ElectroCardioGraphy (ECG) made extra easy
Please support this website by 1 , 3 or 5 $$
Files Size:: 1.3 MB
ElectroCardioGraphy
ECG made extra easy …
medics.cc
—————————————————–Page 1—————————————————–
Overview
Objectives for this tutorial What is an ECG?
Overview of performing
electrocardiography on a patient Simple physiology
Interpreting the ECG
medics.cc
—————————————————–Page 2—————————————————–
Objectives
By the end of this tutorial the student should be able to:
State a definition of electrocardiogram
Perform an ECG on a patient, including explaining to the patient what is involved
Draw a diagram of the conduction pathway of the heart Draw a simple labelled diagram of an ECG tracing
List the steps involved in interpreting an ECG tracing in an ord erly way
Recite the normal limits of the parameters of various parts of t he ECG
Interpret ECGs showing the following pathology:
MI, AF, 1st 2 nd and 3 rd degree heart block, p pulmonale , p mitrale , Wolff – Parkinson – White syndrome, LBBB, RBBB, Left and Right axis deviation, LVH, pericarditis , Hyper – and hypokalaemia , prolonged QT.
medics.cc
—————————————————–Page 3—————————————————–
ECG =
What is an ECG?
Tracing of heart ’ s electrical activity
medics.cc
—————————————————–Page 4—————————————————–
Recording an ECG
medics.cc
—————————————————–Page 5—————————————————–
Overview of procedure
GRIP
Greet, rapport, introduce, identify, privacy, explain procedure, permission
Lay patient down
Expose chest, wrists, ankles
Clean electrode sites
May need to shave
Apply electrodes
Attach wires correctly
Turn on machine
Calibrate to 10mm/mV Rate at 25mm/s
Record and print Label the tracing
Name, DoB , hospital number, date and time, reason for recording
Disconnect if
adequate and remove electrodes
medics.cc
—————————————————–Page 6—————————————————–
10 electrodes in total are placed on the patient
Firstly self – adhesive ‘ dots ’ are attached to the patient. These have single electrical contacts on them
The 10 leads on the ECG machine are then clipped onto the contacts of the ‘ dots ’
medics.cc
—————————————————–Page 7—————————————————–
Electrode placement in 12 lead
6 are chest electrodes
Called V1 – 6 or C1 – 6
4 are limb electrodes
Right arm Left arm Left leg
Right leg
Remember
R ide Y our
G reen B ike
The right leg electrode is a neutral or “ dummy ” !
medics.cc
—————————————————–Page 8—————————————————–
For the chest electrodes
V1 4 th intercostal space right sternal edge V2 4 th intercostal space left sternal edge
(to find the 4 th space, palpate the manubriosternal angle (of Louis)
Directly adjacent is the 2 nd rib, with the 2 nd intercostal space directly below. Palpate inferiorly to find the 3 rd and then 4 th space
V 4 over the apex (5 th ICS mid – clavicular line)
V 3 halfway between V2 and V4
V5 at the same level as V4 but on the anterior axillary line
V6 at the same level as V4 and V5 but on the mid – axillary line
medics.cc
—————————————————–Page 9—————————————————–
Recording the trace
Different ECG machines have different buttons that you have to press.
Ask one of the staff on the ward if it is a machine that you are unfamiliar with.
Ask the patient to relax completely. Any skeletal muscle activity will be picked up as interference.
If the trace obtained is no good, check that all the dots are stuck down properly – they have a tendency to fall off.
medics.cc
—————————————————–Page 10—————————————————–
Electrophysiology
medics.cc
—————————————————–Page 11—————————————————–
Electrophysiology
Pacemaker = sinoatrial node
Impulse travels across atria
Reaches AV node
Transmitted along interventricular septum in Bundle of His
Bundle splits in two (right and left branches)
Purkinje fibres
medics.cc
—————————————————–Page 12—————————————————–
Overall
direction of
cardiac impulse
medics.cc
—————————————————–Page 13—————————————————–
How does the ECG work?
