ECG

ECG by NHS UK. Simple to read and easy to understand

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EElectro lectroCCardio ardioGGraphy raphy
ECG made extra easy ECG made extra easy……

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Overview Overview
ƒƒ
Objectives for this tutorial Objectives for this tutorial
ƒƒ
What is an ECG? What is an ECG?
ƒƒ
Overview of performing Overview of performing
electrocardiography on a patient electrocardiography on a patient
ƒƒ
Simple physiology Simple physiology
ƒƒ
Interpreting the ECG Interpreting the ECG

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Objectives Objectives
By the end of this tutorial the student should be able to: By the end of this tutorial the student should be able to: ƒƒ
State a definition of electrocardiogram State a definition of electrocardiogram
ƒƒ
Perform an ECG on a patient, including explaining to the patient Perform an ECG on a patient, including explaining to the patient
what is involved what is involved
ƒƒ
Draw a diagram of the conduction pathway of the heart Draw a diagram of the conduction pathway of the heart
ƒƒ
Draw a simple labelled diagram of an ECG tracing Draw a simple labelled diagram of an ECG tracing
ƒƒ
List the steps involved in interpreting an ECG tracing in an ord List the steps involved in interpreting an ECG tracing in an ord erly erly
wayway
ƒƒ
Recite the normal limits of the parameters of various parts of t Recite the normal limits of the parameters of various parts of t he he
ECGECG
ƒƒ
Interpret Interpret ECGs ECGsshowing the following pathology: showing the following pathology:
ƒƒMI, AF, 1st 2 MI, AF, 1st 2
ndnd
and 3 and 3
rdrd
degree heart block, p degree heart block, p pulmonale pulmonale, p , p mitrale mitrale, Wolff , Wolff--
Parkinson Parkinson--White syndrome, LBBB, RBBB, Left and Right axis deviation, White syndrome, LBBB, RBBB, Left and Right axis deviation,
LVH, LVH, pericarditis pericarditis, Hyper , Hyper--and and hypokalaemia hypokalaemia, prolonged QT. , prolonged QT.

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What is an ECG? What is an ECG?
ECG = ECG = Electrocardiogram Electrocardiogram
Tracing of heart Tracing of heart’’s electrical activity s electrical activity

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Recording an ECG Recording an ECG

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Overview of procedure Overview of procedure
ƒƒ
GRIP GRIP
ƒƒGreet, rapport, introduce, Greet, rapport, introduce,
identify, privacy, explain identify, privacy, explain
procedure, permission procedure, permission
ƒƒ
Lay patient down Lay patient down
ƒƒ
Expose chest, wrists, Expose chest, wrists,
ankles ankles
ƒƒ
Clean electrode sites Clean electrode sites
ƒƒMay need to shave May need to shave
ƒƒ
Apply electrodes Apply electrodes
ƒƒ
Attach wires Attach wires correctly correctly
ƒƒ
Turn on machine Turn on machine
ƒƒCalibrate to 10mm/mV Calibrate to 10mm/mV
ƒƒRate at 25mm/s Rate at 25mm/s
ƒƒ
Record and print Record and print
ƒƒ
Label Label the tracing the tracing
ƒƒName, Name, DoBDoB, hospital , hospital
number, date and number, date and
time, reason for time, reason for
recording recording
ƒƒ
Disconnect if Disconnect if
adequate and remove adequate and remove
electrodes electrodes

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Electrode placement Electrode placement
ƒƒ
10 electrodes in total are placed on the 10 electrodes in total are placed on the
patient patient
ƒƒ
Firstly self Firstly self--adhesive adhesive ‘‘dots dots’’are attached to are attached to
the patient. These have single electrical the patient. These have single electrical
contacts on them contacts on them
ƒƒ
The 10 leads on the ECG machine are The 10 leads on the ECG machine are
then clipped onto the contacts of the then clipped onto the contacts of the ‘‘dots dots’’

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Electrode placement in 12 lead Electrode placement in 12 lead
ECGECG
ƒƒ
6 are chest electrodes 6 are chest electrodes
ƒƒ
Called V1 Called V1--6 or C1 6 or C1--66
ƒƒ
4 are limb electrodes 4 are limb electrodes
ƒƒRight arm Right armRRideide
ƒƒLeft arm Left arm YYourour
ƒƒLeft leg Left legGGreen reen
ƒƒRight leg Right leg BBikeike
ƒƒRemember Remember
ƒƒ
The The right leg right legelectrode electrode
is a neutral or is a neutral or ““dummy dummy””!!

