges are flow of electrical

3:56activity moving towards positive

3:57electrode, upward deflection.

3:59If there's a positive charge moving away

4:02from the positive electrode, downward

4:04deflection. Okay.

4:06Let's Let's switch it up a little bit.

4:08So, we'll change it up a little bit.

4:10Cuz this is going to become very

4:11important when we go through this entire

4:13EKG waveform in explaining what all

4:15these deflections are indicating.

4:18What if I do one more thing?

4:20I put a negative electrode here on one

4:22side of the tissue.

4:23I put a positive electrode here on this

4:24side of the tissue, right?

4:26And now what I'm going to do is

4:29I'm going to actually have these cells

4:31You know whenever cells depolarize,

4:33right? For example, let's say that we

4:34took this one, it depolarized.

4:37After depolarizes, it then has to start

4:39to repolarize.

4:42So, let's pretend for a second that

4:44these cells will repolarize, right? And

4:46let's say that they're repolarizing just

4:48for the sake of this argument here.

4:50Let's say that they're repolarizing

4:51going in this direction, right? So, for

4:53example,

4:55this cell will become negative, this

4:57cell will become negatively charged,

4:58negatively charged, negatively charged.

4:59So, it's going to be moving

5:01in this direction, just for as an

5:02example, right? So, I have a flow of

5:05negative charges

5:07that is moving from the positive

5:09electrode towards the negative

5:10electrode, right? When negative charges

5:13are flowing towards the negative

5:15electrode, guess what it does? The same

5:17thing that would happen if positive

5:19charges are moving towards the positive

5:20electrode, produces an upward

5:22deflection. So, in this case, negative

5:24charges to negative electrode will

5:25produce a

5:27upward deflection. So, very important,

5:29you'll see why whenever we start going

5:30through this.

5:31The last thing I want you to remember

5:34is that there's parts where there is no

5:35deflection, either upward or downward.

5:38Sometimes it's just flat, right? An

5:40isoelectric line. What could that be

5:42indicative of? Let's say here I take

5:43this tissue.

5:45Negative electrode on this side,

5:46positive electrode on this side. But now

5:48the tissue is oriented in kind of in a

5:49different direction. You know this is an

5:51axis, right? If you kind of imagined an

5:53imaginary line

5:55going from this electrode to this

5:57electrode, there's an axis of that lead,

6:00okay?

6:02If I were to stimulate this end of the

6:04tissue,

6:05which way is it going to go? Upwards,

6:07right? So if I stimulate this end of the

6:08tissue and I cause this to depolarize,

6:10this to depolarize, this to depolarize,

6:12and so on and so forth, what is the

6:14direction of positive charges going to

6:16look like? It's going to start moving

6:18towards the axis of this lead, and then

6:21after it passes through the axis, it'll

6:23move away from the axis of that lead.

6:26You know what actually happens? But your

6:27EKG is so smart, your EKG machines are

6:30so smart. Generally, whenever this kind

6:32of charge, uh this positive charge that

6:34we have flowing here down this tissue

6:37perpendicular to the axis of the lead,

6:40originally,

6:41as it's going towards the axis, it

6:43actually produces a positive deflection.

6:46And then it moves away from the axis of

6:49that lead. But since it's the same

6:51amplitude on both sides of the axis of

6:54that lead,

6:56the deflections will be equal to one

6:58another, equiphasic, and then guess what

7:00happens? The EKG machine actually will

7:03cancel them out and make a kind of an

7:06isoelectric line. So you can remember

7:08two things. Whenever there's like no net

7:10movement of electrical activity,

7:12there'll be kind of a flat line. Or

7:15whenever the electrical activity of the

7:17heart is moving perpendicular

7:20to the axis of whatever lead we may be

7:23looking at, okay? I think we have a

7:25pretty strong idea now about what causes

7:27a positive, negative deflection, or

7:29straight line. Now what I want us to do

7:32is let's take one lead, that's the most

7:34commonly used lead in the rhythm strips

7:35of 12-lead EKGs, lead two, and map out

7:39the entire EKG waveform. All right,

7:42engineers, so now let's go ahead and

7:43take and I want you to trust me for

7:45right now. We'll go through all the 12

7:46different leads and understand them a

7:48little bit more. But for right now, just

7:50trust me that the lead that we are

7:52looking at in this kind of example that

7:54we're going to follow throughout the

7:55entire EKG cycle

7:57is lead two. Lead two usually the

7:59negative electrode is kind of on the

8:01right arm or right side, and then the

8:03positive electrode will be on the left

8:05leg, okay? And so, it creates this axis.

8:08If you imagine an imaginary dotted line,

8:10the axis is going in this direction from

8:12negative to positive, okay?

8:15So,

8:16remember, for the most part, where is

8:19the flow of positive charges going with

8:22respect to the positive electrode? Think

8:24about the positive electrode as an eye

8:26looking towards the negative electrode.

8:28It's looking for those positive charges.

8:30If it's coming to it, it's going to be a

8:31positive. If it's going away from it,

8:33it's going to be a negative, okay?

8:35So, let's start off. Let's start off

8:37with the first part of the EKG. Whenever

8:40a uh the the atrial cells, you know,

8:42with the all this entire EKG activity

8:44starts within the atria.

8:45The atria, they have this structure

8:47called the SA node. You know the SA

8:49node? It's located within the upper kind

8:51of top right portion

8:53of the atria near the entry of the

8:57superior vena cava. So, that would be

8:58our SA node, correct?

9:00That tissue has special types of

9:02pacemaker cells that have the ability to

9:04generate action potentials and spread

9:07those action potentials throughout the

9:08atria going towards a particular

9:11direction. And the ultimate direction

9:14that these electrical potentials want to

9:16go towards is this big fat structure

9:19here sitting at the top of the

9:21interventricular septum, and that is

9:23called our AV node, okay?

9:26So, let's say here that we have our SA

9:28node. It decides, "Hey, baby, I'm going

9:30to fire. I'm going to send some action

9:32potentials." So, it starts sending

9:34action potentials originating in the

9:37right atrium, okay? So, it'll send

9:39action potentials kind of all throughout

9:42this direction, right? Kind of spreading

9:44from the right atrium all the way

9:46towards the left atrium.

9:48Here's what's interesting though. If you

9:49were to take the mean

9:52of all or the average of all of these

9:54vectors that are spread throughout the

9:56atria,

9:57the mean vector that is generated by the

10:00depolarization of the atria from the SA

10:03node to the AV node, one big vector

10:06would really kind of look like it's

10:07going straight to the AV node.

10:10So, really if I took the mean of all of

10:12these little vectors that was generated

10:14by the SA node spreading out to the

10:16atria, the mean vector that's generated

10:19from the SA node to depolarize the atria

10:21is going downward and leftward towards

10:24the AV node.

10:25Now,

10:26that's the positive voltage right there,

10:28right? So, here, let's get rid of all

10:29these like little guys so that we can

10:30completely understand here that this

10:32right here,

10:33just this

10:35arrow here.

10:37This is a flow of positive charge moving

10:39from the SA node to the AV node, but

10:41remember, it's the mean vector of all

10:44atrial depolarization.

10:46Which direction is that positive charge

10:49flowing with respect to the positive

10:50electrode of lead two?

10:52It's moving in the direction of the

10:55positive electrode of lead two. What

10:57does that mean? Positive charge is

10:59flowing towards the positive electrode,

11:01upward deflection.

11:02Pa-boom! We got ourselves a P wave,

11:05baby. So, there is our P wave.

11:08So, we have our P wave, and what does

11:09that indicate? This indicates atrial

11:14depolarization.

11:19Now,

11:20more particularly, if we really, really

11:22want to be particular though,

11:24that P wave, if it looks just the way

11:26it's supposed to, which I know it may

11:28sound a little odd, what else could it

11:30look like? It can look very different

11:31sometimes, and we'll explain that

11:32throughout later videos.

11:34But, if the P wave looks the way it's

11:35supposed to, in other words, it's a

11:36sinus P wave, that means that that P

11:39wave was generated by the SA node. So,

11:42if you have an upright P wave looking

11:43like the same morphology throughout that

11:46atrial depolarization, it actually

11:48occurred because the SA node was the one

11:51that generated the electrical activity

11:54to depolarize the entire atria. Very,

11:56very important. Okay? So, we already

11:59started with the first part of our EKG.

12:02Let's move on to the next part. If you

12:03look here, we have our P wave, right?

12:05So, this is our P wave. But, then we

12:07have this portion

12:09of the EKG where there's this flat line.

12:12Okay? Well, I want you guys to remember,

12:15what does the flat line indicate? The

12:16flat line indicates that there's either

12:19no net movement of electrical activity

12:21or that the electrical activity is being

12:24directed perpendicular to the axis of

12:26that lead. That's what it means, right?

12:29So, let's understand why there is this

12:31flat isoelectric line here. Let's go

12:34back to where we were before. Here we

12:35have our SA node at the top of the

12:37atria. It generated a bunch of

12:39depolarization vectors. And where was

12:42that directed toward? Do you remember

12:43the end point that we want all of this

12:45electrical activity to kind of come to?

12:47We want it to go to the AV node at the

12:49top of the interventricular septum.

12:51We said that there's a bunch of

12:53different depolarization vectors, but

12:54the primary mean depolarization, the

12:57mean vector from all of those is

12:59directed downward and leftwards towards

13:02the AV node. So, that's our atrial

13:04depolarization vector. We said that gave

13:06us a positive type of deflection, right?

13:09The P wave.

13:10Now, let's say that the electrical

13:12activity finally gets to the AV node.

13:14The AV node becomes depolarized. So,

13:17it's starting to become positive,

13:18positive, positive, but guess what? The

13:20AV node is a very nice little waiter. It

13:22takes its time with the electrical

13:23activity.

