Intro to EKG Interpretation - EKG Leads

[@StrongMed]

Erratum: @7:27, I misspoke. I should have said "the voltage as measured by lead I plus the voltage as measured by lead *III* must equal the voltage as measured by lead *II*".

[@SanjaySharma-hu6xl]

Thank you for clearing the confusion, sir.......

[@قمرهاشم-ف8ض]

Thank you for clearing 🥰

[@lemueljohnurbano3705]

I immediately looked in the comments for the correction. Thanks!

[@poppysmick]

This is a good way to check if the audience is paying close attention. Thank you for the amazing content that you have provided on your channel. Indispensable.

[@Steeldust]

@@lemueljohnurbano3705 Me top 😊

[@andyallybic]

You have in 20 mins clarified years of misconceptions that I have had about these leads. Thanks very much.

[@florianfaehling6458]

Dear Dr. strong, I found your EKG course extremely helpeful as it made me actually understand the principles behind the processes instead of just memorizing them. You really helped me a lot and I mean this literally: I just wrote my final exam in med school and there was one EKG leads localization question. While reading it, I actually heard your comment from this video in my head :-) thanks for that point on the exam! Please keep up your insigthful and valuable work!

[@StrongMed]

You're very welcome! More EKG lectures on the way soon!

[@astutely]

My jaw dropped from around the 12th to 13th minute. You’re a living legend, Professor. This was so clear!!!

[@xDomglmao]

I had a hard time learning the ECG (and I am still not done yet) so I thought the following might help some people: 7:36 - instead of trying to understand the formula you can rather prove that it is correct and boost your confidence: 1. Take the qrs complex from lead I and substract the obtained values, e.g. let's say the q wave is -0,5, the r wave is +3 and the s wave is -1,5--> -0,5 + 3 + (-1,5) = +1 2. Take the qrs complex from lead II and substract the obtained values, e.g. let's say the q wave is -0,5, the r wave is +8 and the s wave is -4 --> -0,5 + 8 + (-4) = +3,5 3. Take the qrs complex from lead III and substract the obtained values, e.g. let's say the q wave is 0 the r wave is +4,5 and the s wave is -2,5 --> 0 + 4,5 + (-2,5) = 2,5 Now use the formula I + III = II [or the formula I + (-II) + III= 0 (in my opinion more smexy)] and you can see Einthoven was cool: 1 + 2,5= 3,5 [or: 1 + (-3,5) + 2,5 = 0 ] If you're wondering: You gotta use -II because Einthoven, instead of going clockwise, switched the positions of the electrodes of lead II. www.ems12lead.com/2008/10/04/axis-determination-part-i/ good site btw and got my info there! And the "v" in "avR" etc. stands for "vector", not "voltage" Ah and thanks for the video! Helps a lot! 14:48 - the formulas seem to be difficult but they aren't, see the formulas in the link below rather then in the video and you'll understand soon: ecgwaves.com/wp-content/uploads/2016/08/goldblaw.png To understand them just check your hexaxial system, preferably one with with correct poles, e.g. upload.wikimedia.org/wikipedia/commons/5/56/Hexaxial_reference_system.svg (arrow down means negatve pole, arrow up means positive pole). Then check again the formulas I linked and you'll understand :-) 12:25: The q wave in lead II should be a bit negative, right? It was drawn here to be isoelectric because the septal dep. is nearly perpendicular to lead II, correct? Wouldn't then the major ventricular depol. shown in lead III also be isoelectric rather than showing negative (because again it is nearly perpendicular to lead III)?

[@markyounger1240]

This is great! Thanks for saying a lead and an electrode are not the same thing. Whole lecture is great!

[@adrianbulfon8430]

Im a third year med student and I have to say your channel is by far the best on KZbin for medical education!

[@StrongMed]

Thanks!

[@danielledockrey1264]

I truly appreciate your ability to explain EKG's so well and in a manner slow enough to really take in the concepts. Thank you!!

[@eclaires358]

I wanna cry, you’re amazing

[@emrankhan6578]

Ahh women 😀

[@abdulaimukaje5503]

This is just great! Thanks for your work!. I will recommend your channel to all med students in Sierra Leone

[@angelazhang6980]

I am always confused about reading EKG. This is very very helpful. Thanks a million!

