Observations
Adults
Recording a 12-lead electrocardiogram (ECG)
Edited by Michael Sampson, Senior Lecturer, Cardiac Nursing, London South Bank University,
and Brian Campbell, Chair of Education, Society for Cardiological Science and Technology (SCST)
©2019 Clinical Skills Limited. All rights reserved
Recording a 12-lead electrocardiogram (ECG) is a common part of clinical
assessment in both secondary and primary care. In hospital, an ECG may be part
of pre-assessment for surgery or part of the admission procedure. In an emergency,
an ECG may be used to assess the electrical functioning of the heart and to
detect damage to the myocardium. In primary care, an ECG may be performed as
part of an overall health assessment, or to monitor ongoing clinical conditions.
Position of chest leads for recording a 12-lead ECG
Midclavicular line
An ECG, which is painless for the patient, involves placing electrodes on
specific parts of the chest and limbs, to record the heart’s electrical activity.
The subsequent tracing is recorded on graph paper and consists of 12
specific waveforms, referred to as ‘leads’, each showing cardiac electrical
activity from a different anatomical perspective. The data obtained allow an
overall assessment of the rate and rhythm of the heart; the traces will also
reflect any specific damage or changes to the structure of the heart.
Anterior axillary line
Midaxillary line
First
intercostal
space
A 12-lead ECG can help to diagnose a variety of conditions, such as myocardial
infarction (the death of heart muscle due to a blocked coronary artery),
myocardial ischaemia (inadequate blood supply to the heart), enlargement of
the ventricles, and a whole range of other abnormalities including cardiac
arrhythmias (abnormal and potentially dangerous heart rhythms). The 12-lead
ECG is frequently used as part of a wider assessment, and is therefore a
valuable tool in assessing the overall health status of the patient.
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This procedure is a guide to recording a high-quality 12-lead ECG, a skill that
requires regular practice. The guidance of an experienced practitioner or
mentor is key. It is vital to position the electrodes correctly to ensure you
obtain an accurate ECG recording (Hammond & Spurgeon, 2015).
The 12-lead ECG records 12 different electrical views of the heart, but only 10
electrodes are placed on the skin. There are two groups of electrodes: six chest
electrodes (see right) and four limb electrodes. The four limb electrodes, placed
on the wrists and ankles, provide the electrical information that produces the six
limb leads on the ECG. They are called I, II, III, aVR, aVL and aVF.
The six precordial electrodes are placed across the chest wall (see above).
Each electrode corresponds with a single ECG lead, unlike the limb
electrodes. The precordial leads, also known as the chest leads, are V1, V2,
V3, V4, V5 and V6. On some machines, they are labelled as C1–C6.
The path of the electrical impulse through the heart
(a)
Atrioventricular
(AV) node
P
Sinoatrial
(SA) node
Purkinje
fibres
(b)
(c)
AV
node
Bundle
of His
Right
bundle
branch
Left
bundle
branch
(d)
R
R
T
P
Q
S
Q
S
This illustration demonstrates how the movement of electrical activity through the heart creates normal ECG waveforms. Cardiac electrical activity is created by
the depolarisation of cardiac cells. Depolarisation occurs when sodium ions rapidly enter the cell, causing a transient increase in the electrical charge across the
cell membrane. This electrical change spreads across the heart and triggers mechanical contraction of the upper and lower chambers in turn (Hampton, 2013). In
the normal heart, depolarisation begins in the sinoatrial node, then spreads in a wavefront across both upper chambers until every cell has depolarised; this
creates the P-wave on the ECG (a), and triggers atrial contraction. Depolarisation then reaches the atrioventricular (AV) node and passes slowly through it, which
causes a small electrical delay, before it spreads rapidly through the bundle of His, bundle branches and Purkinje fibres. While this is happening, a small flat line
can be seen on the ECG (b). Once depolarisation reaches the Purkinje fibres, it spreads through the walls of the ventricles, creating the QRS complex of the
ECG (c) and triggering ventricular contraction. Repolarisation of the ventricles, which is the return of the normal, resting electrical charge across the cell
membrane, creates the final waveform on the ECG, the T-wave (d).
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 1 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 2
Assemble the equipment
ECG
machine
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10 disposable pregelled electrodes
Clipper
Gather all the equipment you will need to record the 12-lead ECG. These items are usually kept together with the recording machine for convenience and in
case it is necessary to carry out a 12-lead ECG urgently. You may need to ask the patient to remove a watch or other jewellery; in this case, make sure they are
stored safely.