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Electrode placement Electrode placement
For the chest electrodes For the chest electrodes ƒƒ
V1 V1 44
thth
intercostal intercostalspace right space right sternal sternaledge edge
ƒƒ
V2 V2 44
thth
intercostal intercostalspace left space left sternal sternaledge edge
ƒƒ
(to find the 4 (to find the 4
thth
space, palpate the space, palpate the manubriosternal manubriosternalangle (of angle (of
Louis) Louis)
ƒƒ
Directly adjacent is the 2 Directly adjacent is the 2
ndnd
rib, with the 2 rib, with the 2
ndnd
intercostal intercostalspace space
directly below. Palpate inferiorly to find the 3 directly below. Palpate inferiorly to find the 3
rdrd
and then 4 and then 4
thth
space space
ƒƒ
VV44over the apex (5 over the apex (5
thth
ICS mid ICS mid--clavicular clavicular
line) line)
ƒƒ
VV33halfway between V2 and V4 halfway between V2 and V4
ƒƒ
V5 V5 at the same level as V4 but on the at the same level as V4 but on the
anterior axillary line anterior axillary line
ƒƒ
V6 V6 at the same level as V4 and V5 but on at the same level as V4 and V5 but on
the mid the mid--axillary axillaryline line

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Recording the trace Recording the trace
ƒƒ
Different ECG machines have different buttons Different ECG machines have different buttons
that you have to press. that you have to press.
ƒƒ
Ask one of the staff on the ward if it is a machine Ask one of the staff on the ward if it is a machine
that you are unfamiliar with. that you are unfamiliar with.
ƒƒ
Ask the patient to relax completely. Any skeletal Ask the patient to relax completely. Any skeletal
muscle activity will be picked up as interference. muscle activity will be picked up as interference.
ƒƒ
If the trace obtained is no good, check that all If the trace obtained is no good, check that all
the dots are stuck down properly the dots are stuck down properly ––they have a they have a
tendency to fall off. tendency to fall off.

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Electrophysiology Electrophysiology

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Electrophysiology Electrophysiology
ƒƒ
Pacemaker = Pacemaker = sinoatrial sinoatrialnode node
ƒƒ
Impulse travels across atria Impulse travels across atria
ƒƒ
Reaches AV node Reaches AV node
ƒƒ
Transmitted along Transmitted along interventricular interventricularseptum in Bundle of septum in Bundle of
HisHis
ƒƒ
Bundle splits in two (right and left branches) Bundle splits in two (right and left branches)
ƒƒ
Purkinje fibres Purkinje fibres

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Overall
direction
of
cardiac
impulse

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How does the ECG work? How does the ECG work?
ƒƒ
Electrical impulse (wave of depolarisation) picked up by Electrical impulse (wave of depolarisation) picked up by
placing electrodes on patient placing electrodes on patient
ƒƒ
The voltage change is sensed by measuring the current The voltage change is sensed by measuring the current
change across 2 electrodes change across 2 electrodes ––a positive electrode and a a positive electrode and a
negative electrode negative electrode
ƒƒ
If the electrical impulse travels If the electrical impulse travels towards towardsthe positive the positive
electrode this results in a electrode this results in a positive positive deflection deflection
ƒƒ
If the impulse travels If the impulse travels away awayfrom the positive electrode from the positive electrode
this results in a this results in a negative negativedeflection deflection

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Direction of impulse (axis)
Towards
the
electrode
= positive
deflection
Away from
the
electrode
= negative
deflection

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Types of Leads Types of Leads
ƒƒ
Coronal plane (Limb Leads) Coronal plane (Limb Leads)
1.1.

Bipolar leads Bipolar leads ——

l , l l , l l l l , l l , l l l
2.2.

Unipolar Unipolar

leads leads ——

aVLaVL

, , aVRaVR

, , aVFaVF
ƒƒ
Transverse plane Transverse plane
VV
11

——

VV
66

(Chest Leads) (Chest Leads)

17. Electrodes around the heart Electrodes around the heart

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Leads Leads
How are the 12 leads on the How are the 12 leads on the
ECG (I, II, III, ECG (I, II, III, aVLaVL, , aVFaVF, ,
aVRaVR, V1 , V1 –– 6) formed 6) formed
using only 9 electrodes using only 9 electrodes
(and a neutral)? (and a neutral)? ƒƒ
Lead I is formed using the Lead I is formed using the
right arm electrode (red) right arm electrode (red)
as the negative electrode as the negative electrode
and the and the left arm (yellow) left arm (yellow)
electrode as the positive electrode as the positive
- Lead I +

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Leads Leads
- Lead I +

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Leads Leads
ƒƒ
Lead II is formed Lead II is formed
using the using the right arm right arm
electrode (red) electrode (red)as the as the
negative electrode negative electrode
and the and the left leg left leg
electrode electrodeas the as the
positive positive
Lead II

