title: Intra-individual ECG changes over 25 years: How long can elective ECGs be used as reference for acute ischemia detection?
abstract: BACKGROUND
  The guidelines advocate, in patients with chest pain, comparison of the acute ECG with a previously made, non-ischemic ECG that serves as a reference, to corroborate the working diagnosis of acute coronary syndrome (ACS). Our approach of this serial comparison is to compute the differences between the ST vectors at the J point and 60 ms thereafter (∆ST(J+0), ∆ST(J+60)) and between the ventricular gradient (VG) vectors (∆VG). In the current study, we investigate if reference ECGs remain valid in time.
  
  
  METHODS
  We studied 6 elective non-ischemic ECGs (ECG0, ECG1, …, ECG5), 5 years apart, in 88 patients. Within each patient, serial comparisons were done 1) between all successive ECGs, and 2) between each of ECG1, ECG2, …, ECG5 and ECG0, computing, in addition to ∆ST(J+0), ∆ST(J+60) and ∆VG, the difference in heart rates, ∆HR. Additionally, relevant clinical events and the diagnoses associated with each ECG were collected. Linear regression was used to assess trends in ∆ST(J+0), ∆ST(J+60) and ∆VG; multiple linear regression was used to assess the influence of the clinical events and diagnoses on ∆ST(J+0), ∆ST(J+60) and ∆VG.
  
  
  RESULTS
  There were no trends in the differences between successive ECGs. Positive trends were seen with increasing time lapses between ECGs: ∆ST(J+0), ∆ST(J+60) and ∆VG increased per year by 0.65 μV, 1.45 μV and 3.69 mV∙ms, respectively. Extrapolation to a time lapse of 0 yielded 50.92 μV, 36.63 μV and 20.91 mV∙ms for the short-term reproducibility of ∆ST(J+0), ∆ST(J+60) and ∆VG, respectively. Multiple linear regression revealed that clinical variables could explain only 10%, 17% and 13% of the variability in ∆ST(J+0), ∆ST(J+60) and ∆VG, respectively.
  
  
  CONCLUSIONS
  With a view on ischemia detection thresholds in the order of magnitude of 58 μV for ∆ST and 26 mV·ms for ∆VG, our study suggests that it is important to have a recent ECG available for the detection of myocardial ischemia, as an "aged" ECG may have lost its validity as a reference.
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Marjolein C
authors.initials: MC
authors.lastname: De Jongh
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: C Cato
authors.initials: CC
authors.lastname: Ter Haar
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Sumche
authors.initials: S
authors.lastname: Man
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Roderick W
authors.initials: RW
authors.lastname: Treskes
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Arie C
authors.initials: AC
authors.lastname: Maan
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands.
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Schalij
authors.affiliation: Cardiology Department, Leiden University Medical Center, Leiden, The Netherlands. Electronic address: c.a.swenne@lumc.nl.
authors.forename: Cees A
authors.initials: CA
authors.lastname: Swenne
mesh_terms: D000208:Acute Disease; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000175:diagnosis* / Q000503:physiopathology*; D009426:Netherlands / Q000453:epidemiology; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: Acute coronary syndrome; Ischemia; Serial ECG analysis