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2012 Lippincott Williams & Wilkins. All rights reserved.
ECG Workout:Chapter Review
Chapter 4
Cardiac monitors
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ECG monitoringThe electrocardiogram (ECG) is a recording of the electricalactivity of the heart. The ECG records two basic electricalprocesses:
Depolarizationthe spread of the electrical stimulus throughthe heart muscle, producing the P wave from the atria, and
the QRS from the ventricles. Repolarizationthe recovery of the depolarized muscle to its
resting state, producing the ST segment, the T wave, and theU wave.
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Types of ECG monitoring
There are two types of ECG monitoring:
Hardwire(bedside monitoring) electrode pads are placedon patient's chest and connected to a monitor at the bedside.
Telemetry(portable monitoring) electrode pads are placedon patient's chest and connected to a portable monitor
transmitter.
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Hardwire monitoring5-lead systemWith the hardwire 5-lead system, you can monitor two leads at the same time using a lead selector on themonitor. Leads placed in the arm and leg positions (shown in example A) allow you to view the limb leads(I, II, III, aVR, aVL, and aVF). To view the chest leads (V1- V6) (shown in example B), the chest lead mustbe placed in the specific chest lead position desired. In example A, the chest lead is in V1position.Generally a limb lead (usually I, II, or III) and a chest lead (usually V1or V6) are chosen to be monitored.
A. Hardwire Monitoring5-Lead System B. Chest Lead Positions
This illustration shows you where to place the electrodes and attach leadwires
using a five-leadwire system. The leadwires are color-coded as follows:
white right arm (RA)black left arm (LA)
green right leg (RL)red left leg (LL)
brown chest (C).
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Hardwire monitoring
3-lead system
This illustration shows you where to place the electrodes and attach leadwires
using a three-leadwire system. The leadwires are color-coded as follows:
whiteright arm (RA)blackleft arm (LA)redleft leg (LL).
Leads placed in this position will allow you to monitor leads I, II, or III using
the lead selector on the monitor.
Hardwire Monitoring
3-Lead System
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Telemetry monitoring
5-lead systemThe 5-lead system for telemetry monitoringis connected in the same manner as the 5-lead system for hardwire monitoring. Withthis system, you can view any one of the 12leads using a lead selector on the monitor.
Leads placed in the limb leads allow you toview leads I, II, III, aVR, aVL, and aVF. Toview chest leads V1- V6, the chest leadmust be placed in the specific chest leadposition desired. Only one lead can bemonitored at a time. This illustration shows you where to place the
electrodes and attach leadwires using a five-
leadwire system. The leadwires are color-codedas follows:
Whiteright arm (RA)
blackleft arm (LA)
greenright leg (RL)
redleft leg (LL)
brownchest (C).
Telemetry Monitoring5-Lead System
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Telemetry monitoring3-lead systemWith the 3-lead system for telemetry monitoring, the leads are connected to positive, negative, andground connectors on the telemetry transmitter and attached to specific lead positions ( leads I, II, or III).A lead selector is not available. Only one lead can be monitored at a time.
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Attachment of electrode padsProper attachment of the electrode pads to the skin is the most important step inobtaining a quality ECG tracing. Good contact between the skin and electrodepads helps to prevent distortions of the ECG tracing.
Follow these steps: Choose monitor lead that provides the best QRS amplitude and P wave
identification.
Prep the skin.
- Clip the hair from the skin using a clipper (hair interferes with thetransmission of the electrical currents on the surface of the skin to theconducting gel in the electrode pad).
Attach electrode pads.
- Remove electrodes from packaging and check for presence of moist
conductive gel (dried gel will not conduct electrical activity).- Place electrodes on skin, pressing firmly around periphery of pad. Avoid
bony areas.
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Distortions of the ECG tracingDistortions of the ECG tracing (artifacts) can be caused by activity that is non-cardiac inorigin, such as:
patient movement
seizure activity
ineffective contact between skin, electrode, and lead (dried conductive gel, loose
electrode pad, disconnected lead) muscle tremors
weak ECG signals received over monitoring system
electrical interference
exaggerated respiratory movements (seen in severe lung disease).
Artifacts on the ECG tracing can make identification of the cardiac rhythm difficult or
trigger false monitor alarms.
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Patient movementPatient movement can activate the high-rate alarm (high-voltage artifact potentials are seen bythe monitor system as QRS complexes).
Cause: Patient turning in bed; extremity movement
Solution:Avoid placing electrode pads in areas where extremity movement is greatest (bony areas suchas the clavicles); problem is usually intermittent and will correct itself.
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Cause: Patient movement from seizure
Solution:Treat cause of seizure.
Seizure activitySeizure activity may activate the high-rate alarm due to high-voltage artifact potentials.
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Cause: Disconnected lead, disconnected electrode pad, or dried conductive gel
Solution: Check electrodes and leads; reattach disconnected electrodes and leads.
Note:A straight line could indicate an absence of electrical activity in the heart. Check patient immediatelyfor pulse.
Continuous straight lineA continuous straight line will activate the low-rate alarm (the monitor system does not see QRScomplexes).
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Cause: Ineffective contact between the electrode pads and skin surface
Solution: Make sure hair is clipped and electrode is placed on clean, dry skin. If diaphoresis is a problem,apply some type of skin prep adherent so electrode will adhere to skin surface.
Intermittent straight lineAn intermittent straight line may activate the low-rate alarm since the monitor system does not see thenormal number of QRS complexes.
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Low-voltage QRSLow-voltage QRS complexes may activate the low-rate alarm if the height of the QRS is too low for themonitor system to see it.
Cause:Low-amplitude QRS complexes in monitored lead
Solution:Turn up amplitude knob on monitor or switch to another lead.
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Telemetry-related interferenceArtifacts may occur on the ECG tracing related to problems associated with the telemetry monitoringsystem. Weak signals or a loss of signal may result in spikes on the tracing as well as straight lines.
Cause: Weak batteries; telemetry monitor too far away from antenna; problems with antenna system
Solution: Change batteries; keep patient within antenna range; check antenna system.
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