title: Time course of ECG depolarization and repolarization changes during ischemia in PTCA recordings.
abstract: OBJECTIVE
  In this work we studied the temporal evolution of changes in the electrocardiogram (ECG) as a consequence of the induced ischemia during prolonged coronary angioplasty, comparing the time course of indexes reflecting depolarization and those reflecting repolarization.
  
  
  METHODS
  We considered both local (measured at specific points of the ECG) and global (obtained from the Karhunen-Loève transform) indexes. In particular, the evolution of Q, R and S wave amplitudes during ischemia was analyzed with respect to classical indexes such as ST level. As a measurement of sensitivity we used an Ischemic Changes Sensor (ICS), which reflects the capacity of an index to detect changes in the ECG.
  
  
  RESULTS
  The results showed that, in leads with low-amplitude ST-T complexes, the S wave amplitude was more sensitive in detecting ischemia than was the commonly used index ST60. It was found that in such leads the S wave amplitude initially exhibited a delayed response to ischemia when compared to ST60, but its performance was better from the second minute of occlusion. The global indexes describing the ST-T complex were, in terms of the ICS, superior to the S wave amplitude for ischemia detection.
  
  
  CONCLUSIONS
  Ischemic ECG changes occur both at repolarization and depolarization, with alterations in the depolarization period appearing later in time. Local indexes are less sensitive to ischemia than global ones.
authors.affiliation: Department of Electronic Engineering and Communications, C. P. S., María de Luna 3, 50015 Zaragoza, Spain. epueyo@unizar.es
authors.forename: E
authors.initials: E
authors.lastname: Pueyo
authors.forename: J
authors.initials: J
authors.lastname: García
authors.forename: G
authors.initials: G
authors.lastname: Wagner
authors.forename: R
authors.initials: R
authors.lastname: Bailón
authors.forename: L
authors.initials: L
authors.lastname: Sörnmo
authors.forename: P
authors.initials: P
authors.lastname: Laguna
mesh_terms: D000200:Action Potentials / Q000502:physiology; D015906:Angioplasty, Balloon, Coronary; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008991:Monitoring, Physiologic; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000503:physiopathology* / Q000628:therapy*; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors