In this episode, I’ll discuss whether ICU patients benefit from daily QTc interval monitoring during antipsychotic use for delirium.
QTc prolongation is a known side effect of antipsychotic use. While the QTc itself is only a number on a sheet of paper, a prolonged QTc is often used as a surrogate marker for an increased risk of torsades. Therefore daily monitoring of the QTc interval is frequently suggested when ICU patients are started on antipsychotics.
A group of authors published in JAMA an a priori secondary analysis of a randomized trial looking at the effects of antipsychotics on QTc prolongation in ICU patients. The trial protocol randomized 566 patients 1:1:1 to intravenous haloperidol, ziprasidone, or saline placebo administered twice daily until resolution of delirium, ICU discharge, or 14 days. QTc was measured by 12-lead ECG at baseline, and the telemetry monitor was used to check QTc prior to each administration of medication. From day 1 to day 2, the median QTc changed minimally for all groups. When directly compared with placebo, neither haloperidol nor ziprasidone was associated with increased next-day QTc intervals. Only the baseline QTc and predose QTc values predicted a prolonged QTc interval before the next dose.
There were two cases of nonfatal torsades in the haloperidol group. However, both of these incidents occurred more than four days after the last administration of haloperidol. For this reason, the investigators decided the cases of torsades were not associated with haloperidol administration.
The authors concluded that there was:
In this a priori secondary analysis of a multicenter, double-blind, randomized, placebo-controlled trial, we found no evidence that antipsychotics cause clinically important QTc interval prolongation or ventricular arrhythmias beyond that of placebo when given to critically ill patients with delirium with baseline QTc less than 550 ms and few risk factors for QTc prolongation. Telemetry- and ECG-measured QTc intervals were moderately correlated, suggesting either approach can be used in most cases. Together, these results suggest that, in low-risk patients, the frequency of QTc monitoring during antipsychotic administration should be reexamined.
It is important to note that patients with a history of torsades de pointes and QT prolongation were excluded from the study, so the results can only be applied to low-risk patients. In addition, the authors found a moderate correlation between ECG-based measurements of the QTc interval and telemetry-based measurements, leading them to state that their data suggests either approach can be used to monitor QTc intervals.
The maximum daily doses of the study medications were 20 mg per day for haloperidol and 40 mg per day for ziprasidone, so higher doses might produce differing result for QTc prolongation.
While the study does appear to indicate that low risk ICU patients receiving reasonable doses of antipsychotics are not at risk of QTc prolongation, the incremental cost of checking the QTc in ICU patients in the age of electronic health records is essentially free since the information is collected and charted anyway, and it may be easier to check the QTc in all ICU patients that are receiving antipsychotics rather than trying to first figure out which are high risk vs low risk before checking the QTc.
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