Download An introduction to electrocardiogram monitoring

REVISION NOTES
An introduction to
electrocardiogram monitoring
Phil Jevon
ABSTRACT
The aim of this paper is to provide an introduction to electrocardiogram (ECG) monitoring. The objectives are to:
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define an ECG;
describe how the ECG relates to cardiac contraction, with specific reference to the conduction system of the heart;
recognize sinus rhythm;
list the indications for ECG monitoring;
discuss the important features of a modern bedside cardiac monitor;
describe where to position ECG electrodes;
outline a suggested procedure for ECG monitoring;
discuss the infection control issues related to ECG monitoring.
INTRODUCTION
ECG monitoring is considered one of the most valuable
diagnostic tools in modern medicine (Drew et al., 2005).
In the critical care setting, the goals of ECG monitoring
range from simple heart rate and basic ECG rhythm
interpretation to the diagnosis of complex cardiac
arrhythmias, myocardial ischemia and prolonged QT
interval (Drew et al., 2005).
The aim of this article is to provide an introduction
to ECG monitoring.
DEFINITIONS
An ECG can be defined as a record or display of
a patient’s heartbeat produced by electrocardiography
(electro–relating to or caused by electricity, cardio–from
the Greek word kardia ‘heart’ and gram–from the
Greek word gramma ‘thing written’) (Soanes and
Stevenson, 2006).
Electrocardiography is the measurement of electrical
activity in the heart (using an electrocardiograph, e.g.
cardiac monitor, ECG machine) and recording it as
a visual trace, either on paper or on an oscilloscope
screen, by placing electrodes on the patient’s skin
(Soanes and Stevenson, 2006).
THE ECG AND ITS RELATION TO
CARDIAC CONTRACTION
It is helpful to understand how the ECG relates to
cardiac contraction (Figure 1):
• The sinoatrial (SA) node fires and the electrical
impulse spreads across the atria to the atrioventricular (AV) node (junction), resulting in atrial
depolarization and contraction (P wave).
• On arriving at the AV node, the impulse is
delayed, allowing the atria time to fully contract
and eject blood into the ventricles. This brief
period of absent electrical activity is represented
on the ECG by a straight (isoelectric) line between
the end of the P wave and the beginning of the
QRS complex. The PR interval represents atrial
depolarization and the impulse delay in the AV
node prior to ventricular depolarization.
• The impulse is then conducted down to the
ventricles through the bundle of His, right and
left bundle branches and Purkinje fibres causing
ventricular depolarization and contraction (QRS
complex).
• The ventricles then repolarize (T wave).
(Sources: Resuscitation Council UK, 2006; Jevon, 2009)
Author: Phil Jevon, RN, BSc (Hons), ENB 124 Resuscitation
Officer/Clinical Skills Lead, Manor Hospital, Moat Road, Walsall, West
Midlands, WS2 9 PS, UK
Address for correspondence: Phil Jevon, Manor Hospital, Moat
Road, Walsall, West Midlands, WS2 9 PS, UK
E-mail: [email protected]
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SINUS RHYTHM
Sinus rhythm (Figure 2) is the normal rhythm of the
heart. The impulse originates in the SA node (i.e.
‘sinus’) at a regular rate of 60–100 per min. Each
© 2010 The Author. Journal Compilation © 2010 British Association of Critical Care Nurses, Nursing in Critical Care 2010 • Vol 15 No 1
Revision Notes
Figure 1 The ECG and its relation to cardiac contraction.
Figure 2 Sinus rhythm.
trace can become unrecognizable, either too
small or distorted, leading to the possibility of
misinterpretation.
impulse is conducted down the normal pathways to the
ventricles without any abnormal conduction delays.
INDICATIONS FOR ECG MONITORING
Indications for ECG monitoring include the following:
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post successful cardiopulmonary resuscitation;
acute coronary syndrome;
cardiac arrhythmias;
heart failure;
electrolyte abnormities;
critical illness;
drug overdose (if there is a risk of pro-arrhythmic
complications).
(Sources: Drew et al., 2005; Jevon, 2009)
CARDIAC MONITOR
The bedside cardiac monitor (Figure 3) (oscilloscope)
provides a continuous display of the patient’s ECG.
