More than one in 10 patients taking quetiapine or haloperidol develop severe QT prolongation, increasing their risk of arrhythmia or sudden death.
A study finding as many as one in 10 people taking common antipsychotics develop QT prolongation has prompted calls for routine ECG monitoring before and after commencement of the drugs.
Antipsychotic drugs have been known to cause QT prolongation, which can lead to potentially lethal arrhythmias. But to date, it has been unclear how common QT prolongation is in response to common antipsychotics, and how the prolongation influences the risk of ventricular arrhythmias and sudden cardiac death.
Now, a new Taiwanese retrospective cohort study, published in Heart Rhythms, reveals more than one in 10 patients taking quetiapine and haloperidol develop severe QT prolongation and are at an increased risk of ventricular arrhythmia and sudden death.
“These results suggest it would be prudent to undertake an ECG before and after commencement of an antipsychotic drug, and especially in older patients,” wrote Professor Jamie Vandenberg, deputy director of the Victor Chang Cardiac Research Institute, in an accompanying editorial.
“The risks of cardiac arrhythmias associated with the use of antipsychotics have long been known but we now finally know the scale of the problem in a real-world setting and we need to try and reduce the risk and manage people more closely.”
Researchers examined ECG and medical record data for over 11,000 adult patients prescribed either quetiapine or haloperidol.
Thirteen percent of quetiapine users and 14% of haloperidol users developed drug-related severe QT prolongation (SQTP; defined as a QTc interval greater than 500ms at follow-up or a greater than 60ms increase in QTc interval compared to baseline).
A greater proportion of quetiapine (3.8% versus 1.1%) and haloperidol (3.3% versus 1.6%) users who developed SQTP also experienced ventricular arrhythmias, but this association only remained for quetiapine after controlling for factors such as age, sex, hypertension and hypokalaemia status.
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Quetiapine users with SQTP had a 2.8-fold increase in the odds of developing a ventricular arrhythmia compared to those who did not develop SQTP, while there was no association between SQTP and arrhythmias in haloperidol users.
A greater proportion of quetiapine users with SQTP also experienced sudden cardiac death (2.3% versus 0.8%). This association remained after controlling for relevant factors: these patients had a 2.3-fold increase in the odds of sudden cardiac death compared to quetiapine users without SQTP.
There was no association between SQTP and sudden cardiac death in patients prescribed haloperidol.
Clifford TeBay, a PhD student at the Victor Chang Cardiac Research Institute and co-author of the editorial with Professor Vandenberg, warned these risks were not limited to quetiapine and haloperidol.
“It’s not only antipsychotic drugs that can cause arrhythmias,” he said.
“There is a whole range of drugs ranging from antibiotics to antihistamines that can cause heart rhythm disturbances.
“It’s vital we understand the real risk of these drugs so we can improve the safety of these drugs and monitor patients more closely to ensure no one dies from a sudden cardiac arrest unnecessarily.”
More than 300,000 Australians are prescribed at least one antipsychotic per year, and Professor Vandenberg emphasised the importance of adhering to their treatment despite the risks.
“If it is an option, one could stop a drug causing QT prolongation and try a different antipsychotic,” he said.
“But if this is not practical, one should pay particular attention to reducing other risk factors, such as the prescription of other drugs that may exacerbate prolongation, and be vigilant for hypokalaemia – a common electrolyte imbalance that can raise the risk of developing arrhythmias.”
