title: Choice of an alternative lead for QT interval measurement in serial ECGs when Lead II is not suitable for analysis.
abstract: BACKGROUND
  Conventionally, QT interval is measured in lead II. There are no data to select an alternative lead for QT measurement when it cannot be measured in Lead II for any reason.
  
  
  RESULTS
  We retrospectively analyzed ECGs from 1906 healthy volunteers from 41 phase I studies. QT interval was measured on the median beat in all 12 leads. The mean difference in QT interval between lead aVR and in Lead II was the least, followed by aVF, V5, V6 and V4; lead aVL had maximum difference. The T wave was flat (<0.1 mV) in Lead II in 6.9% of ECGs; it was also flat in 20% of these ECGs (1.4% of all ECGs) in Leads aVR, aVF and V5.
  
  
  CONCLUSIONS
  When QT interval cannot be measured in Lead II, the best alternative leads are aVR, aVF, V5, V6 and V4 in that sequence. It differs maximally from that in Lead II in Lead aVL.
authors.affiliation: Quintiles Cardiac Safety Services, Mumbai, India. vaibhav.salvi@quintiles.com
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Salvi
authors.forename: Dilip R
authors.initials: DR
authors.lastname: Karnad
authors.forename: Vaibhav
authors.initials: V
authors.lastname: Kerkar
authors.forename: Gopi Krishna
authors.initials: GK
authors.lastname: Panicker
authors.forename: Deepak
authors.initials: D
authors.lastname: Manohar
authors.forename: Mili
authors.initials: M
authors.lastname: Natekar
authors.forename: Snehal
authors.initials: S
authors.lastname: Kothari
authors.forename: Dhiraj
authors.initials: D
authors.lastname: Narula
authors.forename: Yash
authors.initials: Y
authors.lastname: Lokhandwala
mesh_terms: D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008133:Long QT Syndrome / Q000503:physiopathology; D008297:Male; D012016:Reference Values; D012189:Retrospective Studies