doi: 10.4037/ccn2009607 2009;29:67-73Crit Care Nurse P. Redfearn, Christopher S. Simpson and Hoshiar AbdollahAdrian Baranchuk, Catherine Shaw, Haitham Alanazi, Debra Campbell, Kathy Bally, DamianElectrocardiography Pitfalls and Artifacts: The 10 Commandments
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Electrode misplacement isanother common artifact. Suchmisplacement may lead to changesin ECG morphology that couldpotentially be interpreted as ischemicin origin.3 Electrode misplacementscan also mimic serious arrhythmiasand lead to misdirected therapeuticdecisions.4 Electrode misplacement
Adrian Baranchuk, MDCatherine Shaw, RCTHaitham Alanazi, MDDebra Campbell, RN, BScN, CCN(C)Kathy Bally, RN, BNSc, CCN(C)Damian P. Redfearn, MD, MB, ChB, MRCPIChristopher S. Simpson, MD, FRCPCHoshiar Abdollah, MD, MB, ChB
Electrocardiography Pitfalls and Artifacts: The 10 Commandments
ECG
Many potentialpitfalls canadversely affectthe interpreta-tion of 12-lead
ambulatory and telemetry electro-cardiograms (ECGs). Artifacts, forexample, are a common finding inpatients who require ECG monitor-ing. Artifacts are defined as ECGabnormalities that may be due tosources other than the electricalactivity of the heart. Failure to cor-rectly distinguish between anarrhythmia and artifact can resultin misdiagnosis and unnecessarytherapeutic interventions.1
The most common causes ofartifacts originate from internal(physiological) and external (non-physiological) sources (Table 1).Artifacts created from thesesources can simulate arrhythmiassuch as atrial flutter and ventricu-lar tachycardia.2
PRIME POINTS
• Artifacts are common inpatients who require ECG monitoring.
• Artifacts can simulatearrhythmias such as atrialflutter and ventriculartachycardia and lead toinappropriate treatment.
• Electrode and lead mis-placements are anothercommon pitfall and canlead to ECG changes thatmay be interpreted asischemic in origin and canmimic serious arrhythmias.
• A simplified algorithm(REVERSE is the mnemonic)may help clinicians correctlyidentify both suspectedelectrode misplacementsand artifacts.
Table 1 Most frequent causes ofelectrocardiographic artifact and otherpitfalls
(wide isoelectric line)Light fixturesElectrocauteryElectrical devices in the room
• Cable and electrode malfunctionInsufficient amount of electrode gelFractured wiresInappropriate filter settingsLoose connectionsMisplaced leadsAccumulation of static energy
is a relatively frequent finding inECGs done in outpatient clinics(0.4%) and is even more common inintensive care units (4%).4 The cor-rect position for precordial ECGelectrodes is illustrated in Figure 1.
Several telltale clues can help cli-nicians identify potential signs ofelectrode misplacements and arti-facts. In this article, we introduce analgorithm that we developed toassist nurses and physicians in rap-idly recognizing those clues andreview 10 of the most common ECGpitfalls and artifacts.
Algorithm to Identify ECGElectrode Misplacements orArtifacts (REVERSE)
The indicators of electrode mis-placements or artifacts that clini-cians need to look for can be easilyremembered by using the mnemonicREVERSE (Table 2). With thismnemonic in mind, careful and sys-tematic examination of ECGs will helprule out problems with the recording.
We describe the 10 most com-mon ECG pitfalls and artifacts seenin our practice, presented in theform of commandments. All theECG examples provided for thisreview were run at 25 mm/s, 10mm/mV, and 100 Hz.
