A patient taking an antipsychotic is found to have a QTc of 490ms, which of the following is the most suitable alternative to the current antipsychotic?
Haloperidol, quetiapine, risperidone, chlorpromazine and trifluoperazine have a tendency to extend the QT interval even at therapeutic doses.
Aripiprazole has little to no effect on QTc interval.
Exam Question Aug 2010Haloperidol, quetiapine, risperidone, chlorpromazine and trifluoperazine have a tendency to extend the QT interval even at therapeutic doses.
Antipsychotics (QTc interval)
All patients requiring treatment with an antipsychotic need an ECG. The most important aspect of the ECG is the QTc interval.
The QT interval is measured from the start of the Q wave to the end of the T wave. The QTc is the QT corrected for heart rate. It is calculated by using Bazett's formula which is the QT interval divided by the square root of the RR interval.
Normal and abnormal values are given in the table below. A QTc >500 represents a substantial risk of Torsades de points. 1 in 10 people with Torsades de points experience sudden death.
The following table (Abdelmawla, 2006) gives values for normal and abnormal QTc intervals in milliseconds.
| Men | Women | |
|---|---|---|
| Normal | <440 | <440 |
| Borderline | 440-450 | 440-460 |
| Prolonged | >450 | >460 |
Aripiprazole is believed to have no effect on the QTc interval. Olanzapine is suggested by the Maudsley Guidelines as an alternative.
The following table outlines the recommended action to be taken when dealing with the QTc interval (taken from the Maudsley Guidelines).
| QTc | Action to be taken |
|---|---|
| <440ms (men) <470ms (women) | No action required unless T-wave morphology |
| >440ms (men) >470ms (women) | Consider reducing dose or switching to drug of lower QTc effect, repeat ECG and refer to cardiology |
| >500ms (men and women) | Stop causative drug and then switch to drug of lower effect and refer to cardiology |
The following table summarises the effect of the most common antipsychotics on the QTc interval.
| Antipsychotic | Effect on QTc interval |
|---|---|
| Haloperidol | High |
| Pimozide | High |
| Quetiapine | Moderate |
| Chlorpromazine | Moderate |
| Zotepine | Moderate |
| Ziprasidone | Moderate |
| Amisulpride | Low |
| Clozapine | Low |
| Olanzapine | Low |
| Risperidone | Low |
| Aripiprazole | None |
| Palperidone | None |
Abdelmawla (2006) Sudden cardiac death and antipsychotics. Part 1: Risk factors and mechanisms. Advances in Psychiatric Treatment 12: 35-44
