title: Hypokalemia in women and methadone therapy are the strongest non-cardiologic factors associated with QT prolongation in an emergency department setting.
abstract: Our primary objective was to determine the adjusted quantitative associations of clinical predictors with QT prolongation, a defining cause of Torsades de Pointes (TdP).
  
  
  
  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.
  
  
  
  1010 patients were included. The strongest predictors of QTc and their coefficients were: antidysrhythmic (26.1ms, 95% CI 15.6-36.6) and methadone (43.6ms, 95% CI 28.1-59.2) therapies, and genetic long QT syndrome diagnosis (32.6ms, 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 3.9mmol/L, QTc increased by 43.0ms (95% CI 26.2-59.7) and 29.5ms (95% CI 19.1-40.0) for every 1mmol/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%.
  
  
  
  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.
authors.affiliation: Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA. Electronic address: kmarill@partners.org.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Marill
authors.affiliation: Department of Emergency Medicine, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA.
authors.forename: Emily S
authors.initials: ES
authors.lastname: Miller
mesh_terms: D000368:Aged; D004562:Electrocardiography; D004636:Emergency Service, Hospital; D005260:Female; D006760:Hospitalization; D006801:Humans; D007008:Hypokalemia / Q000150:complications*; D008133:Long QT Syndrome / Q000209:etiology* / Q000401:mortality; D008691:Methadone / Q000009:adverse effects*; D008875:Middle Aged; D009294:Narcotics / Q000009:adverse effects*; D012189:Retrospective Studies; D012307:Risk Factors; D016171:Torsades de Pointes / Q000209:etiology* / Q000401:mortality
chemical_list: D009294:Narcotics; D008691:Methadone
keywords: Cohort studies; Hypokalemia; Long QT syndrome; Methadone; Torsades de pointes