ECG
From A to Z
Master ECG
Basic Concepts + Advance ECG
From Video Lectures of Dr. Najeeb
By a Kurdish Medico
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How to study this lecture
▪ All of this lecture is transcribed from video lectures of Dr. Najeeb in an
organized way and in somewhere I have taken only a short part and added up
my notes in order to be easy.
▪ You have two way to study:
First, you can watch the videos before and then read the lecture, however the
videos may be too long so you can make the speed of the videos to X2.
Second, you can just read the lecture and I’m pretty sure you face no problem
and I made it in that way.
▪ I put clinical point with each part which my main purpose is to make link
between basic concepts and its clinical ECG.
▪ In the ends of the lecture there is ECG interpretation, therefore it will be easy
for you because you had a background about clinical points.
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Outline
_______________________
▪ Definition
▪ Indications
▪ Electrical activity of the heart
▪ Different ECG patterns
▪ QRS complex Nomenclature
▪ Limb leads
▪ Chest leads
▪ Variants in the Electrical position of heart
▪ How to read an ECG in a systematic and effective manner
▪ ECG artifacts
▪ Some uncommon ECG abnormalities
▪ Summery
▪ Recommendation
▪ Resources
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Definition
______________________________
▪ ECG is means electrical activity of the heart is graphically presented or graphic
presentation of electrical activity of the heart.
▪ Though the basic principles of that era are still in use today, many advances in
electrocardiography have been made since 1937. Instrumentation has evolved
from a cumbersome laboratory apparatus to compact electronic systems that
often include computerized interpretation of the electrocardiogram.
▪ The word is derived from the greek electro, meaning related to electrical
activity; kardia, meaning heart; and graph, meaning "to write".
▪ Willem Einthoven was a Dutch physician and physiologist. He invented the first
practical electrocardiogram in 1895 and received the Nobel Prize in Physiology
or Medicine in 1924 for it.
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Indications
________________________
▪ Symptoms: Palpitation, cyanosis, chest pain, syncope, seizure, poisoning.
▪ Signs: tachycardia, bradycardia, hypothermia, murmur, Shock.
▪ Evaluation of rheumatic heart disease, congenital heart diseases.
Evaluation of suspected electrolyte imbalance.
Evaluation of cases like drowning, electrocution During cardiopulmonary
resuscitation (CPR).
Evaluation of patients with implanted defibrillators and pacemakers To detect
myocardial injury, ischemia, and the presence of prior infarction as well. Effects
and side effects of pharmacotherapy.
Evaluation of metabolic disorders processes among others.
▪ Contraindications: No absolute contraindications.
patient refusal, exist. patients allergies to adhesive used to affix the leads 6
Electrical activity of the heart
_____________________________________
Resting membrane potential = No ion movement:
▪ Is the electrical voltage difference between the inside of the membrane and
outside of the membrane normally resting cells of the ventricular.
▪ The resting potential tells about what happens when a neuron is at rest.
▪ In the resting condition this myocardial cell membrane electrically
negative inside.
▪ The resting membrane potential is minus 90 Milli volt.
7
The cardiac action potential = Movement of ions:
▪ Is a brief change in voltage (membrane potential) across the cell membrane of
heart cells. This is caused by the movement of charged atoms (called ions)
between the inside and outside of the cell, through proteins called ion
channels.
▪ The cardiac action potential differs from action potentials found in other types
of electrically excitable cells, such as nerves. Action potentials also vary within
the heart; this is due to the presence of different ion channels in different
cells .
▪ De polarization (loss of polarization) means in which the cell's internal charge
becomes more positive.(loss of negativity).
▪ Repolarization means where the internal charge returns to a more negative
value.
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When there is appropriate stimulation to a myocardial cells suppose
ventricular myocardium cell so what will happen?
▪ If you stimulate the cell then some cations will come in some positive charges
will come in.
▪ This will take the resting membrane potential towards less negative value
because this positive charges will neutralize the electronegativity, is the right
to some extent.
▪ It become minus 80 and then become minus 70 millivolts.
▪ It moves towards the threshold potential and let's suppose in this cell
threshold potential is minus 70.
▪ Threshold potential is the potential at wedge.
The arrow indicate stimulation
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▪ As soon as it touches the threshold voltage gated sodium channels open up
as soon as voltage-gated sodium channels open in the cell membrane a lot of
sodium comes in.( Normally sodium is more in the outside of the cell and
normally cell is electrically negative inside ).
▪ As more and more sodium is coming in progressively neutralizing the
electronegativity, then the threshold potential which was minus 70. It will
become minus 60, minus50, minus 40 and eventually, it will become ZERO.
▪ This membrane potential is progressively going towards positive value
initially, It is losing the electronegativity and eventually it may become
positive, even it may become plus 10.
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So what has happened?
▪ On the appropriate stimulation lot of potassium come in and these incoming
cations neutralize the electronegativity of the membrane.
▪ So inside of the membrane, which is initially negatively polarized it is lost as
negative polarity or we simply say membrane is depolarized.
▪ We say membrane , please membrane is depolarized, so this event is called
depolarization current once depolarizing current is produced and we say
cell is depolarized.
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What is the next electrical event?
▪ Next event has the depolarization sensitive calcium channels.
▪ And potassium channel both start opening.
▪ Now these red channels are calcium channels and this green channels are
potassium channels.
▪ Normally potassium is more inside the cells as compared to the outside, and
calcium is more outside the cells as compared to the inside.
▪ You stimulated the cell undermanned lot of sodium influx that led to
phenomenon of depolarization then depolarization sensitive calcium channels
and potassium channels opened.
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▪ Potassium will start moving to outside. (because normally high inside)
▪ When there is efflux of potassium means they'll start losing K+ and it comes
towards electro negativity.
▪ But as soon as it is around zero, voltage calcium channels also open.
▪ For a brief duration Potassium is positive charges are lost and calcium as
positive charges are gained to the inside of the cell.
▪ So loss and gain of cations balances the potential, so there is no net change
in potential.
▪ But as time is passing by calcium channel start closing.
▪ And as time passes by potassium channels become more and more active so
potassium losses become very heavy. (more positive charges are going out)
▪ As a result cell will again start developing electronegativity until membrane
potential again becomes at 90 milli volts which come back to its
negative polarization it means membrane is repolarized due to potassium
efflux membrane has gone to the phenomenon of repolarization.
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▪ When one cell undergo depolarization the cations(sodium) some of these
cations which have come into the cell, they go to the next cell through
gap junctions which are very special connections between the adjacent
myocardial cells which also called electrical windows.
▪ So it means depolarization of one cell lead to the depolarization of second cell
and when second cell is depolarized the cell gate gains lot of cations then
trickles the cations into third cell and then third cell will depolarize the next cell
so each cell undergoes the process of depolarization and repolarization.
▪ The membrane fluctuate from resting potential to depolarization and then it
fluctuates back to repolarization this depolarization and repolarization they are
moving in the cell it called action potential.
NO ion movement
Resting membrane
stimulation
Ion movement
Cation efflux
Ion movement
Cation influx
Depolarization
Repolarization
NO ion movement
Resting membrane
Action potential
Cation influx & efflux
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▪ When cells are undergoing depolarization it means cell is gaining cations
usually sodium.
▪ In case of atrial and ventricular cells depolarization they gain sodium cations.
▪ But depolarization of SA node and AV node is not sodium-dependent that is
calcium-dependent.
▪ So it means when we say that atrial tissue or ventricular tissues are drawing
depolarization it means those tissues are gaining sodium and if we say
SA node and AV node are depolarizing it means they are gaining calcium but
anyway depolarization is whenever cell is appropriately stimulated a lot of
sodium or calcium come in and depolarizes the cell .
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Quick recap
▪ A resting myocardial cell it was having resting membrane potential of minus
90 milli volt, so when it was appropriately stimulated some cations trickled in
entered in these cations took the resting membrane potential at threshold
potential which voltage-gated sodium channels open lot of sodium comes in
and then potential goes toward loses all the electronegativity and goes
towards the positive side this phenomenon is depolarization membrane
which is a depolarization in ventricular and atrial cells.
▪ For a brief time potassium is going out but at the same time calcium is coming
in, so cations are lost as well as cations are gained so there is no voltage
difference we say that electrical potential is showing plateau phase but
eventually calcium channels shut down and potassium channels become
progressively more open so lot of potassium leaks out and due to heavy
losses of positive ions membrane become progressively electronegative inside
and potassium keep on going out until the membrane voltage goes back to its
resting negatively polarized state so we say that there is membrane has gone
under the phenomenon of repolarization.
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Clinical Point
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How ECG machine works on the principles of galvanometer in a
piece of myocardial tissue?
▪ Galvanometer machine this is a very small instrument and this electrical
instrument has one positive electrode and one negative electrode and the
function of this galvanometer is to detect the electrical activity in any object
where it has applied.
▪ We will remove a piece of myocardium from ventricle and apply
galvanometer machine on that and we will see that electrical activity in that
piece of myocardium how lead to the fluctuations in the needle of machine.
▪ You must remember all the myocardial cells are connected with each other
through electrical Windows which are called gap junctions.
Galvanometer 21
▪ When there is no electrical activity in this piece of myocardium the needle of
this galvanometer remains that neutral position or needle(pointer) to remain
at zero position.
▪ If there is no movement of electrical charges there is no depolarization nor
electrical activity.
▪ If it is not stimulated it all the cells are displaying resting membrane potentials
it means all the cells are electrically negative.
▪ Suppose this one end of the piece is point A (left side) has negative electrode
and other end point B (Right side) has positive electrode.
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This time we give some electrical stimulation to point A (left side).
▪ If there is appropriate stimulation cells will become depolarized and become
electrically positive so first group of cells when they are stimulated they
undergo depolarization they will stimulate the next group of cells through the
gap junctions.
▪ By stimulating at this point, these cells at this point become depolarized and
the wave of depolarization start moving from point A to the point B within
the myocardial cells so naturally when we say that wave of depolarization is
moving it means (cationic influx or positive charges are moving), so
membranes are becoming electro positive progressively.
▪ Positive charges are moving towards the positive electrode the needle will
deflect positively. (This is principle number 1).
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▪ To represent the force of pointer(electrical forces) of the galvanometer we
use Vector. (The thick green arrow in previous slide image)
▪ The vector is pointing towards the direction in which depolarization is moving.
▪ The length of the vector should be proportionate to the power of the force if
electrical forces (electromagnetic field)of depolarization is more vector has to
be long. (Next slide image)
▪ When depolarization is going on head of the vector is showing positive sign.
▪ NOTE// When it is completely depolarized from one point to the next point
there are no further movement of the charges it means this vector will
disappear and needle will go back to its neutral position(ZERO), because they
could not sense anything because all of it was electro positive and no
movement of the ions chemically.
