Ecg 131022135749-phpapp02

medics.ccmedics.ccmedics.ccmedics.ccmedics.ccmedics.cc
EElectrolectroCCardioardioGGraphyraphy
ECG made extra easyECG made extra easy……

OverviewOverview
Objectives for this tutorialObjectives for this tutorial
What is an ECG?What is an ECG?
Overview of performingOverview of performing
electrocardiography on a patientelectrocardiography on a patient
Simple physiologySimple physiology
Interpreting the ECGInterpreting the ECG

ObjectivesObjectives
By the end of this tutorial the student should be able to:By the end of this tutorial the student should be able to:
State a definition of electrocardiogramState a definition of electrocardiogram
Perform an ECG on a patient, including explaining to the patientPerform an ECG on a patient, including explaining to the patient
what is involvedwhat is involved
Draw a diagram of the conduction pathway of the heartDraw a diagram of the conduction pathway of the heart
Draw a simple labelled diagram of an ECG tracingDraw a simple labelled diagram of an ECG tracing
List the steps involved in interpreting an ECG tracing in an ordList the steps involved in interpreting an ECG tracing in an orderlyerly
wayway
Recite the normal limits of the parameters of various parts of tRecite the normal limits of the parameters of various parts of thehe
ECGECG
InterpretInterpret ECGsECGs showing the following pathology:showing the following pathology:
MI, AF, 1st 2MI, AF, 1st 2ndnd and 3and 3rdrd degree heart block, pdegree heart block, p pulmonalepulmonale, p, p mitralemitrale, Wolff, Wolff--
ParkinsonParkinson--White syndrome, LBBB, RBBB, Left and Right axis deviation,White syndrome, LBBB, RBBB, Left and Right axis deviation,
LVH,LVH, pericarditispericarditis, Hyper, Hyper-- andand hypokalaemiahypokalaemia, prolonged QT., prolonged QT.

What is an ECG?What is an ECG?
ECG =ECG = ElectrocardiogramElectrocardiogram
Tracing of heartTracing of heart’’s electrical activitys electrical activity

Recording an ECGRecording an ECG

Overview of procedureOverview of procedure
GRIPGRIP
Greet, rapport, introduce,Greet, rapport, introduce,
identify, privacy, explainidentify, privacy, explain
procedure, permissionprocedure, permission
Lay patient downLay patient down
Expose chest, wrists,Expose chest, wrists,
anklesankles
Clean electrode sitesClean electrode sites
May need to shaveMay need to shave
Apply electrodesApply electrodes
Attach wiresAttach wires correctlycorrectly
Turn on machineTurn on machine
Calibrate to 10mm/mVCalibrate to 10mm/mV
Rate at 25mm/sRate at 25mm/s
Record and printRecord and print
LabelLabel the tracingthe tracing
Name,Name, DoBDoB, hospital, hospital
number, date andnumber, date and
time, reason fortime, reason for
recordingrecording
Disconnect ifDisconnect if
adequate and removeadequate and remove
electrodeselectrodes

Electrode placementElectrode placement
10 electrodes in total are placed on the10 electrodes in total are placed on the
patientpatient
Firstly selfFirstly self--adhesiveadhesive ‘‘dotsdots’’ are attached toare attached to
the patient. These have single electricalthe patient. These have single electrical
contacts on themcontacts on them
The 10 leads on the ECG machine areThe 10 leads on the ECG machine are
then clipped onto the contacts of thethen clipped onto the contacts of the ‘‘dotsdots’’

Electrode placement in 12 leadElectrode placement in 12 lead
ECGECG
6 are chest electrodes6 are chest electrodes
Called V1Called V1--6 or C16 or C1--66
4 are limb electrodes4 are limb electrodes
Right armRight arm RRideide
Left armLeft arm YYourour
Left legLeft leg GGreenreen
Right legRight leg BBikeike
RememberRemember
TheThe right legright leg electrodeelectrode
is a neutral oris a neutral or ““dummydummy””!!

