ECG Leads

guys we are continuing with a cardiovascular system the lecture now is the ECG leads or 12 lead ECG and what do we mean by the 12 leads and where to the attach and what do they show us this is not about the pathologies instead this is the physiology will do the pathologies when we will do the arrhythmias and the in functions okay so the leads that we have are called as three bipolar limp leads three augmented leads I call them a leads three augmented leads six just leads and one earth so let's see what these leads are and then you start discussing how to see the ECG and what do these leads mean so first of all three bipolar limb leads so leader number one is attached to arms and so this is the lead number one ideally I hope you understand that what happens is I'm just drawing a straight line but ideally the lead one for example will go from here and the negative end goes to the voltmeter or electrocardiograph machines negative end and the positive end goes to the ECGs positive end and then the machine does the rest of the function so that is how it is connected but we say abstractly that the this is the lead one and look at this the keep an eye on the positive side this is the positive side this is important secondly the lead to why do we call this bipolar though we call it bipolar because there is a negative end and there is a positive end this is lead one then is lead to lead to is connected one end negative end to the right arm and the positive end to the leg left leg remember this left leg the leads that have L in them for example the left leg or left arm these are always positive and of course that means right is always negative so here the lead number two abstractly will say it goes like this negative end is here positive end is on the leg you can also see it this way that if this was the ECG machine same machine I do not clutter up here same machine then the negative end from here is connected to the negative end and positive end from here is connected to the positive end so ideally this is the circuit however we make it like this same is the case for the lead number three so this lead number two lead number three connects like this slightly crooked but hopefully thats okay again positive end is here and sorry positive end is here and the negative end is here so left leg has two L's has two positives left arm has one L has one positive right arm has no L so there are no positives they're all negatives in all case again this one you can also see that in the ECG machine the negative will go and attach here the positive will go and attach here on the ECG right so that is they that is the way these leads are set up these are bipolar these are limb blades now the question is how do we understand the electrical activity and what do they do for us look what these leads are doing is so right arm left arm left leg what these leads are doing is they are acting as cameras to look at the heart the question is how do we look at the heart what are the way is to look at look at the heart so let me show you the position of the heart in these slides and then we'll come back and talk about the leads here here is the the heart as it appears in the ribcage so if you see here on this heart they predominantly it is present on the left side of the ribcage it is present more over there then the left atrium left ventricle is present on this side right ventricle is present here somewhere below the sternum which I have removed in this diagram is the interventricular septum so this is the position of the heart inside the chest cavity also see here that this is a view of the heart where we have cut a horizontal section and we are looking at the patient from below this is the left ventricle this is the apex of the heart this is the right ventricle and here is the base side this is the interventricular septum so keep this in mind that if you look at the heart from the sternum from both sides of the sternum if you peek in you are and if the heart is open you look at the interventricular septum that is going to be present between the two ventricles so keep this position in your mind this is a lead one here lead one- on the left arm positive and sorry negative on the right arm positive on the left arm this is Lee - Lee - is right arm negative leg positive left leg lead three left leg positive and left arm negative we will also talk about the Augmented leads which use the iron Thrones triangle so let's talk about that now before we continue further with the limb bleeds and chest leads so the the way these leads are looking at the heart if we put the heart over here the way these leads are looking at the heart is that the left the lead one positive side is this it is looking at the heart from here lead two is positive and is this it is looking at the heart from here lead three is looking at the heart from here remember the cardiac axes lecture in which we said if I draw this in the cardiac axis the X is remember horizontal was the lead one zero degrees to 180 degrees then vertical was lead a VF will draw that right now and then lead to was 60 degrees and lead three was under 20 degrees this is the if you take a if you take a coronal section so if you cut me for example from here all the way half and you insert as circular thing and in the center of that thing is a heart if you have a circular disk this is that disk and this is the views of the leads what that means is this look lead to for example this is the lead to it looks up like this lead three looks up like this so it looks really on the inferior side of the heart lead one looks down and because a positive isn't they on the left side so almost from the left side so that is how to interpret these now let us talk about the Augmented leads before we talk about the Augmented leads first we need to talk about Wilson's Center electrical Center what that is is this what will send dr. Wilson said that if you can sum or average sorry not sum if you average all the electrical potentials from all the leads that average is going to create a mean that is somewhere in the pubis area that is the mean potential that is somewhere in the pubic area this Center is called Wilson's Center and this Center can be can be used as a negative lead and then you can put positive leads in various places so here is how we work what we do is we say augmented so look this is the left this is right arm this is left leg right left leg so