now let's suppose we go to the next stage
first electrical activity second third fourth and here is the fifth now
let's take this electrical graphs electrical vectors right of this heart and apply a
galvanometer there you remember the galvanometer from last lecture let's see it here is this man
he's very happy you know why he's happy
because he understands the ecg to some extent now she's very very happy okay
right i've shown a very big heart there but actually heart is of course smaller
but what i'm showing that this is the heart of this person these are the electrical events in
his heart during one cardiac cycle i have not shown the ventricular repolarization
that i will discuss later right now what we do we apply our galvanometer to this person
and see what are the needle fluctuation due to these vectors it will be fun
now
let's suppose that here is
our galvanometer
and we break down its window and take its needle out
this is that global meter here it has we apply let's suppose positive electrode on
the fourth left foot suppose we apply the positive electrode here and we apply the negative electrode
what is this
right arm so the same galvanometer we have applied to this person and we want to see what
what type of needle fluctuations are produced by the electrical activity of the heart because when
during one cardiac cycle electrical vectors are produced due to electrical events and
these electrical vectors and electrical potentials are very faithfully conducted to the body surface
through the body fluids the electricity with small electrical activity of the heart
produces very miniature voltages up to skin what is a very good volume conductor
right even very small electrical currents which are produced during the
one cardiac cycle or each cardiac cycle they are very faithfully conducted up to the body surface
it is such a volume good conductor if you don't trust that body is a good conductor you can do a
small experiment put your finger into any electrical plug suddenly you will know that
body is very good conductor take care don't do it anywhere all right now listen so electrical
activity of heart come to the body surface so we can apply the electrode on the body surface
and pick up the electrical activity which is going on deep into heart is that right now listen
we could we have applied the positive electrode on the foot because it is convenient to apply here
but actually whatever electrical current is coming to this point
whatever electrical current is coming to this point this will be conducted to the foot so it
means applying the electrode to the foot is equivalent to applying the electrode at the
junction of the left lower limb and the trunk in the same way when you apply the electrode on the
right arm actually position of electrode that position of the electrode will sense the same
electrical activity which electrode could sense when electrode is applied at the junction of
right upper limb and the trunk right again let me repeat it for key convenience i have
applied the negative electrode here and positive electrode on the foot is that right basically
whatever electrical activity is here is the same which is conducted in the arm so either you put
electrode here or here it is it will be doing the receiving the same result in the same way
you apply the electrode here or you apply the electrode on the foot right what really happens
that electrical activity which is reaching here right that will be recorded is that right now
so for practical purposes we can say that positive electrode which is on the foot is
actually here right this is the positive electrode and negative electrode which is on the right
what right arm right this is practically here
right now these are the positions of the electrodes and we have to see that how these
vectors will move this needle let's do a little scientific work what we do we take a paper roll
roll of paper and
this is a roll of paper
is that right this is paper roll we put it vertically and here let's suppose
this is a wooden stand and we have applied this paper roll on the stand
is that right we have we are making ecg machine by one moving paper roll and a galvanometer
that's the simplest form of ecg machine here is a small motor and this motor is
constantly moving the paper in this direction right so paper is moving in this way
is it right paper is moving in this direction now what we do we are ready with our ecg machine this
was galvanometer very sensitive one put positive electrode here here negative electrode on the
right side of the trunk right upper side clear mode rule is speaking on the right
arm now we brought this needle out we brought this needle out and let's suppose on this needle
tip we put some black ink we put a black ink is that right and we make the switch on
and this paper start moving under the needle when this paper is moving under the needle if
there is no electrical activity in the heart listen now carefully rather you have to answer
if there is no electrical activity in the heart right no vectors are there
do you think this needle will fluctuate or it will remain at a steady point neutral position so when
there is no electrical activity in the heart these electron don't sense anything noodle remain at the
neutral position because paper is moving under the needle so it will make a straight
line is that right then suddenly s note fires suddenly asynod fire and first electrical event
start that is the spreading of depolarization on atria and which electrical vector is produced
initial vector is produced what is produced actual vector is produced when this atrial
vector is produced this atrial depolarizing vector is moving towards the positive electrode or away
it is moving towards the positive electron so deflection should be positive you know that when
positive charges move to the positive electrode deflection will be positive so needle will move
upward remember that this side is this is zero position here it is positive side and this is
negative side deflections which are upward the positive deflection deflections which are
downward they are negative deflection so when a tree is undergoing depolarization a small vector
is moving towards the positive electrode so there will be small positive deflection and