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This time myocardial tissue is double thickness
▪ If you have increased the thickness of the myocardial tissue then it means
total number of cells will more.
▪ If we stimulate a thicker myocardium more sodium is going in when more
sodium is going in then naturally stronger vectors are produce because more
number of cells and more membranes are undergoing depolarization.
▪ In previous thinner myocardium amount of the depolarizing current is
small(less cells) so vector is small here myocardial tissue is larger and thicker
so when you depolarize it the depolarizing currents are stronger.
▪ Clinical Point Atrial myocardium is thin so produce weak positive deflection
and ventricular myocardium is thick so the deflection will be really strong.
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This time we give some electrical stimulation to point B(Right side).
▪ The wave of depolarization will be moving from B and to A and so naturally
the vector will be drawn to toward point A.
▪ Positive charges is moving away from the positive electrode (point A), so
deflection in the noodle should fluctuate to negative side.
▪ If positive charges are moving away from the positive electrode deflection is
negative.
▪ Positive charges are moving away to the positive electrode(toward negative)
the needle will deflect negatively. (This is principle number 2)
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Process of Repolarization
▪ When it become completely depolarized vector disappear and needle went
back to its neutral position then after some time process of repolarization will
start.
▪ NOTE// last point to depolarize is the first to repolarize later it means
repolarization occur at the last depolarized cell, we will explain this
phenomenon when we explain the T wave. (Right image)
▪ Repolarization will sweep from B to A and this time vector will be directed
toward point A so the head of the vector will be showing negative sign
because this is progressively establishing electro negativity.
▪ Negative charges is moving towards the negative electrode the deflection is
positive.(This is principle number 3).
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▪ In the ventricular myocardium there is the very special cell it is wide diameter
cell and this group of cells are they are very large so they offer less resistance
to the current flow current can move through it very rapidly(high velocity) we
say this is fast conducting cells such cells in are called Purkinje cells or Purkinje
system so the needle will move very rapidly.
▪ In the atrial myocardium current flow current can move Moderately
(moderate velocity) because tissue is moderately conducting cells so the
needle will move slowly here.
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Quick recap
▪ Principle number 1: Positive charges are moving towards the positive
electrode deflection is positive.
Weaker force
weaker deflection
Stronger force
stronger deflection
+++
Electrode
Electrode
++++
Electrode
Electrode
▪ Principle number 2: Positive charges are moving away to the positive
electrode(toward negative electrode) the deflection is negative.
++++
Electrode
Electrode
▪ Principle number 3: Negative charges is moving towards the negative
electrode the deflection is positive.
____
Electrode
Electrode
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Break
Please, review the clinical points before you go
“I never dreamed about success. I worked for it”
- Este Lauder
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What we studied previously was only in a piece of
myocardium now we are going to study the whole
heart that during one cardiac cycle in the heart which
electrical vectors are produced and how the ECG
machine needle moves and draws the ECG pattern.
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we are going to discuss further discussion in three phases:
1. What are the electrical events in the heart.
2. Different electrical events during one cardio cycle.
3. What type of electrical vectors and cardiac vectors are produced, eventually
how those cardiac vectors are translated into ECG pattern.
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SA(sinoatrial) node
▪ First electrical event.(Atrial depolarization)
▪ In beginning of the cardiac cycle SA node fires which generates the wave of
depolarization(electrical current).
▪ First of all the atrial cells which are near the SA node and the cells which are
adjacent to the SA node are stimulated.
▪ Wave of depolarization which is first produced in the cells near the SA node
then start moving to the next group of cells eventually sweeping from SA node
to o over all the atrial myocardium.
▪ The atrium vectors which are generated due to waves of depolarization are
moving downward and leftward( ) because position of the SA node is on
the right upper side.
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▪ Right atrium and left atrium they are syncytium so due to that reason
electrical current sweeps simultaneously on the right atrium and left atrium
right.
▪ All this these vectors depolarizing currents can be added together and they
will make one single vector which is directed downward and leftward.
▪ Remember the vector is representing the electromagnetic force.
▪ The atrial myocardium is thin so this vector will be small.(small deflection)
▪ Atrium do not have very specialized cells in fast conducting system so undergo
depolarization moderately so we say moderate velocity conducting.
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Drugs act on SA node
In the next slides I am going to show you
ECG abnormality of SA NODE.
Atrial tissues is normal but the problem
is in the SA node conduction
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AV(atrioventricular) node
▪ Second electrical event.
▪ When both atria are completely depolarized then depolarizing waves will hit
the fibrous anulus this fibrous tissue which is present between the atrium and
ventricle.
▪ AV node is the only electrical window between the atria and ventricle.
▪ This is not a very good conductor so most of the depolarizing current which
hit this fibrous partition will die out because from here from these points
depolarization cannot go down.
▪ Only those electrical depolarization which hit the AV node they will be taking
the current gradually to the ventricle.
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Why velocity of depolarization becomes slowed or stopped
in AV node for 0.1s?
That atria complete their contraction and fill the ventricle only when atrium has
completed their contraction then electrically ventricles should be stimulated so
that ventricle start contracting.
42
▪ AV node is very tiny myocardial tissue with a small tissue it will make a very
small vector.
▪ Because the electrical vector is very small that ECG machine will not pick up
electrical activity of AV node.
▪ So for practical purposes when a very miniature depolarization is passing
through AV node heart is electrically silent.
▪ It is like whispers and it does not talk so our machine cannot hear.
▪ Eventually no significant electrical vector is produced to fluctuate the needle it
means there is no deflection.(straight line)
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Drugs act on AV node
In the next slides I am going to show you
ECG abnormality of AV NODE (PR interval).
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(Mobitz 1 )
(Wenckebach)
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(Mobitz 2)
(Complete heart block)
A block above the His bundle produce a narrow
QRS complex escape rhythm, whereas those at or
below the His bundle produce a wide QRS complex
Fixed PR interval with sudden drop beat
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47
Caused by the presence of an abnormal accessory
electrical conduction pathway between the atria and
the ventricles. Electrical signals traveling down this
abnormal pathway (known as the bundle of Kent) may
stimulate the ventricles to contract prematurely.
The next slide shows Junctional rhythms
Junctional rhythms are a condition where
impulses for a cardiac cycle are initiated from
the AV node or bundle of HIS instead of the SA
node (sinoatrial node). Junctional rhythms get
their name from their origin of impulse, coming
from tissues at the junction between the atria
and the ventricles.
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For junctional rhythms look at lead II
Impulses coming from a locus of tissue in the area of the atrioventricular node, the "junction" between atria and ventricles.
Escape beats typically occur when a cardiac rhythm is too slow
and a backup pacemaker site initiates an electrical impulse
•If the P wave occurs before the QRS, the PR interval will likely measure shorter than normal (0.12 second).
•If the P wave is buried or occurs after the QRS, it cannot be measured.
PJC’s occur early and disrupt the
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underlying rhythm.
AV node
▪ A lot of very small cells and arranged right
angle to the direction of current flow.
▪ More cells need to more membranes to be
crossed so it is slow conduction.
▪ The number of gap junctions between the
AV nodal cells are very less.
▪ AV node depolarization is dependent on
calcium and calcium channel works slowly.
▪ Cells are less diameter so they offer more
resistance to the current movement.
▪ AV nodal cell resting membrane potential
is minus 60 millivolt.
Purkinje fibers
▪ Large cells and less cells.
▪ Less cells need to less membranes to be
crossed so it is fast conduction
▪ The number of gap junctions between the
AV nodal cells are too many.
▪ AV node depolarization is dependent on
sodium and sodium channel works fast.
▪ Cells are wide diameter so they offer less
resistance to the current movement.
▪ AV nodal cell resting membrane potential is
minus 90 millivolt so the cations will move
very rapidly in the cell which is more
electronegative.
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Purkinje system
▪ Through bundle of his current will come to the right bundle branch and left
bundle branch and these bundle branches are made of specialized myocardial
cells which are called Purkinje cells and these are specialized in fast
conduction.
▪ That ventricle depolarizes in three stages as the electrical current as soon as it
is released by AV node into Purkinje system first they will depolarize the
1- Septum of the ventricle. Then,
2- Apex of the ventricle. Then,
3- Base of the ventricle.
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1-Septal Depolarization
▪ Remember the interventricular septum upper part is fibrous and lower part is
muscular.
▪ Fibrous tissue make a sleeve around these bundle branches and this fibrous
covering on the bundle branches are acting as insulating layer. (in the same
way as wires have the rubbers leaving electrical wire they were rubber on
them rubber act as insulator.
▪ Septal myocardium is stimulated by the left bundle branch it is not stimulated
by the right bundle branch why because there are some connections here and
left bundle branch gives stimulation to the septal myocardium stimulated by
the left side.
▪ The wave of depolarization is produced in the ventricular septum in its lower
and left portion. (images in the next slide)
▪ The wave of depolarization moves from left to right and from down to up .
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▪ The vector is directed rightward and upward.
Because left bundle branch
stimulated left and lower portion of the myocardium from their current
moves to rightward and upward.
▪ The vector is small why because as compared to the big part of the ventricle
septum is a having small tissue number.
▪ It is fast conductor because they are in purkinje system.
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Rabbit ear or
M shape
In(RBBB) the conduction in the bundle to the right ventricle is slow. As the right ventricles depolarizes the left ventricle is often
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halfway finished and few counteracting electrical activity is left. The last electrical activity is thus to the right, or towards lead V1.
R wave not
present
In left bundle branch block (LBBB) the conduction in the left bundle is slow. This results in delayed depolarization
of the left ventricle, especially the left lateral wall. The electrical activity in the left lateral wall is unopposed by the
usual right ventricular electrical activity. The last activity on the ECG thus goes to the left or away from V1.
A new LBBB is always pathological and can be a sign of myocardial infarction.
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In left anterior fascicular block the current is
conducted to the left ventricle via the left posterior
fascicle, which makes the current travel
downwards and rightwards producing small R
waves in the inferior leads. Depolarization then
travels upwards and leftwards, producing large R
waves in the left-sided leads and deep S waves in
the inferior leads. The QRS is usually only slightly
prolonged.
In left posterior fascicular block the current is
conducted to the left ventricle via the left anterior
fascicle, which makes the current travel upwards
and leftwards producing small R waves in the
lateral leads and small Q waves in the inferior
leads. Depolarization then spreads down and right,
producing tall R waves in the inferior leads and
deep S waves in the lateral leads.
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2- Apical depolarization
▪ Ventricular wall divided into 3 layers which are the inner
myocardium(endocardium), middle layer(myocardium) and outer layer
(pericardium).
