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Principles of Electrocardiography
Chapter 48
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
The Cardiac Cycle

The cardiac cycle includes all of the events occurring in
the heart during one single heartbeat.
– Systole
– Diastole

The electrocardiograph records both the intensity and
the actual time it takes for each part of the cardiac
cycle to occur.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 2
Heartbeat Origin
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The heart beats in response to an electrical signal that
originates in the sinoatrial (SA) node in the right
atrium, spreads over the atria, and causes atrial
contraction.
SA node controls the rate of heart contraction by
initiating electrical impulses every 60 to 100 times per
minute.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 3
Ventricular 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 © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 4
Normal Sinus Rhythm

Refers to a regular heart rate that falls within the
average range of 60 to 80 beats/min
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 5
Normal Sinus Rhythm (cont’d)
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 6
The ECG machine

Six-channel ECG machines

Single channel ECG machines
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 7
The ECG machine (cont’d)
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 8
Electrocardiogram


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 pressure sensitive; it must be handled
carefully to avoid making any additional markings that
would blemish the tracing.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 9
Paper Record

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The stronger the beat, the greater the vertical
deflection on the paper. The vertical lines represent
time.
The large squares each represent 0.2 seconds. Five of
them equal 1 second.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 10
Paper Record (cont’d)
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 11
Electrodes and Leads
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
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Ten electrodes are placed on the patient’s arms, legs,
and chest to pick up the electrical activity of the heart.
Most offices use single-use, self-stick, disposable
electrodes that are packaged with conductive jelly in
the center.
The leads carry the cardiac electrical impulses into the
machine.
The frontal leads include Leads I, II, III, aVR, aVL, and
aVF. Horizontal plane leads include the six precordial or
chest leads.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 12
Electrode Placement

Taking an ECG requires knowledge of where to place
the electrodes accurately and how to connect the leads
to obtain the most accurate recording possible.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 13
Leads

The 12-lead ECG consists of three limb leads
– I
– II
– III


Three augmented leads (aVR, aVL, and aVF)
Six precordial or chest leads (V1, V2, V3, V4, V5,
and V6)
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 14
Heart Function

These leads record the electrical activity from different
directions, giving the physician a picture of the function
of different areas of the heart.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 15
Leads
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 16
ECG Electrode Placement
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 17
Chest Leads
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Slide 18
Obtaining an ECG

Preparation of the room and patient

Applying leads to the patient
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 19
Obtaining an ECG

Recording the ECG (see Procedure 48-1)

Standardization, sensitivity, and speed

Mounting an ECG tracing
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 20
Artifacts

The medical assistant must recognize and correct the
most common types of artifacts on the ECG recording.
– Wandering baseline
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Slide 21
Artifacts
– Somatic tremor
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Slide 22
Artifacts
– Sixty-cycle interference
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 23
Artifacts
– Interrupted baseline
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 24
Sensitivity Standards
Most machines have 3 sensitivity standards that can be
selected
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 25
Sensitivity Standards (cont’d)
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 26
Typical ECG Rhythm Abnormalities

Sinus arrhythmias
– Sinus bradycardia
– Sinus tachycardia
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 27
Typical ECG Rhythm Abnormalities

Atrial arrhythmias
– Premature atrial contraction (PAC)
– Atrial flutter

Ventricular arrhythmias
– Premature ventricular contraction
– Ventricular fibrillation
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 28
Typical ECG Rhythm Abnormalities
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 29
Biochemical Arrhythmias

Digitalis

Potassium
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 30
Stress Test

Conducted to observe and record the patient’s
cardiovascular response to measured exercise
challenges.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 31
Holter Monitor

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A portable system for recording the cardiac activity of a
patient over a 24-hour period or longer.
The patient must keep a journal of all stressful events
and activities during the entire time the monitor is
worn.
A medical assistant is often responsible for instructing
the patient in applying and removing the monitor.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 32
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, brochures.
Copyright © 2007 by Saunders, Inc., an imprint of Elsevier Inc.
Slide 33