# Help clarifying something on ekg's

1. Okay I'm driving myself nuts tonight. So far I got that it's a 12 lead with only 10 leads actually attached b/c some are reading different pathways 12 leads = lead 1,2,3,AVR, AVL, AVF, V1,V2,V3,V4,V5,V6

Lead 1 is reading from + L arm to - R arm

Lead 2 is - R arm to + L foot

Lead 3 is - L arm to + L foot

Where I'm getting tripped up is the L arm seems to be able to generate both + and negative depending on what it's reading is that correct? Because originally I'm thinking that the one electrode is either going to be + or - I get that they're bipolar. Or maybe I don't fully and that's what's tripping me up! Then I started thinking that maybe there are 2 electrodes attached one for positive one for negative but that didn't really make sense.

So basically I'm thinking that the electrode placed isn't necessarily capturing the polarity of positive vs negative at that point (I hope that makes sense I went back over definitions of polar, poles etc...ad nauseam) but it captures the impulse travelling whatever points are being analyzed.

Dubin's book is great...but some things he took for granted that some of us that have to work harder at understanding things would just get!

Thanks to anyone that can dumb this down for me or tell me that I'm finally on the right train of thought. Many hours later!
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Joined: Jun '05; Posts: 551; Likes: 216
Hospice Case Manager; from US
Specialty: 5 year(s) of experience in hospice, ortho,clinical review

3. It's funny this question was posted over 10 hours ago and not one reply, had you put up a complaint about nursing you'd have 20 responses by now LOL ! To answer the question, leads I, II, and III (the limb leads) are bipolar you have both + and -
4. Quote from LelaRN
It's funny this question was posted over 10 hours ago and not one reply, had you put up a complaint about nursing you'd have 20 responses by now LOL ! To answer the question, leads I, II, and III (the limb leads) are bipolar you have both + and -
Ha! That's true.

Not to be redundant but I'm still questioning is the bi polar b/c of the pathway or can the electrode hold both a positive and a negative?

I need to understand the why something works, not just that it does and I think I'm getting confused on polarity in general. Usually when you talk about something having poles there's an axis and it's the 2 points of difference that the polarity comes from. But say in a cell (not sure if that's what I'm trying to say) the inside is negative and the outside is positive then I think it's from the action potential that it briefly becomes positive inside is that depolarization? (K rushing out) and then repolarization is when it goes back to neg inside positive outside? I'm going on memory of what I read, not checking facts b/c I want to see if I'm understanding this to be able to explain it to myself!

So with that said, does it mean that the cell is polarized b/c of the 2 points one being postive and one being negative even though there's not an axis per se? So then brings me to my original question above how is the electrode bi polar, the pathway or the at the source?

If anyone knows of any sites that explain this stuff in common language I'd appreciate it.
5. You really seem to have it...the only thing I would reiterate is that it is because the limb leads are bipolar, that you don't need multiple electrodes on the LA to generate both the - and + charges (and you seem to have already ruled this out).

When it's tracing the Lead I View, LA is +. When it's tracing the Lead III View, LA is -. Because the limb leads are bipolar, they can generate both Lead I and Lead III Views at the same time. That is what is "bipolar" about them.

Try looking at some pictures of Einthoven's Triangle - it's much easier to look at than to explain. I like this picture (scroll down to the "Cardiac Vector" section):

http://noodle.med.yale.edu/~staib/bme355/ecg/prep.htm
6. Quote from juliaann
You really seem to have it...the only thing I would reiterate is that it is because the limb leads are bipolar, that you don't need multiple electrodes on the LA to generate both the - and + charges (and you seem to have already ruled this out).

When it's tracing the Lead I View, LA is +. When it's tracing the Lead III View, LA is -. Because the limb leads are bipolar, they can generate both Lead I and Lead III Views at the same time. That is what is "bipolar" about them.

Try looking at some pictures of Einthoven's Triangle - it's much easier to look at than to explain. I like this picture (scroll down to the "Cardiac Vector" section):

http://noodle.med.yale.edu/~staib/bme355/ecg/prep.htm
Awesome! Thank you for that site. The visuals help. Dubin's book is great, but I guess I like to see different pictures of the same thing to see which ones click for me.

I appreciate it. I sometimes think most people would be happy to know they're bi-polar and how to attach them and they're good to go....me, I have to drive myself crazy with the underlining mechanics of things and that's definately not my strong point. I like your explanation of why they're bi polar...that helps much.

I'm totally looking forward to starting this new job. I had no idea how much I missed studying and learning new things on this level.
7. The hardest thing for me was figuring out that you can have multiple Lead Views (Tracings) from 2 Lead Wires attached to electrodes on the skin. We often think of the tracings as an "impulse" that flows in one direction due to polarity, and that's not entirely helpful! It had me a little hung up on why they call it a "12 Lead EKG" when there are only 10 lead wires.

To be honest, despite the crap they get, I've found Wikipedia's quick summary rather helpful. Maybe it will help you, too! Check out the "Unipolar vs. bipolar leads" section!

Electrocardiography - Wikipedia, the free encyclopedia
8. Quote from juliaann
The hardest thing for me was figuring out that you can have multiple Lead Views (Tracings) from 2 Lead Wires attached to electrodes on the skin. We often think of the tracings as an "impulse" that flows in one direction due to polarity, and that's not entirely helpful! It had me a little hung up on why they call it a "12 Lead EKG" when there are only 10 lead wires.

To be honest, despite the crap they get, I've found Wikipedia's quick summary rather helpful. Maybe it will help you, too! Check out the "Unipolar vs. bipolar leads" section!

Electrocardiography - Wikipedia, the free encyclopedia
Thank you, y'know I actaully already saw that site last night...but when I saw those algebraic looking equations, I thought that just may be a little to deep for my comprehension right now! Maybe later, after I get some practice actually reading ekg's I will probably revisit. I learned in the past that I always try to jump too far ahead in understanding things instead of taking baby steps. I remember when just understanding the heart's blood path seemed daunting and then understanding what was happening where in systole and diastole

I agree it's taken me awhile to understand why the multiple views. And yes, now that you mention it...that's how I was thinking of polarity flowing in one direction toward the positive. I'm glad some sources I've read admit this can be confusing and/or complicated...I don't feel like a total dunce!

I haven't yet worked with the 12 leads though, they only had the 5 leads on the step down I precepted on. It seems that different sources have them attached at different points on the body too!
9. LeLaRN, I just love your comment. I love Allnurses, but like you said, a technical question hardly gets looked at. A complaint, chance to grouse, gets 100's or responses, LOL.

BTW I'm too out of touch with my cardiac nursing to even touch the question. But I'm never too old to grouse a lot!!!!