The ECG Course - Leads

welcome back to the ECG course this is chapter two on the ECG leads in chapter one we discussed the electroc cardiograph uh talked about the different aspects of EKG paper in this chapter we're going to talk about uh the actual leads here's an example of a 12 lead EKG uh when we say leads we're talking about different angles of view of the heart's electrical activity so each lead is a different camera so to speak all right so we have 12 different cameras or 12 different views on a 12v kg for this discussion we're just going to concentrate on the limb leads so I'm kind of separating this in half over on the left side you have your six limb leads okay and over on the right you have your six precordial leads V1 through V6 but we're not going to talk about any of those just yet we're going to save that for a later discussion so in the six limb leads okay leads one two and three those are your standard leads lead 2 is sometimes considered the monitoring lead because a lot of times when you turn on EKG monitor it's automatically in lead 2 and there's a reason for that and then AVR AVL and avf are your augmented leads the a stands for augmented all right so one two and three are bipolar leads that means they use a positive and a negative electrode to obtain those leads the augmented leads AVR AVL and avf they have a positive electrode but they use two other electrodes to cancel out so to speak uh to get the negative side so if you picture the heart and and we'll get into those leads specifically the heart ends up being where the negative pole would be so what do we know about EKG leads well we know that we have to put these different electrodes on the body and we usually use uh nowadays we use four used to just have three okay and we put them somewhere close to the limbs you have your right arm your left arm your right leg and your left leg electrodes now as far as placement goes as long as you're about 10 cm away from the heart you should be okay there's different advantages and different disadvantages for different placement uh ideas so the limb leads when they're first created are meant to go out here on the actual uh limbs so on your ankles and wrists would be ideal to get the electrical picture but you have a problem when the patient starts to move so a lot of times people will put them up here on the chest and on the abdomen but that also creates a problem with heavy breathing and it could end up being too close to the heart to really get an accurate EKG so what I prefer is to have the arm electrodes on the deltoids because you have minimal movement of the arms in that area and it shouldn't be affected by breathing and then the leg electrodes on the tops of the thighs okay so it can go anywhere you can put them on the upper torso as long as you're about 10 cm away from where the heart is and if you're trying to imagine where the heart is just make a fist and put it like right in the middle of the sternum and that'll be right about where your heart should be so that's the electrode placement and that's where we get our leads from we know that we're used to having four electrodes on on the patient but that green electrode the one that goes in the right leg is generally considered a neutral or ground electrode it doesn't give us any of the leads that we use for viewing instead what it does is it minimizes outside electrical activity uh and allows us to view multiple leads at a single time okay so here's here's your standard placement I I got both different uh options here where you can actually put in a limbs on the left or on the right uh more towards the Torso so taking that placement we actually get the leads and you can see that the electrodes are connected in this triangle it's called einthoven's triangle and that gives us each lead all right so your right arm to left arm that's going to give you lead one all right lead two is going to be your left leg to right arm and then lead three is going to be your left leg to left arm and it's going to make more sense as we start to talk about it what these leads are actually viewing I want you to notice that uh the left arm electrode can actually be positive or negative depending on which lead you're viewing from and that's true for the other electrodes as well because when you start talking about the augmented leads for instance uh AVR AVR uses the right arm as a positive electrodes so these electrodes can actually change their polarity depending on the lead that you're looking at all right and remember the lead is the camera angle okay it's the camera angle that you're looking from so how does lead one if you look at the picture here on the left and we know that this is lead one this one on top okay so if that's lead one and the hearts right here how is lead one actually seeing any of the heart's electrical activity well that's what this next picture is kind of depict in physics two uh vectors or in this case two leads are equal as long as they're parallel and that might sound very confusing and advance but basically if you took this lead one you can just kind of mirror it parallel all the way down that's what I did here on the right this right image and it will pick up any of the heart's electrical activity uh as it relates to its electrodes for example if you look at that Arrow going down towards the that would be the patient's left down but it's down towards the right of the image this Arrow here all right is getting get picked up by uh lead one despite the fact that the heart is you know below the actual leads angle of view because of those parallel uh you know you got to pretend that these parallel leads exist all right so it will pick up the electrical activity as it relates to its electrodes because of that because the leads are equal as long as they're parallel we tend to intersect them and you'll see these diagrams and it makes it easier to understand how they are viewing the heart's electrical activity so if I drew the heart here let's use a different color all right if I drew the heart right here if that's your heart then now this is lead one lead two and three now you can kind of picture the way that these leads are looking at the heart for instance lead two is looking up at the heart from its positive electrode all right lead three from its positive electrode and Lead one from its positive electrode this kind of explains why lead two I'm just going to shade this in here this is our heart this kind of explains why leads two and three are actually considered the inferior leads when you start getting into 12 Ed kg interpretation it it'll make a little bit more sense but leads two and three are considered your inferior leads because they look up at the bottom of the heart and Lead one is considered a lateral lead because it's looking over at the left side of the heart from the lateral wall now what is the electrical activity that it's picking up well this is where we start to get our EKG waves whenever the mean vector and if you go into the ECG AIS tutorial and you watch that series of videos You'll kind of understand what mean Vector is just imagine