title: ECG machine QTc intervals are inaccurate in hemodialysis patients.
abstract: BACKGROUND
  Nephrologists need effective screening tools to identify hemodialysis patients at elevated risk for sudden cardiac death, the leading cause of death in this population. QTc intervals longer than 450 ms in males and 470 ms in females, measured by the gold standard tangent method (trueQTc), are prolonged and increase sudden cardiac death in healthy populations and patients with long QT syndrome.
  
  
  METHODS
  We performed a retrospective ECG and chart review of hemodialysis patients. Our first objective was to determine if machine-measured QTc intervals (macQTc) could be used to identify dialysis patients with prolonged trueQTc. Our second objective was to determine at what macQTc could prolonged trueQTc be confidently diagnosed.
  
  
  RESULTS
  macQTc differed from the trueQTc by an average of 16.54 ms, and by at least 20 ms in 46.8, 36.1, 53.6, 50.0 and 57.1% of all, short-hours daily hemodialysis, intermittent conventional hemodialysis, frequent nocturnal hemodialysis and intermittent nocturnal hemodialysis patients, respectively. The positive predictive value, negative predictive value, sensitivity and specificity of prolonged macQTc predicting prolonged trueQTc was 57.6, 92.6, 79.1 and 81.8%, respectively. Thus, macQTc is inaccurate at predicting the gold standard trueQTc in hemodialysis patients. macQTc greater than 480 ms in hemodialysis patients predicts trueQTc prolongation with a positive predictive value of 95.2%, but with a low sensitivity of 32.3%.
  
  
  CONCLUSIONS
  In hemodialysis patients, ECG macQTc intervals are insufficiently sensitive or specific to predict prolonged trueQTc intervals, unless >480 ms.
authors.affiliation: London Health Sciences Centre and Western University, London, Ont., Canada.
authors.forename: B K A
authors.initials: BK
authors.lastname: Thomson
authors.forename: B
authors.initials: B
authors.lastname: Momciu
authors.forename: S H S
authors.initials: SH
authors.lastname: Huang
authors.forename: C T
authors.initials: CT
authors.lastname: Chan
authors.forename: B
authors.initials: B
authors.lastname: Urquhart
authors.forename: A
authors.initials: A
authors.lastname: Skanes
authors.forename: A
authors.initials: A
authors.lastname: Krahn
authors.forename: G
authors.initials: G
authors.lastname: Klein
authors.forename: R M
authors.initials: RM
authors.lastname: Lindsay
mesh_terms: D000368:Aged; D003951:Diagnostic Errors; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000209:etiology*; D008297:Male; D008875:Middle Aged; D006435:Renal Dialysis; D051436:Renal Insufficiency, Chronic / Q000150:complications* / Q000175:diagnosis / Q000628:therapy*; D015203:Reproducibility of Results; D012189:Retrospective Studies; D012680:Sensitivity and Specificity