today we're going to cover r-wave progression through the precordial leads which are V1 through V6 as well as the hexaxial leads which are 1 2 3 AVR AVL and avf we're going to talk about directions of the Qs complexes in each one of those and we're going to discuss the difference between a vector and an axis in the heart how you determine a mean electrical axis as well as give you some practice on axis deviation in the end of the presentation I will also discuss the causes of different axis deviations depolarization occurs in the heart in a threedimensional process when we look at an EKG we are actually looking at a twodimensional result or a two-dimensional readout of a three-dimensional process we just have to remember that whenever we look at the e kg that's what we're looking at as a two-dimensional interpretation having 12 views of the heart or having a 12 L EKG gives us an opportunity to reconstruct this three-dimensional pathway the heart takes when it depolarizes to get this three-dimensional space we look at the hexaxial leads the hexaxial leads are one AVL 2 3 and avf AVR also and I'll talk a little bit about AVR because a lot of people question why do we even have an AVR so I'm going to give you a couple reasons for that but those six leads right there will give you an up down and left right pathway or direction of depolarization we can use V1 through V6 which is right along here we can use these right here to determine a an anterior posterior or a front back depolarization pattern I'm not going to discuss that today what I am going to discuss though is the up down and left right depolarization using the hexaxial leads so because of these 12 views we can determine the spatial orientation of the electrical Direction now just because the electrical Direction might be outside of its normal pathway does not necessarily mean that it's a bad thing most of the time it tells us that there's something going on it could be a physiologic change or it could be what we would call a pathologic change a pathologic change would be bad so first let's discuss rwa progression I'm going to talk first about rwa progression through the hexaxial leads then I'm going to talk about rwa progression through the precordial leads what exactly I mean by rwa progression is if you remember how an EKG is laid out in a horizontal view you have lead one then you have lead two then you will have lead three then up here you have AVR AVL and avf the other six leads over here you're going to have V1 through V6 and I'll get to those here in a little bit let's not worry about those right now though the normal r-wave or the normal QRS complex I should say if you look here at AVL here's your Baseline that goes across right here notice that your r-wave or your QRS complex is primarily positive that means that most of the QRS complex is above Baseline look at Lead 1 2 3 and avf as well as AVL each one of these qrs's are positively deflected what this tells me is that this is a normal rwa progression through the hexaxial leads AVR on the other hand is always going to be negative in a normal hexaxial rway progression so to summarize Lead 1 2 3 should have a positive deflection of the QRS complex and AVR should have a negative deflection of the QRS complex AVL should have a positive and AVS should have a positive this brings me to another topic that I'm going to go ahead and breach the subject now but we're going to talk more about it later in bundle branch and facular blocks what I'm going to talk about is septile depolarization when I talk about septile depolarization I'm talking about depolarization through the inter ventricular septum for me to further discuss this I'm going to go ahead and just do a brief review of the electrical components of the ventricles real quick the ventricular electrical components consist of somewhere up here you're going to have your AV node then you're going to have What's called the bundle of his the proper pronunciation of this is his like what a snake does it's not bundle of His what happens is the hiss bundle will then bifurcate into the right and left bundle branches now that's true but it's not entirely accurate there are three faes that actually come off of the left bundle branch there is what's called a posterior faasle there's also an anterior fasle and there is a very small septal faasle that you that will also come off of the left bundle branch and this right here is your little septal faasle right here what this septal faasle does is it causes the interventricular septum to begin depolarizing on the left side of the septum and then the depolarization wave travels towards the right side now this is actually up here where it occurs it doesn't occur this far down but I think you get the picture so what we see here is if you have a normal sepal depolarization since you have electricity traveling away from lead one and Lead AVL that will give you something called a cute petite little Q wve in the lateral leads notice there's are Q waves there in the ideal setting there is no Q wave in the inferior leads now if you do have Q waves in the inferior leads sometimes you do and it's not a big deal but normally for normal sepal depolarization to occur you will have depolarization that travels from the left side of the septum to the right side of the septum and you will be able to see this as cute petite little Q waves in the lateral leads what happens in abnormal sepal depolarization well let's say that you have a you have your AV node here you have your his bundle here and then you have your right bundle branch and your left bundle branch with your anterior and posterior fices as well as your sepal faasle what will happen is if this area up here is blocking the left bundle