title: Circadian variation of heart rate variability in postinfarction patients with and without life-threatening ventricular tachyarrhythmias.
abstract: BACKGROUND
  Determination of heart rate variability (HRV) is widely used for noninvasive assessment of cardiac autonomic tone. A decreased HRV is associated with an increased mortality in patients surviving an acute myocardial infarction. There are, however, only sparse data about the circadian variation of different components of HRV that may be linked to the well-known circadian fluctuations in the occurrence of sudden death. In addition, the potential prognostic impact of circadian variations of HRV has not been examined.
  
  
  RESULTS
  The present study compared the circadian variation of HRV from 14 postinfarction patients who had survived at least one episode of out-of-hospital cardiac arrest (cardiac arrest group) with that of 14 age- and sex-matched patients without a history of malignant arrhythmias after their index infarct (control group). Several time- and frequency-domain measures of HRV were assessed from 24-hour Holter recordings. Circadian variations of high- (HF), low- (LF), and total-frequency (TF) components were determined by calculating for each parameter the hourly difference from the day's mean. The average of these differences was calculated for every hour as well as for predefined day and night periods. There was no significant difference between the two groups with regard to HRV indices that predominantly reflect vagal tone, such as SDNN (78 +/- 25 vs 96 +/- 24 msec), pNN50 (2.7% +/- 4.6% vs 4.9% +/- 4.2%), or HF (6.3 +/- 3.0 vs 7.8 +/- 3.2 msec; cardiac arrest vs control group). There was also no significant difference in the circadian variation of LF or TF between the two groups during daytime and nighttime. However, a significant difference in circadian variation of HF was found during daytime (0.02 +/- 0.5 vs -0.6 +/- 0.5 msec; P = 0.006) and nighttime (0.19 +/- 0.64 vs 1.5 +/- 0.75 msec; P = 0.0002). In cardiac arrest survivors, there was no difference in the mean deviation of HF between the day- and the nighttime periods.
  
  
  CONCLUSIONS
  These results show an almost complete abolition in circadian variation of parasympathetic tone in postinfarction patients surviving an episode of out-of-hospital cardiac arrest, whereas circadian variation of sympathetic tone is comparable to that of postinfarction patients without arrhythmic episodes. These findings indicate that determination of diurnal variation of HRV may add to the prognostic value of HRV with respect to identifying patients at high risk of sudden death.
authors.affiliation: Department of Cardiology, University Hospital, Frankfurt, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Klingenheben
authors.forename: U
authors.initials: U
authors.lastname: Rapp
authors.forename: S H
authors.initials: SH
authors.lastname: Hohnloser
mesh_terms: D001341:Autonomic Nervous System / Q000503:physiopathology; D002940:Circadian Rhythm / Q000502:physiology*; D016757:Death, Sudden, Cardiac / Q000209:etiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006352:Heart Ventricles / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D018670:Monitoring, Ambulatory; D009203:Myocardial Infarction / Q000150:complications / Q000503:physiopathology*; D017180:Tachycardia, Ventricular / Q000209:etiology / Q000503:physiopathology*; D014693:Ventricular Fibrillation / Q000503:physiopathology