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Chapter 37
Electrocardiography
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Anatomy of the Heart
• Four chambers
– Two upper chambers known as atria
– Two lower chambers known as ventricles
• Deoxygenated blood
• Oxygenated blood
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Anatomy of the Heart
• Coronary arteries
• Click here to see an animation
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Electrical Conduction
System of the Heart
• Sinoatrial (SA) node
• Atrioventricular (AV) node
• Bundle of His and Purkinje fibers
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Electrical Conduction
System of the Heart
• Systole and diastole
• Impulses can be recorded on ECG paper or
displayed on oscilloscope
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The Cardiac Cycle
and the ECG Cycle
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Baseline or isoelectric line
Positive deflection
Negative deflection
Each cardiac cycle takes about 0.8 second
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
The Cardiac Cycle
and the ECG Cycle
• P, QRS, and T waves
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Calculation of Heart Rate
• On ECG graph paper:
– Every fifth line is darker than other lines
– Time is measured on horizontal line
– Voltage is measured on the vertical line
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Types of Electrocardiographs
• Single-channel ECG >>
• Multichannel ECG
• Automatic ECG machines
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Types of Electrocardiographs
• ECG telephone transmissions
• Facsimile electrocardiograph
• Interpretive electrocardiograph
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
ECG Equipment
• Electrocardiograph paper
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Black or dark blue
Wax or plastic coated
Heat and pressure sensitive
Heat of stylus can be adjusted to obtain a sharp tracing
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
ECG Equipment
• Electrolyte
– Help pick up electrical current produced by contraction
and relaxation of heart
– In form of gel, lotion, paste, or pre-saturated pads
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
ECG Equipment
• Sensors or electrodes
– Disposable sensors
– Detect electrical impulses on body surface from the
myocardium and relay them through cables
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
ECG Equipment
• Lead wires
– Once self-adhesive sensors
are placed, lead wires from
the ECG machine are
attached
• Caring for equipment
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Lead Coding
• 12 leads recorded using 10 lead wires
• Necessary for identification and mounting
purposes
• Newer ECGs automatically mark (code)
each lead
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
The Electrocardiograph
and Lead Placement
• 12 leads record heart’s electrical activity
• Allows for 3D interpretation of activity
• Amplification of electrical activity
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
The Electrocardiograph
and Lead Placement
• Galvanometer changes voltage into
mechanical motion
• Stylus records motion
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
The Electrocardiograph
and Lead Placement
• Types of leads
– Standard limb or bipolar
leads
– Augmented leads
– Chest leads, precordial
leads, or V leads
• Placement of
electrodes
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Standardization of the
Electrocardiograph
• Value of recording depends on accuracy
• Universal measurements
• One millivolt of cardiac electrical activity
will deflect stylus exactly 10 mm high
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Standard Resting Electrocardiography
• Performing 12-lead electrocardiogram
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Standard Resting Electrocardiography
Click Here to play the video
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Mounting the ECG Tracing
• Commercially prepared mounting forms
• Mount completed tracing after provider has
reviewed entire recording
• Identify patient, date, age, blood pressure,
height and weight, and cardiac medications
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Interference or Artifacts
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Somatic tremor artifacts
Alternating current (AC) interference
Wandering baseline artifacts
Interrupted baseline artifacts
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Cardiac Conditions and Diseases
• Myocardial infarctions (heart attack)
– Primary cause of death in U.S.
– Offer patient health tips as part of patient education
• Behaviors to adopt for a healthy heart
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Cardiac Arrhythmias
Click Here to play the video
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Cardiac Arrhythmias
• Atrial arrhythmias
– Premature atrial contractions (PAC)
– Paroxysmal atrial tachycardia (PAT)
– Atrial fibrillation
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Cardiac Arrhythmias
• Ventricular arrhythmias
– Premature ventricular contractions (PVCs)
– Ventricular tachycardia
– Ventricular fibrillation
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Defibrillation
• Electrical device that applies countershocks
to heart through electrodes or pads placed
on chest wall (AED)
• Can convert cardiac arrhythmia into normal
sinus rhythm
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Holter Monitor
• Portable ambulatory electrocardiograph
– Portable continuous recording of cardiac activity for a
24-hour period
– Noninvasive test
– Helps diagnose cardiac arrhythmias by correlating them
with patient’s symptoms
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Holter Monitor
• Medical assistant’s
role
– Preparing patient
– Instructing patient
– Applying and removing
monitor
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Holter Monitor
• Patient activity diary
– Record all activities, emotional states, and time of their
occurrence
– Record chest pain and other symptoms and time of their
occurrence
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Holter Monitor
• Removing the Holter Monitor
– Patient returns to office
– Tape is analyzed by scanner or computer
– Written report sent to physician
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Other Diagnostic Tests
• Treadmill stress test
– Diagnose heart disorders and probable cause of
patient’s chest pain
– Assess patient’s cardiac ability following cardiac
surgery
– Noninvasive test
– Patient exercises on treadmill at varying rates of speed
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Other Diagnostic Tests
• Loop ECG
• Thallium stress test
• Echocardiography/ultrasonography
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Cardiac Procedures
• Coronary angioplasty with and without stent
– Balloon inflated inside coronary artery with or without
stent
– Keeps artery open
• Coronary artery atherectomy
– Cutting away of plaque in blocked coronary artery
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.
Other Cardiac Diagnostic Tests
• Coronary artery bypass
– Vein transplanted into blocked coronary artery(ies)
– Blood supply reestablished to myocardium
• Cardiac computerized tomography and
cardiac magnetic resonance
Copyright © 2010 Delmar, Cengage Learning. ALL RIGHTS RESERVED.