In this ECG Cases blog we review 10 cases of possible artifact, lead reversal and lead misplacement. Can you spot the abnormalities and avoid the misdiagnosis?

Written by Jesse McLaren; Peer Reviewed and edited by Anton Helman, March 2022

10 patients presented with ECG abnormalities suggesting a potential diagnosis. Which had artifact, lead reversal or misplacement and how would this change the diagnosis?

Case 1: 55yo with chest pain. Is this a tachydysrhythmia?

Case 2: 70yo history of coronary artery disease with chest pain. Is this a subacute inferior MI?

Case 3: 55yo with epigastric pain. Has there been a lateral MI?

Case 4: 35yo with chest pain. Is this an antero-lateral STEMI?

Case 5: 70yo with weakness. Has there been an an anterior MI?

Case 6: 60yo with chest pain. Is this an anterior MI?

Case 7: 65yo with intermittent chest pain. Old then new ECG. Is this Wellens syndrome?

Case 8: 50yo with chest pain. Is this an old anterior MI?

Case 9: 25yo with chest pain. Is this pulmonary embolism?

Case 10: 45 year old with palpitations. Is this Brugada?

ECG lead placement

ECG interpretation can be affected by artifact as well as three types of lead misplacement: limb lead reversal, precordial lead reversal, and precordial lead misplacement. [1] These can each lead to a variety of misdiagnoses, but can also be identified by systematic interpretation.

  1. Artifact

Artifact can be a result of the patient (eg tremor) or external causes (eg electrode malfunction, electromagnetic interference). This can mimic tachyarrhythmias but can be identified if one of the leads is unaffected at the same time as the others, or by identifying regular R waves that march through the artifact.

  1. Limb lead reversal

Limb leads record the cardiac axis in the frontal plane. Atrial depolarization starts in the sinus node in the upper right atrium and travels down/left, producing an upright P wave in I and II (with P in II>I), and negative P wave in aVR. Ventricular depolarization proceeds down/left, with a normal axis (positive in I/aVF, negative in aVR). Limb lead reversal can produce pseudo-infarction patterns, but axis abnormalities can indicate misplacement.[2] These include: abnormal P wave axis (positive in aVR, negative in I/II), extreme QRS axis, concordantly negative complexes in limb leads (i.e. negative P/QRS/T), very low/isoelectric voltages isolated in one limb lead, and inverted lateral limb leads I/aVL while upright lateral precordial leads V6 (as opposed to dextrocardia where both limb and precordial leads are congruent). For example:

  • Right arm/left arm reversal. Normal sinus rhythm travels from the right to the left atrium, producing a P wave that is positive in I and negative in aVR. Right arm/left arm reversal causes the opposite: it appears as a pseudo-lateral infarct with Q wave and T wave inversion in I/aVL, but the P wave is negative in I and positive in aVR (i.e. not sinus), and the inverted complexes in the lateral limb leads I/aVL don’t match the upright complexes in the lateral chest lead V6. Lead I is inverted, aVR/aVF are switched, II/III are switched
  • Right arm/left leg reversal. Normal ventricular conduction travels down/left, with a normal axis that is positive in I/aVF and negative in aVR. Right arm/left leg reversal causes the opposite: it might appear as a pseudo-inferior infarct with Q wave and T wave inversion inferiorly, or a left anterior fascicular block, but all inferior leads have negative P waves, and there is extreme axis with QRS negative in I/aVF and positive in aVR. Lead II is inverted, I/III are inverted and switched, and aVR/aVF are switched
  • Left arm/left leg reversal. Sinus rhythm is directed more towards II than I (P in II>I). Left arm/left leg reversal causes the opposite. It appears as negative QRS/T in III but there is also a negative P in III, and the P wave I>II. Lead III is inverted, I/II are switched, and aVL/aVF are switched.
  • Reversal involving the right leg (the neutral electrode): moving this eliminates the voltage difference between the leads, resulting in a flatline in one of the limb leads.

For visual examples of lead reversal, see the review article by Mond et al [3] or the blog post from Life in the Fastlane.

  1. Precordial lead reversal

Precordial leads record cardiac activity in the horizontal plane, wrapping around from right/anterior to left/lateral. As leads progress across the precordium, there’s an associated R-wave progression—from V1-2 with S>R waves, to V3-4 with equiphasic R/S waves, to V5-V6 with R>S waves. Early R-wave progression has a differential (R-WAVED mnemonic), as does late R-wave progression (LATE mnemonic), both of which include precordial lead reversal. Depending on the lead, precordial lead reversal can mimic early R wave progression or produce a pseudo-infarction pattern. But if assessing R-wave progression is integrated into routine ECG interpretation, it will highlight an isolated abnormality in R-wave progression that can identify precordial lead reversal.

