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.

Comments 215

  1. Nikhil N T

    Sir,
    The information in the video,although very useful seemed to be insufficient..SO, I would request you to make another video regarding abnormailities in each of the EKG waves..I would be thankful If you would give information about the same
    Yours truly
    Nikhil N T

  2. Nikhil N T

    Sir,
    The information in this video was very useful. But, I wanted a bit more details ..If you would provide information about the abnormalities in each of these waves,it would be very helpful.
    Yours truly
    Nikhil N T

    1. Post
      Author
      Lrsamuel

      There’s always more information that can be added. However, there’s only so much that 1 person can cover. I try to give as much detail as I have. You can always do your own studies by reading textbooks that go into the level of detail you are trying to get.

      1. lisa

        where is more information on reading EKG’S AND INVERTED P WAVES AND inverted T waves.. Also some additional info to focus on mi detections and the contrast to people with pacemakers abd defibs ekg readings ..

        so far I am enjoying your videos ..

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          Author
  3. rotorway133

    hey thanks for the video. I just had a ECG for the Canadian Army and the results says : ALMOST NORMAL. After viewing your video i came to the conclusion that….nah..all seems to check out OK…..with my untrained eyes :) Awaiting the final results

  4. asdf15

    Awesome video, it’s explained really well but I just wondering when the atria repolarise, does it have a peak or is it too insignificant to see?

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      Author
  5. InteractiveBiology

    @missgomes18 All questions are answered in the Interactive Biology community forums from now on. Go to the website in the description and then visit the community. This is to make it as efficient as possible as we have multiple people over there to help answer questions.

    All the best

  6. genius4themostpart

    why is the T wave “positive”? I understand, and it makes sense that the depolarization in the atriums and the ventricles have that effect on the EKG but not why the T wave is positive.
    Thank you for great videos, I just found your channel and i love it!

  7. genius4themostpart

    why is the T wave “positive”? I understand, and it makes sense that the depolarization in the atriums and the ventricles have that effect on the EKG but not why the T wave is positive.
    Thank you for great videos, I just found your channel and i love it!

  8. ojay12341234

    @DiyaBabyee Interactive biology made videos about depolarization and repolarization, check them out.. ther’re pretty good
    There is also a video about action potential it will help as well

  9. ojay12341234

    Interactive biology made videos about depolarization and repolarization, check them out.. ther’re pretty good
    There is also a video about action potential it will help as well

  10. evilmask972

    Great video! You just didn’t explain that the QRS complex mask the repolarisation of the atrium (we can see on the edge of the QRS complex that the curve goes down a little) Thanks a lot for your videos anyway! It helped me a lot! :)

  11. evilmask972

    Great video! You just didn’t explain that the QRS complex mask the repolarisation of the atrium (we can see on the edge of the QRS complex that the curve goes down a little) Thanks a lot for your videos anyway! It helped me a lot! :)

  12. OJASVIVYAS

    thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you

  13. OJASVIVYAS

    thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you

  14. OJASVIVYAS

    thank you so much…sir your video was a grt help..i m student of first year medicine..this was indeed superub..plzz continue the good work..looking forward to see more videos frm you

  15. dpsicose

    Can anyone explain why P,R,T have a positive deflection, and Q,S have a negative deflection? I don’t understand why this is.

  16. PrettyHair09

    Is there a video that show when SA node and AV node fire, when atria relax, when the ventricle relax, when valves open and close, and the points where ventricle pressure and volume is high or low? I really need help with that.

  17. PrettyHair09

    Is there a video that show when SA node and AV node fire, when atria relax, when the ventricle relax, when valves open and close, and the points where ventricle pressure and volume is high or low? I really need help with that.

  18. sherab

    Hi my greatest teacher Leslie Samuel!
    Actually i’m a Tibetan monk who are studying human physiology at Emory university. and this is my second year, i just learned english for one year before i came to here. so my english is so bad and always get language problem in my classes. recently i found your TVs and articles which very clear and more easy to understand to me. then i got really happy. now i watch your videos and read your articles which relevant my classes before i go to the classes. it help me to understand what’s going no in the classes. thank you very much.
    sherab.

  19. DocAvicenna81

    Thank You. This explanation is fantastic. Do you mind if I use this video to show patients in my Cardiology clinic? I would greatly appreciate it. Please advise. Thank You in advance.

  20. DocAvicenna81

    Thank You. This explanation is fantastic. Do you mind if I use this video to show patients in my Cardiology clinic? I would greatly appreciate it. Please advise. Thank You in advance.

  21. InteractiveBiology

    Yes, you can do so. Thank you for using our videos. We hope your patients will find them useful and easy to understand.