13:24It slows down the conduction a little

13:26bit. Sometimes like about a 0.1 second

13:29delay that the AV node just hogs all the

13:31electrical activity and says, "Hey, stay

13:33here with me, baby, and then I'll send

13:35you down to the ventricles." So, what

13:37happens is the electrical activity hits

13:39the AV node. The AV node starts kind of

13:41taking all of this electrical activity.

13:43It becomes depolarized,

13:45but it holds that electrical activity

13:47within it before it decides to send the

13:49action potentials down to the

13:50ventricles.

13:51So, it is positive

13:53charge, but that positive positive flow

13:55of charge is not actually moving in a

13:58particular direction to produce any

14:00upward or downward deflection. So,

14:02that's how we have this isoelectric

14:04line.

14:05Now,

14:06very important to understand here that

14:09if we take from here, that point of

14:12where the P wave ends,

14:14until where this line kind of ends cuz

14:15there's going to be another little

14:16jaggedy point that we'll talk about here

14:18with the EKG,

14:19this right here is a very specific type

14:21of name here. This is called our PR

14:24segment.

14:25segment.

14:27Okay? That's the PR segment.

14:30The next part that we really need to

14:32differentiate here, if I were to draw

14:33like another Let's say I drew another

14:35one. Here's my P wave

14:38and my PR segment there.

14:40If I drew the distance from the

14:42beginning of the P wave all the way

14:44until where that PR segment ends, that

14:47is referred to as the PR

14:51interval.

14:53So, make sure you understand that. Okay?

14:55So, it's very important to remember the

14:56difference between these two.

14:59But, what do we know? We know why we

15:01have this isoelectric line. It's because

15:04the depolarization that moved from the

15:06SA node got to the AV node. AV node is a

15:08very slow conductor, holds the

15:09electrical charges for a certain amount

15:11of time, about a 0.1 second delay. Then

15:14it says, "Okay, I'll send the electrical

15:15activity down to the ventricles."

15:17Now, we understand the P wave and the PR

15:20segment. Now,

15:22the next thing that we're going to do is

15:24move on to the next part. All right, so

15:26now we understand the P wave, the PR

15:28segment, and we kind of formed at this

15:29point our PR interval. Now we start

15:31going to this next part of the EKG. Do

15:33you guys remember what that part is? So

15:35if you guys remember, we have our P

15:36wave, we already understand what that is

15:38indicating, then we have our PR segment.

15:40Together the P wave and the PR segment

15:41make our PR interval. Then we go into

15:43this next part, which is kind of a

15:44downward deflection. Let's kind of

15:46quickly, very, very quickly recap.

15:50P wave is what again? SA node firing,

15:52generating a mean vector

15:55towards what structure? The AV node,

15:57right?

15:58AV node holds on to that electrical

16:00activity because it's kind of a slow

16:02conductor, has and receives all that

16:04positive charge, but does not conduct it

16:07down the bundle bundle of His and bundle

16:09branch system yet.

16:11So that causes that PR segment.

16:13Now,

16:14here's where it gets cool. We have from

16:16the AV node the bundle of His, right? Or

16:19the AV bundle, which then splits into

16:22what's called the right bundle branch,

16:25and then to your left bundle branch. Now

16:26your left bundle branch actually has two

16:28other small branches, left anterior and

16:30left posterior fasciculars, uh but we're

16:32not going to we'll talk about that a

16:33little bit later, okay? When it comes to

16:34axis and deviation.

16:37But for right now, I want you to

16:38remember simply there's a right bundle

16:40branch and a left bundle branch, okay?

16:42Here's what's really, really

16:43interesting.

16:45Whenever that depolarization finally

16:47moves from the AV node down to the

16:49bundle of His and then through your

16:50bundle branches,

16:52do you know what's really interesting?

16:53Your left bundle, this is the left

16:54bundle branch, it is actually

16:56responsible for depolarizing

16:59the interventricular septum.

17:01Not really the right bundle branch. It's

17:04primarily the left bundle branch that

17:06depolarizes your interventricular

17:08septum.

17:09So if you think about that, if it's

17:11causing these small little

17:12depolarization vectors that are moving

17:14towards the right and maybe even a

17:15little bit kind of upwards superiorly,

17:18then what would the mean vector of all

17:21of those little guys look like on this

17:23diagram?

17:25It would look like this.

17:29Right? So, like I said, you should have

17:30all of these vectors that are pointing

17:32towards the right cuz it's going to be

17:34the left bundle branch depolarizing the

17:35interventricular septum from the left

17:37towards the right, and then it even is

17:40oriented a little bit upwards because of

17:42the shift of the heart two-thirds to the

17:44left of the mid-sternal line. So, this

17:46should be the net depolarization vector

17:50of the interventricular septum or septal

17:52depolarization.

17:54Okay, if that's the case, then what

17:57direction

17:58is that flow of positive charge moving

18:02with respect to the positive electrode

18:03of lead two?

18:05It's moving in the opposite direction.

18:08So, if it's moving in the opposite

18:10direction or away from the positive

18:12electrode of lead two, what does that

18:12do? Causes a negative deflection. So,

18:15that's where we get our negative

18:16deflection.

18:17That negative deflection has a very

18:19specific type of name. So, we know we

18:21have P wave.

18:23Right? That's our P wave.

18:26Then here, what do we have? We have our

18:28Q wave.

18:31That's our Q wave. And what does the Q

18:33wave indicate? That's very, very

18:35important. It is indicative of septal

18:37depolarization.

18:39So, what does the Q wave indicative of?

18:41It's best represented in this diagram,

18:43but the Q wave

18:46is indicative of septal

18:49depolarization.

18:55Okay.

18:57One more thing that I really want to

18:58kind of get across here cuz sometimes

19:00when we when we go further throughout

19:01these EKG lectures, you guys will see

19:03that there's something called

19:04pathological Q waves.

19:06Q waves are are are normal. They're

19:08physiological part of our EKGs, okay?

19:12Whenever they become larger, so in other

19:15words, they become very wide and we'll

19:16talk about what that what that actual

19:18distance is, or whenever they become

19:19very deep, they go have a very long kind

19:23of depth that they really have a

19:24negative downward deflection, and a

19:26couple other things, and particularly

19:28like what kinds of locations you really

19:30don't want to see them in, then they can

19:32be called pathological Q waves. So

19:34again, remember, Q waves are normal

19:36physiological part of the EKG. It's just

19:40the size of it really determines whether

19:42it is physiological or pathological.

19:45And sometimes what's very interesting is

19:47you may not even see the Q waves within

19:49a 12-lead EKG.

19:51All right. So we have the basic

19:53understanding here. We know that the P

19:54wave is indicative of atrial

19:55depolarization vector pointing down to

19:57the left. PR segment indicative of

20:00atrial depolarization, but no net

20:02movement. Q wave indicative of septal

20:04depolarization moving upward and to the

20:06right away from the positive electrode.

20:08Let's go to the next part of the EKG.

20:10All right, new interns, so now let's go

20:11on to the next part here. So we have our

20:13P wave, right? We know what that

20:14indicates. We have our PR segment. We

20:16know what that indicates, right? So here

20:18we'll put down here PR segment.

20:22We have our Q wave. We know what that

20:24now indicates. But now we go from this

20:27negative deflection into an upward

20:29deflection. What the heck does that

20:31indicate?

20:33Don't worry, guys, I got you. So again,

20:36SA node, this is going to be built like

20:38just buried into your brains. You guys

20:39will never forget this now. The SA node

20:41sends an atrial kind of de-

20:43depolarization vector that's directed

20:45downward in what direction?

20:47Towards kind of the left.

20:49Okay? Let me just draw your bundle

20:50branch system here. So again, which

20:52direction would that be moving? It'll be

20:54moving atrial depolarization downward

20:57and to the left as you're going towards

20:59the AV node. So that's going to produce

21:01that positive deflection. Atria stay

21:03depolarized, don't have any net movement

21:05cuz they're slow conductors. PR segment

21:08goes down through the bundle branch

21:09system, but remember that the left

21:11bundle branch is what really depolarizes

21:13the septum, and that creates this net

21:16vector that moves in which direction?

21:18Moves to the right.

21:21And then upward, which creates again

21:22that negative deflection.

21:24All right. Now, let's go to the next

21:25part here.

21:27The electrical activity will then

21:28continue to move down the bundle

21:30branches. So, it'll eventually got to,

21:31you know, from here down the left bundle

21:33branch, it'll start to spread outwards

21:35like this.

21:37From the bundle branches through the

21:38Purkinje system,

21:40you kind of get this kind of direction

21:41here. So, then we'll go through the

21:42right bundle branch,

21:44and then through the right Purkinje

21:45system. And you guys get the point.

21:47We're generating these vectors as we're

21:48going down through the interventricular

21:50septum towards the apex and then up

21:52towards kind of the bases.

21:54Here's what I want you guys to think.

21:55They're like, "Holy crap, there's so

21:56many arrows. Where the heck is the net

21:58vector?"

21:59All right. Remember,

22:00which ventricle is supposed to be

22:03thicker? It has more myo- cardium,

22:05meaning that it's going to conduct more

22:06action potentials, meaning that it'll

22:08generate a higher voltages, meaning

22:10it'll generate a larger positive

22:13deflection. Which side?

22:14The left ventricle. That left ventricle

22:16be thick, right? So, the left ventricle

22:19is going to generate more uh intense of

22:22a net vector, right? So, if we were to

22:24kind of say, let's say a imaginary line

22:26here cut in half, right ventricle on

22:28this side, left ventricle on this side.

22:30All of these net vectors here will

22:32create I mean, so all of these little

22:33vectors here will create one net vector.

22:37All right. From here to here. What What

22:39What will that look like? It'll be

22:40pointing like this.

22:43Okay? So, that's going to be the vector

22:45from the left ventricle. So, this is

22:46again flow of positive charge.

