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Analyzing 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.
Heart’s Electrical Activity
• Depolarization and
repolarization of the
atria and ventricles
are electrical events
• The ECG detects this
electrical activity and
displays it on the
oscilloscope or prints it
Fast & Easy ECGs, 2E
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ECG Characteristics
• The electrical activity of the heart produces
waveforms with specific shapes and duration
that occur at a certain rate and regularity
• These are referred to as ECG characteristics
• Each dysrhythmia and cardiac condition
produces certain characteristics that can be
identified through analysis of the ECG tracing
Fast & Easy ECGs, 2E
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Nine-Step Process
• A systematic process such as the Nine-Step
Process can be used to identify the
characteristics of each ECG tracing
Fast & Easy ECGs, 2E
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Analysis and Interpretation
• Once the ECG characteristics in each tracing
are identified they are compared against what
is considered the normal ECG
– commonly referred to as sinus rhythm
Fast & Easy ECGs, 2E
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Characteristics of NSR
•
•
•
•
•
•
Waveforms and intervals that appear at regular intervals at a rate of 60 to 100
beats per minute (in the adult)
Upright and slightly asymmetrical P waves, each followed by a QRS complex of
normal upright contour, duration, and configuration
A PR interval (PRI) of normal duration that precedes each QRS complex
A flat ST segment followed by an upright and slightly asymmetrical T wave
A normal QT interval
Sometimes the presence of a U wave
Fast & Easy ECGs, 2E
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Heart Rate
• The average heart rate in the adult is 60 to
100 beats per minute
• A heart rate that is slower or faster is
considered abnormal and may indicate
significant problems requiring prompt
intervention
– For this reason, it should be checked as soon as
possible
Fast & Easy ECGs, 2E
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Regularity
• Normally the heart beats in a regular,
rhythmic fashion. The cycle repeats itself over
and over again
Fast & Easy ECGs, 2E
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Regularity
• Regular rhythm:
– Distance between the consecutive P waves is the
same, just as the distance between the
consecutive QRS complexes is the same
throughout the tracing
• Irregular rhythm:
– Distances between the consecutive P waves
and/or consecutive QRS complexes differ
Fast & Easy ECGs, 2E
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Morphology
• When assessing the waveforms seen on an
ECG tracing, we look at the appearance or
morphology of the complexes
I
Fast & Easy ECGs, 2E
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P Wave
• Produced by:
– initiation of impulse
in SA node
– depolarization of RA
and LA
– impulse passing
through AV junction
• Waveform is upright
and slightly
asymmetrical
Fast & Easy ECGs, 2E
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QRS Complex
• Represents movement of
electrical impulse through
ventricles causing their
contraction
• Consists of:
– Q wave
• first negative deflection
following PR segment
– R wave
• first positive deflection
following Q wave or PR
segment
– S wave
• next negative deflection
after the R wave
Fast & Easy ECGs, 2E
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PR Interval
• Represents depolarization
of the heart from the SA
node through the atria, AV
node and His-Purkinje
system
• Is the distance from the
beginning of the P wave to
the beginning of the Q
wave
• First portion is the P wave
while the second portion is
the PR segment
I
Fast & Easy ECGs, 2E
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ST Segment and T Wave
• ST segment is flat
line that follows QRS
complex
• T wave is larger,
slightly asymmetrical
waveform that
follows ST segment
I
Fast & Easy ECGs, 2E
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QT Interval
• Distance from onset of
QRS complex until end
of T wave
– Measures time of
ventricular
depolarization and
repolarization
• Has normal duration of
0.36 to 0.44 seconds
I
Fast & Easy ECGs, 2E
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U Wave
• Small upright seen
following the T wave,
but before the next P
wave
• Its voltage is so low,
however, that the U
wave often goes
unnoticed
Fast & Easy ECGs, 2E
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Analyzing the ECG
• Using the monitor
– Follow tracing from left
to right
– Observe the rate,
regularity, and presence
of P waves and get a
general view of the PR
interval, QRS complexes
and T waves
– If you identify anything
abnormal print a tracing
for further analysis
Fast & Easy ECGs, 2E
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Analyzing the ECG
• Using the rhythm strip
– Look at the waveforms, intervals, and durations of
each from left to right
– Compare the findings against normal sinus rhythm
Fast & Easy ECGs, 2E
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Analyzing the ECG
• Using the 12-lead
tracing
– Look at each lead (from
left to right), starting at
the top and moving to
the bottom in the first
column
– Then in the second
column, next in the
third column, and then
lastly, in the fourth
column
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• The key to making sense of what is seen on
any ECG tracing is to approach it in a logical
and systematic manner
• The Nine-Step Process assesses the main
elements of the ECG tracing
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• The average heart rate in the adult is 60 to
100 beats per minute.
– A heart rate that is slower or faster is considered
abnormal
• The heart beats in a regular, rhythmic, cyclical
fashion, producing specific waveforms and
intervals with each heartbeat.
– An irregular rhythm is abnormal
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• Throughout the ECG tracing, there should be
one normal upright P wave preceding each
narrow upright QRS complex
• The PR interval that precedes each QRS
complex should be of the same duration and
within 0.12 and 0.20 seconds
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• After each QRS complex of the ECG tracing,
there should be a flat ST segment, followed by
an upright and slightly asymmetrical T wave
• The QT intervals should be between 0.30 and
0.44 seconds in duration
• U waves may or may not be present
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
Summary
• What is identified in the step-by-step analysis
of an ECG tracing is compared against the
characteristics of normal sinus rhythm
• Each dysrhythmia and cardiac condition has
characteristics that are unique to it, making it
identifiable
• An ECG can be analyzed on the monitor
screen, on a rhythm strip, or on a 12-lead ECG
tracing
Fast & Easy ECGs, 2E
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© 2013 The McGraw-Hill Companies, Inc. All rights reserved.