branch then you're going to have have septal depolarization that occurs on the right side of the septum and then travels towards the left side of the septum this is abnormal you were supposed to depolarize from left to right that's what you're supposed to do giving you the cute petite little Q waves if you depolarize from right to left this will eliminate these cute petite little Q waves this is an example of a normal hexaxial rwa progression just remember lead one should be positive lead two should be positive lead three should be positive AVR should be negative AVL should be positive whoops that's supposed to be positive and AVS should be positive and these are all positive so this would be considered a normal R wve progression through the hexaxial leads let's look at an abnormal noral this would be considered abnormal rwa progression if you look up here in lead one you're supposed to be primarily positive but you're not you're actually primarily negative here if you were to count the up and down boxes and subtract you would see that you would end up with a negative number let's look at lead two lead two is positive lead three is positive AVR is primarily negative AVL is supposed to be primarily positive but it's not it is actually negative avf is primarily positive this would be considered a poor r-wave progression you could even put abnormal rwa progression anything along those lines now rwa progression through the precordial leads rwa through progression through the precordial leads little bit different but still pretty simple as well most textbooks that you start reading will tell you that when you look at ourway progressions through the precordial leads you're primarily going to look at V1 through V4 that is true but other books a few books actually include V5 and V6 so let's look at what our way progression through the precordial leads should look like now please remember when we talk about ourway progression we're talking about is the QRS primarily positive or primarily negative we're not talking about the literal size of the r wve not talking about that at all if you look at the rwa progression I have heard in the past that V1 and V2 should be little little V4 and V5 should be I'm sorry V3 and V4 should be medium medium V5 and V6 should be big big I don't want you to use that delete it don't use it it is okay to use whenever you're first learning but we want to kind of go past that so what I want you to see in an rwa progression V1 and V2 should be primarily negative V3 and V4 should be what we call transition supposed to be an R should be a transition V5 and V6 should be primarily positive now the V1 through V4 thing that a lot of books talk about is V1 should be negative V4 should be positive that's the way it should be but what I want you to understand is that V1 and V2 should be negative V3 and V4 is where you should be transitioning from negative to positive V5 and V6 should be positive what happens if you transition over here in V4 to V5 that's just considered a normal rway progression with a late transition what happens if you transition over here in V2 and V3 well you're starting out primarily negative you're ending up primarily positive here would just be an early transition for example so let's look at a couple of EKGs with just the precordial leads V1 through V6 and Normal and abnormal rwa progressions this would be an EKG with with what we would call a normal rwa progression remember V V1 should start out primarily negative and it is V6 should end up primarily positive and it is so let's look at our process here we have primarily negative and V1 negative and V2 primarily negative in V3 and then we transition to positive in V4 positive in V5 and positive in V6 this would be considered an EKG with a normal r-wave progression on 12 leads you might actually see it printed as good r-wave progression or gr WP that's an acceptable term as well let's look at an EKG with an abnormal or a poor rwa progression here is a 12 lead with just the precordial leads again and it is a poor rwa progression how is it a poor rway progression well you're supposed to start out primarily negative and you don't you start out primarily positive you end up primarily positive but there is no transition it looks like in this one you go from positive this one might be positive I'd have to count all the ups and downs but it might also be bif phasic as well V3 is primarily positive V4 is primarily positive well only positive V5 is primarily positive and V6 is primarily positive if there is a transition it goes from positive to biphasic back to positive so there's no transitioning from negative to positive what this tells me is that this is a poor r-wave progression now you can abbreviate this as p r WP poor rway progression if you have a 12 Le that does have a Poway progression that we will discuss later how you interpret this 12 lead I can tell you why right now this 12 lead has a poor rway progression but I want you to understand that it is a poor rway progression later we will discuss why it's a PO r with progression vectors and axis determination now we're going to discuss the difference between vectors and axis when we're talking about a vector what we're talking about is a diagrammatic method that is illustrating the direction and the strength of an electrical impulse now how we determine this is this is considered for one cardiac cell if you remember in a cardiac cell generally speaking I'm just going to draw out a cardiac cell here generally speaking you're going to have your cardiac cell that's going to be connected to another cardiac cell well if it's all in a straight line it's pretty easy but if it's curved it kind of changes where you're going this depolarization if you