ECG Pitfalls and Artifacts:The 10 Commandments1. You shall not reverse the elec-trodes: reversal of left arm andright arm electrodes
Reversing the electrodes is oneof the most common errors madewhen placing the ECG on a patient.Such reversal produces leads I andAVL with reverse polarity of allnormal deflections (negative P wave,QRS complex, and T wave). In addi-tion, polarity is reversed in lead AVR(positive P and QRS; Figure 2). Thedifferential diagnosis is dextrocardia(the heart is positioned on the rightside). In dextrocardia, however, theprogression of the R wave in pre-cordial leads is reversed, whereas
with electrode reversal, the pro-gression is normal.5
2. You shall not treat the ECG,treat the patient: artifact mimick-ing ventricular tachycardia
The possibility of tremor orother interference inducing an arti-fact that mimics ventricular tachy-cardia should be considered whenthe ECG does not match thepatient’s clinical findings. A normalheart rate obtained by pulse or aus-cultation in an asymptomaticpatient at the same time the ECGshows apparent ventricular tachy-cardia confirms the diagnosis.Reduction of the tremor by holdingthe limb or placing the electrodeson the torso will reduce interfer-ence.2,6,7 “Tracking” the R-R intervalsis helpful if they can be identified
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All authors are in the Department of Cardiology at Queen’s University in Kingston, Ontario,Canada.
Corresponding author: Adrian Baranchuk, MD, Cardiac Electrophysiology and Pacing, Kingston General Hospital,Queen’s University, Kingston, Ontario, Can ada K7L 2V7 (e-mail: [email protected]).
To purchase electronic or print reprints, contact The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656.Phone, (800) 899-1712 or (949) 362-2050 (ext 532); fax, (949) 362-2049; e-mail, [email protected].
Authors
Figure 1 A, Standard position of precordial electrodes. B, Normal 12-lead electro-cardiogram.
B
A• V1: Right sternal border, 4th intercostal
• V2: Left sternal border, 4th intercostal
• V4: Midclavical, 5th intercostal
• V3: Midway between V2 and V4
• V5 and V6: Anterior and midaxillary respectively and in line with V4
• LA and RA: Left and right arms/wrists
• LL and RL: Left and right lower/upper legs
V1 V2 V3 V4 V5V6
I
II
III
VI
aVF
aVL
aVR V1
V2
V3 V6
V5
V4
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before the pseudo– ventriculartachycardia. Look for R-R intervalsthat continue into the wide complexrhythm to see the presence of normal ventricular depolarizationsthroughout the pseudo–ventriculartachycardia. With careful measur-ing to see where normal beatsshould be, they will often “jumpout” at the observer and becomeobvious, whereas at first glance they may be completely obscured.Pseudo–ventricular tachycardia has3 characteristic signs8
(Figure 3):
1. Sinus sign: one of thefrontal leads (I, II, or III)shows normal P waves,QRS complexes, and Twaves because usually oneof the upper limbs is freeof tremor or movement.
2. Spike sign: tiny spikes canbe seen among wide QRS-like complexes.
3. Notch sign: notches aresuperimposed in the wideQRS-like complex artifactthat “time out” with pre-ceding R-R intervals.
3. You shall not reverse the electrodes: reversal of left armand left leg electrodes
Amplitude of the P wave in lead Igreater than in lead II and/or P-waveterminal positive component in leadIII (Abdollah sign) will confirmreversal of the left arm and left legleads.9 Confirmation with a secondECG is usually required (Figure 4).
4. You shall not reverse the electrodes: reversal of precordialleads (V1 and V6)
The most common reversal ofthe precordial leads is an exchangeof V1 and V6. The way to recognizethis problem is by assessing the R-wave progression in the precor-dial leads. Normally, the R wavewill increase its amplitude from V1to V6 and the S wave will decreaseits amplitude. In the reversal situa-tion, a tall R wave can be seen inV1 and a deep S wave in V6.10-13
Potential diagnostic misinterpreta-tions include right bundle branchblock, old posterior myocardialinfarction, right ventricular hyper-trophy, and left-sided accessorypathways (Figure 5).