▪ Purkinje fibers are located in the deep pf endocardium.
▪ Inner myocardium will be first depolarized and wave of depolarization are
start in the endocardium then depolarization moves outward.
▪ Left ventricle is three times thicker than the right ventricle so naturally
depolarizing current are produced in the left ventricle stronger than that
produced in the right ventricle which relatively weak(vector is smaller).
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▪ Right vectors directed (downward and rightward ) represent depolarization
of right ventricle.
▪ Left vectors directed (downward and leftward) represent depolarization of
left ventricle.
▪ All these vectors are produced almost simultaneously.
▪ Because both of them are generated at the same times so they can be added
together and if we add them together the vector which represent the
depolarization of apex part of both ventricles downward and leftward.
▪ It means the net vector is directed downward and leftward.
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3-Basal Depolarization
▪ Eventually depolarization wave will reach to the basal area.
▪ Basal part of both ventricles they will be the last to be depolarized.
▪ The current will be moving from down to up and rightward.
▪ There will be small vectors made by the depolarization process in the basal
part of the both ventricles.
▪ NOTE// Remember all these electrical vectors which are produced in the
ventricles these are fast vector because ventricle they're special fast
conduction system which is called Purkinje system.
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Drugs act on ventricle
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Break
Please, review the clinical points before you go
“Hard work beats talent when talent doesn’t work hard”
-Tim Notke
63
Now we apply our galvanometer to a person and see
what are the needle fluctuation due to the vectors of
heart, so we apply positive electrode on the left foot
and the negative electrode on the right arm.
64
What we will do next?
▪ Number one during one cardiac cycle what are the electrical
events.
▪ Step number two how those electrical events produce the
electrical vectors.
▪ Step number three how different electrical vectors which are
called cardiac vectors how they produce ECG pattern.
65
How the ECG machine pick up electrical activity on
the body surface?
The electrical vectors which is an electrical potential 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 which is a very good volume conductor even very small electrical currents
which are produced during the one cardiac cycle they are very faithfully
conducted up to the body surface it is such a volume good conductor if you do
not trust that body is a good conductor you can do a mini small experiment
put your finger into any electrical plug suddenly you will noted body is very
good conductor take care do not do it (LOL).
66
Why we put electrodes of ECG in specific place?
We have applied the positive electrode on the left foot because it is
convenient to apply there but actually whatever electrical current is coming to
this point this will be conducted to 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 negative electrode
on the right arm actually position of electrode will sense the same electrical
activity which electrode could sense when electrode is applied at the junction
of it right upper limb and trunk.
67
In the next slides we will know how the ECG machine
generate the waves(on ECG paper) of heart
depolarization and repolarization with each electrical
activity through positive and negative deflection in
which they pick up the electrical current on left arm by
negative electrode and electrical current in left foot by
positive electrode.
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The beginning straight line
▪ If there is no electrical activity in the heart there is no vectors so the needle
remain at the neutral position because these electrons don't sense anything
new and the paper is moving under the needle so it will make a straight line.
69
P wave Normal duration is 0.06-0.11 seconds (1.5 to 2.75 small boxes)
▪ Suddenly as SA node fires, first electrical events starts that lead to atrial
depolarization so the vector (positive charges) is moving towards the positive
electrode(left foot) so deflection will be positive.
▪ First wave is called P wave so P wave represent atrial depolarization.
▪ You know that when positive charges move to the positive electron deflection
will be positive so needle will move upward.
▪ Small vector is moving towards the positive electrode(left foot) 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.
▪ After they completely depolarized, the needle will come back to ZERO.
70
Why atrial repolarization is not presented during the ECG tracing?
There is no wave and no fluctuation for showing the atrial repolarization
because when it really polarizing at that time QRS complex is being formed,
also the end atrial repolarization is weak electrical activity but QRS complex
which is representative of ventricular depolarization spread QRS complex is a
very strong electrical activity so atrial repolarization is masked or it is
covered and it is unable to move the needle independently so atrial
repolarization is not presented during the ECG tracing.
71
In the next slides I will show you ECG
abnormality of P wave which It means
the problem is in the atrial tissue
72
An interaction between initiating triggers, often in the form of rapidly
firing ectopic foci located inside one or more pulmonary veins, and an
abnormal atrial tissue substrate capable of maintaining the arrhythmia.
Is caused by a re-entrant rhythm. Typically initiated by
a premature electrical impulse arising in the atrial tissue
73
They are generally due to one of two mechanisms :
re-entry of current to av node or increased automaticity.
When a number of different clusters of cells outside
of the SA node take over control of the heart rate,
and the rate exceeds 100 beats per minute
74
PACs occur when another region of the atria depolarizes before
the sinoatrial node and thus triggers a premature heartbeat.
When a PAC follows every sinus
beat, the rhythm is termed atrial
bigeminy; if every third beat is a
PAC, the term is atrial trigeminy,
and if every fourth beat is a PAC,
the rhythm is atrial quadrigeminy.
Shifting of the pacemaker from the SA node to adjacent
tissues is identifiable on ECG Lead II by morphological
changes in the P-wave;
75
PR segment
▪ The next electrical wave event is AV nodal depolarization when AV node is
undergoing depolarization so we say this electrically heart is silent because
the electrode do not pick up any activity so needle will remain straight so
after the end of the atrial depolarization and before the beginning of
ventricular depolarization the current is held in AV node but that current
activity is so small that needle don't sense anything so needle will not move
and there will be a straight line.
▪ The straight line (PR segment) represent that needle is not fluctuating.
▪ NOTE// Ideally it should be called PQ segment but in some readings Q wave is
not seen so they call it PR segment.
76
▪ PR segment depression can be a signal for pericarditis or atrial infarction.
▪ PR segment elevation occurs in lead aVR in the setting of pericarditis.
77
Q wave
▪ The next electrical event, suddenly current is released into Purkinje system
as soon as current is released into Purkinje system ventricular depolarization
start.
▪ First electrical event in ventricle is septal depolarization, when the septal is
undergoing depolarization a small vector is produced so there will be small
deflection but this vector (positive charges) is moving away from the positive
electrode(toward right arm which is negative electrode) so deflection will be
negative.
▪ In Septal depolarization the needle will move fast with little deflection down
and then come back.
▪ Q wave represent ventricular septal depolarization
78
▪ Pathologic Q waves are a sign of previous myocardial infarction. They are the
result of absence of electrical activity. A myocardial infarction can be thought
of as an electrical 'hole' as scar tissue is electrically dead and therefore results
in pathologic Q waves.
LBBB: Absence of Q waves in lateral leads (I, V5-V6;
small Q waves are still allowed in aVL)
79
R wave
▪ Now the next electrical event is major(apical) ventricular depolarization
during major ventricular depolarization a very strong and fast vector is
produced downward and leftward
this vector(positive charges) is moving
towards the positive electrode(left foot) so deflection will be positive.
▪ A strong big high amplitude deflection in a fast fashion move upward and
comes down.
▪ R wave is represent major(apical) ventricular depolarization.
Current European (ESC) guidelines suggest that R-waves may also be used to diagnose
previous myocardial infarction. Criteria for pathological R-waves:
▪ R-wave 20,04 s in V1-V2 and R/S ratio 21 with concordant positive T wave in absence
of conduction defect.
▪ R/S ratio> 1 implies that the R-wave is larger than the S-wave.
80
S wave
▪ Last electrical event is now current goes to the basal part of the ventricles it
will produces small vectors which are moving upward and rightward.
▪ The vectors (positive charges) are moving away from the positive electrode
(toward right arm which is negative electrode) they will produce a negative
deflection.
▪ There will be small negative but fast deflection so needle will move a little
down and then back.
▪ S wave is representative of basal ventricular depolarization.
Deep S waves in LVH because it produces depolarization
current flowing away from these leads.
81
Those three waves together are called QRS complex
(Ventricular Depolarization):
▪ Q wave is representing ventricular septal develop.
▪ R wave shows that depolarization spreading over major ventricular part.
▪ S wave is showing the depolarization s into basal ventricular part.
▪ The normal duration (interval) of the QRS complex is between 0.08 and 0.10
seconds (2 to 2.5 small squares)
82
83
J-Point: The point at which the QRS complex finishes and the ST segment
begins. Used to measure the degree of ST elevation or depression present.
84
Drugs act on ventricle
In the next slides I will show
ECG abnormality of QRS complex
In which the problem is in the
ventricular tissues.
85
When the heart quivers instead of pumps due to
disorganized electrical activity in the ventricles
Arises from improper electrical activity in the
ventricles of the heart
86
87
Is widely thought to be triggered by reactivation of calcium
channels, reactivation of a delayed sodium current, or a
decreased outward potassium current that results in early
afterdepolarization (EAD), in a condition with enhanced TDR
usually associated with a prolonged QT interval
prolonged QT interval
88
89
90
VT vs SVT in wide complex tachycardia with LBBB and RBBB configuration
LBBB
91
where the heartbeat is initiated by Purkinje fibers
in the ventricles rather than by the sinoatrial
node, the normal heartbeat initiator.
92
Multifocal PVCs all look different from each other on
the same ECG. They occur at different intervals, at various
times in the QRS cycle, with different coupling intervals.
93
The physiological pacemaker of the heart is the sinoatrial node. If the
sinoatrial node is rendered dysfunctional, the AV node may act as the
pacemaker.. If both of these fail, the ventricles begin to act as the dominant
pacemaker in the heart. The ventricles acting as their own pacemaker gives
rise to an idioventricular rhythm
The accelerated idioventricular rhythm occurs when depolarization rate
of a normally suppressed focus increases to above that of the "higher
order" focuses (the sinoatrial node and the atrioventricular node). This
most commonly occurs in the setting of a sinus bradycardia.
94
ST segment Normally the ST segment is flat relative to the baseline.
▪ Electrically at the end of the QRS complex the whole ventricle septal area ,
major area and basal area all the complete ventricular tissue is completely
depolarized so there is no more electrical current moving.(See slide number 20)
▪ If there is no current moving( plateau phase) the needle will not move.
▪ Until this remains completely depolarized needle will not show any
fluctuation it will remain at neutral position(ZERO) it will be a straight line.
▪ ST segment(straight line) represent that needle is not fluctuating.
95
Most common causes of ST elevation is:
▪ STEMI (in specific leads)
▪ Pericarditis(in all leads)
▪ Printzmetal angina.
Most common causes of ST depression is:
▪ Myocardial ischemia
▪ Digoxin effect(sagging down sloping)
▪ Hypokalemia(widespread down sloping).
96
T wave
▪ So after sometime repolarization process will start and in the ventricles
repolarization start from outer layer of ventricular wall.
▪ The rule is that the part which is depolarized last will repolarizes first.
