Comprehensive Guide to Vector Electrocardiography and Axis Determination

[Music] [Music] welcome to this course on

electrocardiogram interpretation and application in clinical practice in this lecture series today's talk will

be on vector electrocardiography and myself dr brinda associate professor department of

physiology chettinad hospital and research institute the learning objectives of today's talk will be

electrical circuits and recording of electrical events principles of factorial analysis of ecg determining

the axis axis deviation and extrocardia to start with the electrical circuits

and recording of electrical events as we already know electrocardiogram is the record of the electrical events of the

heart these electrical events of the heart are mainly due to the depolarization and repolarization of the

muscles of the heart that is the atrium and the ventricles so first let us know how this

depolarization affects the ecg on the when we try to record it as an electrode so when an electrode is placed on the

surface of the body the even that happens in the heart will be recorded as an ecg

so the first event that will be happening in the heart is a depolarization event so when a wave of

depolarization passes through the heart muscle as you can see in this picture considering a heart muscle as the wave

of depolarization goes towards the heart muscle and and positive electrode placed in the center of the heart muscle will

record the ecg how does it record so when the wave of depolarization passes before the positive electrode it will be

indicated as a positive deflection on the ecg as this wave of depolarization now

passes along that is it goes near to the positive electrode that is it is nearer to the positive electrode

now so when it reaches the positive electrode the deflection will come back

downwards again to the baseline next when

the depolarization goes or passes away from the positive electrode

the deflection on the ecg will move downward and forms a negative wave

hence when the complete depolarization of the muscle takes place it will be recorded

as a biphasic wave on ecg so the final depolarizing wave will as it moves perpendicularly to the positive

electrode will produce a biphasic wave on the ecg this is the basis of recording of ecg

due to the effect of depolarization of the heart muscle as i said in this previous slide

considering the same fact in the heart now considering the heart with a wave of depolarization

the depolarization usually passes from the atrium to the ventricles and it is always downwards slightly

towards the left side and when an electrode is placed for example electrode a is placed towards or on to

the direction of the depolarization the depolarization will be a positive deflection on the ecg that is

depolarizing wave toward a surface electrode that is a electrode a will be recorded as a positive deflection

similarly when an electrode b

which is away from the wave of depolarization will produce a negative deflection in the ecg and any

depolarization wave which moves perpendicularly to the electrode considering electrode c will produce a

biphasic wave so the effects of repolarization are precisely the opposite of those of

depolarization so now considering heart as a three-dimensional organ we keep the 12

standard ecg leads that is the six limb leads and six precordial leads which we have discussed previously

will view the heart at different angles and that is called as angle of orientation and it will when considering

the six limb leads which will view the heart in a vertical plane that is called as the

frontal plane as depicted in this figure these leads show the electrical forces of the heart

moving up and down or left and right and is viewed as a circle in the frontal plane and the angle of these lead is

determined by drawing a line from positive to negative electrodes these principles are very important in

understanding the vectorial analysis of ecg so considering the

and to determine the angle of orientation for all the leads that is the limb leads and chest leads

let's see what will be the angle of orientation first for the three standard limb bleeds

that is the lead one so in this figure the lead one the left arm is positive and the right

arm is negative hence the angle of orientation is at zero degrees for limp for lead 2

the legs are positive the right arm is negative hence the angle of orientation is plus 60 degree

for lead 3 the legs are positive the left arm is negative and the angle of orientation is

plus 120 degree coming to the augmented limb leads first with the avl

the left arm is positive the other limbs are negative and the angle of orientation is minus 30 degree

for the augmented limb lead avr the other limbs are negative and the angle of orientation is minus 150 degree

for the lead avf the legs are positive the other limbs are negative and the angle of

orientation is plus 90 degree so this picture now shows all the six leads in the frontal plane with their

angles of orientation and it is necessary to memorize these angles to determine the axis of ecg to

re-emphasize you can see the lead one is that angle of zero degree lead to at an angle of plus 60 degree which means it

views the heart at an angle of 60 degree and lead 3 at 1 plus 120 degree lead avf use the heart at plus 90 degree angle

avl at minus 30 degree angle and avr at minus 150 degree angle and i

re-emphasize it is necessary to memorize these angles to determine the axis of an ecg

so this slide again gives the chart on the lead angle of orientation of the different leads

lead avr is at minus 150 degree which is considered as a right sidedly and the inferior reads are li 2 at plus 60

degree lead 3 at plus 120 degree and lead avf at plus 90 degree the left lateral leads are lead 1 at plus

