12 Lead ECG Recording and Basic Interpretation Delegate …

12 Lead ECG Recording

and Basic Interpretation

Delegate Notes

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© 2019 ECG – All rights reserved LessonPlans/ECG12Lead/Pack&Kit/R&I/Handout December 2019

2

Anatomy and Physiology of the Heart

The Cardiac Cycle

o Veins bring blood into the heart which collects in the atria.

o The atria contract and blood moves to the ventricles through valves which prevent the

backflow of blood (step 1 below).

o Once the ventricles are full of blood, they contract to pump blood out through valves

into arteries which take blood away from the heart (step 2 below).

o Blood circulates around this system, taking up oxygen in the lungs and giving it up to

the tissues and organs of the body.

o The heart has four chambers – the right atrium, the

left atrium, the right ventricle and the left ventricle.

o The right side of the heart pumps deoxygenated

blood to the lungs.

o The left side of the heart pumps oxygenated blood

to the body.

o Veins bring blood towards the heart, while arteries

take blood away from the heart.

A tip to remember this:

VeIN – IN to the heart

Arteries – take blood Away

Right

Atrium

Left

Atrium

Right

Ventricle

Left

Ventricle

Step 1 Step 2


3

The Structure of the Heart

The Electrical Conduction System of the Heart

Contraction of the heart muscle is associated with electrical activity. The electrical conduction

system of the heart is made up of specialised cells. These specialist cells can initiate a heartbeat

and transmit the impulses through the heart in an organised manner. The change in electrical

charge of a cell is known as depolarization.

1) The impulse is initiated from the

Sino-Atrial (SA) node, which is the

hearts natural pacemaker and

beats between approximately

60-100 times per minute at

rest.

2) The wave of depolarisation travels

across the atria to the

Atrioventricular (AV) node.

3) The depolarisation continues down

through the Bundle of His which

branches off into the left and right

bundle branches.

4) Purkinje fibres emerge from these

branches and innervate the

myocardial cells.

5) After depolarisation the cells return

to their original electrical state

known as repolarisation (which

causes relaxation of the muscle).

The heart consists of three layers:

o Pericardium – a thin outer lining that

protects and surrounds your heart.

o Myocardium – a thick muscular middle

layer that contracts and to squeeze blood

out of your heart.

o Endocardium – The innermost layer of the

heart.


4

How an ECG complex is formed

The depolarisation of cardiac cells is detected by electrodes on the skin when we perform an

ECG. A standard ECG complex consists of three main components.

A wave is a deflection from the baseline that represents a cardiac event.

P wave – this deflection shows the depolarisation of the atria, which causes atrial contraction.

QRS complex – this deflection shows the depolarisation of the ventricles, which causes the

ventricles to contract.

T wave – this deflection shows the repolarisation of the ventricles, which causes the ventricles

to relax.

A specific portion of a complex is described as a segment, for example the segment between

the end of the P wave and the beginning of the QRS complex is known as the PR segment.

The distance occurring between two cardiac events measured as time is known as the interval.

The time interval between the beginning of the P wave and the beginning of the QRS complex

is known as the PR interval (note there is a PR interval as well as a PR segment).


5

The ECG Paper

The standard calibration settings should be set to:

Paper speed: 25mm/s Voltage: 10mm/mV

The ECG paper runs at a rate of 25mm per second. Each 1mm square is therefore is 1/25th of

a second or 0.04 seconds. Each large box is made up of 5 smaller boxes, it represents 5 X

0.04 seconds = 0.2 seconds. Therefore 5 large boxes make 1 second.

The ECG should print 10mm of height per 1mV of electrical activity detected. When talking

about the height of a wave we use millimetres.

The paper is also broken down into four strips, the top 3 strips are made up of the 12 leads

which are appropriately labelled for easy identification. The 4th, a continual strip found at the

bottom of the page is a rhythm strip (lead II). The complete ECG is 10 seconds long.

See the example ECG below.

1 second = 5 large

squares

5mm

=

0.5m

V

0.2 sec.

0.04

sec

1mm


6

How does the ECG ‘look’ at the heart?

This is helpful to understand the term ’12 lead ECG’. This is more advanced information for

your reference.

To make sense of an ECG we need to understand the concept of the ‘lead’, this term does not

refer to the wires that connect the patient to the machine, but the different viewpoints of the

heart’s electrical activity.

An ECG machine uses the information it collects via its four limb electrodes and six chest

electrodes to compile a comprehensive picture of the electrical activity in the heart as

observed from 12 different viewpoints (hence the name ’12 Lead ECG’).