start if your depolarization is going in this direction what will happen is as you depolarize this cell this is giving you a vector of a particular direction what happens if your cardiac cell as it comes to the junction because it's part of the heart where it curves it starts curving this way well this dipolarization is going to give you a vector in that direction what direction is this dipolarization going to occur it's actually going to occur in that direction so now we have two different vectors if you average out these all of these vectors right here let's say that this one depolarizes in this direction as well this will give you these four directions will give you what we call a mean electrical axis the heart has millions of vectors that depolarize per cardiac cycle basically if you can see on the picture here there's depolarizations that are heading in that direction that direction there's one that's traveling up here one just traveling down here some are traveling down that way uh right here some are traveling actually in this direction they're all over the place each one of these depolarizations is considered a depolarization of individual cells so let's look at it this way if you have two cells and let's say that each one of these arrows here is considered a cell a depolarizing cell if you have two cardiac cells that are depolarizing in the opposite direction that is going to give you a net Vector of zero that is your net Vector what happens if you have two cardiac cells traveling in the same direction well that's going to basically amplify the electrical activity so that is going to give you a large net Vector we do have some cells that are kind of sort of traveling in the same direction in this case they're both traveling up but this one is traveling more towards the left this one is traveling more towards the right but generally speaking they're both traveling up so that's going to give us an upward net Vector but notice that even though the vectors themselves are twos your overall net Vector is not as powerful because you're losing amplitude or you're losing some net Vector as you travel away from each other so this is also going to be your net Vector if we average out all of these vectors here that will give us a mean electrical axis if we average out all of these vectors what we end up with is a general depolarization of the heart which gives us the mean electrical axis as you can see here this is a picture with all these little arrows traveling in all these different directions but this big puppy right here this is your mean electrical axis to reillustrated one more time just in case you didn't understand the difference between vectors and axis I like to use a map as it were this makes it a little bit easier for me let's say that we're going to start way up here this is a map of Las Vegas we're starting way up here at Lake me Boulevard and Highway 95 now we're going to need to get to Eastern and desert End Road right here this is our eventual Target we're taking surface streets now if we were to be in a chopper or something it'd be pretty straightforward we could just fly straight down and have not not have a problem but we're going to have to take Surface Street so first we're going to start here at Lake me and Highway 95 we're going to travel southbound from first then we're going to hit this rainbow curve here then we're going to travel Eastbound and then we're going to do this little divot here then we're going to hit the interchange and then we're going to start traveling kind of a southwesterly direction a little bit before we start traveling south again then we're going to start traveling in another southwesterly Direction until we finally get down to Sahara and then I'm going to exit off of Sahara Avenue and now I'm traveling back East again and then when I get over here to Sahara and Eastern then I'm going to start traveling south again each one of these little Surface Street directions is considered a vector if we were to average all the distances what we would end up with is a general mean electrical Axis or a general direction of Southeast this would be considered our main electrical axis Southeast each one of these little generally speaking the main electrical axis follows this general direction down to the left and towards the front of the body this is the direction that it is supposed to travel as a normal direction if it travels any other direction it is considered an abnormal depolarization why do we care about axis deviations well like I said before any deviation away from us Norm path is indicative of some kind of abnormality in the conduction system usually this deviation is caused by a problem with The myocardium what are some problems that we could have with The myocardium that would cause this axis deviation generally speaking some things that could occur and outside of just saying a general disease process specifically it could be an MI or myocardial infarction what that means is if you have your little little heart right here if your mean electrical axis is traveling in this direction generally speaking if I have a heart attack on this side what's going to happen to all of my vectors on this area that had the heart attack well these vectors aren't going to play a role in the average anymore because they're dead so what will happen is my electricity will then my Axis will then kind of shift in this direction what happens if I have an inferior wall Mi right here what happens to all these vectors they're not influencing the axis anymore so what would happen here is my Axis would no longer go down and left to the front it might travel in this direction over here so an MI can change the axis the overall axis some other things that could