title: Changes in QRS duration and R-wave amplitude in electrocardiogram leads with ST segment elevation differentiate epicardial and transmural myocardial injury.
abstract: BACKGROUND
  Acute transmural ischemia increases QRS duration and R-wave amplitude owing to depressed intramyocardial activation. Theoretically, when myocardial injury is confined to the epicardium, the intramyocardial activation is preserved without affecting QRS duration.
  
  
  OBJECTIVE
  The purpose of this study was to distinguish epicardial from transmural myocardial injury based on the analysis of the QRS complex in leads with ST segment elevation.
  
  
  METHODS
  Electrophysiological effects of epicardial injury induced by topical application (n = 7) or intrapericardial injection (n = 10) of potassium were assessed in pigs in local electrograms recorded with needles in the left ventricle and in the peripheral 12-lead electrocardiogram (ECG), respectively, and were compared with transmural injury induced by acute left anterior descending (LAD) occlusion in the same pig.
  
  
  RESULTS
  Epicardial application of 50 mM potassium induced ST segment elevation in epicardial (0.2 ± 0.06 to 0.5 ± 0.09 mV; P <.05) but not in midmyocardial local electrograms (0.1 ± 0.07 to -0.1 ± 0.09 mV). Local midmyocardial activation times were not affected by epicardial applied potassium (182 ± 5.9 vs. 183 ± 5.8 ms) but increased significantly during acute LAD occlusion (246 ± 20.9 ms; P <.01). Intrapericardial injected potassium induced ST segment elevation on average in nine of 12 ECG leads but did not change QRS duration and R-wave amplitude. Acute LAD occlusion induced ST segment elevation (five of 12 leads) associated with increased QRS duration (69 ± 1.2 to 89 ± 3.6 ms; P <.001) and R-wave amplitude (0.1 ± 0.01 to 0.7 ± 0.09 mV; P <.001) in the ECG.
  
  
  CONCLUSIONS
  Transmural but not epicardial myocardial injury delays intramural local activation and is associated with QRS prolongation and enlarged R-wave amplitude in leads with ST segment elevation. This differential ECG pattern may help to distinguish acute pericarditis (epicardial injury) from acute transmural ischemia in clinical practice.
authors.affiliation: Department of Cardiology, Institute of Biomedical Research (IIB Sant Pau), Autonomous University of Barcelona, Barcelona, Spain. rwiegerinck@santpau.cat
authors.forename: Rob F
authors.initials: RF
authors.lastname: Wiegerinck
authors.forename: Carolina
authors.initials: C
authors.lastname: Gálvez-Monton
authors.forename: Esther
authors.initials: E
authors.lastname: Jorge
authors.forename: Roser
authors.initials: R
authors.lastname: Martínez
authors.forename: Elisabet
authors.initials: E
authors.lastname: Ricart
authors.forename: Juan
authors.initials: J
authors.lastname: Cinca
mesh_terms: D000818:Animals; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000503:physiopathology; D010493:Pericarditis / Q000175:diagnosis* / Q000503:physiopathology; D010496:Pericardium / Q000503:physiopathology*; D013552:Swine