title: Reversed circadian rhythms of heart rate variability and morning peak occurrence of sustained ventricular tachyarrhythmias in patients with implanted cardioverter defibrillator.
abstract: BACKGROUND
  It is generally supposed that diurnal fluctuations of heart rate variability (HRV) are associated with diurnal variability of occurrence of sudden cardiac death, usually caused by tachyarrhythmias. To date, however, there have been no data comparing circadian rhythms of HRV and circadian variability of malignant ventricular tachyarrhythmias in the same patients.
  
  
  METHODS
  We studied 20 consecutive recipients of implantable cardioverter defibrillators in long-term follow-up, comparing the circadian rhythms of HRV in patients with and without typical morning peak occurrence of ventricular tachyarrhythmias.
  
  
  RESULTS
  The HRV marker of vagus activity (RMSSD and HF power) displayed physiological circadian variability (highest values during sleep time, morning dip) only in patients without morning peak of arrhythmic events, and inverse circadian variability in patients with tachyarrhythmic morning peak. The variations in LF power and LF/HF ratio in both groups were not statistically significant, but with respect to the time interval between midnight and noon again showed inverse diurnal variation in patients with and without morning peak of arrhythmic events.
  
  
  CONCLUSIONS
  These data suggest an association between a reversed circadian rhythm of HRV and morning peak frequency of tachyarrhythmic events in patients with ICD. As pronounced adrenergic hyperactivity in heart failure is the probable reason for paradoxically reversed circadian HRV variation, this association supports the hypothesis that the morning peak frequency of cardiovascular events may be interpreted as a sign of cardiovascular overload by the natural change from sleep to activity after awakening.
authors.affiliation: Medical Clinic, Internal Medicine III, Cardiology/Angiology, Saarland University Clinics, Homburg/Saar, Germany. fries@med-in.uni-saarland.de
authors.forename: Roland
authors.initials: R
authors.lastname: Fries
authors.forename: Sandra
authors.initials: S
authors.lastname: Hein
authors.forename: Jochem
authors.initials: J
authors.lastname: K nig
mesh_terms: D000368:Aged; D002940:Circadian Rhythm; D017147:Defibrillators, Implantable; D005260:Female; D005500:Follow-Up Studies; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D017180:Tachycardia, Ventricular / Q000503:physiopathology* / Q000628:therapy; D013997:Time Factors