▪ The direction of repolarization is opposite to the direction of depolarization
because depolarization was from inside to outside and repolarization is from
outside to inside.
▪ During repolarization outer myocardial cells start losing the potassium from
the cell to the extracellular fluid and cells again become electrically negative
or we say they are again polarized negatively.
97
▪ Repolarizing current makes a single important vector which is moving
rightward and upward carrying negative current in its head.
▪ When ventricles are repolarizing the vector(negative charges) is moving
towards the negative electrode(right arm) so the deflection will be positive.
▪ The repolarization is a moderate speed process so needle will move gradually
the wave is produced positive but gradual wave and this wave called T wave.
▪ T wave represents ventricular repolarization.
98
Why outer ventricular myocardium repolarizes first and the inner
myocardium repolarizes last?
During QRS and ST segment ventricles were in contracting so when ventricles
contract strongly the blood flow or capillary bed the inner myocardium
compressed by middle and outer myocardium and the blood again when
ventricle squeezes, the outer myocardium compresses the middle myocardium
and inner myocardium because contraction is inward so what will happen that
blood flow in inner myocardium will be stopped but blood flow to outer
myocardium will be better than inner myocardium because blood flow is
maintained better in outer myocardium during the systole so repolarization
start from the outer myocardium.
99
Why the depolarization is a fast process but repolarization is
a slow process?
Because sodium channels which major channels in starting of depolarization
are fast channels but potassium channels which is major channels in
repolarization are not that fast.
100
Process of ventricular repolarization?
▪ When septum has started its repolarization it has not finished yet, the major
ventricular repolarization start and it has not finished yet, the basal
repolarization start so because the repolarization is a slow process so three
area of the ventricles when they start the repolarization their repolarizing
current are overlapped in their time so septal repolarization, major
ventricular repolarization, and basal repolarizing vectors they are almost
overlapping with each other.
▪ Then the strongest vector will move the needle and strongest vector of major
ventricular repolarization, septal repolarization and basal repolarization is
fused.
101
▪ T waves are considered tall if they are:
> 5mm in the limb leads AND > 10mm in the chest leads.
Hyperkaliemia (“Tall tented T waves”)- Hyperacute STEMI
▪ T waves are normally inverted in V1 and inversion in lead III is a normal variant, but
inverted T waves in other leads are a nonspecific sign of a wide variety of conditions,
may be considered to be evidence of myocardial ischemia if: At least 1 mm deep,
Present in ≥ 2 continuous leads that have dominant R waves (R/S ratio > 1), Dynamic —
not present on old ECG or changing over time.
▪ Flattened T waves are a non-specific sign, that may represent ischemia or
electrolyte imbalance.
▪ Biphasic T waves have two peaks and can
be indicative of ischemia and hypokalemia.
102
Quick recap
▪ P wave represent atrial depolarization.
▪ PR segment is representing activity of AV node in which the needle is not
fluctuating.
▪ Delay Q wave is showing the onset of ventricular depolarization and it
specifically represent ventricular septal depolarization.
▪ R wave is representative of major ventricular depolarization.
▪ S wave is representative of basal ventricular depolarization.
▪ QRS complex represents spread of ventricular depolarization
▪ ST segment is representing that that time during which all the ventricle is
completely depolarize and yet repolarization has not started.
▪ T wave represents ventricular repolarization.
103
104
Break
Please, review the clinical points before you go
“The best deal for a Doctor in his/her life is
Work hard for ability and get
Responsibility free.”
-Khushboo Patel
105
Different ECG patterns
________________________________
Wave:
▪ Waves are flux pattern produced due to deflections of the needle during the
ECG recording for example when needle is deflected upward P wave is formed
but T wave is produced with deflection down.
▪ Wave means there is electrical activity either depolarization or repolarization.
▪ Types of wave: P wave – Q wave – R wave – S wave – T wave.
106
Straight line
▪ It find between the waves.
▪ Also called isoelectric line.
▪ Straight lines are drawn by machine when the needle is not fluctuating so it
does not recording any electrical activity, but the paper is moving under the
needle so it makes a straight line.
▪ PR segment : start at the end of the P wave and end that the beginning of
QRS complex.
▪ It signifies that electrical activity when current is passing through AV node.
107
▪ ST segment: starts at the end of the QRS complex and end at the beginning
of T wave.
▪ It shows when ventricle is completely depolarized and there is no current
moving no vector moving through the ventricle but phase of repolarization
has not started there.
▪ It represent a plateau phase in which cations are going into cell as well as
cations are coming out of the cell, so no significant electrical changes in the
potential so electrode do not record any significant electrical activity in the
heart due to that reason needle remains static it does not fluctuate and a
straight line is made.
▪ TP segment: isoelectric line is the line between the
T wave and the onset of next P wave, ECG recorders
pointer draws the isoelectric line when there
no electrical activity in the heart.
108
Interval
Normally this interval is 0.12 to 0.20 seconds (3 to 5 small boxes) in adults,
longer in elderly people
▪ More than one wave together or wave plus segment are called intervals .
▪ PR interval: from the beginning of the P wave up to the beginning of that
QRS complex.
▪ PR interval = P wave + PR segment, but PR segment = only the isoelectric
line with no wave.
▪ PR segment there is only conduction through the AV node but if we are talking
PR interval it means we are talking about the spread of depolarization the
atrium plus conduction through the AV node just before the onset of
ventricular depolarization.
▪ As QRS complex start PR segment PR interval terminates.
109
▪ QRS interval because there is more than one wave so this can be regarded
as interval is the QRS interval is the duration during which current is spreading
over septum, major and basal ventricular depolarization.
▪ QT interval: Normally, the QT interval is 0.36 to 0.44 seconds (9-11 boxes).
▪ start from here at the beginning of QRS and end at the end of T wave.
▪ It shows ventricular depolarization then the duration for which heart remains
in plateau phase of action potential and then the onset and termination of
ventricular repolarization.
110
Causes of a prolonged QTc
(>440ms)
▪ Hypokalemia
▪ Hypomagnesaemia
▪ Hypocalcemia
▪ Hypothermia
▪ Myocardial ischemia
▪ ROSC Post-cardiac arrest
▪ Raised intracranial pressure
▪ Congenital long QT syndrome
▪ Medications/Drugs
111
NOTE:
Ideally it should be called PQ segment and PQ interval but
when we change the position of the electrode for different
leads sometimes Q wave is not drawn due to that reason
conventionally doctor started calling the segment
PR segment and PR interval.
112
U wave
▪ Is due to electrical activity in the ventricular papillary muscle is out of phase
with the rest of the ventricle so ventricular depolarization and repolarization
terminate and if there is after that there is electrical activities being shown
and that pixel reversals of the ventricle they may make small vectors which
flow fluctuate on needle little bit and that may lead to the presence of
independent U wave.
▪ When ventricle contract mitral valve closes but if there are no papillary
muscles then due to strong contraction of ventricle mitral valve may revert
and blood me go back to regurgitate into atrium.
▪ The U wave is a > 0.5mm deflection after the T wave best seen in V2 or V3.
Classically U waves are seen in various electrolyte
imbalances, hypothermia and secondary to antiarrhythmic
therapy (such as digoxin, procainamide or amiodarone).
113
Timings and duration of different ECG pattern
1 big square = 0.20s
1 small square = 0.04s
1 small square = 0.1mV
ECG pattern is drawn by the Machine on a special calibrated paper.
▪ Paper is moving under the direction of pointer movement
▪ The speed of the rolling paper is adjusted in such a way during one minute
300 big squares pass under the pointer it means all the electrical activity of
the heart during one minute will be drawn over 300 big squares
▪ 300 big squares = 60 seconds = 1one minute
▪ So 1 big square = 60/300 = 0.20s.
▪ And 1 big square = 5 small squares = 0.20s.
▪ So 1 small square = 0.20/5 = 0.04s.
114
115
▪ P wave is drawn over two and a half small square It means P wave is drawn
over 0.10s also it means electrical current from the SA node it took 0.1s to
spread over both atria and reach to AV node
▪ PR segment that is also two and a half small square it means that the
duration of PR segment 0.1 second so the current to pass through AV node it
will need 0.10 second.
▪ 0.04(1 square) + 0.04(1 square) + 0.02(half of square) = 0.10
▪ So when your heart rate is about 72 per minute P wave takes two and a half
small square PR segment take two and a half small squares.
116
▪ PR interval =P wave plus PR segment, the duration two and a half small
square plus two and a half small square equals five small square or one big
square so it become 0.20 seconds with some variation from person to
person but just remember the middle values.
▪ QRS interval when QRS complex is coming that again is two and a half small
square it means what is the duration of QRS complex 0.10 second.
▪ Rule of two and half : we have done three (two and a half) so it makes seven
and you put one more two and half it becomes ten.
▪ QT interval it takes 10 to 11 small square so the duration of QT interval is
0.47s.
117
118
119
120
Break
Please, review the clinical points before you go
“Success doesn’t come to you,
You go to it”
–Marva Collins
121
QRS complex Nomenclature
____________________________________
▪ QRS complexes a graphic representation of electrical activity of the heart
when ventricles are undergoing the process of depolarization.
▪ QRS complex may have one wave or two wave or three waves or sometimes
more than three waves.
▪ All the deflections which are above the isoelectric line are positive waves and
below the isoelectric line they are negative wave.
▪ 3 basic parameters would determine nomenclature:
1- Is it positive or negative deflection?
2- The position of the 3 waves in reference to each other.
3- Degree of deflection there small are or large deflection.
122
The principles of nomenclature
1. In the QRS complex, if the First deflection was negative we called Q wave if
it is small or capital Q.
2. In the QRS complex, if any deflection was positive we called R wave if it is
small or capital R.
3. In the QRS complex, if there any negative wave before R wave it would be
Q wave and any negative wave after it would be S wave.
4. In the QRS complex, if you have free second positive deflection it called R
prime (R`), then followed by another negative after the R Prime that is S
Prime(S`).
5. In the QRS complex, small amplitude deflections are designated by small
letter like q, r, s or r`, s` if less than 3 three small squares.
6. In the QRS complex, large deflections are designated by capital like Q, R, S or
R`, S`, if more than 3 three small squares.
123
▪ Triphasic QRS complex
▪ Biphasic QRS complex
▪ Monophasic QRS complex
If there is single negative wave we cannot decide it is
Q or S because there is no R Wave to help us for the
decision that is why we called QS or qs complex.
124
125
126
Note:
▪ Electrodes are wires that you attach to a patient to record an ECG, they are
placed on different parts of a patient’s limbs and chest to record the electrical
activity.
