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prolonged QTc

see also:

  • 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


  • 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
  • Bazett's formula: QTc = QT / square root (RR interval)

aetiology of prolonged QTc

prolongedqtc.txt · Last modified: 2017/11/03 11:29 (external edit)