22:48Then let's say over here you have the

22:50right ventricle. The right ventricle is

22:52generating all these electrical activity

22:53that's moving in this direction, right?

22:56So, it's going to have a smaller, okay?

22:58It's not as thick. So, its electrical

23:00vector may be a little bit tinier.

23:02Okay? and then they kind of look like

23:04this. Because again, the left ventricle

23:05is way thicker than the right ventricle.

23:08And again, this is going to be a flow of

23:09positive charge. So, here's what our

23:11different vectors would look like if we

23:14only imagined it generating the left

23:16ventricle or the right ventricle. But we

23:19want the mean QRS vector. In other

23:21words, we want the equivalent of what

23:23the vectors would be additive of the

23:26left ventricular vector and the right

23:27ventricular vector. So, it should be if

23:30I take this one and this one, which

23:32one's bigger? Usually when I kind of go

23:33in the middle if they're equal. But

23:35they're not equal, right? That left side

23:36is way bigger. So, because of that, it's

23:40going to start the mean of these two

23:42will lean a little bit more towards the

23:44left. So, your net vector here

23:47between these two is going to look like

23:49this.

23:51So, this is our net

23:53QRS vector. And again, it's a flow of

23:55positive charge. And I erased it before,

23:57but let's say here's our positive

23:59electrode of

24:00lead two.

24:02If this is our mean QRS vector, which is

24:04the net sum of the left ventricular

24:06vector and the right ventricular vector,

24:08which direction is that flow of positive

24:11charge moving towards with respect to

24:13the positive electrode? It's moving

24:14towards it, right? If it's moving

24:16towards the positive electrode, what

24:17does that cause? A nice positive

24:20deflection. What do we get? A positive

24:22deflection. What does this mean vector

24:24indicate? Well, we know it's going to

24:25cause a positive deflection. Why?

24:27Because there's a flow of positive

24:28charges from this mean vector moving

24:30towards the positive electrode of lead

24:32two. And we know that based upon our

24:34discussion, that causes a positive

24:35deflection. What is that positive

24:37deflection here called? That is called

24:39our R wave. Okay, so you're that's your

24:42R wave. So, if you want to think about

24:44it, this would be the R wave This would

24:46be the vector, particularly, for the R

24:48wave in the left ventricle, and this

24:49would be the vector for the R wave in

24:51the right ventricle. So, this is the

24:52mean of them. So, we could kind of say

24:54if we want to, this is the mean

24:58R wave

25:01vector.

25:03Okay?

25:05All right. So, that discusses that part

25:07of the EKG. Now, let's move on to the

25:08next part. So, we have our P wave that

25:10we generated, which was again what? That

25:12was when the SA node was firing

25:13generating a atrial depolarization

25:16vector aimed towards what structure?

25:19The AV node, right? And the AV node once

25:21it's actually depolarized, it holds on

25:24to that electrical activity for a bit.

25:26It doesn't let it move down through the

25:29ventricular bundle system. And that is

25:31going to be the PR segment, right?

25:34Collectively,

25:35the P wave and the PR segment is called

25:38what? That is called your PR interval.

25:42Then what happens is

25:44these AV bundle will then finally say,

25:47"Okay, time to send this stuff down to

25:49the bundle system." So, send it through

25:50the AV bundle, the right bundle branch,

25:53and the left bundle branch. If you guys

25:55remember, the left bundle branch will

25:56generate depolarization vectors that are

25:58aimed towards the the right and upwards

26:01moving away from the positive electrode

26:03and that causes this downward deflection

26:05here called the Q wave. So, now we have

26:08our Q wave. Then what happens is

26:11the depolarization vectors will then

26:14move down into the left and down into

26:17the right. They'll create a vector

26:19moving towards the right, a vector

26:21moving towards the left. We want the

26:23mean of those two, but because the left

26:25ventricle is thicker, it's going to

26:27cause the mean R wave vector to be

26:29pointed downwards and to the left more.

26:32So, you should get a downward vector

26:34like this.

26:36And that's what caused our R wave.

26:38Well, now we go to the next part.

26:41The next part here

26:43is we had the depolarization spreading

26:46from the inner part of the myocardium

26:48all the way to the outer outer part of

26:49the myocardium.

26:51After it depolarizes the inner to outer

26:53part of the myocardium, it's not only

26:55going down in this way, so it goes down

26:58and it goes from inwards to outwards,

27:00but it also moves superiorly towards the

27:03base of the heart.

27:05As it does that, look at the direction

27:07here.

27:08Let's use our purple marker here.

27:10This kind of depolarization as we're

27:12saying here, it moves down like this.

27:15It also moves like this.

27:17And it starts moving towards the actual

27:20base of the heart. And the same thing

27:21for this side, it moves downwards like

27:23this, but it also

27:25move upwards like this.

27:28As it does that, there's going to be

27:29this kind of like basal

27:32uh ventricular kind of depolarization.

27:35And if you look at it, which direction

27:37is it actually kind of pointing? It's

27:39pointing upwards and then towards the

27:41left for both of them. So, if I were to

27:42draw kind of a little depolarization

27:44vector on this side, it should go this

27:45way.

27:46And a little depolarization vector on

27:48this side should go this way. Okay? So,

27:51these are going to be the depolarization

27:53of the ventricles towards the bases. And

27:55again, it's because they're moving down

27:57and upwards. So, if it's moving upwards

28:01and generally towards the left, and it's

28:03a flow of positive charge,

28:07what direction is that moving with

28:08respect to the positive electrode of

28:10lead two? It's moving away from it. What

28:12does that cause? A downward deflection.

28:15What do we get? A downward deflection.

28:18What in the world is that downward

28:20deflection called? This is called

28:23the S wave. We'll actually put that in

28:26here, S wave for this part.

28:28Okay?

28:29So, what is the S wave indicating? It is

28:31still ventricular depolarization,

28:34but at this point, it's more towards the

28:35base part of the ventricles, rather than

28:38the entire kind of like thickness of the

28:40ventricular myocardium, right and left

28:42ventricle thickness part from inner to

28:44outer. That was more the R wave, okay?

28:46And then the Q wave is more septal

28:48depolarization.

28:50All right, we've covered that. Let's pop

28:52right over into the next part here.

28:55All right. Quick recap. We're not going

28:58to go through all of this intensely

28:59again. We're not going to draw the

29:00vectors. I think by now you guys should

29:01know it all. But we'll draw here our

29:03kind of our bundle system here to just

29:05be consistent.

29:07Okay, here's our right bundle branch.

29:10Here's our left bundle branch. Okay.

29:12So, we know now

29:14we definitely We're professionals, I

29:15think, right? Engineers at this point.

29:17We know the P wave. We know what it

29:18means. We know the PR segment.

29:21We know what that means.

29:25We know the Q wave. We know what that

29:27means. We know the R wave. We know what

29:29that means. And we know the S wave. And

29:30we know what that means.

29:32Okay, here we go.

29:34And you get to this next part, which is

29:36very interesting.

29:38Which is going to be kind of like this

29:40flat segment here. Kind of There's kind

29:42of a little upstroke here, but really

29:43it's this isoelectric line that we

29:45really need to focus on.

29:47This isoelectric point here, where it's

29:50staying kind of in a flat line just like

29:52the PR segment was.

29:54This is called the ST segment. Now, ST

29:57segment is basically

29:59when the entire ventricular myocardium

30:02is completely depolarized. Remember how

30:05in the AV node, the AV node was

30:07depolarized and it stayed depolarized,

30:09but it didn't actually kind of like

30:10cause a movement of charge down into the

30:13AV bundle. It kind of just stayed in

30:15that AV node. In the same way,

30:18the entire

30:20ventricular myocardium has already been

30:23completely depolarized. It's super

30:26positive. It hasn't begun to repolarize

30:29yet. And there's no more movement of any

30:32kind of charge. It's just been

30:34depolarized, and it's just about getting

30:37ready to repolarize. But it's stuck in

30:39this depolarization state.

30:42But there is no net movement of any of

30:45that electrical charge. If there's no

30:46net movement of electrical charge, what

30:48will that do to the EKG? Is it positive?

30:51Is it negative?

30:52It's an isoelectric line. So, that's

30:54where we get this part here,

30:57which is called our

30:59ST segment.

31:02And this is a very, very important

31:04segment when it comes to pathology. So,

31:06we'll talk about this in future videos,

31:09okay?

31:10All right, so we understand that. Let's

31:11go into the last part of the EKG

31:14analysis here. All right, so the last

31:16part of the EKG, okay, so we we we know

31:19this by now. Now, engineers, we should

31:20be professionals at this whole waveform

31:22stuff. We know the P wave, okay? We know

31:25our PR segment. We know what all of this

31:27stuff indicates by now. We know our Q

31:30wave. We know our R wave. We know our S

31:32wave. Let's lengthen this ST segment

31:35here a little bit more though, so we can

31:36make sure it's a super profound ST

31:38segment there. And then we have one more

31:40wave that we have to talk about here.

31:41And again, what is this part here that

31:43we just finished discussing? This is our

31:46ST

31:47segment.

31:50Okay.

31:53All right, here we go. So, the first

31:54thing that we need to do is understand

31:56how the heck we get this upward

31:58deflection, which is the T wave, okay?

32:00Let's make sense of everything that

32:01we've done so far.

32:02So far, without going through all of

32:04those vectors,

32:06here's our AV node. We'll just draw our

32:08SA node here. SA node,

32:10AV node, we got our bundle of His, we

32:13got our right bundle branch, we got our

32:14left bundle branch, right?

32:16What did we leave off with? At the last

32:19point here, this entire ventricular

32:21myocardium, the entire thickness of the

32:23ventricular myocardium was depolarized.

32:26Now, here's where it gets good, baby.

32:30Whenever a tissue depolarizes, in order

32:33for it to relax, in in for it to be

32:35stimulated again, it has to repolarize.