Electrical impulse (wave of depolarisation) picked up by placing electrodes on patient
The voltage change is sensed by measuring the current change across 2 electrodes – a positive electrode and a negative electrode
If the electrical impulse travels towards the positive electrode this results in a positive deflection
If the impulse travels away from the positive electrode this results in a negative deflection
medics.cc
—————————————————–Page 14—————————————————–
Away from
Towards
the
the
electrode
electrode
= negative
= positive
deflection
deflection
Direction of impulse (axis)
medics.cc
—————————————————–Page 15—————————————————–
Types of Leads
Coronal plane (Limb Leads)
1. Bipolar leads — l , l l , l l l
2. Unipolar leads — aVL , aVR , aVF
Transverse plane
V 1 — V 6 (Chest Leads)
medics.cc
—————————————————–Page 16—————————————————–
Electrodes around the heart
—————————————————–Page 17—————————————————–
Leads
How are the 12 leads on the
ECG (I, II, III, aVL , aVF , aVR , V1 – 6) formed
using only 9 electrodes (and a neutral)?
Lead I is formed using the right arm electrode (red) as the negative electrode and the left arm (yellow) electrode as the positive
– Lead I +
medics.cc
—————————————————–Page 18—————————————————–
Leads
– Lead I +
medics.cc
—————————————————–Page 19—————————————————–
Leads
Lead II is formed
using the right arm
electrode (red) as the negative electrode and the left leg electrode as the positive
Lead II
medics.cc
—————————————————–Page 20—————————————————–
Lead II
medics.cc
—————————————————–Page 21—————————————————–
Leads
Lead III is formed using the left arm
electrode as the negative electrode and the left leg electrode as the positive
aVL , aVF , and aVR are composite leads , computed using the information from the other leads
medics.cc
—————————————————–Page 22—————————————————–
Leads and what they tell you
Limb leads
Limb leads look at the heart in the coronal
plane
aVL , I and II = lateral II, III and aVF = inferior
aVR = right side of the heart
medics.cc
—————————————————–Page 23—————————————————–
Leads look at the heart from
different directions
axis
—————————————————–Page 24—————————————————–
Leads and what they tell you
Each lead can be thought of as ‘ looking at ’ an area
of myocardium
Chest leads
V 1 to V 6 ‘ look ’ at the heart on the transverse plain V 1 and V 2 look at the anterior of the heart and R
ventricle
V 3 and V 4 = anterior and septal
V 5 and V 6 = lateral and left ventricle
medics.cc
—————————————————–Page 25—————————————————–
Elements of the trace
medics.cc
—————————————————–Page 26—————————————————–
What do the components
represent?
P wave =
QRS =
T=
atrial depolarisation
ventricular depolarisation
repolarisation of the ventricles
medics.cc
—————————————————–Page 27—————————————————–
Interpreting the ECG
medics.cc
—————————————————–Page 28—————————————————–
Interpreting the ECG
Check
Name DoB
Time and date
Indication e.g. “ chest pain ” or “ routine pre – op ” Any previous or subsequent ECGs
Is it part of a serial ECG sequence? In which case it may be numbered
Calibration Rate
Rhythm Axis
Elements of the tracing in each lead
medics.cc
—————————————————–Page 29—————————————————–
Calibration
Check that your ECG is calibrated correctly
Height
10mm = 1mV
Look for a reference pulse which should be the rectangular looking wave somewhere near the left of the paper. It should be 10mm (10 small squares) tall
Paper speed
25mm/s
25 mm (25 small squares / 5 large squares) equals one second
medics.cc
—————————————————–Page 30—————————————————–
Rate
If the heart rate is regular
Count the number of large squares between R waves
i.e. the RR interval in large squares
Rate = 300
RR
e.g. RR = 4 large squares 300/ 4 = 75 beats per minute
medics.cc
—————————————————–Page 31—————————————————–
Rate
If the rhythm is irregular (see next slide on rhythm to check whether your rhythm is regular or not) it may be better to estimate the rate using the rhythm strip at the bottom of the ECG (usually lead II)
The rhythm strip is usually 25cm long (250mm i.e.
10 seconds)
If you count the number of R waves on that strip
and multiple by 6 you will get the rate
medics.cc
—————————————————–Page 32—————————————————–
Rhythm
Is the rhythm regular?
The easiest way to tell is to take a sheet of paper and line up one 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 tips
Move the paper along the rhythm strip so that your first mark li nes up with another R wave tip
See if the subsequent R wave tips line up with the subsequent marks on your paper
If they do line up, the rhythm is regular. If not, the rhythm i s irregular
medics.cc
—————————————————–Page 33—————————————————–
Sinus Rhythm
Definition
Rhythm
Cardiac impulse originates from the sinus node. Every QRS must be preceded by a P wave.
