QT prolongation

(Redirected from Prolonged QTc)


  • Prolonged ventricular repolarization → increased risk of ventricular arrhythmias
    • Males >440-450 ms
    • Females >500 ms
    • Rule of thumb: Normal QT interval is less than half of preceding RR interval
  • QT interval is from the beginning of the Q wave to the end of the T wave
    • Rate dependent and should become proportionately shorter with increasing heart rate

List of Drugs Causing QT Prolongation

Clinical Features

  • Most are asymptomatic
  • History may include:
  • Medication history may include QT prolonging medications

Differential Diagnosis

Syncope Causes



  • ECG
  • CBC
  • Chem 10


Acquired QT prolongation
  • ECG
    • On visual inspection, QT takes up more than half the R-R distance
    • Measure QT interval in lead II or V5-6
    • QTc = QT /√R-R

Determining Cause


Pause Dependent (precipitated by bradycardia)

Adrenergic Dependent (precipited by tachycardia)


  • Consider admission, especially for QT >500 or if symptomatic
  • May require consultation for discontinuation of QT prolonging medications
  • Avoid prescribing medications that may contribute to prolonged QT

See Also

External Links


  1. Simon HL, Behr ER. Pharmacological treatment of acquired QT prolongation and torsades de pointes. Br J Clin Pharmacol. 2016 Mar; 81(3): 420–427. doi: 10.1111/bcp.12726