Common features of a cardiac monitor include:
• screen: a dull/bright switch can be adjusted if the
screen is too light or too dark;
• ECG printout facility: to record cardiac arrhythmias (helpful for both diagnosis and record keeping). On most Critical Care Units, the printout
facility will be at the central console;
• heart rate counter: to calculate the heart rate
(counts the QRS complexes);
• monitor alarms: to alert the nurse to changes
in the patient’s heart rate if it differs from preset limits. Some cardiac monitors can identify
important cardiac arrhythmias and changes in
the ST segment, and alarm accordingly;
• lead select switch: to select the desired monitoring
lead, e.g. lead II;
• ECG gain: to alter the size of the ECG complex.
If it is set too low or too high the ECG
(Source: Jevon, 2009)
POSITIONING OF ECG ELECTRODES
An ECG electrode can be defined as a conductor
through which electrical current enters or leaves an
object (Soanes and Stevenson, 2006). Either a three or
five ECG cable monitoring system is usually used for
ECG monitoring on an intensive care unit.
Three ECG cable system
• Red ECG cable: below the right clavicle;
• Yellow ECG cable: below the left clavicle;
• Green ECG cable: left lower thorax/hip region.
These bipolar leads, which record the potential
difference between two electrodes, can be used to
monitor lead I, lead II, lead III or a modified chest
lead such as MCL1 (Drew et al., 2005).
Five ECG cable system
The standard positioning for ECG electrodes is
illustrated in Figure 4 and is as follows:
• RA (red ECG cable): below the right clavicle;
• LA (yellow ECG cable): below the left clavicle;
• RL (black ECG cable): right lower thorax/hip
region;
• LL (green ECG cable): left lower thorax/hip
region;
• (white ECG cable): on the chest in the desired V
position, usually V1 (fourth intercostal space just
right of the sternum).
(Drew et al., 2005)
© 2010 The Author. Journal Compilation © 2010 British Association of Critical Care Nurses
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Revision Notes
Figure 4 Standard electrode positions for ECG monitoring (five cable system).
Figure 3 Bedside cardiac monitor.
PROCEDURE FOR ECG MONITORING
Correct electrode placement and adequate skin
preparation are important to ensure an accurate
and reliable ECG trace (Sharman, 2007). Examples
of incorrect treatment because of inaccurate or poor
ECG monitoring techniques have been reported in
the literature, e.g. unnecessary cardiac catheterization
because of false ST-segment monitor alarms (Drew
et al., 2001), unnecessary electrophysiology testing
and device implantation because of muscle artefact
simulating ventricular tachycardia (Knight et al., 1999).
A suggested procedure to establish ECG monitoring
is as follows:
• Establish why ECG monitoring is required.
• Explain the procedure to the patient; this is
particularly important as some patients can find
it quite daunting.
• If it is necessary to do so, carefully shave the
patient’s chest to remove excess chest hair (Drew
et al., 2005). This will help to ensure a better
skin-electrode contact and will also make it less
uncomfortable for the patient when removing the
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ECG electrodes (Perez, 1996). It is important to
take care not to graze the skin as this increases
the risk of infection (this is why some authorities
advocate cutting chest hair instead of shaving).
To reduce skin oil and debris, gently rub the
skin with alcohol or some gauze. Mild abrasion
of the skin helps reduce impedance between the
skin and electrode, thus reducing interference
(Thompson, 1997).
Ensure the skin is dry. This will help the ECG
electrodes to adhere to the skin.
Check that the ECG electrodes are in date, still
moist and not dry.
Remove the protective backing from each ECG
electrode and expose the gel disc.
Apply the ECG electrodes to the patient’s chest
following locally agreed protocols. The electrodes
should lie flat. If the electrodes have an offset
connector (to absorb tugs), these should be
pointed towards the ECG cables.
Using a circular motion, smooth down the
adhesive area; take care not to press on the gel disc
itself as this may result in a decrease in electrode
conductivity and adherence (Thompson, 1997).
© 2010 The Author. Journal Compilation © 2010 British Association of Critical Care Nurses
Revision Notes
• Attach the ECG cables to the electrodes. (If ‘snapon’ ECG cables are being used with central stud
electrodes, it is preferable to connect them to
the electrodes before applying the latter to the
patient’s skin.)
• Switch the cardiac monitor on and select the
required monitoring ECG lead.
• Ensure the ECG trace is clear and rectify any
difficulties encountered.
• Set the alarms within safe parameters following
locally agreed protocols and appropriate to the
patient’s clinical condition (Docherty, 2003; Drew
et al., 2005). Typically, this will be <50 and >120
(Docherty, 2003).