[@lillpingguo]

Your lecture series is SO helpful! So thankful that I found this. Thanks for creating these videos.

[@pnewdt2213]

Thank you sir , it was a pleasure , we being students cant buy all the coursed , it was so generous of you for making it free

[@StrongMed]

Strong Medicine: Anytime Anywhere Always free

[@pnewdt2213]

@@StrongMed thanks teacher

[@Mindova]

As an accelerated program nursing student, thank you!!

[@mateusfernandes7347]

Honestly, I would hug you if I could! Thank you for this classes!

[@ronaldmcdonald9538]

Hey Mr. Strong. Thank you for your videos, Im in my first year as an intern in internal med and find them very useful to refresh my ECG knowledge every now and then. The rhythmologist (a cardiologist) at our hospital said Lead I and II are best for atrial activity, 2nd choice at best would be V1. Best, Dr. R.

[@xoliswasokhela3627]

You're so gentle and informative 💖💕💖

[@Boricuaamada]

This is probably way more info than I need for my ccma certification, but it’s soooo interesting. Very informative. Now, I gotta go back to my notes and fix that ☺️

[@deir525]

Thank you great lecture...will surely watch more of your videos these will definitele help me in my step 2ck exam

[@DuePancho]

Your videos are the most complete, competent and easy to learn. i finally got to fully understand this topic in particular thanks to you. this is definitely the best medicine related channel in youtube. i hope you keep updating it and teaching us :)

[@niskarsharijal7414]

Thankyou soo much for such a clear presentation. Cryatal clear on the orientation of leads

[@sunving]

Thank you Dr Strong. You are a good teacher. No doubt that Stanford would make excellent doctor ,just example that you are one of clinical teacher,instructor. This is my second or third watch of this video. I am glad that I ran into your lecture series. I have no examination to face, that I might help me learn better :) .

[@walziman8181]

Thanks for this wonderful lecture, clear and easy to follow.

[@MedicalNemesis]

Wonderful, no one has explained this so well to me before. You were a terrific help, thank you!

[@arodusaf]

the spatial relationships between leads explanation was great, ty

[@Neisan9]

These videos are extremely helpful and easy to understand. Thank you so much

[@jamshidbaheer]

thank you very much for the kind work Sir. I hope the ecg lectures also continue even more

[@jonemorice9731]

Thank you. i really enjoy watching your lectures.i hope you cover different branches in future by the way after i have watch ABG lectures.all of my colleague and consultant like the way i analyze the ABG. Great thanks

[@briannawatson3521]

BEST video I HAVE CAME ACROSS!!!!

[@1Matthew421]

Thank God for you

[@tonibarber8595]

I have a test Wednesday so thank you for posting the EKG and lead videos. I wasn't grasping my instructor's lectures and you are a lifesaver.

[@RomkeRozema]

Eric, you're the best! I absolutely appreciate your time and effort for these video's. Thanks

[@jonahansen]

The reason that Einthoven's triangle represents voltages in the chest even though the electrodes are on the arms and legs is because the voltage on, for instance, the right arm is the same at every point until it reaches the torso. Essentially the arm can be thought of as a wire connected to the torso, and carries the voltage at the point where it attaches to the torso; same with the legs. Voltages only change when currents are flowing, and current only flows when there is a closed path, taking the path of least resistance. No current generated by the heart flows down an arm and then back up, as that would have more resistance than just returning from where the arm meets the torso. Hence, the legs and arms each are at the same voltage as the point where they connect to the torso in which currents from the heart are flowing. Hope that helps; it's a little difficult to put into words, but if one draws a body and models it as a network of resistors, it becomes apparent that no heart-driven current would go down and then back up an arm or leg, it would just return from the point where the arm or leg connects to the body as that is a lower resistance and shorter path. The whole shebang depends on the fact that the body is a conducting but resistive media, and air is insulating, so all current is confined to the body.

[@zasa9618]

you couldn’t explain it any better! thank you sir!