Each lead is given a name. I, II, III, aVR, aVL, aVF, V1, V2, V3, V4, V5 & V6.

Leads I, II and III are bipolar (measure electrical potentials between a negative and a positive

electrode). All other leads are unipolar using a nominal centre point of the heart (use a single

positive electrode and use a combination of all other electrodes to act as a negative

electrode).

The measured electrical potentials from the four limb electrodes are used by the ECG

machine to create the six limb viewpoints (Leads I, II, III, aVR, aVL & aVF – see below).

V1, V2, V3, V4, V5, V6 correspond to each of the six chest electrodes. This is useful to

know when dealing with artefact on the ECG.

The different sections on the ECG represent the different regions of the heart -

lateral being the left side of the heart, anterior being the front of the heart and the inferior

being the lower area of the heart.


7

Preparing the Patient

Prior to undertaking the procedure, the following should be checked:

• That the ECG machine is safe and ready to use (date & time settings are correct)

• The patient area is clean and tidy

• There is enough paper, electrodes, razors and skin preparation equipment

• The identity of the patient should be confirmed and cross-checked with the request

• Room to be warm and private to maintain dignity.

Once the electrodes are positioned and the connecting wires are appropriately attached, the

patient should be covered with a gown to preserve his/her dignity during the procedure.

Patients may feel uncomfortable about being touched on their upper torso. The ECG

procedure requires sensitivity. Operators must take every effort to respect the sensitivities of

patients and minimise any discomfort. Operators must adhere to the organisation’s chaperone

policy and ensure that patients are made aware of the policy.

Skin preparation:

Skin preparation is required to help produce an artefact-free and accurate ECG. Various

methods are available, all of which are designed to minimise the skin-to-electrode problems.

Considerations include:

The removal of chest hair may be required to ensure adequate contact with the skin. Verbal

consent should be obtained from the patient and a clean razor used which should be disposed

of in a sharps bin immediately afterwards.

Exfoliation may be required and should be undertaken with very light abrasion using either a

paper towel, gauze swab or proprietary abrasive tape designed specifically for this purpose.

On occasions the skin may require cleansing. A variety of methods exist ranging from

washing with mild soap to cleaning with an alcohol wipe. However, care must be taken in

patients with sensitive or broken skin.

Check the wires and connection areas as occasionally gel can accumulate on the clips which

can affect contact. Clean with alcohol wipes.


8

Chest Electrode Placement

Chest electrodes should be accurately placed as according to the SCST Guidelines (2017).

Step one:

Find the Angle of Louis by feeling for the ‘bump’ on the

sternum. Direct your finger down and leftwards until you feel

the space between two ribs. This is an accurate way to locate

the second intercostal (rib) space. From this position, count

down two more rib spaces and place an electrode in the fourth

intercostal space at the right sternal edge (V1).

Repeat on the patients left side (moving your finger to the

right from the Angle of Louis) and place an electrode on in the

fourth intercostal space at the left sternal edge (V2).

Step two:

Look at the patient’s clavicle (collar bone) and estimate the

midway distance across this bone. Follow a straight line down

from this point by eye. Place the electrode in the fifth

intercostal space by counting one space lower and following

across to the level of the mid-clavicle (V4). Where there is

breast tissue, the electrode should be placed at the level of the

mid-clavicle underneath the breast.

Step three:

Place an electrode at the mid-point between the second and

fourth electrodes (V3) (as shown).

Step four:

Place an electrode at the same horizontal level as V4, on the

anatomical ‘mid-axillary line’ – this is usually where you would

find the line of the seam of a tshirt. From here you can place

an electrode between V4 and V6 – known as the enterior

axillary line.


9

Recording an ECG

It is vital to get the electrode placement, wire connections and overall recording procedure

correct as an inaccurate ECG could result in inappropriate diagnosis and treatment.

Electrode Position

V1

V2

V3

V4

V5

V6

Fourth intercostal space at the right sternal edge

Fourth intercostal space at the left sternal edge

Midway between V2 and V4

Fifth intercostal space in the mid-clavicular line

Left anterior axillary line at same horizontal level as V4

Left mid-axillary line at same horizontal level as V4 & V5


10

Recording an ECG

Colours on the wires are useful, but if you are new to recording ECGs or do so infrequently,

we recommend you read the numbers labelled 1-6 on the wires which should be placed from

left to right in order across the chest electrodes.

