title: Newer QT Correction Formulae to Correct QT for Heart Rate Changes During Exercise.
abstract: BACKGROUND
  The QT interval is a marker for drug-induced cardiac toxicity, electrolyte abnormalities and genetic mutations with a high risk of sudden death.
  
  
  OBJECTIVE
  The objective was to determine the optimal QT-heart rate correction when heart rate is increased.
  
  
  METHODS
  A total of 40 persons had QT interval measured before at the end of each stage of a Bruce protocol. Currently used heart rate correction formulae (QTc) were compared to recently proposed QTc formulae derived from large population studies.
  
  
  RESULTS
  Comparing the data at each stage of exercise found that QTc using the Bazett formula (QTcBZT) increased with exercise while the QTc proposed by Fridericia (QTcFRD) and by Framingham (QTcFRM) decreased with exercise. In contrast QTc proposed by Dmitrienko (QTcDMT) and Rautaharju (QTcRTHa) were relatively constant despite the increase in heart rate during exercise, whereas QTc proposed by Hodges (QTcHDG) was more variable. With exercise, the differences between QTcBZT or QTcFRD and the other correction formulae became greater and highly significant. Next, the slope of QTc or RR regression was calculated for each individual during the exercise test. The rank order of the slopes (from the smallest to largest absolute value) was QTcRTHa, QTcDMT, QTcBZT, QTcHDG, QTcFRD and QTcFRM. Furthermore the slope of the QT/heart rate relationship was significantly (P < 0.0001) different between the older formulae proposed by Bazett or Fridericia compared to the newer formulae QTcDMT or QTcRTHa.
  
  
  CONCLUSIONS
  The 2 newer QT-heart rate correction formula should be used when evaluating QT interval at faster heart rates especially those associated with exercise.
authors.affiliation: Department of Medicine (Cardiology), University of British Columbia, Vancouver, BC, Canada. Electronic address: rabkin@mail.ubc.ca.
authors.forename: Simon W
authors.initials: SW
authors.lastname: Rabkin
authors.affiliation: Department of Medicine (Cardiology), University of British Columbia, Vancouver, BC, Canada.
authors.forename: XinBo Justin
authors.initials: XJ
authors.lastname: Cheng
mesh_terms: D000328:Adult; D000368:Aged; D004562:Electrocardiography / Q000379:methods*; D015444:Exercise; D005080:Exercise Test; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged
keywords: Exercise; Heart rate; QT interval