Association between QTc prolongation and mortality in patients with suspected poisoning in the emergency department: a transnational propensity score matched cohort study

OBJECTIVES: Poisoning is a frequent cause of admission to the emergency department (ED) and may involve drugs known to prolong the QT interval. This study aims to describe the prevalence of QTc prolongation among ED patients with suspected poisoning and to calculate the absolute and relative risk of mortality or cardiac arrest associated with a prolonged QTc interval. METHODS: We performed a register-based cohort study, including all adult first-time contacts with suspected poisoning to the ED of two Swedish hospitals (January 2010–December 2014) and two Danish hospitals (March 2013–April 2014). We used propensity score matching to calculate HRs for all-cause mortality or cardiac arrest (combined endpoint) within 30 days after contact comparing patients with a prolonged QTc interval (≥450 ms men, ≥460 ms women) with patients with a QTc interval of <440 ms. RESULTS: Among all first-time contacts with suspected poisoning that had an ECG recorded within 4 hours after arrival (n=3869), QTc prolongation occurred in 6.5%. The overall mortality after a 30-day follow-up period was 0.8% (95% CI 0.6 to 1.2), with an absolute risk of mortality or cardiac arrest in patients with QTc prolongation of 3.2% (95% CI 1.4 to 6.1). A prolonged QTc interval on arrival was associated with a HR of 3.6 (95% CI 1.0 to 12.2). CONCLUSION: In the ED, a prolonged QTc interval in patients arriving with suspected poisoning seems to be associated with a threefold increased risk of 30-day all-cause mortality or cardiac arrest.