Limb electrodes:

• Right arm limb lead (RA, red) - right forearm, proximal to wrist

• Left arm limb (LA, yellow) - left forearm, proximal to wrist

• Left leg limb lead (LL, green) - left lower leg, proximal to ankle

• Right leg limb lead (N, black) - right lower leg, proximal to ankle

This may help you remember

the order of limb positions:

Red, Yellow, Green, Black

‘Ride Your Green Bike’


11

Recording an ECG

• Begin by asking the patient to lie down (at an angle of 45 degrees – halfway between flat and upright) and relax, this reduces artefact and ensures consistency between ECGs.

• Attach the chest and limb electrodes as described and connect wires.

• Check that paper is loaded and ensure the date and time is correct.

• Enter patient’s details – name, DOB, gender.

• Press start and allow the machine to follow its process until printing is complete. • Inform the necessary clinician that the ECG has been done. Any changes on the ECG that

might require urgent medical attention should be identified and advice sought from a senior member of staff if necessary.

• If the patient has any cardiac symptoms at the time of recording, such as chest pain or

palpitations then this should be noted on the tracing and brought to the immediate attention of a senior member of staff.

• It is imperative that any changes from the standard procedure of recording are noted on

the ECG to prevent misinterpretation (e.g. patient sat upright in wheelchair).

Once the ECG has been printed you should check the following:

• Calibration – calibration markers are printed on the ECG alongside a rectangular box

that measures 10 small squares (10mm) in height. The paper speed is usually printed

on the bottom left corner of the ECG. Standard setting is 25mm/second. Any alterations

to this will alter the analysis. The vertical axis of the ECG measures the amplitude (size)

of the waveforms. The standard calibration is 10mm/mv. Alterations to the amplitude

settings can alter the size of the waveforms and lead to incorrect analysis of the ECG.

• Quality of the trace – the ECG should be clear with no artefact, wandering baseline,

electrical or muscle interference or missing leads.

• aVR should always be negative –if aVR is positive, it is usually because the right and

left arm wires have accidently been switched.

• The relevant patient details including name, date and time of the ECG need to be on

the printout. It is also useful to make a note of any symptoms that the patient was

experiencing e.g. chest pain when the ECG was being recorded.


12

Examples of poor-quality ECGs

Wandering baseline

Caused by poor skin to electrode contact.

Muscle interference

Caused by patient movement/muscle tension.

Electrical interference

Caused by electrical devices/sources of AC artefact. Internal neurostimulators (e.g. DBS).


13

Other Types of ECG Recording

There are other ways that an ECG may be recorded. Although you might not be involved in

these, your patient may be asked to have further testing because of the initial ECG. The 12

lead ECG may not pick up on abnormalities occurring less frequently.

Other tests include:

Exercise stress test – this is usually performed to see if there are any changes to the

heart that occur during exercise. The test may be performed with the individual on an

exercise bike or walking on a treadmill. They are also connected to an ECG and this is

monitored as the intensity increases to look for heart rhythm abnormalities or signs of

ischaemia.

Holter monitor (also known as ambulatory monitoring) – a small device is connected to

the individual via 3 or 6 electrodes which are worn for 24-72 hours. The patient is advised

not to shower or bath while wearing the device. They would usually be asked to keep a

diary of activities during this time so that this can be compared to the recording.

7-day Holter monitor – this is the same device as above however the device can be

removed when the patient wishes to bath or shower.

Cardiac event recorder – this is useful if the patient’s symptoms are infrequent. There

are no wires or electrodes. The patient would hold this to the chest when they are having

symptoms.

Implantable loop recorder – this is a small device (approximately the size of a

computer memory stick). It is implanted under the skin in the upper left chest area. The

battery can last up to three years. When the patient experiences symptoms they hold a

hand-held activator over the loop recorder and press a button to record the activity.

For further information regarding any of these investigations, please see the British Heart

Foundation website: www.bhf.org.uk/heart-health/tests


14

Basic ECG interpretation

The next section of the course will be concentrating on rhythm analysis using the six-stage

approach.

We break the analysis of the ECG into two parts:

1) Analysis of the rhythm strip (bottom line of ECG)

2) Looking at the main body of the ECG (top three lines of ECG)

Rhythm Analysis

Accurate analysis requires experience, but six basic principles can help with the interpretation

of most rhythms encountered and lead to a diagnosis on which to base appropriate treatment.

It is important to always look at the ECG in the context of the patient’s clinical condition. It is

a useful diagnostic tool, however it is important to act on any symptoms they may be

experiencing.

