Hypokalemia in women and methadone therapy are the strongest non-cardiologic factors associated with QT prolongation in an emergency department setting

Background: Our primary objective was to determine the adjusted quantitative associations of clinical predictors with QT prolongation, a defining cause of Torsades de Pointes (TdP). Methods: A retrospective cohort study was performed on consecutive emergency department patients identified by ECG acquisition date, and heart rate corrected QT (QTc) and QRS durations. QTc was modeled as a function of clinical predictors with multiple linear regression. Results: 1010 patients were included. The strongest predictors of QTc and their coefficients were: antidysrhythmic (26.1 ms, 95% CI 15.6-36.6) and methadone (43.6 ms, 95% CI 28.1-59.2) therapies, and genetic long QT syndrome diagnosis (32.6 ms, 95% CI -4.7-70.0). The association of QTc with serum potassium was approximated by a two piecewise linear function that differed by sex. For potassium below 3.9 mmol/L, QTc increased by 43.0 ms (95% CI 26.2-59.7) and 29.5 ms (95% CI 19.1-40.0) for every 1 mmol/L decrease in potassium in women and men, respectively. TdP occurred in only 4/686 (0.6%) of patients with QTc >= 500 and QRS < 120, but mortality during the visit including hospitalization was 8.0%. Conclusions: QTc duration is highly sensitive to hypokalemia, particularly in women. Methadone prolongs QTc remarkably compared to other non-cardiologic medicines. QTc > 500 with normal QRS often signifies profound illness and substantial mortality risk, though not necessarily imminent TdP. (C) 2017 Elsevier Inc. All rights reserved.