Electrode placementElectrode placement
For the chest electrodesFor the chest electrodes
V1V1 44thth intercostalintercostal space rightspace right sternalsternal edgeedge
V2V2 44thth intercostalintercostal space leftspace left sternalsternal edgeedge
(to find the 4(to find the 4thth
space, palpate thespace, palpate the manubriosternalmanubriosternal angle (ofangle (of
Louis)Louis)
Directly adjacent is the 2Directly adjacent is the 2ndnd
rib, with the 2rib, with the 2ndnd
intercostalintercostal spacespace
directly below. Palpate inferiorly to find the 3directly below. Palpate inferiorly to find the 3rdrd
and then 4and then 4thth
spacespace
VV44 over the apex (5over the apex (5thth ICS midICS mid--clavicularclavicular
line)line)
VV33 halfway between V2 and V4halfway between V2 and V4
V5V5 at the same level as V4 but on theat the same level as V4 but on the
anterior axillary lineanterior axillary line
V6V6 at the same level as V4 and V5 but onat the same level as V4 and V5 but on
the midthe mid--axillaryaxillary lineline

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

ElectrophysiologyElectrophysiology

ElectrophysiologyElectrophysiology
Pacemaker =Pacemaker = sinoatrialsinoatrial nodenode
Impulse travels across atriaImpulse travels across atria
Reaches AV nodeReaches AV node
Transmitted alongTransmitted along interventricularinterventricular septum in Bundle ofseptum in Bundle of
HisHis
Bundle splits in two (right and left branches)Bundle splits in two (right and left branches)
Purkinje fibresPurkinje fibres

Overall
direction
of
cardiac
impulse

How does the ECG work?How does the ECG work?
Electrical impulse (wave of depolarisation) picked up byElectrical impulse (wave of depolarisation) picked up by
placing electrodes on patientplacing electrodes on patient
The voltage change is sensed by measuring the currentThe voltage change is sensed by measuring the current
change across 2 electrodeschange across 2 electrodes –– a positive electrode and aa positive electrode and a
negative electrodenegative electrode
If the electrical impulse travelsIf the electrical impulse travels towardstowards the positivethe positive
electrode this results in aelectrode this results in a positivepositive deflectiondeflection
If the impulse travelsIf the impulse travels awayaway from the positive electrodefrom the positive electrode
this results in athis results in a negativenegative deflectiondeflection

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

Types of LeadsTypes of Leads
Coronal plane (Limb Leads)Coronal plane (Limb Leads)
1.1. Bipolar leadsBipolar leads —— l , l l , l l ll , l l , l l l
2.2. UnipolarUnipolar leadsleads —— aVLaVL ,, aVRaVR ,, aVFaVF
Transverse planeTransverse plane
VV11 —— VV66 (Chest Leads)(Chest Leads)

Electrodes around the heartElectrodes around the heart

LeadsLeads
How are the 12 leads on theHow are the 12 leads on the
ECG (I, II, III,ECG (I, II, III, aVLaVL,, aVFaVF,,
aVRaVR, V1, V1 –– 6) formed6) formed
using only 9 electrodesusing only 9 electrodes
(and a neutral)?(and a neutral)?
Lead I is formed using theLead I is formed using the
right arm electrode (red)right arm electrode (red)
as the negative electrodeas the negative electrode
and theand the left arm (yellow)left arm (yellow)
electrode as the positiveelectrode as the positive
- Lead I +

LeadsLeads
- Lead I +

LeadsLeads
Lead II is formedLead II is formed
using theusing the right armright arm
electrode (red)electrode (red) as theas the
negative electrodenegative electrode
and theand the left legleft leg
electrodeelectrode as theas the
positivepositive
Lead II