[@tinyanl]

Your videos are super helpful! Please keep making educational videos for medical students. Thank you for your great work :)

[@ahmedsameer8592]

Thank you, sir. As usual your videos are very informative and easy to follow

[@syedabulhasaan2353]

Thanku & God bless u for this selfless effort sir ❤

[@StrongMed]

Almas, I'm glad you enjoyed it. Thanks so much for the catching my misspeak! (I've added an annotation to correct it)

[@chamnanlay6182]

Thank you so much for your best video.

[@jamshidbaheer]

always pleasure to watch your videos sir. Waiting impatiently for the last lecture on antibiotics

[@amermh144]

I think the reason these 3 are used in the rhythmal strip is due to V1 being most sensitive to the right side of the heart while V5 to the left isde of the heart ( v5 is chosen over v6 because the latter's magnitude value is affected by the pleural tissue) and ofcourse limb lead2 due to it being the most parallel with normal heart activity.

[@JohnCarrFitness]

Can you please teach all my classes!!! You are the best!

[@JosipAngeloBorovac]

Phenomenal stuff and great approach! Thank you very much, sir!

[@friendlyovertones]

Great Lecture. The vector addition worked best for me with Einthoven's Law. In degrees it doesn't work out. I was taught how to place ECG leads by a very picky Emergency Room Resident. Most of the time my recordings were good but occasionally the problematic ones were people fidgeting about and women with huge pendulous breasts- until an RN told me to tape the breast out of the way so I could palpate the ribs. I'm a physics geek so I figured out a lot about the electrical stuff on my own so if the ECG didn't look right I would repeat it to double check. That resident became an OBG guy!!!!!

[@BizarreSuzanne]

Fascinating from an OLDER non-med person (a retired engineer) with a right bundle branch block to learn about placement of leads and what they should show...would love to see an EKG strip of my own...not as a criticism, but for knowledge...would be interested in How the leads are differentiated...

[@oldcardigan1734]

Hi, thanks for your great content, just a question, where does the formula for calculating augmented limb leads come from? I mean from the lead I and II.

[@ahmedsuhaib6252]

Respected Sir, you have provided a crystal clear explanation to all these scary lead vectors.Thanks I want to know when we measure potential difference as measured by lead I do we assume right wrist/hand and left hand have different potentials. I am stuck with the point that both the right wrist and left wrist are at same distance from the heart ,then the potential drop should be same in both the cases as we go down towards the wrists !

[@venkatadoddapaneni2962]

lecture is awesome

[@victorsun5622]

Dear Dr Eric: thanks for your amazing videos, but I have a question, I can see only 5 out of 15 advanced EKG videos here only, where are the other 10 videos?

[@StrongMed]

Hoping to finish off the antibiotics lectures next week...

[@JohnnyJitsu11]

Thank you, simply thank you!

[@tchalgren1]

The reason why lead V5 is on the 12-lead printout is because that lead is good for monitoring ventricular ischemia. During the case, CRNA's keep their monitors usually on II and V5 to best pick up arrhythmias and ischemia. Amazing lectures! I sent an email to your standford.edu email with my notes of your other lectures. Hopefully, that is your current address.

[@maisinhaa]

it helped me a lot :) very nice channel, thank you!

[@adrianaramirezgarcia4407]

Thank you so much, this is gold

[@romeolhk1008]

Damn this is fucking outstanding, even better than DD's book

[@alihaarshad1245]

AWESOME VIDEO AND YES I SUBSCRIBED

[@makku2101990]

Thank you for the excellent video...

[@amielv.3381]

Thank you so much for the explanations! I wish I had encountered this earlier while studying first year physiology :)

[@edeason1384]

incredibly helpful thanks so much

[@lemueljohnurbano3705]

Hello Dr. Strong, when you talk about modern EKGs measuring only leads I and II, does that mean that they only have to attach 2 electrodes in the chest? And how does the accuracy of modern EKGs fare with the 12-lead EKG? I saw a device that you only need to hold and put into your left limb. It's called KardiaMobile and it comes with an app.

[@D___A]

Professor, the Wilson’s central terminal I believe is composed by two limb leads as a negative and one as a positive for example for aVR RA will be positive and the average of LA and LL will be the negative, not as stated in the video at 8:25 that it is composed by the potentials of the 3 limbs.