32:38In other words, has to go back to its

32:40resting membrane potential, which is

32:43what kind of voltage inside of the cell?

32:45Negative voltage.

32:47So, at one point it was all positive

32:49charge throughout this entire

32:50ventricular myocardium.

32:52But, what happens is imagine the charges

32:55flipping from the outside of the

32:57myocardium to the inside of the

33:00myocardium. So, it's positive here, then

33:02it goes negative. And then it was

33:04positive here, negative. So, imagine

33:06like this. Let's say that we kind of use

33:07it as an example here. Positive,

33:09positive, positive, positive. That

33:11entire ventricular myocardium was

33:12positive, right? And during the ST

33:14segment. I'm going to flip each one, but

33:16I'm going to move in this direction.

33:19I'm going to repolarize that one,

33:21repolarize that part of the myocardium,

33:22repolarize that one, and repolarize that

33:25one. The negative charge is flipping in

33:28which direction?

33:29It's going backwards in the direction

33:31that the mean

33:32R wave vector was, right?

33:35Cuz if you think about it, it's going to

33:36be the same thing. It's going to be

33:38negative charge flowing this way

33:40from the right ventricles.

33:42Negative charge flowing this way

33:46from the left ventricles.

33:48So, this is going to create a nice

33:50vector, thick vector,

33:52right? That would be pointing

33:55upwards

33:56and towards the right. And this would be

33:58kind of creating like a little baby

34:01negative charge vector

34:04that's going to be pointing upwards and

34:05towards the left.

34:07But again, we want kind of the net

34:09vector between those two.

34:11So, what's the net vector? Well, again,

34:13this one's the bigger net vector This

34:15one has the bigger vector, the bigger

34:16amplitude. So, we want between we want

34:18in the middle. We want the net of those

34:20two, but it's going to be leaning more

34:22towards this side. So, what happens is

34:25in this case, this vector will kind of

34:27look like

34:29this.

34:33This is going to be the net vector

34:35between these two. And what kind of

34:37charge does it actually have? What what

34:40flow of charge is moving in this

34:44direction from the outer part of the

34:45myocardium to the inner part of the

34:47myocardium?

34:48Negative charge.

34:51Now, here's where we got to go back to

34:53remember what we talked about. If

34:55positive flows towards positive, it's an

34:57upward deflection. If positive moves

34:59away from positive, it's a downward

35:00deflection. What do we say happens when

35:02negative charge moves towards negative

35:05charge or negative electrode?

35:07It's going to produce an upward

35:08deflection. Negative charge oriented

35:12upwards towards that negative electrode.

35:14That is where we get our upward

35:16deflection, and that upward deflection

35:18is indicative of This is our T

35:21wave.

35:22And what does the T wave indicate? It

35:24indicates the ventricles repolarizing.

35:27So, what does it indicate? It is

35:28indicative of ventricular

35:34repolarization.

35:40Beautiful. So, at the end of this, to

35:42really quickly recap this, what does the

35:44P wave indicate? Atrial depolarization.

35:47What does the QRS indicate? Ventricular

35:49depolarization. What does the T wave

35:52indicate? Ventricular repolarization.

35:55Now that we've understood where these

35:57waveforms come, how they're actually why

35:59it's up, why it's down, why it's

36:01isoelectric, let's do the same thing

36:04with all the other 12 leads that are a

36:06part of our EKG. All right, engineers.

36:09So, at this point in time, we've covered

36:10what the EKG kind of waves and segments

36:13and all the different components of that

36:15should look like in one lead, right?

36:17Lead two, I told you. And usually lead

36:19two is the common most common lead used

36:21in a rhythm strip of a 12-lead EKG.

36:24But we only looked at one out of a total

36:25of 12 total leads that you can have in

36:27an EKG.

36:29And so that's important to remember that

36:30what are these different 12 leads? We'll

36:32talk about them individually, but

36:34there's what's called three limb leads,

36:36lead one, two, three, not too bad. Then

36:38there's three augmented unipolar limb

36:41leads, and that's AVR, AVL, and AVF. And

36:44then there's six precordial or chest

36:47leads, V1 to V6. So if you add all of

36:50that up, that's 3 + 3 6, 6 + 6 12, 12

36:53total leads. So we should, we don't have

36:56to, but we should see what all of these

36:59waves would look like if we utilize the

37:03vector format that we talked about above

37:06in each of those 12 leads. Now,

37:10these are tiny little arrows and there's

37:11a lot of them. So it's going to be kind

37:13of like confusing, so we're going to go

37:14through it each one by one, but we're

37:16going to kind of I'll use my hands to

37:17kind of gesture when what direction it's

37:19moving when in as well.

37:21Before we start going through this, you

37:23should know what the heck lead am I

37:25looking at where the negative electrode

37:27is on this side, the positive electrode

37:29is here, same thing with these. So let's

37:31quickly take There was this guy who made

37:34up this lead system, Eindhoven. He came

37:36up with what's called Eindhoven's

37:37triangle, right? So Eindhoven's triangle

37:40is this simple kind of method where the

37:44heart is kind of situated here in the

37:46center, and we create these axis of

37:49particular leads with lead one, two, and

37:51three. So what happens is we take an

37:53electrode and we put that on the right

37:55arm, we put one on the left arm, we put

37:58one on the left leg, and then we put a

38:00neutral one usually on the right. So

38:02let's say here I recommend this as right

38:04arm,

38:06left arm, left leg.

38:09There's three total leads. This is going

38:11to be lead one, this is going to be lead

38:13two, and this is going to be lead three.

38:16And you can kind of already see that if

38:18I were to take kind of like look with

38:19the respect to the heart, this one's

38:21kind of going horizontal here. That's

38:23going to be lead one. This one's kind of

38:25going diagonal in this way. That's lead

38:27two. And this one's kind of going

38:28diagonal in this way. That's lead three.

38:30But let's see if make sense of where the

38:31negative and the positive is.

38:33For the axis of lead one, there's a

38:36negative electrode that's placed on the

38:37right arm

38:39and a positive electrode that we have on

38:40the left arm.

38:42Then that creates an axis, and that's

38:44that axis that we see right here. Okay,

38:46that's the axis of lead one that we kind

38:47of situated on the heart there.

38:49Lead two, the axis of lead two, you have

38:52a negative electrode on the right arm

38:53and a positive electrode on the left

38:55leg, and that creates this axis that's

38:57coming down diagonally. And again, if

38:59you imagine I took this kind of a dotted

39:01line and put it over the heart, you can

39:03see there negative electrode here at the

39:04top, positive electrode here at the

39:06bottom towards the left.

39:08Same thing. Lead three, put the negative

39:10electrode here on the left arm, positive

39:12electrode here on the left leg. What

39:15does that create? It kind of creates

39:16this axis here

39:18that's going down this way. If I were to

39:20take this, put that over the heart,

39:22negative electrode should be over here,

39:24positive electrode should be down here.

39:26So that's where I'm getting all of these

39:27electrodes. I don't want you to just

39:28think I just made them up and put them

39:30there willy-nilly, right? So this is

39:32lead one.

39:34This is lead two.

39:35This is lead three.

39:37The beauty of all of this is that we

39:38already know what lead two should look

39:40like, right? We we should already know.

39:42So if I were to draw out that utilizing

39:44all those vectors that we talked about,

39:46we should already know that there should

39:47be an upward up right P wave, a PR

39:50segment, QRS,

39:52ST segment,

39:55and then our T wave, right?

39:57Here, for right now, I want you to trust

39:59me, but guess what? Lead one, lead two,

40:03lead three, all of them are pointing in

40:06the same direction. So for right now, I

40:08want you to trust me, but we'll go

40:09through it. There may be slight

40:11variations because of the the axis of

40:13those leads with the the respect to the

40:15vectors, but for the most part

40:19you're going to get the same kind of

40:21waveform here that you would get in lead

40:23two

40:25that you would get in lead one in lead

40:26three. So, let's go ahead and look at

40:27this.

40:28Okay, here's where my positive electrode

40:29Let's start with the P wave.

40:31Which way is it going? I have this arrow

40:33up here, but which way is it going?

40:35Downwards and to the left. Is it going

40:36towards the positive electrode? Yeah.

40:38Upward deflection.

40:39Then I go septal depolarization, right?

40:41That's my Q wave. It's going upwards and

40:44kind of towards the right. Is it Which

40:45way is it going with respect to the

40:46positive electrode? It's going away from

40:48it. So, that's going to be a downward

40:50deflection.

40:51Then I go to my sep- uh to my actual

40:53entire kind of like mean R wave vector.

40:56It's going down and to the left. It

40:58might not look like it's going straight

41:00towards the positive electrode, but it

41:01in general, the direction of where it's

41:04going is moving towards the positive

41:06electrode. So, that's going to produce a

41:08positive deflection.

41:09Then you have the depolarization at the

41:11bases of the ventricles. That's moving

41:14upwards and towards the right. That's

41:16moving away from the positive electrode.

41:18That's going to be the S wave. And then

41:20again, your T wave is this negative

41:23depolarization

41:24that's moving in which direction? It's

41:26going this way. What is it moving

41:28towards?

41:29The negative electrode. So, it should be

41:31a

41:32positive deflection.

41:34The same exact thing happens with lead

41:37three.

41:38So, if you look at it, the positive

41:40charge is down there. So, if you were to

41:41do this, we don't have to do this

41:43because it's going to make the exact

41:44same sense. If you were to follow all of

41:47these vectors, you would get the same

41:48kind of situation there for lead three.

41:50Okay? So, what I want you to remember is

41:53lead one, two, and three

41:55their waveforms should be pretty much

41:58the same on a 12-lead.

42:00Here's the next thing I really, really

42:02need you guys to know.

42:04Imagine the positive charge as an

42:07eyeball.

42:08Okay, imagine it as an eye, and you are

42:10looking at the heart from that view.

