ANSWER KEYS INCLUDED
WORKBOOK
,Contents
Preface to the third edition vii
About the authors viii
1 Recording a readable electrocardiogram (ECG) 1
2 The electrical conducting system of the heart 7
3 A systematic approach to rhythm strip analysis 11
4 Heart blocks 19
5 Common Arrhythmias 27
6 Ectopics and Extrasystoles 35
7 The 12 lead ECG 39
8 Axis deviation 47
9 Ischaemia, injury and necrosis 55
10 Sites of infarction 63
11 Bundle branch blocks 73
12 Chamber enlargement 79
13 Hemiblocks, bifascicular blocks and trifascicular blocks 85
14 Paced rhythms 91
15 A systematic approach to ECG interpretation 95
Answers to activities 97
References 105
Glossary 107
Index 109
v
,Chapter 1
Recording a readable electrocardiogram
(ECG)
An ECG is a graphic tracing of electrical patterns produced by the heart. This test is frequently
used for patients who have heart problems and is an important diagnostic procedure. However,
the ECG has limitations and so it is important to evaluate it in conjunction with the patient’s
clinical status. ECG abnormalities can occur in healthy individuals; and it can also be possible for
a person to have a heart attack and yet have a normal ECG. The nature of the abnormality and its
effect on the patient influence the clinical importance of the findings, so the ECG should never be
used in isolation.
Before we start to interpret the ECG, it is important to learn how to obtain a readable
recording (see fig 1.1). We will learn in the following chapters that slight changes can have huge
implications for the patient. These days it is common for ancillary staff to take on the task of
recording ECGs. To the untrained eye a recording may seem readable but it is not until we learn
to interpret an ECG recording that we really gain an understanding of the importance of
producing a readable tracing. It is possible to misdiagnose patients or miss their diagnosis if the
recording is not clear.
Before interpreting the ECG, it is therefore essential to ensure that the recording was
obtained correctly. Common errors are incorrect paper speed and standardisation, artefact and
incorrect lead placement. Any of these problems can make it extremely difficult, and in some
cases impossible, to measure the intervals and the segments that we are going to learn about in
this book.
Paper speed and standardisation
The ECG is made up of a series of horizontal and vertical lines that measure the duration and
amplitude of the various deflections. The small boxes on the paper are 1 millimetre (mm) in
height and I mm in width. The amplitude of the ECG deflection is measured vertically and the
duration of the ECG event horizontally. Recordings are usually made at 25 mm per second
(mm/s). It is therefore important to ensure that the ECG machine has not been set, at say,
50mm/s before the ECG is recorded. The paper speed should be printed on the ECG itself when
it is recorded (see fig 1.2).
A standard deflection (a box that looks like half a rectangle) should be inscribed at the
beginning or end of the ECG. The ECG is usually standardised so that the amplitude of a 1 millivolt
impulse causes a deflection of 10 mm (see fig 1.3). An increased amplitude (or voltage) usually
indicates increased muscle mass of the heart.
Note: If the ECG is not set at 25 mm/s, all the usual ECG measurements that we are about to learn will
not apply.
1
, Figure 1.1: A 12 lead ECG with many normal features
The ECG workbook
2
, Recording a readable electrocardiogram
Figure 1.2: The paper (or ‘sweep’) speed printed on an ECG.
Figure 1.3: The standard deflection at the end of an ECG.
Artefact
To obtain a good-quality ECG tracing you need to make sure that there is no outside interference,
as this can create artefact. The three most common causes of artefact are:
1 mains interference
2 patient movement
3 wandering baseline.
Mains interference
Mains interference may produce a fuzzy trace. Too much or too little heat stimulus will produce a
tracing that is too thick or too faint. Mains interference usually comes from electrical interaction at
or near the patient’s bedside. For this reason, any pumps or electric fans situated nearby should be
switched off or left to run on battery while the ECG is being recorded. Interference can also occur
if the patient is in contact with metal, such as the end of the bed, or if an ECG lead is in contact
with metal (e.g. touching a watch) or the ECG leads are tangled. Recording the ECG with the
machine on battery status instead of mains also helps to eliminate mains interference.
