CLINICAL
ACQUIRING THE 12-LEAD ELECTROCARDIOGRAM: DOING IT RIGHT EVERY TIME Author: Tony Garcia, MS, APRN, ACNP, CEN, CPEN, Dallas, TX
he electrocardiogram (ECG) is a ubiquitous, noninvasive procedure used extensively in diagnostic cardiology. The purposes of the acquisition of an ECG are varied, from bedside monitoring to ambulatory event monitoring. In the emergency department, the 12-lead ECG is the initial test for the patient with chest discomfort or any other acute coronary syndrome (ACS), and it must be obtained within 10 minutes of patient arrival according to established standards. In the United States, the incidence of a new myocardial infarction (MI) is approximately 610,000 annually, and the recurrence rate of a subsequent MI is approximately 325,000 per year. 1 In this context, the ECG becomes an invaluable tool for the rapid identification of a patient undergoing a cardiac event. Subsequently, the interpretation of an ECG may identify patients who need to go to the catheterization laboratory for emergent reperfusion through a percutaneous coronary intervention (PCI) or, if PCI is unavailable or contraindicated, the administration of thrombolytics. Considering this degree of importance, why are nurses not provided adequate training on accurately obtaining 12-lead ECGs? Many essential nursing skills have been relegated to “on-the-job” training, but if the trainer/preceptor never learned proper form, the trainee is subjected to improper techniques and a vicious cycle is created. This article will focus exclusively on properly acquiring a 12-lead ECG in the ED setting for a patient with cardiovascular symptoms.
T
Why is the ECG Clinically Important?
In a systematic review of 10 studies, Khunti 2 found that nurses had limited knowledge and skills in the correct placement of electrodes; they commonly misplaced electrodes because of a reliance on a “visual” approach. 3 With
Tony Garcia, Member, Texas ENA, is Nurse Practitioner, University of Texas Southwestern Medical Center, Dallas, TX. For correspondence, write: Tony Garcia, MS, APRN, ACNP, CEN CPEN; E-mail: [email protected]. J Emerg Nurs ■. 0099-1767 Copyright © 2015 Emergency Nurses Association. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jen.2015.04.014
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this in mind, it is important to note that several sources have documented ECG abnormalities due to various operator factors. Cable misplacement may lead to conduction disturbances that can simulate or conceal myocardial ischemia or MI, 3,4 such as mimicking a lateral-wall MI in a true case of inferior-wall MI. 5 The common practice of placing the limb electrodes on the torso can result in false ST-segment elevation. 6,7 Some or all of the aforementioned scenarios can create a situation in which an ST elevation myocardial infarction (STEMI) is inappropriately identified. The cost of diagnostic catheterization is often more than $5,000 depending on ensuing hospitalization and critical care. The ramifications of a false-positive identification of a STEMI are also costly for the patient. The patient is exposed to various medications as part of the standard treatment regimen, and if taken to the catheterization laboratory, he or she is exposed to contrast material, which may be nephrotoxic. 3 Despite the frequency with which it is performed, coronary angiography is not an innocuous procedure. It places the patient at potential risk of inadvertent complications from excessive bleeding due to femoral artery puncture, aortic laceration, coronary artery laceration, or induction of an MI. If the patient receives fibrinolytics, he or she is placed at high risk of hemorrhage despite all the pre-administration safeguards. Timely recognition of a STEMI to achieve reduced door-to-balloon or door-to-needle times may come at the risk of false-positive identifications. McCabe et al 8 reported a 36% prevalence of false-positive STEMI activations in ED patients presenting to 2 PCI-capable centers. The subgroup analysis of the same study did not include ECG quality as a factor in determining false-positive activations.