0 degree and lead avl at minus 30 degree so far we have seen the limb leads coming on to the chest leads or the

precordial leads we've already seen in the previous lectures where regarding the positioning of all these precordial

leads so there are six precordial leads v1 to v6 which are placed over the ventricle for example lead 1 is placed

directly over the right ventricle lead v2 and v3 over the interventricular septum lead four focuses on the apex of

the left ventricle and lead 5 and lead v5 and v6 over the lateral left ventricle

and both these limb leads and the precordial leads will form a group of leads which has been emphasized in this

table the anterior group of leaves will include v2 v3 and v4 the left lateral group of leads includes 1 avl v5 and v6

the inferior group of leads includes lead 2 lead 3 and avf and the right ventricular leads include avr and v1

so based on this let's go on to understand the principles of factorial analysis in ecg

to understand what is a vector i would like to give an analog of a football game considering the football ground as

the goalkeeper strikes the ball we can see that the ball can go on to any direction but the final area where the

ball has to go is into the opposite net so similarly the vector is the sum of all the average forces of these

direction similarly in ecg it the ecg

electrode records only the average current flow at any given movement so what is a vector the average

electrical movement which is represented by a single arrow is called as a vector and the vector is recorded by the ecg

electrodes this vector has two things one is the angle and the length the angle of the

vector represents the average direction of the current flow and the length of the vector represents the voltage

this vector is translated as ecg wave patterns when recorded by the 12 ecg leads

as the ecg reads records this vector it is been represented as waveforms and we know the

waves of ecg which include p wave qrs complex and t wave now how can we apply this vector analysis on these waves of

ecg coming to the p wave we know that p wave represents atrial depolarization so the vector current flow for this

is from the atria that is which points down from right to left slightly inferiorly so any lead that views this

wave of depolarization as moving toward it will pro will record as a positive reflection on ecg paper in

this figure you can see that this wave moves towards the lead 1 hence it is recorded as a positive deflection on ecg

paper so the p wave will be a positive wave on lead 1 in the ecg in the frontal plane

additionally avl also will have a positive deflection inferior leads like avr will show a negative deflection

because the wave is moving against the lead avr so it's a negative deflection on the ecg whereas the d3 will produce a

biphasic wave because the angle is perpendicular to the position of the lead

considering the horizontal plane that is with the chest leads v1 to v6 the left lateral leads v5 and v6 will produce a

positive wave as the wave is towards those sleeve leads and the b1 lead will produce a biphasic wave because this

lead is perpendicular to the wave of depolarization in the atria hence the normal range of p wave vector

will always lie between 0 to 70 degrees next wave of ecg is the qrs complex which is first initiated by the septal q

wave which represents the depolarization of the interventricular septum and it is the first to depolarize and usually

begins from left to right direction and it and this is viewed as a tiny negative deflection in leads such as lead 1 avl

v5 and b6 the remainder of the ventricles will depolarize next then that will dominate the remainder of

the qrs complex especially the r wave and the vector current will also flow leftwards as you can see in this

diagram and this vector points from 0 to 90 degree and it is considered to be normal coming to the r wave of the qrs

complex in the frontal plane the r wave is considered as a positive deflection in lead

1 and lead 2 as the wave of depolarization is going towards these two lead lead 1 and lead 2

whereas the s wave will be a deep negative deflection which will be seen in lead avr lying rightward

in the horizontal plane lead v1 and v2 we will record a deep s wave as the current is moving away from them and

lead v 5 and v 6 will have a positive deflection as the wave of current is moving towards them and that is

considered to be tall positive r waves whereas lead v3 and v4 they are called as transition zones and they are called

a biphasic wave this pattern of increasing in the r wave amplitude from right to left in the

precordial leads is called as r wave progression where v 1 is the smallest r wave and v 6 is the largest r wave

coming to the t wave which represents ventricular repolarization it has a variable variability in its appearance

that is repolarization usually begins in the last area of the heart to have been depolarized and usually travels

backwards because both an approaching wave of depolarization and a receding wave of

repolarization generate a positive deflection on ecg and the same electrodes that will record a positive

deflection during depolarization which is tall r wave will also record a positive deflection during

repolarization a positive t wave it is typical and normal to find positive t waves in the same leads that have the

