title: Appearance of abnormal Q waves early in the course of acute myocardial infarction: implications for efficacy of thrombolytic therapy.
abstract: OBJECTIVE
  The purpose of this study was to determine the time course of the appearance of abnormal Q waves on the electrocardiogram (ECG) over the first 6 h of symptoms of myocardial infarction and to determine what implications, if any, such Q waves have for the efficacy of thrombolytic therapy.
  
  
  BACKGROUND
  Severe myocardial ischemia can produce early QRS changes in the absence of infarction. Abnormal Q waves on the baseline ECG may not be an accurate marker of irreversibly injured myocardium.
  
  
  METHODS
  Data from 695 patients who had no past history of myocardial infarction and whose admission ECG allowed prediction of myocardial infarct size in the absence of thrombolytic therapy (Aldrich score) were pooled from four prospective trials of thrombolytic therapy. The presence and number of abnormal Q waves on each patient's initial ECG were recorded. Four hundred thirty-six patients had left ventricular infarct size measured using quantitative thallium-201 tomography a mean (+/- SD) of 52 +/- 43 days after admission.
  
  
  RESULTS
  Of patients admitted within 1 h of symptoms, 53% had abnormal Q waves on the initial ECG. Both predicted and final infarct size were larger in patients with abnormal Q waves on the initial ECG independent of the duration of symptoms before therapy (p < 0.001). Despite this finding, the presence of abnormal Q waves on the admission ECG did not eliminate the effect of thrombolytic therapy on reducing final infarct size (p < 0.0001).
  
  
  CONCLUSIONS
  Abnormal Q waves are a common finding early in the course of acute myocardial infarction. However, there is no evidence that abnormal Q waves are associated with less benefit in terms of reduction of infarct size after thrombolytic therapy.
authors.affiliation: Division of Cardiology, University of Washington Medical Center, Seattle, Washington 98195.
authors.forename: M H
authors.initials: MH
authors.lastname: Raitt
authors.forename: C
authors.initials: C
authors.lastname: Maynard
authors.forename: G S
authors.initials: GS
authors.lastname: Wagner
authors.forename: M D
authors.initials: MD
authors.lastname: Cerqueira
authors.forename: R H
authors.initials: RH
authors.lastname: Selvester
authors.forename: W D
authors.initials: WD
authors.lastname: Weaver
mesh_terms: D004562:Electrocardiography; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000175:diagnosis* / Q000188:drug therapy* / Q000503:physiopathology; D017202:Myocardial Ischemia / Q000503:physiopathology; D011237:Predictive Value of Tests; D011877:Radionuclide Imaging; D013300:Streptokinase / Q000627:therapeutic use; D013794:Thallium Radioisotopes; D015912:Thrombolytic Therapy; D013997:Time Factors; D010959:Tissue Plasminogen Activator / Q000627:therapeutic use
chemical_list: D013794:Thallium Radioisotopes; D013300:Streptokinase; D010959:Tissue Plasminogen Activator