Page 189 - Clinical Pearls in Cardiology

Ischemic Heart Disease 177

Fig. 12: Torsades de pointes or polymorphic ventricular tachycardia

The QT interval is measured from the onset of the QRS
complex to the point at which the T wave ends (usually
in lead II). The QT interval should be measured for three
to five consecutive beats and averaged. The QT interval
varies inversely with the heart rate. Therefore, the QT
measurement is adjusted for the heart rate, resulting in
the corrected QT interval or QTc (Fig. 13).

Fig. 13: QT interval

QT interval
QTc =
Square root of the RR interval (in seconds)