the electrocardiogram
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2. The Electrocardiogram. Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program. Electrocardiogram. An electrocardiogram is a tracing of the heart’s electrical activity An electrocardiograph is the machine that produces it. Electrocardiograph. - PowerPoint PPT PresentationTRANSCRIPT
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Fast & Easy ECGs, 2EFast & Easy ECGs, 2E© 2013 The McGraw-Hill Companies, Inc. All rights reserved.
The Electrocardiogram
Fast & Easy ECGs, 2nd E – A Self-Paced Learning Program
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Electrocardiogram
• An electrocardiogram is a tracing of the heart’s electrical activity
• An electrocardiograph is the machine that produces it
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Electrocardiograph
• Also called the ECG machine, it detects heart’s electrical activity through electrodes positioned on patient’s skin
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ECG Machines
• A variety of ECG machines are available – Some monitor from one
to five different leads– Some are capable of
monitoring up to twelve or more leads simultaneously
– Some are used for continuous monitoring
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The Input• Lead wires and cables
transfer the ECG signal detected through the electrodes to the ECG machine– There may be 3, 4, or 5
lead wires for monitoring purposes and up to 10 lead wires for 12-lead ECGs
– Each lead wire has a labeled clip, snap, or pin-type connector on the distal end which attaches to the electrode
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Using Lead Wires and Cables• Keep the lead wires
separated from each other to avoid tangling
• Position them loosely across the patient so they do not pull on and lift the electrodes away from the skin
• Properly clean and decontaminate then after each use
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ECG Electrodes
• Are typically disposable • Consist of a: – wet or dry electrolyte gel
(which acts to assure good signal pick-up),
– metal snap or tab (where the ECG lead wire is attached),
– self-adhesive pad that holds the electrode to the skin
Metal snap
Self-adhesive pad
Electrolyte gel
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Placing ECG Electrodes• To achieve a noise-
free recording: – Clean the skin site to
remove dead skin cells and oils
– Clip dense hair present at the sites where the electrodes are to be placed
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Placing ECG Electrodes
• Eliminate muscle tension by placing the patient’s arms and legs in a comfortable position in which the extremities are resting on a supportive surface – If artifact is still present and the patient tolerates
it, try laying him or her in a flat position
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Placing Electrodes
• Avoid removing electrodes from their sealed protective envelope before use as the conductive gel may dry
• With snap-on lead wires, attach the electrode to the lead wire before placing the electrodes onto the patient’s skin
• With clip-on type lead wires, apply the connector to the metal snap of the electrode after the electrode has been placed
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Placing Electrodes
• Place the electrodes in the correct locations – Know where each
electrode is supposed to be positioned
– Look for a flat surface and sites over soft tissues
– Avoid areas where large bones are near the skin surface and areas where there are thick muscles or skin folds
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ECG Leads
• Are a combination of electrodes that form an imaginary line in the body along which the electrical signals, detectable during the time course of the heartbeat, are measured
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ECG Leads
• Each lead provides a different view of the heart: – Electrodes are placed on chest, arms and legs– Sites vary depending on which view of the heart's
electrical activity is being assessed
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ECG Leads
• Deflection of the waveforms seen on the ECG depend on where the positive electrode is placed in comparison to the direction of the electrical forces
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ECG Leads
• ECG leads are either bipolar or unipolar
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Bipolar Leads
• Record the flow of the electrical impulse between two (one is positive, the other is negative) selected electrodes
• Includes I, II and III
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Bipolar Leads
• Record difference in electrical potential between a positive and negative electrode
• Uses a third electrode called a ground
• Include leads I, II and III
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Unipolar Leads
• Use only one positive electrode and a reference point calculated by the ECG machine
• Includes leads aVR, aVL, aVF, and V1 through V6
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Planes of the Heart• Electrodes are
placed on the extremities and chest wall to view the heart’s electrical activity from the frontal and horizontal planes– Provides a cross-
sectional view of the heart
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Frontal Plane• Leads that view this
plane are called limb leads
• Include leads I, II, III, aVR, aVL and aVF
• Provide inferior, superior, and lateral views of heart
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Horizontal Plane• Leads that view this
plane are called precordial or chest leads
• Include leads V1, V2, V3, V4, V5, and V6
• Provide inferior, superior, and lateral views of heart
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Different Leads Uses
• A given lead may be used to highlight: – A specific part of ECG complex – Electrical events of a specific cardiac cycle – Conditions such as an enlargement of heart
muscle or presence of ischemia, injury and infarction
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Limb Lead Locations• RA electrode
– positioned anywhere on the right arm or below the right clavicle in the midclavicular line
• LA electrode– positioned anywhere on the left
arm or below the left clavicle in the midclavicular line
• LL electrode– positioned anywhere on the left
leg or left midclavicular line below the last palpable rib
• RL electrode– positioned on the right leg or
right midclavicular line below the last palpable rib
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Chest Leads
• Positioned in order across the chest
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Lead II
• ECG electrode polarity– Positive electrode – LL lead wire– Negative electrode – RA lead wire– Ground electrode – LA lead wire (and RL lead wire)
• Produces positively deflected waveforms
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The Output
• ECG machine translates the electrical impulses generated in the heart into wave-like signals that are recorded on paper or displayed on a monitor
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Oscilloscope
• ECG rhythms displayed on the oscilloscope are called dynamic ECGs
• Represent real time electrical activity or what is presently occurring in the heart
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Printouts
• ECGs printed on graph paper are called static ECGs
• Show what has already occurred • Much easier to analyze a static ECG to identify
abnormalities than it is to examine an image moving across a screen
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Printouts• As the stylus moves
across the moving ECG paper it inscribes waveforms representing the heart’s electrical activity
• Vertical lines on the ECG paper represent amplitude in electrical voltage while horizontal lines represent time or duration
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ECG Paper
• Each small square equals– 0.04 sec in duration and
0.1 mV in amplitude
• Five small squares (1 large box) equals– 0.20 seconds in duration
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Isoelectric Line• Is the flat line that
occurs when no electrical activity is occurring or impulses are too weak to be detected
• Used as a baseline to identify changing electrical movement
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Calibration or Registration Mark
• Helps ensure ECG machine is properly calibrated
• Serves as reference point on ECG tracing
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Artifact
• Markings on ECG tracing that are not a product of heart’s electrical activity– Patient movement is
among its many causes
– Can mimic life-threatening dysrhythmias
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Summary
• Graphic record or tracing is called an electrocardiogram while the machine that produces it is called the electrocardiograph
• Electrodes placed on patient’s skin detect heart’s electrical activity
• Abnormalities in cardiac rate and/or rhythm are called dysrhythmias
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Summary
• Each lead provides a different view of heart. • Impulses traveling toward a positive electrode
are recorded on ECG as upward deflections. • Impulses traveling away from a positive
electrode or toward a negative electrode are recorded as downward deflections.
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Summary
• Limb leads are produced by placing electrodes on right arm (RA), left arm (LA) and left leg (LL). – Include leads I, II, III, augmented vector right
(aVR), augmented vector left (aVL) and augmented vector foot (aVF).
• Precordial leads include leads V1, V2, V3, V4, V5, and V6.
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Summary
• ECG paper consists of horizontal and vertical lines that form a grid.
• Horizontal measurements used to determine heart rate and duration of various waveforms, segments and intervals.
• Vertically on ECG paper, distance between lines, or boxes, represents amplitude in millimeters (mm) or electrical voltage in millivolts (mV).
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Summary
• Calibration• Artifact is markings on ECG tracing that have
no relationship to electrical activity of the heart.
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