QT interval

The QT interval is a measurement made on an electrocardiogram used to assess some of the electrical properties of the heart. It is calculated as the time from the start of the Q wave to the end of the T wave, and correlates with the time taken from the beginning to the end of ventricular contraction and relaxation. It is technically the duration of the aggregate ventricular myocyte action potential. An abnormally long or abnormally short QT interval is associated with an increased risk of developing abnormal heart rhythms and even sudden cardiac death. Abnormalities in the QT interval can be caused by genetic conditions such as long QT syndrome, by certain medications such as fluconazole, sotalol or pitolisant, by disturbances in the concentrations of certain salts within the blood such as hypokalaemia, or by hormonal imbalances such as hypothyroidism.