5. You shall check if the patientis calm and quiet: tremor
Tremor-induced artifact maymimic supraventricular arrhythmias(atrial flutter/atrial fibrillation) orif the artifact has sufficient ampli-tude, it can also mimic ventriculartachycardia and ventricular fibrilla-tion. The correct diagnosis can bemade on the basis of simple obser-vations such as the presence of thepseudoarrhythmia when the patientmoves (tremor). Careful analysismay reveal discrete components ofthe QRS complexes (matching the
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Table 2 REVERSE mnemonic: an easy approach to remember the most frequentcauses of electrocardiographic artifacts and pitfalls
R
E
V
E
R
S
E
Abnormal finding
R wave is positive in lead aVR (P wave also positive)
Extreme axis deviation: QRS axis between+180° and -90° (negative R wave in lead I,positive R wave in AVF)
Very low (<0.1 mV) amplitude in an isolatedlimb lead (isolated “flat” lead)
Exchanged amplitude of the P waves (P wavein lead I greater than in lead II)
R wave abnormal progression in the precor-dial leads (predominant R wave in V1, pre-dominant S wave in V6)
Suspect dextrocardia (negative P waves inlead I)
Eliminate noise and interference (artifactmimicking tachycardias or ST-T changes)
Significance
Reversal of left arm and right armelectrodes
Reversal of left arm and right armelectrodes
Reversal of right leg and left armor right arm electrodes
Reversal of left arm and left legelectrodes
Reversal of precordial electrodes(V1 through V6)
Left arm-right arm electrode reversal
Figure 2 Reversal of electrodes for left arm and right arm. Note reverse polarity(arrows) in leads I and AVL (negative P, QRS, and T deflections). Note also reversepolarity in AVR (positive P and QRS deflections).
I
II
III aVF
aVL
aVR V1
V2
V3 V6
V5
V4
↓ ↓
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previous R-R intervals if present)through the pseudoarrhythmia(“notches sign”).8,14-16 Misinterpreta-tion of tremor-induced artifact maylead to serious medical errors suchas the initiation of long-term use ofanticoagulants for pseudo– atrial fib-rillation.17 Figure 6 showspseudo–atrial flutter that was atremor-induced artifact.
6. You shall turn off your cellphone: electromagnetic interference
Electromagnetic interference(EMI) with medical devices by cellphones is a well-recognized prob-lem.18-21 Even though considerablecontroversy remains about the useof cell phones in hospitals, the evi-dence is clear that cell phones canproduce EMI with many different
medical devices (eg, ECG monitor,ventilator, infusion pump, dialysismachine, apnea monitor, externalpacemaker, internal pacemaker,and defibrillator). The ability of acell phone or a wireless device toinduce EMI depends on the dis-tance, the ability of medical equip-ment to resist EMI, and thetechnology of the cell phone (digitalvs analog, which are the 2 basic sys-tems cell phones use to operate,and single-band of operation vsdual and frequency band of opera-tion).19 As shown by previousinvestigators,19 a 1-m (3.28 ft) dis-tance between the source of EMIand medical devices safely elimi-nates EMI. Only a few cases inwhich cell phones and wirelessdevices interfered with ECGmachines have been reported.20 Wesimulated a case created in our lab-oratory by activating a cell phone(digital) less than 25 cm (9.8 in)from the ECG machine acquisitionmodule (MAC 5000 Resting ECGAnalysis System, GE Medical Sys-tems, Waukesha, Wisconsin). Therapid, sharp, and low-amplitudesignals disappeared when the cellphone was removed or deactivated(Figure 7). ECG technicians andnurses should avoid using cellphones when they are recordingECGs until further research in thisarea is available. This limitationmay also have implications forparamedics and ambulance atten-dants who obtain and interpretECGs on patients in the field.
7. You shall know where the limbsare: electrodes placed on the torso
Electrodes are placed on the torsonear the extremities rather than onthe limbs for different reasons.
Figure 3 Artifact that mimics ventricular tachycardia. Note the “sinus” sign (aster-isk) in lead I (a P wave is visible before the second QRS complex). The “spike” and“notch” signs (arrows) can be seen by tracking the previous R-R interval among thewide-QRS-like complexes.
I
↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓ ↓
II
III
VI
aVF
aVL
aVR
*V1
V2
V3 V6
V5
V4
Figure 4 Reversal of left arm and left leg electrodes. Note that the amplitude of theP wave in lead I is greater than that in lead II (arrows), and the P wave in lead IIIhas a small positive terminal component (Abdollah sign).
V4
V5
V6V3
V2
V1aVR
aVL
aVFIII
II
I ↓↓
Figure 5 Reversal of precordial electrodes. Tall R wave is seen in V1, and small Rwave and deep S wave (arrows) are seen in V6, indicating V1 to V6 electrode reversal.
