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Long QT Syndrome

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Other Names



Clinical Features

  • Episodes of syncope and asyncope may occur, possibly accompanied by seizures
  • May be asymptomatic
  • Patients with LQTS type 1 have symptoms with exercise and type 2 have symptoms with emotion triggers

Differential Diagnosis

Risk Factors

  • Most cases in the general population are acquired but in the case of athletes, the main risk factor is genetics
  • 17 known genetic causes of Long QT syndrome (as of 2019), the specific etiologies are broad and involve ion channel defects
  • Acquired long QT is more common in the general population and may co-exist with congenital long QT syndrome in the athlete population
    • Certain medications can prolong the QT interval as well as hypokalemia, hypomagnesemia and hypothermia.


  • ECG evaluation is the first step to assessing long QT syndrome
    • The QT interval is calculated into the QTc (to adjust for heart rate) with one of several formulas, of which Bazzet's is the most common
    • A normal QTc is <440ms in men and <460ms in women but the upper limit of normal can be up to 470ms or 480ms.
  • The Schwartz criteria exists to thoroughly assess Long QT syndrome.
    • QTc greater than 480ms = 3 points
    • QTc 460 to 479mc = 2 points
    • QTc 450 to 459 (male) = 1 point
    • QTc greater than 480ms after 4th minute of exercise = 1 point
    • Torsades de pointes = 2 points
    • T wave alternans = 1 point
    • Notched T wave in 3 leads = 1 point
    • Clinical bradycardia = 1 point
    • Syncope with stress or exertion = 2 points
    • Syncope at rest = 1 point
    • Congenital deafness = 0.5 points
    • Family members with diagnosed Long QT syndrome = 1 point
    • Unexplained sudden death under age 30 among immediate family members = 0.5 points
  • Result evaluation
    • A score of less than or equal to 1 is equal to low probability
    • A score of 2 to 3 is equal to intermediate probability
    • A score greater than 3.5 is equal to a high probability of congenital long QT syndrome.
  • Depending on the score and clinical suspicion, then genetic testing may be considered.


  • 17 types of Long QT syndrome exist
    • The first 3 types make up over 90% of cases.


  • A beta blocker is commonly prescribed to diagnosed cases of Long QT syndrome
  • Other options include sodium channel blocking drugs and for severe cases, an ICD.
  • Supplementation of potassium and magnesium is common
  • Avoiding exercise is highly debatable and is a decision best made between the patient and physician.
  • Drug induced cases are best treated with discontinuation of the offending medication.


  • Long QT syndrome can lead to torsades de pointes, a type of polymorphic ventricular tachycardia
    • This is an unstable and often pulseless rhythm which can lead to ventricular defibrillation and sudden death
    • Patients who are silent carriers and have QTc <500ms are less likely to have episodes of sudden cardiac death

See Also


Created by:
John Kiel on 13 June 2019 09:10:52
Last edited:
27 August 2019 11:38:30