The Six Steps Approach

This 6-step systematic approach can be applied to all rhythm

strips:

1. Is there any electrical activity?

2. What is the ventricular rate? (QRS)

3. Is the QRS rhythm regular or irregular?

4. Is the QRS complex width normal or prolonged?

5. Is atrial activity present?

6. How is atrial activity related to ventricular activity?


15

1 Is there any electrical activity?

If there is no electrical activity, check the patient first, then the gain, leads and electrical

connection.

If electrical activity is present and there are recognisable complexes, then follow the remaining

steps.

2 What is the ventricular rate?

The normal rate is between 60 – 100 beats per minute.

• A rate below 60bpm = bradycardia

• A rate above 100 bpm = tachycardia

• Easy way to calculate the rate:

• Starting with an ‘R’ wave, count 30 large boxes (6 seconds) and then count the number

of QRS complexes within that distance.

• Multiply that number by 10 which will give you the rate

30 large boxes shown

5 complexes visible between lines

5 x 10 = 50bpm

This method is useful for both regular and irregular rhythms.


16

Activity 7: Work out the rate of the following rhythms

DO NOT WRITE IN THIS BOOKLET

Please write your answers in your workbooks

7A) Rate = ? write the answer in your workbook

7B) Rate = ? write the answer in your workbook

3 Is the QRS rhythm regular or irregular?

This is often easy to decide, however, problems arise as the rate becomes faster, as the beat

to beat variation become less pronounced.


17

• An easy way to work this out is to place another piece of paper over the rhythm strip,

ensuring the R waves are still visible

• Mark on the top sheet the position of 3 to 4 R waves

• Move that paper along the rhythm strip to see if the distance remains the same

throughout

If the QRS rhythm is irregular you must decide whether it is:

• Totally irregular (irregularly irregular) OR

• A repeated pattern to the irregular rhythm (regularly irregular)

Activity 8: Is this rhythm regular or irregular?


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4 Is the QRS complex width normal or prolonged?

The normal QRS interval is up to 0.12 secs (3 small squares). This tells us that the rhythm

originates from above the bundle of his. (This is often helpful when naming the rhythm e.g.:

atrial fibrillation)

If the QRS width is longer than 0.12 secs the rhythm originates in the ventricles (again giving

clues with its name e.g.: ventricular tachycardia)

Activity 9: Are these QRS complexes normal or prolonged?

Write the answer in your workbooks!


19

5 Is atrial activity present?

Having looked at the rhythm in terms of rate, regularity and QRS with, the rhythm strip should

then be looked at carefully for atrial activity (seen as the P wave). This is often difficult to identify

(if not impossible) especially in fast rates.

The rate and regularity of a P wave can be determined in the same way as we did for the QRS

complex.

6 How is atrial activity related to ventricular activity?

Is there a consistent time interval between each P wave and the nearest QRS complex? This is

useful for the more experienced practitioner who is diagnosing heart blocks.

Rhythm recognition – basic interpretation This section gives examples of some of the rhythm abnormalities that they may see. It is important to remind them though that this should be done in conjunction with the patient’s clinical symptoms and these need to be addressed first. Then you can go onto looking at the rhythm strip, initially we can put the patient’s rhythm into

4 categories:

• Normal sinus rhythm (all 6 questions present with ‘normal’ answers)

• Broad Complex Tachycardia

• Narrow complex Tachycardia

• Bradycardia


20

ECG 1

The rhythm is Ventricular Tachycardia.

In ventricular tachycardia (VT) the ECG shows wide QRS complexes with no identifiable P wave.

Most importantly – how is your patient!

The heart rate is fast (over 100bpm) and the rhythm is usually regular. The rhythm is originating

in the ventricles hence the bizarre looking complexes. When the rate is too fast for the heart to

effectively pump blood, this is known as pulseless VT which and is one of the shockable cardiac

arrest rhythms.

This is normally a shockable cardiac arrest rhythm and therefore should be treated

accordingly.

ECG 2

We can refer to this rhythm as a Narrow Complex Tachycardia (because the width of the QRS

is narrow). Most importantly – how is your patient!

Different types of rhythm will present as narrow complex tachycardia such as atrial fibrillation,

atrial flutter and junctional tachycardia. This example of narrow complex tachycardia is atrial

fibrillation (AF). This is the most common type of rhythm abnormality that you are likely to see.

The patient’s heart rate can be >100bpm unless the rhythm is being controlled with medication.


21

The rhythm is irregular. There are no discernible P waves however the ECG will show wavy

deflections (from the chaotic contractions of the atria) between the QRS complexes.

