avoid prescribing drugs known to cause prolonged QTc to patients at high risk of, or known to have prolonged QTc!
patients are particularly at risk if they also have bradycardia
introduction
the QT interval on the ECG is measured from the start of QRS complex to end of the T wave
QTc refers to a QT interval “corrected” for the effect of differing heart rate to give a QT value as if the heart rate is 60bpm
prolonged QTc represents delayed repolarisation & predisposes to early after-depolarisations, re-entrant tachycardias, especially potentially fatal torsade de pointes VT which is most likely if bradycardia is present too.
calculating QTc
if rate 60-100bpm, then QT should be less than half the RR interval