title: ST depression in lead aVL differentiates inferior ST-elevation myocardial infarction from pericarditis.
abstract: BACKGROUND
  ST-segment elevation (STE) due to inferior STE myocardial infarction (STEMI) may be misdiagnosed as pericarditis. Conversely, this less life-threatening etiology of ST elevation may be confused for inferior STEMI. We sought to determine if the presence of any ST-segment depression in lead aVL would differentiate inferior STEMI from pericarditis.
  
  
  METHODS
  Retrospective study of 3 populations. Cohort 1 included patients coded as inferior STEMI, cohort 2 included patients with a discharge diagnosis of pericarditis who presented with chest pain and at least 0.5 mm of ST elevation in at least 1 inferior lead. We analyzed the presenting electrocardiogram in both populations, with careful assessment of leads II, III, aVF, and aVL. In addition, we retrospectively studied a third cohort of patients with subtle inferior STEMI (<1-mm STE with occluded artery on catheterization) and assessed the sensitivity of ST depression in lead aVL for this group.
  
  
  RESULTS
  Of 154 inferior STEMI patients, 154 had some amount of ST depression in lead aVL (100%; confidence interval, 98%-100%). Of the 49 electrocardiograms in the pericarditis group, all 49 had some inferior STE but none had any ST-segment depression in lead aVL (specificity, 100%; confidence interval, 91%-100%). In the third cohort, there were 272 inferior MIs with coronary occlusion, of which 54 were "subtle." Of these, 49 had some ST depression in lead aVL.
  
  
  CONCLUSIONS
  When there is inferior ST-segment elevation, the presence of any ST depression in lead aVL is highly sensitive for coronary occlusion in inferior myocardial infarction and very specific for differentiating inferior myocardial infarction from pericarditis.
authors.affiliation: Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, MN. Electronic address: Johanna.bischof@gmail.com.
authors.forename: Johanna E
authors.initials: JE
authors.lastname: Bischof
authors.affiliation: Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, MN.
authors.forename: Christine
authors.initials: C
authors.lastname: Worrall
authors.affiliation: Department of Emergency Medicine, Hennepin County Medical Center, Minneapolis, MN. Electronic address: rpetethompson@gmail.com.
authors.forename: Peter
authors.initials: P
authors.lastname: Thompson
authors.affiliation: Department of Cardiology, Defense Central Hospital Gomez Ulla, University of Alcala, Madrid, Spain. Electronic address: docalcala@hotmail.com.
authors.forename: David
authors.initials: D
authors.lastname: Marti
authors.affiliation: Department of Emergency Medicine, Hennepin County Medical Center, University of Minnesota, Minneapolis, MN. Electronic address: smith253@umn.edu.
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Smith
mesh_terms: D003937:Diagnosis, Differential; D004562:Electrocardiography; D005260:Female; D006801:Humans; D008297:Male; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000503:physiopathology; D010493:Pericarditis / Q000175:diagnosis* / Q000503:physiopathology; D012189:Retrospective Studies; D012680:Sensitivity and Specificity