Lead II

LeadsLeads
Lead III is formed using theLead III is formed using the left armleft arm
electrodeelectrode as the negative electrode andas the negative electrode and
thethe left leg electrodeleft leg electrode as the positiveas the positive
aVLaVL,, aVFaVF, and, and aVRaVR areare composite leadscomposite leads,,
computed using the information from thecomputed using the information from the
other leadsother leads

Leads and what they tell youLeads and what they tell you
Limb leadsLimb leads
Limb leads look at the heart in the coronalLimb leads look at the heart in the coronal
planeplane
aVLaVL, I and II = lateral, I and II = lateral
II, III andII, III and aVFaVF = inferior= inferior
aVRaVR = right side of the heart= right side of the heart

Leads look at the heart fromLeads look at the heart from
different directionsdifferent directions
axis

Leads and what they tell youLeads and what they tell you
Each lead can be thought of asEach lead can be thought of as ‘‘looking atlooking at’’ an areaan area
of myocardiumof myocardium
Chest leadsChest leads
VV11 to Vto V66 ‘‘looklook’’ at the heart on the transverse plainat the heart on the transverse plain
VV11 and Vand V22 look at the anterior of the heart and Rlook at the anterior of the heart and R
ventricleventricle
VV33 and Vand V44 = anterior and= anterior and septalseptal
VV55 and Vand V66 = lateral and left ventricle= lateral and left ventricle

Elements of the traceElements of the trace

What do the componentsWhat do the components
represent?represent?
P wave =P wave = atrialatrial depolarisationdepolarisation
QRS =QRS = ventricular depolarisationventricular depolarisation
T =T = repolarisation of therepolarisation of the
ventriclesventricles

CheckCheck
NameName
DoBDoB
Time and dateTime and date
Indication e.g.Indication e.g. ““chest painchest pain”” oror ““routine preroutine pre--opop””
Any previous or subsequentAny previous or subsequent ECGsECGs
Is it part of a serial ECG sequence? In which case it may beIs it part of a serial ECG sequence? In which case it may be
numberednumbered
CalibrationCalibration
RateRate
RhythmRhythm
AxisAxis
Elements of the tracing in each leadElements of the tracing in each lead

CalibrationCalibration
Check that your ECG is calibrated correctlyCheck that your ECG is calibrated correctly
HeightHeight
10mm = 1mV10mm = 1mV
Look for a reference pulse which should be theLook for a reference pulse which should be the
rectangular looking wave somewhere near therectangular looking wave somewhere near the
left of the paper. It should be 10mm (10 smallleft of the paper. It should be 10mm (10 small
squares) tallsquares) tall
Paper speedPaper speed
25mm/s25mm/s
25 mm (25 small squares / 5 large squares)25 mm (25 small squares / 5 large squares)
equals one secondequals one second

RateRate
If the heart rate isIf the heart rate is regularregular
Count the number of large squares betweenCount the number of large squares between
R wavesR waves
i.e. the RR interval in large squaresi.e. the RR interval in large squares
Rate =Rate = 300300
RRRR
e.g. RR =e.g. RR = 44 large squareslarge squares
300/300/44 = 75 beats per minute= 75 beats per minute

RateRate
If the rhythm isIf the rhythm is irregularirregular (see next slide on rhythm(see next slide on rhythm
to check whether your rhythm is regular or not) itto check whether your rhythm is regular or not) it
may be better to estimate the rate using themay be better to estimate the rate using the
rhythm strip at the bottom of the ECG (usuallyrhythm 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 stripIf you count the number of R waves on that strip
and multiple by 6 you will get the rateand multiple by 6 you will get the rate

RhythmRhythm
Is the rhythm regular?Is the rhythm regular?
The easiest way to tell is to take a sheet of paper and line upThe easiest way to tell is to take a sheet of paper and line up oneone
edge with the tips of the R waves on the rhythm strip.edge with the tips of the R waves on the rhythm strip.
Mark off on the paper the positions of 3 or 4 R wave tipsMark off on the paper the positions of 3 or 4 R wave tips
Move the paper along the rhythm strip so that your first mark liMove the paper along the rhythm strip so that your first mark linesnes
up with another R wave tipup with another R wave tip
See if the subsequent R wave tips line up with the subsequentSee if the subsequent R wave tips line up with the subsequent
marks on your papermarks on your paper
If they do line up, the rhythm is regular. If not, the rhythm iIf they do line up, the rhythm is regular. If not, the rhythm is irregulars irregular