▪ Lead refers to an imaginary line between two ECG electrodes, the electrical
activity of a lead is measured and recorded as part of an ECG it producing 12
separate graphs on a piece of ECG paper.
▪ Only 10 physical electrodes are attached to the patient, to generate the 12
leads.
▪ The data gathered from the electrodes allows the 12 leads of the ECG to be
calculated.
▪ Circuit: Those two electrode along with their wire with the electrographic
machine holds the system is called circuit.
127
Limb leads
_________________
▪ We have 6 limb leads (3 bipolar and 3 unipolar)
▪ We look heart from frontal plane which is a vertical plane that divides the
heart into anterior and posterior sections (belly and back).
▪ when this electrical Vector is generated by the depolarization of the major
part of ventricles this electrical current spreads all over the body, and all fluids
around the heart and then it spreads into trunk and from the trunk this
electrical current will spread into arms and legs so can be picked up by leads
from the surface of the body and recorded by ECG machine.
128
Bipolar limb leads
▪ 3 leads which are lead I,II and III.
▪ This leads should be having two poles one positive pole and one negative
pole.
▪ They are looking at the heart from different angle.
▪ You have to look from front and back and left so you are looking from multiple
angles on the same electrical activity of the heart.
▪ But they will get different snapshots, they will get different electrical pictures
with same electrical activity because recording of the angle is different.
▪ You can imagine just like a person in front of you and you want look every
body part of him so you should use different angles to know him well and to
describe him.
▪ Those electrodes will measure the difference of potentials from both poles
that lead to fluctuation of this needle and making QRS complex graphically
recording in a deferent pattern.
129
Note//
▪ Electrical axis of the lead: An imaginary line which have drawn from the
negative electrode toward positive electrode. Electrical axis of the lead is
determined by the placement of the electrodes on the body, it changes by
changing position of electrodes.
▪ Positive electrode also called exploring electrode which means you have to
look heart in an angle from positive pole.
▪ Exploring electrode = Eye of the lead.
▪ Positive electrode = your eye to look that person from any angle.
130
Note//
▪ If the lead axis moving toward cardiac Vector or positive electrode it will
generate Positive deflection.
▪ If the lead axis moving away from cardiac Vector or negative electrode it will
generate Negative deflection.
▪ If the lead axis moving perpendicular to cardiac Vector it will generate Positive
and negative deflection with same magnitude and the sum of them will be
zero.
1.Moving toward positive axis
it generate positive deflection.
2.Moving away from positive axis
it generate negative deflection.
1
2
131
How the axis of leads are different from the axis of electrical activity
of the heart is?
QRS activity mean QRS Vector which a net of cardiac axis is directed downward
and leftward in the frontal plane which is also constant, but Lead axis is an
imaginary line from Negative electrode to Positive electrode which change with
the position of electrodes.
Axis of lead I
132
▪ How Much part of the cardiac Vector (axis of heart) is along the electrical axis
of the lead will determine size of deflection.
▪ We determine the size of vector in each lead by drawing parallel components
between cardiac vector and lead axis.
▪ Remember the lead axis is not the vector of the lead is just an imaginary line
but in the heart the cardiac axis is the vector of QRS complex.
▪ In the next we will see the parallel component and size of the deflection they
generate in each lead .
133
How they decide to put each electrode in its specific place?
Mr. Tobin decided to finalize the position of the electrode along cardiac axis and
the QRS complex should be mainly positive which is s major ventricular
depolarization, its vector axis downward and left world, so to get positive
deflection in all the leads the positive and negative electrodes must be put in
their specific place.
134
Lead I=Lateral view
▪ We apply positive electrode in left arm and negative electrode in right arm.
▪ Axis of the lead I is an imaginary line which have drawn from the negative
electrode(right arm) to the positive electrode(left arm).
▪ The left arm is the exploring electrode.
▪ So lead I is looking the left lateral part heart.
▪ QRS Vector(cardiac axis) not parallel to axis of lead I, so only a component of
it can be drown, so the projection of QRS Vector along the axis of the lead is
less(small vector), and the positive deflection will be less.
▪ This pattern will be recorded like ( image in next slide)
135
Lead I
136
Lead II=Inferior view
▪ The positive electrode of the machine is applied on the ankle on left leg and
negative electrode applied on right arm.
▪ Axis of the lead II is an imaginary line which have drawn from the negative
electrode(right arm) to the positive electrode(left leg ankle),so is directed
downward and leftward.
▪ The left leg ankle is the exploring electrode.
▪ Lead II is looking the inferior part of heart .
▪ Lead II are almost parallel to cardiac vector so exact components we can draw
and will cause greater vector projection of QRS with higher magnitude along
that lead, the positive deflection will be more.
137
Lead II
138
Lead III = Inferior view
▪ The positive electrode of the machine is applied on the ankle on left leg and
negative electrode applied on left wrist.
▪ Axis of the lead III is an imaginary line which have drawn from the negative
electrode(left wrist) to the positive electrode(left leg ankle) so is directed
downward and rightward.
▪ The left leg ankle is the exploring electrode.
▪ Lead III is looking the inferior part of heart
▪ QRS Vector(cardiac axis) not parallel to axis of lead III, so only a component of
it can be drown, so the projection of QRS Vector along the axis of the lead is
less(small vector), and the positive deflection will be less.
139
Lead III
140
Look at the different length of lead vector (parallel components with cardiac
axis) which produced by the its circuit along that lead Axis and look the different
deflection size.
Note// lead vector means only this magnitude of voltage picked up by that lead.
141
What is the benefit of multiple leads in cardiac pathology?
When there are cardiac pathologies which result in alteration in electrical
activity of the heart ,t o look where is the pathology and where is the change in
electrical activity of the heart? You need to look at the cardiac electrical vectors
from different angles.
As if you have to see to make a real concept, how is dr. Najeeb? Not only you
need to look from the front. You have to see from the sides have to see from
the top you to see from the back, then you have a three dimensional concept
exactly.
Or we can say we need to look for multiple leads So if there is a pathology
that may be recorded better by one lead and poorly by the other lead.
142
143
Einthoven triangle
▪ Is an imaginary triangle drown around the heart the by 3 bipolar leads,
formed by the two shoulders and the pubis. The shape forms an inverted
equilateral triangle with the heart at the center. It is named after
Willem Einthoven, who theorized its existence
▪ When ventricular depolarization is going on the electrical current is spreading
in the body and the Leads recording that potential difference between their
two electrodes to know the difference at these two points.
144
Einthoven law
▪ Lead I + lead III = Lead II
▪ When ventricular depolarization is going on, electrical Vector of ventricular
depolarization is moving down and left in the frontal plane, so positive
charges are moving down and left so down side and left side should be
positive because of that direction of QRS vector.
▪ So the right upper corner of the triangle should be negative and left upper
corner with the inferior side should be positive.
▪ We want to know what are the potentials in the leads that they pick up as
compared to the average potential in the heart.
145
▪ Now imagine when QRS complexes or when major ventricular depolarization
is going on Potential in right corner is -0.2 millivolt, in the left corner is
+0.3, and in the inferior side is +1.0 mV. (image in the next slide)
▪ Regarding lead I it measure the difference potentials between left and right
corner of the triangle so it will be like that:
lead I difference potentials = 0.3 – (-0.2) = 0.3+0.2 = 0.5mV
▪ Regarding lead III it measure the difference potentials between inferior side
of the triangle and left corner so it be like that:
lead III difference potentials = 1.0 – 0.3 = 0.7mV
▪ Regarding lead II it measure the difference potentials between inferior side
of the triangle and right corner so it will be like that:
lead II difference potentials = 1.0 – (-0.3) = 1+0.3 = 1.3 mV
▪Lead I (0.5) + Lead III (0.7) = Lead II (1.3)
146
147
▪ Each small square height in ECG paper is 0.1mv.
▪ Lead I QRS complex height will be 5 small squares.
▪ Lead III QRS complex height will be 7 small squares.
▪ Lead II QRS complex height will be 13 small squares.
148
Clinical Point
If you look at an ECG paper you
will see that Lead I + lead III = Lead II,
but if they do not, it means the
electrodes placed wrong.
149
▪Angle of orientation of lead I is 0
▪Angle of orientation of lead II is +60
▪Angle of orientation of lead III is +120
150
Unipolar limb leads
▪ We have 3 unipolar leads which are (aVR, aVF, aVL).
▪ A=augmented V= voltage R=right L= left F= left foot.
▪ Unipolar Leads are modified bipolar.
▪ Unipolar lead has positive electrode which can be applied at one part of the
skin, but negative electrode in the unipolar lead has been modified in such a
way, by multiple connections and through resistance heavy resistance about
5000 omega, and converted into indifferent electrode negative, that it sends
almost zero potential.
▪ It means has two poles which are positive and modified negative.
▪ Three unipolar limb leads are recorded along with the standard bipolar limb
leads. Unipolar leads measure the potential difference between an exploring
electrode(positive electrode) that is affected by the cardiac dipole and an
indifferent electrode that records the sum of the their two electrodes. 151
Why negative electrode should be zero?
As we know positive electrode could not generate potentials lonely, so should
be positive and negative electrode to generate potentials.
And if there is positive and negative electrode in unipolar limb leads the
difference potentials of them it will affect the potential of bipolar limb leads.
Therefore they decided to make the negative potentials almost ZERO in the
center of the heart order to that lead in 90 degree will not affect lead II and III.
152
How they decide to make unipolar leads?
Mr. Wilson in 1930 is he decided that I should make a lead, which should be
filled the gap of between the 60 degree (angle of lead III) and 120 degree(angle
of lead II) should look straight at 90 degree to look the bottom of the heart.
Wilson and their friends use the concept of geometry and Mathematics and use
the concept of equilateral triangle. And if you pick up the current at the
equilateral triangle, and if you pick up the current from three episodes and add
them together, they will cancel each other and end up with potential almost
ZERO, therefor in that case we cannot say that electrode is here or there.
They want to achieve the indifferent electrode or to achieve what is near zero
potential in negative electrode, so negative terminal was divided into three
wires(to make a triangle) connected to three wires (one to right arm one to left
arm the other one to left leg), and all these wires are having resistance so
minimal current flow should be there.
But they faced a problem which is the voltage that produced is too little to
153
picked up by the machine.
The summation of all three indifferent negative electrode is become ZERO
in the center of the heart because each of them it cancels the other one.
154
Why augmented?
Because without augmentation the voltage is too little which cannot be
determined well by the machine because the 3 connected wires to negative
electrode it neutralize the positive potentials therefore they augmented to be
picked up by their leads.
Goldberger decided to inactivate or disconnected one negative wire which is
located beside positive electrode so by this way he could reduce the effect of
negative wires on the positive potentials and the voltage is now high.
