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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: • • • • • • • • 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] 34 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: • • • • • • • 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 35 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 36 • • • • • • 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 • • • • 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 37 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 To order your copy contact our Customer Services Department: Phone: UK Dial Free 0800 243407; Overseas +44 (0) 1243 843407; E-mail: [email protected] Online: www.wiley.com 38 © 2010 The Author. Journal Compilation © 2010 British Association of Critical Care Nurses Copyright of Nursing in Critical Care is the property of Blackwell Publishing Limited and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.