Operator-Related Factors
Orientation of new emergency nurses should include a review of equipment operating instructions provided by the manufacturer. Acquisition of a reliable 12-lead ECG begins with a thorough knowledge of the equipment being used within the emergency department because machines within the emergency department can vary. It is incumbent on the emergency nurse to be familiar with the specifications and limitations of the various devices in use. Each manufacturer has its own proprietary algorithm that is used to decode the
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ECG signal and provide a tracing and interpretation. 9–11 The accuracy of the algorithm is dependent on the operator setting up the test according to specifications so that it may function as intended. 9–11 FREQUENCY RESPONSE
The frequency response is a technical term for “noise” filtering. It is an essential component within the machine circuitry because of the various applications of the ECG. When one is performing bedside monitoring for identification of dysrhythmias or evaluating heart rate, monitorquality mode is sufficient for this task. This implies that the filter is on and the device is eliminating noise outside the prescribed bandwidth (0.5-40 Hz). 12 Unfortunately, discrete changes in the ST segment will be undetectable in this mode, and it should never be used in the evaluation of ST-segment elevation or depression. Therefore 12-lead ECGs must be obtained in diagnostic-quality mode. In this mode the filter is off and the signal bandwidth is widened (0.5-150 Hz) to identify the finer details. 12 However, there are some drawbacks when operating within the diagnostic-quality bandwidth; movements (eg, breathing or tremors) become accentuated in this mode. In the recorded 12-lead ECG, this can obscure the details that are integral for proper identification. To explain this concept another way, frequency response is like the curtain during a theatrical performance. When the curtain is only partially opened, the viewer’s attention is drawn to the specific area the director wants to showcase (monitor quality). When the curtain is opened wide, everything comes into view (diagnostic quality) but that comes at the expense of possible distractions. DEVICE SETTINGS
Another component of the standard 12-lead ECG revolves around the output of the printed tracing. Calibration of the device is a function that identifies the amplitude of the waveform in relation to the ECG graph paper. The standard is 1 mV = 10 mm and can be verified by the phrase “1×” being printed at the bottom of the ECG tracing. 12 Any setting other than standard calibration will distort STsegment elevation or depression, as well as other features, such as the identification of hypertrophy. Correct paper speed affects the timing of the ECG with respect to measurement of rate and duration of intervals. The standard paper speed is 25 mm/s, and this will also be printed at the bottom of the ECG tracing. 12 The paper speed can be changed, but this will interfere with the proper identification of heart rate or the measurement of intervals, such as the PR and QT intervals, and QRS width.
2
For the purpose of quality assurance, the emergency nurse should verify the frequency response, calibration, and paper speed on the printed ECG before delivering the 12-lead ECG to the provider. In addition, the nurse should observe lead aVR to determine if the complexes are positive or negative. Positive complexes in lead aVR with negative complexes in lead I can indicate 1 of 2 conditions— dextrocardia or a possible arm lead reversal, the latter of which is easier to confirm. 13 If any of the aforementioned items are not according to standard, a new tracing must be obtained. 12 CABLES
The devices used in the emergency department are subject to extreme amounts of use, and as such, problems related to wear may be present. Similar to electrical extension cords, ECG cables are covered in rubberized material that shields the transmission of the signal. If this coating becomes worn, there could be a loss of signal to one, some, or all channels (leads). Interference can also be a factor that leads to artifacts in the ECG signal. 12,13 When a tracing has excessive artifacts, a change in patient cables or electrodes may be necessary. Therefore the emergency nurse should examine the ECG cables on a regular basis to ensure that they are not worn and are still suitable for patient use. PATIENT DATA PROGRAMMING
The ECG is part of the patient’s comprehensive medical record and will be stored for possible retrieval in the future. To preserve the ECG for the purpose of cataloging serial test findings, information such as patient name and medical record number will need to be entered into the device. In addition, the device requires minimum data input of age and sex to apply the correct algorithm to the analysis of the ECG. 9–11 In the absence of this crucial information, the device will “default” to the settings for an adult male patient. As such, the software will analyze incorrect data, possibly yielding an erroneous interpretation, especially in the case of women or pediatric patients. The emergency nurse needs to remember that, at its core, the ECG machine is operated by a computer processor and failure to adhere to the basic manufacturer recommendations may result in an inaccurate end product. As is said in the computer industry, garbage in equals garbage out (GIGO).
Patient-Related Factors SKIN PREPARATION
The electrode is the interface between the device and the patient. Because the skin itself is a poor conductor of
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electricity, the operator should take certain steps to ensure that there is good electrode-to-skin contact. 12 In the case of men, hair removal is an absolute necessity to achieve proper electrode contact. An excessive amount of hair plus a diaphoretic patient prevents adequate skin contact. Although hospital-acquired infections are not usually associated with ECGs, it would be prudent to use clippers instead of shaving with a razor to avoid the possibility of creating small nicks that can serve as portals of entry for infectious organisms. This method is also faster, and there are several brands of medical hair clippers designed for single-patient use. Once the hair is removed, the skin must be adequately prepared for the gel to achieve adequate penetration. 12 Each designated electrode position should be cleaned with an alcohol swab to remove any oils from the skin and dried by vigorous rubbing with a piece of 4 × 4–inch gauze. This step will remove any remaining alcohol while simultaneously debriding any dead skin particles from the site. 12 Some manufacturers have developed ECG “prep” pads, 10 which are essentially fine sandpaper, but 4 × 4–inch gauze will do just as well and is readily available within the emergency department. Proper skin preparation is an essential step to reduce artifacts and increase quality in the final ECG product. Failure to take the extra moment to achieve this might mean the difference between a good tracing and a poor tracing. In the case of gel electrodes, the emergency nurse should ensure that the package has not expired and that there is a sufficient amount of gel to promote good conductivity. It is also a good idea to pre-attach the lead wire to the electrode itself to prevent the gel from being squeezed out during patient attachment. PATIENT POSITIONING
The position of the heart within the chest is not static and will change as the patient bends and rotates. 14,15 However, the electrodes on the body are fixed and will not move. A change in patient position will move the heart, thus altering the ECG tracing. 14 This is similar to the change that occurs in the heart tones an examiner hears as a patient is repositioned to accentuate such different sounds. The standard 12-lead ECG is intended to be performed with the patient in the supine position. 12 In the emergency department, this can present a challenge, especially if the patient is having acute dyspnea and cannot lie in a supine position. It has become a generally accepted practice to perform the test with the patient in a recumbent (semiFowler) position. 15 To achieve adequate reproducibility in serial tracings, the emergency nurse should note the patient’s position on the initial tracing so that all subsequent tracings are performed with the patient in the same position.
