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Principles of Electrocardiography
Chapter 49
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
1
Learning Objectives
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Define, spell, and pronounce the terms listed
in the vocabulary.
Apply critical thinking skills in performing
patient assessment and care.
Illustrate the electrical conduction system
through the heart.
Explain the concepts of cardiac polarization,
depolarization, and repolarization.
Summarize the properties of the
electrocardiograph.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
2
Learning Objectives
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Describe the electrical views of the heart
recorded by the 12-lead electrocardiograph.
Discuss the process of recording an
electrocardiogram.
Perform an accurate recording of the
electrical activity of the heart.
Compare and contrast electrocardiograph
artifacts and the probable cause of each.
Identify a typical electrocardiograph tracing.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
3
Learning Objectives
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Describe common electrocardiograph
arrhythmias.
Summarize cardiac diagnostic tests.
Apply a Holter monitor.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
4
The Cardiac Cycle
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The cardiac cycle includes all of the events
occurring in the heart during one single
heartbeat.
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Systole
Diastole
The electrocardiograph records both the
intensity and the actual time it takes for each
part of the cardiac cycle to occur.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
5
Heartbeat Origin
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The sinoatrial (SA) node controls the rate of heart
contraction by initiating electrical impulses every
60 to 100 times per minute.
The heart beats in response to an electrical signal
that originates in the SA node in the right atrium,
spreads over the atria, and causes atrial
contraction.
This impulse continues to the atrioventricular (AV)
node, through the bundle of His, and then through
the right and left bundle branches, eventually
causing ventricular contraction.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
6
Cardiac Rhythms
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Normal sinus rhythm (NSR) refers to a regular
heart rate that falls within the average range of
60 to 80 beats/min
Sinus bradycardia is a heart rate less than
60 beats/min
A rate of greater than 100 beats/min is called sinus
tachycardia
An irregular cardiac rhythm is called an arrhythmia.
Conditions that interrupt the conduction pathway,
SA node to AV node to bundle of His to right and
left bundle branches, can cause arrhythmias.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
7
Electrical Conduction System
From Hunt SA: Saunders fundamentals of medial assisting,
Philadelphia, 2002, Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
8
Cardiac Contraction
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Polarization – resting state of the myocardial
wall: no electrical activity in the heart;
recorded on the ECG as a flatline
Depolarization – contraction phase; electrical
system of the heart stimulates the
myocardium
Repolarization – resting state after
depolarization; the myocardium must return
to a resting state before it can be electrically
stimulated again
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
9
PQRST—Table 49-1
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P wave – first deflection from baseline; atrial
depolarization
PR segment – return to baseline after atrial
contraction
PR interval – time from the beginning of atrial
contraction to the beginning of ventricular contraction
QRS complex – contraction of both ventricles
ST segment – time between the end of ventricular
contraction and the beginning of ventricular recovery
T wave – repolarization of the ventricles
QT interval – between the beginning of the QRS
complex through the T wave
U wave – occasionally seen as a small waveform
after the T wave
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
10
The ECG Machine
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Six-channel ECG machines – Leads placed
at specific anatomic locations; records all
12 leads automatically and marks each lead
with identifying letters; multichannel ECG
tracings take seconds to perform and can be
placed into chart without mounting
Single-channel ECG machines – Older
machines that record the 12 leads one at a
time; strips must be cut apart and mounted
onto a card before placement in the chart
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
11
Critical Thinking Application
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Martha has not been taught how to use the
ECG machine in Dr. Lee’s office. What steps
should she take to learn how to use this
machine and feel comfortable and confident
using it to obtain ECGs?
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
12
Sample ECG Machines
From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
13
Electrocardiograph Paper
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The horizontal lines on the ECG paper permit
the determination of the intensity of the
electrical activity or the relative strength of the
heartbeat.
