Article date: March 2007
By: Paul Newbold, Nick Sanders, Stots B. Reele, in Volume 63, Issue 3, pages 279-287
What is already known about this subject
• When this study was conducted it was already known that the ‘standard’ methods of correcting the QT interval for heart rate were not optimal and that bias could result in their use in certain circumstances, in particular when drugs or conditions also induced wide fluctuations in heart rate.
What this study adds
• A subject specific correction factor for QT correction can be calculated from a wide range of heart rates using exercise testing and the relationships between QT and RR are unique for a given individual.
Aims
We sought to investigate subject specific QT interval correction factors (SSCF) determined at rest and after exercise and to determine the validity of these factors after the administration of a probe drug known to increase heart rate without directly affecting cardiac repolarization.
Methods
Thirty‐two healthy volunteers underwent graded exercise, multiple recordings of electrocardiogram during rest over a day and a treatment phase administering inhaled placebo or sibenadet (a β2‐adrenoceptor/dopamine D2‐receptor agonist) at 250, 500 or one of 750 or 1000 µg. SSCF were determined from linear regression of plots of log RR interval vs. log QT after exercise (QTcX), rest (QTcR), and combined data (QTcC). The SSCFs along with Bazett & Fridericia corrections were applied to the ECGs after inhalation of sibenadet.
Results
SSCFs obtained from the combination of the exercise and resting day (mean QTcC = 0.41) and exercise alone (mean QTcX = 0.40) were similar with a good fit to the data (mean r2 = 0.92 and 0.93, respectively) while data at rest resulted in a less pronounced slope (mean QTcR = 0.27) and poorer fit (mean r2 = 0.52). After the administration of sibenadet, none of the SSCFs, Bazett or Fridericia corrections adequately corrected QT for heart rate induced changes.
Conclusions
Neither a SSCF from exercise, Bazett’s or Fridericia’s correction factors, adequately corrected the QT interval after the administration of a sympathomimetic agonist drug to increase heart rate in healthy volunteers demonstrating the potential need for QT/RR correction factors to be tailored for each drug studied.
DOI: 10.1111/j.1365-2125.2006.02763.x
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