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Time interval (ms) from beginning of the QRS complex to the end of the T wave.
Represents the time taken to depolarize and repolarize the ventricles (ventricular systole).
Measured from the beginning of the QRS to the end of the T wave (use lead with large T wave and distinct termination (eg. II & V2))
Length of the QT interval strongly correlated with risk of life threatening ventricular arrhythmias
Long QT intervals can cause unstable form of PVT called torsade de pointes.
Short QT interval is also arrhythmogenic and can cause short QT syndrome.
Long QT syndrome occurs when a long QT interval causes ventricular arrhythmia
QT is inversely related to heart rate
As heart rate goes up, the QT interval shortens
As heart rate comes down, the QT interval lengthens
QTc adjusts the QT interval for the heart rate
Normal QTc for HR 60-100 = 300-440 ms
Prolonged QTc = > 450 ms (caution when 500 ms)
Short QTx = < 300 ms
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