In aVF he disconnected the negative wire in left leg.
In aVR he disconnected the negative wire in right arm.
In aVL he disconnected the negative wire in left arm.
155
aVF lead (Inferior viwe)
▪ Augmented voltage foot(left)
▪ The positive electrode is applied on the right arm and indifferent negative
electrode applied on left arm and left foot.
▪ It means located between lead II and III.
▪ The axis of aVF is from the center of heart which almost zero poitrinals (that
produced by right and left arm) toward left leg.(straight downward)
▪ It is looking bottom of the heart.(positive electrode is exploring eye)
▪ The length of lead vector is between the length if lead vector II and III, and
is going along cardiac vector so it generate positive defection.
▪ The size of deflection is between size of lead II and III and is the biggest on
between the unipolar leads.
156
157
Why the axis of aVF is from the center of right arm and left arm
toward left leg?
The exploring eye of aVF is the positive electrode in left leg so we look at the
heart from left leg upward, but there is two negative indifferent electrode in
right and left arm therefore to keep balance of visual field between them it
must look at the center.
Just imagine like, if you have two most lovely friend so you should keep your
eye in balance between them, not caring too much about one and less care
about the other one then you know what will happen. LOL
Is the same principle for aVR and aVL.
158
aVL (Lateral view)
▪ Augmented voltage left arm.
▪ The positive electrode is applied on the left arm and indifferent negative
electrode applied on right arm and left foot.
▪ The axis of aVL is from the center of the heart which almost zero poitrinals
(that produced by right arm and left foot) towards left arm.
▪ It is looking lateral side of the heart.(positive electrode is exploring eye)
▪ The axis of vector is going toward cardiac vector(QRS complex) so it generate
posetive defection.
▪ The length of lead vector(parallel components with cardiac vector) is short
so it generates small deflection is almost like lead I.
159
160
aVR (Lateral view)
▪ Augmented voltage Right arm.
▪ The positive electrode is applied on the right arm and indifferent negative
electrode applied on left arm and left foot.
▪ The axis of aVR is from the center the heart which almost zero poitrinals (that
produced by left arm and left foot) towards right arm.
▪ It is looking lateral side of the heart.(positive electrode is exploring eye)
▪ The axis of vector is going away from the cardiac vector(QRS complex) so it
generate negative defection.
▪ Therefore all waves in aVF are reversed and it is normal.
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162
QRS complex variants in aVR:
▪ The small vector of septal depolarization is moving toward the axis of aVR,
therefore it generate a small positive deflection.
▪ The big vector of major ventricular depolarization is moving away from the
axis of aVR, therefore it generate a large negative deflection.
▪ The small vector of basal depolarization is moving toward the axis of aVR,
therefore it generate a small positive deflection.
▪ Now before labeling generated waves please review QRS complex
nomenclature that you studied before.
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▪ The voltage summation of those three unipolar leads is ZERO.
▪ Lets imagine if voltage of aVF = +5mV, aVL=+1mV, aVR= -6mV
▪ So aVF(5) + aVL(1) + aVR(-6) =0
▪ When you look at ECG paper the summation of the three unipolar
leads must be ZERO otherwise means there is something wrong
with lead placement.
The summation of
QRS height
must be ZERO
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165
NOTE//
▪ All the process of measurement of electrical activity by bipolar limb leads and
unipolar leads through the lead axis, augmentation of unipolar leads with zero
potentials in the center of the heart and the indifferent electrodes are all done
through automated ECG machine by putting 4 electrodes in limb leads it
generate 6 leads.
▪ So do not need to think how is done is just an automated process.
▪ The right leg electrode always acts as a ground electrode. The acts in
protection and to eliminate some background electrical interference. It acts as
a backup to keep the patient from getting an electrical shock if the machine
malfunctions.
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▪ Angle of orientation of aVF +90
▪ Angle of orientation of aVL is -30
▪ Angle of orientation of aVR is -150
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168
▪ Between -30º and +90º: normal heart axis.
▪ Between -30º and -90º: left-axis deviation.
▪ Between +90º and +180º: right-axis deviation.
▪ Between -90º and -180º: extreme axis deviation.
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Variants in the Electrical position of heart
______________________________________
▪ There is different electrical position not anatomical position of the heart that
produce different size of patterns among limb leads.
▪ We have (Horizontal-Vertical-Intermediate) electrical position.
▪ Note// Basal depolarization has a small vector, therefore most of the time
leads could not pick it up because they not able to sense its electrical current,
that is why they will not generate its wave.
▪ Here we only focus on septal and major ventricular depolarization.
▪ In all positions aVR has reversed patterns because always away from positive
electrode.
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▪ To be easy for us we use a fast way nomenclature for patterns:
❑ If the major depolarization of ventricle moving toward Positive pole it
generate qR complex.
❑ But if the major depolarization of ventricle moving away from Positive pole it
generate rS complex, or we can say if septal vector moving toward positive
pole it produce rS pattern.
▪ In the next slides you can apply this fast way in each lead to know how the
patterns generated.
Septal
Vector
Major Vector
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Horizontal Electrical Position
▪ In this position Major cardiac vector is directed leftward (toward lead I) and
septal vector directed rightward backward.
▪ The size of deflection depend on parallel component of cardiac vector with
that lead axis.
✓ lead I has strongest wave because
the major vector is directed to it.
✓ aVF has biphasic wave because
It is perpendicular to major vector
173
Vertical Electrical Position
▪ In this position Major cardiac vector is directed downward (toward aVF) and
septal vector directed upward.
▪ The size of deflection depend on parallel component of cardiac vector with
that lead axis.
✓ aVF has strongest wave because
the major vector is directed to it.
✓ Lead I has biphasic wave because
It is perpendicular to major vector
174
Intermediate Electrical Position
▪ In this position Major cardiac vector is directed downward leftward (toward
lead II) and septal vector directed rightward upward.
▪ The size of deflection depend on parallel component of cardiac vector with
that lead axis.
✓ lead II has strongest wave because
the major vector is directed to it.
✓ aVL has biphasic wave because
It is perpendicular to major vector
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Break
Please, review the clinical points before you go
“The key to success is not through achievement buy through enthusiasms.”
- Malcolm Forbis
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Chest leads
_____________________
▪ We have 6 chest leads which are (V1, V2, V3, V4, V5, V6).
▪ They are looking at electrical activity of heart from horizontal plane (Anterior
and posterior part).
▪ The leads are unipolar, they have positive electrode (exploring electrode) and
indifferent negative electrode.
▪ The positive electrode applied on the surface of chest.
▪ The indifferent electrode which have 3 connection are applied on Right arm,
Left arm and Left leg.
▪ The potential in indifferent electrode almost ZERO in the center of the heart.
▪ Positive electrode is put in different position but the negative indifferent
177
electrode always in the center of heart which almost ZERO.
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179
Anatomical placement of chest leads
V1 and V2
V3 and V4
V5 and V6
located at the Right side of heart.
located at the Septum of heart.
located at the Left side of heart..
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Functional placement of chest leads
V1 and V2
V3 and V4
V5 and V6
Electrical activity of the Septum of Ventricle.
Electrical activity of the Anterior of Ventricle.
Electrical activity of the left lateral of ventricle.
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Myocardial Infarction Dx
V1 + V2
V3 + V4
V5 + V6
V1+V2+V3 +V4
V3 +V4+V5+V6
V2+V3 +V4+V5
All leads
MI in the Septum of Ventricle.
MI in the Anterior of Ventricle.
MI in the left lateral of ventricle.
AnteroSeptal MI.
AnteroLateral MI.
Major MI.
Massive MI.
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183
Normal QRS complex variants in chest leads
▪ Chest leads from V1 to V6 generate different shapes of QRS complex.
▪ Leads that these are you are looking at the electrical activity of the heart from
different angles the so pattern which you receive that may be different
▪ You should know in these leads in which measure electrical activity in
horizonal plane somehow have different wave pattern from limb leads.
▪ Remember, in here any first positive deflection(in QRS complex) is represent R
wave, therefore if there any wave before of it would be Q wave and any wave
after it would be S wave.
▪ We only focus on septal vector which is rightward and major ventricle
vector which more leftward in horizontal plane.
184
▪ If the axis of the leads(or we can say by their position of the leads) moving
away from cardiac vector it generate negative deflection and if moving
towards it generate positive deflection, but if moving perpendicular then
positive and negative deflection produced.
▪ Therefore it means V1 produce negative deflection but V6 positive deflection.
185
V1 (rS pattern)
▪ Septal depolarization produces a little positive deflection(septal vector is
toward V1 axis) and major ventricular depolarization produces a big negative
deflection (major ventricular vector is away from V1 axis).
▪ Any first positive deflection is called r wave and because this wave is small so
represented by small r, and after this wave if there is a negative deflection is
called S wave so should be shown with large Capital (S).
▪ We named it rS pattern.
▪ So here r wave represent septal depolarization and S wave represent major
ventricular depolarization.
r
S
186
V6 (qR pattern)
▪ Septal depolarization produces a little negative deflection(septal vector is
away from V1 axis) and major ventricular depolarization produces a big
positive deflection (major ventricular vector is toward V1 axis).
▪ Any first megative deflection is called q wave and because this wave is small
so represented by small q, and after this wave if there is a positive deflection
is called R wave so should be shown with large Capital (R).
▪ We named it qR pattern.
▪ So here q wave represent septal depolarization and R wave represent major
ventricular depolarization.
R
q
187
V2 V3 V4 V5
Transitional zone
▪ As you move from right-sided chest lead to the left side of the chest late,
R wave pattern will gradually become taller but S wave will become smaller
or disappear in the end, this concept is called Normal R wave progression
▪ V3 or V4 which id different from one to one another you find that R wave and
S wave are almost equal, therefore lead is called transitioning lead.
▪ If someone has heart little rotated towards the then transition may occur in
V2 that is called early transition zone and in some other people transition may
occur after the V4, maybe V6 then we say delayed transition zone.
188
Why V5 has taller amplitude than V6?
Due to axillary in which between the heart and V6 electrode, so the voltages
will be little attenuated which are perceived or recorded or sensed by the V6
electrode and also there is more tissue involved then between the heart, that is
why V6 is little smaller than V5.
But generally speaking as you move from V1 lead to V6 lead, we see gradual
increasing amplitude of R wave and decreasing S wave amplitude.
189
190
Normal ECG
191
192
193
194
Normal R wave progression
▪ The Vector is representing left ventricular depolarization which directed
leftward and slightly anteriorly is greater than right ventricular vector which is
rightward and downward, but they are occurring simultaneously so they can
be added together, so the resultant net vector is smaller than the only left
ventricular Vector because right ventricular Vector partially cancels partially
masked partially neutralized the left ventricular so resultant net vector which
directed leftward and slightly backward represent both ventricular
depolarization.
