ECG measurement and interpretation

so in this video we're going to have a look at an ECG readout and what that readout means physiologically when we look at the heart so let's say you've got your patient patients lying down you have the ECG machine let's say you have a 12-lead ECG which means you have the 10 electrodes placed on your patient if you're unsure where these 10 electrodes go please watch the ECG placement video so you've got these 10 electrodes placed on the patient which is giving you 12 views of the heart and again these give you 12 individual views as to what's happening in regards to depolarization and repolarization events and again I've done another video looking at depolarization repolarization okay first things this we're just going to take one example late so let's say we have a lead that's placed here so it's looking at the Huff in that direction right so you can pretend that it's looking up at the heart and this set of eyes here let's say it's lead v5 or lead to will give you a view of the heart from around about this angle okay it's looking at that heart from this angle like this okay so that means whatever is happening in its direction or whatever is happening away from it electrically it's gonna see and it spits out some sort of reading so let's have a quick talk about that generally what you're gonna find is that the heart in a healthy individual will begin its contraction starting and this little group of specialized myocardium a group of specialized heart muscle cells in a little area here which we call the sinoatrial node the SA node okay now these group of cells automatically will spontaneously depolarize okay what does that mean I showed you in the heart muscle self depolarization repolarization video that when you have a cell that you have sodium channels and sodium wants to come in and you have potassium channels Tass Ian wants to come out so potassium wants to come out I told you that some stimulus needs to happen in order to open sodium channels to let it in well with these sinoatrial mode know themselves there doesn't need to be an external stimulus they have already some sodium channels open which means sodium trickles in at all times remember what that means I told you so you have to remember with that graph when the cells at rest that's negative 90 you have a threshold at negative 70 and you have a maximum around about positive 28 positive 30 go back to the video looking at heart muscle repolarization depolarization cells at rest nothing's happening some sodium channels open up and some sodium starts that come in and it shifts up into the positive until it hits negative 70 then it depolarizes I told you for every other heart muscle so it needs a stimulus in order for that portion to happen except the cells of the sinoatrial node they always they spontaneously hit depolarization they spontaneously hit the threshold okay so we have these cells these cells of the sinoatrial node and they've started to depolarize now remember what that means the polarization is sodium coming in sodium is positive so you get a wave of depolarization which is a wave of sodium coming into the cell and I told you one heart muscle cells connected to another connected to another connected to another which means and sodium comes into one cell it trickles through and sodium comes into next trickles through comes into next that's why it's a wave of depolarization when these so know the cells of the Sun I turn on depolarize they depolarize they get across all the myocardium of the atrium in this direction okay that's the wave of depolarization meeting all those cells are connected to each other sodium comes in goes in that direction which means remember it's going from inside the cell negative to positive which means you have a wave of positive stuff going in that direction like that okay so first thing is this you need to have a look at the lead and where the leads looking at and then have a look at the depolarization event and see what that's going to if you see that the lead is looking at the depolarization event or the depolarization event is happening in the direction of the lead what you'll find on your ECG readout is every time depolarization happens in the direction of the lead you will always get a bump up on the lid okay let's have a look at the cheat sheet that I always tell you about okay so if you were to draw one lead two leads three leads all leaves draw four leads for me if depolarization occurs in the direction of the lead and depolarization as you can see it's positive stuff coming into the cell if this happens in the direction the lead you will get a buff up on your ECG okay so under that logic thinking via that means if depolarization therefore occurred away from the lead what do you think that ECG readout would give you know if positive towards gives you up then positive or Y should give you a downward deflection okay okay let's make it a little bit more difficult what if so this is depolarization what about repolarization so let's just say this all the muscle of the atria have now depolarized become positive and then can track contracts because I told you that depolarization precedes calcium influx which that relieves the contraction and then repolarization occurs meaning the potassium comes out and becomes negative again okay so if we want to reset this and repolarize this heart muscle cell that means negative stuff moving around what if repolarization happened in the direction of the lead so again use the same logic you've been using if positive stuff in the direction leg gives a bump up then negative stuff in the direction lead should give you so positive and negative opposite so positive stuff and directionally gives you a bump up negative stuff and directionally it should give you a Bock yeah so a deflection in the ECG readout and again using the same logic what if repolarization happened away from the lead repolarization away from the lead well it's going to be the opposite that's the opposite it's going to be a bump up okay this is the cheat sheet for an ECG this tells you what's going on so again let's look at this either v5 or lead to it's viewing the half in this direction so now a chill mode it's stimulated depolarization event automatically spontaneously it's happened and it sends a wave with this positive depolarization through the heart in that direction like that and this is in the direction of the lead overall you can say that it's going in the direction of the lead and if the depolarization goes in the direction lead you get a bump up okay alright next point once that's happened it hits this fibrous tissue there is a fibrous HIO ventricular septum separates that a tube for the ventricles and it stops the depolarization wave so depolarization cannot move through such stops it so once that's happened no positive stuffs moving through the atria or the ventricles so you get our flatline because there's no positive or negative stuff moving anywhere