Background New methods based on nonlinear theory have been developed to give more insight into complex heart rate (HR) dynamics. This study was designed to test the hypothesis that altered HR dynamics, as analyzed with complexity and fractal measures, may precede the spontaneous onset of paroxysmal atrial fibrillation (PAF). Secondly, the difference in the temporal change of these measurements between the different types of atrial fibrillation (AF) was assessed. Methods and Results From 105 Holter tapes in which PAF was recorded, 44 PAF (≥5 min) episodes in 33 patients (22 men, 58±12 years), preceded by sinus rhythm for more than 1 h, were selected and submitted to timeand frequency-domain HR variability analyses, along with detrended fluctuation analysis, approximate entropy (ApEn) and sample entropy (SampEn). The 60 min before the onset of AF were divided into 6 10-min periods and studied using repeated measures ANOVA. PAF episodes were divided into 3 subgroups: an increased HF component and decreased L/H ratio (vagal type, n=20); increased L/H ratio and decreased HF component (sympathetic type, n=14); and non-related type (n=10). None of the time-or frequency-domain parameters showed any significant change before AF in any type of AF. The 1 showed a tendency to decrease before the onset of AF and the change in 1 was divergent according to the AF type. The ApEn decreased before the onset of AF (1.005±0.046, 60-50 min before AF to 0.894±0.052, 10-0 min before AF; p=0.032). The SampEn also decreased progressively before the start of AF (1.165± 0.085, 60-50 min before AF to 0.887±0.077, 10-0 min before AF, p=0.003). The decrease in both the ApEn and SampEn was irrespective of the AF type. Conclusions A reduction in the ApEn and SampEn, which reflects the nonlinear complexity of HR variability, is a hallmark of altered HR dynamics preceding the spontaneous onset of AF. (Circ J 2006; 70: 94 -99)
Circulation Journal Official Journal of the Japanese Circulation Society http://www. j-circ.or.jp inus node dysfunction (SND), also referred to as "sick sinus syndrome", is a common cause of cardiac syncope. 1 Sinus bradycardia (SB) is not only an incidental finding in otherwise healthy individuals, particularly in young adults, but also an electrocardiographic manifestation of SND. 2-5 Differentiation of so-called pathologic SB (due to intrinsic SND), from normal SB, is important in the diagnosis and management of SND.Heart rate variability (HRV) analysis, through classical linear methods, either in the time or the frequency domain, provides quantitative and non-invasive measures of the activity of the autonomic nervous system. 6,7 Information carried by the heart rate signal, however, may not be totally explained by this linear approach. 8-13 Non-linear dynamical system analysis based on the theories of fractal scaling and complexity have gained interest, because they may reveal information hidden in the regulatory system that cannot be detected using conventional methods. 14-20 Pathological states and aging are associated with distinctive alterations in these scaling properties, which could be of practical diagnostic and prognostic use. To date, the short-term scaling exponent (DFAα1) of detrended fluctuation analysis (DFA) has demonstrated greater clinical discrimination of various cardiac diseases.Most previous studies regarding heart rate dynamics and its interpretations were carried out in the presence of intact sinus node activity. We assumed that, if a dysfunctional sinus node does not respond appropriately to neuroautonomic input, then alteration or breakdown of the fractal scaling and complexity of heart rate dynamics would ensue. Little information exists concerning the non-linear behavior of sinus node pacemaker activity in SND. The purpose of the present study was to characterize the heart rate dynamics of SB in SND and to test 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.
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