Patient movement
If the patient is tense or moving during the recording, artefact will result. What may be a routine
procedure to a healthcare professional is not always a routine procedure to a patient. Learning that
the healthcare professional wants to take a tracing of their heart is not exactly conducive to
relaxation! For instance, patients have been known to express concern that they might get
electrocuted if the healthcare professional gets the leads in the wrong order! For all these reasons
it is important to explain to the patient the aim of the procedure, that it will not hurt, that it will
only take a few minutes and that it will help if they can relax as much as possible, as this will
produce a clearer recording. It is often helpful to ask patients to close their eyes and imagine
themselves somewhere relaxing.
Many patients feel embarrassed about having their chests exposed for an ECG recording.
Always ensure their privacy during the recording. Remember also that some patients may
concentrate on your facial expression in an attempt to assess your reaction to the ECG as it is being
printed. You should therefore try to keep your expression as neutral as possible.
3
, The ECG workbook
Wandering baseline
Wandering baseline makes it difficult to identify ECG changes, as many of these changes are
measured from the baseline. This problem is often caused by poor electrode contact with the skin.
You might need to ask permission to shave some of the hair off the patient’s chest in order to obtain
good electrode contact. It may also be necessary to dry the skin if the patient is sweating, or clean
the skin if talcum powder has been applied. Ensure that the skin is completely dry after cleaning.
Lead placement
ECG electrodes must be placed in the correct positions on the body. If they are not, changes could
appear on the recording that are simply caused by looking at the heart from a slightly different
angle. This could easily lead to misdiagnosis. It would also make comparison of the patient’s ECG
recordings unreliable.
The limb leads are labelled: R (right), L (left), F (foot) and N (neutral). The R lead should be
attached to the patient’s inner, right wrist; the L lead to the inner, left wrist; the F lead to the inner
left leg (just above the ankle); and the N lead in the same position on the right leg (see fig 1.4).
Ideally electrodes should be placed over fleshy surfaces, as flesh conducts electricity much
better than bone. It is important to have the leads the right way round, otherwise this could change
the polarity of the ECG complexes. What is being measured from these leads is simply the
difference in electrical potential between two points, so if these points vary slightly (e.g. in a patient
with an amputation), one would simply attach the leads higher up the leg.
It is vital, however, to get the position of the chest electrodes correct (see fig 1.5):
1 V1 should be positioned in the fourth intercostal space counting down from the patient’s right
sternal notch on the right sternal edge;
2 V2 should be positioned in the fourth intercostal space counting down from the patient’s left
sternal notch on the left sternal edge;
3 V3 should be positioned midway between V2 and V4;
4 V4 should be positioned in the fifth intercostal space, counting down from the middle of the
patient’s clavicle;
5 V5 should be positioned in line with V4 but on the anterior axillary line;
6 V6 should be positioned in line with V4 but in the midaxillary line.
The position of the patient will also make a difference to the ECG recording, as different
positions alter the way the heart lies within the chest wall. The ECG should be recorded with the
patient lying flat, with two pillows under their head. Some patients (e.g. patients with acute
breathlessness) will not tolerate lying flat. In such cases it should be noted on the ECG that the
patient was not lying flat, so that the interpreter can take this into account when analysing the ECG.
Before the leads are disconnected, the quality of the ECG should be examined. If there is any
distortion of the trace, the source of the distortion must be identified and corrected, and the ECG
must then be carried out again.
It is essential to record the patient’s name and the date and time of the recording on the ECG.
The interpreter of the ECG will also find it useful to know whether the patient was experiencing any
symptoms at the time of the recording.
Remember to leave the ECG machine clean, untangled and ready for use at all times, as it is
often needed in emergency situations.
Chapter 1, Activity 1 (page 6) describes the process of recording a cardiac rhythm strip for
analysis.
4
, Recording a readable electrocardiogram
Figure 1.4: Limb lead positions.