if you add an Augmented lead over here what that means is I'm going to make it in black if you take the pot positive from here and attach to the ECG and if you take the average of all the other and attach the hat to the negative then really pay attention now then what we are seeing is we have a lead like this negative is here positive is here this lead is looking at the heart from the right side so it is a camera attached attached here in the shoulder and is looking at the heart from the right side this is augmented VR augmented voltage lead so this is the right side augmented voltage lead if we do the same thing on this side what we do is we take the positive let me continue making it in black we take this lead and attach it to the positive end this is the positive and this is negative end and we take this lead from the center and attach it here then that becomes this new lead a abstract lead you can't see the lead here but that is all mathematical calculation what now we have gotten is we have gotten a new lead that looks like this this is the Augmented voltage based left lead and how does it look at the heart it looks at the heart as if there is a camera here and that is looking at the heart like this a VR was looking at the heart like this from the from the shoulders so that is why the AV AV augmented V L sorry augmented ve s and augmented V R are shown as minus 30 and minus 150 degrees they are looking at the heart from here so we have cameras that we are attaching to look at the heart in a circular way and also will attach cameras that would look at the heart from the front and the side so we'll have 12 cameras attached and we look at the heart so these are the AVL's and AV r so what do you think AVL is going to look at it is looking at the lateral side of the heart which is what lateral side of the heart on the left side is the ventricle left ventricle okay how about the AV f so AV f again instead of making more I am just going to make it this way from here to the foot so the positive end is on the foot that is why it is called AV F augmented voltage based foot lead and it looks up from here towards the heart what do you think is going to look at inferior surface so before we go to the chest leads now we have gotten the Augmented leads and the limp leads what do you think what is this central piece this is called the Wilson's main center for the voltage it is a calculated center it can act as a negative this is the same negative center that will be used with the chest lead as well these are the Augmented leads are called unipolar because this is taken as the center common center of the body okay so now what kind of view are we going to look at pay attention here we are looking at the lateral left lateral side of the heart that is left ventricle we are looking at that through which leads look at this here please don't memorize the tables I've seen students putting the tables in front of them and saying this lead is this this lead is that's not the right way just look at it lead number one is looking at the heart from laterally so one is lateral how about the AVL is also looking at the heart from the lateral side so AVL also looks at that so lead 1 and AVL would look at the heart from the left lateral side how about the lead AVR it looks at the heart from the right lateral side it is also called a lone lead it is also called a forgotten lead why because AVR is the opposite of AVL so if you really want to extrapolate what AVR should look like take the AVL and inverse it because one is seeing from here and the other one is seeing from here they are seeing at the same exact thing the only thing is their electrical current that they are going to see are going to be reverse of each other so if the current is going this way this way then this is going to see as positive but this is going to see that as negative if the current goes this way then this is going to see that as positive and this is going to see that as negative that is why a VR is usually not used it is not used because it does not provide as useful information it is not used because that information can be extrapolated from the AVL from the lead one from the lead five and six as well so that is why it is a lone forgotten lead but it is there it looks at the heart from the top right side okay how about the AVF the foot lead it is looking at the inferior who else is looking at the inferior the lead number two and the lead number three let me make those in blue arrows this will lead to this is lead three this is lead one got it got it okay how about just leads look just leads are very simple we are seeing the heart left side is this this is left this is right so what you are seeing is this is the left ventricle this is the right ventricle this is the interventricular septum this is why I actually made this diagram here the chest leads are also called unipolar leads they also actually use the negative without a negative probe no lead will ever work voltage meter does not work with one lead this wilsons lead is going to act as a negative end so that means actually this is the excellent excellent dr. point that means that even for the chest leads when they are present here these just leaves at all positive ends and the negative end is here so this is how the chest leads are looking at the heart it is funny so the negative end is somewhere over here so if you you bring the patient's body down here near the pubis there there is a negative end at the bellybutton pubis is a little or so negative end is there and positive ends are placed here so we place one probe here another probe here then one probe here one here and I'll tell you about the the views exact placement but this is how it looks so the lead v1 and v2 will look at ad interior and septum so when they look down when they look down from here they actually look at the septum so while the septum why not the ventricle look the ventricle is sitting like this and the septum is this and you are looking in from here so when you're looking in what are you going to say the septum so V one and two are actually called nth receptor leads they look at the septum we lead three is looking at the anterior surface of the heart four is looking at antral lateral not this septa lateral or entra septal this is enter lateral and five and six are looking at the lateral so six five four three two and one so we actually are looking at all the left side and