▪ As you move from right-sided chest lead to the left side of the chest late,
R wave pattern will gradually become taller (more positive) but S wave will
become smaller(less negative) or disappear in the end, this concept is called
Normal R wave progression.
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Accentuated R wave progression
▪ Left ventricle hypertrophy: adding the tissues and forces to the left side so
result in powerful depolarization that lead to accentuated R wave.
▪ Left bundle branch block: left ventricle cannot go under depolarization
through its bundle branch and so the cells from right ventricle it will move
from myocardial cells to one myocardial cells to left ventricle and this is with
moderate speed because it is not helped by purkinje system, so this will be
delayed left ventricular depolarization(longer time depolarization) and right
ventricle power reduced that can not partially cancel left ventricular
depolarization.
▪ Right side MI: is simply loss of forces on the right side ventricle which is rare.
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Reversed R wave progression
▪ Right ventricle hypertrophy: This hypertrophy lead to strong depolarization
that it cancel the leftward strong vector of left ventricle and still able to
produce current which is moving rightward.
▪ Right bundle branch block: right ventricle cannot go under depolarization
through its bundle branch and so the cells from left ventricle it will move from
myocardial cells to one myocardial cells to right ventricle and this is with
moderate speed because it is not helped by purkinje system, so this will be
delayed right ventricular depolarization(longer time depolarization) this will
produce powerful vector that left ventricle could not cancel it.
▪ Posterior MI: forces of left ventricle will become reduced so unable to
cancel the right ventricular depolarization vector.
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200
Poor R wave progression
▪ In this case it tries to accentuate send but failed to go properly.
▪ Anterior MI: If the myocardial infarction occur in anterior part forces are
present in lead V3 and V4 will be less but still some power that going towards
V6 and V5, but is not diagnostic of anterior Mi it is suggestive because the
other causes also we have.
▪ Left ventricle hypertrophy: Resultant Vector will swing upward backward and
more powerful so when it swings V3 and V4 no longer passing perpendicular
to the vector so the waves remain small.
▪ So LVH can happen in poor and accentuated R wave progression.
▪ Right ventricle hypertrophy: When the right ventricle vector swings too much
rightward lead to poor R wave progression.
▪ So RVH van happen in Poor and Reversed R wave progression.
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202
Break
Please, review the clinical points before you go
“Nothing is impossible. The word itself says I’m possible
- Audrey Hepburn”
203
How to read an ECG in
a systematic and
effective manner
204
Confirm Details
▪ Confirm the name and date of birth of the patient matches the details on the
ECG.
▪ Check the date and time the ECG was performed.
1) Rate
2) Rhythm
3) Axis
4) P waves
5) PR interval
6) QRS complex
7) ST segment
8) T waves
9) QT interval
205
Step 1 – Heart Rate
What’s a normal adult heart rate?
▪ Normal – 60-100 bpm
▪ Tachycardia > 100 bpm
▪ Bradycardia < 60 bpm
Regular Heart Rhythm
▪ If a patient has a regular heart rhythm their heart rate can be calculated using
the following method:
▪ Count the number of large squares present within one R-R interval.
▪ Divide 300 by this number to calculate the heart rate.
Example
▪ 4 large squares in an R-R interval
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▪ 300/4 = 75 beats per minute
207
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Irregular Heart Rhythm
If a patient’s heart rhythm is irregular the first method of heart rate calculation
doesn’t work (as the R-R interval differs significantly throughout the ECG). As a
result, you need to apply a different method such as:
▪ Count the number of QRS complexes on the rhythm strip (each rhythm strip is
typically 10 seconds long)
▪ Multiply the number of QRS complexes by 6 (giving you the average number of
complexes in 1 minute)
Example
▪ 10 QRS complexes on a rhythm strip
▪ 10 x 6 = 60 beats per minute
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Step 2 – Heart rhythm
▪ A patient’s heart rhythm can be regular or irregular.
▪ Irregular rhythms can be either:
Regularly irregular (i.e. a recurrent pattern of irregularity)
Irregularly irregular (i.e. completely disorganized)
▪ Mark out several consecutive R-R intervals on a piece of paper, then move
them along the rhythm strip to check if the subsequent intervals are similar.
Hint
▪ If you are suspicious that there is some atrioventricular block (AV block), map
out the atrial rate and the ventricular rhythm separately (i.e. mark the P waves
and R waves). As you move along the rhythm strip, you can then see if the PR
interval changes, if QRS complexes are missing or if there is complete
dissociation between the two.
211
▪
212
Normal rhythm
Regularly irregular
Irregularly irregular
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214
Step 3 – Cardiac axis
▪ Cardiac axis describes the overall direction of electrical spread within the heart.
▪ In a healthy individual, the axis should spread from 11 o’clock to 5 o’clock.
▪ In healthy individuals, you would expect the axis to lie between -30° and +90º.
▪ To determine the cardiac axis you need to look at leads I, II and III.
▪ lead II showing the most positive deflection as it is the most closely aligned to
the overall direction of electrical spread.
215
▪
216
Right axis deviation
▪ Right axis deviation (RAD) involves the direction of depolarization
being distorted to the right (between +90º and +180º).
▪ The most common cause of RAD is right ventricular hypertrophy.
▪ RAD is commonly associated with conditions such as pulmonary hypertension,
as they cause right ventricular hypertrophy.
▪ Extra right ventricular tissue results in a stronger electrical signal being
generated by the right side of the heart.
▪ This causes the deflection in lead I to become negative and the deflection
in lead aVF/III to be more positive.
▪ RAD can, however, be a normal finding in very tall individuals.
217
▪
218
Left Axis Deviation
▪ Left axis deviation (LAD) involves the direction of depolarization being distorted
to the left (between -30° and -90°).
▪ Lead I has the most positive deflection.
▪ The deflection of lead III becoming negative (this is only considered significant
if the deflection of lead II also becomes negative).
▪ LAD is usually caused by conduction abnormalities.
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▪
220
Extreme axis deviation
▪ Also known as extreme right axis deviation, northwest axis or “no-man's land”
axis, is a rare electrocardiographic finding, and it represents an extreme rightor left-axis deviation .
▪ Extreme axis deviation is when the QRS axis is between -90° and -180º.
Causes of Extreme Axis Deviation:
▪ Misplacement of the limb leads: right arm and left leg leads reversal
▪ Ventricular rhythms: ventricular tachycardias, accelerated idioventricular
rhythm, ventricular escape rhythm.
▪ Hyperkalemia.
▪ Emphysema.
▪ Ventricular pacing.
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Step 4 – P waves
The next step is to look at the P waves and answer the following questions:
▪ Sinus = P wave
▪ Are P waves present?
▪ If so, is each P wave followed by a QRS complex?
▪ Do the P waves look normal (check duration, direction and shape)?
▪ If P waves are absent, is there any atrial activity?
▪ Sawtooth baseline → flutter waves
▪ Chaotic baseline → fibrillation waves
▪ Flat line → no atrial activity at all
Hint
▪ If P waves are absent and there is an irregular rhythm it may suggest a
diagnosis of atrial fibrillation.
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▪
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Common P Wave Abnormalities Common P wave abnormalities include:
▪ P mitrale (bifid P waves), seen with left atrial enlargement.
‘M’ like pattern. It is due left atrial hypertrophy, which is
usually secondary to mitral stenosis.
▪ P pulmonale (peaked P waves), in right atrial enlargement.
P pulmonale occurs secondary to right atrial hypertrophy, which is
usually secondary to pulmonary hypertension or tricuspid stenosis.
▪ P wave inversion, seen with ectopic atrial and junctional rhythms.
▪ Variable P wave morphology, seen in multifocal atrial rhythms.
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Step 5 – PR interval
Images in slide number 45-48
Tips for remembering heart block types (Prolonged PR Interval, >0.2 seconds)
▪ To help remember these degrees of AV block, it is useful to remember the
anatomical location of the block in the conducting system:
First-degree AV block:
▪ Occurs between the SA node and the AV node (i.e. within the atrium)
Second-degree AV block:
▪ Mobitz I AV block (Wenckebach) – occurs IN the AV node (this is the only piece
of conductive tissue in the heart which exhibits the ability to conduct at
different speeds)
▪ Mobitz II AV block – occurs AFTER the AV node in the bundle of His or Purkinje
fibers.
Third-degree AV block:
▪ Occurs anywhere from the AV node down causing complete blockage of
conduction.
227
Shortened PR Interval
If the PR interval is shortened, this can mean one of two things:
▪ Simply, the P-wave is originating from somewhere closer to the AV node so the
conduction takes less time (the SA node is not in a fixed place and some
people’s atria are smaller than others).
▪ The atrial impulse is getting to the ventricle by a faster shortcut instead of
conducting slowly across the atrial wall. This is an accessory pathway and can
be associated with a delta wave (see below which demonstrates an ECG of a
patient with Wolff Parkinson White syndrome).
228
Step 6 – QRS complex
When assessing a QRS complex, you need to pay attention to the following
characteristics:
▪ Width
▪ Height
▪ Morphology
229
Width
▪ Width can be described as NARROW (< 0.12 seconds) or BROAD (> 0.12
seconds)
▪ A narrow QRS complex occurs when the impulse is conducted down the
bundle of His and the Purkinje fiber to the ventricles. This results in well
organized synchronized ventricular depolarization.
▪ An atrial ectopic would result in a narrow QRS complex because it would
conduct down the normal conduction system of the heart.
▪ A broad QRS complex occurs if there is an abnormal depolarization sequence –
for example, a ventricular ectopic where the impulse spreads slowly across the
myocardium from the focus in the ventricle.
Images are in slide 90
▪ Similarly, a bundle branch block results in a broad QRS complex because the
impulse gets to one ventricle rapidly down the intrinsic conduction system then
has to spread slowly across the myocardium to the other ventricle.
230
Height
▪ Describe this as SMALL or TALL:
▪ Small complexes are defined as < 5mm in the limb leads or < 10 mm in the
chest leads, in obese patient, hyperthyroid and plural effusion.
▪ Tall complexes imply ventricular hypertrophy (although can be due to body
habitus e.g. tall slim people). There are numerous algorithms for measuring
LVH, such as the Sokolow-Lyon index or the Cornell index.
231
Morphology
▪ To assess morphology, you need to assess the individual waves of the QRS
complex.
Delta wave
▪ The mythical ‘delta wave’ is a sign that the ventricles are being activated earlier
than normal from a point distant to the AV node. The early activation then
spreads slowly across the myocardium causing the slurred upstroke of the QRS
complex.
