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The Electrocardiogram
Fast & Easy ECGs, 2nd E – A SelfPaced Learning Program
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Electrocardiogram
• An electrocardiogram is a tracing of the
heart’s electrical activity
• An electrocardiograph is the machine that
produces it
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Electrocardiograph
• Also called the ECG
machine, it detects
heart’s electrical
activity through
electrodes
positioned on
patient’s skin
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ECG Machines
• A variety of ECG
machines are available
– Some monitor from one
to five different leads
– Some are capable of
monitoring up to twelve
or more leads
simultaneously
– Some are used for
continuous monitoring
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
The Input
• Lead wires and cables
transfer the ECG signal
detected through the
electrodes to the ECG
machine
– There may be 3, 4, or 5
lead wires for monitoring
purposes and up to 10 lead
wires for 12-lead ECGs
– Each lead wire has a
labeled clip, snap, or pintype connector on the
distal end which attaches
to the electrode
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Using Lead Wires and Cables
• Keep the lead wires
separated from each
other to avoid tangling
• Position them loosely
across the patient so
they do not pull on
and lift the electrodes
away from the skin
• Properly clean and
decontaminate then
after each use
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
ECG Electrodes
• Are typically disposable
• Consist of a:
– wet or dry electrolyte gel
(which acts to assure
good signal pick-up),
– metal snap or tab
(where the ECG lead
wire is attached),
– self-adhesive pad that
holds the electrode to
the skin
Self-adhesive pad
Electrolyte gel
Metal snap
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Placing ECG Electrodes
• To achieve a noisefree recording:
– Clean the skin site to
remove dead skin
cells and oils
– Clip dense hair
present at the sites
where the electrodes
are to be placed
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Placing ECG Electrodes
• Eliminate muscle tension by placing the
patient’s arms and legs in a comfortable
position in which the extremities are resting
on a supportive surface
– If artifact is still present and the patient tolerates
it, try laying him or her in a flat position
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Placing Electrodes
• Avoid removing electrodes from their sealed
protective envelope before use as the
conductive gel may dry
• With snap-on lead wires, attach the electrode
to the lead wire before placing the electrodes
onto the patient’s skin
• With clip-on type lead wires, apply the
connector to the metal snap of the electrode
after the electrode has been placed
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Placing Electrodes
• Place the electrodes in
the correct locations
– Know where each
electrode is supposed to
be positioned
– Look for a flat surface and
sites over soft tissues
– Avoid areas where large
bones are near the skin
surface and areas where
there are thick muscles or
skin folds
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ECG Leads
• Are a combination of electrodes that form an
imaginary line in the body along which the
electrical signals, detectable during the time
course of the heartbeat, are measured
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ECG Leads
• Each lead provides a different view of the
heart:
– Electrodes are placed on chest, arms and legs
– Sites vary depending on which view of the heart's
electrical activity is being assessed
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ECG Leads
• Deflection of the
waveforms seen on
the ECG depend on
where the positive
electrode is placed in
comparison to the
direction of the
electrical forces
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ECG Leads
• ECG leads are either bipolar or unipolar
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Bipolar Leads
• Record the flow of
the electrical
impulse between
two (one is positive,
the other is
negative) selected
electrodes
• Includes I, II and III
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Bipolar Leads
• Record difference in
electrical potential
between a positive
and negative
electrode
• Uses a third electrode
called a ground
• Include leads I, II and
III
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Unipolar Leads
• Use only one
positive electrode
and a reference
point calculated by
the ECG machine
• Includes leads aVR,
aVL, aVF, and V1
through V6
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Planes of the Heart
• Electrodes are
placed on the
extremities and
chest wall to view
the heart’s
electrical activity
from the frontal
and horizontal
planes
– Provides a crosssectional view of
the heart
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Frontal Plane
• Leads that view this
plane are called limb
leads
• Include leads I, II, III,
aVR, aVL and aVF
• Provide inferior,
superior, and lateral
views of heart
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Horizontal Plane
• Leads that view this
plane are called
precordial or chest
leads
• Include leads V1, V2,
V3, V4, V5, and V6
• Provide inferior,
superior, and lateral
views of heart
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Different Leads Uses
• A given lead may be used to highlight:
– A specific part of ECG complex
– Electrical events of a specific cardiac cycle
– Conditions such as an enlargement of heart
muscle or presence of ischemia, injury and
infarction
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Limb Lead Locations
• RA electrode
– positioned anywhere on the right
arm or below the right clavicle in
the midclavicular line
• LA electrode
– positioned anywhere on the left
arm or below the left clavicle in
the midclavicular line
• LL electrode
– positioned anywhere on the left
leg or left midclavicular line
below the last palpable rib
• RL electrode
– positioned on the right leg or
right midclavicular line below the
last palpable rib
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Chest Leads
• Positioned in order
across the chest
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Lead II
• ECG electrode polarity
– Positive electrode – LL lead wire
– Negative electrode – RA lead wire
– Ground electrode – LA lead wire (and RL lead wire)
• Produces positively deflected waveforms
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The Output
• ECG machine translates
the electrical impulses
generated in the heart
into wave-like signals
that are recorded on
paper or displayed on a
monitor
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Oscilloscope
• ECG rhythms displayed on the oscilloscope are
called dynamic ECGs
• Represent real time electrical activity or what
is presently occurring in the heart
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Printouts
• ECGs printed on graph paper are called static
ECGs
• Show what has already occurred
• Much easier to analyze a static ECG to identify
abnormalities than it is to examine an image
moving across a screen
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Printouts
• As the stylus moves
across the moving ECG
paper it inscribes
waveforms representing
the heart’s electrical
activity
• Vertical lines on the ECG
paper represent
amplitude in electrical
voltage while horizontal
lines represent time or
duration
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ECG Paper
• Each small square
equals
– 0.04 sec in duration and
0.1 mV in amplitude
• Five small squares (1
large box) equals
– 0.20 seconds in duration
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Isoelectric Line
• Is the flat line that
occurs when no
electrical activity is
occurring or
impulses are too
weak to be detected
• Used as a baseline to
identify changing
electrical movement
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Calibration or Registration Mark
• Helps ensure ECG
machine is properly
calibrated
• Serves as reference
point on ECG tracing
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Artifact
• Markings on ECG
tracing that are not a
product of heart’s
electrical activity
– Patient movement is
among its many
causes
– Can mimic lifethreatening
dysrhythmias
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Graphic record or tracing is called an
electrocardiogram while the machine that
produces it is called the electrocardiograph
• Electrodes placed on patient’s skin detect
heart’s electrical activity
• Abnormalities in cardiac rate and/or rhythm
are called dysrhythmias
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Each lead provides a different view of heart.
• Impulses traveling toward a positive electrode
are recorded on ECG as upward deflections.
• Impulses traveling away from a positive
electrode or toward a negative electrode are
recorded as downward deflections.
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Limb leads are produced by placing electrodes
on right arm (RA), left arm (LA) and left leg
(LL).
– Include leads I, II, III, augmented vector right
(aVR), augmented vector left (aVL) and
augmented vector foot (aVF).
• Precordial leads include leads V1, V2, V3, V4,
V5, and V6.
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• ECG paper consists of horizontal and vertical
lines that form a grid.
• Horizontal measurements used to determine
heart rate and duration of various waveforms,
segments and intervals.
• Vertically on ECG paper, distance between
lines, or boxes, represents amplitude in
millimeters (mm) or electrical voltage in
millivolts (mV).
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Calibration
• Artifact is markings on ECG tracing that have
no relationship to electrical activity of the
heart.
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.