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Combined Factors ELECTRODE PLACEMENT
The standard 12-lead ECG provides 12 views of the electrical activity within the heart using only 10 electrode positions. The “extra” views are created through an internal change in the central terminal lead position. The calculations and internal analysis by the device rely on the precise application and positioning of the electrodes. As mentioned previously, the electrodes are the interface between the device and the patient. Therefore the electrode positions are the “windows” through which the device “views” the heart. Any change in the electrode position distorts the view. LIMB ELECTRODES
In his original experiment, Einthoven (father of electrocardiography) placed the wrists and left ankle in buckets of water to record the first ECG. Therein lies the premise that the limb electrodes are intended to be applied to the wrists and ankles of the patient. Although ECG voltages and durations can be affected by limb electrode position, 12 various limb positions from proximal to distal on the extremity have been evaluated without leading to significant alteration of the standard ECG. 16 In the case of patients with amputations, it is important to place the electrodes in the same position bilaterally. Mason and Likar 17 proposed a system of electrode positioning for the exercise ECG in which all the electrodes are placed on the chest. Over the years, the limb electrodes have “migrated” to the upper chest and lower abdomen in this configuration, likely because of speed and ease of application. 13 The emergency nurse needs to understand that this is not the standard for a 12-lead ECG and that this configuration can shift the electrical axis and create a distortion of the ECG morphology to the magnitude of simulating the presence of infarction or ischemia by altering the ST segment. 2–4,6,7,12 Therefore this practice should be abandoned, and limb leads should always be placed on the extremities (FIGURE 1). PRECORDIAL ELECTRODES
Placement of the precordial electrodes requires strict attention to detail because these are the electrodes closest to the heart and minute shifts in position can result in substantial changes in ECG morphology and diagnostic errors related to anterior or septal STEMI. 12,16,18 Attempting to estimate correct positioning is unacceptable in the performance of this procedure. The application of the
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The angle of Louis, which is adjacent to the second rib, and the second ICS, which is just below the second rib, are located. 2. Once the second ICS has been located, the operator can palpate down the chest wall adjacent to the sternum until he or she arrives at the fourth ICS. 3. When the operator is facing the patient, the electrode for V1 is placed in the fourth ICS to the left of the sternum (patient’s right) and the electrode for V2 is placed in the fourth ICS to the right of the sternum (patient’s left). 4. The next electrode placement is V4, which is located in the fifth ICS in the midclavicular line on the patient’s left precordium. 5. The electrode for V3 is then located midway between the electrodes for V2 and V4. 6. The remaining 2 electrodes for V5 and V6 are located in a straight line from V4. The electrode for V5 is located in the anterior axillary line, even with V4, and the electrode for V6 is located in the midaxillary line, even with V5. 1.
FIGURE 1 Placement of limb leads.
precordial electrodes, as with the limb electrodes, is also a defined process with a great deal of variation depending on the operator. 2,3 Precordial electrode positioning begins with the crucial first step of correctly identifying the fourth intercostal space (ICS) for the placement of the V1 and V2 leads. 3,13,16,18 This is accomplished as follows (FIGURE 2):
FIGURE 2 Placement of precordial electrodes.