RhythmRhythm
Sinus RhythmSinus Rhythm
DefinitionDefinition Cardiac impulse originates from theCardiac impulse originates from the
sinus node. Every QRS must besinus node. Every QRS must be
preceded by a P wave.preceded by a P wave.
(This does not mean that every P wave must be(This does not mean that every P wave must be
followed by a QRSfollowed by a QRS –– such as in 2such as in 2ndnd degree heartdegree heart
block where some P waves are not followed by ablock where some P waves are not followed by a
QRS, however every QRS is preceded by a P waveQRS, however every QRS is preceded by a P wave
and the rhythm originates in the sinus node, hence itand the rhythm originates in the sinus node, hence it
is a sinus rhythm. It could be said that it is not ais a sinus rhythm. It could be said that it is not a
normalnormal sinus rhythm)sinus rhythm)

RhythmRhythm
Sinus arrhythmiaSinus arrhythmia
There is a change in heart rate depending on the phase ofThere is a change in heart rate depending on the phase of
respirationrespiration
Q. If a person with sinus arrhythmia inspires, what happens to tQ. If a person with sinus arrhythmia inspires, what happens to theirheir
heart rate?heart rate?
A. The heart rate speeds up. This is because on inspiration thA. The heart rate speeds up. This is because on inspiration there isere is
aa decreasedecrease inin intrathoracicintrathoracic pressure, this leads to an increasedpressure, this leads to an increased
venous return to the right atrium. Increased stretching of thevenous return to the right atrium. Increased stretching of the rightright
atrium sets off a brainstem reflex (Bainbridgeatrium sets off a brainstem reflex (Bainbridge’’s reflex) that leads tos reflex) that leads to
sympathetic activation of the heart, hence it speeds up)sympathetic activation of the heart, hence it speeds up)
This physiological phenomenon is more apparent in children andThis physiological phenomenon is more apparent in children and
young adultsyoung adults

RhythmRhythm
SinusSinus bradycardiabradycardia
Rhythm originates in the sinus nodeRhythm originates in the sinus node
Rate of less than 60 beats per minuteRate of less than 60 beats per minute
Sinus tachycardiaSinus tachycardia
Rhythm originates in the sinus nodeRhythm originates in the sinus node
Rate of greater than 100 beats per minuteRate of greater than 100 beats per minute

AxisAxis
The axis can be though of as the overallThe axis can be though of as the overall
direction of the cardiac impulse or wave ofdirection of the cardiac impulse or wave of
depolarisation of the heartdepolarisation of the heart
An abnormal axis (axis deviation) can giveAn abnormal axis (axis deviation) can give
a clue to possible pathologya clue to possible pathology

AxisAxis
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

Axis deviationAxis deviation -- CausesCauses
WolffWolff--ParkinsonParkinson--WhiteWhite
syndrome can cause both Leftsyndrome can cause both Left
and Right axis deviationand Right axis deviation
A useful mnemonic:A useful mnemonic:
““RAD RALPHRAD RALPH thethe LADLAD fromfrom
VILLAVILLA””
RRightight AAxisxis DDeviationeviation
RRight ventricular hypertrophyight ventricular hypertrophy
AAnterolateralnterolateral MIMI
LLefteft PPosteriorosterior HHemiblockemiblock
LLefteft AAxisxis DDeviationeviation
VVentricular tachycardiaentricular tachycardia
IInferior MInferior MI
LLeft ventricular hypertrophyeft ventricular hypertrophy
LLefteft AAnteriornterior hemiblockhemiblock

