Transcript Heart 2

Pearson's Comprehensive
Medical Assisting
Administrative and Clinical Competencies
Second Edition
CHAPTER
CHAPTER
49
Electrocardiography
Lesson 2:
Performing an Electrocardiogram
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Lesson Objectives
•
•
•
•
Upon completion of this lesson, students
should be able to …
Define and spell the terms for this chapter.
Explain the significance of each ECG
wave.
Maintain and operate electrocardiogram
equipment.
Identify by name and function the controls
on an electrocardiograph machine.
Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e
Beaman • Fleming-McPhillips • Routh • Gohsman • Reagan
Copyright ©2011 by Pearson Education, Inc.
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Lesson Objectives
• Name the standard 12 leads and the
locations of their sensors.
• State the cause and correction of artifacts.
Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e
Beaman • Fleming-McPhillips • Routh • Gohsman • Reagan
Copyright ©2011 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
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Critical Thinking Question
1. What is the medical assistant’s role in
ECGs?
Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e
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Copyright ©2011 by Pearson Education, Inc.
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The Electrocardiogram (ECG)
• Electrical charges created by the
conduction system can be sensed
throughout the body
• These charges can be picked up by
placing sensors in specific areas of the
skin
• Sensors transmit the electrical charge to a
computer for amplification of the signal
Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e
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The Electrocardiogram (ECG)
• Amplified signal is recorded on graph paper
– A flat line means that no electrical signal is
sensed
– A deflection above or below the flat line means
that there is an electrical signal of some kind
– A positive (up) or negative (down) deflection is
called a wave
– The height of the wave reflects strength of the
electrical signal
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The ECG
• A normal cardiac cycle is one series of
PQRST waves.
– P – initial atrial depolarization (change in
electrical activity)
– QRS complex – ventrical depolarization
– T – repolarization (return to the resting
electrical state)
• Then it all starts over again
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ECG Tracing
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Time and the Cardiac Cycle
• The P wave represents the impulse that
originated in the SA node and spread
through the atria (called atrial
depolarization)
• A normal looking P wave reflects a
normally-functioning SA node
• The P-R interval is the time from the
beginning of P to the beginning of QRS
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Time and the Cardiac Cycle
• This time is between
0.12 and 0.20
seconds (2-5 small
boxes on the EKG
graph paper)
• A deviation could
represent an
abnormality in the
electrical system or
structure of the heart
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Time and the Cardiac Cycle
• A P-R Interval that is
too short means that
the impulse has
reached the ventricles
through a shorter than
normal pathway
• A P-R Interval that is
too long means that
there is a conduction
delay in the AV node
possibly
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Critical Thinking Question
1. In the previous two examples, how many
small boxes are between the P and R?
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Time and the Cardiac Cycle
• The QRS complex represents
the time necessary for the
impulse to travel through the
bundle of His, the bundle
branches, and the Purkinje
fibers to complete ventricular
contraction
• This is ventricular depolarization
• This usually takes less than 0.12
second (3 small ECG boxes)
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Critical Thinking Question
1. In this example, how many small boxes
are between the Q and S?
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Time and the Cardiac Cycle
• The ST segment and the T wave
represent repolarization of the
ventricles
• The ST segment is normally flat (on
the baseline) or only slightly
elevated
• The T wave represents a part of
recovery of the ventricles after
contraction
• The QRS complex and T wave
typically point in the same direction
• Anything else may indicate a
problem in the heart or its electrical
system
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Critical Thinking Question
1. Is this a normal ST segment? Why?
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ECG Machines
• All ECG machines are
calibrated to align with the
international standard
• The paper moves at a
speed of 25 mm/second
• Given the same amount of
electrical energy, the
recording stylus also moves
the same distance
• 1 mV of electricity input will
cause the stylus to deflect
10 mm
• This allows uniform
recordings worldwide
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ECG Machines
• Older models are manual; newer models
complete many of the procedures
automatically via a computer
• During patient preparation, all ten sensors
are placed on the patient
• The computer then switches from lead to
lead in rapid succession
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ECG Machines
• Patient data is entered into the machine
(name, date of birth, diagnoses, height,
weight, age, bp, medications, and other
information)
• You can override the automatic controls, if
desired
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Critical Thinking Question
1. What can you do to help the patient relax
during the preparation and testing? Why
is relaxing important?
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ECG Machines
• Each lead is recorded in a separate channel or
pathway for the signal
• Many machines record more than one channel
(typically 3) at once
• Some machines will print out a statement about
the status of the heart
• Some even can fax the report to a physician’s
office
• Computerized ECGs should still be carefully
examined to make sure that a clear ECG is
made before disconnecting the sensors
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The ECG Control Panel
• Main power switch: Allows for a warm-up
as specified by the manufacturer before
using
• Record switch: This switch moves the
paper at the “run 25” speed
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The ECG Control Panel
• Lead selector: This determines from which
sensors (electrodes) the machine will
record:
– Standard (limb) leads: Record from two
electrodes placed on all extremities
– Augmented leads: Record from the midpoint
between two limb electrodes to a third limb
sensor
– Chest leads: Record from various positions on
the thorax
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Beaman • Fleming-McPhillips • Routh • Gohsman • Reagan
Copyright ©2011 by Pearson Education, Inc.
