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Airway Management | Patient Monitoring & Diagnostics |
Emergency Care
A Pocket Guide to Common Arrhythmias
Interpretation and Management
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PrefaceIn a patient with suspected or known heart disease, the
electrocardiogram should be regarded as an extension of the
patients history and physical examination. Indeed,
electrocardiography is a fundamental part of any cardiovascular
assessment. As such, it is an essential tool for accurately
diagnosing cardiac-rhythm disorders, ischemic chest pain, and
estimating the extent of coronary artery disease. Moreover, the
electrocardiogram gives invaluable information about the workload
of the individual chambers of the heart, besides being helpful in
diagnosing systemic diseases that affect the heart and disturbances
in electrolyte metabolism. Because the electrocardiogram is such a
powerful tool, it should be well understood for use by medical
practitioners, medical students, nurses in intensive and coronary
care units, and by paramedics in emergency services.It should be
kept in mind, however, that a patient with an organic heart
disorder could have a normal electrocardiogram, whereas a perfectly
healthy individual may display non-specific electrocardiographic
abnormalities. Thus the electrocardiogram should always be
interpreted in conjunction with the clinical findings and never in
isolation.
This ECG booklet is part of the educational concept Professional
Advisory that the Cardiology group from Ambu A/S is offering to
provide users and purchasers with greater knowledge by imparting
new learning, supplying better clinical documentation and sharing
other helpful experiences.Ambu has made this booklet in cooperation
with Dr. Christian Lange, Cardiologist, and it can be useful for
doctors, nurses, technicians and anybody working within cardiology
to analyze ECG patterns.It provides both examples of ECG patterns
and diagnosis to match, symptoms and signs to be aware of and what
treatment to offer. It also explains the function of the heart and
the basic ECG pattern.
Thank you to Lars Ramlse for helping with illustrations in the
book.
Another helpful tool Ambu has produced is an ECG ruler for fast
and accurate diagnosis based on an ECG pattern. Please contact your
local Ambu sales representative for more information.
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3ContentsAnatomy and electricity of the heart
............................................4Conduction system
......................................................................5Heart
rate, time and voltage
........................................................6The
12-lead ECG
.........................................................................8P
wave
......................................................................................10PR
interval
................................................................................11QRS
complex
.............................................................................12ST
segment
...............................................................................14T
wave
......................................................................................15QT
interval
................................................................................16U
wave
.....................................................................................17Sinus
rhythm
.............................................................................18Sinus
bradycardia
......................................................................19Sinus
tachycardia
......................................................................20Sinus
arrhythmia
.......................................................................22Sinoatrial
(SA) block
..................................................................23Second-degree
SA block
............................................................24Third-degree
SA block and sinus arrest
......................................26Atrial fibrillation (AF)
.................................................................28
Atrial flutter
..............................................................................32Atrial
tachycardia
......................................................................34Multifocal
supraventricular tachycardia
......................................36AV nodal re-entry
tachycardia
....................................................38Ventricular
tachycardia (VT)
.......................................................40Ventricular
fibrillation (VF)
.........................................................44Atrioventricular
(AV) block
.........................................................46First-degree
AV block
.................................................................47Second-degree
AV block
............................................................48Second-degree
AV block Mobitz type I (Wenckebach) ..............49Second-degree
AV block Mobitz type II
...................................50Advanced second-degree AV
block ............................................52Third-degree
(complete) AV block
..............................................54Extrasystoles
(ectopic beats)
......................................................56Ventricular
extrasystoles (ventricular ectopic beats)
....................58Supraventricular extrasystoles (atrial
ectopic beats) ....................62Escape rhythms
.........................................................................64Common
Tracing Problems
........................................................66
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Anatomy and electricity of the heartContraction and relaxation
of cardiac muscle occurs as a result of electrical changes within
the myocardial cells, referred to as depolarisation and
re-polarisation. Electrodes attached to the skin on the limbs and
chest wall can sense this electrical activity and transmit it to an
electrocardiograph. The electrocardiograph then converts this
information into waveforms, which are recorded on graph paper to
produce an electrocardiogram, commonly known as an ECG.
Although the heart has four chambers, from the electrical point
of view it can be thought of as having only two, since the two
atria contract simultaneously and the two ventricles contract
simultaneously.
The muscle mass of the atria is relatively small and the
electrical changes accompanying the contraction are therefore
equally small. Contraction (i.e. depolarisation) of the atria
causes the ECG wave called P. Since the ventricular mass is large,
there is a large deflection of the ECG when the ventricles contract
(i.e. depolarise) and this is called the QRS complex. The T wave of
the ECG is caused by the return of this ventricular mass to the
resting electrical state called re-polarisation. Electrical events
and corresponding ECG components.
The SA node depolarises - no deflection
The atria depolarise - P wave
The AV node and the bundle of His depolarise - no deflection
The free walls of the ventri-cles depolarise - QRS complex
The ventricles are totally depolarised - no deflection (ST
segment)
The ventricles repolarise - T wave
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5Conduction systemThe myocardium contains a system of highly
specialised tissue that can conduct impulses faster than the
surrounding muscle tissue. Parts of this specialised conducting
tissue can discharge spontaneously and set up a wave of
depolarisation through the rest of the conducting system of the
entire heart.The sinoatrial (SA) or sinus node high in the right
atrium, has the highest spontaneous discharge rate of 60100
beats/min at rest, and therefore acts as a natural pacemaker and
initiates atrial depolarisation. The impulse spreads from the
sinoatrial node through the muscle mass of the atria to reach the
atrioventricular (AV) node.Here the impulse is delayed before
rapidly continuing through the bundle of His, which is normally the
only pathway between the atria and the ventricles. In the septum
between the ventricles, this single pathway divides into the right
and left bundle branch. The left bundle branch then divides in two,
an anterior and a posterior fascicle. At the lower part of the
ventricular septum the conducting branches spread out in a complex
network called Purkinje fibres. Therefore, after a delay in the
atrioventricular node, atrial contraction is followed by rapid
coordinated contraction of the ventricles.