Figure 1.5: Chest lead positions.
5
, The ECG workbook
Activitiy 1
Chapter 1 activity
Chapter 1 explains how to carry out an accurate recording of a 12 lead ECG.
Make sure that you have read through the chapter and that you have fully understood the key concepts
presented. Then work through the following activity.
Once you have completed this activity, you should be able to:
● place leads in the correct position for a 12 lead ECG recording;
● record a clear, accurate 12 lead ECG.
Activity 1.1: Recording a 12 lead ECG
Approximate time needed to complete this exercise: 10 minutes
What you will need:
● a 12 lead ECG recorder;
● ECG electrodes;
● a subject (a patient or colleague) who has about 10 minutes to spare.
1 Ask your subject to lie down as flat as possible. Tell them to relax and rest their arms at their
sides and to loosen any items of clothing that are tight or may cause them discomfort.
2 Remove clothing from the patient’s upper body as necessary in order to expose the chest. Any
items of clothing that will obstruct the application of the chest electrodes should be moved or
removed. Remember to protect the subject’s dignity and privacy at all times.
3 Identify the important anatomical landmarks required for lead positioning (see fig 1.4 and 1.5
on p. 4 if you need to remind yourself of where these are).
4 Identify any potential problems with the lead placement. For example, do any clothes or
underwear need to be removed?
5 Assess the skin areas where the leads will be placed. Is the skin clean and dry? Is the skin
excessively hairy? Identify the measures required to ensure that the electrodes will make good
contact with the skin.
6 Place the leads on the limbs and the chest in accordance with the diagrams in fig 1.4 and 1.5
(p. 5).
7 Record the ECG in accordance with the manufacturer’s instructions for your ECG recorder.
8 Examine your ECG for the following:
● the paper (“sweep”) speed should be printed on the ECG paper (see fig 1.2, p. 2);
● the electrical calibration signal should be printed – this is often shown at the end of each
printed rhythm on the paper (see fig 1.3, p. 3);
● check for signs of interference or wandering baseline;
● check that each section of the 12 lead ECG has recorded properly and that there is not a
straight line.
9 If you are happy that your ECG has recorded properly, remove the electrodes and thank your
subject for their cooperation.
You should now have a well-recorded 12 lead ECG. Don’t worry if you don’t understand what all these
ECG complexes mean at the moment. Keep this recording and use it for later activities in this book. Soon
it will all make sense!
6
,Chapter 2
The electrical conducting system
of the heart
The heart has specialised cells that form its conducting system. Electrical impulses are initiated and
conducted from within the heart. These impulses produce myocardial contraction. It is these
electrical impulses that are recorded on cardiac monitors and the electrocardiogram.
Figure 2.1:
The electrical conducting
system of the heart.
Figure 2.1 shows the electrical conducting system of the heart. Normally, an electrical impulse
comes from the sino-atrial (SA) node, which is situated in the right atrium close to the entrance of
the vena cava. The impulse then spreads across the atria to the atrioventricular node (AV), which
lies in the right atrial wall above the tricuspid valve. It then reaches the ventricles by passing
through the Bundle of His and into the bundle branches. The left and right bundle branches, which
extend along the interventricular septum, conduct the impulse to the ventricular myocardium to
cause it to contract. The first part of the ventricles to be activated is the septum, followed by the
endocardium and then the epicardium.
7
, The ECG workbook
The ECG records the movement of these electrical impulses and the wave pattern generated
is known as the PQRST complex.
Figure 2.2: The PQRST complex.
1 The P wave represents the spread of the impulse from the SA node across the atria (often
referred to as atrial depolarisation).
2 The PR interval represents the time taken for the impulse to spread over the atrium and through
the AV node, where the impulse pauses for a short time.
3 The QRS complex represents the spread of the impulse through the ventricles
(ventricular depolarisation).
4 The T wave represents ventricular recovery (often referred to as repolarisation).
If an impulse travels through the conducting system, being initiated from the SA node in the
manner described above, the rhythm is described as a sinus rhythm.