A patient in fast AF may experience palpitations, breathlessness, fatigue and dizziness. The most

serious consequence is a thromboembolic stroke, so it is important that it is diagnosed and

treated quickly.

This is one of the most common arrhythmias you are likely to encounter. The patient may feel

very unwell, particularly if the rhythm is fast and may not be able to lie flat for the ECG to be

recorded. They may have a low blood pressure too.

ECG 3

Again, answer the 6 questions with this rhythm

1) Is there electrical activity?

2) What is the ventricular rate?

3) Is the QRS rhythm regular or irregular?

4) Is the QRS complex width normal or prolonged?

5) Is atrial activity present?

6) How is the atrial activity related to ventricular activity?

This is a Bradycardia because the rate is less than 60 beats per minute. Most importantly – how

is your patient!

Heart Blocks.

Other types of bradycardia that you may encounter include heart blocks. There are different

types of heart blocks however the one we are looking at is complete (3rd degree) heart block.


22

4. Complete (3rd degree heart block)

In complete heart block there is no relationship between the conduction system in the atria and

ventricles. The atria will be stimulated by the SA node and a P wave will be shown on the ECG.

These impulses will be blocked from going through to the ventricles. The ventricles will be

stimulated by automatic foci in or below the AV node. The QRS complex may be narrow or broad

depending where the impulse originates from. The rate is slow but the rhythm is usually regular.

The rhythm strip will show P waves at a consistent rate and QRS complexes at a consistent rate,

however there is no relationship between the two sets of waves.

The pulse rate of the patient will be slow and they may have symptoms such as shortness of

breath, dizziness and chest pain. Complete heart block will always require immediate treatment

as there is a risk of deterioration.

ECG Analysis

This course will only look at the analysis of the ST segment so that delegates can start to

recognise ischaemia or acute infarction on an ECG. The 10 rules given are just for information

purposes. There are other tools that they may come across, but this is one of the most

common ones. Using a tool such as this can ensure that a practitioner is systematic in their

analysis of the ECG and does not miss anything. It is useful to highlight though that some

abnormalities on an ECG may be normal for an individual and may not have clinical

significance. Where possible it is useful to compare the ECG to a baseline one if available.


23

In this course we will just be focusing on how to identify ischaemia and / or a myocardial

infarction. It is essential that you get expert help to diagnose the ECG and review your patient

if you are worried about their condition!

ECGs provide the evidence in diagnosing many cardiac abnormalities such as heart blocks but

for this package, we will be focusing on MIs and Ischaemia.

Both can be diagnosed by examining the QRS complexes within each region.

Ischaemia can be diagnosed by the presence of the ST segment lying below the baseline or

an inverted T wave.

Baseline

An example of where the ST segment is lying below the baseline.

ST elevation, with or without T wave changes, is a sign of myocardial injury.

An Acute Myocardial Infarction (AMI) is characterised by ST segment elevation above

the baseline. The ECG patterns in an AMI are not static, they change with the progression of a

normal state to that of a full infarct. The first thing that happens is T wave inversion in ischaemia,

then you will see ST elevation as the condition deteriorates. The amount of tissue infarcted

depends on the size and location of the artery blocked, and the amount of area that it perfuses.

Examples of ST elevation


24

A Normal ECG:

Remember to always seek expert help if you are worried about your patient’s

condition, even if their ECG appears normal!


25

INFERIOR AMI

Remind yourself which leads represent the inferior wall

Inferior wall AMIs will produces changes in II, III, and aVF. These are often combined with

other areas of the heart i.e.: inferolateral AMIs (affecting the Inferior wall & Lateral wall)


26

References

12-Lead ECG. The Art of Interpretation. Garcia & Holtz.2001.

Making Sense of the ECG. A Hands-On Guide. Houghton & Gray 2003.

Cardiology. Lowe et al 1997.

Advanced Life Support manual. (Fifth Edition) Resuscitation Council UK 2006.

Some pictures have been reproduced thanks to Nigel Barraclough. First on Scene Training Ltd

Campbell B, Richley D, Ross C, Eggett CJ. Clinical Guidelines by Consensus: Recording a

standard 12-lead electrocardiogram. An approved method by the Society for Cardiological

Science and Technology (SCST) 2017. Available at:

http://www.scst.org.uk/resources/SCST_ECG_Recording_Guidelines_2017

Emergency Care Gateway

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Alston Drive

Milton Keynes

MK13 9AP

Tel: 0845 423 8993

www.ecgtraining.co.uk

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