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Lead II

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Leads Leads
ƒƒ
Lead III is formed using the Lead III is formed using the left arm left arm
electrode electrodeas the negative electrode and as the negative electrode and
the the left leg electrode left leg electrodeas the positive as the positive
ƒƒ
aVLaVL, , aVFaVF, and , and aVRaVRare are composite leads composite leads, ,
computed using the information from the computed using the information from the
other leads other leads

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Leads and what they tell you Leads and what they tell you
Limb leads Limb leads
Limb leads look at the heart in the coronal Limb leads look at the heart in the coronal
plane plane ƒƒ
aVLaVL, I and II = lateral , I and II = lateral
ƒƒ
II, III and II, III and aVFaVF= inferior = inferior
ƒƒ
aVRaVR= right side of the heart = right side of the heart

24. Leads look at the heart from Leads look at the heart from
different directions different directions
axis

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Leads and what they tell you Leads and what they tell you
Each lead can be thought of as Each lead can be thought of as ‘‘looking at looking at’’

an area an area
of myocardium of myocardium
Chest leads Chest leads
VV
11
to V to V
6 6
‘‘look look’’ at the heart on the transverse plain at the heart on the transverse plain
ƒƒ
VV
11
and V and V
22
look at the anterior of the heart and R look at the anterior of the heart and R
ventricle ventricle
ƒƒ
VV
33
and V and V
44
= anterior and = anterior and septal septal
ƒƒ
VV
5 5
and V and V
66
= lateral and left ventricle = lateral and left ventricle

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Elements of the trace Elements of the trace

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What do the components What do the components
represent? represent?
ƒƒ
P wave = P wave = atrial atrialdepolarisation depolarisation
ƒƒ
QRS = QRS =ventricular depolarisation ventricular depolarisation
ƒƒ
T = T = repolarisation of the repolarisation of the
ventricles ventricles

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Interpreting the ECG Interpreting the ECG

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Interpreting the ECG Interpreting the ECG
ƒƒ
Check Check
ƒƒName Name
ƒƒDoBDoB
ƒƒTime and date Time and date
ƒƒIndication e.g. Indication e.g. ““chest pain chest pain””or or ““routine pre routine pre--opop””
ƒƒAny previous or subsequent Any previous or subsequent ECGs ECGs
ƒƒIs it part of a serial ECG sequ ence? In which case it may be Is it part of a serial ECG sequ ence? In which case it may be
numbered numbered
ƒƒ
Calibration Calibration
ƒƒ
Rate Rate
ƒƒ
Rhythm Rhythm
ƒƒ
Axis Axis
ƒƒ
Elements of the tracing in each lead Elements of the tracing in each lead

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Calibration Calibration
Check that your ECG is calibrated correctly Check that your ECG is calibrated correctly
Height Height ƒƒ
10mm = 1mV 10mm = 1mV
ƒƒ
Look for a reference pulse which should be the Look for a reference pulse which should be the
rectangular looking wave somewhere near the rectangular looking wave somewhere near the
left of the paper. It should be 10mm (10 small left of the paper. It should be 10mm (10 small
squares) tall squares) tall
Paper speed Paper speed
ƒƒ
25mm/s 25mm/s
ƒƒ
25 mm (25 small squares / 5 large squares) 25 mm (25 small squares / 5 large squares)
equals one second equals one second

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Rate Rate
ƒƒ
If the heart rate is If the heart rate is regular regular
ƒƒCount the number of large squares between Count the number of large squares between
R waves R waves
ƒƒ
i.e. the RR interval in large squares i.e. the RR interval in large squares
ƒƒ
Rate = Rate = 300300
RRRR
e.g. RR = e.g. RR = 44

large squares large squares
300/ 300/44

= 75 beats per minute = 75 beats per minute

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Rate Rate
If the rhythm is If the rhythm is irregular irregular

(see next slide on rhythm (see next slide on rhythm
to check whether your rhythm is regular or not) it to check whether your rhythm is regular or not) it
may be better to estimate the rate using the may be better to estimate the rate using the
rhythm strip at the bottom of the ECG (usually rhythm strip at the bottom of the ECG (usually
lead II) lead II)
The rhythm strip is usually 25cm long (250mm i.e. The rhythm strip is usually 25cm long (250mm i.e.
10 seconds) 10 seconds)
If you count the number of R waves on that strip If you count the number of R waves on that strip
and multiple by 6 you will get the rate and multiple by 6 you will get the rate

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Rhythm Rhythm
Is the rhythm regular? Is the rhythm regular? ƒƒ
The easiest way to tell is to ta ke a sheet of paper and line up The easiest way to tell is to ta ke a sheet of paper and line up one one
edge with the tips of the R waves on the rhythm strip. edge with the tips of the R waves on the rhythm strip.
ƒƒ
Mark off on the paper the positions of 3 or 4 R wave tips Mark off on the paper the positions of 3 or 4 R wave tips
ƒƒ
Move the paper along the rhythm strip so that your first mark li Move the paper along the rhythm strip so that your first mark li nes nes
up with another R wave tip up with another R wave tip
ƒƒ
See if the subsequent R wave tips line up with the subsequent See if the subsequent R wave tips line up with the subsequent
marks on your paper marks on your paper
ƒƒ
If they do line up, the rhythm is regular. If not, the rhythm i If they do line up, the rhythm is regular. If not, the rhythm i s irregular s irregular

