Comprehensive Guide to ECG Lead Systems and Their Clinical Importance

[Music] [Music] good morning i am dr a ahmed basha

professor of physiology chettinad hospital and research institute today i will be speaking about

ecg lead system ecg and

electrocardiogram is a record of cardiac electrical activity

and this electrical activity is recorded and the procedure of recording is

electrocardiography it is a non-invasive procedure

this electrical activity is detected by placing an electrode over the body surface

and that electrode picks up the electrical potential and it is transferred to the ecg mission

electrocardiograph ecg machine records the electrical activity in a moving paper

electrodes electrode is a conductor material which conducts electrical potential

over the body surface so whenever a electrode is placed over the body surface it conducts cardiac

electrical potential and then it transmits to the ecg machine lead

a lead is two or more electrode which connected to the

one end is connected to the body surface and the other end is connected to the ecg machine

so if there are two leads the potential difference between those two leads are picked up

from the body surface and it is conducted to the ecg machine intern ecg machine records the electrical activity

in a moving paper william eindhoven inventor of practical electrocardiogram

he invented the practical electrocardiogram and he was awarded a nobel prize in the year 1924 for his

discovery of the mechanism of electrocardiogram so what are the basis of ecg leads

heart generate its own electrical potential that electrical potential is picked up by the electrodes we are

placing the electrodes over the body surface so whatever the electrical potential is generated from the heart it

is viewed by the electrodes in a three dimensional manner that means if two electrodes are placed

the potential travels towards one direction if the

depolarization that is a spread of depolarization if it is towards a positive end then we get a

positive wave if the spread of depolarization is towards a negative pole then we get a

negative wave in the ecg if the spread of depolarization wave perpendicular to the lead then we get a

biphasic deflection so depending upon the conduction of impulse towards positive

or negative the waves of ecg either a positive wave or a negative wave or a biphasic wave

so standard lead system in the standard lead system are called as 12 lead system

it is classified into two category one limb leads

other one is chest leads limb leads indicates

leads placed over the limbs chest plates are the leads placed over the precordial surface that is on the

chest area over the chest area the limb leads again classified into bipolar limb bleeds and unipolar limb

bleeds we can see one by one what is bipolar and what is unipolar in this subsequent slides

unipolar chest plates are placed over the precordial surface so these are the

lymph fleets these are the areas to place the chest leads precordial area to place the

chest leads so bipolar limb leads bipolar lymph leads are

indicated as l1 l2

and l3 electrodes that form these signals are located on the limbs

unipolar limb leads in unipolar limb plates the electrodes are

same as l1 l2 and l3 but

here the electrodes that is two and two terminals are connected to a common end with a resistance closer to zero and the

other terminal is connected to the positive pole so that is about the unipolar limp leads

so unipolar limp plates are indicated as avr avl and avf a stands for augmented

unipolar chest leads these leads as i mentioned earlier are placed over the precordial surface

they are indicated as v1 v2 v3

v4 and v5 and v6 so the it is indicated from v1 to v6 here the wilson central terminal is used

as a negative pole next we move on to the eindhoven's law as i mentioned earlier eindhoven is the

father of practical electrocardiogram he constructed an imaginary triangle and assumed that heart is at the center of

that triangle so how he placed heart as the center of the triangle and all the three ends of

the triangle he connected the limb leads if an ecg taken simultaneously with the

three limb leads at any given instant the potential of one lead is equal to the arithmetic sum of the

potential of other two leads in general we used to say as lead to equal to lead one plus lead

three so lead to is equal to the potential difference of lead one and potential

difference of lead 3 this is called as eindhoven's law l2 equal to l1 plus l3 so bipolar lymph leads in bipolar limb

leads as i mentioned earlier it is indicated as l1 l2 and l3 now we can see what is l1 from weight to where it is

connected and what is the potential difference l1 lead is connected between

left arm to the right arm and l1 lead view the heart from the superior aspect

next l2 that is lead 2 is connected between right arm and the left leg

this lead view the heart from the right side that is it view right side aspect of the heart

next lead 3 lead 3 is connected between

left arm and left leg it views the left side of the heart that is left aspect of the heart so these

three leads view the heart from the three views one from lead one superior aspect

lead to right aspect and lead three left aspect here one more leader is there that is

right leg in the ecg right leg lead serve as an earth for the reference electrode as act as a

reference electrode next we move on to the unipolar limb leads

in unipolar limb bleed one terminal is connected to the positive that is one limb is connected to the positive and

the other two limbs are connected through a high resistance making the potential close to zero so what is the

use of this it increases the voltage recorded it increases about 50 percentage of the voltage recorded when

compared to l1 l2 and so avr

avr here the positive limb is right arm the abl

the positive terminal is left arm

in avf the positive terminal is left leg so here avr avl and avf are this

recorded from this same electrode as l one l two and l three but the difference is it is these waves are augmented waves

when compared to the l one l two and l three so they are called as unipolar limb leads

here also the right leg serve as a earth a think purpose it act as a reference electrode

next we move on to the unipolar chest leads unipolar chest leads name indicate these

leads are placed over the precordial surface it is indicated as we to v6

v1 v1 is placed at the level of fourth intercostal space nearer to the

sternum v1 right fourth intercostal space nearer to

the sternum v2 exact opposite to the v1 but on the left hand side so the

location for v2 is left fourth intercostal space nearer to the sternum

next we move on to the v4 we can see v3 later v4 is placed at the fifth intercostal

space left hand side at the level of mid clavicular line mid clavicular line is an imaginary line

that falls from the center of the clavicle downwards towards

thorax so v4 is placed at left fifth intercostal

space at the level of mid clavicular line now

v3 v3 has to be placed just center in between v2 and v4 so v3 is placed between v2 and

v4 next we move on to the v5

v5 is also placed at the same plane as v4 but at the level of anterior axillary line

anterior axillary line is also an imaginary line in the front of the axilla so same plane at the as v4 but

little lateral at the level of anterior axillary line is v phi

next lead is v6 v6 is also in the same plane v4 and v5

but at the level of mid axillary line okay

mid axillary line so the summary of the leads are l 1 from left arm to the right arm that

is the potential difference between left arm to the right arm l2

from the right arm to the left leg l3 from the left arm to the

left leg so the potential difference of between these two leads are recorded as l 1 l 2 and l 3.

