QT-interval prolongation caused by antipsychotics

For advice on monitoring for and preventing antipsychotic adverse effects, see Overview of antipsychotic adverse effects.

Seek specialist advice on preventing and managing QT-interval prolongation in a child taking an antipsychotic.

Because of the potential for QT-interval prolongation, an electrocardiogram (ECG) is recommended before starting an antipsychotic, unless therapy is expected to be short term (eg shorter than 24 hours). If it is not possible to perform an ECG before starting an antipsychotic in a patient with acute symptoms, perform an ECG as soon as practical. If the patient is at risk of developing prolonged QT interval, repeat ECG once the antipsychotic has reached steady state (usually after 3 to 5 half-lives of the drug). Risk factors for QT-interval prolongation include¹:

• age 70 years or older
• concurrent therapy with a drug that can prolong the QT interval²
• history of syncope or palpitations
• congenital disposition to QT-interval prolongation (eg congenital long-QT syndrome)
• structural heart disease (eg heart failure, coronary heart disease)
• significant bradycardia
• hypothyroidism
• electrolyte abnormalities, particularly hypokalaemia, hypomagnesaemia or hypocalcaemia
• family history of sudden cardiac death or long‐QT syndrome
• baseline QTc interval above the upper limit of normal (ie 440 milliseconds for males and 460 milliseconds for females).

For information on assessing QTc interval, see here.

If the baseline QTc interval is longer than 500 milliseconds:

• address modifiable causes, including:
  • electrolyte abnormalities—see hypokalaemia, hypomagnesaemia and hypocalcaemia
  • medical conditions (eg hypothyroidism, heart failure)
  • bradycardia
  • suspected congenital long-QT syndrome—refer the patient to a cardiac electrophysiologist
  • concurrent use of other drugs that prolong the QT interval²—if possible, reduce the dose or stop the drug
• avoid using an antipsychotic with a high risk of QT-interval prolongation (eg haloperidol, ziprasidone). Choose an antipsychotic with a low risk of QT-interval prolongation (eg aripiprazole)³. Regularly perform ECGs (particularly after increasing the antipsychotic dose, or starting or stopping an interacting drug) and assess electrolytes; consider cardiologist review.

During antipsychotic therapy, if QTc interval becomes longer than 500 milliseconds or lengthens by more than 60 milliseconds, address modifiable risk factors (as above) and:

• reduce the antipsychotic dose or switch to an antipsychotic less likely to prolong the QT interval³
• if the above measures are impossible or ineffective, continue the antipsychotic and regularly perform ECGs (particularly after increasing the antipsychotic dose, or starting or stopping an interacting drug) and assess electrolytes; consider cardiologist review.

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