What is the QT interval on electrocardiography (ECG)?

Updated: Mar 11, 2019
  • Author: Tarek Ajam, MD, MS; Chief Editor: Terrence X O'Brien, MD, MS, FACC  more...
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The QT interval measures the depolarization and repolarization  of the ventricles. QT prolongation is associated with development of ventricular arrhythmias and sudden death. [24] It is commonly caused by various medications or can be a manifestation of an underlying ion channelopathy.

The QT interval is dependent on the heart rate.  A faster heart rate leads to a shorter QT interval, whereas a slower heart rate leads to a longer QT interval. A corrected QT interval (QTc) corrects for the variations in heart rate. QTcb is the QT interval divided by the square root of the RR interval in seconds when using the Bazett formula. The normal value of for QTcb in men is 0.44 seconds or less; in women, it is 0.46 seconds or less. [25]  

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