QT-interval prolongation

Some antidepressants can prolong the QT interval, which can lead to life-threatening arrhythmias (torsades de pointes) and sudden cardiac death. To determine whether an antidepressant is likely to prolong the QT interval, refer to Drugs highly associated with QT-interval prolongation and torsades de pointes and, for more detail, the CredibleMeds website (registration required).

Perform a baseline electrocardiogram (ECG) before starting treatment with an antidepressant that can prolong the QT interval (eg citalopram, escitalopram, a tricyclic antidepressant [TCA])¹. Also perform a baseline ECG before prescribing any antidepressant if the patient has risk factors for developing a prolonged QT interval, such as²:

• concurrent therapy with a drug that can prolong the QT interval¹
• a history of syncope
• congenital disposition to QT prolongation (eg congenital long-QT syndrome)
• structural heart disease (eg heart failure, coronary heart disease)
• significant bradycardia
• hypothyroidism
• kidney failure
• electrolyte abnormalities, particularly hypokalaemia, hypomagnesaemia or hypocalcaemia
• family history of sudden cardiac death or long‐QT syndrome.

For information on assessing QTc interval, see here.

If a patient has a prolonged QT interval or risk factors for developing a prolonged QT interval:

• avoid using an antidepressant with a risk of QT-interval prolongation (eg citalopram, escitalopram, a TCA)¹
• address modifiable risk factors, including:
  • electrolyte abnormalities—see Hypokalaemia, Hypomagnesaemia and Hypocalcaemia
  • medical conditions (eg hypothyroidism, heart failure)
  • bradycardia
  • concurrent use of other drugs that prolong the QT interval¹—if possible, reduce the dose or stop the drug
  • suspected congenital long-QT syndrome—refer the patient to a cardiac electrophysiologist
• regularly perform ECGs (particularly after increasing the antidepressant dose, or starting or stopping an interacting drug) and assess electrolytes; consider cardiologist review. This is only required in patients with QT-interval prolongation, not those with risk factors.

If a patient develops torsades de pointes, see here for advice.