episode48

048 How to Read an Electrocardiogram (ECG/EKG)

Leslie Samuel IBTV, Physiology, The Circulatory System 215 Comments

Have you seen an ECG reading? What do those lines mean? How does it measure heart activity? Watch and learn as Leslie once again teaches us about this topic. Enjoy!

Transcript of Today’s Episode

Hello and welcome to another episode of Interactive-Biology TV where we’re making Biology fun. My name is Leslie Samuel and in this episode, Episode 48, I’m going to show you how to read an electrocardiogram. For short, it’s called ECG or EKG.

So, let’s get right into it.

First, I want to answer the question, what is an electrocardiogram? An electrocardiogram is a test that records the electrical activity of the heart. We looked at how the  SA node starts the signal and we looked at how that signal spreads to the rest of the heart. You can always go back to Episode 46 for more details on how that works.

The ECG is used to test for irregularities in how the heart functions. You’ve probably either seen this first hand in a hospital or on TV. You can look at the electrocardiogram and it will tell you if the heart is working the way it should. The way this is conducted is by placing skin electrodes on different parts of the body.

These electrodes are able to detect the electrical activity of the heart. When you look at the electrocardiogram, it looks kind of like this {Leslie shows an animation of an electrocardiogram} and you’ve probably seen this.

Normally when you see this, there’s a beep associated with it. There’s no beep in this animation but, you get the point. What we’re going to do is we’re going to look at this and we’re going to look at each component of the electrocardiogram. Let’s look at it right now.

We’re looking at an electrocardiogram and you can see that we have a number of things. We have this peak over here. We’re going to call this the P wave, this peak right here. And then, we have this section that we’re going to call the QRS complex. Then, we have the T wave and sometimes we get this U wave. We’re going to talk about what these different waves show. The P wave. We’ve looked at how the SA node generates the signal and then that signal spreads to the muscle cells in the atria.

What this P wave shows us is the depolarization of the atria. Okay, so, when the atria depolarizes, we see this peak. We have the QRS complex, you probably guessed it by now but, this shows the depolarization of the ventricles. That is what is represented by the QRS complex. Then, we have the T-wave which comes after the QRS complex and this shows the repolarization of the ventricles.

Now, you’re probably wondering why the signals that come from the ventricles are significantly larger than this little signal that comes from the atria. But, if you look at the heart, you’ll see that the atria is significantly smaller than the ventricles. So, when the cells in the ventricles depolarize, that’s going to have a much greater effect on the EKG or the ECG because you have more cells depolarizing so you can get a stronger signal.

And then of course, you get the repolarization. The U wave is one that you don’t always see. It’s sometimes hard to see and in most cases, you don’t really see it. But, in some cases, you do see it. In some cases it can tell you something about when things are going wrong with the heart. We’re not going to go into all those details but, I included it here because it was shown in this pictures that I found and because it does show up sometimes.

Some people think it’s the repolarization of the Purkinje fibers. And it’s also thought to be the repolarization of some other specialized muscle cells. But, we’re not going to go into that. The main things are the P wave, the QRS complex and the T wave. The P wave being the depolarization of the atria; the QRS complex being the depolarization of the ventricles and; the T wave being the repolarization of the ventricles.

If you ever need a refresher on what the terms depolarization and repolarization mean, you can always go back and to Episodes 9 and 10 and that will give you more details. Well, that’s all for this video.

As usual, I’d like to invite you to check out the website at Interactive-Biology.com for more Biology videos and other resources to help make Biology fun. This is Leslie Samuel. That’s it for this video and I’ll see you on the next one.

228 comments
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Ove
Ove

This might come as a stupid question but why doesnt the atria repolarize? Is this somhow masked by the QRS complex? Like if its inside/behind the QRS complex. Is this wrong? Or is there some other explanation?

nouss mo
nouss mo

can you tell me what is the difference between a QS wave and a necrosis Q wave

Blundo blunden
Blundo blunden

its safe to say your bloody fantastic!! i reckon ive passed all my previous subject because of you!

naldus1
naldus1

the vector is going in the opposite direction than of depolarisation. thats why it is upward. Source : Guyton.

innocentloyal
innocentloyal

Could you do a video on what an ekg look like when the leads are placed on backward.

Womb2Tomb1
Womb2Tomb1

excuse me how come the t wave is repolarizing if the hump is going up isnt that depolarization?

Raymond Palmer
Raymond Palmer

That the direction of electrical depolarization is retrograde to what it normal is. When seen in lead 2, it implies the vector is moving away from Lead 2 (when you think of Einthoven's triangle)

JUDY HERNANDEZ
JUDY HERNANDEZ

I was told that the U wave is due to electrolyte imbalance

essamhaitham
essamhaitham

the u wave is due to contraction of the papillary muscle .. small,positive, and rare wave and the atria Re-polarization is masked by the stronger QRS complex ( ventricles depolarization ) because they happen at the same time ;) ..hoped i helped

raziagloop95
raziagloop95

Omg you just made it seem so simple than what my biology book was blabbering on about.

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pinknurse101
pinknurse101

You make understanding EKG really easy! This is what exactly I've been searching for! Thanks a lot!!!

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Rhonda Junaid
Rhonda Junaid

another great video! I learn more from this than actual lecture in class...(=^D

Politicsgetmenkilled
Politicsgetmenkilled

Thank God a man that speaks english and knows more than my college teacher. Daymar College EKG class is awful because of the teacher. I've learned more on these videos than the teachings at the school. Thank you!

Kanhaiya Bheergoonath
Kanhaiya Bheergoonath

Remember AVDA A- Atrial systole (depolarisation of atria/contraction of atria/P) V-Ventricular Systole (depolarisation of the ventricles/contraction of the ventricles/P) D-Diastole (repolarisation of the ventricles/relaxation of both atria and venticles/QRS complex) A-- Atrial systole (depolarisation of atria/contraction of atria/P)-ommiting U Correct me if I'm wrong or thumbs me up for others to see.

priyalji
priyalji

during the QRS complex. which is why you don't see a wave for it. (If I'm not wrong,what I got from lecture) .

Brenda Jedra
Brenda Jedra

I love these videos! Thank you so much for taking your time to teach. They are so helpful and explain things that the instructors are not in class!

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Kareem Latif

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Ladyknight C
Ladyknight C

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mooreal5
mooreal5

During the depolarization of the ventricles. Due to the large signal the ventricles send out, you just can't see it :)

simone84gabriel
simone84gabriel

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VR6BLAIZE
VR6BLAIZE

brilliant thank you so, clean and simple to understand