8
WORKBOOK
,Contents
Preface to the third edition vii
About the authors viii
1 Recording a readable electrocardiogram (ECG) 1
2 The electrical conducting system of the heart 7
3 A systematic approach to rhythm strip analysis 11
4 Heart blocks 19
5 Common Arrhythmias 27
6 Ectopics and Extrasystoles 35
7 The 12 lead ECG 39
8 Axis deviation 47
9 Ischaemia, injury and necrosis 55
10 Sites of infarction 63
11 Bundle branch blocks 73
12 Chamber enlargement 79
13 Hemiblocks, bifascicular blocks and trifascicular blocks 85
14 Paced rhythms 91
15 A systematic approach to ECG interpretation 95
Answers to activities 97
References 105
Glossary 107
Index 109
v
,Chapter 1
Recording a readable electrocardiogram
(ECG)
An ECG is a graphic tracing of electrical patterns produced by the heart. This test is frequently
used for patients who have heart problems and is an important diagnostic procedure. However,
the ECG has limitations and so it is important to evaluate it in conjunction with the patient’s
clinical status. ECG abnormalities can occur in healthy individuals; and it can also be possible for
a person to have a heart attack and yet have a normal ECG. The nature of the abnormality and its
effect on the patient influence the clinical importance of the findings, so the ECG should never be
used in isolation.
Before we start to interpret the ECG, it is important to learn how to obtain a readable
recording (see fig 1.1). We will learn in the following chapters that slight changes can have huge
implications for the patient. These days it is common for ancillary staff to take on the task of
recording ECGs. To the untrained eye a recording may seem readable but it is not until we learn
to interpret an ECG recording that we really gain an understanding of the importance of
producing a readable tracing. It is possible to misdiagnose patients or miss their diagnosis if the
recording is not clear.
Before interpreting the ECG, it is therefore essential to ensure that the recording was
obtained correctly. Common errors are incorrect paper speed and standardisation, artefact and
incorrect lead placement. Any of these problems can make it extremely difficult, and in some
cases impossible, to measure the intervals and the segments that we are going to learn about in
this book.
Paper speed and standardisation
The ECG is made up of a series of horizontal and vertical lines that measure the duration and
amplitude of the various deflections. The small boxes on the paper are 1 millimetre (mm) in
height and I mm in width. The amplitude of the ECG deflection is measured vertically and the
duration of the ECG event horizontally. Recordings are usually made at 25 mm per second
(mm/s). It is therefore important to ensure that the ECG machine has not been set, at say,
50mm/s before the ECG is recorded. The paper speed should be printed on the ECG itself when
it is recorded (see fig 1.2).
A standard deflection (a box that looks like half a rectangle) should be inscribed at the
beginning or end of the ECG. The ECG is usually standardised so that the amplitude of a 1 millivolt
impulse causes a deflection of 10 mm (see fig 1.3). An increased amplitude (or voltage) usually
indicates increased muscle mass of the heart.
Note: If the ECG is not set at 25 mm/s, all the usual ECG measurements that we are about to learn will
not apply.
1
, Figure 1.1: A 12 lead ECG with many normal features
The ECG workbook
2
, Recording a readable electrocardiogram
Figure 1.2: The paper (or ‘sweep’) speed printed on an ECG.
Figure 1.3: The standard deflection at the end of an ECG.
Artefact
To obtain a good-quality ECG tracing you need to make sure that there is no outside interference,
as this can create artefact. The three most common causes of artefact are:
1 mains interference
2 patient movement
3 wandering baseline.
Mains interference
Mains interference may produce a fuzzy trace. Too much or too little heat stimulus will produce a
tracing that is too thick or too faint. Mains interference usually comes from electrical interaction at
or near the patient’s bedside. For this reason, any pumps or electric fans situated nearby should be
switched off or left to run on battery while the ECG is being recorded. Interference can also occur
if the patient is in contact with metal, such as the end of the bed, or if an ECG lead is in contact
with metal (e.g. touching a watch) or the ECG leads are tangled. Recording the ECG with the
machine on battery status instead of mains also helps to eliminate mains interference.