[@D___A]

For the precordial leads the statement in the video is valid of course as the positive will be V1 V2 etc and the negative will the the average of the three limbs.

[@maheshmacharla]

The interventricular septum is actually depolarised from left to right ,and also in upward direction ,(maintaining left to right) but not in inferior direction(maintaining left to right) as told by you. please clarify.The arrow should be slightly upward, & from left to right.

[@StrongMed]

Thanks for the comment. According to a figure in Braunwald's Heart Disease (the only one of 6 cardiology texts I looked through which addressed this), the very initial 20-30 ms of ventricular depolarization originates from the middle of the left side of the septum, and is oriented down and to the right, as shown in the video (Braunwald 10th ed, Fig 12-10; unfortunately the figure does not appear to be publicly available.) The remaining part of septal depolarization does depolarize up, back, and to the right, but this is occurring simultaneously as depolarization of the ventricles, and not as an chronologically separated event. Another way I look at this, if the initial direction of septal depolarization was up and to the right, we would expect to see septal q waves in lead II, instead of lead aVL. Please let me know of any references that might contradict this.

[@zhigangtian5815]

That is really helpful, thank you very much

[@Faghazn]

Please put numbers for your videos , it is good to know the sequences of videos .

[@StrongMed]

I sincerely appreciate the suggestion, but with the exception of the first 3 videos in the series (waveforms, leads, rate/axis), they can be viewed in almost any order.

[@Will-yz7oi]

Thanks for the clear, concise intro. I read Dale Dubin's basic book, but am now interested in a textbook that students don't like because it is vast, too informative, and contains extra technical and clinical info. Which one is that? I have considered Mariott's. Any recommendations? Appreciate it -

[@StrongMed]

One of my motivations for this series was the fact that such a book doesn't exist, at least not a great one. Marriot is fine, but not awesome. Wang's Atlas of Electrocardiography is a decent reference for a budding cardiologist, but as the title suggests, it teaches only through examples without ever giving broad summaries of a topic. Also, there is a huge leap between Dubin and Wang that might make Wang feel inaccessible. I think the closest a book has come to being an intermediate to advanced ECG textbook was Phibbs' Advanced ECG: Boards and Beyond, but it's pretty dated at this point. It also gets into the weeds with things that may be academically interesting but of near zero clinical relevance. Phibbs' reminds me of Jules Constant's Bedside Cardiology and Sapira's Art and Science of Bedside Diagnosis - fascinating books from an earlier era that today are better as a bedtime read than as something that will teach you modern medicine.

[@Will-yz7oi]

@@StrongMed Thanks for the reply! Maybe I'll just get Marriots (it has a workbook) and then keep my eye out. AI will soon be changing diagnostics, but it's not really reliable - at least yet.

[@CalvinZDR]

this was great!!! Thank you so much!!!

[@zakiyare885]

Thank you so much Proffesor, we would like to get the ppt if it is Possible

[@AmandaHamze]

Hello Dr. Strong, I know you made this video 10 years ago so I hope you see this. My question is when looking at lead III, specifically at the second deflection, why is it not negligible almost? isnt the second vector almost 90 degrees to lead III? I hope my question makes sense

[@samcollins9524]

that was a perfect lecture!

[@gmieomvan6833]

Hello Dr. Strong, I had a question about the PR Segment. Why is this segment at the same level as the TP segment? During the PR segment, there is a great difference in potential between different poles of the heart since the Atria are fully depolarized but the ventricles are still polarized? Is the EKG actually measuring current? This might make more sense because the AV node allows so little current through it.

[@aprilsoto4564]

SUPER DUPER HELPFUL!!! THANK YOU!

[@asheriko26]

Hi. Great course but you are missing one important part to be lecture 2 or 3: how to approach the ecg paper - what are the X and Y axis ? what does the small and big squares mean time wise and voltage wise ? what is a positive and negative waves, how to sum them up and how they relate to vector deflections? and so on...

