QT prolongation

Revision as of 18:40, 1 May 2018 by Ktanner777 (talk | contribs) (Background)


  • Prolonged ventricular repolarisation → increased risk of ventricular arrythmias
  • QT interval is from the beginning of the Q wave to the end of the T wave; it is rate dependent and should become proportionately small with increasing rate rate
  • An abnormal QT is >440-450 ms (males) and >460-470 ms (females); >500 may result in torsades
  • A useful rule of thumb is that a normal QT is less than half the preceding RR interval

Clinical Features

  • Most are asymptomatic
  • History may or may not include
    • Syncope, cardiac arrest, family history of long QT or sudden death
    • Medication history should always be obtained especially so to avoid interactions and further QT prolongation.

Differential Diagnosis

Drug List


  • ECG
    • quick/imprecise measure: QT takes up more than half the R-R distance
    • Measure QT interval in lead II or V5-6
    • QTc = QT /√R-R
    • Long QT: QTc >440 (male), >460 (female)
    • >500 = real concern (may result in torsades)


Pause Dependent (precipitated by bradycardia)

Adrenergic Dependent (precipited by tachycardia)


  • Highly consider admission, especially for QT >500

See Also

External Links