Patient movement
If the patient is tense or moving during the recording, artefact will result. What may be a routine
procedure to a healthcare professional is not always a routine procedure to a patient. Learning that
the healthcare professional wants to take a tracing of their heart is not exactly conducive to
relaxation! For instance, patients have been known to express concern that they might get
electrocuted if the healthcare professional gets the leads in the wrong order! For all these reasons
it is important to explain to the patient the aim of the procedure, that it will not hurt, that it will
only take a few minutes and that it will help if they can relax as much as possible, as this will
produce a clearer recording. It is often helpful to ask patients to close their eyes and imagine
themselves somewhere relaxing.
Many patients feel embarrassed about having their chests exposed for an ECG recording.
Always ensure their privacy during the recording. Remember also that some patients may
concentrate on your facial expression in an attempt to assess your reaction to the ECG as it is being
printed. You should therefore try to keep your expression as neutral as possible.
3
, The ECG workbook
Wandering baseline
Wandering baseline makes it difficult to identify ECG changes, as many of these changes are
measured from the baseline. This problem is often caused by poor electrode contact with the skin.
You might need to ask permission to shave some of the hair off the patient’s chest in order to obtain
good electrode contact. It may also be necessary to dry the skin if the patient is sweating, or clean
the skin if talcum powder has been applied. Ensure that the skin is completely dry after cleaning.
Lead placement
ECG electrodes must be placed in the correct positions on the body. If they are not, changes could
appear on the recording that are simply caused by looking at the heart from a slightly different
angle. This could easily lead to misdiagnosis. It would also make comparison of the patient’s ECG
recordings unreliable.
The limb leads are labelled: R (right), L (left), F (foot) and N (neutral). The R lead should be
attached to the patient’s inner, right wrist; the L lead to the inner, left wrist; the F lead to the inner
left leg (just above the ankle); and the N lead in the same position on the right leg (see fig 1.4).
Ideally electrodes should be placed over fleshy surfaces, as flesh conducts electricity much
better than bone. It is important to have the leads the right way round, otherwise this could change
the polarity of the ECG complexes. What is being measured from these leads is simply the
difference in electrical potential between two points, so if these points vary slightly (e.g. in a patient
with an amputation), one would simply attach the leads higher up the leg.
It is vital, however, to get the position of the chest electrodes correct (see fig 1.5):
1 V1 should be positioned in the fourth intercostal space counting down from the patient’s right
sternal notch on the right sternal edge;
2 V2 should be positioned in the fourth intercostal space counting down from the patient’s left
sternal notch on the left sternal edge;
3 V3 should be positioned midway between V2 and V4;
4 V4 should be positioned in the fifth intercostal space, counting down from the middle of the
patient’s clavicle;
5 V5 should be positioned in line with V4 but on the anterior axillary line;
6 V6 should be positioned in line with V4 but in the midaxillary line.
The position of the patient will also make a difference to the ECG recording, as different
positions alter the way the heart lies within the chest wall. The ECG should be recorded with the
patient lying flat, with two pillows under their head. Some patients (e.g. patients with acute
breathlessness) will not tolerate lying flat. In such cases it should be noted on the ECG that the
patient was not lying flat, so that the interpreter can take this into account when analysing the ECG.
Before the leads are disconnected, the quality of the ECG should be examined. If there is any
distortion of the trace, the source of the distortion must be identified and corrected, and the ECG
must then be carried out again.
It is essential to record the patient’s name and the date and time of the recording on the ECG.
The interpreter of the ECG will also find it useful to know whether the patient was experiencing any
symptoms at the time of the recording.
Remember to leave the ECG machine clean, untangled and ready for use at all times, as it is
often needed in emergency situations.
Chapter 1, Activity 1 (page 6) describes the process of recording a cardiac rhythm strip for
analysis.
4
, Recording a readable electrocardiogram
Figure 1.4: Limb lead positions.
