title: Peak time of occurrence of myocardial ischemia in the coronary care unit.
abstract: BACKGROUND
  The onset of acute myocardial infarction and sudden cardiac death has a circadian variation, with the peak occurrence between 6 AM and 12 noon.
  
  
  OBJECTIVE
  To determine if a circadian variation exists for transient myocardial ischemia in patients admitted to the coronary care unit with unstable coronary syndromes.
  
  
  METHODS
  The sample was selected from patients enrolled in a prospective clinical trial who had had ST-segment monitoring for at least 24 hours and had had at least one episode of transient ischemia. The 24-hour day was divided into 6-hour periods, and comparisons were made between the 4 periods.
  
  
  RESULTS
  In 99 patients, 61 with acute myocardial infarction and 38 with unstable angina, a total of 264 (mean +/- SD, 3 +/- 2) ischemic events occurred. Patients were more likely to have ischemic events between 6 AM and noon than at other times. A greater proportion of patients complained of chest pain between 6 AM and noon than during the other 3 periods. However, more than half the patients never complained of chest pain during ischemia between 6 AM and noon.
  
  
  CONCLUSIONS
  Transient ischemia occurs throughout the 24-hour day; however, ischemia occurs more often between 6 AM and noon. An important nursing intervention for detecting ischemia is continuous electrocardiographic monitoring of the ST segment, even during routine nursing care activities, which are often at a peak during the vulnerable morning hours.
authors.affiliation: University of California, San Francisco, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Pelter
authors.forename: M G
authors.initials: MG
authors.lastname: Adams
authors.forename: S F
authors.initials: SF
authors.lastname: Wung
authors.forename: S M
authors.initials: SM
authors.lastname: Paul
authors.forename: B J
authors.initials: BJ
authors.lastname: Drew
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D015400:Clinical Nursing Research; D003325:Coronary Care Units; D003422:Critical Care / Q000379:methods; D004562:Electrocardiography / Q000379:methods; D005260:Female; D006801:Humans; D007297:Inpatients; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D017202:Myocardial Ischemia / Q000175:diagnosis / Q000451:nursing / Q000503:physiopathology*; D009730:Nursing Assessment / Q000379:methods; D011446:Prospective Studies; D013997:Time Factors