the next unipolar limb leads are avr for right arm avl for left arm avf for left foot the precordial leads a v1

to v6 so these are the 12 lead system in a standard ecg

we can ask why these 12 leads are being used what is the importance these 12 leads viewing the

heart in at a different angle till now we saw about various lead system that is various leads 12

leads what are the names of the 12 leads and where it has to be placed now we can get a question why there are

12 leads what is its importance the importance of 12 ecg leads are it records the electrical activity of the

heart from different angle and therefore they align with the different anatomical areas of the heart

for example any two leads which view a particular area or particular

wall for example if any two leads view the anatomical wall then they are said to be contiguous

in the 128 system there are groups of leads which view the same wall of the heart they are said to be contiguous

example septal leads scepter leads inceptor leads v1 and v2 are said to be contiguous

if any two leads view anterior wall then they are called as anterior leads example in the 12 lead system v3 and v4

are said to be anterior leads similarly lead to lead 3 and avf as inferior leads

lead 1 avl v5 and v6 are lateral leads so all the leads view the heart from a different angle it gives a graphical

representation through ecg machine till now we saw 12 lead system in ecg

and their placement and their importance now we moving on to the additional lead placement there are several additional

lead placement techniques but here i am going to say only a few important additional lead placement that is the

same electrodes are being placed in a different areas of the precordial surface and we are going to learn one by

one so right sided ecg electrode placement is one of the additional lead placement

here a complete set of right sided lead is obtained by placing v1 to v6 in a mirror image position on the right side

of the chest so which is the same precaudill recording but it is opposite to the standard ecg precordial recording

so what is the importance it is more important especially in the case of diagnosis of

right ventricular myocardial infarction where the amplitude of st elevation is higher when

compared to the normal precordial chest leads

next additional lead is v4 recg lead placement here use of right sided precordial lead

v4 r is alone kept on the opposite side when

compared to the normal precordial ecg recording v4 is kept exactly opposite at right

side it is helpful for the diagnosis of right ventricular involvement in inferior

myocardial infarction next additional lead is posterior leads in posterior leads they are indicated as

v7 v8 and v9 v7 is placed

at the same level of v6 but at the level of posterior

axillary line next v8

v8 is placed in the same level of v6 in the left hand side but at the tip of scapula

next lead is v9 which is placed at the level of v6 on the left side

but nearer the para spinal region that is left paraspinal region in the same horizontal plane as

v6 so what are the importance of these posterior leads the degree of st

elevation seen in v7 to v9 is required to make the diagnosis of posterior

myocardial infarction next additional lead placement is levis lead

this lead is useful in detecting the atrial activity and its relationship to the

ventricle activity the electrodes for lewis lead are the same limb lead electrode

but the electrode placement example right arm limb lead electrode placed

over the manubrium left arm limb lead electrode placed over the

right fifth intercostal space left leg electrode placed over the

right lower costal margin the recording of levi's lead

red in the lead one of the ecg it is important especially in during the atrial flutter waves that is for the

diagnosis of atrial flutter this leaves lead is highly beneficial another

additional lead system is three electrode system here in the three electrode system three

limb electrodes right arm left arm and left leg are used and the monitor displays the bipolar leads that is lead

1 lead 2 and lead 3 the next additional lead system is 5 electrode system as the name indicates

phi here it uses five electrodes right arm right leg

left arm left leg and any one chest electrode depending upon the requirement

so these are the additional lead system the other additional leads are esophageal lead in esophageal lead

a lead inserted into the esophagus approximately 35 centimeter from the external nostrils

this ecg lead is beneficial especially in the diagnosis of atrial flutter

and wolf parkinson syndrome next is intracardiac electrocardiogram here ecg along with the standard ecg

electrodes some added electrodes are placed inside the heart that is two to four intracardiac electrodes are added

via cardiac catheterization a record of changes in the electrical potential of specific

cardiac loki is done with the help of intracardiac electrocardiogram this slide shows

lead to ecg that is in a recording of 12 lead ecg system if i take a lead to recording alone it will represent a

graphical representation like this if you see the graphical representation of a lead to ecg i can see some waves

some downward deflection positive waves some negative waves the waves are labeled as

p wave q wave r

s t and u

generally this qrs is called as qrs complex so any ecg recorded from a 12 lead ecg system it contains p wave qrs

complex t wave and u wave but in some cases u wave may not be visible

but still u wave has to be considered so with this i am concluding this module

we learnt about what are the ecg lead system but

this presentation is to be used as an adjunct to other learning methodology and not a substitute for appropriate

clinical training and qualification i would like to thank

my institute chettinad hospital and research institute and swayam neptal for giving me an opportunity to present

this session the sources of references are gayten and genong thank you