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It cannot be stressed enough that proper chest electrode placement hinges on the correct identification of the fourth ICS, where V1 and V2 are located; superior displacement of the V1 or V2 electrode (or both) will likely result in the superior displacement of all the precordial electrodes. 6,13,16,18 Studies have shown that many operators will identify positions that are inappropriately superior to the fourth ICS. 2,3 Failure to adhere to these specifications can lead to false myocardial injury patterns, 6 as well as other diagnostic errors, with a variation of as little as 2 cm. 12 One issue that seems to confound some operators is where to place electrodes on the precordium of women with large breasts, above or below the breast tissue. 12 With respect to ECG distortion or alteration, the data are equivocal 12,13,18; however, the guideline states that the electrode should be placed under the breast as close to the chest wall as possible. 12,13 It is possible that misplacement of ECG electrodes in women contributes to the disparity in ACS identification that exists between men and women. The final point is the concept of reproducibility in serial tracings. Reproducibility is an absolute necessity when determining whether ST elevation is resolving or worsening. 6 Once affixed to the patient, electrodes should remain in place for the duration of the ED stay. To make accurate comparisons, the electrode positions must remain the same because a change in electrode position can create variability in serial ECGs. 6,7 If it becomes necessary to remove electrodes (for radiographs or other studies), some type of skin marking should be used to accurately replace these electrodes. 12
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Conclusion
6. Drew BJ. Psuedo myocardial injury patterns because of nonstandard electrocardiogram electrode placement. J Electrocardiol. 2008;41(3):202-204.
Because the emergency department is the gateway into the hospital during an ACS episode, it is essential for emergency nurses to be the “experts” in the acquisition of the 12-lead ECG. Emergency nurses should also serve as the quality-control monitors to identify ECGs obtained in a nonstandard fashion. In doing so, nurses perform their highest function as advocates for high-quality patient care and safety.
7. Drew BJ, Kligfield P. Standardizing electrocardiographic leads: introduction to a symposium. J Electrocardiol. 2008;41(3):187-189.
Acknowledgment
The author thanks Bimbola Akintade, PhD, ACNP; Ms. Jane Sellman; and John Greenwood, MD, for their careful review and valuable suggestions.
REFERENCES 1. Go AS, Mozaffarian D, Roger V, et al. Heart disease and stroke statistics—2013 update: a report from the American Heart Association. Circulation. 2013;127(1):e6-e245. 2. Khunti K. Accurate interpretation of the 12-lead ECG electrode placement: a systematic review. Health Educ J. 2013: 1-14. 3. Rajaganeshan R, Ludlam CL, Francis DP, Parasramka SV, Sutton R. Accuracy in ECG lead placement among technicians, nurses, general physicians, and cardiologists. Int J Clin Pract. 2008;62(1):65-70. 4. Batchvarov VN, Mailik M, Camm AJ. Incorrect electrode cable connection during electrocardiographic recording. Europace. 2007;9(11):1081-1091. 5. Karur S, Patra S, Shankarappa RK, et al. Left arm-left leg lead reversal in a case of inferior wall myocardial infarction mimics as high lateral wall infarction. J Cardiovasc Dis Res. 2013;4(3):201-203.
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8. McCabe JM, Armstrong EJ, Kulkarni A, et al. Prevalence and factors associated with false-positive ST-segment elevation myocardial infarction diagnoses at primary percutaneous coronary intervention-capable centers. Arch Intern Med. 2012;172(11):864-871. 9. GE Healthcare. Marquette 12SL. http://www3.gehealthcare.com/en/ Products/Categories/Diagnostic_ECG/ECG_Analysis. Published 2012. Accessed June 1, 2014. 10. Philips Healthcare. Philips ECG algorithms. http://www.healthcare. philips.com/main/products/cardiography/products/articles/algorithms. wp. Published 2014. Accessed June 01, 2014. 11. Macfarlane PW, Devine B, Clark E. The University of Glasgow (Uni-G) ECG analysis program. Comput Cardiol. 2005: 451-454. 12. Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram: part I: the electrocardiogram and its technology. J Am Coll Cardiol. 2007;49(10):1109-1127. 13. Garcia-Niebla J, Llontop-Garcia P, Valle-Racero JI, et al. Technical mistakes during the acquisition of the electrocardiogram. Ann Noninvasive Electrocardiol. 2009;14(4):389-403. 14. Adams MG, Drew BJ. Body position effects on the ECG: implications for ischemia monitoring. J Electrocardiol. 1997;30(4):285-291. 15. Baevsky RH, Haber MD, Blank FS, Smithline H. Supine vs semirecumbent and upright 12-lead electrocardiogram: does change in body position alter the electrocardiographic interpretation for ischemia? Am J Emerg Med. 2007;25(7):753-756. 16. Drew BJ. Pitfalls and artifacts in electrocardiography. Cardiol Clin. 2006;24:309-315. 17. Mason RE, Likar I. A new system of multiple-lead exercise electrocardiography. Am Heart J. 1966;71:196-205. 18. Kania M, Rix H, Fereniec M, et al. The effect of precordial lead displacement on ECG morphology. Med Biol Eng Comput. 2014;52(2):109-119.