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Rhythm Rhythm
Sinus Rhythm Sinus Rhythm
ƒƒDefinition DefinitionCardiac impulse originates from the Cardiac impulse originates from the
sinus node. Every QRS must be sinus node. Every QRS must be
preceded by a P wave. preceded by a P wave.
ƒƒ(This does not mean that every P wave must be (This does not mean that every P wave must be
followed by a QRS followed by a QRS ––such as in 2 such as in 2
ndnd
degree heart degree heart
block where some P waves are not followed by a block where some P waves are not followed by a
QRS, however every QRS is preceded by a P wave QRS, however every QRS is preceded by a P wave
and the rhythm originates in the sinus node, hence it and the rhythm originates in the sinus node, hence it
is a sinus rhythm. It could be said that it is not a is a sinus rhythm. It could be said that it is not a
normal normalsinus rhythm) sinus rhythm)

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Rhythm Rhythm
Sinus arrhythmia Sinus arrhythmia ƒƒ
There is a change in heart rate depending on the phase of There is a change in heart rate depending on the phase of
respiration respiration
ƒƒ
Q. If a person with sinus arrhythm ia inspires, what happens to t Q. If a person with sinus arrhythm ia inspires, what happens to t heir heir
heart rate? heart rate?
ƒƒ
A. The heart rate speeds up. This is because on inspiration th A. The heart rate speeds up. This is because on inspiration th ere is ere is
a a decrease decrease in in intrathoracic intrathoracicpressure, this leads to an increased pressure, this leads to an increased
venous return to the right atrium . Increased stretching of the venous return to the right atrium . Increased stretching of the right right
atrium sets off a brainstem reflex (Bainbridge atrium sets off a brainstem reflex (Bainbridge’’s reflex) that leads to s reflex) that leads to
sympathetic activation of the heart, hence it speeds up) sympathetic activation of the heart, hence it speeds up)
ƒƒ
This physiological phenomenon is more apparent in children and This physiological phenomenon is more apparent in children and
young adults young adults

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Rhythm Rhythm
Sinus Sinus bradycardia bradycardia ƒƒ
Rhythm originates in the sinus node Rhythm originates in the sinus node
ƒƒ
Rate of less than 60 beats per minute Rate of less than 60 beats per minute
Sinus tachycardia Sinus tachycardia
ƒƒ
Rhythm originates in the sinus node Rhythm originates in the sinus node
ƒƒ
Rate of greater than 100 beats per minute Rate of greater than 100 beats per minute

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Axis Axis
ƒƒ
The axis can be though of as the overall The axis can be though of as the overall
direction of the cardiac impulse or wave of direction of the cardiac impulse or wave of
depolarisation of the heart depolarisation of the heart
ƒƒ
An abnormal axis (axis deviation) can give An abnormal axis (axis deviation) can give
a clue to possible pathology a clue to possible pathology

38. Axis Axis
A normal axis
can lie
anywhere
between -30
and +90
degrees
or +120 degrees
according to
some
An axis falling outside the normal
range can be left
axis deviation
right axis deviation
or extreme
axis deviation

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Axis deviation Axis deviation --

Causes Causes
ƒƒ
Wolff Wolff--Parkinson Parkinson--White White
syndrome can cause both Left syndrome can cause both Left
and Right axis deviation and Right axis deviation
A useful mnemonic: A useful mnemonic:
ƒƒ
““RAD RALPH RAD RALPHthe the LAD LAD from from
VILLA VILLA””
ƒƒ
RRight ight AAxis xis DDeviation eviation
ƒƒ
RRight ventricular hypertrophy ight ventricular hypertrophy
ƒƒ
AAnterolateral nterolateralMIMI
ƒƒ
LLeft eft PPosterior osterior HHemiblock emiblock
ƒƒ
LLeft eft AAxis xis DDeviation eviation
ƒƒ
VVentricular tachycardia entricular tachycardia
ƒƒ
IInferior MI nferior MI
ƒƒ
LLeft ventricular hypertrophy eft ventricular hypertrophy
ƒƒ
LLeft eft AAnterior nterior hemiblock hemiblock

