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J Electrocardiol. 2014 Mar-Apr;47(2):155-7. doi: 10.1016/j.jelectrocard.2013.11.004. Epub 2013 Nov 27.

Drug-induced QT prolongation when QT interval is measured in each of the 12 ECG leads in men and women in a thorough QT study.

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Quintiles Cardiac Safety Services, Mumbai, India. Electronic address:
Quintiles Cardiac Safety Services, Mumbai, India.


Lead II is commonly used to study drug-induced QT prolongation. Whether other ECG leads too show comparable QT prolongation is not known. We studied moxifloxacin-induced QT prolongation in a thorough QT study in healthy subjects (54 males, 43 females). Placebo-subtracted change from baseline in QTc corrected by Fridericia's method (ΔΔQTcF) at 1, 1.5, 2 and 4 hours after moxifloxacin was studied in all 12 leads. Unacceptably wide 90% confidence interval (CI) for ΔΔQTcF was seen in three leads; these leads also had maximum ECGs with flat T waves (60% in aVL, 45% in lead III and 42% in V1). After excluding ECGs with flat T waves, 90% lower CI of ΔΔQTcF was ≥ 5 ms in all leads except leads III, aVL and V1 in men. The 90% lower CI exceeded 5 ms in these leads in women despite wide 90% CIs because of greater mean ΔΔQTcF. Leads III, aVL and V1 should be avoided when measuring QT interval in thorough QT studies.


Assay sensitivity; Cardiac repolarization; Gender differences; Pharmacodynamics

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