change the overall axis hypertrophies hypertrophies could cause a change in the axis because basically a hypertrophy is an enlargement of the muscle so if we have an enlargement of the left ventricle over here what happens is the muscle gets bigger because it gets bigger it uses more electricity which means it's going to now pull the axis up towards the left ventricular side even though it's traveling in this direction on the piece of paper we're going to see it traveling more in this direction at the same time let's say we have right ventricular hypertrophy it's going to pull because there's more electricity because it's a larger muscle or it's a large it's going to appear to be a larger muscle it's going to have more electrical influence over the axis so hypertrophies are going to pull the axis in the direction Mis are usually going to push the uh electrical axis away from itself some other things that could occur is something like a mechanical shift so usually obese people or pregnant women will have larger abdomens for example and it will push the abdominal contents up a little bit and it will cause the heart to mechanically shift inside the chest what that means is you can have a normal axis but on paper it's going to appear that it is deviated when in reality it's a mechanical shift it's because the heart mechanically shifted its position in the chest those are just a couple of examples that would cause a deviation of The myocardium oh also uh bundle branch blocks or something we'll cover later facular blocks these can also change the direction of the axis determining the axis there's a couple of different methods that you can use to determine the axis and I'm going to show you a shortcut method after I show you how we actually determine the QRS axis what you will need to determine an axis is well obviously you're going to need a 12 lead and then you're also going to need some calipers the reason you need calipers is because it makes it a lot easier to count Little Boxes if you use a calipers you're going to need a straight edge because you're going to plot points on this hexaxial reference plane right here which is what the next thing was hexaxial reference plane now I drew this one out right here I got a ruler and started going crazy with with a protractor and everything and Drew one out so it was a little bit easier for me to explain how you determine an axis one thing I want to point out about this hexaxial reference plane first of all notice that lead one is over here and it's circled this means that this is the positive electrode AVL this is the positive electrode 23 and avf are down here and these are the positive electrodes and of course r as way up here to determine the axis the two leads that we're going to use is lead one and lead avf the reason that we use those two is you have to plot axis on perpendicular leads if you use AVL for example you can't use avf you have to use lead 2 well we're going to kind of stick with the traditional cartisian plane that way we can easily plot left down up right Axis to determine what the axis is in the the hexaxial leads one other thing I want to point out in the normal cartisian plane if you travel this direction it's positive if you travel this direction from your Central Terminal which is right here it's going to be negative this is true but in this case the up down is actually backwards so if you were to travel up on this particular reference plane this is going to be your negative number if you travel down this is going to be your positive number in the normal traditional mathematical cartisian plane that's backwards so please remember if your avf number and I'll explain how you get that here in a minute if your avf number is positive you have to go down on the hexaxial reference plane since we know that a normal depolarization occurs down to the left and to the front of the body we can now use this hexaxial reference plane to determine if the axis is a normal axis a left a right or an indeterminant axis direction that is the direction of the depolarization so what they did was they broke the hexaxial reference plane into four quads what I decided to do was I decided to go ahead and keep it as four quadrants other people other books kind of go outside of a four quadrant method I like to keep it four quadrants keep it simple you can learn the variations later if you want to a normal axis goes from 0 de right here around here to positive 90° anywhere that you land in your little plotting that I'll show you here in a minute that lands anywhere here is considered a normal axis this is not a normal axis deviation because if it's a deviation it's not normal so don't put normal axis deviation you will be marked wrong for that if you put that down on a test a right Axis deviation is if you plot the axis from a positive 91 around here to a positive 180 this would be a right Axis deviation you can abbreviate it as R A that's an acceptable abbreviation a left axis deviation has both pathologic and physiologic axis shifts now because the left ventricle is a larger muscle than the right ventricle it is not UNC commmon in some people for example athletes to have what's called a physiologic left axis deviation so a physiologic left axis deviation goes from about -1 notice -1° to about -30° different books will say different will say something different some of them stop at -20 some of them stop at -40 I decided to stop at -30 because that's the angle of AVL if you go past 30 -30° anywhere over here is considered pathologic anything that is pathologic is bad that's not normal so this whole yellow area here is considered a left axis deviation up to here is considered physiologic past here is considered patholog finally the 91 