The paper is heat and pressure sensitive; it
must be handled carefully to avoid making any
additional markings that would blemish the
tracing.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
14
Paper Record
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The horizontal axis of the paper represents time and the
vertical axis represents amplitude
Each small square measures 1 mm on each side
Every fifth line, both vertically and horizontally, is darker
than the other lines creating a larger square measuring
5 mm on each side
One small 1-mm square passes the stylus every
0.04 second; one large 5-mm square passes the stylus
every 0.2 second; in 1 second, 5 large squares pass the
stylus
Large squares represent 0.2 second; 5 of them equals
1 second; ECG paper travels past the stylus at 25 mm
per second
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
15
ECG Paper
From Chester GA: Modern medical assisting, Philadelphia, 1999, Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
16
Electrodes and Leads
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Two electrodes are placed on the arms and legs;
six electrodes are placedon the chest
Electrodes must be applied to specific locations to
record the heart’s electrical activity from different
angles and planes
Most offices use single-use, self-stick, disposable
electrodes that are packaged with conductive jelly in
the center
Ten color-coded and labeled lead wires ending in a
small metal clip are attached to the electrodes
The leads carry the cardiac electrical impulses into the
machine.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
17
Lead Recordings
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Each lead records the electrical activity of the
heart between two different electrodes, one
positive and one negative
If depolarization occurs toward the positive
electrode the deflection is upright; if it moves
toward the negative electrode it is deflected
downward
ECG records views of the heart on both a frontal
and a transverse plane
Frontal leads include leads I, II, III, aVR, aVL,
and aVF. Horizontal plane leads include the
six precordial or chest leads
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
18
Standard Leads
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The first three leads recorded are called the
standard or bipolar leads; they each use two limb
electrodes to record the heart’s electrical activity
Lead I records tracings between the right arm
and left arm
Lead II records tracings between the right arm
and left leg; it is the lead recorded on a cardiac
monitor or on the rhythm strip at the bottom of
the 12-lead ECG
Lead III records tracings between the left arm
and left leg
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
19
Augmented Leads
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Unipolar leads with a single positive electrode
that uses the right leg for grounding
aVr – records the electrical activity of the atria
from the right shoulder; P waves and QRS
complexes are deflected below the baseline
aVl – records the electrical activity of the lateral
wall of the left ventricle from the left shoulder
aVf – records the electrical activity of the
inferior surface of the left ventricle from the
left leg
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
20
Standard and Augmented Leads
From Chester GA: Modern
medical assisting,
Philadelphia, 1999, Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
21
Precordial Leads
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Transverse plane view of the heart; QRS
complex is a negative deflection in V1 and
V2, views with each subsequent lead
becoming more positive
Measure the electrical activity among
six specific points on the chest wall and a
point within the heart
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
22
Precordial Lead Placement
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V1—the electrode is placed in the fourth intercostal
space, just to the right of the sternum
V2—the electrode is placed in the fourth intercostal
space, just to the left of the sternum
V3—the electrode is placed midway between V2
and V4
V4—the electrode is placed in the fifth intercostal
space, at the left midclavicular line
V5—the electrode is placed horizontal to V4 in the
left anterior axillary line
V6—the electrode is placed horizontal to V4 in the
left midaxillary line.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
23
Chest Leads
From Chester GA:
Modern medical
assisting,
Philadelphia, 1999,
Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
24
Electrode Placement
Courtesy CompuMed, San Diego, Calif.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
25
Critical Thinking Application

Dr. Lee has asked Martha to perform her first
ECG on a patient who just came into the
office. Martha is not confident that she knows
how to properly place the chest leads in the
correct location. How should she handle this
situation? Should she perform the ECG
procedure “the best that she can”? Why or
why not?
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
26
Preparation of Room and Patient
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Pick the quietest location in the office, as far
away as possible from all electrical equipment
Patient should empty the bladder and rest for at
least 10 minutes
Patient should disrobe to the waist; gown open
in front; pantyhose removed and limbs exposed
Supine position with pillows to support head,
back, and under knees
If patient is in a seated position the feet must
rest comfortably on the floor or on a footstool;
record any alternative position
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
27
Preparation of Patient
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Record vital signs and current medications on
the medical record or ECG
Explain the procedure and purpose of
the ECG
Make the patient as comfortable as possible
Stress importance of not moving during entire
procedure; observe that he or she is
breathing normally
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
28
Apply Electrodes and Leads
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Applying leads to the patient
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
29
Recording an ECG—Procedure 49-1
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Enter specific information about the patient
including age, sex, prescriptions, etc.
