title: Weekly variation of the QT dispersion in healthy subjects and in patients with coronary heart disease.
abstract: BACKGROUND
  A circadian and seasonal variation of QT dispersion (QTd) has been shown in healthy individuals. Nevertheless, no data exist regarding the weekly influences on the QTd in healthy individuals and in patients with coronary heart disease (CHD).
  
  
  METHODS
  This study was designed to determine whether there is a weekly variability of QTd in healthy individuals and in patients with CHD.
  
  
  METHODS
  In this prospective registry study, 53 patients with documented CHD and 57 healthy control subjects were involved. Resting electrocardiograms (ECGs) with double amplitude were recorded at a speed of 50 mm/s on Monday and Friday mornings. QT intervals were measured and QTd were determined by calculating the difference between maximum and minimum QT intervals. Then, rate-corrected QTd (QTcd) were calculated using Bazett's formula.
  
  
  RESULTS
  There was a significant weekly variation of QTd in control subjects (39.3 +/- 6.3 vs. 36.2 +/-6.1 ms) (p < 0.05) and in patients (56 +/- 7.3 vs. 47.4 +/- 5.4 ms) (p < 0.0001). There was also a significant weekly variation of QTcd both in control subjects (33 +/- 5.3 vs. 30.7 +/- 5.6 ms) (p < 0.05) and in patients (47.4 +/- 6.4 vs. 41.9 +/- 5.4 ms) (p < 0.0001).
  
  
  CONCLUSIONS
  There is a weekly variation of QTd and QTcd in healthy individuals and in patients with CHD, both with a Monday preference. This fact should be taken into consideration during the chronopharmacological treatment or advisal of primary or secondary preventive measures to these subjects or patients.
authors.affiliation: Department of Cardiology, Türkiye Yüksek Ihtisas Hospital, Ankara, Turkey. husoren@hotmail.com
authors.forename: Hüseyin
authors.initials: H
authors.lastname: Oren
authors.forename: Ayhan
authors.initials: A
authors.lastname: Cosgun
mesh_terms: D000328:Adult; D017677:Age Distribution; D000368:Aged; D016022:Case-Control Studies; D003324:Coronary Artery Disease / Q000175:diagnosis* / Q000401:mortality*; D016757:Death, Sudden, Cardiac; D004562:Electrocardiography; D005080:Exercise Test; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D015994:Incidence; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000401:mortality*; D008297:Male; D008875:Middle Aged; D009203:Myocardial Infarction / Q000175:diagnosis / Q000401:mortality; D015588:Observer Variation; D011336:Probability; D011446:Prospective Studies; D012016:Reference Values; D012042:Registries; D012307:Risk Factors; D012720:Severity of Illness Index; D017678:Sex Distribution; D016019:Survival Analysis