Medical toxicologists' practice patterns regarding drug-induced QT prolongation in overdose patients: a survey in the United States of America, Europe, and Asia Pacific region

Abstract

Objective: To describe practice patterns of medical toxicologists in the United States of America (USA), Europe, and Asia Pacific Region regarding management of drug induced QT prolongation and torsades de pointes in overdose.

Methods: A survey was developed to assess current practice patterns and consistency with guidelines published by the American Heart Association (AHA), American College of Cardiology (ACC), and European Society of Cardiology (ESC). It was reviewed by our department research committee and the American College of Medical Toxicology (ACMT). The ACMT, European Association of Poisons Centres and Clinical Toxicologists, and Asia Pacific Association of Medical Toxicology electronically disseminated the survey to their physician members in the USA, Europe and Asia Pacific Region.

Results: The overall response rate was 37% (229/617) (36% USA; 32% Europe; 52% Asia Pacific Region). Twelve toxicologists from Asia Pacific Region and Europe used the QT nomogram (Australia-5, New Zealand-1, United Kingdom-1) or QT alone (France-1, Russia-1, Romania-1, Germany-1, Philippines-1), in lieu of the corrected QT (QTc) to determine risks of developing torsades de pointes. Because only those who used QTc could proceed through the remainder of the survey, only 217 could do so. Approximately half of the respondents (52%) did not calculate QTc manually and based decisions on the electrocardiogram machines automated measurement. For those who corrected the QT interval themselves, the most common formula used was Bazett's (40%). There is great variation in the QTc value considered prolonged. Most responders considered QTc greater than 450 ms in men (28%) and 460 ms in women (25%) to be prolonged. Interestingly, approximately 15% of participants did not consider the QTc prolonged until it exceeded 500 ms in both men and women. Given an overdose scenario of a male patient with a QTc of 560 ms, heart rate of 90 beats/minute, 59% would not recommend administering intravenous magnesium sulfate. Forty-five percent and 36% believed magnesium could shorten QTc and prevent torsades de pointes, respectively. In addition, almost 90% believed administering 1-2 boluses of intravenous magnesium is safe, even when serum magnesium is not available. In regards to cardiac pacing of patients with QT prolongation and torsades de pointes, only 38% of the participating toxicologists' responses agreed with AHA/ACC/ESC recommendations. Furthermore, 21% would not pace a patient who developed torsades de pointes regardless of the scenario.

Discussion and conclusions: The results indicate that medical toxicologists have considerable heterogeneity in terms of management practices for overdose patients with QT prolongation and torsades de pointes. Medical toxicologists may benefit from developing evidence-based consensus guidelines for the management of this relatively common finding in overdose of QT-prolonging drugs.

Keywords: Long QT; Management; Poisoning; QTc prolongation; Torsades de pointes; Treatment.