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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
For the Dental Hygienist
CHAPTERCHAPTER
Understanding EKGsA Practical Approach
5The ElectrocardiogramThe Electrocardiogram
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
The Electrocardiogram
• Objectives– Define the term electrocardiogram– Describe the basics of EKG monitoring– List the types of EKG leads– Discuss the relevance of Einthoven’s triangle– Identify and explain the grids and markings
on a representative strip of EKG graph paper
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Copyright ©2010 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
The Electrocardiogram
• Objectives (continued)– Describe the relationship of the following EKG
waveforms to the electrical events in the heart P wave PR interval QRS complex ST segment T wave
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
The Electrocardiogram
• Electrocardiogram– Graphic representation of the electrical
activity of the heart
• Electrocardiograph– Machine used to record the
electrocardiogram, or EKG machine
• EKG– Graphic tracing of electrical activity of the
heart, not mechanical activity
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
The Electrical Basis of the EKG
• Electrical activity is sensed by electrodes placed on the skin surface
• Recorded in the form of an electrocardiogram
• Cardiac monitor depicts electrical impulses on monitor screen or oscilloscope
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
The Electrical Basis of the EKG
• Electrical impulses present on the skin surface are very low voltage; impulses are amplified by an EKG machine
• The printed record of the electrical activity of the heart is called a rhythm strip or an EKG strip
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Leads
• Electrode– An adhesive pad that contains conductive gel
and attaches to patient’s skin
• Leads– How electrodes are connected to the cardiac
monitor – 3 leads must have a positive, a negative,
and a ground
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
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Copyright ©2010 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
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Copyright ©2010 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Leads
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Leads
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Leads
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Leads
• Einthoven’s triangle– Imaginary inverted triangle
formed around heart by proper placement of bipolar leads
– Top formed by lead I, right side formed by lead III, and left side formed by lead II
– Each lead represents a different look at, or view, of the heart
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Graph Paper
• Leaves the machine at constant speed of 25 mm/s
• Time– Measured on horizontal
line
• Amplitude or voltage – Measured on vertical line
on graph paper
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Graph Paper
• Electrocardiographic – Paper divided into
small squares– 1 mm in width– Time interval of 0.04
seconds
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Graph Paper
• Electrocardiographic paper– Darker lines divide paper
every fifth square– Vertically and horizontally– Large squares measure
5 mm in height and width– Represents time interval
of 0.20 seconds– Five small squares in
each large square
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Waveforms
• Wave or waveform refers to movement away from the baseline or isoelectric line (beginning and ending of all waves)
• Positive deflection– Above isoelectric line
• Negative deflection– Below isoelectric line
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
EKG Waveforms
• Electrical impulse leaves SA node, produces waveform on graph paper
• One complete cardiac cycle = P, Q, R, S, (QRS complex) and T wave
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
P Wave
• First wave produced by electrical impulse from SA node
• Smooth, rounded upward deflection
• Depolarization of left and right atria
• 0.10 seconds in length
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
PR Interval
• Time impulse travels from SA node through internodal pathways in atria toward ventricles
• Time interval from start of P wave to start of QRS
• 0.12-0.20 seconds in length
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
QRS Complex
• Consists of Q, R, and S waves
• Represents conduction of impulse from bundle of His through ventricular muscle
• Ventricular depolarization
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
QRS Complex
• Q wave– First downward deflection
• R wave– First upward deflection– Largest deflection seen in
lead I and II
• S wave– Downward deflection after
R wave
• Measures less than 0.12 seconds (3 small boxes)
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
ST Segment
• Time interval during which ventricles depolarized and repolarization of ventricles begin
• Isoelectric or consistent with baseline
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
T Wave
• Follows ST segment• Represents
ventricular repolarization
• Slightly rounded, positive deflection
• Resting phase of cardiac cycle
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Understanding EKGs: A Practical Approach, Third Edition Brenda M. Beasley
Summary of EKG Waveforms
• P wave– Atrial depolarization
• QRS complex– Ventricular
depolarization, atrial repolarization
• T wave– Ventricular
repolarization