around to positive 180 all the way around here this is considered indeterminant axis it's also sometimes called Extreme right Axis deviation either a term I've seen both of them either term or fine indeterminant Axis or extreme right Axis deviation if this doesn't make a whole lot of sense right now be patient I'm going to show you how to plot an axis and maybe that'll make a little bit more sense now let's look how we determine an axis step one there's a few steps here in step one so kind of bear with me a little bit you want to find lead one here's lead one and remember the opposite lead we're going to use in lead one is lead avf because in the hexaxial reference plane lead one went this way and Lead avf went this way we have to use leads that are perpendicular to each other so let's look at lead one we are now going to count the number of positive millimeters or positive deflection of lead one of the QRS complex so it looks like it begins right here so we're going to say one 2 3 4 so we're going to say the positive deflection is going to be A+ 4 in lead one now let's count the number of negative deflections of the QRS complex in lead one in lead one it looks like it returns back to Baseline all of this here it's right here at Baseline so we have no negative deflections easy math + 4 minus 0 is going to give you a net Vector of positive4 please put positive four don't just put four and imply that it's positive in this case you should always Mark a positive number or a negative number with the appropriate sign this is the number that I'm looking for right here the positive four this is what I'm going to plot on the line of lead one in the hexa reference plane where we start is we start right here at the Central Terminal and then we will count four little boxes towards the positive remember this is the positive aspect this is the negative aspect of lead one so let's start right here in the Central Terminal and let's count positive 1 2 3 4 this is where our positive lead or I'm sorry our lead one is going to be plotted determining the XIs step two basically what we're going to do is we're just going to duplicate what we did in step one with lead one and we're just going to do it in avf so let's look down here at avf remember you have to use a perpendicular axis to lead one which is avf step one we're going to count the number of positive millimeters of deflection in the QRS complex so we'll say that this looks like to be our Baseline right about here so we're going to go 1 2 that's 2 mm that looks like 5 mm and that's 1 2 that's 3 mm right there so that's 5 6 7 8 9 10 so we now have a positive 10 as our first number The Next Step that we do is we count the number of negative deflections negative millimeters in lead avf in the QRS complex this looks to be about one so I'm going to say that's a negative one I'm going to sub subract one from uh the number up here and I'm going to subtract the ne1 from 10 and what I'm going to come up with is a net Vector of positive 9 this is my net Vector this is the number that I'm going to plot onto the cartisian plane or I'm sorry the hexaxial reference plane this is lead one that's lead avf now remember positive lead one was over here negative lead one was over here positive avf is here negative avf is here this becomes important now that we're plotting the avf point so as you can see here this is our plot right here from our lead one let's go ahead and plot our lead avf we always start here at the Central Terminal now it's a positive 9 avf this is your posit positive direction this up here is your negative Direction so let's start right here and we're going to go 1 2 3 4 five 6 7 8 9 there's going to be your plot for your avf mark now that we plotted leads one and avf the first thing we need to do and this is where your straight edge comes into play draw a perpendic particular line or a vertical line if you want to call it through lead one at the spot marked so we're going to take a vertical line and we're going to draw it through lead one the next step is to draw a perpendicular line through avf this is going to be a horizontal line through avf so we're going to take the line and we're going to draw a horizontal line through avf next you're going to draw a third line line now this is where you're going to draw an intersection line you're going to start at the Central Terminal which is the exact middle through the intersection of the one and avf lines that you plotted and continue the line to the edge of the circle so what that means is you're going to start here at the Central Terminal draw a line through this intersection and continue to somewhere out here at the edge of the circle so let's go ahead and draw our line as you can see the line ended up out here and we're going to call this close enough to be a positive 75 I'm sorry positive 65° wherever your line ends up at the edge of the hexaxial plane is the axis and in this case about 65° is where our line ended up now let's go back to the four quadrants if you remember the four quadrants starting here at Zero from here to here down to avf and then back up this way this was considered a normal axis what would to happen if you were to plot your line to land somewhere over here well this area across here is considered a left axis deviation you can easily call it an l and you would be correct at the same time what happens if you plotted it over here somewhere anywhere between a positive 91 up to the positive negative 180 this area here is considered a right Axis deviation this is how we determine an axis using the hexaxial reference plane and leads one and avf let's go ahead and practice real quick with a couple of these just to kind of zero in on these skills first thing we do is we take