(This does not mean that every P wave must be followed by a QRS – such as in 2 nd degree heart block where some P waves are not followed by a QRS, however every QRS is preceded by a P wave and the rhythm originates in the sinus node, hence it is a sinus rhythm. It could be said that it is not a normal sinus rhythm)
medics.cc
—————————————————–Page 34—————————————————–
Rhythm
Sinus arrhythmia
There is a change in heart rate depending on the phase of respiration
Q. If a person with sinus arrhythmia inspires, what happens to t heir heart rate?
A. The heart rate speeds up. This is because on inspiration th ere is a decrease in intrathoracic pressure, this leads to an increased venous return to the right atrium. Increased stretching of the right atrium sets off a brainstem reflex (Bainbridge ’ s reflex) that leads to sympathetic activation of the heart, hence it speeds up)
This physiological phenomenon is more apparent in children and young adults
medics.cc
—————————————————–Page 35—————————————————–
Rhythm
Sinus bradycardia
Rhythm originates in the sinus node Rate of less than 60 beats per minute
Sinus tachycardia
Rhythm originates in the sinus node
Rate of greater than 100 beats per minute
medics.cc
—————————————————–Page 36—————————————————–
Axis
The axis can be though of as the overall direction of the cardiac impulse or wave of depolarisation of the heart
An abnormal axis (axis deviation) can give a clue to possible pathology
medics.cc
—————————————————–Page 37—————————————————–
Axis
An axis falling
outside the normal range can be left
or extreme axis
deviation
axis deviation
right axis deviation
A normal axis can lie
anywhere
between -30 and +90 degrees or +120 degrees
according to some
—————————————————–Page 38—————————————————–
Axis deviation – Causes
Wolff – Parkinson – White
syndrome can cause both Left and Right axis deviation
A useful mnemonic:
“ RAD RALPH the LAD from VILLA ”
R ight A xis D eviation
R ight ventricular hypertrophy A nterolateral MI
L eft P osterior H emiblock
L eft A xis D eviation
V entricular tachycardia I nferior MI
L eft ventricular hypertrophy L eft A nterior hemiblock
medics.cc
—————————————————–Page 39—————————————————–
The P wave
The P wave represents atrial
depolarisation
It can be thought of as being
made up of two separate
waves due to right atrial
depolarisation and left atrial depolarisation.
Which occurs first?
Right atrial depolarisation
Sum of
right and
left waves
right atrial depolarisation left atrial depolarisation
medics.cc
—————————————————–Page 40—————————————————–
The P wave
Dimensions
No hard and fast rules
Height
a P wave over 2.5mm should arouse suspicion
Length
a P wave longer than 0.08s (2 small squares) should arouse suspicion
medics.cc
—————————————————–Page 41—————————————————–
The P wave
Height
A tall P wave (over
2.5mm) can be called P pulmonale
Occurs due to R atrial hypertrophy
Causes include:
pulmonary hypertension, pulmonary stenosis tricuspid stenosis
normal P pulmonale
>2.5mm
medics.cc
—————————————————–Page 42—————————————————–
The P wave
Length
A P wave with a length >0.08 seconds (2 small squares) and a bifid
shape is called P mitrale
It is caused by left atrial hypertrophy and delayed left atrial depolarisation
Causes include:
Mitral valve disease LVH
normal P mitrale
medics.cc
—————————————————–Page 43—————————————————–
The PR interval
The PR interval is measured between the start of the P wave to the start of the QRS complex
(therefore if there is a Q wave before the R wave the PR interval is measured from the start of the P wave to the start of the Q wave, not the start of the R wave)
medics.cc
—————————————————–Page 44—————————————————–
The PR interval
The PR interval corresponds to the time period between depolarisation of the atria and ventricular depolarisation.
A normal PR interval is between 0.12 and 0.2 seconds ( 3 – 5 small squares)
medics.cc
—————————————————–Page 45—————————————————–
The PR interval
If the PR interval is short (less than 3 small
squares) it may signify that there is an accessory electrical pathway between the atria and the ventricles, hence the ventricles depolarise early giving a short PR interval.
