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J Electrocardiol. 2011 Mar-Apr;44(2):96-104. doi: 10.1016/j.jelectrocard.2010.11.010. Epub 2011 Jan 15.

Comparison of 5 methods of QT interval measurements on electrocardiograms from a thorough QT/QTc study: effect on assay sensitivity and categorical outliers.

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  • 1Research Section, Quintiles Cardiac Safety Services, Mumbai, India.



We studied moxifloxacin-induced QT prolongation and proportion of categorical QTc outliers when 5 methods of QT measurement were used to analyze electrocardiograms (ECGs) from a thorough QT study.


QT interval was measured by the threshold, tangent, superimposed median beat, automated global median beat, and longest QT methods in a central ECG laboratory in 2730 digital ECGs from 39 subjects during placebo and moxifloxacin treatment.


All 5 methods were able to demonstrate statistically significant moxifloxacin-induced QTcF prolongation. However, lower bound of 95% 1-sided confidence interval of QTcF prolongation did not exceed 5 milliseconds with the longest QT method. More QTcF outliers were observed with the longest QT and tangent methods, whereas the other 3 methods were comparable. QTcF values greater than 500 milliseconds were observed only with moxifloxacin by the tangent method, and with moxifloxacin and placebo by the longest QT method.


The method of QT measurement must be considered when interpreting individual thorough QT/QTc studies.

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