title: Distinction between myocardial ischemia and postural changes in continuous ECG monitoring based on ST-segment amplitude and vector orientation--preliminary results.
abstract: BACKGROUND
  Myocardial ischemia, commonly defined as ST-segment elevation or depression on the electrocardiogram (ECG), is plagued by a large number of false positive events.
  
  
  OBJECTIVE
  To present a new method that attempts to distinguish between 'highly probable ischemia' and positional changes.
  
  
  METHODS
  Continuous three-lead orthogonal ECG monitoring was performed in three groups of subjects: 16 healthy volunteers undergoing a body position change protocol, 22 patients undergoing percutaneous transluminal coronary angioplasty (PTCA) and 17 patients with acute coronary syndromes (ACS). For each event (ischemic or postural), the change in ST-segment amplitude was calculated, as well as the angle between the ST-segment vector of the reference beat and the beats demonstrating ST-segment elevation or depression. Angles and ST-segment amplitude changes from well-documented ischemic events obtained from the PTCA patients and from the healthy volunteers in six different body positions were compared.
  
  
  RESULTS
  Using both ST-segment amplitude and vector angle changes, ischemic events could be detected and differentiated from a postural change with a sensitivity of 91% and a specificity of 96%. Finally, the approach was blindly applied to continuous ECG recordings of ACS patients. The method allowed the classification of 37% of all ST-segment changes detected as highly probable ischemic events as opposed to only 7% using the standard 100 microV threshold.
  
  
  CONCLUSIONS
  The current approach showed that highly probable ischemic events could be better distinguished from positional changes with objective criteria using ST-segment amplitude and vector orientation.
authors.affiliation: Research Centre, Université de Montréal, Montréal, Canada. pharandc@crhsc.umontreal.ca
authors.forename: Chantal
authors.initials: C
authors.lastname: Pharand
authors.forename: James B
authors.initials: JB
authors.lastname: Nasmith
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Rajaonah
authors.forename: Bruno
authors.initials: B
authors.lastname: Dubé
authors.forename: A Robert
authors.initials: AR
authors.lastname: LeBlanc
mesh_terms: D000328:Adult; D000368:Aged; D015906:Angioplasty, Balloon, Coronary; D003937:Diagnosis, Differential; D015716:Electrocardiography, Ambulatory; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000175:diagnosis / Q000503:physiopathology / Q000628:therapy; D017202:Myocardial Ischemia / Q000175:diagnosis* / Q000503:physiopathology / Q000628:therapy; D011187:Posture / Q000502:physiology; D011237:Predictive Value of Tests; D012016:Reference Values; D013577:Syndrome; D014672:Vectorcardiography