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ACQUIRING THE 12-LEAD ELECTROCARDIOGRAM: DOING IT RIGHT EVERY TIME Author: Tony Garcia, MS, APRN, ACNP, CEN, CPEN, Dallas, TX
he electrocardiogram (ECG) is a ubiquitous, noninvasive procedure used extensively in diagnostic cardiology. The purposes of the acquisition of an ECG are varied, from bedside monitoring to ambulatory event monitoring. In the emergency department, the 12-lead ECG is the initial test for the patient with chest discomfort or any other acute coronary syndrome (ACS), and it must be obtained within 10 minutes of patient arrival according to established standards. In the United States, the incidence of a new myocardial infarction (MI) is approximately 610,000 annually, and the recurrence rate of a subsequent MI is approximately 325,000 per year. 1 In this context, the ECG becomes an invaluable tool for the rapid identification of a patient undergoing a cardiac event. Subsequently, the interpretation of an ECG may identify patients who need to go to the catheterization laboratory for emergent reperfusion through a percutaneous coronary intervention (PCI) or, if PCI is unavailable or contraindicated, the administration of thrombolytics. Considering this degree of importance, why are nurses not provided adequate training on accurately obtaining 12-lead ECGs? Many essential nursing skills have been relegated to “on-the-job” training, but if the trainer/preceptor never learned proper form, the trainee is subjected to improper techniques and a vicious cycle is created. This article will focus exclusively on properly acquiring a 12-lead ECG in the ED setting for a patient with cardiovascular symptoms.
T
Why is the ECG Clinically Important?
In a systematic review of 10 studies, Khunti 2 found that nurses had limited knowledge and skills in the correct placement of electrodes; they commonly misplaced electrodes because of a reliance on a “visual” approach. 3 With
Tony Garcia, Member, Texas ENA, is Nurse Practitioner, University of Texas Southwestern Medical Center, Dallas, TX. For correspondence, write: Tony Garcia, MS, APRN, ACNP, CEN CPEN; E-mail: [email protected]. J Emerg Nurs ■. 0099-1767 Copyright © 2015 Emergency Nurses Association. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jen.2015.04.014
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this in mind, it is important to note that several sources have documented ECG abnormalities due to various operator factors. Cable misplacement may lead to conduction disturbances that can simulate or conceal myocardial ischemia or MI, 3,4 such as mimicking a lateral-wall MI in a true case of inferior-wall MI. 5 The common practice of placing the limb electrodes on the torso can result in false ST-segment elevation. 6,7 Some or all of the aforementioned scenarios can create a situation in which an ST elevation myocardial infarction (STEMI) is inappropriately identified. The cost of diagnostic catheterization is often more than $5,000 depending on ensuing hospitalization and critical care. The ramifications of a false-positive identification of a STEMI are also costly for the patient. The patient is exposed to various medications as part of the standard treatment regimen, and if taken to the catheterization laboratory, he or she is exposed to contrast material, which may be nephrotoxic. 3 Despite the frequency with which it is performed, coronary angiography is not an innocuous procedure. It places the patient at potential risk of inadvertent complications from excessive bleeding due to femoral artery puncture, aortic laceration, coronary artery laceration, or induction of an MI. If the patient receives fibrinolytics, he or she is placed at high risk of hemorrhage despite all the pre-administration safeguards. Timely recognition of a STEMI to achieve reduced door-to-balloon or door-to-needle times may come at the risk of false-positive identifications. McCabe et al 8 reported a 36% prevalence of false-positive STEMI activations in ED patients presenting to 2 PCI-capable centers. The subgroup analysis of the same study did not include ECG quality as a factor in determining false-positive activations.