Explain the procedure and gain consent
Explain to the patient what you are going to do, and obtain consent. Even
though the patient may have had an ECG before, explain that it is painless
and why you need to take the recording. The ECG will be useful to aid
diagnosis (Hammond & Spurgeon, 2015). Provide reassurance.
Wash and dry your hands
Decontaminate your hands with alcohol-based sanitiser or with soap and
water, drying well, before the procedure.
Position the patient
Pull the curtains or close the door to ensure privacy. The evidence on how
position affects the ECG recording is incomplete, so for consistency and
practicality, help the patient into a semi-recumbent position of approximately
45° to the horizontal (Campbell et al., 2017).
Clean the patient’s skin
Prepare the patient’s skin in line with your hospital or practice area’s policy.
You may need to cleanse the skin with soap and water, or a non-alcohol
wipe. If the skin is dry, exfoliate very lightly using a paper towel, gauze swab
or proprietary abrasive tape (Campbell et al., 2017). The aim is to ensure
good contact between the skin and electrodes.
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 2 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 3
Apply electrode to right wrist
In all the electrode placements, try to avoid bony prominences in order to gain
a clear tracing. Peel an electrode off the sheet and place it on the right wrist.
An exact anatomical placement of the limb leads is not necessary.
Apply electrode to left ankle
Place an electrode at ankle level on the left foot.
Skin preparation
Apply electrode to left wrist
Place another electrode on the left wrist.
Apply electrode to right ankle
Place an electrode at ankle level on the right foot.
Lead V1
Angle
of Louis
First
intercostal
space
2
Sternum
For some patients who have a hairy chest, you will need to shave the area
where the electrodes are to be attached, using clippers. Try to avoid shaving
if possible, because of the risk of infection if the skin is grazed (Hammond &
Spurgeon, 2015). You must obtain the patient’s consent for shaving. It is not
necessary to shave the whole chest. Once again, prepare the skin if it is
particularly oily or very dry.
3
4
Place the first chest electrode (V1) in the fourth intercostal space, at the right
sternal margin (Campbell et al., 2017). To identify this correctly, first locate the
manubriosternal joint (the angle of Louis, see inset), by running your finger
down the sternum from the top until you encounter a bony ridge. From here, if
you feel to the patient’s right side, you will locate the second intercostal space
(the space between the second and third ribs). Now count down to the third
and fourth intercostal spaces. Slide your finger towards the sternum until you
feel the edge. Place the electrode for V1 here (Campbell et al., 2017).
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 3 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 4
Lead V2
Lead V4
Midclavicular line
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2
4
Repeat this procedure on the patient’s left side to correctly place the V2
electrode in the fourth intercostal space, at the left sternal margin (Campbell
et al., 2017).
Lead V3
Place the V4 electrode next. Move down to the fifth intercostal space, and place
the electrode in the midclavicular line (Campbell et al., 2017). In women, V4 is
usually not placed on the breast, although there is some debate. Crawford &
Doherty (2010) recommend placing the V4 electrode under the left breast in
women. V4 is usually not in line with the nipple—this is a common myth.
Lead V5
Midclavicular line
Midclavicular
line
1
2
Anterior axillary
line
3
4
The electrode for V3 is placed next, midway between V2 and V4 (Campbell
et al., 2017).
Place the V5 electrode at the same level as V4, but in the left anterior axillary
line, as shown here (Campbell et al., 2017).
Position of chest electrodes
Lead V6
Midclavicular
line
Anterior axillary
line
Sternal notch
Clavicle
Manubrium
First rib
Angle
of Louis
First
intercostal
space
Sternum
Fourth
intercostal
space
Midaxillary
line
Place the V6 electrode at the same level as V4 and V5, but in the left
midaxillary line (Campbell et al., 2017).
This illustration offers an overview of where the chest electrodes should lie.
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 4 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 5
Lead box
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C2
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F
C1
C3
C2
C1
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N
Attach limb leads
The leads from the recording machine usually converge in a plastic box. If
you put this box on the patient’s lower chest, it makes it easier to join the
correct leads to the electrodes. The leads are usually labelled to indicate
which electrode they should be connected to.
Untangle the leads and lay them out against the corresponding electrodes,
using the labels on the leads as a guide. First, using the crocodile clips on the
leads, attach each of the limb leads.
C1
C2
C3
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C1
C2
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1
F
2
3
45
6
C3
Position of leads
Chest leads
Take time to review all the leads. Ensure that each one is attached to the
correct electrode.
One by one, attach each of the six chest leads.
