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    Corrected QT Interval (QTc)

    Corrects the QT interval for heart rate extremes.


    Note: uses Bazett's formula, which is the most widely used, but has been shown to overestimate prolonged QT.

    When to Use
    Why Use
    • Patients with syncope.
    • Patients receiving multiple QT-prolonging medicines.
    • A prolonged QT interval is associated with an increased risk of torsade de pointes.
    • The QT shortens at faster heart rates; this formula corrects the QT to the QT at a heart rate of 60.
    • The QT lengthens at slower heart rates; this formula corrects the QT to the QT at a heart rate of 60.


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    Next Steps
    Creator Insights


    Consider common etiologies for prolonged QT interval, including:

    • Electrolyte abnormalities.
    • Intrinsic cardiac causes.
    • Central causes.
    • Medications.

    See also Facts & Figures.


    Corrected QT (QTc) = Bazett's Formula = QT Interval / √ (RR interval)
    RR interval = 60/HR

    Facts & Figures

    Normal QTc ≤ 440 msec. A longer QTc puts the patient at increased risk for torsade de pointes.

    Some causes of prolonged QT:

    • Electrolyte abnormalities.
      • Hypocalcemia.
      • Hypokalemia.
      • Hypomagnesemia.
    • Intrinsic cardiac causes.
      • Myocardial ischemia.
      • After cardiac arrest.
      • CAD.
      • Cardiomyopathy.
      • Severe bradycardia, high-grade AV block.
      • Congenital long QT syndrome.
    • Central causes.
      • Raised intracranial pressure.
      • Autonomic dysfunction.
      • Hypothyroid.
      • Hypothermia.
    • Medications
      • Anti-arrhythmics.
      • Psychotropic drugs.
      • Other drugs.
    Dr. Henry Cuthbert Bazett

    About the Creator

    Henry Cuthbert Bazett, MD, (d. 1950) was the head of the Department of Physiology at the University of Pennsylvania and was a leader of the American Society of Physiology. He served in the British Medical Corps in World War I. Dr. Bazett is best known for his work with electrocardiogram interpretation and contributed greatly to the study of circulation in humans by using invasive catheterization.

    To view Dr. Henry Cuthbert Bazett's publications, visit PubMed

    About the Creator
    Dr. Henry Cuthbert Bazett