Operator-Related Factors
Orientation of new emergency nurses should include a review of equipment operating instructions provided by the manufacturer. Acquisition of a reliable 12-lead ECG begins with a thorough knowledge of the equipment being used within the emergency department because machines within the emergency department can vary. It is incumbent on the emergency nurse to be familiar with the specifications and limitations of the various devices in use. Each manufacturer has its own proprietary algorithm that is used to decode the
■ • ■
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Master Proof ymen2771.pdf
1
CLINICAL/Garcia
ECG signal and provide a tracing and interpretation. 9–11 The accuracy of the algorithm is dependent on the operator setting up the test according to specifications so that it may function as intended. 9–11 FREQUENCY RESPONSE
The frequency response is a technical term for “noise” filtering. It is an essential component within the machine circuitry because of the various applications of the ECG. When one is performing bedside monitoring for identification of dysrhythmias or evaluating heart rate, monitorquality mode is sufficient for this task. This implies that the filter is on and the device is eliminating noise outside the prescribed bandwidth (0.5-40 Hz). 12 Unfortunately, discrete changes in the ST segment will be undetectable in this mode, and it should never be used in the evaluation of ST-segment elevation or depression. Therefore 12-lead ECGs must be obtained in diagnostic-quality mode. In this mode the filter is off and the signal bandwidth is widened (0.5-150 Hz) to identify the finer details. 12 However, there are some drawbacks when operating within the diagnostic-quality bandwidth; movements (eg, breathing or tremors) become accentuated in this mode. In the recorded 12-lead ECG, this can obscure the details that are integral for proper identification. To explain this concept another way, frequency response is like the curtain during a theatrical performance. When the curtain is only partially opened, the viewer’s attention is drawn to the specific area the director wants to showcase (monitor quality). When the curtain is opened wide, everything comes into view (diagnostic quality) but that comes at the expense of possible distractions. DEVICE SETTINGS
Another component of the standard 12-lead ECG revolves around the output of the printed tracing. Calibration of the device is a function that identifies the amplitude of the waveform in relation to the ECG graph paper. The standard is 1 mV = 10 mm and can be verified by the phrase “1×” being printed at the bottom of the ECG tracing. 12 Any setting other than standard calibration will distort STsegment elevation or depression, as well as other features, such as the identification of hypertrophy. Correct paper speed affects the timing of the ECG with respect to measurement of rate and duration of intervals. The standard paper speed is 25 mm/s, and this will also be printed at the bottom of the ECG tracing. 12 The paper speed can be changed, but this will interfere with the proper identification of heart rate or the measurement of intervals, such as the PR and QT intervals, and QRS width.
2
For the purpose of quality assurance, the emergency nurse should verify the frequency response, calibration, and paper speed on the printed ECG before delivering the 12-lead ECG to the provider. In addition, the nurse should observe lead aVR to determine if the complexes are positive or negative. Positive complexes in lead aVR with negative complexes in lead I can indicate 1 of 2 conditions— dextrocardia or a possible arm lead reversal, the latter of which is easier to confirm. 13 If any of the aforementioned items are not according to standard, a new tracing must be obtained. 12 CABLES
The devices used in the emergency department are subject to extreme amounts of use, and as such, problems related to wear may be present. Similar to electrical extension cords, ECG cables are covered in rubberized material that shields the transmission of the signal. If this coating becomes worn, there could be a loss of signal to one, some, or all channels (leads). Interference can also be a factor that leads to artifacts in the ECG signal. 12,13 When a tracing has excessive artifacts, a change in patient cables or electrodes may be necessary. Therefore the emergency nurse should examine the ECG cables on a regular basis to ensure that they are not worn and are still suitable for patient use. PATIENT DATA PROGRAMMING
The ECG is part of the patient’s comprehensive medical record and will be stored for possible retrieval in the future. To preserve the ECG for the purpose of cataloging serial test findings, information such as patient name and medical record number will need to be entered into the device. In addition, the device requires minimum data input of age and sex to apply the correct algorithm to the analysis of the ECG. 9–11 In the absence of this crucial information, the device will “default” to the settings for an adult male patient. As such, the software will analyze incorrect data, possibly yielding an erroneous interpretation, especially in the case of women or pediatric patients. The emergency nurse needs to remember that, at its core, the ECG machine is operated by a computer processor and failure to adhere to the basic manufacturer recommendations may result in an inaccurate end product. As is said in the computer industry, garbage in equals garbage out (GIGO).
Patient-Related Factors SKIN PREPARATION
The electrode is the interface between the device and the patient. Because the skin itself is a poor conductor of
■ ■ • ■
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Garcia/CLINICAL
electricity, the operator should take certain steps to ensure that there is good electrode-to-skin contact. 12 In the case of men, hair removal is an absolute necessity to achieve proper electrode contact. An excessive amount of hair plus a diaphoretic patient prevents adequate skin contact. Although hospital-acquired infections are not usually associated with ECGs, it would be prudent to use clippers instead of shaving with a razor to avoid the possibility of creating small nicks that can serve as portals of entry for infectious organisms. This method is also faster, and there are several brands of medical hair clippers designed for single-patient use. Once the hair is removed, the skin must be adequately prepared for the gel to achieve adequate penetration. 12 Each designated electrode position should be cleaned with an alcohol swab to remove any oils from the skin and dried by vigorous rubbing with a piece of 4 × 4–inch gauze. This step will remove any remaining alcohol while simultaneously debriding any dead skin particles from the site. 12 Some manufacturers have developed ECG “prep” pads, 10 which are essentially fine sandpaper, but 4 × 4–inch gauze will do just as well and is readily available within the emergency department. Proper skin preparation is an essential step to reduce artifacts and increase quality in the final ECG product. Failure to take the extra moment to achieve this might mean the difference between a good tracing and a poor tracing. In the case of gel electrodes, the emergency nurse should ensure that the package has not expired and that there is a sufficient amount of gel to promote good conductivity. It is also a good idea to pre-attach the lead wire to the electrode itself to prevent the gel from being squeezed out during patient attachment. PATIENT POSITIONING
The position of the heart within the chest is not static and will change as the patient bends and rotates. 14,15 However, the electrodes on the body are fixed and will not move. A change in patient position will move the heart, thus altering the ECG tracing. 14 This is similar to the change that occurs in the heart tones an examiner hears as a patient is repositioned to accentuate such different sounds. The standard 12-lead ECG is intended to be performed with the patient in the supine position. 12 In the emergency department, this can present a challenge, especially if the patient is having acute dyspnea and cannot lie in a supine position. It has become a generally accepted practice to perform the test with the patient in a recumbent (semiFowler) position. 15 To achieve adequate reproducibility in serial tracings, the emergency nurse should note the patient’s position on the initial tracing so that all subsequent tracings are performed with the patient in the same position.