42:14Wherever that positive charge, imagine

42:16that is where you're looking at the

42:17heart.

42:18If that's the case, then lead one is

42:20looking at what part of the heart

42:22directly? What's the first thing that

42:23that eyeball sees?

42:26This portion here.

42:27It sees that left ventricle, but

42:30particularly like the lateral wall more

42:32towards the top. So, we call that a high

42:35lateral wall of the left ventricle. So,

42:38if I were to highlight over here, let's

42:40highlight in a very nice color here.

42:42Let's use this beautiful like turquoise

42:43color here. This portion right here

42:46would be what one lead one sees. So,

42:50lead one would give us an idea of what

42:53kind of electrical activity is taking

42:55place in which part of the heart? The

42:57high

42:58lateral

43:01wall

43:03of the left ventricle. Okay?

43:07That's very, very important, especially

43:09when we get to STEMIs. Okay? The next

43:11one. Lead two and lead three. You know

43:13what? We're so lucky cuz if you look

43:15here,

43:16lead two and lead three are both looking

43:20at the heart from the bottom.

43:22So, the first part that they see is this

43:24part here

43:25and this part there.

43:27That's the inferior portion of the

43:30actual what? That's the inferior portion

43:33of the ventricles. So, it looks at the

43:35inferior portion of the heart. So, this

43:37would be what portion would be looking

43:39at this? This would be leads

43:42two

43:44and lead three would be looking at the

43:46inferior

43:49wall

43:51of the heart. Okay? And that includes

43:54the right ventricle and even a little

43:55bit of the left ventricle.

43:57All right? So, that's important to

43:59remember that. So, now we have a pretty

44:01good idea of what lead one, lead two,

44:04lead three EKG waveform should look like

44:07and what part of the heart they tell us

44:09where the electrical activity is kind of

44:11altered in some way. All right? Now,

44:14let's talk about the augmented unipolar

44:16limb leads. Do the same kind of thing

44:17with these vectors, and then talk about

44:19what views or what portions of the heart

44:20they tell us about. All right, so we

44:22finished our limb leads. Now, let's talk

44:23about the augmented unipolar limb leads.

44:26Now, the thing is is that these can be

44:28kind of annoying and complicated if you

44:29really get into the physics of them.

44:30We're not going to do that. We don't

44:31need to. It's not necessary. Because you

44:33know what? Your EKG machines are so

44:35smart that they have the ability to kind

44:37of switch the electrodes kind of

44:38simultaneously. Um and so it's really

44:40kind of cool what they can do. We'll go

44:42into a brief discussion of what I'm

44:43talking about. So, remember I told you

44:45that there is three types of augmented

44:48uh unipolar limb leads. So, what are

44:49those?

44:50The first one that we'll talk about is

44:52AVR. So, this is going to be AVR,

44:55augmented unipolar limb leads. That's

44:56going to be for the right side. And AVL.

45:00And AVF.

45:03Okay.

45:04So, what happens is is you're still kind

45:06of using that same lead system, the same

45:08triangle. There was another guy named

45:10Wilson who came up with this idea.

45:12But it's the same kind of concept from

45:14the limb leads, okay? The only thing

45:16that's different is is that what happens

45:19is that the EKG machine will switch the

45:22negative electrodes on two corners, like

45:24on the like for the in this case,

45:26there'll be a negative electrode on that

45:27left arm, and a negative electrode on

45:29the left leg, and it'll put a positive

45:31electric electrode on that right arm.

45:34And what happens is

45:36that means that if you were to kind of

45:38again follow the axis, where does that

45:39mean the axis of AVR is?

45:42Whenever you have two negative charges,

45:45the actual kind of mean point is

45:48actually situated here in the center.

45:50So, actually, when you look at this, the

45:53vector is actually going to be kind of

45:55pointing this way towards that right

45:58side. So, that's where that kind of AVR

45:59comes from. So, if you were to imagine

46:02here for a second, imagine that's where

46:04that vector starts. This is where I

46:05would imagine I had this negative

46:07electrode situated. This

46:11is the axis of that AVR.

46:14Okay? So, I want you to again imagine

46:16here this is the eyeball. You're looking

46:19at the heart from this direction. Let's

46:22follow all the waveforms. P wave, where

46:26is it going? I know it's right there,

46:28but there's a lot of these uh waves very

46:29close. But again, this top one right

46:31there, that's your P wave. It's going

46:32downwards and to the left. With respect

46:35to the positive electrode of AVR,

46:37where is it moving? Away from the

46:39positive electrode. Ooh, what does that

46:41mean?

46:42That is a

46:43downward deflection. So, that means

46:45you're going to get something like this.

46:47Oh, shoot. Then we go here. We got this

46:50next part. What is this? That's septal

46:52depolarization. That moves towards the

46:54right and upwards. That means it's going

46:57to the positive charge. That's going to

47:00be a upward deflection. Maybe a little

47:02guy like that.

47:04Then

47:05the ventricles, right? You have your

47:07mean R wave vector. That's pointing

47:09downwards to the left. That's moving

47:12away from the positive electrode. That's

47:14a downward deflection.

47:17And then you have this depolarization

47:19that's occurring at the bases of the

47:20ventricles. That's moving

47:23towards the positive electrode. That's a

47:25upward deflection. Okay?

47:28And then from there you go into your ST

47:30segment, right? Which is where the

47:31entire ventricles are depolarized. They

47:34aren't having a net movement. And then

47:36what happens? Ventricular

47:37repolarization. I know you can't really

47:39see it, but this was the positive

47:40charge. That was for the R wave. What do

47:42you think that negative charge is?

47:44That's for the T wave, right? So, then

47:46after the ventricles depolarize, what

47:49happened? Do you guys remember what

47:50happened from above?

47:51Then what happens is you start to have

47:53this ventricular repolarization, which

47:55is a negative charge, a negative charge,

47:58moving towards the positive electrode,

48:00okay? In other words, if you were to

48:02imagine, remember, we imagine that this

48:04is our negative our imaginary negative

48:07electrode between these two points here.

48:09This is moving in which direction with

48:11respect to that negative electrode? Away

48:14from it. And so, because it's moving

48:16away from it, that is going to produce

48:19a negative deflection.

48:21And this is what you would get here for

48:23your actual EKG waveform with respect to

48:26this

48:28AVR. All right, so now, if you think

48:30about this, we now kind of see what our

48:32waveform would look like, our EKG in

48:34AVR. Do you know what's really

48:35interesting about this?

48:37It's literally the exact opposite of

48:41lead two. And technically, lead one and

48:44lead three, but lead two is kind of like

48:46our poster child of what the EKG would

48:48really look like.

48:49So, if you imagine, remember what lead

48:51two did? It had an upward P wave.

48:53Remember what the uh the Q wave was? It

48:56was a downward deflection. Remember what

48:57the R wave was? Upward deflection.

48:59Remember what the S wave was? A downward

49:00deflection. Do you remember what the T

49:02wave was? An upward deflection. This is

49:04the exact opposite. That is going to

49:05become so so important later when we

49:08start talking about how to determine

49:10rate and rhythm, if something is in

49:11sinus rhythm or not, if there is ectopic

49:14foci that are developed. We'll go into

49:15all of that later. So, it's very

49:17important, out of all of this stuff that

49:18we're just talking about leads, remember

49:20that AVR and lead two should be opposite

49:23of one another in their their waveforms.

49:26Now, we can go through this all again. I

49:28think it's going to be kind of

49:29repetitive, but if you follow the same

49:31thing, AVL, again, the EKG machine is

49:35smart, creates negative electrodes on

49:36the right arm and left leg. And then

49:39what happens is the imaginary negative

49:41charge then would form between those

49:43two, going towards the positive

49:45electrode that way. So, you would have

49:46an axis like this. Right? So, that means

49:49that the AVL, the I, that positive

49:52charge will be looking at the heart

49:55like this, okay? And if you followed

49:57every single waveform from that point

50:00on, utilizing everything we talked

50:01about, guess what? It's the exact same

50:04as lead one, lead two, lead three. Hey,

50:07let's take it another step. Guess what?

50:08The next one below this

50:09the exact same. The only one that really

50:12should be opposite is AVR. Every single

50:16other one of them, lead one, two, three,

50:18AVL, AVF, should all pretty much look

50:21the exact same. The only one that should

50:23really look different is AVR. There may

50:26be variations from EKG to EKG, but for

50:29the most part, in a perfect world, lead

50:31one, two, three, AVL, AVF should look

50:33the same.

50:34Okay? So, we should have an up upright P

50:36wave,

50:37QRS, T,

50:39upright P wave, QRS, T.

50:43If you wanted to go through these,

50:45definitely stop the video and follow

50:47each of these depolarization vectors and

50:49try to map all of them out. And again,

50:52you'll get pretty much this. Again,

50:54there may be a small variance from

50:56either one from all of these, but for

50:58the most part, same for AVL, AVF as one,

51:02two, and three. AVR should be the one

51:04that's completely different.

51:06All right.

51:07We now understand that. Before we go

51:09into the heart and showing the portions

51:10of the heart, we should actually finish

51:12explaining this AVF though. So, again,

51:14same thing as we talked about before

51:16with AVR and AVL, the machine's very

51:18smart, right? So, what it does is it

51:20turns a negative electrode on the right

51:21arm,

51:22negative electrode on the left arm, and

51:24creates a positive electrode here on

51:26that left leg. And again, if you imagine

51:28kind of the null electrode would form

51:30where? Somewhere in the center between

51:32those two, directed towards that

51:35positive electrode

51:37in this direction here.

51:38And so, it would be like this positive

51:40electrode is the eye looking at the

51:42heart from below. That already kind of

51:45tells you what we need to know. The next

51:46part.

51:48What portion of the heart do these leads

51:51tell us about or they really are good

51:53at? So, take a look here. If you imagine

51:56AVR,

51:57it's kind of like a positive charge kind

51:58of situated like right here.

