title: Natural variability of transient myocardial ischaemia during daily life: an obstacle when assessing efficacy of anti-ischaemic agents?
abstract: OBJECTIVE
  To assess the degree of variability of transient myocardial ischaemia during daily life in patients with coronary artery disease, which could confound the interpretation of trials of the therapeutic effects of anti-ischaemic agents.
  
  
  METHODS
  Prospective method evaluation.
  
  
  METHODS
  Tertiary referral centre, outpatient clinic.
  
  
  METHODS
  Patients with stable angina, confirmed coronary artery disease, and a positive treadmill exercise test for ischaemia. Patients were not preselected on the basis of prior documented transient ischaemia during ambulatory ST segment monitoring.
  
  
  METHODS
  A simulated drug-study with 4 monitoring phases in 16 subjects. To minimise variability in ischaemic activity, patients underwent weekly 48 hour ambulatory ST segment monitoring outside hospital off all prophylactic therapy on the same weekdays for 4 weeks.
  
  
  METHODS
  Variability in the frequency and duration of transient myocardial ischaemia.
  
  
  RESULTS
  There was marked variability in both ischaemic activity and mean duration of ischaemia in patients with confirmed ischaemia, the greatest degree of variability being between patients and from day to day within weeks within patients, with a further contribution to variability being noted between fortnights within patients.
  
  
  CONCLUSIONS
  Despite assessment off all therapy and an adequate period of monitoring (48 hours) with small intervals between monitoring periods (5 days), marked variability in ischaemic activity was noted, and regression towards the mean was clearly shown. Ambulatory ST segment monitoring outside hospital is not a reliable method for assessing the therapeutic effects of anti-ischaemic agents.
authors.affiliation: Department of Cardiology, Royal Brompton Hospital, London.
authors.forename: D J
authors.initials: DJ
authors.lastname: Patel
authors.forename: D
authors.initials: D
authors.lastname: Mulcahy
authors.forename: J
authors.initials: J
authors.lastname: Norrie
authors.forename: C
authors.initials: C
authors.lastname: Wright
authors.forename: D
authors.initials: D
authors.lastname: Clarke
authors.forename: I
authors.initials: I
authors.lastname: Ford
authors.forename: K M
authors.initials: KM
authors.lastname: Fox
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D002986:Clinical Trials as Topic; D015716:Electrocardiography, Ambulatory; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000188:drug therapy / Q000503:physiopathology*; D012107:Research Design