• Anchor the ECG cables. They should not be
allowed to tug on the ECG electrodes.
• Position the cardiac monitor so it is clearly visible.
• Document in the patient’s notes that ECG
monitoring has commenced and the ECG rhythm
identified.
• Regularly monitor the electrode sites for signs
of allergy–redness, itching and erythema. ECG
electrodes should be regularly replaced.
INFECTION CONTROL ISSUES
There is a potential risk for infection from reusable
ECG wires that are poorly decontaminated between
patients (Brown, 2006). Contaminated ECG wires had
previously been cited as a source of an outbreak of
vancomycin-resistant enterococci (Falk et al., 2000). In a
small study, 77% of supposedly clean wires were found
to be contaminated with antibiotic-resistant bacteria
(Jancin, 2004).
It is important to ensure that local infection
control policies advise on how to clean wires after
use; for example, using a hospital-grade disinfectant
according to manufacturer’s instructions (Houghton,
2006).
KEY LEARNING POINTS
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ECG monitoring is integral to the management of the ICU patient.
It is important to be familiar with the use of the bedside cardiac monitor in order to maximize the benefits of ECG monitoring.
ECG monitoring should be meticulously performed to help ensure an accurate and reliable ECG trace.
Infection control measures should be followed to help prevent cross infection.
RECOMMENDED TEXTS FOR FURTHER READING
• Jevon P. (2009). ECGs for Nurses 2nd edn. Oxford: Wiley Blackwell.
• Jevon P, Ewens B. (2007). Monitoring the Critically Ill Patient, 2nd edn, Oxford: Blackwell Publishing.
REFERENCES
Brown D. (2006). Electrocardiography wires: a potential source of
infection. AACN News; 23: 12–15.
Drew B, Adams M. (2001). Clinical consequences of ST segment
changes caused by body position mimicking transient
myocardial ischaemia: hazards of ST-segment monitoring?
J Electrocardiol; 34: 261–264.
Drew B, Califf R, Funk M et al. (2005). AHA Scientific Statement:
Practice Standards for Electrocardiographic Monitoring in
Hospital Settings. An American Heart Association Scientific
Statement from the Councils on Cardiovascular Nursing,
Clinical Cardiology, and Cardiovascular Disease in the Young:
Endorsed by the International Society of Computerized
Electrocardiology and the American Association of CriticalCare Nurses. Journal of Cardiovascular Nursing; 20: 76–106.
Docherty B. (2003). 12 lead ECG interpretation and chest pain
management British. Journal of Nursing; 12: 1248–1255.
Falk P, Winnike J, Woodmansee C. et al. (2000). Outbreak of
vancomycin-resistant enterococci in a burn unit. Infection
Control Hospital and Epidemiology; 21: 575–582.
Houghton D. (2006). ECG equipment: wired for infection?
Nursing; 36/12: 71.
Jancin B. (2004). Antibiotic-resistant pathogens found on 77% of
EKG lead wires. Cardiology News; 2: 14.
Jevon P. (2009). ECGs for Nurses. 2nd edn. Oxford: WileyBlackwell.
Knight B, Pelosi F, Michaud G et al. (1999). Clinical consequences
of electrocardiographic artifact mimicking ventricular tachycardia. The New England Journal of Medicine; 341: 1270–1274.
Perez, A. (1996). Cardiac monitoring: mastering the essentials.
Registered Nurse; 59: 32–39.
Resuscitation Council UK. (2006). Advanced Life Support Manual,
5th edn. London: Resuscitation Council UK.
Sharman J. (2007). Clinical Skills: cardiac rhythm recognition and
monitoring British. Journal of Nursing; 16: 306–311.
Soanes C, Stevenson A. (2006). Oxford Dictionary of English.
2nd edn. Oxford: Oxford University Press.
Thompson, P. (1997). Coronary Care Manual. London: Churchill
Livingstone.
© 2010 The Author. Journal Compilation © 2010 British Association of Critical Care Nurses
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Revision Notes
ECGs for Nurses
2nd Edition
Phil Jevon
ECGs for Nurses provides everything a nurse needs
to know about the electrocardiogram. Accessible yet
comprehensive, and packed with case studies, this
portable guide enables nurses to become skilled
practitioners in an area often seen as highly complex.
Using real ECG traces as examples, possible effects on
the patient and treatment options are discussed, with
a focus on the role of a nurse.
296 pages | 9781405181624 | paperback | Sep 2009
|£21.99
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