it is moderate velocity so this will be needle will go upward positively with moderate speed
not fast speed so as paper is moving under it so during actual depolarization when needle is
gradually lifted upward as this vector is moving towards the positive electrode this
wave will be generated on the paper this wave represent what thing atrial depolarization
this wave is generated by the needle in response to atrial depolarizing vector
right and this is a slow wave not a fast wave is that right and a small deflection because atrial
vector is small one what is the next electrical event now here completely depolarized when atrial
completely depolarized needle will come back to neutral position clear now the next electrical
event is what is this av nodal depolarization when av node is undergoing depolarization do you
think there is any significant current which will move the needle no so we say this electrically
heart is silent we say there's av nodal silence so when current is conducting through ev node these
electrode don't pick up any activity so needle will remain straight so after the end of the
atrial depolarization and before the beginning of ventricular depolarization current is held
in av node but that current activity is so small that needle is not electrode don't sense anything
needle will not move so there will be a straight line so this straight line represent that
needle is not fluctuating why the needle is not fluctuating because right now current is
passing through av node and if you notice a small tissue electrical activity is so small
the needle does not fluctuate is that right so this small piece right this represent conduction
through av node is that right what is the next electrical event suddenly current is released into
perkins system as soon as current is released into per kenja system ventricular depolarization start
depolarization wave spreads through the ventricle the first electrical event is
septal depolarization now when ventricular septal is undergoing depolarization a
small vector is produced so there will be small deflection but this vector is moving
towards the positive electrode or this vector is moving away
because this vector is moving away from the positive electrode so deflection will be negative
but small deflection and because it is fast vector so there's small deflection which is negative
but slower fast fast so needle will move when ventricular deprivation is there needle will move
fastly a little deflection down and then come back so when it will rapidly move it will make a
wave like this so this wave this neutral fluctuation represent
ventricular septal depolarization is that right the first wave is called p wave so
p wave represent atrial depolarization after that this straight line represent
conduction through av node then this is showing the onset of ventricular depolarization
and the small but fast negative wave here it is representing
what ventricular septal depolarization right now what is the next electrical event
next electrical event is current is going now to the major part of the both ventricles and both
ventricles when major ventricular depolarization is start going on now the next electrical event
is after the septual depolarization there is major ventricular depolarization during major
ventricular depolarization a very strong vector is produced downward and leftward strong and fast
the strong and fast vector which is representing the electrical activity in major ventricular
depolarization this vector is moving towards the positive electrode or away it is moving towards
the positive electrode so deflection will be negative or positive it will be positive because
positive charge is moving towards the positive electrode so deflection will be positive number
one number two deflection will be slower fast fast and deflection will be small or big so what
happens strong big deflection in a fast fashion so when needle when major ventricular deposition is
going on a very strong and fast vector approaching the positive electrode needles suddenly move
strongly positively but fastly so needles slowly move upward and comes down so this
this wave is this is called r wave and this wave is due to
major ventricular depolarization this r wave is produced by the sudden upward deflection of
needle and this deflection is fast it reaches rapidly to the p can come down and what is
it is representing it is representing the major ventricular depolarization which is
strong depolarization but fast depolarization and deposition is moving downward and leftward
toward the positive electrode so because deposition moving towards the positive electrode
deflection is positive because it is strong vector so deflection is high amplitude and because fast
vector so deflection is sudden up and down am i clear after that what is the next electrical event
next electrical event is the last electrical event in spread of ventricular depolarization
so last electrical event is now current goes to the basal part of the ventricle
when depolarizing current reaches basal part of the ventricle it produces small vectors
which are moving upward and rightward now listen carefully these basal ventricular depolarization
produces small vectors which are moving upward and rightward so these vectors are moving towards the
positive electrode are away away so when these vectors are generated they are moving away from
the positive electrode they will produce a negative deflection and because these are
small vectors so they will produce small negative deflection and fast vector so there will be small
negative but fast deflection so needle will move a little down and then back so that will produce
small negative deflection is that right and this is s wave so s wave is representative of
s wave is represented of representative of basal ventricular depolarization now let us look at
whole this complex the three waves q r s three waves together are called qrs complex
again listen q wave represent here in this uh study which we are doing q wave is representing
ventricular septal depolarization r wave shows the depolarization spreading over major ventricular
part and s wave is showing the depolarization spread into basal ventricular part am i clear