The P waveThe P wave
The P wave representsThe P wave represents atrialatrial
depolarisationdepolarisation
It can be thought of as beingIt can be thought of as being
made up of two separatemade up of two separate
waves due towaves due to rightright atrialatrial
depolarisation anddepolarisation and leftleft atrialatrial
depolarisation.depolarisation.
Which occurs first?Which occurs first?
RightRight atrialatrial depolarisationdepolarisation
right atrial depolarisation
Sum of
right and
left waves
left atrial depolarisation

DimensionsDimensions
No hard and fast rulesNo hard and fast rules
HeightHeight
a P wave over 2.5mm should arouse suspiciona P wave over 2.5mm should arouse suspicion
LengthLength
a P wave longer than 0.08s (2 small squares) shoulda P wave longer than 0.08s (2 small squares) should
arouse suspicionarouse suspicion

HeightHeight
A tall P wave (overA tall P wave (over
2.5mm) can be called2.5mm) can be called PP
pulmonalepulmonale
Occurs due toOccurs due to RR atrialatrial
hypertrophyhypertrophy
Causes include:Causes include:
pulmonary hypertension,pulmonary hypertension,
pulmonarypulmonary stenosisstenosis
tricuspidtricuspid stenosisstenosis
normal P pulmonale
>2.5mm

LengthLength
A P wave with a lengthA P wave with a length
>0.08 seconds (2 small>0.08 seconds (2 small
squares) and a bifidsquares) and a bifid
shape is calledshape is called PP mitralemitrale
It is caused by leftIt is caused by left atrialatrial
hypertrophy and delayedhypertrophy and delayed
leftleft atrialatrial depolarisationdepolarisation
Causes include:Causes include:
Mitral valve diseaseMitral valve disease
LVHLVH
normal P mitrale

The PR intervalThe PR interval
The PR interval is measured between theThe PR interval is measured between the
start of the P wave to the start of the QRSstart of the P wave to the start of the QRS
complexcomplex
(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 thewave the PR interval is measured from the
start of the P wave to the start of thestart 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)

The PR interval corresponds to the timeThe PR interval corresponds to the time
period between depolarisation of the atriaperiod between depolarisation of the atria
and ventricular depolarisation.and ventricular depolarisation.
A normal PR interval is between 0.12 andA normal PR interval is between 0.12 and
0.2 seconds ( 30.2 seconds ( 3--5 small squares)5 small squares)

If the PR interval is short (less than 3 smallIf the PR interval is short (less than 3 small
squares) it may signify that there is an accessorysquares) it may signify that there is an accessory
electrical pathway between the atria and theelectrical pathway between the atria and the
ventricles, hence the ventricles depolarise earlyventricles, hence the ventricles depolarise early
giving a short PR interval.giving a short PR interval.
One example of this is WolffOne example of this is Wolff--ParkinsonParkinson--WhiteWhite
syndrome where the accessory pathway issyndrome where the accessory pathway is
called the bundle of Kent. See next slide for ancalled the bundle of Kent. See next slide for an
animation to explain thisanimation to explain this

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

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

If the PR interval looks as though it isIf the PR interval looks as though it is wideningwidening
every beat and then a QRS complex is missing,every beat and then a QRS complex is missing,
there isthere is 22ndnd degree heart block,degree heart block, MobitzMobitz type Itype I..
The lengthening of the PR interval inThe lengthening of the PR interval in
subsequent beats is known as thesubsequent beats is known as the WenckebachWenckebach
phenomenonphenomenon
(remember ((remember (ww)one,)one, WWenckebachenckebach,, wwidens)idens)
If the PR interval isIf the PR interval is constantconstant but then there is abut then there is a
missed QRS complex then there ismissed QRS complex then there is 22ndnd degreedegree
heart block,heart block, MobitzMobitz type IItype II

