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