title: Significance of long term components of heart rate variability for the further prognosis after acute myocardial infarction.
abstract: OBJECTIVE
  The study examined heart rate variability to find out whether shorter ECG records can predict long term mortality following acute myocardial infarction as efficiently as 24 h recordings.
  
  
  METHODS
  Heart rate variability was assessed in 24 h electrocardiograms recorded during the first 2 weeks following acute myocardial infarction and in separate 1 h portions of the complete recording. The spectral analysis of complete 24 h records was performed and different short and long term components of heart rate variability were used to distinguish between patients with and without later complications.
  
  
  METHODS
  20 patients who initially survived acute myocardial infarction but later experienced serious events (death or symptomatic sustained ventricular tachycardia) during a 6 month follow up (group I) were compared with 20 patients (group II) who remained free of complications for more than 6 months after discharge and who were matched with group I for age, gender, infarct site, ejection fraction, and beta blocker treatment.
  
  
  RESULTS
  The distinction based on components limited to changes of heart rate within periods less than or equal to 1 h was as significant (p less than 0.001, paired t test) as when using the components limited to changes of periods less than or equal to 10 h. However, heart rate variability of separate 1 h portions of the complete 24 h records differed between the groups significantly only for certain 1 h intervals of the day (the p values varied from 0.2 to 0.0005).
  
  
  CONCLUSIONS
  Whilst the maximum value of short term heart rate variability is sufficient for stratification of the high risk post-myocardial infarction patients, an arbitrarily selected short term ECG recording is unlikely to register the maximum heart rate variability. It is concluded that the heart rate variability assessed from arbitrary 1 h electrocardiographic records is not as prognostically important as the variability estimated from 24 h recordings.
authors.affiliation: Department of Cardiological Sciences, St George's Hospital Medical School, London.
authors.forename: M
authors.initials: M
authors.lastname: Malik
authors.forename: A J
authors.initials: AJ
authors.lastname: Camm
mesh_terms: D000818:Animals; D015716:Electrocardiography, Ambulatory / Q000379:methods; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000503:physiopathology*; D011379:Prognosis