a look at lead one and we count the positive deflections this one's easy because the positive deflections start right here off a baseline so there's five there's five that looks like one two three so that is a positive 13 do we have any negatives here well we do actually we have one negative deflection right here before we hit J the J point so that is a netive - 1 well 13 minus 1 is a positive2 now let's plot this positive 12 on the hexaxial reference plane because this posi 12 here is your net Vector so we're going to start in our Central Terminal right here and we're going to go 1 2 3 4 5 6 7 8 9 10 11 12 there's our positive 12 right here let's look at avf just pick any one of these down here because there is a little bit of alternating going on in reality the computer would probably take all of these and then average it well we're not going to take the time to do that so let's go ahead and pick one and let's say that we pick Let's just pick this middle one here so here's Baseline so there's going to be one there and that looks like we'll just call that a five so we have a positive six how many negatives do we have there's 1 2 3 4 five maybe we'll just stick with a six we'll go with a -6 okay well positive 6 and negative 6 gives me net Vector of zero so what that means is and this is probably a good thing that we're doing this what that means is my avf is not going to go up or down at all all my avf is going to be plotted right here so what that did was it plotted me I'm going to connect these two points here there is no reason to draw any other lines other than this right here so my Axis is going to be just about zero the computer would give me an exact number to tell me if it's truly a normal or a left axis deviation but technically a Zer degree axis is considered normal let's look at another one and see if we can get a better axis let's look at this one here starting out with lead one we count the number of positive deflections 1 2 3 we'll call that four that's a positive four looks like we have a -1 deflection here's your little negative down here this is going to give us a net Vector of positive3 that's a number that we're going to plot over here on the hexaxial reference plane we start here there's 's a 1 2 and three there's our positive three looking at avf we're going to this Baseline is a little wavy so let's use this one here this EKG here I'm sorry this Rhythm strip here let's use this QRS here I'll get it let's count the positive deflections one 2 3 so that's a positive3 how many negative deflection do we have 1 2 3 4 5 6 it looks like a - 6 I'm going to end up with a negative number here if you have a positive three you subtract six you end up with A3 our net Vector is -3 in avf now remember avf negative you travel upwards to plot your point so here's our zero Mark here's our Central Terminal 1 2 and three so there is that line right there or that plot right there now we would take a straight edge and I don't have a straight Ed Ed here so just kind of bear with me a little bit but a straight line as straight as possible going that direction and then a straight line as much as possible going in that direction then you take another straight edge and this is going to get interesting you start here in your Central Terminal and you draw a straight line all the way out to the edge of your mark or of your hexaxial reference plane this is going to give me about my Axis so my Axis is somewhere between -40 and -50° remember this quadrant here is considered a left axis deviation you could go a step further and say is this a pathologic or a physiologic left axis deviation in this case it's going to be considered a pathologic left axis deviation what is the number itself that we're looking at we're going to call it -46 de because we're pretty good that way there is a way easier method to determine this and let me kind of explain what it is real quick here because once you look at it it's going to make perfect sense once you start looking at EKGs you're still going to look at lead one and Lead avf if you look at lead one and the QRS is pointed up in lead one and the QRS is pointed up in avf this is considered a normal axis if they are pointed together now let me explain what I mean by the QRS is pointed together if lead one is pointed down and avf is pointed up they're pointed towards each other or they're pointed together if you see that lead one is pointed down and Lead avf is pointed up this is considered a right Axis deviation if they're pointed together what happens if they're pointed apart well what that means is if you look at lead one and Lead one is pointed up and avf is pointed down they're pointed away from each other or pointed apart if they're pointed apart that would give you a left axis deviation if they're pointed down what that means is if lead one is pointed down and Lead avf is pointed down that will give you an indeterminant or extreme right Axis deviation but that gives you an axis that is so far off the grid that who knows what it could be the way that I remember this is very simple I just remember the phrase right together left apart right together left apart what that tells me I know that an up and an up in one an avf is normal if they're pointed together or towards each other it's a right Axis deviation if they're pointed apart or away from each other it's a left axis deviation what happens if they're pointed down that just tells me it's an ex an extreme right or an indeterminant axis the only drawback is that this doesn't give you an actual number do you care about having an actual number you may want to care about having an actual number just because you know that the patient has a normal axis doesn't mean that nothing is going on and the