title: Breakdown of the intermediate-term fractal scaling exponent in sinus node dysfunction. New method for non-invasive evaluation of sinus node function.
abstract: BACKGROUND
  The aim of the present study was to characterize the heart rate dynamics of sinus bradycardia (SB) from sinus node dysfunction (SND) using non-linear dynamical system analysis. No data are yet available on how the dynamics change in the presence of SND.
  
  
  RESULTS
  Conventional time and frequency domain analysis, the short- (DFAα(1)) and intermediate-term fractal scaling exponent (DFAα(2)), approximate entropy (ApEn) and sample entropy (SampEn) were calculated in 60-min sinus RR interval data of SB from 24-h ambulatory electrocardiograms of 110 patients: 44 SND patients, 44 age-matched controls, and 22 younger controls. All of the time and frequency domain parameters, ApEn and SampEn, were significantly reduced in the age-matched control group, compared with the young control group. DFAα(1) and DFAα(2) increased with aging. Both the DFAα(1) and DFAα(2) of SND patients were paradoxically reduced, which was not appropriate for their age. Only the percentage of consecutive RR intervals with absolute differences >50ms (pNN(50)), low-frequency power, and DFAα(2) made a significant contribution to prediction of SND on logistic regression analysis. Among them, DFAα(2) was the most significant variable for prediction of SND (odds ratio, 0.927; 95% confidence interval: 0.888-0.969, P=0.001). DFAα(2) remained as a significant variable for prediction of SND, when compared with overall control patients, combining the 2 control groups.
  
  
  CONCLUSIONS
  Inappropriate reduction of DFAα(2) is a robust measure and could be an adjunctive tool for improvement of diagnostic performance in detection of SND.
authors.affiliation: Cardiovascular Division, Internal Medicine, Yeungnam University Hospital, Daegu, South Korea. dgshin@med.yu.ac.kr
authors.forename: Dong-Gu
authors.initials: DG
authors.lastname: Shin
authors.forename: Sang-Hee
authors.initials: SH
authors.lastname: Lee
authors.forename: Sang-Hoon
authors.initials: SH
authors.lastname: Yi
authors.forename: Cheol-Seung
authors.initials: CS
authors.lastname: Yoo
authors.forename: Geu-Ru
authors.initials: GR
authors.lastname: Hong
authors.forename: Ung
authors.initials: U
authors.lastname: Kim
authors.forename: Jong-Seon
authors.initials: JS
authors.lastname: Park
authors.forename: Young-Jo
authors.initials: YJ
authors.lastname: Kim
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D001919:Bradycardia / Q000175:diagnosis / Q000503:physiopathology; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012804:Sick Sinus Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D012849:Sinoatrial Node / Q000503:physiopathology*