52:01And it's looking at the heart kind of

52:02down this way.

52:03It really is good at telling us about

52:06two parts of the heart.

52:08The one part is it tells us about the

52:10very beginning part of the

52:12interventricular septum.

52:14And it tells us about parts of the right

52:16ventricle as well.

52:18So, again, what does AVR tell us about?

52:20It tells us about the activity of the

52:21right ventricle and what's called the

52:23basal septum.

52:28Okie dokie.

52:29So, that would be four. Let's write that

52:30up here. This is for AVR.

52:34The next one here is for AVL.

52:37AVL, where is the eye kind of situated?

52:40The eye is situated right over here,

52:42right? So, the positive charge would be

52:44here kind of looking down at the heart

52:45this way. So, that's going to tell us

52:47about what part here? Well, if you can

52:48kind of follow this down here, it's

52:50going to tell us kind of about the same

52:52thing that one did. Do you remember what

52:54one told us about? That high lateral

52:57wall of the left ventricle? It's the

52:59same thing for AVL. So, AVL will tell us

53:03about what?

53:04AVL will tell us about the

53:06high

53:09lateral wall

53:12of the left ventricle. Okay?

53:15And last but not least is AVF.

53:18AVF is it going to be again, imagine the

53:20eyeball is on the bottom. So, you're

53:22going to have the positive charge and

53:23it's looking upwards at the heart. What

53:26part does that hit? If you kind of draw

53:27an imaginary line, you're going to get

53:29kind of this portion here. What's this

53:31portion? We already kind of seen this

53:32before. It's going to kind of hit like

53:34from here to here.

53:36Do you remember what that looked like

53:37before with the limb leads?

53:39Leads two and three.

53:40So, leads two and three and AVF tells us

53:43about the inferior wall, okay, of the

53:46heart. So, this is going to be about

53:48inferior

53:50wall

53:52of heart. So, if we were to combine some

53:54of these to kind of tell us about what

53:55we know already, we can add on to help

53:57us to remember all of this in one thing,

53:59not in separate pieces, right? So, we

54:01know that AVF sees the inferior wall of

54:04the heart, but what else sees the

54:05inferior wall of the heart or kind of

54:06gives us a an idea of what's going on

54:07with the inferior wall of the heart? You

54:09can add on two,

54:11three,

54:13and AVF. That's going to tell us about

54:14the inferior wall of the heart. We

54:15already know that, though.

54:16And then again,

54:18what tells us about that high lateral

54:19wall of the left ventricle? AVL, but

54:22remember what else tells us about it?

54:23One.

54:24So, one and AVL tells us about the high

54:27lateral wall of the left ventricle. Two,

54:28three, AVF tells us about the inferior

54:30wall of the heart, and AVR is just kind

54:32of like a lone rider that tells us about

54:33the right ventricle and the basal

54:35septum.

54:36All right, let's go to the next part.

54:38Now that we got limb leads down, we got

54:40augmented unipolar limb leads down. We

54:42know now that all of the limb leads are

54:45having a upright kind of direction.

54:48We know that all of the augmented except

54:50for AVR have all of an upright

54:53direction. And we now appreciate the

54:55portions of the heart that those leads

54:57tell us about. Now, let's do the same

55:00thing for the precordial leads. I'm an

55:02engineer, so now at this point time

55:04we've covered our limb leads, we've

55:05covered our augmented unipolar limb

55:07leads, and we've talked about a lot of

55:08these deflections and what their ECG

55:10should look like, what portions of the

55:12heart these leads tell us about. We're

55:14going to do the same thing for the

55:15precordial leads. Now, the precordial

55:17leads are probably one of the more

55:19important leads

55:21out of all of the 12 limb leads because

55:22they can tell us a lot about pathology,

55:25okay? These are interesting ones. So,

55:27these are unipolar limb leads. So, they

55:29only have one kind of positive electrode

55:32that we put on the chest at different

55:34portions. So, these are unipolar leads,

55:37and we put them on the chest at

55:39different regions. So, let's actually

55:41kind of annotate where those ones would

55:43go. All right. First thing here,

55:46you put one of these V1, we call it, the

55:49first one, which again is a positive

55:50electrode. All of them will have a

55:51positive electrode that we place on the

55:53chest wall. V1, we actually go to the

55:56sternal angle, okay? That's usually

55:59around the second intercostal space and

56:00you feel down, you go to about the right

56:03fourth intercostal space and that's

56:05where you'll put V1, okay?

56:08Then you go to the next one. So, go back

56:09over to the left side and you go to the

56:11left fourth intercostal space

56:13parasternal line. That's going to be V2.

56:17You skip V3 for a second because you

56:20come back to him a little bit later.

56:22Then you go to V4. V4, you go down to

56:26the fifth intercostal space on the left

56:29and you go to about midclavicular line.

56:31You place V4 there.

56:35V5, you stay in the left fifth

56:37intercostal space, but you move to the

56:39anterior axillary line, which is about

56:41right here, okay? So, that's going to be

56:43V5.

56:45And the last one is you again stay in

56:47that left fifth intercostal space, but

56:49keep moving, moving, moving until you

56:51get into the middle of the armpit and

56:53that's called midaxillary line. So,

56:56that's V6. Now, we got to come back

56:58though and place V3. Where do we place

57:00V3? We just make sure it fits between

57:03somewhere between V2, which is that left

57:06fourth intercostal space parasternal

57:07angle or parasternal region,

57:09between V4, which was left fifth

57:12intercostal space midclavicular line.

57:14So, as long as you just place it between

57:15them, doesn't really matter. So, that's

57:17V3.

57:19Okay? So, these are our precordial or

57:22our chest leads. We know kind of now

57:23where they go, right? Right fourth, left

57:26fourth, both parasternal. This one goes

57:28between V2 to V4. V4 is left fifth

57:31midclavicular. V5 left fifth, anterior

57:34axillary line. V6 left fifth,

57:36mid-axillary line.

57:39We know that these are unipolar. They

57:40only have a positive electrode that we

57:42place on the chest. So, they only can

57:44pick up kind of the vectors that are

57:46moving either towards them or away from

57:48them and what plane. That's what's

57:50really important. This is what's really

57:51cool about them.

57:53So,

57:54they tell us about the electrical

57:56activity in a what's called a horizontal

57:58or kind of a transverse

58:01which is very, very cool. So, what we

58:03did here is we took a cross-section,

58:05okay, of the thorax to where you're

58:07going to see the heart. You can't

58:08obviously this is where your lungs would

58:09be here on the sides. But, we're taking

58:12a kind of a cross-section or transverse

58:14section of the thorax and looking at it.

58:17Now,

58:18these leads we kind of try to have them

58:21all converge on a point here at like

58:23that AV node basal septal portion. But,

58:26each one of these tells us about a

58:29particular portion of the heart. Before

58:31we start getting into that though, we

58:33should have an understanding very, very

58:35importantly about the what's called the

58:37progression

58:39of the R wave

58:41and the S wave as we go from V1 all the

58:44way to V6. I'm not too concerned about

58:45the P and Ts. I'm very It's very

58:47important we understand the R wave

58:48progression as well as the S wave as we

58:51go from V1 to V6. When you talk about

58:53the EKG, right? So, if we were to kind

58:55of just draw out the EKG waveform, we

58:56kind of know all the parts by now. Uh

58:59definitely it's it's it's we we're good

59:01at it now. P wave QRS T wave.

59:04There's two waves that I primarily want

59:06us to focus on throughout the process

59:08here. That's the R wave and the S wave.

59:11That's the ones I want us to really,

59:13really discuss about.

59:14The reason why is that Q waves sometimes

59:17you see them, sometimes you don't and

59:18really you shouldn't really see them um

59:20at least big ones in V1 to V3. So,

59:23again, we're going to focus primarily on

59:25the R wave and the S wave and the ratio

59:27as you go from V1 to V6. Very, very

59:29important. We have to understand this as

59:31a basic concept of EKGs.

59:34So,

59:35remember the first positive deflection

59:38in the QRS is the R wave. The second

59:41deflection, if it comes after whatever

59:43any positive deflection, that is going

59:44to be the S wave.

59:46So, let's say that we take here and we

59:47kind of look at the ventricles.

59:50I like to look at them a little bit

59:52separately with respect to the R wave.

59:55If you think about it, remember whenever

59:57the ventricles are depolarizing, right?

59:59We're at this phase, you create a small

1:00:02right ventricular vector for the R wave,

1:00:05and you create a large

1:00:08ventricular vector, a bigger one,

1:00:11for the left ventricle, right? And you

1:00:12know that you would create a mean one

1:00:14that would be a little bit more directed

1:00:15between the two of them, but it would

1:00:17definitely be leaning more towards that

1:00:19larger left ventricular R wave vector.

1:00:22For right now, before we even look at

1:00:23the mean one, I like to look at just the

1:00:25individual ones. I think it helps me to

1:00:27make sense of this.

1:00:29So, let's look at that. V1, if you kind

1:00:31of follow the lines here, you obviously

1:00:34can tell that V1 tells us about the

1:00:36right ventricle. V2 tells us about the

1:00:38right ventricle. V3, it does a little

1:00:41bit of the right ventricle as well, but

1:00:43V1, V2, V3, they should tell us a little

1:00:46bit about that right ventricle, but

1:00:47primarily V1 and V2.

1:00:50So,

1:00:51if that's the case then, if I have a R

1:00:53wave vector that's coming from that

1:00:55right ventricle, and it's little, cuz

1:00:57it's not going to be as big as the left

1:00:58ventricular one because of the

1:00:59thickness,

1:01:01what kind of R wave would I get for V1,

1:01:04V2, and maybe even V3? Would I get a big

1:01:08R wave, or would I get a like a smaller

1:01:10R wave? I get a smaller R wave, right?