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The P wave The P wave
The P wave represents The P wave represents atrial atrial
depolarisation depolarisation
It can be thought of as being It can be thought of as being
made up of two separate made up of two separate
waves due to waves due to right right

atrial atrial
depolarisation and depolarisation and left left

atrial atrial
depolarisation. depolarisation.
Which occurs first? Which occurs first?
Right Right

atrial atrial

depolarisation depolarisation
right atrial

depolarisation
Sum of
right and
left

waves
left atrial

depolarisation

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The P wave The P wave
Dimensions Dimensions
ƒƒ
No hard and fast rules No hard and fast rules
Height Height
ƒƒa P wave over 2.5mm should arouse suspicion a P wave over 2.5mm should arouse suspicion
Length Length
ƒƒa P wave longer than 0.08s (2 small squares) should a P wave longer than 0.08s (2 small squares) should
arouse suspicion arouse suspicion

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The P wave The P wave
Height Height ƒƒ
A tall P wave (over A tall P wave (over
2.5mm) can be called 2.5mm) can be called P P
pulmonale pulmonale
ƒƒ
Occurs due to Occurs due to R R atrial atrial
hypertrophy hypertrophy
ƒƒ
Causes include: Causes include:
ƒƒpulmonary hypertension, pulmonary hypertension,
ƒƒpulmonary pulmonary stenosis stenosis
ƒƒtricuspid tricuspid stenosis stenosis
normalP pulmonale
>2.5mm

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The P wave The P wave
Length Length ƒƒ
A P wave with a length A P wave with a length
>0.08 seconds (2 small >0.08 seconds (2 small
squares) and a bifid squares) and a bifid
shape is called shape is called P P mitrale mitrale
ƒƒ
It is caused by left It is caused by left atrial atrial
hypertrophy and delayed hypertrophy and delayed
left left atrial atrialdepolarisation depolarisation
ƒƒ
Causes include: Causes include:
ƒƒMitral valve disease Mitral valve disease
ƒƒLVHLVH
normalP mitrale

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The PR interval The PR interval
ƒƒ
The PR interval is measured between the The PR interval is measured between the
start of the P wave to the start of the QRS start of the P wave to the start of the QRS
complex complex
ƒƒ
(therefore if there is a Q wave before the R (therefore if there is a Q wave before the R
wave the PR interval is measured from the wave the PR interval is measured from the
start of the P wave to the start of the start of the P wave to the start of the QQ
wave, not the start of the R wave) wave, not the start of the R wave)

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The PR interval The PR interval
ƒƒ
The PR interval corresponds to the time The PR interval corresponds to the time
period between depolarisation of the atria period between depolarisation of the atria
and ventricular depolarisation. and ventricular depolarisation.
ƒƒ
A normal PR interval is between 0.12 and A normal PR interval is between 0.12 and
0.2 seconds ( 3 0.2 seconds ( 3--5 small squares) 5 small squares)

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The PR interval The PR interval
ƒƒ
If the PR interval is short (less than 3 small If the PR interval is short (less than 3 small
squares) it may signify that there is an accessory squares) it may signify that there is an accessory
electrical pathway between the atria and the electrical pathway between the atria and the
ventricles, hence the ventricles depolarise early ventricles, hence the ventricles depolarise early
giving a short PR interval. giving a short PR interval.
ƒƒ
One example of this is Wolff One example of this is Wolff--Parkinson Parkinson--White White
syndrome where the accessory pathway is syndrome where the accessory pathway is
called the bundle of Kent. See next slide for an called the bundle of Kent. See next slide for an
animation to explain this animation to explain this

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Depolarisation begins at
the SA node
The wave of depolarisation spreads
across the atria
It reaches the AV node
and the accessory bundle
Conduction is delayed as
usual by the in-built delay
in the AV node
However, the accessory bundle has no such delay
and depolarisation begins
early in the part of the
ventricle served by the
bundle
As the depolarisation in this part of the ventricle
does not travel in the high speed conduction
pathway, the spread of depolarisation across the
ventricle is slow, causing a slow rising delta wave
Until rapid depolarisation resumes via the normal
pathway and a more normal
complex follows

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The PR interval The PR interval
ƒƒ
If the PR interval is long (>5 small squares If the PR interval is long (>5 small squares
or 0.2s): or 0.2s):
ƒƒ
If there is a constant long PR interval 1 If there is a constant long PR interval 1
stst
degree heart block is present degree heart block is present
ƒƒ
First degree heart block is a longer than First degree heart block is a longer than
normal delay in conduction at the AV node normal delay in conduction at the AV node