After the ECG is programmed, remind the patient
to lie still and press the appropriate key to run
the ECG strip
Six-channel machines will print and label all
12 leads with a rhythm strip across the bottom
of the paper in lead II in a matter of seconds
Review the printout; if acceptable give it to the
physician
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
30
Standardization, Sensitivity, and Speed
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Stylus should deflect exactly 10 mm when the
standardization button is depressed with a quick
pecking motion
Most machines have three sensitivity standards
that can be selected
If QRS complex is too tall the STD should be set
to 1/2 STD; if QRS complex is too short the STD
should be set to 2 STD
Usual speed for an ECG recording is 25 mm/sec
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
31
Sensitivity Standards
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
32
Mounting an ECG Tracing
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The facility will select the mount that is best
suited to the type of ECG equipment used in
that particular office
Paper clips and staples are never used; they
scratch and mark a tracing; tape should not
be used because it yellows with age
A photocopy can be made of the tracing and
placed in the medical record
With electronic medical records the tracing is
scanned into the patient’s record
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
33
Labeling ECG Strip
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Patient’s full name, sex, age
Date and time of ECG
List of all medications and/or supplements
Variations from normal sensitivity and normal
speed
A very nervous or anxious patient
Lack of rest before test
Smoking immediately before test
Failure to follow any pretest instructions
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
34
Telephone Transmission
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An ECG machine can transmit a recording
over a telephone to an interpretation center
Recording is interpreted by a computer at the
data center and verified by a cardiologist
Patient information that is important to
interpretation such as medications and vital
signs sent with the ECG
Printout with interpretations returned to
sender by fax or email
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
35
Artifacts
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Erratic movement of stylus on ECG paper
from outside interference
ECG is extremely sensitive to any kind of
nearby electrical activity
Medical assistant should have thorough
understanding of the causes of and remedies
for artifacts
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
36
Wandering Baseline
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Stylus gradually shifts away from center of paper
Caused by patient movement or poor electrode
attachment
Remind patient to remain as still as possible; make
patient more comfortable
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
37
Somatic Tremor
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Any muscle movement produces a measurable electrical
impulse causing stylus movement during the tracing
Shows up as jagged peaks of irregular height and
spacing with a shifting baseline
Causes: patient discomfort, apprehension, movement,
talking, or having a condition that causes uncontrollable
body tremors.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
38
Alternating Current (AC) Interference
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Appears as series of uniform small spikes
Electrical currents in nearby equipment or wiring can
leak small amounts of electrical energy that the ECG
picks up
Management – use three-pronged grounded outlet; do
not cross lead wires; unplug other electrical appliances
in room; move table away from wall; and turn off
fluorescent lights
From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
39
Interrupted Baseline
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Electrical connection is interrupted
Stylus moves erratically up and down across the
paper, or it may record a straight line across the top or
the bottom of the paper
Patient movement that dislodges electrodes causes
most baseline interruption; also from broken lead wires
or detached leads
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
40
Critical Thinking Application
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Dr. Lee asks Martha to explain to her the
causes of artifacts and the methods for
correcting ECG recordings that show outside
interference. Based on what you have
learned about ECG artifacts, what are the
typical causes, and how would you
recommend correcting each?
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
41
Normal ECG Appearance
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Table 49-2
NSR – each beat of the heart is initiated with
an impulse from the SA node that then
travels, without interruption, along the normal
conduction pathway of the heart
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Each beat of the heart shows a P wave followed
by a QRS complex
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
42
Rate and Rhythm
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To calculate heart rate count the number of P
waves in a 6-second strip (30 large squares)
and multiply by 10
Ventricular contraction rate – count the number
of complete QRS complexes in 6 seconds and
multiply that number by 10 to get the number of
contractions in 1 minute
If the patient’s heart is in a regular rhythm each
cardiac cycle occurs within the same time
frame and each cardiac cycles occur exactly
the same length of time apart
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
43
Typical Rhythm Abnormalities
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Sinus rhythm – heart’s electrical activity begins in
the SA node and follows through the electrical
system, ending in atrial and ventricular
depolarization
Sinus arrhythmias – pathway of the electrical
charge is normal but the rate or rhythm of the
heartbeat is altered
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Sinus bradycardia – heart rate less than
60 beats/min
Sinus tachycardia – heart rate more than
100 beats/min
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
44
ECG Rhythm Abnormalities
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Atrial arrhythmias
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Premature atrial contraction (PAC) – atria contract before they
should; show up as abnormally shaped P wave or an extra P
Atrial flutter – extremely rapid atrial rate, up to 300 beats/min
Ventricular arrhythmias
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Premature ventricular contraction (PVC) – ventricles contract
before they should; QRS complex appears before P wave
Ventricular tachycardia – (V-tach) 101 to 250 beats/min
Ventricular fibrillation – (V-fib) life-threatening arrhythmia; heart
muscle quivering uncontrollably; unable to pump blood; there
is no pulse
Asystole – no heartbeat; flatline on ECG
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
45
Rhythm Abnormalities
From Chester GA:
Modern medical
assisting, Philadelphia,
1999, Saunders.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
46
Biochemical Arrhythmias
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Digitalis – causes scooping of ST segment in
V5 and V6
From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby.