reason I say that is because if you have a person to use Simple numbers let's say that you have a person that the computer calculated 2 hours ago that the axis is 17 positive 17° that is considered a normal axis 2 hours later you show up to transport the patient who is complaining of chest pain as you look at this sequence of 12 leads what you find on his last 12 lead is that now your QRS axis is positive 80° is that still considered normal of course it is both of these are considered a normal axis now we're going to leave out the possibility that the 12 lead was placed differently each time that you did it let's pretend that each one of the electrodes were placed in the exact same spot you now have an axis shifting it is not deviated but it is Shifting towards the right this could be a problem shifting axes towards the right which means the axis is Shifting in this direction could mean that there's an MI going on on the left side and the only way you can determine that is by the axis is actually changing so while the short phrase right together left apart doesn't give you an actual number it's always a good idea to kind of keep the numbers in mind it's always good to know the numbers too now using a quick method here let's just use the right together left apart really fast and it'll tell you immediately if the axis is normal right left or extreme let's look at the first 12 lead it is you look at lead one is pointed up lead f is primarily pointed up this is going to tell us that this EKG has a normal axis now what this does is if you look at lead one you have a positive or A positive QRS that means that your plot is going to end up somewhere over here avf is a positive so your plot is going to end up somewhere over here that tells me that this area here I don't know exactly where but I know somewhere it will be normal let's look at another one right together left apart let's look at lead one is primarily pointed Down lead f is primarily pointed up this means that they're pointed together or towards each other this is going to be a right Axis deviation this is why it's a right Axis deviation look at lead one primarily negative starting at your Central Terminal you're going to be going primarily negative lead f is pointed up so you're going to be primarily positive this right here gives you a a direction that you're going to have a right Axis deviation that's why that right together left apart works so well what is the actual number I don't know you'd have to plot the points and do the math to find out what your exact direction is now let's look at this one lead AV I'm sorry lead one is pointed up lead f is pointed down right together left apart since they're pointed apart it is considered considered a left axis deviation what that means is lead one is pointed up so that's where this is right here avf is pointed down which is a negative Direction that's going to go up on this hexaxial reference plane right here is your left AIS deviation quadrant is this a physiologic or pathologic left axis deviation we don't know we'd have to do the math plot the points and find out exactly where we end up on this degrees chart over here what I want to do now is I want to talk briefly about what causes left and right Axis deviations these are in no particular order just because I listed first does not mean that it is the most common cause but all of these can cause a left AIS deviation first of all a left ACC AIS deviation is normal in older or obese people it could also have a high diaphragm and pregnancy which would basically be a mechanical shift osma something called left ventricular hypertrophy or LVH left anterior facular block or lfb inferior wall Mi or I wmi that's a very common abbreviation for that left bundle branch blocks can sometimes cause a left access deviation and finally ventricular tacac cardias can also cause a left AIS deviation one thing about ventricular Tac cardias they can cause any kind of deviation they can cause right left indeterminant they could have a normal axis I'm not sure how but they can cause any kind of an axis shift now a right Axis deviation could be caused by osma right ventricular hypertrophy COPD a left posterior facular block could be caused by a right bundle branch block and could also be caused by ventricular tacac cardia that's supposed to be a t not a j an indeterminant or extreme right Axis deviation can be caused by ventricular tacac cardia or something called a bif facular block ourway progression applies to both hexaxial and precordial leads but I do want to mention though that when the computer on the 12 lead talks about a poor r-wave progression it is primarily talking about r-wave progressions through the precordial leads I only teach you hexaxial r-wave progression because it's a good thing to know it's helps you better understand and interpret a 12 lead but a poor rway progression in the interpretation of a 12 lead is usually referring to the precordial leads only multiple vectors in the heart average out to find a mean electrical axis just remember that an individual Vector is like the depolarization of a specific cell of a single cell in the heart average out all of those individual directions and you end up with a mean electrical axis the normal axis is traveling down to the front and to the left side of the body any deviation away from this just tells you that there is something going on hopefully through history or 12 lead interpretation you'll be able to figure out what that is the axis that we use is determined by looking at leads one and avf those are the two simplest leads that we like to use so those are the ones that we talk about if you have any other questions about this please feel free to contact your lecture instructor