12 Lead EKG (ECG)

so in a 12-lead ECG we are provided with 12 views of the heart so how does this come about because we've got an electrode on the patient's left leg and on their right leg on their right arm and on their left arm and we have as we will see later six chest electrodes six electrodes on the chest so if we've got six pickups on the chest six seven eight nine ten that gives us ten leads but it's called a 12 lead ECG so how do we explain the fact that it's a 12 lead ECG well what we can imagine is what is called einthoven's triangle a nine Homans triangle is just that it's a triangle there's an imaginary line going from there to there like that that's one side of the triangle there's another line going from here down to the left leg down to the foot which is there like this and there's another imaginary line of the triangle going up here to the left arm and as you'll notice the right leg is ignored altogether and the reason for this is the electrode on the right leg is just an earth it's not a detecting electrode is just an earth so what we have here is an electrode of the right arm an electrode on the left arm and an electrode on the left leg which we call the foot now we're picking up electrical impulses from here an electrical impulses from here and these are going away into our clever ECG machine and as you know the first lead on the 12-lead ECG is lead one lead one now what the ECG machine does is it's very clever and it takes part of the information that it's picked up here part of the information that it's picked up here and it cleverly and electrically combines it into one view so lead one is called a dipolar lead there's two polls so information is picked up from there it's picked up from there the Machine splices this information together and gives us lead one and what this actually means is lead one is looking at the heart from on top so we think that the heart is about here somewhere around there then lead one is essentially looking at the heart from this direction it's looking at it from on top that's lead one now lead two is another dipolar lead and again this clever ECG machine is taking some of the information from the right arm some of the information from the foot it's combining that electrical information together in a clever way and it essentially gives us a view which is combining this in this and essentially is giving us a view from the tooth in this direction towards the heart from that direction so it's giving us a second view that is lead to and lead 3 is the third dipolar lead again information is taken from two electrodes from this one and this one it's cleverly electrically combined in the machine so lead 3 is essentially looking at the heart from this direction so we have a third view of the heart so leads one two and three looking at the heart from different directions using bipolar electrical information now the next view is a VR and a VR is looking at the heart from the right arm so it's essentially looking at the heart in this direction so again that's another view now the a V stands for augmented voltage right because again the machine is adding a bit of voltage to this now the voltage is already there is picked up here but the way I think of it is because it's a long way from the heart it needs a bit of a boost so it's augmented voltage right looking at the heart from this side and this is just a one pole view it's a unipolar electrode and the next one after AVR is a V L so AVL is augmented voltage left and that's again unipolar and it's as if it's looking at the heart through the left shoulder it's looking at it from this direction here so again that's giving us another view of the heart and then the next lead the sixth lead is a VF that stands for augmented voltage foot again it's a unipolar electrode and that's looking at the heart from this direction so you can see we've now got six views of the heart looking at it from one from two from three from a VR from a VL and from a VF we've now got six of to give us anatomical positional information of what's going on and then of course we've got six chess leads so we've got V 1 V 2 V 4 V 6 V 3 and V 5 so we've got v1 v2 v3 v4 v5 and v6 and these are looking at the heart from a plane going around the heart that way so these ones are looking at the heart and this the 1 2 3 AV are AVL AVF looking at the heart in this direction in this plane the chest electrodes v 1 2 3 4 5 and 6 are looking at it in this plane so we've got a lot of positional information about the heart here so for example if someone has an inferior in fact that can be seen on the inferior leads so the in facts at the bottom of the heart that's going to give St elevation on leads to 3 and AVF they're the leads that see the bottom of the heart they're looking at it from the bottom or if there's an anterior infarct that's going to be these these leads v 1 2 3 you're on the anterior surface of the chest they're looking in that way so there's an anterior infarction would expect to see that on leads one two three maybe four if there's a lateral in fact on the side of the heart we'd expect to see that looking from the side and the leads that look from the side are particularly v5 and v6 so we have 10 electrodes on the surface of the patient's body we need the earth but we can take that away but then we have one two and three as well giving us a total of 12 views of the heart giving us essential anatomical information for example if it's an inferior in fact then the thrombus is most likely to be in the right coronary artery in 80 or 90% of patients it'll be in the right coronary artery if there's an anterior infarct over the front of the heart that will most commonly be a thrombus in the left anterior descending artery in the lad if there's a lateral in fact that will tell us that the thrombus is most likely in the circumflex branch of the left coronary artery but all this information is only available because the 12-lead ECG gives us anatomically accurate positioning information

Channel: Dr. John Campbell

Views: 651,788

Rating: 4.9052982 out of 5

Keywords: ECG, electrocardiogram, EKG, 12 lead EKG

Id: JSxd0UTt5gQ

Length: 10min 5sec (605 seconds)

Published: Thu Nov 01 2012