III
II
I aVR
aVL
aVF V3
V2
V1 V4
V5
V6
↓
↓
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During an emergency, placing leadson the torso reduces the timeneeded for undressing the patientand in most cases will allow a correctECG diagnosis.22 However, in mostcircumstances, the torso positionshould not replace the standardposition on the limbs. The torsoposition induces a change in howthe electrical vectors are recorded.Pseudo–Q waves and pseudo–ST-segment elevation in the inferiorleads5,23,24 could potentially be mis-interpreted as myocardial infarc-tion (Figure 8).
8. You shall not place telemetryelectrodes on top of ECG elec-trodes: telemetry interference
Placing the telemetry electrodeson top of the ECG electrodes or viceversa is a common mistake. Usually,
telemetry electrodes are placed inthe same region where the ECG elec-trodes need to be placed. This
superimposition of electrodes maycreate a distortion of the ST seg-ment that mimics ST-segment ele-vation or arrhythmias due to EMIof the telemetry on the ECGmachine25 (Figure 9).
9. You shall not reverse the elec-trodes: reversal of right leg andleft arm or right arm electrodes
If a reversal involves the rightleg and one of the arms, the record-ing will be zero potential differencebetween the legs.5 This pseudoasys-tole in an isolated lead may occur inlead II (reversal of right arm andright leg electrodes) or in lead III(reversal of left arm and right legelectrodes; Figure 10).
10. The patient should be lyingdown, calm and relaxed (if pos-sible): ECG done with patientsitting at 90º
In some clinical situations (eg,decompensated heart failure, respi-ratory insufficiency, orthopediclimitations), the ECG must be
Figure 7 Electromagnetic interference. Sharp and fast spikes (arrowheads) wereinduced by a digital cell phone activated less than 25 cm from the acquisition module of the electrocardiography machine.
III
III
I
II
aVF
aVL
aVR
V3
V2
V1 V4
V5
V6
Figure 8 Torso position of the electrodes. A, Baseline. B, Torso position. Note fast Qwaves and ST-segment elevation in the inferior leads.
III
II
I
B
A
III
II
I aVR
aVL
aVF
aVR
aVL
aVF V3
V2
V1
V3
V2
V1 V4
V5
V6
V4
V5
V6
Figure 6 Tremor-induced artifact. Note pseudo–flutter waves (arrowheads) in theinferior leads. Normal P waves (arrow) are visible in the rest of the leads.
III
VI
aVR
aVL
aVF V3
V2
V1 V4
V5
V6
II
I
↓
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recorded with the patient sittingupright or in a semi-Fowler’s posi-tion. Changing the body position
can affect the QRS axis and QRSamplitude.26,27 Currently, no distinc-tions in the recording methods needto be made when an ECG is recordedwith the patient sitting (~90º); how-ever, recognizing slight alterationsof the QRS complex may be helpfulto avoid wrong interpretations. Anannotation indicating the positionof the patient (if different than usual)
may be helpful for the physicianinterpreting the recordings. In thiscase, note the reduction of the QRSamplitude in lead III, which is a leadthat is particularly sensitive to changesin diaphragmatic position (Figure 11).
ConclusionsThe ECG is one of the most
valuable tools in our daily practice.Many health care providers inter-pret ECGs and initiate therapeuticinterventions on the basis of suchinterpretations. Recognizing ECGartifacts and other pitfalls will enableclinicians to avoid unnecessary ther-apeutic interventions and may allowthem to correct the recording meth-ods to obtain a proper ECG. CCN
3. Rudiger A, Schöb L, Follath F. Influence ofelectrode misplacement on the electrocardio-graphic signs of inferior myocardial ischemia.Am J Emerg Med. 2003;21(7):574-577.
4. Rudiger A, Hellermann JP, Mukherjee R, etal. Electrocardiographic artifacts due toelectrode misplacement and their fre-quency in different clinical settings. Am JEmerg Med. 2007;25(2):174-178.
5. Drew BJ. Pitfalls and artifacts in electrocar-diography. Cardiol Clin. 2006;24(3):309-315.
6. Knight BP, Pelosi F, Michaud GF, Strick-berger SA, Morady F. Physician interpreta-tion of electrocardiographic artifact thatmimics ventricular tachycardia. Am J Med.2001;110(5):335-338.