If there isIf there is no discernable relationshipno discernable relationship
between the P waves and the QRSbetween the P waves and the QRS
complexes, thencomplexes, then 33rdrd
degree heartdegree heart block isblock is
presentpresent

Heart block (AV node block)Heart block (AV node block)
SummarySummary
11stst degreedegree
constant PR, >0.2 secondsconstant PR, >0.2 seconds
22ndnd degree type 1 (degree type 1 (WenckebachWenckebach))
PR widens over subsequent beats then a QRS is droppedPR widens over subsequent beats then a QRS is dropped
22ndnd degree type 2degree type 2
PR is constant then a QRS is droppedPR is constant then a QRS is dropped
33rdrd degreedegree
No discernable relationship between p waves and QRSNo discernable relationship between p waves and QRS
complexescomplexes

The Q waveThe Q wave
Are there any pathological QAre there any pathological Q
waves?waves?
A Q wave can be pathologicalA Q wave can be pathological
if it is:if it is:
Deeper than 2 small squaresDeeper than 2 small squares
(0.2mV)(0.2mV)
and/orand/or
Wider than 1 small squareWider than 1 small square
(0.04s)(0.04s)
and/orand/or
In a lead other than III or oneIn a lead other than III or one
of the leads that look at theof the leads that look at the
heart from the left (I, II,heart from the left (I, II, aVLaVL,,
V5 and V6) where small QsV5 and V6) where small Qs
(i.e. not meeting the criteria(i.e. not meeting the criteria
above) can be normalabove) can be normal
Normal if in
I,II,III,aVL,V5-6
Pathological
anywhere

The QRS heightThe QRS height
If the complexes in the chest leads lookIf the complexes in the chest leads look
very tall, consider left ventricularvery tall, consider left ventricular
hypertrophy (LVH)hypertrophy (LVH)
If the depth of the S wave in VIf the depth of the S wave in V11 added toadded to
the height of the R wave in Vthe height of the R wave in V66 comes tocomes to
more than 35mm, LVH is presentmore than 35mm, LVH is present

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

LBBBLBBB
IfIf leftleft bundle branch blockbundle branch block
is present, the QRSis present, the QRS
complex may look like acomplex may look like a
‘‘WW’’ in Vin V11 and/or anand/or an ‘‘MM’’
shape in Vshape in V6.6.
New onset LBBB withNew onset LBBB with
chest pain considerchest pain consider
Myocardial infarctionMyocardial infarction
Not possible to interpretNot possible to interpret
the ST segment.the ST segment.

RBBBRBBB
It is also called RSRIt is also called RSR
patternpattern
IfIf rightright bundle branchbundle branch
block is present, thereblock is present, there
may be anmay be an ‘‘MM’’ in V1in V1
and/or aand/or a ‘‘WW’’ in V6.in V6.
Can occur in healthyCan occur in healthy
people with normal QRSpeople with normal QRS
widthwidth –– partial RBBBpartial RBBB

QRS widthQRS width
It is useful to look at leads VIt is useful to look at leads V11 and Vand V66
LBBB and RBBB can be remembered by theLBBB and RBBB can be remembered by the
mnemonic:mnemonic:
WWiiLLLLiaiaMM MMaaRRRRooWW
Bundle branch block is caused either byBundle branch block is caused either by
infarction or fibrosis (related to the ageinginfarction or fibrosis (related to the ageing
process)process)

The ST segmentThe ST segment
The ST segment should sit on theThe ST segment should sit on the isoelectricisoelectric lineline
It is abnormal if there is planar (i.e. flat) elevationIt is abnormal if there is planar (i.e. flat) elevation
or depression of the ST segmentor depression of the ST segment
Planar ST elevation can represent an MI orPlanar ST elevation can represent an MI or
PrinzmetalPrinzmetal’’ss ((vasospasticvasospastic) angina) angina
Planar ST depression can representPlanar ST depression can represent ischaemiaischaemia