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Potassium – hyperkalemia or hypokalemia can
both cause life-threatening arrhythmias
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
47
Pacemaker Rhythm
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Pacemakers stimulate the electrical activity of the
heart
Implanted under the skin; it is a small metal pulse
generator with a battery and electronic leads that
extend from the generator to the myocardium
Programmed to fire according to individual patient
needs
Readings transmitted over phone
From Lewis S et al: Medical-surgical nursing, ed 7, St Louis, 2007, Mosby.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
48
Implanted Cardioverter
Defibrillator (ICD)
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Monitors heart rhythm and delivers shock to the
heart if it detects a dangerous tachycardia or
fibrillation
A small, battery-operated device that is implanted
under the skin in the chest or abdomen
Can reverse V-tach and V-fib, especially after the
patient has had an MI
Generator programmed to treat the patient’s
particular or potential cardiac arrhythmia
Patient can telephone in periodic readings
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
49
Myocardial Infarction
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Causes specific ECG changes based on the
phase that the patient is in when the ECG is
recorded (Table 49-4).
Three most common changes – elevated ST
segments, inverted (upside-down) T waves,
and abnormal (pathological) Q waves.
From Aehlert B: ECGs made easy, ed 3, St Louis, 2006, Mosby.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
50
MI Treatment
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Sooner treatment is initiated the more effective
and the better the patient outcome
Immediate treatment – nasal oxygen, sublingual
nitroglycerin (to dilate coronary arteries), narcotic
analgesic (to eliminate pain), aspirin (to reduce
inflammation and decrease clotting time), and
possibly a thrombolytic agent to dissolve the clot
in the coronary arteries
After discharge – quit smoking, modify diet, enter
cardiac rehabilitation program to improve cardiac
strength and recovery by exercise
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
51
Cardiac Stress Test
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Conducted to observe and record the patient’s
cardiovascular response to measured exercise
challenges.
Courtesy Cardiac Science
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
52
Critical Thinking Application

Mr. Sonderford actually had an MI when he
was previously at Dr. Lee’s office. He has
now completed cardiac rehabilitation and is at
the office for a checkup. Dr. Lee wants him to
be scheduled for a stress test. Mr. Sonderford
has never had one before. He confides to
Martha that he is afraid if he takes the test, he
will die from another heart attack. How should
Martha handle this situation?
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
53
Holter Monitor
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A portable system for recording the cardiac activity of a
patient over a 24-hour period or longer.
Courtesy Welch Allyn,
Skaneateles Falls, NY.
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The patient must keep a journal of all stressful events
and activities during the entire time the monitor is worn
and press the event button if symptoms occur.
A medical assistant is often responsible for instructing
the patient in applying and removing the monitor.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
54
Critical Thinking Application

Mrs. Jamison was fitted with a Holter monitor
at the office yesterday at 4 pm. When Martha
arrived at the office at 8 o’clock this morning,
she found Mrs. Jamison had left a message
with the answering service to call her as soon
as possible. When Martha returned the call,
she told her she took a shower last night and
she noticed when she got up to go to the
bathroom that the “light is not on” on the
monitor. How should Martha handle this
situation?
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
55
Cardiac Event Monitor
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Recording device that can be worn up to 30 days to
catch events that are difficult to record in a 24-hour
Holter monitor period
Patients trigger the recording when feel any
symptoms
Remove during bathing – patient must be taught how
to remove and reapply the electrodes
Patient education – do not alter lifestyle; record
activities when events occur; change electrodes daily
and batteries at the same time each day; instructions
on how to transmit recordings by phone
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
56
Electron Beam Tomography Heart
Scan (EBT)
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Noninvasive method of assessing possible
cardiac risk
Takes less than 5 minutes and does not require
any needles or injections
Records amount of plaque present in coronary
arteries by showing the presence of calcium
deposits
Calcium makes up approximately 20% of arterial
plaque deposits
The patient’s calcium score can predict future
cardiac problems
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
57
Patient Education
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Heart disease and stroke account for more
than one-third of all deaths.
Talk to the patient about factors that could be
modified, and give him or her encouragement
for any attempt at complying with these
suggestions.
Include visual aids, posters, and brochures.
Copyright © 2011, 2007, 2003, 1999 by Saunders, an imprint of Elsevier Inc. All rights reserved.
58