[@StrongMed]

+asheriko26 Thanks for the feedback. The X and Y axes are discussed in the video on Rate and Axis. And vector addition is touched upon qualitatively in scattered places throughout the course. I agree there isn't a dedicated section to that, and when it is discussed, it's done so very informally. However, when I've taught EKGs in person, I find that a lot of learners (basically everyone who was not an engineering major) tune out when you start discussing vectors too much, just like they tune out when discussing relevant cellular physiology (e.g. why most T waves are upright, etc...), and the circuitry underlying the machine. They're all interesting topics for some learners though, and if I ever get around to finishing the core topics (e.g. differentiating SVTs, electrolytes disorders, effects of antiarrhythmics, etc...), I hope to have time to cover those as well, maybe as "accessory videos" or some similar designation.

[@mariaangeladeserio4616]

this was so useful. Thank you.

[@suethammavong181]

This is so helpful! Thanks!

[@ploop3350]

@13:52, for interseptum voltage, I plus III should be positive, why II is negative instead?

[@rollnumber-10ashwinikumar33]

Best of the best

[@Dr.BNO47]

Teşekkürler, gayet faydalı olmuş.

[@Photoguy15]

How is the depolarization of intraventricular septum angled down and to the right? I thought the direction of the intraventricular septum was down and to the left???? Please some one help?

[@aldocosta7567]

Excellent! very helpful. Just one question: Why at 10:34 the event angle is down and directed to right. What does define the direction and angle of the vectors showed in yellow?. Is the only thing I couldn´t understand. Thanks!

[@StrongMed]

The 2 vectors shown in yellow represent 2 sequential phases of ventricular depolarization. The first phase is depolarization of the septum, which occurs from the left bundle, and therefore the net depolarization of the septum during this phase is in a left to right and slightly inferior direction (since this direction is perpendicular to the "plane" of the interventricular septum). The second phase is depolarization of the bulk of the right and left ventricles, which occurs simultaneously; since the left ventricle is more massive than the right, the net depolarization vector is directed more to the left. In reality, ventrcular depolarization does not exist as 2 discrete and seperate phases as the diagram suggests, but such simplifications explain the sharply biphasic/triphasic nature of the QRS complex. You may find a discussion of this issue in my video on chamber enlargement (around 13:18) helpful, as it goes through the same sequence of depolarization, but from the view of an axial cross-section/axial plane.

[@aldocosta7567]

Thanks doctor!

[@ilovecanines]

Very good video!

[@kaze123ckr]

Hello Dr. Strong! For the six limb leads, there's 4 electrode placed on the extremities. I'm wondering whether this statement is true? "Limb leads can be placed on any part of the patient's respective limbs. Just make sure the leads are symmetrical. " Some put the electrode just proximal to the wrist, while others put it anterior to the shoulder. I've seen both kinds in the hospital. Wondering it should alter the voltage or lead axis , and therefore affect the analysis?

[@StrongMed]

For a long time, I didn't think it mattered much where on the limb the electrodes were placed (i.e. anywhere from the shoulder to the wrist on the arm, thigh to ankle on the legs - some people even place the leg electrodes on the lower torso just above the inguinal region). However, it actually does matter. Placing the electrodes too proximal can lead to clinically relevant errors including a rightward shift of the QRS axis, decreased sensitivity for picking up inferior ischemia/old MIs, and misidentifying the location of VT/PVCs. Proper location is arm electrodes on the wrists, and leg electrodes on the shins. A few relevant references: pubmed.ncbi.nlm.nih.gov/18790505/ academic.oup.com/europace/article/17/12/1840/2398514 pubmed.ncbi.nlm.nih.gov/3653124/

[@TheWeirdF]

Perhaps this is covered later, but I have been taught that aVR and I are the 'superior leads', which would mean that aVR is part of a group. Is this a useful way to think of things or should I forget it?

[@StrongMed]

I've rarely heard of either aVR and aVL, or aVR, I, and aVL being referred to as "superior leads". But for routine, beginning-level EKG diagnosis, I don't think this grouping is helpful. The situations in which it might be helpful to consider aVR and aVL as belonging to the same lead group is the localization of atrial tachycardia, ventricular tachycardia, and PVCs (i.e. where specifically in the atria or ventricle is the rhythm originating), which is a relatively advanced topic. (I don't have a video on this yet, but it's on the list of upcoming EKG topics)

[@TheWeirdF]

@@StrongMed thanks so much for the reply and the series as a whole!

