This study explores the heart rate (HR) variability (V) in order to detect whether the chaotic component of the sinusal R-R intervals (SRRI) can be interpreted as an early indicator of a silent cardiac neurovegetative dysautonomia in apparently uncomplicated Type 2 diabetic patients (DP). The SRRI were provided by the 24-h Holter ECG of 10 Type 2 DP (5 M and 5 F, mean age = 41 +/- 5 years). Control data were obtained by the 24-h Holter ECG of 10 clinically healthy subjects (CHS, 5 M and 5 F, mean age = 38 +/- 6 years). The chaotic component of HRV was investigated via the correlation dimension (CD) analysis (A) of the SRRI, performed per each hour of the ECG recording. The hourly-qualified series of SRRI, HR and CD index (I) were, in turn, analyzed via methods of conventional statistics and chronobiology, the latter ones for assessing the circadian rhythm (CR). The CDI CR was found to peak during the night in CHS, and to be unphysiologically rotated to the diurnal hours of the day in Type 2 DP. The diurnal inversion of the CDI CR in Type 2 DP suggests that the chaotic component of HRV shows an abnormal rhythnic pattern over the day-night period. Considering that the investigated Type 2 DP were lacking of documentable signs of cardiac neuropathy, it is hypothesized that the diurnal phase of shift CDI CR might be a potential indicator of a silent autonomic cardiac dysfunction in Type 2 DP. Such a hypothesis waits for further confirmations.

OBJECTIVE:This study investigates the hypothesis that the nonlinear component of human heart rate (HR) variability might show a periodic structure over the 24-h span. Such a postulate could explain how the chaotic component might coexist with the deterministic periodic variability of instantaneous HR in beat per minute.MATERIALS AND METHODS:The sinusal R-R intervals (sRRi) of the Holter EKG of 10 clinically healthy subjects (5 M, 5 F, 23-30 years) were analyzed per each hour of the day-night span according to two methods for the nonlinear chaotic variability, i.e., the correlation dimension method, and the linear periodic variability, i.e., periodic regression analysis.RESULTS:The hourly-qualified correlation integrals were found to show a significant circadian rhythm, with an acrophase located during the night in coincidence with the longest duration of the sRRi and the lowest rate of cardiac pulse.CONCLUSIONS:The rhythmic structure of the chaotic component of the human HR variability let us to think that a deterministic periodic chaos of fractal type regulates the nonlinear cardiac dynamics. Such a periodic structure allows the chaos to be compatible with the deterministic linear periodicity of circadian type which characterizes the within-day variability of human HR.

The aim of this study was to investigate the circadian variability of heart rate in acute myocardial infarction (AMI) in identifying patients at high risk for malignant ventricular arrhythmias (MVA) and sudden death within 1 year of the acute event. The investigation was carried out in 43 patients, who underwent 24-hour Holter monitoring within 3 months of AMI. Besides the time domain indexes of heart rate variability (SDNN, SDNN index, pNN50, rMSSD), the circadian rhythm of hourly total beats (HTB) and hourly qualified beats (HQB) has been analyzed by the Cosinor method. The AMI patients with MVA and those with MVA who died within 1 year the acute event showed SDNN, SDNN index and pNN50 values lower than subjects without MVA and survived patients with MVA, respectively; the individuals with AMI at high risk for MVA and for sudden death had an SDNN value < 105 ms and 50 ms, respectively. The circadian rhythm of HTB and HQB was statistically validated only in the group without MVA; patients without the circadian rhythm of HTB and HQB showed a higher mortality rate within 1 year of AMI, and the majority was in the group with MVA. The contemporary evidence of an SDNN value < 105 ms and the lack of HTB and HQB circadian rhythm increased sensitivity for identifying patients with MVA to 75%. On the other hand, the contemporary evidence of an SDNN value < 50 ms and the lack of HTB and HQB circadian rhythm increased sensitivity for identifying patients who died within 1 year of AMI to 100%. In conclusion, the assayed methods seem to be both useful and complementary in identifying patients at high risk for MVA and sudden death within 1 year of AMI.