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The PR interval The PR interval
ƒƒ
If the PR interval looks as though it is If the PR interval looks as though it is widening widening
every beat and then a QRS complex is missing, every beat and then a QRS complex is missing,
there is there is 22
ndnd
degree heart block, degree heart block, Mobitz Mobitztype I type I. .
The lengthening of the PR interval in The lengthening of the PR interval in
subsequent beats is known as the subsequent beats is known as the Wenckebach Wenckebach
phenomenon phenomenon
ƒƒ
(remember ( (remember (ww)one, )one,WWenckebach enckebach, , wwidens) idens)
ƒƒ
If the PR interval is If the PR interval is constant constantbut then there is a but then there is a
missed QRS complex then there is missed QRS complex then there is 22
ndnd
degree degree
heart block, heart block, Mobitz Mobitztype II type II

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The PR interval The PR interval
ƒƒ
If there is If there is no discernable relationship no discernable relationship
between the P waves and the QRS between the P waves and the QRS
complexes, then complexes, then 33
rdrd
degree heart degree heartblock is block is
present present

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Heart block (AV node block) Heart block (AV node block)
Summary Summary ƒƒ
11
stst
degree degree
ƒƒconstant PR, >0.2 seconds constant PR, >0.2 seconds
ƒƒ
22
ndnd
degree type 1 ( degree type 1 (Wenckebach Wenckebach))
ƒƒPR widens over subsequent beats then a QRS is dropped PR widens over subsequent beats then a QRS is dropped
ƒƒ
22
ndnd
degree type 2 degree type 2
ƒƒPR is constant then a QRS is dropped PR is constant then a QRS is dropped
ƒƒ
33
rdrd
degree degree
ƒƒNo discernable relationship between p waves and QRS No discernable relationship between p waves and QRS
complexes complexes

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The Q wave The Q wave
Are there any pathological Q Are there any pathological Q
waves? waves?
ƒƒ
A Q wave can be pathological A Q wave can be pathological
if it is: if it is:
ƒƒDeeper than 2 small squares Deeper than 2 small squares
(0.2mV) (0.2mV)
and/or and/or
ƒƒWider than 1 small square Wider than 1 small square
(0.04s) (0.04s)
and/or and/or
ƒƒIn a lead other than III or one In a lead other than III or one
of the leads that look at the of the leads that look at the
heart from the left (I, II, heart from the left (I, II, aVLaVL, ,
V5 and V6) where small Qs V5 and V6) where small Qs
(i.e. not meeting the criteria (i.e. not meeting the criteria
above) can be normal above) can be normal
Normal if in
I,II,III,aVL,V5-6
Pathological anywhere

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The QRS height The QRS height
ƒƒ
If the complexes in the chest leads look If the complexes in the chest leads look
very tall, consider left ventricular very tall, consider left ventricular
hypertrophy (LVH) hypertrophy (LVH)
ƒƒ
If the depth of the S wave in V If the depth of the S wave in V
11
added to added to
the height of the R wave in V the height of the R wave in V
66
comes to comes to
more than 35mm, LVH is present more than 35mm, LVH is present

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QRS width QRS width
ƒƒ
The width of the QRS complex should be less The width of the QRS complex should be less
than 0.12 seconds (3 small squares) than 0.12 seconds (3 small squares)
ƒƒ
Some texts say less than 0.10 seconds (2.5 Some texts say less than 0.10 seconds (2.5
small squares) small squares)
ƒƒ
If the QRS is wider than this, it suggests a If the QRS is wider than this, it suggests a
ventricular conduction problem ventricular conduction problem ––usually usually
right or right or
left bundle branch block (RBBB or LBBB) left bundle branch block (RBBB or LBBB)

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LBBB LBBB
ƒƒ
If If left leftbundle branch block bundle branch block
is present, the QRS is present, the QRS
complex may look like a complex may look like a
‘‘WW’’in V in V
11
and/or an and/or an ‘‘MM’’
shape in V shape in V
6. 6.
ƒƒ
New onset LBBB with New onset LBBB with
chest pain consider chest pain consider
Myocardial infarction Myocardial infarction
ƒƒ
Not possible to interpret Not possible to interpret
the ST segment. the ST segment.

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RBBB RBBB
ƒƒ
It is also called RSR It is also called RSR
pattern pattern
ƒƒ
If If right rightbundle branch bundle branch
block is present, there block is present, there
may be an may be an ‘‘MM’’in V1 in V1
and/or a and/or a ‘‘WW’’in V6. in V6.
ƒƒ
Can occur in healthy Can occur in healthy
people with normal QRS people with normal QRS
width width ––partial RBBB partial RBBB

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QRS width QRS width
It is useful to look at leads V It is useful to look at leads V
11

and V and V
66
ƒƒ
LBBB and RBBB can be remembered by the LBBB and RBBB can be remembered by the
mnemonic: mnemonic:
ƒƒ
WWiiLLLLiaiaMMMMaaRRRRooWW
ƒƒ
Bundle branch block is caused either by Bundle branch block is caused either by
infarction or fibrosis (related to the ageing infarction or fibrosis (related to the ageing
process) process)