7. Knight BP, Pelosi F, Michaud GF, Strick-berger SA, Morady F. Clinical consequencesof electrocardiographic artifact mimickingventricular tachycardia. N Engl J Med. 1999;341(17):1270-1274.
8. Huang CY, Shan DE, Lai CH, et al. Anaccurate electrocardiographic algorithm
Figure 9 Telemetry interference. Telemetry electrodes were placed on top of the elec-trocardiographic electrodes. Note pseudo–ST-segment elevation (arrows) in leads V2and V6.
III
II
I aVR
aVL
aVF V3
V2
V1 V4
V5
V6
↓
↓↓
Figure 10 Reversal of right arm and right leg electrodes. Note pseudoasystole (arrow)in lead III.
III
II
I aVR
aVL
aVF V3
V2
V1 V4
V5
V6
↓
Figure 11 Electrocardiogram recorded with patient sitting upright at 90°. Note low-amplitude QRS complex (arrows) in lead III.
III
II
I aVR
aVL
aVF V3
V2
V1 V4
V5
V6
↓ ↓
d•tmoreTo learn more about ECG algorithms, read“ECG Computer Algorithms,” by MicheleM. Pelter and Mary G. Carey in the Ameri-can Journal of Critical Care 2008;17:581-582.Available at www.ajcconline.org.
�
eLettersNow that you’ve read the article, create or con-tribute to an online discussion about this topicusing eLetters. Just visit www.ccnonline.org andclick “Respond to This Article” in either the full-text or PDF view of the article.
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14. Llinas R, Henderson VH. Tremor as a causeof pseudo-ventricular tachycardia. N Engl JMed. 1999;341:1275.
15. Bhatia L, Turner DR. Parkinson’s tremormimicking ventricular tachycardia. Age Age-ing. 2005;34(4):410-411.
16. Ortega-Carnicer J. Tremor-related artifactmimicking ventricular tachycardia. Resusci-tation. 2005;65(3):243-244.
17. Finsterer J, Stollberger C, Gatterer E. Oralanticoagulation for ECG tremor artifact sim-ulating atrial fibrillation. Acta Cardiol. 2003;58(5):425-429.
18. Morrissey JJ, Swicord M, Balzano Q. Char-
acterization of electromagnetic interferenceof medical devices in the hospital due tocell phones. Health Phys. 2002;82(1):45-51.
19. Lawrentschuk N, Bolton DM. Mobilephone interference with medical equipmentand its clinical relevance: a systematicreview. Med J Aust. 2004;181(3):145-149.
20. Baranchuk A, Kang J, Shaw C, et al. Electro-magnetic interference of communicationdevices on ECG machines. Clin Cardiol. Inpress.
21. Klein AA, Djaiani GN. Mobile phones inthe hospital—past, present and future.Anaesthesia. 2003;58(4):353-357.
22. Takuma K, Hori S, Sasaki J, et al. An alter-native limb lead system for electrocardio-graphs in emergency patients. Am J EmergMed. 1995;13(5):514-517.
23. Jowett NI, Turner AM, Cole A, Jones PA.Modified electrode placement must berecorded when performing 12-lead electro-cardiograms. Postgrad Med J.2005;81(952):122-125.
24. Kligfield P, Gettes LS, Baileiy JJ, et al. Rec-ommendations for the standardization andinterpretation of the electrocardiogram, I:the electrocardiogram and its technology.Circulation. 2007;115(10):1306-1324.
25. Mirvis DM, Berson AS, Goldberger AL, etal. Instrumentation and practice standardsfor electrocardiographic monitoring in spe-cial care units. A Report for Health Profes-sionals by a Task Force of the Council on
Clinical Cardiology, American Heart Asso-ciation. Circulation. 1989;79(2):464-471.
26. Nelwan SP, Meij SH, van Dam TB, Kors JA.Correction of ECG variations caused bybody position changes and electrode place-ment during ST-T monitoring. J Electrocar-diol. 2001;34(suppl):213-216.
27. Madias JE. Comparability of the standingand supine standard electrocardiograms andstanding sitting and supine stress electrocar-diograms. J Electrocardiol. 2006;39(2):142-149.
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