Measuring Electrocardiographic Parameters
All patients underwent a 12-lead resting ECG using a 25mm/second paper
speed and standardised at 0.1mV/mm. The patient’s heart rhythm was
analysed by a cardiology registrar or consultant. Heart rate (HR), PR
and QRS intervals were calculated automatically by the ECG apparatus.
The QT interval was measured from multiple leads (chest leads V3-V6 and
lead II) and the median QT was calculated. Due to the discrepancies in
formulae used for correcting QT intervals; all four commonly used
formulae (Bazett, Fredericia, Framingham and Hodges) were included. The
QT intervals were plotted on a QT nomogram (a plot of uncorrected QT
interval against heart rate) to predict arrhythmogenic risk (Chan &
Isbister et al., 2007).