One example of this is Wolff – Parkinson – White syndrome where the accessory pathway is
called the bundle of Kent. See next slide for an animation to explain this
medics.cc
—————————————————–Page 46—————————————————–
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
Until rapid depolarisation
does not travel in the high speed conduction
resumes via the normal
pathway, the spread of depolarisation across the ventricle is slow, causing a slow rising delta wave
pathway and a more medics.cc normal
complex follows
medics.cc
—————————————————–Page 47—————————————————–
The PR interval
If the PR interval is long (>5 small squares or 0.2s):
If there is a constant long PR interval 1 st degree heart block is present
First degree heart block is a longer than normal delay in conduction at the AV node
medics.cc
—————————————————–Page 48—————————————————–
The PR interval
If the PR interval looks as though it is widening every beat and then a QRS complex is missing, there is 2 nd degree heart block, Mobitz type I . The lengthening of the PR interval in
subsequent beats is known as the Wenckebach phenomenon
(remember ( w )one, W enckebach , w idens)
If the PR interval is constant but then there is a missed QRS complex then there is 2 nd degree heart block, Mobitz type II
medics.cc
—————————————————–Page 49—————————————————–
The PR interval
If there is no discernable relationship between the P waves and the QRS
complexes, then 3 rd degree heart block is present
medics.cc
—————————————————–Page 50—————————————————–
Heart block (AV node block)
Summary
1 st degree
constant PR, >0.2 seconds
2 nd degree type 1 ( Wenckebach )
PR widens over subsequent beats then a QRS is dropped
2 nd degree type 2
PR is constant then a QRS is dropped
3 rd degree
No discernable relationship between p waves and QRS complexes
medics.cc
—————————————————–Page 51—————————————————–
The Q wave
Are there any pathological Q waves?
A Q wave can be pathological if it is:
Deeper than 2 small squares (0.2mV)
and/or
Wider than 1 small square (0.04s) and/or
In a lead other than III or one of the leads that look at the heart from the left (I, II, aVL , V5 and V6) where small Qs (i.e. not meeting the criteria above) can be normal
Normal if in
I,II,III,aVL,V5-6
Pathological anywhere
medics.cc
—————————————————–Page 52—————————————————–
medics.cc
—————————————————–Page 53—————————————————–
The QRS height
If the complexes in the chest leads look very tall, consider left ventricular hypertrophy (LVH)
If the depth of the S wave in V 1 added to the height of the R wave in V 6 comes to
more than 35mm, LVH is present
medics.cc
—————————————————–Page 54—————————————————–
QRS width
The width of the QRS complex should be less than 0.12 seconds (3 small squares)
Some texts say less than 0.10 seconds (2.5 small squares)
If the QRS is wider than this, it suggests a
ventricular conduction problem – usually right or left bundle branch block (RBBB or LBBB)
medics.cc
—————————————————–Page 55—————————————————–
LBBB
If left bundle branch block is present, the QRS
complex may look like a
‘ W ’ in V 1 and/or an ‘ M ’ shape in V 6.
New onset LBBB with chest pain consider Myocardial infarction
Not possible to interpret the ST segment.
medics.cc
—————————————————–Page 56—————————————————–
RBBB
It is also called RSR pattern
If right bundle branch block is present, there may be an ‘ M ’ in V1 and/or a ‘ W ’ in V6.
Can occur in healthy
people with normal QRS width – partial RBBB
medics.cc
—————————————————–Page 57—————————————————–
QRS width
It is useful to look at leads V 1 and V 6
LBBB and RBBB can be remembered by the mnemonic:
W i LL ia M M a RR o W
Bundle branch block is caused either by infarction or fibrosis (related to the ageing process)
medics.cc
—————————————————–Page 58—————————————————–
The ST segment
The ST segment should sit on the isoelectric line
It is abnormal if there is planar (i.e. flat) elevation or depression of the ST segment
Planar ST elevation can represent an MI or Prinzmetal ’ s ( vasospastic ) angina
Planar ST depression can represent ischaemia
medics.cc
—————————————————–Page 59—————————————————–
Myocardial infarction
Within hours:
T wave may become peaked ST segment may begin to rise
Within 24 hours:
T wave inverts (may or may not persist)
ST elevation begins to resolve
If a left ventricular aneurysm forms, ST elevation may persist
Within a few days:
pathological Q waves can form and usually persist
medics.cc
—————————————————–Page 60—————————————————–
Myocardial infarction
The leads affected determine the site of the infarct
Inferior II, III, aVF Anteroseptal V1 – V4
Anterolateral V4 – V6, I, aVL
Posterior Tall wide R and ST ↓ in V1
and V2
medics.cc
—————————————————–Page 61—————————————————–
Acute Anterior MI
ST elevation
medics.cc
—————————————————–Page 62—————————————————–
Inferior MI
ST elevation
medics.cc
—————————————————–Page 63—————————————————–
The ST segment
If the ST segment is elevated but slanted, it may not be significant
If there are raised ST segments in most of the leads, it may indicate pericarditis – especially if the ST segments are saddle shaped. There can also be PR segment depression
medics.cc
—————————————————–Page 64—————————————————–
Pericarditis
medics.cc
—————————————————–Page 65—————————————————–
The T wave
Are the T waves too tall?