■
Combined Factors ELECTRODE PLACEMENT
The standard 12-lead ECG provides 12 views of the electrical activity within the heart using only 10 electrode positions. The “extra” views are created through an internal change in the central terminal lead position. The calculations and internal analysis by the device rely on the precise application and positioning of the electrodes. As mentioned previously, the electrodes are the interface between the device and the patient. Therefore the electrode positions are the “windows” through which the device “views” the heart. Any change in the electrode position distorts the view. LIMB ELECTRODES
In his original experiment, Einthoven (father of electrocardiography) placed the wrists and left ankle in buckets of water to record the first ECG. Therein lies the premise that the limb electrodes are intended to be applied to the wrists and ankles of the patient. Although ECG voltages and durations can be affected by limb electrode position, 12 various limb positions from proximal to distal on the extremity have been evaluated without leading to significant alteration of the standard ECG. 16 In the case of patients with amputations, it is important to place the electrodes in the same position bilaterally. Mason and Likar 17 proposed a system of electrode positioning for the exercise ECG in which all the electrodes are placed on the chest. Over the years, the limb electrodes have “migrated” to the upper chest and lower abdomen in this configuration, likely because of speed and ease of application. 13 The emergency nurse needs to understand that this is not the standard for a 12-lead ECG and that this configuration can shift the electrical axis and create a distortion of the ECG morphology to the magnitude of simulating the presence of infarction or ischemia by altering the ST segment. 2–4,6,7,12 Therefore this practice should be abandoned, and limb leads should always be placed on the extremities (FIGURE 1). PRECORDIAL ELECTRODES
Placement of the precordial electrodes requires strict attention to detail because these are the electrodes closest to the heart and minute shifts in position can result in substantial changes in ECG morphology and diagnostic errors related to anterior or septal STEMI. 12,16,18 Attempting to estimate correct positioning is unacceptable in the performance of this procedure. The application of the
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The angle of Louis, which is adjacent to the second rib, and the second ICS, which is just below the second rib, are located. 2. Once the second ICS has been located, the operator can palpate down the chest wall adjacent to the sternum until he or she arrives at the fourth ICS. 3. When the operator is facing the patient, the electrode for V1 is placed in the fourth ICS to the left of the sternum (patient’s right) and the electrode for V2 is placed in the fourth ICS to the right of the sternum (patient’s left). 4. The next electrode placement is V4, which is located in the fifth ICS in the midclavicular line on the patient’s left precordium. 5. The electrode for V3 is then located midway between the electrodes for V2 and V4. 6. The remaining 2 electrodes for V5 and V6 are located in a straight line from V4. The electrode for V5 is located in the anterior axillary line, even with V4, and the electrode for V6 is located in the midaxillary line, even with V5. 1.
FIGURE 1 Placement of limb leads.
precordial electrodes, as with the limb electrodes, is also a defined process with a great deal of variation depending on the operator. 2,3 Precordial electrode positioning begins with the crucial first step of correctly identifying the fourth intercostal space (ICS) for the placement of the V1 and V2 leads. 3,13,16,18 This is accomplished as follows (FIGURE 2):
FIGURE 2 Placement of precordial electrodes.