  22. Maria

    Lessley you have succeeded in making this site the best available biology resource in the whole world wide web and I mean it. I am preparing for an Axam in the next 2 hrs and you have no idea how much your lectures are helping me right now. Thank you for being a greater person having others in mind and not just your self.

    May God bless you for this

    1. Post
      Author
  23. albelaaaa44

    @ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx

  24. albelaaaa44

    @ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx

  25. albelaaaa44

    @ocbtalf you are correct. I was looking everywhere for the best way to put on huge muscles mass. Listen to this If you want something that builds huge muscle which showed me exactly what i was doing wrong. The video is public now. Have a look > bit.ly/Ks5n0K?=nbqtyx

  26. hisprincess1513

    I’m currently studying Cardio MedSurg in my nursing course and i was wondering could you make a video showing what the heart looks like when its in the different kinds of dysrhythmias? Its something i would be able to understand better if i can see how the heart beats during each kind. If you cant do you know where i can find a video like this?

  27. hisprincess1513

    I’m currently studying Cardio MedSurg in my nursing course and i was wondering could you make a video showing what the heart looks like when its in the different kinds of dysrhythmias? Its something i would be able to understand better if i can see how the heart beats during each kind. If you cant do you know where i can find a video like this?

  28. Mike

    What software and hardware do you use to make these videos? I’m about to go into medical school and I think it would be great if I could make videos as I go through school as a resource for people that follow behind me.

    If you could help me to learn the software – and I am able to make the videos without legal restrictions (or time restrictions), I would allow you to host a copy of the videos.

    Thanks!

    1. Post
      Author
  29. Mike

    Everyone is wondering – I just found the answer:
    “You might be surprised that ventricular depolarization (the QRS wave) and repolarization (the T wave) point in the same direction, although they are produced by opposite potential changes. This is because depolarization of the ventricles occurs from endocardium to epicardium, whereas repolarization spreads in the opposite directoin, from epicardium to endocardium.”

    Source: Human Physiology, By Stuart Ira Fox, Twelfth edition (copyright 2011) page 424

  30. TheSoniablue

    Thank you sire! I am gonna download this….;)…i did have problem in ecg interpretation a bit now cleared….but still wanna keep this video as a rememberance….and revision point for exams…thanks once again…

  31. havingfun122

    awesome! wish Doctors here were like you. :) most of them here get offended if I even ask them what they understood and what they think they will do to combat the problem. :)

  32. havingfun122

    thanks interactivebiology!.. the place where I live.. Doctors (most of them – actually every doctor I have met) do get offended if I even ask them what they are doing to combat a problem based on these readings..

  33. Squism Chaser

    Outstanding. I sat through a two hour lecture and I was more confused than when I came in. This is straight to the point and very clear. Thanks.

  34. alexeo111

    It can be recognised not by using conventional ECGs but during some specialised electro physiology tests when both the atrial and ventricular waves are separated

  35. SCSUguy85

    Love this thanks for posting the video. I’m going into emergency medicine and this helps me understand EKG PQRST waves a lot better then what I learned in class!

  36. lponced2002

    I’m currently in pharmacy school and every one of your heart videos has helped me more than the lectures of my professors. thanks!

  37. rodrigonewton

    Hey Leslie, amazing video ! I’m not a Biology enthusiast (by the way, I’m an engineer), but you got my attention during all the explanation… You were born to teach and help others to understand things !! Keep it up man !! Congrats !

  38. A.S.Fathima Rizwana Salam

    so thanks of you…. am not a doctor but an engineer … for my project sake i just cme across this ….. very crisp and clear

  39. Azmat Yousafani

    Your videos are quite helpful. Can you please explain the terms depolarization and repolarization in simple words?

  40. caramelje22

    I enjoyed #048 how to read ECG. But could you do another video in more detail. I like how you teach and I would like to become better at reading the ECG. Maybe like a video for 10mins or so all about ECG/EKG..thank you again for all your videos!!

  41. Jorge Viana

    SI SOS MEDICO O ESTUDIANTE DE LA SALUD!! NO TE PODES PERDER EN MI CANAL
    DALE ME GUSTA Y SUSCRIBITE PARA RECIBIR LOS VIDEOS Y MEJORE EL CANAL! NO TE PIERDAS LOS ULTIMOS VIDEOS DE EJE HEXAXIAL EN ECG

  42. Ted P

    I have hard time learning to figure out the heart rate by the rule of 300 of ECG , is there anyway you upload video show me the easy way to learn.

  43. 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!

  44. 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) .

  45. 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.

  46. 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!

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  49. 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

  50. 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)

  51. naldus1

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

  52. 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?

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