  1. Precordial lead misplacement

Even if the ECG leads are placed in the correct sequence, there can be a number of abnormalities and potential misdiagnoses if leads V1-2 are placed too high on the chest. But this misplacement leaves clues, as emergency physician Dr. Brooks Walsh explains:

“The resulting ECG may generate erroneous ECG patterns: e.g. in-complete right bundle branch block, anterior T wave inversion, septal Q waves, ST-segment elevation. These features may falsely suggest acute or old cardiac ischemia, pulmonary embolism, or a type-2 Brugada pattern… Precordial lead misplacement can often be identified from the ECG. When the leads are properly placed on a healthy patient in the 4th ICS, V2 will show a biphasic P wave in 2% of cases, while V1 will essentially never show a fully negative P wave. Upwards misplacement of the lead may be strongly suspected when the P wave in V2 is biphasic, and presumed when the P wave is fully negative.”[4]

Precordial lead misplacement often repeats mistakes based on faulty images, which is part of a broader problem. As Dr. Walsh has also found, Google Images of lead placement lacks not only correct lead placement but also gender and racial diversity. In a review of Google Images of human torsos with precordial ECG leads and without bone or cardiac anatomy, the only images available were of white men and the majority had incorrect lead placement.[5]

In summary, ECG artifact and lead misplacement can produce a variety of abnormalities that can lead to misdiagnoses. But systematic ECG interpretation can help identify the errors and prevent misdiagnosis:

  • Heart rate/rhythm: pseudo-tachyarrhythmia with unaffected leads or regular R-R intervals (artifact)
  • Electrical conduction: negative P in lead I (limb lead reversal), incomplete RBBB without upright P wave in V2 (precordial misplaced)
  • Axis: extreme axis (limb lead reversal)
  • R-wage: isolated R wave progression abnormality (precordial lead reversal)
  • Tall/small: tiny/flat voltage isolated to one limb lead (limb lead reversal)
  • ST/T: pseudo-infarct with concordantly negative P/QRS/T waves (limb lead reversal); pseudo-Brugada/infarct/Wellens without upright P wave in V2 (precordial misplaced)

Back to the cases

Case 1: artifact
  • Heart rate/rhythm: normal sinus rhythm with artifact – regular R waves in rhythm strip, and lead I unaffected
  • Electrical conduction: normal
  • Axis: normal
  • R-wave progression: delayed
  • Tall/small voltages: normal voltages
  • ST/T waves: no obvious changes but need to repeat

Impression: artifact. Repeat ECG normal, and had negative workup

Case 2: limb reversal right arm/left leg, unnecessary cath lab activation

  • H: inverted P wave in II
  • E: normal conduction
  • A: extreme axis (negative in I/aVF, positive in aVR)
  • R: anterior Q waves
  • T: normal voltages
  • S: concordantly negative P/QRS/T waves inferiorly, lateral ST depression

Impression: right arm/left leg lead reversal mimicking subacute inferior MI. Cath lab activated: normal obstructive lesion, negative troponin, and repeat ECG revealed resolution of inferior changes:

Case 3: limb lead reversal right arm/left arm

  • H: negative P in I
  • E: normal conduction
  • A: extreme axis
  • R: normal R wave progression
  • T: normal voltages
  • S: concordantly negative P/QRS/T in I/aVL which don’t match normal complxes in lateral chest leads

Impression: limb lead reversal right arm/left arm. Repeat ECG normal and negative workup.

Case 4: limb lead reversal left arm/left

  • H: sinus bradycardia
  • E: normal conduction
  • A: left axis
  • R: normal R wave progression
  • T: tall voltages in I/aVL don’t correlate with voltage in V6
  • S: inverted P/QRS/T in III

Impression: left arm/left leg reversal. ECG repeated with correct lead placement: early repolarization pattern. Serial ECG unchanged and troponin negative:

Case 5: precordial lead reversal

  • H: normal sinus rhythm
  • E: normal conduction
  • A: normal axis
  • R: normal R wave progression interrupted by V3
  • T: normal voltage
  • S: normal except for negative P/QRS/T in V3

Impression: precordial lead reversal. Repeat with correct placement was normal, and troponin negative.