1:01:13Because that's a smaller R wave vector.

1:01:16So, if that's the case then, my first

1:01:17upward deflection has to be little,

1:01:20right? Like this.

1:01:22And then like this.

1:01:25And then like that maybe a little bit

1:01:28maybe a little bit bigger as you go to

1:01:29V3 because look where V3 is starting to

1:01:31kind of look at. It's starting to get

1:01:33more towards that left ventricle. So, if

1:01:36you kind of look at it, V1, V2 maybe the

1:01:38same size, but V3 that that R wave

1:01:41should be getting a little bit bigger at

1:01:44that point time.

1:01:46Okay, let's keep following that over

1:01:47here to V4.

1:01:49V4 is actually what's called our

1:01:51transition point cuz now we have that

1:01:54leftward kind of vector here that left

1:01:56ventricular R wave vector that's

1:01:57pointing towards the left side here. And

1:01:59V4 is getting a good shot of it. V5 is

1:02:02getting a really good shot at and so is

1:02:04V6. So, what do you think?

1:02:07Should the R wave be big for four, five,

1:02:10and six or should it be small?

1:02:12That's a big R wave vector coming from

1:02:15the left ventricle. So, it should be a

1:02:16big R wave, right? So, it guess what we

1:02:18do. We get a nice R wave.

1:02:21Even bigger here in V5.

1:02:24And then a decent size one here in V6,

1:02:27right?

1:02:28Actually don't need that yet. We're

1:02:29going to get to the S wave in a second.

1:02:31But you get the point here. Look at

1:02:33what's happening.

1:02:34With the R waves as we go from V1 to V6.

1:02:38For the most part they should be getting

1:02:41smaller, little bit bigger, little bit

1:02:43bigger, bigger, bigger, bigger.

1:02:46That's kind of the whole process of the

1:02:48R wave as you start to transition

1:02:51throughout these.

1:02:52Let's do the same thing.

1:02:54But with the S wave.

1:02:56So, the S wave is usually indicating

1:02:58what? So, you're going to have this kind

1:02:59of depolarization

1:03:01of the bases and then this kind of

1:03:03depolarization of the bases as well.

1:03:07Same thing.

1:03:09If you're kind of looking at these, it's

1:03:10the same kind of concept here, right?

1:03:13That these are moving away from the

1:03:15positive electrodes, okay? So, this is

1:03:18what happens is

1:03:20it's moving away from the positive

1:03:21electrodes.

1:03:23So, this will produce a downward

1:03:24deflection, okay? Because again, if

1:03:26you're looking at this one here, it's

1:03:28going to be moving again away from the

1:03:30positive electrode. That should produce

1:03:31a downward deflection.

1:03:33If you look in V2, same thing. It should

1:03:36produce a

1:03:37downward deflection.

1:03:39In V3, it should produce a downward

1:03:42deflection. But guess what? That

1:03:43downward deflection starts to decrease

1:03:46as you move from V3 all the way till V6.

1:03:51So now, watch what happens now. This

1:03:53should kind of become a like a little

1:03:55bit smaller like a little bit there.

1:03:57And then here, this one will kind of

1:03:59almost become like isoelectric.

1:04:02This one will be really tiny. And this

1:04:04one will kind of be almost non-existent.

1:04:06So, do you see what's happening now with

1:04:08the R to S ratio here?

1:04:11Is that as you progress, the R wave

1:04:14should be getting bigger as you go from

1:04:15V1 to V6.

1:04:17And the S wave should be getting smaller

1:04:20as you go from V1 to V6. That's very,

1:04:23very important, especially when we start

1:04:26talking about axis deviation and other

1:04:29types of pathologies like ventricular

1:04:31hypertrophy, so on and so forth. Okay?

1:04:34So again, what do I want you to get out

1:04:36of this?

1:04:37R wave

1:04:39progression.

1:04:41As you go from V1 to V6, what happens to

1:04:44the R wave? It should get bigger. As you

1:04:47follow the S wave

1:04:50from V1 to V6, what should happen?

1:04:53It should get smaller, okay? That's very

1:04:55important to remember.

1:04:57All right. So, I think we now have a

1:04:58pretty good idea of what the R to S

1:05:00ratio should look like through V1 to V6

1:05:02and what these kind of precordial leads

1:05:03are telling us about. All right. So now,

1:05:05at this point in time, we should have a

1:05:06pretty strong idea about where do we

1:05:08place the precordial chest leads, right?

1:05:11We should understand what kind of a way

1:05:13they're looking at the heart from a

1:05:14horizontal or transverse plane.

1:05:17We should very, very importantly

1:05:18understand the progression of the R wave

1:05:20as we go from V1 to V6 is increasing and

1:05:23that the S wave as we go from V1 to V6

1:05:25is decreasing. So, the R to S ratios

1:05:28usually less than one for V1 to V3,

1:05:30greater than one for V5 to V6.

1:05:34And the next thing that we need to

1:05:35understand here is what portions of the

1:05:38heart do V1 all the way to V6 tell us

1:05:41about because that's very important

1:05:43again when it comes to STEMIs.

1:05:45So, to make it easy, there's the

1:05:48different parts that we're going to

1:05:49color in here for us, right? So, this

1:05:51first one here, right ventricle.

1:05:54Right ventricle is definitely going to

1:05:56be told to us by V1, V2, and even a

1:05:59little bit of V3. So, I want you to

1:06:01remember here, V1 to V3 will tell us

1:06:05about the activity of what? It'll tell

1:06:07us about the activity of the right

1:06:09ventricle.

1:06:10Now,

1:06:12do you guys remember what other

1:06:14lead that we talked about? Like the limb

1:06:17leads or augmented unipolar limb leads

1:06:19tell us about the right ventricle, which

1:06:21one?

1:06:21AVR. So, AVR you can also add into this

1:06:25if you want to also gives us an idea

1:06:27about that right ventricle. Pretty cool,

1:06:29right?

1:06:30So, if you wanted to add in from what we

1:06:31remember, you can also add in there

1:06:34AVR like we did before. All right, so we

1:06:37know that V1 to V3 and we can add on

1:06:39that little AVR there as well to help us

1:06:41remember stuff, recognition there. That

1:06:43that kind of tells us a little bit about

1:06:45the right ventricle.

1:06:46Now, the basal septum though, the top

1:06:48part of the interventricular septum if

1:06:51you will,

1:06:52that is going to be pretty much picked

1:06:55up by the active by the electrodes V2

1:06:57and V3. So, V2 to V3 tell us about that

1:07:01basal septum. But, what else told us

1:07:03about the basal septum? Remember AVR

1:07:05told us about the right ventricle and

1:07:06the basal septum. So, if we want to, we

1:07:08can also add in AVR.

1:07:10Okay?

1:07:12Let's come over to the next part.

1:07:13So, now we have the anterior portion of

1:07:16the heart. So, the anterior

1:07:19wall

1:07:21of the heart.

1:07:23So, the anterior wall of the heart is a

1:07:25very good big chunk of the heart, and

1:07:27that's going to be from V2

1:07:30all the way to V4. So, V2 to V4 tell us

1:07:33about the anterior wall of the heart.

1:07:35Very, very important one. Okay?

1:07:38The last one here, which is going to be

1:07:40telling us about the kind of the lateral

1:07:42wall of the left ventricle. So, again,

1:07:44which part of the left ventricle here?

1:07:46The lateral

1:07:48wall

1:07:50of the LV, which is your left ventricle.

1:07:52That's going to be what? V5 and V6,

1:07:55which will be giving us a good

1:07:56representation of that part of the

1:07:58heart. So, V5

1:08:00to V6.

1:08:01Now, if you wanted to add on here

1:08:04and think a little bit about this,

1:08:06remember the lateral wall of the left

1:08:07ventricle is V5 to V6. But, do you

1:08:09remember what kind of the higher part of

1:08:11the left lateral wall of the the lateral

1:08:13wall of the left ventricle was covered

1:08:14by? One and AVL.

1:08:17So, sometimes, if some people develop

1:08:18STEMIs in V5 V6, they may also they have

1:08:22elevations in V5 and V6, they may also

1:08:25have some elevations in one and AVL if

1:08:27it hits those higher parts. So,

1:08:28sometimes you can also combine one, AVL,

1:08:32V5, and V6 together because they really

1:08:35give you a good idea about that entire

1:08:36lateral wall of the left ventricle.

1:08:38Okay?

1:08:40All right. I think we have a pretty good

1:08:42idea now about these precordial leads,

1:08:45and I think we have a pretty good idea

1:08:47about all of these different waveforms

1:08:49and vectors and physics, which I know is

1:08:51mind-numbing sometimes.

1:08:53What I want us to do is now start taking

1:08:55everything, all these basics kind of

1:08:58topics that we've gone over, and start

1:09:00start

1:09:00that to EKGs now.

1:09:03What I really want to do is give you the

1:09:04very basics about what an EKG kind of

1:09:08strip or paper looks like.

1:09:11What are some of the bare minimum things

1:09:13that you really need to know whenever we

1:09:14start reading them, and then also talk

1:09:17about a quick little recap of the

1:09:21different deflections, and maybe what

1:09:23the actual parameters or distance of

1:09:25those intervals or waves, what how wide

1:09:29they should be, how long they should be,

1:09:31so on and so forth. So, let's now come

1:09:33over here, finish off our lecture with

1:09:34that. All right, so we've really built

1:09:36up our foundation now. We have a very

1:09:37strong foundation that we've built.

1:09:40Let's go ahead and really quickly,

1:09:41before we really start getting into

1:09:42looking at lectures and reading real

1:09:44EKGs, have a basic idea of some of the

1:09:47components of the EKG strip itself.

1:09:50So, if I were to take here, I want you

1:09:51guys to know first thing. You see this

1:09:53big large red box.