tall r waves to summarize the vector aspects of electrocardiography

the p wave is usually small and it is positive in left lateral and inferior leads it's biphasic in lead 3 and v1 and

the normal range of p wave vector is 0 to 70 degrees with the qrs complex it is usually large

with tall r waves in left lateral and inferior leads with r wave progression seeing from v1 to v5 and a small q wave

is seen as in one or several of the left lateral leads and the vector for qrs complex always points from 0 to 90

degree this is very important while we studying well while we study the axis determination the t wave is variable

with positive in all leads along with the r wave coming to the next concept that is

determining the axis in an ecg to determine the axis in an ecg we need to know what is the mean electrical axis

in ventricular depolarization which is represented as qrs complex in ecg the first vector here you can see number one

represents the septal depolarization and the successive vector 2 3 4 5 until 8 represents the progressive

depolarization of the ventricles and you can see these vector will swing leftward because the electrical activity of the

left ventricle is of larger and predominates the ecg the average of all these vectors 1 to 8

at one instant that is called as mean vector and the direction of this vector mean vector is called as the mean

electrical axis and this is very important in determining the axis of ecg

so now axis is how to determine the axis of an ecg the axis of an ecg is mostly determined by by the qrs complex wave

the mean qrs vector as we see points leftward and inferiorly and it represents the average direction of

current flow and we already seen the normal direction of the of the qrs mean vector is between 0 and plus 90 degree

that is from here 0 to plus 90 degree so with this false the normal qrs axis how to determine the axis based on this

qrs complex three methods are identified for axis determination first is the quadrant method second

three lead analysis and third is the isoelectric lead analysis let's see in detail about each of these methods

first is the quadrant method of axis determination this is the most efficient way to estimate the access of an ecg and

because it is using lead 1 and lead avf

and in these leads we examine the qrs complex and determine whether it is positive that is it's an upward

deflection or a biphasic deflection or a negative deflection so based on these we will determine the axis of an ecg

so if ah so when there is a positive qrs complex in an ecg in lead 1 that puts the axis in the same direction as that

of the lead 1 that is at 0 degrees and positive qrs complex in lead f q arms positive qrs com

positive qrs complex in lead avf will align the axis with the lead avf that is at plus 90 degree so combining both

these colored areas the quadrant of overlap this is the quadrant of overlap which determines the axis of ecg and it

is normally between 0 to plus 90 degree so if lead 1 and lead avf have positive qrs complex then the axis always lies

between 0 and 90 degree plus 90 degree and that is considered to be normal axis the next step in determining the access

of an ecg is by the three lead analysis method which includes three leads that is lead 1 lead 2 and lead avf

in lead 1 a positive qrs complex puts the axis in the same direction as lead 1 a positive qrs complex in lead 2 aligns

it with the direction of lead 2 at plus 60 degree and lead avf you already see so when we combine all these areas the

area of overlap will determine the axis as before and if both lead 1 and lead 2 are positive the axis will lie between

minus 30 and plus 90 degree and that is considered to be normal so it is from here minus 30

degree to plus 90 degree that is considered to be a normal axis the next method to identify is by means

of an isoelectric lead analysis it is a more precise method of estimation of the axis

if the qrs is positive at any given lead the axis will be in the same direction of the lead if the qrs is negative at

any given lead the axis will be in the opposite direction this concept we have already seen before i am trying to

re-emphasize again if the qrs is biphasic at any given lead the axis will be

90 degree or perpendicular to that of the lead so in this method there are three steps in determining the axis step

one you have to find the biphasic lead of the ecg step two you have to find the positively

that is lead with the tallest r wave step three you have to calculate the axis that is the qrs axis is

plus or minus 90 degree perpendicular to the biphasic lead and the direction is always pointing towards that of the

positive leaves so based on this method let's try to solve this example to understand uh the best the better way of

determining the axis of an ecg so considering this ecg strip how do you determine the axis of an ecg by using

the three method the first method is the quadrant method where we use lead 1 and lead avf so let's see what is the qrs

complex in lead 1. so it is considered to be positive how about avf here also the qrs complex is positive

so coming to the next method that is the three lead analysis in addition we have to look at lead 2 also so lead 2 also

gives a positive qrs complex so the axis for since it is positive in all three

leads the axis of the quadrant usually lies between 0 and plus 90 degree and it is considered to be a normal axis

