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Evaluation of a QT nomogram for risk assessment after antidepressant overdose
Author(s) -
Waring W. Stephen,
Graham Ann,
Gray Julie,
Wilson Allen D.,
Howell Catherine,
Bateman D. Nicholas
Publication year - 2010
Publication title -
british journal of clinical pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.216
H-Index - 146
eISSN - 1365-2125
pISSN - 0306-5251
DOI - 10.1111/j.1365-2125.2010.03728.x
Subject(s) - torsades de pointes , nomogram , mirtazapine , medicine , qt interval , venlafaxine , antidepressant , anesthesia , citalopram , drug overdose , emergency medicine , poison control , hippocampus
WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Overdose with citalopram is associated with QT prolongation and torsades de pointes, whereas this arrhythmia has not been reported after venlafaxine or mirtazapine overdose. • Uncertainty exists concerning the best means of identifying poisoned patients at greatest risk of arrhythmia, and a nomogram comparing QT and heart rate has recently been proposed based on published cases of torsades de pointes. • Few data are available concerning the performance of the nomogram in patients that present to hospital after antidepressant overdose. WHAT THIS STUDY ADDS • After antidepressant overdose patients had a broad range of heart rate and QT values, which were below the nomogram in 98% of cases (95% confidence interval 96, 99%). • Citalopram overdose was associated with a higher proportion of patients with QT values above the nomogram than venlafaxine and mirtazapine overdose, especially in those who had low heart rates. • The nomogram allowed discrimination between the different antidepressant agents and may have a role in predicting arrhythmia in clinical practice. AIMS A QT‐heart rate nomogram has recently been proposed as a means of identifying patients at risk of torsades de pointes after antidepressant overdose, based on published cases of drug‐induced torsades de pointes. The present study sought to examine the performance of the nomogram in patients who ingest an antidepressant overdose but do not develop arrhythmia. METHODS A retrospective case control study of patients presenting to hospital after overdose of citalopram, mirtazapine and venlafaxine was carried out. The primary outcome variable was QT higher than the nomogram, and was compared with occurrence of QT c (QT corrected by Bazett's formula) greater than ≥440 ms and QT c ≥500 ms, with comparison between drugs. Data are expressed as proportions in each group with 95% confidence intervals. RESULTS There were 858 electrocardiograms from 541 patients. QT was higher than the nomogram in 2.4% (1.4, 4.1%), whereas QT c was ≥440 ms in 23.1% (95% CI 19.8, 26.8%), and QT c was ≥500 ms in 1.1% (0.5, 2.5%). Citalopram overdose was more likely to be associated with QT higher than the nomogram compared with the other agents (difference 7.0%, 95% CI 2.9, 11.9%, P = 0.001) and more likely to be associated with QT c ≥440 ms (difference = 11.0%, 95% CI 2.6, 19.0%, P = 0.013). CONCLUSIONS The QT nomogram was associated with a lower false positive rate than widely accepted QT c criteria, and allowed detection of different effects of individual drugs. The nomogram offers potential advantages over QT c criteria and merits further investigation in a clinical setting.