11 Facts About QT interval

QT interval is a measurement made on an electrocardiogram used to assess some of the electrical properties of the heart.

An abnormally long or abnormally short QT interval is associated with an increased risk of developing abnormal heart rhythms and sudden cardiac death.

Abnormalities in the QT interval can be caused by genetic conditions such as long QT syndrome, by certain medications such as sotalol or pitolisant, by disturbances in the concentrations of certain salts within the blood such as hypokalaemia, or by hormonal imbalances such as hypothyroidism.

QT interval is most commonly measured in lead II for evaluation of serial ECGs, with leads I and V5 being comparable alternatives to lead II.

The accurate measurement of the QT interval is subjective because the end of the T wave is not always clearly defined and usually merges gradually with the baseline.

The 12 median beats are superimposed on each other and the QT interval is measured either from the earliest onset of the Q wave to the latest offset of the T wave or from the point of maximum convergence for the Q wave onset to the T wave offset.

Where QTcB is the QT interval corrected for heart rate, and RR is the interval from the onset of one QRS complex to the onset of the next QRS complex.

An abnormally prolonged QT interval could be due to long QT syndrome, whereas an abnormally shortened QT interval could be due to short QT syndrome.

Traditionally, the QT interval had been evaluated by having an individual human reader measure approximately nine cardiac beats per clinical timepoint.

The researchers proposed that inflammation prolonged the QTc QT interval and created arrhythmias that were associated with higher mortality rates.

Anti-hypertensive drugs increased the QTc QT interval, but were not an independent predictor of mortality.