QT Interval

QT interval is measured from the beginning of the QRS complex to the end of the T wave on the ECG and represents the period from the onset of depolarisation to the completion of repolarisation of the ventricular myocardiumQTc interval of 450 ms ( men ) and 460 ms

( women ) are generally accepted as upper limits of normal

Recognized risk factor for the occurrence of cardiac arrhythmias○ VT /TdP○ syncope○ sudden death Particularly torsades de pointes ( TdP )○ polymorphic ventricular tachyarrhythmia○ on ECG → continuous twisting of the vector of the QRS complex around isolelectric baseline○ Marked feature of TdP is pronounced prolongation of the QT interval in the supraventricular beat preceding the arrhythmia○ TdP can degenerate into ventricular fibrillation leading to sudden death Qt interval varies greatly and is affected by age , sex , sympathetic tone and diurnal pattern The magnitude of the ↑↑ in QT interval from baseline is also helpful in evaluating the risk.

QT interval is from the beginning of the QRS complex to the end of the T wave- so it represents the complete ventricular depolarisation and repolarisation phase QT prolongation usually happens when there is a delay between the onset...