[@dochawk9449]

time to get an EKG, G!

[@enricoiraldo9057]

Hello, Can anybody clarify to me why the first of the two vectors on the heart, the one that represents the depolarization of the IV septum, is directed south-west? Doesn't the septum, on the heart, have the same direction as the left ventricle (south-east)? Thank you so much!! x

[@KarenCHS2008]

Hi Dr. Strong, Thanks for the video! I was wondering if you have a video on normal T-wave morphology for each leads vs "strain" associated t-wave inversions vs bundle branch block t-wave inversions, please? Tall order but thanks!

[@StrongMed]

I don't have a video that specifically talks about T wave changes in depth (yet), but the video on EKG chamber enlargement discusses the "strain" pattern briefly around minute 16:00, and I discuss ST and T changes in my bundle branch video from 3:55 - 8:00 (within the context of all the findings in bundle branch blocks).

[@hanibalweredebrhan3411]

Hi Eric. There are your 24 videos together in you tube. I want to follow and watch consecutevely. Are they arranged sequentially?

[@StrongMed]

The sequence in the EKG Interpretation playlist is the most logical to go through if starting from scratch: kzbin.info/aero/PLYojB5NEEakXhL1WoDvNPm1cG57pjE0d7

[@charankumarms]

excellent video .... thank u

[@nishoo98]

Dr. Eric Strong, i think there is a correction at 7:27

[@StrongMed]

Thanks for pointing this out. There used to be an annotation with the correction included there, but KZbin got rid of annotations a few years ago. I've added a pinned comment with the correction, which is the best I can do without taking the video down and reuploading it.

[@rcorty]

When you say "inferior wall" do you mainly mean "inferior wall of the LV"? I noticed that when you said "lateral wall" you later clarified that you meant "lateral wall of the LV".

[@StrongMed]

Yes, references to the "inferior wall" when discussing cardiac anatomy refers to the inferior wall of the left ventricle unless otherwise specified.

[@DrSyedMuhammadAsgher]

Is it sufficient for FMG examination

[@AliRaza-ro8ev]

Why avF has both positive deflections?

[@hanibalweredebrhan3411]

Dr. Eric ,thank you very much for your interesting and Goal Oriented videos. My question IS on your explanation OF I+III=II you Said " At any given time the voltage measured by lead one plus à voltage measured by lead two must be equal the voltage measured by lead 3" I could not understand B/se the formula and the explanation do not fit.

[@StrongMed]

You are quite right. There is an annotation on the video pointing out that I misspoke, but you probably either have annotations turned off, or are watching on mobile (on which annotations don't work).

[@hanibalweredebrhan3411]

Hi Eric! I am watching your videos using Ipad and mobile. I think it could affect annotations. Thanks!!!

[@SudiptaNaskar]

You said that right leg is not included in EKG leads as it acts in earthing. But you said that an electrode is places in measuring EKG. So, what's the importance of that electrode ?

[@StrongMed]

Sudpita, I'm sorry but I'm afraid my knowledge of circuits is not strong enough to provide a more detailed explanation of why the right leg electrode is critical in EKG recordings. Interestingly, I've been told by EKG technologists that you can actually place the right leg electrode anywhere on the body without noticeably changing the EKG, but I've never actually tested this out.

[@dhillon09]

9:55 things get hectic

[@قمرهاشم-ف8ض]

For me 11:11

[@rayasguadalupe]

Helped me lots:)

[@WaqarAhmed-ec5xp]

u r awesome...

[@J3ug]

aVR is -150° !!! not +210°. big mistake. please repeat the hexaxial system.

[@StrongMed]

I appreciate that most references list the direction of aVR as -150, but that's likely only to provide a sense of symmetry. -150 is geometrically identical to +210.

[@DannyWiratama1987]

thank you very much!

[@osheaallen4429]

THANK YOU!!!

[@Medstudy2778]

you are more prestigious the the most prestigious of the three pyramids