QTc-Prolongation

QTc Calculation: Put away your calipers and find EKG’s calculated value. For reference…

  • QTc = QT/RR

  • RR = square root of the difference between R waves of any two QRS complexes

Definition and Significance

  • Cut-off values may vary

  • QTc >450 milliseconds is generally considered prolonged in both males and females

  • QTc >500 milliseconds increase risk for torsades de pointes (see below)

Torsades de Pointes (TdP)

Torsades de Pointes (TdP)

The following list includes drug classes commonly associated with QT-prolongation and the most common offending agents within those classes. Not all drugs in a particular class may cause QT-prolongation and many drugs have been omitted because they are not commonly used in practice.

  • Anti-arrhythmics

    • Class I, e.g. procainamide

    • Class III, e.g. amiodarone

  • Anti-depressants, e.g.

    • SSRIs

      • Greatest risk: Citalopram/escitalopram

      • Lowest risk: Fluoxetine (Prozac) and sertraline (Zoloft)

    • Venlafaxine (Effexor)

    • Amitriptyline

  • Anti-psychotics, e.g.

    • Haloperidol

    • Quetiapine (Seroquel)

    • Ziprasidone (Geodon)

  • Antibiotics

    • Fluoroquinolones, e.g. levofloxacin, ciprofloxacin, moxifloxacin

    • Macrolides, e.g. clarithromycin, erythromycin

  • Antifungals, e.g. ketoconazole, itraconazole

  • Other

    • Anti-emetics, e.g. ondansetron

    • Triptans, e.g. sumatriptan

    • Methadone

Further Reading