ECG pdf - عملي - Muhadharaty

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lectro

ardio

raphy

ECG made extra easy

…

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Overview

Objectives for this tutorial

What is an ECG?

Overview of performing

electrocardiography on a patient

Simple physiology

Interpreting the ECG

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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

ECG

Interpret

ECGs

showing the following pathology:

MI, AF, 1st 2

and 3

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.

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What is an ECG?

ECG =

Electrocardiogram

Tracing of heart

’

s electrical activity

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Recording an ECG

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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

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Electrode placement

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

’

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Electrode placement in 12 lead

ECG

6 are chest electrodes

Called V1

6 or C1

4 are limb electrodes

Right arm

ide

Left arm

our

Left leg

reen

Right leg

Bike

ike

Remember

The

right leg

right leg electrode

electrode

is a neutral or

“

dummy

”

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Electrode placement

For the chest electrodes

intercostal

space right

sternal

edge

intercostal

space left

sternal

edge

(to find the 4

space, palpate the

manubriosternal

angle (of

Louis)

Directly adjacent is the 2

rib, with the 2

intercostal

space

directly below. Palpate inferiorly to find the 3

and then 4

space

over the apex (5

ICS mid

clavicular

line)

halfway between V2 and V4

at the same level as V4 but on the

anterior axillary line

at the same level as V4 and V5 but on

the mid

axillary

line

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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.

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Electrophysiology

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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

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Overall
direction
of
cardiac
impulse

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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

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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

Coronal plane (Limb Leads)

Bipolar leads

—

l , l l , l l l

Unipolar

leads

—

aVL

aVR

aVF

Transverse plane

—

(Chest Leads)

Electrodes around the heart

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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 +

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Leads

Lead I +

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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

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Lead II

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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

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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

Leads look at the heart from

different directions

axis

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Leads and what they tell you

Each lead can be thought of as

‘

looking at

’

an area

of myocardium

Chest leads

to V

‘

look

’

at the heart on the transverse plain

and V

look at the anterior of the heart and R

ventricle

and V

= anterior and

septal

and V

= lateral and left ventricle

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Elements of the trace

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What do the components

represent?

P wave =

atrial

depolarisation

QRS =

ventricular depolarisation

T =

repolarisation of the

ventricles

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Interpreting the ECG

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Interpreting the ECG

Check

Name

DoB

Time and date

Indication e.g.

“

chest pain

”

“

routine pre

”

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

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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

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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

e.g. RR =

large squares

300/

= 75 beats per minute

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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

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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

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Rhythm

Sinus Rhythm

Definition

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

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)

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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

decrease

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

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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

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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

Axis

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

extreme

axis
deviation

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Axis deviation

Causes

Wolff

Parkinson

White

syndrome can cause both Left

and Right axis deviation

A useful mnemonic:

“

RAD RALPH

the

LAD

from

VILLA

”

ight

xis

eviation

ight ventricular hypertrophy

nterolateral

eft

osterior

emiblock

eft

xis

eviation

entricular tachycardia

nferior MI

eft ventricular hypertrophy

eft

nterior

hemiblock

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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

right atrial

depolarisation

Sum of

right

and

left

waves

left atrial

depolarisation

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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

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The P wave

Height

A tall P wave (over

2.5mm) can be called

pulmonale

Occurs due to

atrial

hypertrophy

Causes include:

pulmonary hypertension,

pulmonary

stenosis

tricuspid

stenosis

normal

P pulmonale

>2.5mm

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The P wave

Length

A P wave with a length

>0.08 seconds (2 small

squares) and a bifid

shape is called

mitrale

It is caused by left

atrial

hypertrophy and delayed

left

atrial

depolarisation

Causes include:

Mitral valve disease

LVH

normal

P mitrale

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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

wave, not the start of the R wave)

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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)

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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

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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

If the PR interval is long (>5 small squares

or 0.2s):

If there is a constant long PR interval 1

degree heart block is present

First degree heart block is a longer than

normal delay in conduction at the AV node

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The PR interval

If the PR interval looks as though it is

widening

every beat and then a QRS complex is missing,

there is

degree heart block,

Mobitz

type I

The lengthening of the PR interval in

subsequent beats is known as the

Wenckebach

phenomenon

(remember (

)one,

enckebach

idens)

If the PR interval is

constant

but then there is a

missed QRS complex then there is

degree

heart block,

Mobitz

type II

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The PR interval

If there is

no discernable relationship

between the P waves and the QRS

complexes, then

degree heart

block is

present

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Heart block (AV node block)

Summary

degree

constant PR, >0.2 seconds

degree type 1 (

Wenckebach

)

PR widens over subsequent beats then a QRS is dropped

degree type 2

PR is constant then a QRS is dropped

degree

No discernable relationship between p waves and QRS

complexes

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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

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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

added to

the height of the R wave in V

comes to

more than 35mm, LVH is present

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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)

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LBBB

left

bundle branch block

is present, the QRS

complex may look like a

‘

’

in V

and/or an

‘

’

shape in V

New onset LBBB with

chest pain consider

Myocardial infarction

Not possible to interpret

the ST segment.

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RBBB

It is also called RSR

pattern

right

bundle branch

block is present, there

may be an

‘

’

in V1

and/or a

‘

’

in V6.

Can occur in healthy

people with normal QRS

width

–

partial RBBB

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QRS width

It is useful to look at leads V

and V

LBBB and RBBB can be remembered by the

mnemonic:

Bundle branch block is caused either by

infarction or fibrosis (related to the ageing

process)

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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

’

(

vasospastic

) angina

Planar ST depression can represent

ischaemia

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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

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Myocardial infarction

The leads affected determine the site of

the infarct

Inferior

II, III,

aVF

Anteroseptal

Anterolateral

V6, I,

aVL

Posterior

Tall wide R and ST

↓

in V1

and V2

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Acute Anterior MI

elevation

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Inferior MI

elevation

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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

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Pericarditis

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The T wave

Are the T waves too tall?

No definite rule for height

T wave generally shouldn

’

be taller than half the size

of the preceding QRS

Causes:

Hyperkalaemia

Acute myocardial

infarction

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The T wave

If the T wave is flat, it may indicate

hypokalaemia

If the T wave is inverted it may indicate

ischaemia

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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)

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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

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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

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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

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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

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Atrial

Fibrillation

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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

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Ventricular Tachycardia

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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

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Ventricular Fibrillation

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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

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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/

√

interval

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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