The conduction system.
Sinoatrial node
Atrioventricular node
Right bundle branch
Left posterior hemifascicle
Left anterior hemi-fascicle
Left bundle branch
Electrically inert atrioventricular region
Rightatrium
Left atrium
Right ventricle
Left ventricle
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The heart rate can be calculated rapidly by remembering the
following sequence:
Number of large squaresbetween 2 QRS complexes
Heart rate(beats/min)
1 3002 1503 1004 755 606 50
Rate rulers are sometimes used to calculate heart rate; these
are used to measure two or three consecutive R-R intervals, of
which the average is expressed as the rate equivalent. When using a
rate ruler, one must take care to count the correct numbers of
beats (two or three) and restrict the technique to regular
rhythms.
Heart rate, t ime and voltageThe electrocardiogram is recorded
on standard paper travelling at a rate of 25 mm/s. The paper is
divided into large squares, each is 5 mm wide - the equivalent of
0.2 seconds. Each large square is five small squares wide, and each
small square is 1 mm wide - the equivalent of 0.04 seconds.
The heart rate is the number of heartbeats occurring in 1
minute. On an ECG, the heart rate is measured from R wave to R wave
to determine the ventricular rate, and P wave to P wave to
determine the atrial rate. The QRS complexes represent ventricular
depolarisation and the P waves represent atrial depolarisation.The
term tachycardia is used to describe a heart rate greater than 100
beats/min and bradycardia is defined as a rate less than 60
beats/min (or < 50 beats/min during sleep).
One large square of recording paper is equivalent to 0.2
seconds, so 5 large squares pass per second and 300 per minute.
Thus, when the rhythm is regular and the paper is moving at the
standard speed of 25 mm/s, the heart rate can be calculated by
counting the number of large squares between two consecutive R
waves, and dividing this number into 300.
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7When an irregular rhythm is present, the heart rate may be
calculated from the rhythm strip. It takes one second to record 2.5
cm of trace; therefore the heart rate per minute can be calculated
by counting the number of intervals between QRS complexes every 6
seconds (namely, 15 cm of recording paper) and multiplying by
10.
On the vertical axis, the electrical activity detected by the
electrocardiogram machine is measured in millivolts. Machines are
calibrated so that a signal with an amplitude or height of 1 mV
moves the recording stylus vertically 1 cm (2 large squares). Most
commonly and throughout this text, the amplitude of waveforms is
expressed as 0.1 mV = 1 mm = 1 small square. Thus each small square
is 1 mm high and each large square 5 mm high.
Time and voltage.Vertical axis: 1smallsquare=1mm(0.1mV)
1largesquare=5mm(0.5mV) 2largesquares=10mm(1.0mV)
Horizontal axis: 1smallsquare=0.04s 1largesquare=0.2s
5largesquares=1.0s
P-R Interval
Q-T Interval
QRSDuration
1 sec0.04 sec
0.2 sec
P
R
Q
S
TU
1mm
5mm
1mV
PAPER SPEED - 25mm/sec
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The 12- lead ECGTo make sense of an ECG, it is important to
appreciate that the various leads view the heart from different
directions. The term lead does not refer to the wires that connect
the patient to the ECG machine, but rather to different views of
the hearts electrical activity. An ECG machine uses the information
it collects via its four limb and 6 chest electrodes to compile a
comprehensive picture of the electrical activity in the heart as
observed from 12 different angles.
The six chest leads (V1 to V6) view the heart from a horizontal
plane. The information from the limb electrodes is combined to
produce the six limb leads (I, II, III, aVR, aVL and aVF). The limb
electrodes can be thought of as looking at the heart in a vertical
plane (that is, from the sides or the feet). The information from
these 12 leads is combined to form a standard
electrocardiogram.
Position of the six chest electrodes for standard 12-lead
electrocardiography.
V1: right sternal border, 4th intercostal space;
V2: left sternal border, 4th intercostal space;
V3: between V2 and V4;
V4: mid-clavicular line, 5th intercostals space;
V5: anterior axillary line, horizontally in line with V4;
V6: mid-axillary line, horizontally in line with V4
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9The positions of the leads produces the following anatomical
relationships: leads II, III and aVF view the inferior surface of
the heart; leads V1 to V4 view the anterior surface; leads I, aVL,
V5 and V6 view the lateral surface; and leads V1 and aVR look
through the right atrium directly into the cavity of the left
ventricle.
Anatomical relations of leads in a standard 12-lead ECG
II, III and aVF Inferior surface of the heart
V1 to V4 Anterior surface
I, aVL, V5 and V6 Lateral surface
V1 and aVR Right atrium and cavity of left ventricle
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P waveThe sinoatrial (SA) node is high in the wall of the right
atrium and initiates atrial depolarisation which produces the P
wave on the electrocardiogram. The P wave thus represents atrial
depolarisation and not SA node depolarisation, as is
sometimes mistakenly believed. Although anatomically the atria
are two distinct chambers, electrically they act almost as one.
They have relatively little muscle and generate a single, small P
wave. The duration of the P wave should not exceed 0.12 seconds. P
wave amplitude (height) rarely exceeds 0.25 mV. Sinus P waves are
usually most prominently seen in leads II and V1.
Characteristics of the P wave Representsatrialdepolarisation
Positive(upright)inleadsIandII BestseeninleadsIIandV1 Duration