▪ Note – the presence of a delta wave does NOT diagnose Wolff-Parkinson-White
syndrome. This requires evidence of tachyarrhythmias AND a delta wave.
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Q waves
▪ Isolated Q waves can be normal.
▪ A pathological Q wave is > 25% the size of the R wave that follows it or > 2mm
in height and > 40ms in width.
▪ A single Q wave is not a cause for concern – look for Q waves in an entire
territory (e.g. anterior/inferior) for evidence of previous myocardial infarction.
234
R and S waves
▪ Look for R wave progression across the chest leads (from small in V1 to large in
V6).
▪ The transition from S > R wave to R > S wave should occur in V3 or V4.
▪ Poor progression (i.e. S > R through to leads V5 and V6) can be a sign of
previous MI but can also occur in very large people due to poor lead position.
235
J point segment
▪ The J point is where the S wave joins the ST segment.
▪ This point can be elevated resulting in the ST segment that follows it also being
raised (this is known as “High take-off”)
▪ High take-off (or benign early repolarization to give its full title) is a normal
variant that causes a lot of angst and confusion as it LOOKS like ST elevation
Key points for assessing the J point segment:
▪ Benign early repolarization occurs mostly under the age of 50 (over the age of
50, ischemia is more common and should be suspected first)
▪ Typically, the J point is raised with widespread ST elevation in multiple
territories making ischemia less likely.
▪ The T waves are also raised (in contrast to a STEMI where the T wave remains
the same size and the ST segment is raised)
▪ The ECG changes do not change! During a STEMI, the changes will evolve – in
benign early repolarization, they will remain the same.
236
Step 7 – ST segment
Images are in slide number 96
▪ The ST segment is the part of the ECG between the end of the S wave and the
start of the T wave.
▪ In a healthy individual, it should be an isoelectric line (neither elevated or
depressed).
▪ Abnormalities of the ST segment should be investigated to rule out pathology.
ST-elevation
▪ ST-elevation is significant when it is greater than 1 mm (1 small square) in 2 or
more contiguous limb leads or >2mm in 2 or more chest leads.
▪ It is most commonly caused by acute full-thickness myocardial infarction.
ST depression
▪ ST depression ≥ 0.5 mm in ≥ 2 contiguous leads indicates myocardial ischemia.
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238
STEMI and Myocardial ischemia localization
239
240
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Step 8 – T waves
▪ T waves are considered tall if they are:
> 5mm in the limb leads AND > 10mm in the chest leads.
Hyperkaliemia (“Tall tented T waves”)- Hyperacute STEMI
▪ T waves are normally inverted in V1 and inversion in lead III is a normal variant,
but inverted T waves in other leads are a nonspecific sign of a wide variety of
conditions, may be considered to be evidence of myocardial ischemia if:
oAt least 1 mm deep.
oPresent in ≥ 2 continuous leads that have dominant R waves (R/S ratio > 1).
oDynamic — not present on old ECG or changing over time.
▪ Flattened T waves are a non-specific sign, that may represent ischemia or
electrolyte imbalance.
▪ Biphasic T waves have two peaks and can
be indicative of ischemia and hypokalemia.
242
243
243
244
U waves
▪ U waves are not a common finding.
▪ The U wave is a > 0.5mm deflection after the T wave best seen in V2 or V3.
▪ These become larger the slower the bradycardia – classically U waves are seen
in various electrolyte imbalances, hypothermia and secondary to
antiarrhythmic therapy (such as digoxin, procainamide or amiodarone).
245
Step 9 – QT interval
▪ Normally, the QT interval is 0.36 to 0.44 seconds (9-11 boxes). The QT interval
will vary with patient gender, age and heart rate.
▪ Another guideline is that normal QT Intervals is less than half of the R-R
Interval for heart rates below 100 bpm.
246
Document your interpretation
You should document your interpretation of the ECG in the patient’s
247
ECG artifacts
______________________
Atrial Pacemaker Rhythm
▪ Presence of a pacing spike immediately preceding the P wave.
▪ Not all pacing spikes will look exactly the same. They may be below or above the isoelectric line or be
partially above and below.
Ventricular Pacemaker Rhythm
▪ The wide QRS suggests that the pacemaker was implanted in the ventricles.
248
Reversed leads / misplaced electrodes
If one were to accidentally confuse the red and white lead cables
(i.e. place the white one where the red one should go, vice versa),.
When this happens, you are essentially viewing the rhythm in a
completely different lead.
AC interference
Alternating current (AC) describes the type of electricity that we get
from the wall. When an ECG machine is poorly grounded or not
equipped to filter out this interference, you can get a thick looking
ECG line.
Muscle tremor / noise
When your skeletal muscles undergo tremors, the ECG is
bombarded with seemingly random activity. The term noise does
not refer to sound but rather to electrical interference. Low
amplitude muscle tremor noise can mimic the baseline seen in atrial
fibrillation.
249
Wandering baseline
The isoelectric line changes position. One possible cause
is the cables moving during the reading. Patient
movement, dirty lead wires/electrodes, loose electrodes,
and a variety of other things can cause this as well.
Absolute heart block
Absolute heart block (or 4th degree heart block) results
from over-exposure to imported-liquor advertisements in
magazines. QRS complexes are wide and bottle-shaped
and show no relationship with the P wave. It occurs very
rarely, and even then, only in fictional settings. This
should not be confused with the real arrhythmia complete
heart block.
250
Some uncommon ECGs
_______________________________
251
252
Summery of all ECG abnormalities
classified according to their
different morphology of the waves
253
P wave
Wide P wave:
Variable P wave morphology:
Left atrial hypertrophy or enlargement
Wandering pacemaker
Tall P wave:
Right atrial hypertrophy or enlargement
Small P wave:
▪
▪
▪
▪
High nodal rhythm
High nodal ectopic
Atrial tachycardia
Atrial ectopic
Inverted P wave:
▪ Nodal rhythm with retrograde conduction
▪ Low atrial and high nodal ectopic beats
▪ Dextrocardia
Multiple P waves:
▪
▪
Third degree heart block
Atrial flutter (saw teeth)
Absent P wave:
▪
▪
▪
▪
▪
▪
▪
▪
Atrial fibrillation
Atrial flutter
Mid nodal rhythm
Ventricular ectopic 5
Ventricular tachycardia
Supraventricular tachycardia
Idioventricular rhythm
Hyperkalemia
254
PR Interval
Prolonged P- R interval:
First degree heart block
Short P-R interval:
▪
▪
▪
▪
WPW syndrome. Here delta wave is present.
Lown-Ganong-Levin (LGL) syndrome. Here delta wave is absent.
Nodal rhythm
High nodal ectic
Variable P-R interval:
Mobitz type 1 heart block.
255
QRS complex
High voltage QRS:
▪
▪
▪
Improper standardization
Thin chest wall Ventricular hypertrophy
WPW syndrome
Low voltage QRS
(less than 5 mm in leads I, II, Ill and
<10 mm in chest leads)
▪
▪
▪
▪
▪
▪
▪
Improper standardization
Obesity or thick chest wall
Pericardial effusion
Emphysema
Chronic constrictive pericarditis
Hypothyroidism
Hypothermia
Wide QRS:
▪
▪
▪
▪
▪
▪
LBBB and RBBB
Ventricular ectopic
Ventricular tachycardia
Idioventricular rhythm
WPW syndrome
Hyperkalemia
Change in shape of QRS:
▪
▪
▪
▪
▪
RBBB
LBBB
Ventricular tachycardia
Ventricular fibrillation
WPW syndrome
Variable QRS:
▪ Torsades de pointes
▪ Multifocal ventricular ectopics
▪ Ventricular fibrillation
256
R & Q wave
Tall R wave in V1:
Poor progression of R wave
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
▪
Right ventricular hypertrophy
True posterior MI
WPW syndrome
RBBB
Dextrocardia
Small R wave:
▪ Improper ECG standardization
▪ Obesity
▪ Emphysema
▪ Pericardial effusion
▪ Hypothyroidism
▪ Hypothermia
Anterior or anteroseptal MI
LBBB
Dextrocardia
Left sided massive pleural effusion
COPD
Left sided pneumothorax
Marked clockwise rotation of heart
Pathological Q wave:
▪
▪
▪
▪
▪
MI
Left ventricular hypertrophy (in V1, V2 and V3)
LBBB
pulmonary embolism (only in lead l)
WPW syndrome (in lead ll and aVF)
257
T wave
Tall T wave:
T wave inversion
▪ Hyperkalemia
▪ Acute MI
▪ Acute true posterior MI (in V1 and v2)
Small T wave:
▪ Hypokalemia
▪ Hypothyroidism
▪ Pericardial effusion
258
QT interval
Short QT interval:
▪
▪
▪
▪
▪
Tachycardia
Hyperthermia
Hypercalcemia
Digoxin effect
Vagal stimulation
Long QT interval:
▪ Bradycardia
▪ Hypocalcemia
▪ Acute MI
▪ Acute myocarditis
▪ Cerebrovascular accident
▪ Hypertrophic cardiomyopathy
▪ Hypothermia
▪ Hereditary syndrome
a. Jervell, Lange-Nielsen syndrome
(congenital deafness, syncope and sudden death)
b. Romano-Ward syndrome
(syncope and sudden death)
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ST segment
ST elevation:
▪
▪
▪
▪
▪
Acute myocardial infarction
Acute pericarditis
Prinzmetal's angina (Non-infarction transmural ischemia)
Normal variant (Early repciarization pattern)
Ventricular aneurys
ST depression:
▪
▪
▪
▪
▪
Acute MI
Angina pectoris
Ventricular hypertrophy with strain
Acute true posterior MI (in V1 and V2)
Digoxin toxicity
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U wave
Prominent U wave:
▪
▪
▪
▪
▪
▪
Normally present
Hypokalemia
Bradycardia
Ventricular hypertrophy
Hypercalcemia
Hyperthyroidism
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Recommendation
______________________________
Try to correlate ECG interpretation with Clinical history and
Examination, therefore I give you some good sources for daily practice:
▪ Book: ECGs BY EXAMPLE (Dean Jenkins and Stephen Gerrard).
▪ Website: https://ecg.bidmc.harvard.edu/maven/mavenmain.asp
▪ Website: https://www.practicalclinicalskills.com/
▪ Website: https://www.skillstat.com/tools/ecg-simulator
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Resources
_________________________
▪ Transcription of Video lectures of Dr. Najeeb about ECG.
▪ ECG interpretation part: https://geekymedics.com/how-to-read-an-ecg/
▪ ECG images: https://www.practicalclinicalskills.com/
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Feedback
▪ I will be glad to see your feedback and feel free to write anything.
▪ Send your feedback to this Email:
ecg.kurd@gmail.com
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Thank You
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