Case 6: proximal LAD occlusion + precordial lead reversal

  • H: normal sinus rhythm
  • E: normal conduction
  • A: normal axis
  • R: abnormal R wave progression V1-3
  • T: normal voltages
  • S: STE and hyperacute T waves in aVL/V2 (in V1 position), with inferolateral reciprocal changes

Impression: Proximal LAD or first diagonal occlusion with V1-2 reversed, diagnosed despite lead reversal. ECG repeated 30 minutes later with correct lead placement, after nitro/aspirin/ticagrelor/heparin and prior to cath:

Decreased ST elevation/reciprocal ST depression from partial reperfusion. Cath: 95% proximal LAD occlusion, trop rise from 2ng/L (normal<26) to 800.

Case 7: V1-2 misplaced

  • H: normal sinus rhythm
  • E: normal conduction
  • A: normal axis
  • R: normal R wave
  • T: normal voltage
  • S: negative T wave in V2 concordant with P/QRS

Impression: V2 misplaced. Serial ECG repeated with progressively corrected lead placement: first with biphasic P wave and saddleback ST segment, then upright P wave with normal ST segment. Negative workup.

Case 8: infero-postero-lateral Occlusion MI + precordial lead misplacement

  • H: normal sinus rhythm
  • E: normal conduction
  • A: normal axis
  • R: late R wave progression
  • T: normal voltages
  • S: the anterior “T wave inversion” is concordant to P/QRS from V2 misplacement, but the TWI in aVL is discordant to its QRS are reciprocal to hyperacute inferior T waves, and associated with lateral hyperacute T waves

Impression: inferolateral OMI with precordial lead misplacement. Repeat: with V2 in normal position (upright P wave) there now evidence of ST depression from associated posterior OMI, and the ST elevation in III has become convex.

Cath lab activated: 99% circumflex occlusion, first trop 10 ng/L (normal<26) and peak 7,000. Post-cath resolution of hyperacute T waves inferolaterally, normalization of reciprocal change in aVL, and tall T wave in V2 from posterior reperfusion

Case 9: V1-2 misplaced

  • H: sinus tach
  • E: pseudo-incomplete RBBB but biphasic P in V2
  • A: normal axis
  • R: normal R wave
  • T: normal voltage
  • S: no ST/T changes

Impression: V1-2 misplaced. Repeat ECG normal, and negative workup.

Case 10: V1-2 misplaced

  • H: normal sinus rhythm
  • E: pseudo-Brugada pattern in V1-V2 but inverted P wave
  • A: normal axis
  • R: normal R wave
  • T: normal voltage
  • S: no ST/T changes

Impression: V1-2 misplaced. Repeated with correct placement: normal ECG and negative workup.

Take home points on ECG Misdiagnosis from Lead Misplacement, Artifact and Lead Reversal

  • Artifact can mimic tachyarrhythmias but can be identified by finding an unaffected lead or mapping out unaffected R-R intervals
  • Limb lead reversal can produce pseudo-infarct pattern. Look for inverted P waves in I/II and upright complexes in aVR, concordantly inverted P/QRS/T, extreme axis deviation, tiny voltages isolated to one limb lead, and a QRS vector in I that doesn’t match V6
  • Precordial lead reversal can produce abnormally early R waves or pseudo-infarction pattern, but can be identified by an isolated abnormality in R-wave progression
  • V1-2 misplacement can give the appearance of infarction, Wellens, RBBB or Brugada, but can be identified by biphasic/inverted P wave in V2
  • Lead placement should be taught with images that include gender and racial diversity, as well as correct lead placement

References for ECG Cases 29: ECG lead misplacement artifact and lead reversal

  1. Harrigan et al. Electrocardiogarphic electrode misplacement, misconnection, and artifact. J of Emerg Med 2012
  2. Rudiger A, Hellerman JP, Mukherjee R, et al. Electrocardiographic artifacts due to electrode misplacement and their frequency in different clinical settings. Am J of Emerg Med 2007, 25:174-178
  3. Mond HG, Garcia J, and Visagathilagar T. Twisted leads: the footprints of malpositioned electrocardiographic leads. Heart Lung and Circ 2016;25:61-67
  4. Walsh B. Misplacing V1 and V2 can have clinical consequences. Am J of Emerg Med 2018;36:865-870
  5. Walsh B, Smith SW, Sifford D, et al. Examples of precordial 12-lead electrocardiogram lead placement found on Google images are often incorrect and lack gender and racial diversity. (Published May 18, 2017)