title: Significance of lead strength during exercise testing.
abstract: BACKGROUND
  The aim of the study was to evaluate the contribution of relative lead strengths to exercise-induced ECG changes (ST depression) to predict the degree of myocardial ischemia as compared to the angiograms. This was accomplished by comparing the magnitude of ST depression to the ST/R ratio. Studies have shown that the diagnostic strength of a lead is directly related to the R wave amplitude and that sensitivity is significantly improved.
  
  
  METHODS
  Three hundred patients, who underwent treadmill exercise testing and coronary angiography revealing significant coronary narrowing (> or = 70% luminal diameter narrowing), were studied, along with 150 patients clear of significant coronary artery disease (<70% luminar diameter narrowing). Our goal was to determine the correlation between the relative lead strengths, using a constructed ST/R ratio, to exercise induced ECG changes (ST depression) to predict the presence of myocardial ischemia as compared to angiographic findings. Using a cutoff of 0.1 for the ST/R ratio, our data were compared to the sensitivity and specificity of 1.0 mm ST depression.
  
  
  RESULTS
  Overall sensitivity was improved for the ST/R ratio (84% vs 78%), while specificity was slightly decreased (81% vs 92%) in comparison to standard ST depression. When differentiating between R wave amplitudes, those with R wave < or = 10 mm showed significantly improved sensitivity (88% vs 54%) and a minor decrease in specificity (90% vs 92%). In those with R wave > or = 20 mm, the sensitivity of ST depression was higher (88% vs 71%) but the ST/R ratio was much more specific (88% vs 46%). No significant difference was observed when differentiating between male and female patients.
  
  
  CONCLUSIONS
  We found that the correction of ST depression for R wave amplitude results in improved sensitivity in patients with low R waves and specificity in patients with very tall R waves (R > or = 20 mm).
authors.affiliation: Long Beach Memorial Heart Institute, Long Beach, CA 90801, USA.
authors.forename: George
authors.initials: G
authors.lastname: Polizos
authors.forename: Myrvin H
authors.initials: MH
authors.lastname: Ellestad
mesh_terms: D017023:Coronary Angiography; D004562:Electrocardiography; D004566:Electrodes; D005080:Exercise Test / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000175:diagnosis*; D012680:Sensitivity and Specificity; D012737:Sex Factors