Psychotropic medicines and QT interval prolongation — Frequently asked questions (FAQ)
1) What does this table cover?
This table summarises the clinical relevance of the QT interval, the main risk factors for QTc prolongation, reference values in men and women, and the risk profile of different antidepressants and antipsychotics.
2) Why is assessment of the QT interval clinically important?
QT interval prolongation may predispose to torsades de pointes, a potentially fatal ventricular arrhythmia. Risk increases when QTc prolongation is associated with abnormal T-wave morphology, heart disease, electrolyte disturbances or concomitant use of several medicines that prolong the QT interval.
3) What are the main risk factors for QT prolongation?
The main factors include female sex, older age, structural heart disease, recent myocardial infarction, heart failure, bradyarrhythmia, hypokalaemia, hypomagnesaemia, renal impairment, congenital long QT syndrome and concomitant use of two or more medicines with the potential to prolong the QT interval.
4) Which QTc values are considered prolonged?
As a practical reference, QTc is generally considered prolonged when it exceeds 470 ms in men and 480 ms in women, although some consensus statements use slightly lower thresholds. A QTc ≥500 ms should be regarded as a marker of increased risk of torsades de pointes and requires careful clinical assessment.
5) Which antidepressants carry a higher risk of QT prolongation?
Among antidepressants, the risk is more relevant with tricyclic antidepressants, citalopram, escitalopram and, in some settings, venlafaxine and trazodone. Risk increases with high doses, drug interactions, older age and associated cardiac or metabolic factors.
6) Which antidepressants have a lower impact on the QT interval?
Antidepressants with a lower impact on the QT interval include bupropion, agomelatine, mirtazapine, vortioxetine, reboxetine, duloxetine, paroxetine, sertraline, fluoxetine and fluvoxamine, although treatment decisions should be individualised.
7) Which antipsychotics carry a higher risk of QT prolongation?
Antipsychotics of greater concern include amisulpride, haloperidol, particularly when administered intravenously, chlorpromazine and ziprasidone. Risperidone, quetiapine, olanzapine and paliperidone may carry an intermediate risk, particularly when additional risk factors are present.
8) Which antipsychotics are generally considered to have a lower QT risk?
Antipsychotics with a lower effect on the QT interval include aripiprazole, lurasidone, brexpiprazole and cariprazine. Nevertheless, monitoring should still be considered when additional risk factors or polypharmacy are present.
9) When should an ECG be performed before starting psychotropic treatment?
A baseline ECG should be considered in patients with heart disease, a history of unexplained syncope, known long QT syndrome, older age, electrolyte disturbances, significant renal or hepatic impairment, use of multiple QT-prolonging medicines or when a higher-risk medicine is being considered.
10) What should be done if the QTc is markedly prolonged?
When QTc is markedly prolonged, particularly if ≥500 ms, medication should be reviewed, hypokalaemia and hypomagnesaemia corrected, drug interactions assessed, dose reduction or discontinuation of the suspected medicine considered, and referral to or discussion with Cardiology or Psychiatry considered according to the clinical context.
11) Does combining several psychotropic medicines increase the risk?
Yes. Combining several psychotropic medicines, or combining psychotropic medicines with other QT-prolonging drugs, may produce a cumulative risk. This risk should be assessed before prescribing, particularly in older adults, patients receiving multiple medicines and those with heart disease.
12) Who is this content intended for?
This table is intended for healthcare professionals who prescribe or monitor psychotropic medicines. Clinical decisions should take into account the individual context, comorbidities, drug interactions, psychiatric risk and the need for electrocardiographic monitoring.