Figure 1.5: Chest lead positions.
5
, The ECG workbook
Activitiy 1
Chapter 1 activity
Chapter 1 explains how to carry out an accurate recording of a 12 lead ECG.
Make sure that you have read through the chapter and that you have fully understood the key concepts
presented. Then work through the following activity.
Once you have completed this activity, you should be able to:
● place leads in the correct position for a 12 lead ECG recording;
● record a clear, accurate 12 lead ECG.
Activity 1.1: Recording a 12 lead ECG
Approximate time needed to complete this exercise: 10 minutes
What you will need:
● a 12 lead ECG recorder;
● ECG electrodes;
● a subject (a patient or colleague) who has about 10 minutes to spare.
1 Ask your subject to lie down as flat as possible. Tell them to relax and rest their arms at their
sides and to loosen any items of clothing that are tight or may cause them discomfort.
2 Remove clothing from the patient’s upper body as necessary in order to expose the chest. Any
items of clothing that will obstruct the application of the chest electrodes should be moved or
removed. Remember to protect the subject’s dignity and privacy at all times.
3 Identify the important anatomical landmarks required for lead positioning (see fig 1.4 and 1.5
on p. 4 if you need to remind yourself of where these are).
4 Identify any potential problems with the lead placement. For example, do any clothes or
underwear need to be removed?
5 Assess the skin areas where the leads will be placed. Is the skin clean and dry? Is the skin
excessively hairy? Identify the measures required to ensure that the electrodes will make good
contact with the skin.
6 Place the leads on the limbs and the chest in accordance with the diagrams in fig 1.4 and 1.5
(p. 5).
7 Record the ECG in accordance with the manufacturer’s instructions for your ECG recorder.
8 Examine your ECG for the following:
● the paper (“sweep”) speed should be printed on the ECG paper (see fig 1.2, p. 2);
● the electrical calibration signal should be printed – this is often shown at the end of each
printed rhythm on the paper (see fig 1.3, p. 3);
● check for signs of interference or wandering baseline;
● check that each section of the 12 lead ECG has recorded properly and that there is not a
straight line.
9 If you are happy that your ECG has recorded properly, remove the electrodes and thank your
subject for their cooperation.
You should now have a well-recorded 12 lead ECG. Don’t worry if you don’t understand what all these
ECG complexes mean at the moment. Keep this recording and use it for later activities in this book. Soon
it will all make sense!
6
,Chapter 2
The electrical conducting system
of the heart
The heart has specialised cells that form its conducting system. Electrical impulses are initiated and
conducted from within the heart. These impulses produce myocardial contraction. It is these
electrical impulses that are recorded on cardiac monitors and the electrocardiogram.
Figure 2.1:
The electrical conducting
system of the heart.
Figure 2.1 shows the electrical conducting system of the heart. Normally, an electrical impulse
comes from the sino-atrial (SA) node, which is situated in the right atrium close to the entrance of
the vena cava. The impulse then spreads across the atria to the atrioventricular node (AV), which
lies in the right atrial wall above the tricuspid valve. It then reaches the ventricles by passing
through the Bundle of His and into the bundle branches. The left and right bundle branches, which
extend along the interventricular septum, conduct the impulse to the ventricular myocardium to
cause it to contract. The first part of the ventricles to be activated is the septum, followed by the
endocardium and then the epicardium.
7
, The ECG workbook
The ECG records the movement of these electrical impulses and the wave pattern generated
is known as the PQRST complex.
Figure 2.2: The PQRST complex.
1 The P wave represents the spread of the impulse from the SA node across the atria (often
referred to as atrial depolarisation).
2 The PR interval represents the time taken for the impulse to spread over the atrium and through
the AV node, where the impulse pauses for a short time.
3 The QRS complex represents the spread of the impulse through the ventricles
(ventricular depolarisation).
4 The T wave represents ventricular recovery (often referred to as repolarisation).
If an impulse travels through the conducting system, being initiated from the SA node in the
manner described above, the rhythm is described as a sinus rhythm.
8