1:09:55This big large kind of red box right

1:09:57here, there's a couple things I want you

1:10:00to know about it. So, large

1:10:02box.

1:10:04First thing I want you to know is I want

1:10:05you to know a couple things about its

1:10:07width.

1:10:08Less significant with respect to these,

1:10:11I want you to know the height.

1:10:14So, the width and the height,

1:10:16thankfully, are the same.

1:10:19It's 5 mm in width, 5 mm in height.

1:10:24You're probably like, "Okay, what the

1:10:25heck is that supposed to mean?" I'll

1:10:27tell you, don't worry. Width is a little

1:10:29bit more of the important one, okay?

1:10:32So, I like to turn width particularly,

1:10:35and cuz this is measured over time. So,

1:10:37width is really helpful when it comes to

1:10:39time.

1:10:40Height is determining kind of the

1:10:42amplitude or the voltage

1:10:45that the wave is actually kind of

1:10:46generating. So, they're more dependent

1:10:48upon the voltage or the amplitude.

1:10:51So, when it comes to width, I look at

1:10:53that with respect to time. So, I want I

1:10:54need to have some kind of conversion

1:10:56factor, if you will, between 5 mm and

1:10:58some type of seconds or milliseconds.

1:11:01I like seconds.

1:11:03So, what actually it happens here is 5

1:11:05mm is actually equal to 0.20

1:11:10seconds.

1:11:11So, one large box means that 0.20

1:11:15seconds has gone by with some electrical

1:11:18activity that's occurred occurred right

1:11:19there on the EKG strip.

1:11:21Height-wise, that's 5 mm, right? So, 5

1:11:25mm tells us a little bit about the

1:11:28voltage, like I told you.

1:11:31So, voltage for this is generally going

1:11:34to be about 0.5

1:11:36mV. So, 0.5 mV

1:11:40is how much 5 mm is equal to. So, one

1:11:44large box in height tells us that there

1:11:46is a voltage of about 0.5 mV. Is that

1:11:50important? Not necessarily. We'll see

1:11:52later that sometimes you can have low

1:11:54QRS voltages in certain conditions, but

1:11:56the real important one that I really

1:11:58want you to remember, I think it's very

1:11:59important to remember, is the width,

1:12:02because that's going to become very

1:12:03significant when we start talking about

1:12:05is the PR interval too long? Is it too

1:12:06short? Is the QT interval too long? Is

1:12:09the um

1:12:11is another thing is the QRS waves uh

1:12:13wide? Are they narrow? So on and so

1:12:14forth.

1:12:16The next thing is if you look in these

1:12:17large boxes, there is so many small

1:12:20boxes.

1:12:22And you know how many there is? So,

1:12:23within one large box,

1:12:26there's actually equivalent to 25

1:12:29small boxes.

1:12:31Okay?

1:12:33So, there's kind of like five rows, five

1:12:35in each one. So, it's kind of like if

1:12:36you want to think about it, it's 5 mm

1:12:38squared uh for these actual the the

1:12:40small boxes, okay?

1:12:42So, when we talk about the small boxes,

1:12:44what I really want you to know is the

1:12:45same thing. I want you to know width,

1:12:48important,

1:12:50and I want you to know height.

1:12:53So, for the small boxes, the width is

1:12:57actually very interesting here. You

1:12:59think about it, 1 2 3 4 5. Five little

1:13:02boxes make up one large box. It's 5 mm

1:13:06in in width. What do you think the the

1:13:08width of a small box will be? 1 mm. So,

1:13:11it's 1 mm.

1:13:14Then, if you take five and divide it

1:13:16from So, you take 0.20 and you divide it

1:13:19by five, that'll give you your time that

1:13:21it takes for that one small box.

1:13:23And that's equal to about 0.04

1:13:27seconds. Also very important, okay?

1:13:30Now, height, same thing. It's equal to 1

1:13:33mm, which is equal to 0.01 mV, right?

1:13:36Cuz it's the same thing. It's just off

1:13:38by

1:13:39a factor of In this case, it's off by a

1:13:40factor of 10.

1:13:42Okay? So, what do I really want you to

1:13:45know about the height stuff? I'm not

1:13:47really concerned about you knowing the

1:13:48millivoltages.

1:13:50I'm more concerned about you knowing

1:13:52that one small box is 1 mm, one large

1:13:56box is 5 mm. The reason why is when we

1:13:59have to measure ST segments. Is the ST

1:14:03segment elevated? Well, sometimes it

1:14:05needs to be 1 mm elevation. So, you have

1:14:07to go in and see is the ST segment

1:14:09elevated more than one box?

1:14:11Or maybe it's super elevated and you see

1:14:14an ST segment that has elevation beyond

1:14:16one large box, 5 mm. So, the whole point

1:14:20is why do I really want you to know the

1:14:22height? Not super important for the

1:14:24voltages, more important for measuring

1:14:26those ST segments. Okay?

1:14:30That's the basic concept. If you really

1:14:31wanted to know a little bit more,

1:14:34so again, width is the big one. Height

1:14:35is going to be a little bit more. It's,

1:14:37you have particular for the small boxes,

1:14:39the 1 mm. Hopefully, you don't see ST

1:14:41segments that are beyond 5 mm

1:14:44in elevation, but again, you can. But

1:14:46again, I think we have a basic concept

1:14:48of that.

1:14:49The other thing I want you guys to know

1:14:50about this

1:14:51is whenever we look at this EKG, we see

1:14:54the various waves, right? We already

1:14:55kind of have a pretty strong idea about

1:14:58these. But, if we were to quickly recap,

1:15:01this is our P wave,

1:15:03Q,

1:15:05R,

1:15:06S,

1:15:07ST segment, and our T wave, right?

1:15:11Same thing, but now let's talk about

1:15:12maybe some extra stuff.

1:15:15This is our

1:15:17PR

1:15:18interval.

1:15:20This, from this point here

1:15:23to this point here, is our QT interval.

1:15:27And then, this part here

1:15:31is our ST segment, right? And we already

1:15:34kind of talked a little bit about that

1:15:35ST segment there. But, what I really

1:15:36want you to know

1:15:38is that these are going to become very

1:15:40important in certain types of

1:15:42pathologies. Okay? So, I want you to

1:15:44have a basic idea of some of these. So,

1:15:47the first one that I want you to

1:15:48remember is your PR interval.

1:15:51So, your PR interval, we already kind of

1:15:52talked a little bit about that. It's

1:15:54from the beginning of the P wave all the

1:15:55way until we get to the beginning of the

1:15:56QRS complex, right?

1:15:58A PR interval should normally

1:16:02be

1:16:03from It should be less than 0.20

1:16:07seconds. So, it should be less than one

1:16:11large box.

1:16:12That's kind of the goal. If it's less

1:16:14than 0.20 seconds, it's considered to be

1:16:16a normal PR interval. If it's greater

1:16:18than that, it's prolonged. It's going to

1:16:20become important in different types of

1:16:21blocks.

1:16:23Okay, so this is considered to be

1:16:25normal.

1:16:28The next one that I want you to remember

1:16:29is your QRS complex. So, your QRS.

1:16:34The width of that,

1:16:36usually, you want that to be less than

1:16:400.12

1:16:42seconds.

1:16:44Okay? Which if you count that up, one

1:16:46little box is .04 seconds.

1:16:49So if I do .04 * 3, that's .12 seconds.

1:16:53So I want it to be less than three

1:16:55little boxes. If it's greater than that,

1:16:57it's considered to be a wide QRS, a

1:17:01pathologically wide QRS. Now some

1:17:03textbooks will even go and be a little

1:17:04bit like and stingy and they'll even say

1:17:06technically like greater than .10

1:17:09seconds is considered to be a a little

1:17:12bit wide of a QRS, but it's easier to

1:17:14remember and for the sake of it, if

1:17:16you're starting to like question it, is

1:17:17it wide, is it narrow? You're taking too

1:17:19much time. If it's greater than .12

1:17:21seconds, three little boxes, it's wide.

1:17:24If it's less than that, it's narrow.

1:17:26Don't make it too complicated, right?

1:17:28So this is going to be normal or

1:17:30sometimes what we call, you'll see us

1:17:32we'll refer to it a lot, kind of they're

1:17:33synonymous in a way, they're kind of

1:17:35referred to as narrow.

1:17:37Which is normal. All right, the last one

1:17:39here is the QT interval that I want you

1:17:41to know. So the QT interval is important

1:17:44because whenever that sucker is

1:17:45prolonged, it increases the risk of a

1:17:48particular type of arrhythmia called

1:17:49torsades de pointes, which is a type of

1:17:50polymorphic V-tach. And so this number,

1:17:54it literally it can vary from textbook

1:17:55to textbook, it can vary from gender to

1:17:57gender, so male, females, there can be a

1:17:59lot of different ones. The

1:18:01consensus that's kind of been I've seen

1:18:03here within the textbooks that I

1:18:04utilized was that if you're a a male or

1:18:08female

1:18:09and if it's a male less than 430

1:18:12milliseconds. Now this is utilizing

1:18:14rates particularly at like 60. It

1:18:17depends if you're going a little bit

1:18:19faster, you have to adjust and we'll

1:18:20talk about those things later, you have

1:18:21to use like corrected QTC formulas and

1:18:23we'll get into all that stuff. But for

1:18:25the most part, less than 430

1:18:27milliseconds is considered to be normal

1:18:29in males.

1:18:31And then less than 460 milliseconds in

1:18:34females is considered to be normal. Now

1:18:36again, I don't want you to get too

1:18:38bogged down into that detail.

1:18:41I usually don't consider something to be

1:18:43super dangerously like prolonged QT

1:18:46until I start approaching 500. But

1:18:48again, to really kind of be thorough,

1:18:50these are the numbers that are generally

1:18:52thrown around, but we'll talk about this

1:18:53a lot more when we get into the

1:18:55arrhythmias, okay?