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The ST segment The ST segment
ƒƒ
The ST segment should sit on the The ST segment should sit on the isoelectric isoelectricline line
ƒƒ
It is abnormal if there is planar (i.e. flat) elevation It is abnormal if there is planar (i.e. flat) elevation
or depression of the ST segment or depression of the ST segment
ƒƒ
Planar ST elevation can represent an MI or Planar ST elevation can represent an MI or
Prinzmetal Prinzmetal’’ss((vasospastic vasospastic) angina ) angina
ƒƒ
Planar ST depression can represent Planar ST depression can represent ischaemia ischaemia

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Myocardial infarction Myocardial infarction
ƒƒ
Within hours: Within hours:
ƒƒT wave may become peaked T wave may become peaked
ƒƒST segment may begin to rise ST segment may begin to rise
ƒƒ
Within 24 hours: Within 24 hours:
ƒƒT wave inverts (may or may not persist) T wave inverts (may or may not persist)
ƒƒST elevation begins to resolve ST elevation begins to resolve
ƒƒIf a left ventricular aneurysm form s, ST elevation may persist If a left ventricular aneurysm form s, ST elevation may persist
ƒƒ
Within a few days: Within a few days:
ƒƒpathological Q waves can form and usually persist pathological Q waves can form and usually persist

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Myocardial infarction Myocardial infarction
ƒƒ
The leads affected determine the site of The leads affected determine the site of
the infarct the infarct
ƒƒ
Inferior InferiorII, III, II, III, aVFaVF
ƒƒ
Anteroseptal AnteroseptalV1V1--V4V4
ƒƒ
Anterolateral AnterolateralV4V4--V6, I, V6, I, aVLaVL
ƒƒ
Posterior PosteriorTall wide R and ST Tall wide R and ST↓↓in V1 in V1
and V2 and V2

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Acute Anterior MI Acute Anterior MI
ST

elevation

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Inferior MI Inferior MI
ST

elevation

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The ST segment The ST segment
ƒƒ
If the ST segment is elevated but slanted, If the ST segment is elevated but slanted,
it may not be significant it may not be significant
ƒƒ
If there are raised ST segments in most of If there are raised ST segments in most of
the leads, it may indicate the leads, it may indicate pericarditis pericarditis––
especially if the ST segments are saddle especially if the ST segments are saddle
shaped. There can also be PR segment shaped. There can also be PR segment
depression depression

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Pericarditis Pericarditis

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The T wave The T wave
ƒƒ
Are the T waves too tall? Are the T waves too tall?
ƒƒNo definite rule for height No definite rule for height
ƒƒT wave generally shouldn T wave generally shouldn’’t t
be taller than half the size be taller than half the size
of the preceding QRS of the preceding QRS
ƒƒCauses: Causes:
ƒƒ
Hyperkalaemia Hyperkalaemia
ƒƒ
Acute myocardial Acute myocardial
infarction infarction

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The T wave The T wave
ƒƒ
If the T wave is flat, it may indicate If the T wave is flat, it may indicate
hypokalaemia hypokalaemia
ƒƒ
If the T wave is inverted it may indicate If the T wave is inverted it may indicate
ischaemia ischaemia

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The QT interval The QT interval
ƒƒ
The QT interval is measured from the The QT interval is measured from the start startof the of the
QRS complex to the QRS complex to the endendof the T wave. of the T wave.
ƒƒ
The QT interval varies with heart rate The QT interval varies with heart rate
ƒƒ
As the heart rate gets faster, the QT interval gets As the heart rate gets faster, the QT interval gets
shorter shorter
ƒƒ
It is possible to correct the QT interval with It is possible to correct the QT interval with
respect to rate by using the following formula: respect to rate by using the following formula:
ƒƒQTcQTc= QT/ = QT/√√RR ( RR (QTcQTc= corrected QT) = corrected QT)

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The QT interval The QT interval
ƒƒ
The normal range for The normal range for QTcQTcis 0.38 is 0.38--0.42 0.42
ƒƒ
A short A short QTcQTcmay indicate may indicate hypercalcaemia hypercalcaemia
ƒƒ
A long A long QTcQTchas many causes has many causes
ƒƒ
Long Long QTcQTcincreases the risk of developing increases the risk of developing
an arrhythmia an arrhythmia

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The U wave The U wave
ƒƒ
U waves occur after the T wave and are U waves occur after the T wave and are
often difficult to see often difficult to see
ƒƒ
They are thought to be due to They are thought to be due to
repolarisation of the repolarisation of the atrial atrialseptum septum
ƒƒ
Prominent U waves can be a sign of Prominent U waves can be a sign of
hypokalaemia hypokalaemia, hyperthyroidism , hyperthyroidism

