Aetiology and risk factors

In individual cases of torsades de pointes there are often multiple risk factors present (1,2):

• electrolyte disturbances (in particular, hypokalaemia, hypomagnesaemia and more rarely hypocalcaemia). Consider the risk of electrolyte disturbance if the patient has gastrointestinal upset
• bradycardia
• concomitant use of more than one drug that may prolong the QT interval for example (and not an exhaustive list) (1,2):
  • procainamide
  • quinidine
  • citalopram
  • ondansetron
  • quinine
  • amiodarone
  • methadone
• Congenital long QT syndrome.
• cardiac disease (of multiple origins, including congestive heart failure, ventricular hypertrophy, myocardial infarction, recent conversion from atrial fibrillation).
• impaired hepatic/renal function (due to effects on drug metabolism/excretion).
• thyroid disease (more common with hypothyroidism and usually normalises with treatment)
• female sex.
• age over 65 years
• hypothermia

Reference:

1. Current Problems in Pharmacovigilance (2006);31:1-12.
2. NHS Specialist Pharmacy Service (January 2020). What issues should be considered regarding drug-induced QT prolongation?