coming to the third method to have a precise estimation of access by means of the isoelectric or biphasic lead

analysis method in that the step one is to find the biphasic wave in this easy strip where do we find the biphasic wave

you can see it is at the avl and step two you have to find the positive leads we already know there are

three positive leads lead 1 e2 and lead avf step 3 the qrs access it is at plus or

minus 90 degree to that of the biphasically so the biphasic lead is avl so avl is at minus 30 degree

so this should be plus or minus 90 degree to minus 30 which will be equivalent to plus 60 degree or

minus 120 degree the final step in analysis is it is the direction is always towards the positive

electrode that is the positive electrodes here are 1 2 and avf so the direction showed towards the positive

electrode hence the qrs axis is considered to be normal that is at plus 60 degree and that is considered to be a

normal qrs axis so considering this let us go to some deviation aspects that is axis deviation

the normal qrs axis again i emphasize is between 0 and 90 degree with a positive qrs complex in lead 1 and avf

if the axis lies between 90 and 180 degree that is called as a left right axis deviation here

and here how the ecg will appear lead 1 will be negative and lead avf will be positive

and if the axis lies between 0 and 90 degree that is called as a left axis deviation and how does the ecg appear in

lead 1 it will be positive qrs complex and avf will have a negative qrs complex there's another type of deviation called

as extreme right axis deviation it happens rarely where the axis becomes totally disoriented and lies between

minus 90 and plus 180 degree that's called as extreme axis right axis deviation here the qrs complex will be

negative in both the leads that is lead 1 and lead avf also the p wave has its contribution

towards the axis the normal p wave lies approximately between 0 and 70 degree and the t wave axis is usually variable

and it approximates with the qrs axis lying to about 550 to 60 degree of the qrs axis why do we have to study the

concept of access it's very important in clinical application in diagnosing hypertrophy of the heart and enlargement

of the heart especially right and left right and left ventricular hypertrophy and atrial enlargement

so this is a summary slide which says about the axis of the heart most of which have been it has been covered in

the previous slides so axis refers to the direction of the mean electrical vector and it represents the average

direction of the current flow three methods of determining the axis quadrant method tree lead analysis and

isoelectric lead analysis the most precise method is the isoelectric lead analysis and you can memorize this table

to understand what type of deviation could be possible in relation to the lead 1 and lead avf

and now let's solve this graph in of ecg to determine the axis so on this ecg

comment on the qrs axis tell if it's normal or is there any deviation so what type of method do we

choose we'll do all the three methods to sort this first quadrant method lead one and lead

avf so lead one it is a negative wave and lead avf it is a positive way so

when when lead one is negative and the avf is positive we have seen in earlier that it could be a right axis deviation

the next method three lead analysis we would include lead two here in lead two it is a biphasic wave hence in right

axis deviation the quadrant could be between plus 90 degree or plus 180 degree

coming to a precise estimation of axis with isoelectric lead analysis method step one we need to find the biphasic

wave which we already know it is lead to step two we will find the positive lead that is lead avf which will denote the

direction of the axis step three we have to take the qrs axis plus or minus 90 to that of the biphasic wave so here the

lead 2 is by basic so it is plus 60 degree which is by phasic so it should be plus or minus 90 to 60 which will be

equal to plus 150 degree or minus 30 degrees so it should be either from minus 130 or

2 plus 150 degree but we already know that the direction is always towards the

positive lead that is the positive lead here is avf so the direction is downward here with the right axis deviation hence

the correct axis for this ecg is at plus 150 degree with right axis deviation based on this i would like you to solve

this ecg and practice on your own uh using the three method of determination of the

axis to complete this session a few points on dextrocardia dextrocardia is defined as

a condition where the location of the heart is in the right hemithorax with the apex pointing towards the right we

already we already know that the apex is always pointing towards left leftwards this is an abnormal condition where the

apex points towards the right there are a lot of investigations that can be done to determine this a chest x-ray could

show a mirror edge of the heart on the right side ecg is very classical it will show a right axis deviation and all the

complexes in the ecg will be inverted predominantly negative p wave qrs complex and t wave in lead 1 and a

positive qrx in lead avr and there will be low voltage v3 to v6 leads and reverse r wave

progression in the prog in the precordial leads and an extra abdomen can also be done which could show fungal

gas shadow on the right side and the left lobe on the left dome of the diaphragm is at a higher level thank you

for your patient listening and a happy learning