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It cannot be stressed enough that proper chest electrode placement hinges on the correct identification of the fourth ICS, where V1 and V2 are located; superior displacement of the V1 or V2 electrode (or both) will likely result in the superior displacement of all the precordial electrodes. 6,13,16,18 Studies have shown that many operators will identify positions that are inappropriately superior to the fourth ICS. 2,3 Failure to adhere to these specifications can lead to false myocardial injury patterns, 6 as well as other diagnostic errors, with a variation of as little as 2 cm. 12 One issue that seems to confound some operators is where to place electrodes on the precordium of women with large breasts, above or below the breast tissue. 12 With respect to ECG distortion or alteration, the data are equivocal 12,13,18; however, the guideline states that the electrode should be placed under the breast as close to the chest wall as possible. 12,13 It is possible that misplacement of ECG electrodes in women contributes to the disparity in ACS identification that exists between men and women. The final point is the concept of reproducibility in serial tracings. Reproducibility is an absolute necessity when determining whether ST elevation is resolving or worsening. 6 Once affixed to the patient, electrodes should remain in place for the duration of the ED stay. To make accurate comparisons, the electrode positions must remain the same because a change in electrode position can create variability in serial ECGs. 6,7 If it becomes necessary to remove electrodes (for radiographs or other studies), some type of skin marking should be used to accurately replace these electrodes. 12
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Conclusion
6. Drew BJ. Psuedo myocardial injury patterns because of nonstandard electrocardiogram electrode placement. J Electrocardiol. 2008;41(3):202-204.
Because the emergency department is the gateway into the hospital during an ACS episode, it is essential for emergency nurses to be the “experts” in the acquisition of the 12-lead ECG. Emergency nurses should also serve as the quality-control monitors to identify ECGs obtained in a nonstandard fashion. In doing so, nurses perform their highest function as advocates for high-quality patient care and safety.
7. Drew BJ, Kligfield P. Standardizing electrocardiographic leads: introduction to a symposium. J Electrocardiol. 2008;41(3):187-189.
Acknowledgment
The author thanks Bimbola Akintade, PhD, ACNP; Ms. Jane Sellman; and John Greenwood, MD, for their careful review and valuable suggestions.
REFERENCES 1. Go AS, Mozaffarian D, Roger V, et al. Heart disease and stroke statistics—2013 update: a report from the American Heart Association. Circulation. 2013;127(1):e6-e245. 2. Khunti K. Accurate interpretation of the 12-lead ECG electrode placement: a systematic review. Health Educ J. 2013: 1-14. 3. Rajaganeshan R, Ludlam CL, Francis DP, Parasramka SV, Sutton R. Accuracy in ECG lead placement among technicians, nurses, general physicians, and cardiologists. Int J Clin Pract. 2008;62(1):65-70. 4. Batchvarov VN, Mailik M, Camm AJ. Incorrect electrode cable connection during electrocardiographic recording. Europace. 2007;9(11):1081-1091. 5. Karur S, Patra S, Shankarappa RK, et al. Left arm-left leg lead reversal in a case of inferior wall myocardial infarction mimics as high lateral wall infarction. J Cardiovasc Dis Res. 2013;4(3):201-203.
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8. McCabe JM, Armstrong EJ, Kulkarni A, et al. Prevalence and factors associated with false-positive ST-segment elevation myocardial infarction diagnoses at primary percutaneous coronary intervention-capable centers. Arch Intern Med. 2012;172(11):864-871. 9. GE Healthcare. Marquette 12SL. http://www3.gehealthcare.com/en/ Products/Categories/Diagnostic_ECG/ECG_Analysis. Published 2012. Accessed June 1, 2014. 10. Philips Healthcare. Philips ECG algorithms. http://www.healthcare. philips.com/main/products/cardiography/products/articles/algorithms. wp. Published 2014. Accessed June 01, 2014. 11. Macfarlane PW, Devine B, Clark E. The University of Glasgow (Uni-G) ECG analysis program. Comput Cardiol. 2005: 451-454. 12. Kligfield P, Gettes LS, Bailey JJ, et al. Recommendations for the standardization and interpretation of the electrocardiogram: part I: the electrocardiogram and its technology. J Am Coll Cardiol. 2007;49(10):1109-1127. 13. Garcia-Niebla J, Llontop-Garcia P, Valle-Racero JI, et al. Technical mistakes during the acquisition of the electrocardiogram. Ann Noninvasive Electrocardiol. 2009;14(4):389-403. 14. Adams MG, Drew BJ. Body position effects on the ECG: implications for ischemia monitoring. J Electrocardiol. 1997;30(4):285-291. 15. Baevsky RH, Haber MD, Blank FS, Smithline H. Supine vs semirecumbent and upright 12-lead electrocardiogram: does change in body position alter the electrocardiographic interpretation for ischemia? Am J Emerg Med. 2007;25(7):753-756. 16. Drew BJ. Pitfalls and artifacts in electrocardiography. Cardiol Clin. 2006;24:309-315. 17. Mason RE, Likar I. A new system of multiple-lead exercise electrocardiography. Am Heart J. 1966;71:196-205. 18. Kania M, Rix H, Fereniec M, et al. The effect of precordial lead displacement on ECG morphology. Med Biol Eng Comput. 2014;52(2):109-119.
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