Obtaining a calibration trace
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10 mm
Pat
5 mm
5 small squares = 0.20 seconds
Most machines will automatically provide a calibration trace, but you may have to do this manually. Here, the clinician is pressing the 10-mm calibration button.
The calibration trace provides a standard 10-mm box at one or both ends of the ECG. This ensures that 1 mV of sensed electrical activity causes the stylus to
move up 10 mm on the paper (a standard calibration). The amplitude of the ECG waveforms (for example the height or depth of the QRS complex) can have
diagnostic significance, so the electrical activity of the heart must be accurately represented on the paper trace.
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 5 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 6
Setting the paper speed
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25 mm/s
The machine will often set the paper speed automatically. If not, it should be set at an internationally agreed speed of 25 mm/s. The final trace should show the paper
speed; this information is important as the graph paper represents time on the 12-lead ECG. In a healthy person, each electrical part of the cardiac cycle should take
a specific amount of time to pass through the heart. If the machine prints at a standard speed, these times can be calculated from the tracing on the graph paper.
Print ECG
Record the patient’s details
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WARD
Enter the patient’s name and identification number into the machine. This is
essential as many departments store the ECG electronically and there is a
significant risk of incorrect patient management if an ECG result is linked to
the wrong patient record. Document the time the recording was made, and
any notes on significant clinical signs or symptoms, such as chest pain.
Troubleshooting — amputee
In an amputee, you can place the electrodes towards the end of the stump,
provided that they are not on the torso itself. Note the limb that is missing on
the ECG recording.
When you are confident that everything is ready, print the ECG. Some
machines allow you to view the ECG on a screen before printing, so that you
know the trace is of a good quality.
Check patient’s name and details
Date: 18 5 2019 Time: 10:29
Ensure that you are happy with the quality of the tracing before taking all the
leads off the patient. Once again, check that the tracing carries details of the
patient’s name and identification number, and the date and time of recording.
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 6 of 7
Observations
Adults
Recording a 12-lead electrocardiogram (ECG) Page 7
(b) Muscle tremor
Artefacts: (a) Electrical interference
Electrical activity in the environment can produce a characteristic thickened
line on the ECG, as shown. Move electrical appliances, such as syringe
drivers, further from the patient. Try changing electrodes to improve skin
contact. Using the machine’s manual filter button (if present) helps to reduce
extraneous electrical activity, but activate this only when absolutely
necessary because it can distort the recording (Campbell et al., 2017). You
should write on the recording that the filter has been applied.
Muscle tremor occurs if the patient is not lying still, or is moving due to
involuntary movement or shivering. Reassure the patient and ask them to lie
as still as possible. Try to avoid moving the leads up the limbs, as this may
affect the recording (Campbell et al., 2017), but if needed you may have to do
this, as described for someone with an amputation. Once again, utilise the
filter button, but only if absolutely necessary. Always add a comment to the
ECG when a change from the 'standard' recording is made.
L
F
N
R
C1
C2
C3
C1
L
C2
45
F
1
R
Check equipment
Patient Notes
General Notes
23
6
Documentation
Disconnect the leads, clean them according to local protocol, and carefully
put away all equipment (Jevon, 2010). If the patient’s condition is unstable (for
example, ongoing chest pain), the sticky tabs may be left in place so that
another 12-lead ECG can be undertaken quickly. If further recordings are not
planned, skin electrodes should be removed.
N
A wandering baseline appears as a trace that does not align with the
horizontal lines of the graph paper. It is important to correct this as it will make
it difficult to detect ECG abnormalities. Change the electrodes and ensure
that the skin where they are attached is adequately shaved of hair. You may
need to roughen the skin with an emery pad. A flat line on the ECG tracing for
a specific lead usually means a disconnection of that lead (Hammond &
Spurgeon, 2015).
C3
Disconnect ECG
(c) Wandering baseline
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Allergy Notes
ECG recorded
By Staff Nurse Graham
Dr Greene informed
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1
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C1
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OK
Cancel
Record in the notes that a 12-lead ECG has been taken and note which
clinician has been informed. If able, note any changes to the normal ECG
and any subsequent care or treatment undertaken.
Put the ECG machine away carefully without tangling the wires. If necessary,
top up the supplies, such as ECG paper or electrodes, or delegate a member
of staff to do this.
Do not undertake or attempt any procedure unless you are, or have supervision from, a properly trained, experienced and competent person.
Always first explain the procedure to the patient and obtain their consent, in line with the policies of your employer or educational institution.
Page 7 of 7