the lead won't pick anything up so you have a flatline next thing is this there is in actual fact another group of cells similar to sa mode let's sit right there now that's the SA node sinoatrial node sets the science rhythm this is the AV node the atrioventricular node because it sits between the atria and the ventricles okay so this IV node once the depolarization wave is spread throat the only place that it can continue through from the atrium it can't get through this fibrous septum it can only slowly travel through the AV node very slowly takes point one of a second so that means that the polarization of the atrium then contraction then there's a point one second break while the depolarization wave moves through and then it continues to propagate you have a flatline while it's propagating throat so once that's happened once the action potential or the depolarization runners move through this AV node branches off like this okay and the left breath so this is called the bundle of hiss okay the bundle of hiss branches into the left and right Purkinje fibers but the bundle of hiss you'll see the left branch branches off like that okay so that means once this depolarization about is rich Navy node flatline it then propagates through these fibers then these fibers are really fast okay very very fast and as the depolarization wave spreads down as it goes down you can see that it goes down like that but also down the left bundle and starts to fire up like that all these branches firing up so depolarizes the septum between the left and right ventricle like that in that direction you can see in that direction that means positive stuff is moving in direction so that means look at the lead is this the polarization of it going towards the leader away from the lead overall away from the lead because as it moves down these ones are going up like that okay so that means what you get is the polarization away from the lead a deflection a bump down now this deflection is it nice and rounded like that because these fives are very fast and because it's not a thick tissue doesn't last very long you get a bump down like that okay all right once the depolarization event has reached towards the apex these bundle branches move through and turn into the kingi fibers that move up like that and these Purkinje fibers branch off either okay so that means sleep polarized down we get a deflection because it's going away for then it reaches here and what you'll find is it starts to depolarize like that so have a look is that overall in the direction of the leader away then you may think well this parts in the direction lead so the left ventricle is but the right ventricle is going away from the lead so you may go I don't know what direction this is happening well remember the left ventricular wall is about three times thicker than the right so what's happening in the left ventricular walls can overpower what you read on the ECG - what's happening on the right so what's happening over here predominantly the depolarization event which is positive stuff is going in the direction of the lead and because the tissue is thick and they're very fast fibers you have a very high bump up like that okay now once it's reached toward that what we call towards the base so remember that's the base of the heart apex once this depolarization of it has reached towards the base of the ventricles the depolarization event moves up like that so this is the part we're looking at now you can see it moves up and away so we have depolarization going away from the lead it's not a very big bit of tissue in there fast fibers so we get another deflection another bump down come all right what's the next part we have now just deep polarized the entire heart it's all positive now right and it's all contracted so sodium comes in calcium contracts sodium comes in calcium contract now what do we need to do well we need to repolarize it okay that's where the so that's where the potassium leaves the cell to make it negative again inside okay so that means we need to make all this negative again now what you need to realize this even though depolymerization started here and moved like that and then went to the AV node and moved like that and then like that repolarization does not start with depolarization started repolarization starts where depolarization finished up here okay which means now repolarization goes in this direction okay repolarization goes in this direction so as it goes down you all you need to do is look at the opposite of the D pole it goes in the opposite direction to D Pole and you saw D pole predominantly go in that direction for that big bump so repolarization goes in the opposite direction okay and that's going making it negative again so you can see this is happening away from the lead right so we have a repolarization event going away from the lead what do we get we get a bump and this is your ECG that's gonna reset now that's going to go back to negative and then the next cycle can happen so this is one cardiac cycle this is one bumbum resets bum bum resets bum bum resets boom-boom okay so this is what we call just a general ECG readout and you can see it's basically an ECG ran out from the v v or lead to cable so what does that mean overall it means this if we look at this first wave this first wave represented atrial depolarization okay the next big complex here represented overall ventricular depolarization okay and then the last bump represented a ventricular repolarization and that's what an ECG is measuring now you may ask okay hld politic Euler deep olive ejaculatory poll where's atrial repolarization happened because think dipole-dipole when that did that that repol and because the vertical walls are so much thicker it basically is hidden the atrial repolarization is hidden behind the ventricular depolarization with them okay letters of the alphabet hey chill D Pole the first wave is called the P wave the first little dip here is called the Q wave and then s then T which means atrial depolarization is represented by the P waves ventricular depolarization is represented by the QRS complex and the T wave represents ventricular repolarization and that's all from the view from the v v or lead to think about if the lead is up here so that AVR lead what if the AVR lead was up here looking at the heart from that direction what do you think would happen it's meant it's just looking at deep Oh Lori politics either away or towards it views the heart from the opposite direction so what do you think that ECG readout should look like it should look like the opposite the inverse and it does an AVR readout should look like this the opposite okay I'm gonna do another video just probably condensing all this in a very quick summative form but I hope all this made sense

Channel: Dr Matt & Dr Mike

Views: 102,650

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Id: elVAkFENfxI

Length: 18min 34sec (1114 seconds)

Published: Tue Aug 09 2016