it as all of the heart's electrical activity averaged into a single Direction okay so specifically the ventricles is what we're talking about right now when all the ventricles all the electricity in the ventricles are averaged into a single Direction that's what your mean Vector is okay so as the ventricles depolarize whichever way that that electricity is traveling the average of that electricity whichever way it's traveling is going to depict what comes up on the electroc cardiogram so if that electricity is traveling towards the positive electrode of a lead okay towards the positive electrode of a lead then it's going to cause a positive deflection in that lead now this again is very dependent on which lead you're looking at if that mean electrical activity is traveling away from that positive electrode it's going to give you a negative deflection and if it's traveling in a perpendicular Direction okay it's basically a 90° angle it would give you this equa phasic okay equas meaning it's just as positive as it is negative uh deflection so this kind of should give you some intuition as to where all these different lines are coming from on an EKG so here we go I I've actually put the cameras in to really drive home the point if you're looking at when you're looking at the different leads you're looking at different angles of view all right so in this picture I drew an arrow over the heart and that arrow is kind of showing you where the average of all the wave of depolarization the average direction that it's going and you can see that it's going to give you a different wave or a different type of complex in each lead uh depending on which lead you're looking at so if we were looking at lead one this same wave of depolarization ventricular polarization might show up mostly positive because it's going more towards the positive electrode than away from it but it have a little bit of a negative deflection because it's not going completely towards lead one and then in lead 2 it's even more positive with a smaller negative deflection because even though it's going almost completely towards lead 2 you could see that if we follow that Arrow out it's not going completely towards the positive electrode um and then in lead three you kind of had the same thing it's going definitely more towards lead 3 than away from all right but it's almost completely perpendicular so you have a little bit more of a positive uh deflection and a larger negative deflection than the other leads uh but it's not equal phased because it's not quite perpendicular it's a little bit more towards lead three than away from and if you just drew that 90 Deere angle line you'd see what I'm talking about this would be perpendicular to lead three and you can see that the arrow is a little bit more on the left side meaning that it's going more towards lead 3's positive electrode than away from it so hopefully that's kind of giving you a little bit of an idea of where these different waveforms come from all right so that's leads one two and three those are your standard leads but using those same electrodes those same four electrodes we actually get our augmented leads leads AVR AVL and avf now what does that stand for AVR stands for augmented voltage or Vector to the right arm and then you have augmented uh Vector to the left arm and then augmented Vector to the foot meaning the left foot okay so that's where AVR AVL and avf come from and they're augmented because it's not using an electrode a single electrode as a negative electrode it's using the heart so to speak as the uh center of the negative electron and here's what we're talking about so avf you uses the two arm electrodes so to speak to kind of cancel out and create its negative electrode in the middle and that's where we're going to place our heart if you look now kind of picture each one of those look now over here to the image and where I put the cameras and you can see now it they do like for instance AVR looks like it's almost going in the same angle as leite 2 but it's completely opposite of lead 2 lead 2 would be more like right here and it's positive electrode is down at the left leg av's positive electrode is up at the right arm so it's looking at an opposite angle so if you think about the wave of depolarization AVR would look almost completely opposite on an EKG as lead 2 it would have a positive uh deflection where lead 2 would have a negative and and so on and so forth so putting all of those together you would get your six limb leads okay and this is called the hexaxial reference diagram each one of these different uh end end points positive or negative has a different angle and when you start talking about the electrical axis uh that angle becomes even more important we're not going to talk about that for this discussion uh but it really can give you kind of a comprehensive understanding what what's happening with the heart's electrical activity so I've put the heart in in the middle of that and now I've added the uh labels for each lead so you can kind of see how each lead is looking at the heart AVR let's start at AVR and we'll go clockwise AVR is looking down at the heart from the right arm AVL looking down at the heart from the left arm because remember it's looking from its positive electrode towards the heart so so any electrical activity coming away from the heart as long as it's going towards that a positive electrode it's going to cause a positive deflection if it's going away from the positive electrode it'll cause a negative deflection all right uh lead one looking over at this lateral wall so AVL and Lead one are looking at a a very close portion of the heart together uh and when we start talking about 12 Ed kg interpretation you will see that those two leads are often grouped together same thing with 2 three and avf those three leads are considered your inferior leads because they look up at the bottom of the heart at the inferior wall of the heart all right so that's it for the discussion on EKG leads we're going to bring back some of that as we get into the EKG interpretation stuff I just don't want to spend too much time on it now without actually showing you any EKG rhythms okay if you wanted to go back and review chapter one on the electrocardiograph you can go ahead and do that by clicking on the left image or you can move on to chapter 3 by clicking on the Right image but don't forget to subscribe to our Channel and to leave us some feedback uh in the comments section below all right I'll see you next time

Channel: The Resuscitationist

Views: 71,710

Keywords: ECG, Cardiology, Paramedic, EMS, Prehospital, EKG, 12-lead, arrhythmia, clinical, emergency, emergency medicine, EMT, advanced life support, ALS, P101, paramedicine101, meducator, ER, CEU, CME, drug math, clinical education, medicine, ambulance, trauma, medical, electrocardiogram, ETCO2, capnography, premed, med student, medical school, physician, axis determination, meducator01, adam thompson, EMT-P, nurse, RN, LPN, CEN, board review, education

Id: dVTHn6WnlQQ

Length: 15min 2sec (902 seconds)

Published: Sun Jan 05 2014