the left ventricle and the septum and the interior surface why not the right ventricle one we can extrapolate that from the left secondly most common diseases most common ischemic problems or hypertensive problems or in fact if problems are on the left side thirdly left side is the most bulky one and has the most electrical current so it is easy to start picking up the currents on that side so there are many many reasons to to look at that side these are the chest leads so let me show you in a diagram how to place the chest leads so now we understand that five and six v five and six these are the chest leads they are looking at the left lateral side of the heart which is the left letter side of the left ventricle what else was looking at the left side AVL was looking at the left side what do you think about one one was also looking at the left side so basically one AVL and the five and six look at the left lateral how about two three and AVF they all look at the heart from the inferior it's simple you have it here now how about a VR it looks at the heart from the right side but it is a reciprocal reciprocal of a VL + 1 + 5 & 6 how about lead 1 & 2 they look at entró septal interventricular septum issues or the electrical activity plus some part of the interior lead how about 3 & 4 they look at the anterior surface of the heart one more thing is important to note v2 and v3 are supposed to be almost overlapping that means if we two is looking at the septum and v3 is looking at the interior side then v2 is also looking at some part of the interior surface similarly if we four is looking at the interior surface and v5 is looking at the lateral surface then v4 is looking at little bit of lateral and v5 is looking at little bit of the interior surface so the wherever there is a change in the tissue that the lead is seeing it overlaps with the previous lead just keep that in mind now with this let's look at quickly how these leads will pick up the problems first first important thing lead t2 is our hero why because lead to is the most in line with the cardiac axis remember cardiac access we did it is 59 degree centigrade or wider this is centigrade 59 degrees and lead to is 60 degrees so this is almost the same direction that is why heart normal heart's best action potentials can be seen in lead to hero is two not one so keep looking at the lead to whenever you look at the lead so that would give you the best current amplitudes similarly on the for the ventricle left side v 5 & 6 so let's say a patient has developed inferior infarction what leads would show you the problem what leads look at the inferior side lead number to lead number 3 and AVF so inferior wall and what kind of an artery will cause inferior wall problem right circumflex artery right how about if there is a problem on the interior surface of the heart who is going to look at that remember we have v1 v2 so that is the interceptor side V 1 2 & 3 so there is a problem with the intermolicular septum which could be left anterior descending or problem with the interior surface which is also left anterior descending then we want to and some part of v3 will give you the septum and anterior surface of the heart how about if there is a problem with the lateral side which is the most common side lateral left ventricle or and before that what is the artery for the interior surface left anterior descending now how about the problem infarction on the left side of the heart that would be left circumflex artery and who is going to look at it v5 and v6 even lead one even AVL but primarily 5 and 6 now you say why don't we want to see the AVR if there is a problem on the right side well you can see the opposite of all of that in the AVL and 1 & 5 & 6 that is why you don't really care too much about the AVR so with this let us now quickly look at an ECG and see the relationship of the leads together to lead to 3 and the a VF they look at the inferior surface this is the inferior surface then lead 1 and AVL with lead 5 & 6 look at the lateral surface then lead 1 & 2 V 1 and V 2 look at entró septal part and lead v3 and v4 look at the interior surface of the ventricle okay so if you want you to know the about the leads and the general properties we are done if you want to hang around we're going to go a little deeper and talk about the Wilsons lead and talk about the Augmented lead math so just a quick math if you don't want to listen to it you can just stop here and move on so look the guys were interested org mented lead let's say augmented we voltage based lead left means you take the left lead voltage in the left arm and then you subtract the voltage some of the the remaining two leads so what are the two leads we have so the left is covers the right arm plus left leg so this becomes augmented lead similarly AVR will be right arm here and their other two leads here if EF will be foot here or the left leg here and the other two leads here so that is how we calculate that about to Wilson's lead that is even simple so Wilson's lead is basically you take all these three so left arm plus right arm plus left leg and you average them that is divided by three and that gives you the lead one more thing here in einthoven's triangle i'm tomans triangle says and Tobin said that lead one two and three if you know the voltage is of any two leads you can do the voltage of third lead or he said it this way he said if you add the lead one plus the negative of the lead two plus the lead three it should be zero so that is the the on Tobin's triangle what that means for us practically is that if you have lead let us say one's potential then if you have lead Stew's potential then you can extrapolate you can figure out that what should be the lead 3s potential and you can see if the ECG is working correctly and you are looking at the right readings similarly if you have leads 3s potential and ones potential you can accept late through so any two leads if present you can get the third lead and that is the einthoven's triangle so just very quickly the math for the Augmented lead Wilson's lead and the enterance triangle thank you very much

Channel: Drbeen Medical Lectures

Views: 134,862

Keywords: CVS Electrophysiology Physiology Step 1, subject:3:physiology, EKG Leads, ECG Leads, ECG, EKG, USMLE Step 1, USMLE Step 2, USMLE, Einthoven's triangle

Id: YZ67_wAyXWU

Length: 26min 12sec (1572 seconds)

Published: Sun Apr 23 2017