title: Prevalence and prognostic significance of long QT interval among patients with chest pain: selecting an optimum QT rate correction formula.
abstract: BACKGROUND
  Little is known about the prevalence and prognostic significance of long QT interval among patients with chest pain during the acute phase of suspected cardiovascular injury.
  
  
  OBJECTIVE
  Our aim was to investigate the prevalence and prognostic significance of long QT interval among patients presenting to the emergency department (ED) with chest pain using an optimum QT rate correction formula.
  
  
  METHODS
  We performed secondary analysis on data obtained from the IMMEDIATE AIM trial (N, 145). Data included 24-hour 12-lead Holter electrocardiographic recordings that were stored for offline computer analysis. The QT interval was measured automatically and rate corrected using seven QTc formulas including subject specific correction. The formula with the closer to zero absolute mean QTc/RR correlation was considered the most accurate.
  
  
  RESULTS
  Linear and logarithmic subject specific QT rate correction outperformed other QTc formulas and resulted in the closest to zero absolute mean QTc/RR correlations (mean±SD: 0.003±0.002 and 0.017±0.016, respectively). These two formulas produced adequate correction in 100% of study participants. Other formulas (Bazett's, Fridericia's, Framingham's, and study specific) resulted in inadequate correction in 47.6 to 95.2% of study participants. Using the optimum QTc formula, linear subject specific, the prevalence of long QTc interval was 14.5%. The QTc interval did not predict mortality or hospital admission at short and long term follow-up. Only the QT/RR slope predicted mortality at 7year follow-up (odds ratio, 2.01; 95% CI, 1.02-3.96; p<0.05).
  
  
  CONCLUSIONS
  Adequate QT rate correction can only be performed using subject specific correction. Long QT interval is not uncommon among patients presenting to the ED with chest pain.
authors.affiliation: Department of Physiological Nursing, University of California, San Francisco, CA 94143, USA. amer.hasanien@ucsf.edu
authors.forename: Amer A
authors.initials: AA
authors.lastname: Hasanien
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Drew
authors.forename: Jill
authors.initials: J
authors.lastname: Howie-Esquivel
authors.forename: Gordon
authors.initials: G
authors.lastname: Fung
authors.forename: Patricia
authors.initials: P
authors.lastname: Harris
mesh_terms: D016477:Artifacts; D002637:Chest Pain / Q000175:diagnosis* / Q000401:mortality*; D015897:Comorbidity; D003936:Diagnosis, Computer-Assisted / Q000379:methods / Q000706:statistics & numerical data*; D015716:Electrocardiography, Ambulatory / Q000706:statistics & numerical data*; D005260:Female; D006339:Heart Rate; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D015995:Prevalence; D011379:Prognosis; D015203:Reproducibility of Results; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016019:Survival Analysis; D014481:United States