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Prolonged QT Interval : Mnemonics

Normal QT Interval

Duration: 0.3-0.44 s (0.46 s for women); tends to increase as the heart rate decreases

Bazett’s formula for corrected QT interval (QTc): QTc = QT/ √RR

Prolonged QT Interval

Duration: >0.44 s (men) and >0.46 s (women)

Can lead to: Polymorphic VT (Torsades de pointes)

Causes:

Mnemonic: CDEF

  1. Congenital:
    • Lange-Nielsen syndrome (Autosomal recessive, Deafness)
    • Romano-Ward syndrome (Autosomal dominant, No deafness)
  2. Drugs: Mnemonic – “Anti-ABCDEF
    • Anti-Arrhythmics (Class IA, e.g. Quinidine, Procainamide, Disopyramide and Class III, e.g. Amiodarone, Sotalol, Ibutilide)
    • Anti-Anginal (Ranolazine)
    • Anti-Allergics (Diphenhydramine)
    • Anti-Biotics (Fluoroquinolones, Macrolides, Trimethoprim)
    • Anti-Cychotics (Haloperidol, Thioridazine, Quetiapine, Risperidone)
    • Anti-Depressants (SSRIs, TCAs)
    • Anti-Emetics (Ondansetron, Metoclopramide)
    • Anti-Fungals (Azoles)
  3. Electrolytes: All decreasing (‘hypo’)
    • Hypocalcemia
    • Hypokalemia
    • Hypomagnesemia
  4. Further more:
    • Acute MI
    • Myocarditis
    • Hypothermia
    • Subarachnoid hemorrhage

Management:

Mnemonic: ABCDE

  1. Avoid etiologic drugs
  2. Beta-blockers (Propanolol or Nadalol)
  3. Cardiac Device (ICD)
  4. Electrolyte correction
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