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Supraventricular Supraventricular

tachycardias tachycardias
ƒƒ
These are These are tachycardias tachycardiaswhere the impulse is initiated in where the impulse is initiated in
the atria ( the atria (sinoatrial sinoatrialnode, node, atrial atrialwall or wall or atrioventricular atrioventricular
node) node)
ƒƒ
If there is a normal conduction pathway when the If there is a normal conduction pathway when the
impulse reaches the ventricles, a narrow QRS complex impulse reaches the ventricles, a narrow QRS complex
is formed, hence they are narrow complex is formed, hence they are narrow complex tachycardias tachycardias
ƒƒ
However if there is a conduction problem in the However if there is a conduction problem in the
ventricles such as LBBB, then a broad QRS complex is ventricles such as LBBB, then a broad QRS complex is
formed. This would result in a form of broad complex formed. This would result in a form of broad complex
tachycardia tachycardia

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Atrial Atrial

Fibrillation Fibrillation
Features: Features: ƒƒ
There maybe tachycardia There maybe tachycardia
ƒƒ
The rhythm is usually irregularly irregular The rhythm is usually irregularly irregular
ƒƒ
No P waves are discernible No P waves are discernible ––instead instead
there is a shaky baseline there is a shaky baseline
ƒƒThis is because there is no order to This is because there is no order to atrial atrial
depolarisation, different areas of atrium depolarisation, different areas of atrium
depolarise at will depolarise at will

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Atrial Atrial

Fibrillation Fibrillation

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Atrial Atrial

flutter flutter
ƒƒ
There is a saw There is a saw--tooth baseline which rises above and tooth baseline which rises above and
dips below the dips below the isoelectric isoelectricline. line.
ƒƒ
Atrial Atrialrate 250/min rate 250/min
ƒƒ
This is created by circular circuits of depolarisation This is created by circular circuits of depolarisation
set up in the atria set up in the atria

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Ventricular Tachycardia Ventricular Tachycardia

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Ventricular Tachycardia Ventricular Tachycardia
ƒƒ
QRS complexes are wide and irregular in shape QRS complexes are wide and irregular in shape
ƒƒ
Usually secondary to infarction Usually secondary to infarction
ƒƒ
Circuits of depolarisation are set up in damaged Circuits of depolarisation are set up in damaged
myocardium myocardium
ƒƒ
This leads to recurrent early repolarisation of the This leads to recurrent early repolarisation of the
ventricle leading to tachycardia ventricle leading to tachycardia
ƒƒ
As the rhythm originates in the ventricles, there is a As the rhythm originates in the ventricles, there is a
broad QRS complex broad QRS complex
ƒƒ
Hence it is one of the causes of a broad complex Hence it is one of the causes of a broad complex
tachycardia tachycardia
ƒƒ
Need to differentiate with Need to differentiate with supraventricular supraventriculartachycardia tachycardia
with aberrant conduction with aberrant conduction

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Ventricular Fibrillation Ventricular Fibrillation

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Ventricular fibrillation Ventricular fibrillation
ƒƒ
Completely disordered ventricular Completely disordered ventricular
depolarisation depolarisation
ƒƒ
Not compatible with a cardiac output Not compatible with a cardiac output
ƒƒ
Results in a completely irregular trace Results in a completely irregular trace
consisting of broad QRS complexes of consisting of broad QRS complexes of
varying widths, heights and rates varying widths, heights and rates

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Elements of the tracing Elements of the tracing
P wave P wave
ƒƒMagnitude and shape, Magnitude and shape,
ƒƒe.g. P e.g. P pulmonale pulmonale, P , P mitrale mitrale
PR interval PR interval
(start of P to start of QRS) (start of P to start of QRS)
ƒƒNormal 3 Normal 3--5 small squares, 5 small squares,
0.12 0.12--0.2s 0.2s
Pathological Q waves? Pathological Q waves?
QRS complex QRS complex
ƒƒMagnitude, duration and Magnitude, duration and
shape shape
ƒƒ≤≤3 small squares or 0.12s 3 small squares or 0.12s
duration duration
ST segment ST segment
ƒƒShould be Should be isoelectric isoelectric
T wave T wave
ƒƒMagnitude and direction Magnitude and direction
QT interval QT interval

(Start QRS to end of T) (Start QRS to end of T)
ƒƒNormally Normally < 2 big squares or < 2 big squares or
0.4s at 60bpm 0.4s at 60bpm
ƒƒCorrected to 60bpm Corrected to 60bpm
ƒƒ((QTcQTc) = QT/ ) = QT/√√RRRR
interval interval

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Further work Further work
ƒƒ
Check out the various quizzes / games Check out the various quizzes / games
available on the Imperial Intranet available on the Imperial Intranet
ƒƒ
Get doctors on the wards to run through a Get doctors on the wards to run through a
patient patient’’s ECG with you s ECG with you