Everything about Qt Interval totally explained
In medicine, specifically
cardiology, the
QT interval is a measure of the time between the start of the
Q wave and the end of the
T wave in the heart's
electrical cycle. The QT interval is dependent on the
heart rate in an obvious way (the faster the heart rate, the shorter the QT interval) and has to be adjusted to aid interpretation.
The standard clinical correction is to use
Bazett's formula, named after
physiologist Henry Cuthbert Bazett, calculating the heartrate-corrected QT interval
QTc.
The formula is as follows:
.
There are several other methods, but a regression based approach is the most accurate according to the current knowledge. An example of the regression-based approach is that developed by Sagie et al., as follows:
.
Normal values for the QT interval are between 0.30 and 0.44 (0.45 for women) seconds.
QT interval can be measured by different methods such as the threshold method in which the end of the T wave is determined by the point at which the component of the T wave merges with the isoelectric baseline or the tangent method in which the end of the T wave is determined by the intersection of a line extrapolated from the isoelectric baseline and the tangent line which touches the terminal part of the T wave at the point of maximium downslope.
Abnormal intervals
If abnormally prolonged or shortened, there's a risk of developing
ventricular arrhythmias.
Genetic causes
An abnormal prolonged QT interval could be due to
Long QT syndrome, whereas an abnormal shortened QT interval could be due to
Short QT syndrome.
Due to adverse drug reactions
Prolongation of the QT interval may be due to an
adverse drug reaction. Many drugs such as
haloperidol can prolong the QT interval.
Further Information
Get more info on 'Qt Interval'.
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