Within hours:Within hours:
T wave may become peakedT wave may become peaked
ST segment may begin to riseST segment may begin to rise
Within 24 hours:Within 24 hours:
T wave inverts (may or may not persist)T wave inverts (may or may not persist)
ST elevation begins to resolveST elevation begins to resolve
If a left ventricular aneurysm forms, ST elevation may persistIf a left ventricular aneurysm forms, ST elevation may persist
Within a few days:Within a few days:
pathological Q waves can form and usually persistpathological Q waves can form and usually persist

The leads affected determine the site ofThe leads affected determine the site of
the infarctthe infarct
InferiorInferior II, III,II, III, aVFaVF
AnteroseptalAnteroseptal V1V1--V4V4
AnterolateralAnterolateral V4V4--V6, I,V6, I, aVLaVL
PosteriorPosterior Tall wide R and STTall wide R and ST↓↓ in V1in V1
and V2and V2

Acute Anterior MIAcute Anterior MI
ST elevation

Inferior MIInferior MI
ST elevation

The ST segmentThe ST segment
If the ST segment is elevated but slanted,If the ST segment is elevated but slanted,
it may not be significantit may not be significant
If there are raised ST segments in most ofIf there are raised ST segments in most of
the leads, it may indicatethe leads, it may indicate pericarditispericarditis ––
especially if the ST segments are saddleespecially if the ST segments are saddle
shaped. There can also be PR segmentshaped. There can also be PR segment
depressiondepression

PericarditisPericarditis

The T waveThe T wave
Are the T waves too tall?Are the T waves too tall?
No definite rule for heightNo definite rule for height
T wave generally shouldnT wave generally shouldn’’tt
be taller than half the sizebe taller than half the size
of the preceding QRSof the preceding QRS
Causes:Causes:
HyperkalaemiaHyperkalaemia
Acute myocardialAcute myocardial
infarctioninfarction

The T waveThe T wave
If the T wave is flat, it may indicateIf the T wave is flat, it may indicate
hypokalaemiahypokalaemia
If the T wave is inverted it may indicateIf the T wave is inverted it may indicate
ischaemiaischaemia

The QT intervalThe QT interval
The QT interval is measured from theThe QT interval is measured from the startstart of theof the
QRS complex to theQRS complex to the endend of the T wave.of the T wave.
The QT interval varies with heart rateThe QT interval varies with heart rate
As the heart rate gets faster, the QT interval getsAs the heart rate gets faster, the QT interval gets
shortershorter
It is possible to correct the QT interval withIt is possible to correct the QT interval with
respect to rate by using the following formula:respect to rate by using the following formula:
QTcQTc = QT/= QT/√√RR (RR (QTcQTc = corrected QT)= corrected QT)

The QT intervalThe QT interval
The normal range forThe normal range for QTcQTc is 0.38is 0.38--0.420.42
A shortA short QTcQTc may indicatemay indicate hypercalcaemiahypercalcaemia
A longA long QTcQTc has many causeshas many causes
LongLong QTcQTc increases the risk of developingincreases the risk of developing
an arrhythmiaan arrhythmia

The U waveThe U wave
U waves occur after the T wave and areU waves occur after the T wave and are
often difficult to seeoften difficult to see
They are thought to be due toThey are thought to be due to
repolarisation of therepolarisation of the atrialatrial septumseptum
Prominent U waves can be a sign ofProminent U waves can be a sign of
hypokalaemiahypokalaemia, hyperthyroidism, hyperthyroidism

SupraventricularSupraventricular tachycardiastachycardias
These areThese are tachycardiastachycardias where the impulse is initiated inwhere the impulse is initiated in
the atria (the atria (sinoatrialsinoatrial node,node, atrialatrial wall orwall or atrioventricularatrioventricular
node)node)
If there is a normal conduction pathway when theIf there is a normal conduction pathway when the
impulse reaches the ventricles, a narrow QRS compleximpulse reaches the ventricles, a narrow QRS complex
is formed, hence they are narrow complexis formed, hence they are narrow complex tachycardiastachycardias
However if there is a conduction problem in theHowever if there is a conduction problem in the
ventricles such as LBBB, then a broad QRS complex isventricles such as LBBB, then a broad QRS complex is
formed. This would result in a form of broad complexformed. This would result in a form of broad complex
tachycardiatachycardia

