title: Does modifying electrode placement of the 12 lead ECG matter in healthy subjects?
abstract: BACKGROUND
  Limb electrodes for the 12 lead ECG are routinely placed on the torso during exercise stress testing or when limbs are clinically inaccessible. It is unclear whether such electrode modification produces ECG changes in healthy male or female subjects that are clinically important according to the 2009 AHA, ACCF, HRS guidelines. We therefore measured whether ECG modification produced clinically important or false positive ECG changes e.g., appearance of Q waves in leads V(1-3), ST changes greater than 0.1 mV, T wave changes greater than 0.5 mV (frontal plane) or 1 mV (transverse plane), QRS axis shifts or alterations to QTc/P-R/QRS intervals.
  
  
  METHODS
  The 12 lead ECG was measured in 18 healthy and semi-recumbent subjects using the standard and Takuma modified limb placements.
  
  
  RESULTS
  In the frontal plane we demonstrate that the modification of limb electrode placement produces small Q, R and T wave amplitude and QRS axis changes that are statistically but not clinically significant. In the transverse plane it produces no statistically or clinically significant changes in the ECG or in ST segment morphology, P-R, QRS or QTc intervals.
  
  
  CONCLUSIONS
  We provide better and more robust evidence that routine modification of limb electrode placement produces only minor changes to the ECG waveform in healthy subjects. These are not clinically significant according to the 2009 guidelines and thus have no effect on the clinical specificity of the 12 lead ECG.
authors.affiliation: Wellcome Trust Clinical Research Facility, University Hospitals Birmingham NHS Foundation Trust, Birmingham B15 2TH, UK.
authors.forename: James P
authors.initials: JP
authors.lastname: Sheppard
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Barker
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Ranasinghe
authors.forename: Thomas H
authors.initials: TH
authors.lastname: Clutton-Brock
authors.forename: Michael P
authors.initials: MP
authors.lastname: Frenneaux
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Parkes
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods*; D004566:Electrodes; D005080:Exercise Test; D005121:Extremities; D005260:Female; D006801:Humans; D008297:Male