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.
Methods and 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. (
Circ J 2011;
75: 2775-2780)
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