No definite rule for height T wave generally shouldn ’ t be taller than half the size of the preceding QRS
Causes:
Hyperkalaemia
Acute myocardial infarction
medics.cc
—————————————————–Page 66—————————————————–
The T wave
If the T wave is flat, it may indicate hypokalaemia
If the T wave is inverted it may indicate ischaemia
medics.cc
—————————————————–Page 67—————————————————–
The QT interval
The QT interval is measured from the start of the QRS complex to the end of the T wave.
The QT interval varies with heart rate
As the heart rate gets faster, the QT interval gets shorter
It is possible to correct the QT interval with respect to rate by using the following formula:
QTc = QT/ √ RR ( QTc = corrected QT)
medics.cc
—————————————————–Page 68—————————————————–
The QT interval
The normal range for QTc is 0.38 – 0.42
A short QTc may indicate hypercalcaemia
A long QTc has many causes
Long QTc increases the risk of developing an arrhythmia
medics.cc
—————————————————–Page 69—————————————————–
The U wave
U waves occur after the T wave and are often difficult to see
They are thought to be due to
repolarisation of the atrial septum
Prominent U waves can be a sign of hypokalaemia , hyperthyroidism
medics.cc
—————————————————–Page 70—————————————————–
Supraventricular tachycardias
These are tachycardias where the impulse is initiated in the atria ( sinoatrial node, atrial wall or atrioventricular node)
If there is a normal conduction pathway when the
impulse reaches the ventricles, a narrow QRS complex is formed, hence they are narrow complex tachycardias
However if there is a conduction problem in the
ventricles such as LBBB, then a broad QRS complex is formed. This would result in a form of broad complex tachycardia
medics.cc
—————————————————–Page 71—————————————————–
medics.cc
—————————————————–Page 72—————————————————–
Atrial Fibrillation
Features:
There maybe tachycardia
The rhythm is usually irregularly irregular No P waves are discernible – instead there is a shaky baseline
This is because there is no order to atrial depolarisation, different areas of atrium depolarise at will
medics.cc
—————————————————–Page 73—————————————————–
Atrial Fibrillation
medics.cc
—————————————————–Page 74—————————————————–
medics.cc
—————————————————–Page 75—————————————————–
Atrial flutter
There is a saw – tooth baseline which rises above and dips below the isoelectric line. Atrial rate 250/min
This is created by circular circuits of depolarisation set up in the atria
medics.cc
—————————————————–Page 76—————————————————–
Ventricular Tachycardia
medics.cc
—————————————————–Page 77—————————————————–
Ventricular Tachycardia
QRS complexes are wide and irregular in shape Usually secondary to infarction
Circuits of depolarisation are set up in damaged myocardium
This leads to recurrent early repolarisation of the ventricle leading to tachycardia
As the rhythm originates in the ventricles, there is a broad QRS complex
Hence it is one of the causes of a broad complex tachycardia
Need to differentiate with supraventricular tachycardia with aberrant conduction
medics.cc
—————————————————–Page 78—————————————————–
Ventricular Fibrillation
medics.cc
—————————————————–Page 79—————————————————–
Ventricular fibrillation
Completely disordered ventricular depolarisation
Not compatible with a cardiac output
Results in a completely irregular trace consisting of broad QRS complexes of varying widths, heights and rates
medics.cc
—————————————————–Page 80—————————————————–
Elements of the tracing
P wave
Magnitude and shape,
e.g. P pulmonale , P mitrale
PR interval (start of P to start of QRS)
Normal 3 – 5 small squares, 0.12 – 0.2s
Pathological Q waves?
QRS complex
Magnitude, duration and shape
≤ 3 small squares or 0.12s duration
ST segment
Should be isoelectric
T wave
Magnitude and direction
QT interval (Start QRS to end of T)
Normally < 2 big squares or 0.4s at 60bpm
Corrected to 60bpm
( QTc ) = QT/ √ RR interval
medics.cc
—————————————————–Page 81—————————————————–
Further work
Check out the various quizzes / games available on the Imperial Intranet
Get doctors on the wards to run through a patient ’ s ECG with you
medics.cc
—————————————————–Page 82—————————————————–
Leave a Reply