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Chapter 37
Electrocardiography
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Anatomy of the Heart
• Four chambers
– Atria: two upper chambers
– Ventricles: two lower chambers
• Deoxygenated and oxygenated blood
– Cycle begins with each heartbeat
• Coronary arteries
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Electrical Conduction
System of the Heart
• Sinoatrial (SA) node: body’s natural
pacemaker
• Atrioventricular (AV) node: responds to
signals from SA node
• Bundle of His and Purkinje fibers:
disperses electrical impulses
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Electrical Conduction
System of the Heart
• Systole: contraction
• Diastole: relaxation
• ECG cycle
– Graphic representation of cardiac cycle
– Electrical impulses recorded on ECG paper or
displayed on oscilloscope
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
The Cardiac Cycle
and the ECG Cycle
• Baseline or isoelectric line
• Positive and negative deflection
• P, QRS, T waves: depolarization and
repolarization of myocardial cells
• Each cardiac cycle takes about 0.8
second
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
The Cardiac Cycle
and the ECG Cycle
• Electrical impulses in cardiac cycle
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Calculation of Heart Rate
• On ECG graph paper:
– Every fifth line darker than other lines (squares 5
X 5 mm)
– Time measured on horizontal line
– Voltage measured on vertical line
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Types of Electrocardiographs
• Multichannel ECG
• Automatic ECG
machines
• Single-channel ECG >>
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Types of Electrocardiographs
• ECG telephone transmissions
• Facsimile electrocardiograph
• Interpretive electrocardiograph
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
ECG Equipment
• Electrocardiograph paper
–
–
–
–
Black or dark blue
Wax or plastic coated
Heat and pressure sensitive
Heat of stylus can be adjusted to obtain sharp
tracing
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
ECG Equipment
• Electrolyte
– Applied with each electrode to pick up electrical
current
– In form of gel, lotion, paste, or pre-saturated pads,
contained within adhesive sensors
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
ECG Equipment
• Sensors or electrodes
– Detect electrical impulses on body surface; relay
them through cables, or lead, wires to ECG
machine
– Disposable sensors (electrodes) contain layer of
electrolyte gel on adhesive surface; used on limbs
and chest
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
ECG Equipment
• Lead wires
– Once self-adhesive
sensors are placed, lead
wires from ECG
machine are connected
to them
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
ECG Equipment
• Electrocardiograph machine
– Electrical activity from body small; made larger by
amplifier of ECG machine
• Care of equipment
–
–
–
–
Remove lead wires from sensors
Remove sensors from patient
Dispose of sensors
Change paper when necessary
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Lead Coding
• 12 leads recorded using 10 lead wires
• Necessary for identification and
mounting purposes
• Newer ECGs automatically mark (code)
each lead
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
The Electrocardiograph
and Sensor Placement
• 10 sensors that record 12 leads of
heart’s electrical activity
• Allows for 3D interpretation of activity
• Electrodes placed on patient’s four
limbs and chest
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
The Electrocardiograph
and Sensor Placement
• Types of leads
– Standard limb or
bipolar leads
– Augmented leads
– Chest leads or
precordial leads
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Standardization and Adjustment of
the Electrocardiograph
• Value of recording depends on
accuracy
• Universal measurements
• One millivolt (mV) of cardiac electrical
activity will deflect stylus exactly 10 mm
high
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Standard Resting Electrocardiography
•
•
•
•
Patient preparation
Placement of limb and chest leads
Attachment of lead wires
Elimination of artifacts vary little from
one electrocardiograph to another
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Mounting the ECG Tracing
• Commercially prepared mounting forms
• Mount completed tracing after provider
has reviewed entire recording
• Patient’s name, date, address, age, sex,
blood pressure, height and weight,
cardiac medications
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Interference or Artifacts
• Somatic tremor artifacts: muscle tremor
• Alternating current (AC) interference:
electrical interference
• Wandering baseline artifacts: stylus
moves from center of ECG paper
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Interference or Artifacts
• Interrupted baseline artifacts: break
seen between waves
• Patients with unique problems
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Myocardial Infarctions (Heart Attacks)
• Number one cause of death in United
States
• Behaviors to adopt for healthy heart
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Cardiac Arrhythmias
• Atrial arrhythmias
– Premature atrial contractions (PAC)
– Paroxysmal atrial tachycardia (PAT)
– Atrial fibrillation
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Cardiac Arrhythmias
• Ventricular arrhythmias
– Premature ventricular contractions (PVCs)
– Ventricular tachycardia
– Ventricular fibrillation
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Defibrillation
• Electrical device that applies
countershocks to heart through
electrodes or pads placed on chest wall
• Can convert cardiac arrhythmia to
normal sinus rhythm
• Automated external defibrillators (AED)
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Holter monitor (portable ambulatory
electrocardiograph)
– Portable continuous recording of cardiac activity
for 24-hour period
– Noninvasive test helps to diagnose cardiac
arrhythmias
– Digital, three-channel ECG; Windows-based
software
– Electrode placement not the same as for standard
12-lead resting ECG
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Holter monitor
– Prepare patient
– Instruct patient
– Check and replace
battery
– Apply and remove
monitor
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Holter monitor
– Patient activity diary
• Record all activities, emotional states, time of their
occurrence
• Record chest pain and other symptoms and time of
occurrence
– Removal
• Patient returns to office
• Tape analyzed by scanner or computer
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Loop ECG
– Uses only two electrodes
– Records few minutes of ECG at a time on
computer chip
– Recorded event transmitted by telephone to
provider
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Treadmill stress test or exercise
tolerance ECG
– Diagnose heart disorders
– Probable cause of patient’s chest pain
– Assess patient’s cardiac ability following cardiac
surgery
– Noninvasive test
– Patient exercises on treadmill at prescribed rates
of speed
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Treadmill stress test or exercise
tolerance ECG
– Complications ( myocardial infarction or serious
arrhythmia) can occur during testing
– Further diagnostic tests such as cardiac
catheterization (angiogram) may be necessary
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Thallium stress test
– Similar to treadmill stress
– Patient given injection of radioactive (thallium)
– Test shows how well blood flows to heart muscle
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Other Cardiac Diagnostic Tests
• Echocardiography/ultrasonography
– Noninvasive, diagnostic test
– Ultrasound to image internal structures of heart
• CT and MRI coronary imaging
– Identify location and thickness of cardiac muscle
scars due to damage
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Cardiac Procedures
• Percutaneous transluminal coronary
angioplasty (PTCA)
– Widens narrowed or blocked coronary artery
– Balloon angioplasty
– Stents: small mesh tubes compressed around
balloon; permanent intervention
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.
Cardiac Procedures
•
•
•
•
Atherectomy and laser angioplast
Coronary artery bypass
Heart valve: repaired or replaced
Procedures for arrhythmias
© 2014 Cengage Learning. All Rights Reserved. May not be scanned, copied
or duplicated, or posted to a publicly accessible website, in whole or in part.