AtrialAtrial FibrillationFibrillation
Features:Features:
There maybe tachycardiaThere maybe tachycardia
The rhythm is usually irregularly irregularThe rhythm is usually irregularly irregular
No P waves are discernibleNo P waves are discernible –– insteadinstead
there is a shaky baselinethere is a shaky baseline
This is because there is no order toThis is because there is no order to atrialatrial
depolarisation, different areas of atriumdepolarisation, different areas of atrium
depolarise at willdepolarise at will

AtrialAtrial FibrillationFibrillation

AtrialAtrial flutterflutter
There is a sawThere is a saw--tooth baseline which rises above andtooth baseline which rises above and
dips below thedips below the isoelectricisoelectric line.line.
AtrialAtrial rate 250/minrate 250/min
This is created by circular circuits of depolarisationThis is created by circular circuits of depolarisation
set up in the atriaset up in the atria

Ventricular TachycardiaVentricular Tachycardia

Ventricular TachycardiaVentricular Tachycardia
QRS complexes are wide and irregular in shapeQRS complexes are wide and irregular in shape
Usually secondary to infarctionUsually secondary to infarction
Circuits of depolarisation are set up in damagedCircuits of depolarisation are set up in damaged
myocardiummyocardium
This leads to recurrent early repolarisation of theThis leads to recurrent early repolarisation of the
ventricle leading to tachycardiaventricle leading to tachycardia
As the rhythm originates in the ventricles, there is aAs the rhythm originates in the ventricles, there is a
broad QRS complexbroad QRS complex
Hence it is one of the causes of a broad complexHence it is one of the causes of a broad complex
tachycardiatachycardia
Need to differentiate withNeed to differentiate with supraventricularsupraventricular tachycardiatachycardia
with aberrant conductionwith aberrant conduction

Ventricular FibrillationVentricular Fibrillation

Ventricular fibrillationVentricular fibrillation
Completely disordered ventricularCompletely disordered ventricular
depolarisationdepolarisation
Not compatible with a cardiac outputNot compatible with a cardiac output
Results in a completely irregular traceResults in a completely irregular trace
consisting of broad QRS complexes ofconsisting of broad QRS complexes of
varying widths, heights and ratesvarying widths, heights and rates

Elements of the tracingElements of the tracing
P waveP wave
Magnitude and shape,Magnitude and shape,
e.g. Pe.g. P pulmonalepulmonale, P, P mitralemitrale
PR intervalPR interval (start of P to start of QRS)(start of P to start of QRS)
Normal 3Normal 3--5 small squares,5 small squares,
0.120.12--0.2s0.2s
Pathological Q waves?Pathological Q waves?
QRS complexQRS complex
Magnitude, duration andMagnitude, duration and
shapeshape
≤≤ 3 small squares or 0.12s3 small squares or 0.12s
durationduration
ST segmentST segment
Should beShould be isoelectricisoelectric
T waveT wave
Magnitude and directionMagnitude and direction
QT intervalQT interval (Start QRS to end of T)(Start QRS to end of T)
NormallyNormally < 2 big squares or< 2 big squares or
0.4s at 60bpm0.4s at 60bpm
Corrected to 60bpmCorrected to 60bpm
((QTcQTc) = QT/) = QT/√√RRRRintervalinterval

Further workFurther work
Check out the various quizzes / gamesCheck out the various quizzes / games
available on the Imperial Intranetavailable on the Imperial Intranet
Get doctors on the wards to run through aGet doctors on the wards to run through a
patientpatient’’s ECG with yous ECG with you

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