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The ECG Control Panel
• Sensitivity control: Allows the operator to
increase or decrease the recording size to
enlarge or shrink the deflections to fit on
the paper
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The ECG Control Panel
• Standard button: Allows verification of
calibration to the international standard
• Stylus control: Centers the recording in the
middle of the page or the center of each
channel by moving the stylus
• Stylus heat control: Increases or decreases
heat and adjusts for the sharpest tracing
• Marker: Indicates, by a code, which lead is
being recorded
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The ECG Paper
• Paper is pressure sensitive and must be
handled carefully
• If this paper is exposed to light for long
periods, the markings will fade with time
• Many newer models use an ink cartridge
to supply the stylus and provide a longerlasting printout
• Paper records both time (horizontally) and
voltage (vertically)
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Time Markers on ECG Paper
• Time markers (3-second markers) are printed
on the ECG paper
– Located at the top of single-channel paper and
between channels in multi-channel paper
– Small squares with a light line and larger squares
of a darker line
– Small squares: 1 mm by 1 mm square = 0.1 mV
in height and .04 second time in the width
– Large squares: 5 mm by 5mm square = 0.5 mV of
voltage in the height and 0.20 second time in the
width
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Heart Rate
• You can estimate the heart rate from an ECG
6-second Method
– Begin at one 3-second marker and go to the
right for two additional markers, for a total of 6
seconds
– Count the number of QRS complexes
between the first and third markers, and add a
zero
– This is estimated ventricular rate per minute
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Copyright ©2011 by Pearson Education, Inc.
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Heart Rate
• You can estimate the heart rate from an ECG
Count-off Method
– Locate a QRS complex close to a 5-mm line
– Move to the next deflection at the right or the
left
– Count how many 5-mm lines intersect the
tracing before the next QRS complex
– Count off at each 5-mm line saying “zero,
300, 150, 100, 75, 60, 50”
– Stop counting when you reach the next QRS
complex
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Heart Rate
• You can estimate the heart rate from an ECG
Exact Calculation
– Paper moves at a standard speed of 25
mm/second = 1500 mm/minute
– Count the millimeter boxes between two QRS
complexes
– Divide the number into 1500
 Example: if there are 20 mm between two QRS
complexes, 1500 divided by 20 = 75 beats per
minute
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Rhythm
• The regularity of the occurrence of heartbeats
• Ventricular rhythm is determined by
measuring the distance between QRS
complexes
– There should be a consistent space between
complexes
• Atrial rhythm is determined by measuring
the distance between P waves
– There should be a consistent space between
waves
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Sensor Placement
• The ECG machine records the cardiac
cycle through sensors placed on the
patient’s bare skin
• Sensors are placed:
– Over the fleshy part of the inner aspect of
both lower legs (RL and LL)
– Over both upper arms or both forearms,
avoiding the bony prominences (RA and LA)
– Chest sensors (V) are placed in 6 locations
(V1 – V6)
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ECG Leads
• Each lead will record from a specific
combination of sensors
• By recording from different combinations
of sensors, the electrical activity of the
heart is seen from different angles
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Einthoven’s Triangle
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Patient Preparation for an ECG
• Explain to the patient the equipment and
procedure as well as what you will expect
the patient to do
• The surroundings should be pleasant and
the table wide enough for adequate
support
• Patients will need to be bare to the waist
so privacy should be provided for
disrobing
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Patient Preparation for an ECG
• Position patient in the supine or semiFowler’s position
• Jewelry, particularly metal jewelry, must
be removed so that it does not interfere
with the electrical current of the ECG
• Prepare the skin where the sensors will be
applied
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Preparation of Equipment
for an ECG
• ECG machine that has been calibrated
and is in good working order
• Good supply of paper
• Supply of electrolyte or conduction cream,
gel, or pads
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The ECG Recording
• Normally, the ECG recording is made in
sensitivity 1 = 10mm deflection per 1 mV
of electricity
• If size is doubled, it is sensitivity 2
• If size is cut in half, it is sensitivity 1/2
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Satisfactory Tracings
•
•
•
•
•
Accurate
Readable
Clear
Travels down the center of the page
Has a consistently horizontal baseline
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Artifacts
• Electrical activity from a source other than
the heart that the sensors detect
• Can impair accurate interpretation of the
tracings
• Causes include:
– Somatic tremors
– Wandering baseline and baseline shifts
– 60 cycle or AC interference
– Erratic stylus
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Mounting an ECG
• Select the best part of the recording for
that lead
• Cut and trim it
• Place it in the appropriate area of the
folder
• Double-check to ensure you have read the
lead’s international code correctly
• Repeat the process until all 12 leads have
been properly mounted
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Normal Sinus Rhythm
• Has three distinct waves
– P wave
– T wave
– QRS complex between the P and T waves where
the Q is a downward deflection, the R is an
upward deflection, and the S is a downward
deflection following an R
• The beats come at regular intervals
• Within the lead being recorded, each cardiac
cycle appears the same as previous ones
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Abnormalities Caused by Cardiac
Pathology
•
•
•
•
•
•
•
•
Atrial fibrillation
Atrial flutter
AV heart block
Myocardial infarction (MI)
Paroxysmal atrial tachycardia (PAT)
Premature atrial contractions (PACs)
Premature ventricular contractions (PVCs)
Sinus arrhythmia
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Abnormalities Caused by Cardiac
Pathology
•
•
•
•
Sinus bradycardia
Sinus tachycardia
Ventricular fibrillation
Ventricular tachycardia
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Copyright ©2011 by Pearson Education, Inc.
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Questions?
Pearson's Comprehensive Medical Assisting: Administrative and Clinical Competencies, 2/e
Beaman • Fleming-McPhillips • Routh • Gohsman • Reagan
Copyright ©2011 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.