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.
Aim
The objective was to determine the optimal QT-heart rate correction when heart rate
is increased.
Materials and 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.
Conclusion
The 2 newer QT-heart rate correction formula should be used when evaluating QT interval
at faster heart rates especially those associated with exercise.
Key Indexing Terms
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Article info
Publication history
Accepted:
September 1,
2015
Received:
May 28,
2015
Footnotes
The authors have no financial or other conflicts of interest to disclose.
Identification
Copyright
© 2016 Southern Society for Clinical Investigation. Published by Elsevier Inc. All rights reserved.
