Corrected QT Interval - MedSchool
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The QT interval shortens with rapid heart rates and lengthens at slower heart rates, as a compensatory mechanism. In order to truly estimate risk of ventricular arrhythmia it is important to correct for the heart rate, i.e. estimating what the QT interval would be at 60 beats per minute.

Adjust the QT interval according the to heart rate using the Bazett, Fridericia or Framingham method. The Bazett formula is the most commonly used, and is validated for heart rates between 60-100bpm. In the presence of tachycardia or bradycardia, one of the other two formulae should be used.
QT Interval
Heart Rate
RR Interval =
60 Heart Rate

QTc =
QT √RR Interval

QTc =
QT RR 1/3

QTc = QT + 0.154(1000 - RR Interval)