| Background:The electrophysiological activity of the heart is regulated by the autonomic nervous system(ANS).The sympathetic and vagal nerves of ANS are in a dynamic balance under normal physiological conditions.When this balance is damaged,it may leads to malignant cardiac events,such as atrial fibrillation,ventricular arrhythmia,and so on.It is important to evaluate the changes of ANS activity to avoid the risk of heart-related diseases.Based on the time interval series from ECG,this study is to investigate the evaluation of autonomic nervous state under physiological and pathological changes by analyzing the response of QT variability(QTV)to heart rate variability(HRV)as well as the time interval from peak to end of T wave(Tpe).Methods:The Holter data were provided by THEW,database Normal was selected as normal controls(Normal,n=186)and database ESRD as typical subjects of ANS dysfunction with high risk for cardiac arrhythmias and sudden cardiac death(ESRD,n=41).5 min RR interval(RRI)and the corresponding QT interval(QTI)at rest were extracted both in daytime and on night,the response of QTV to HRV was analyzed by using linear parametric model in frequency domain and nonlinear information decomposition method.The QTV fraction related to HRV(LR)in the frequency domain and the predictive information(PI)from RRI to QTI in the information theory were calculated,combined with time-domain indexes,frequency domain indexes and symbolic dynamic analysis(SDA)of RRI,to explore the possible difference of QTV response to HRV in the two groups and its potential mechanism.At the same time,the RRI and QTI before and after head-up tilt(HUT)from database PRCP of PhysioNet were analyzed,to explore the changes of the corresponding indexes and the reliability of the methods when the physiological conditions changed.The healthy individual ECG from database Fantasia of PhysioNet were selected and the 5 min static Tpe interval of each person were extracted,combined with the Tpe interval in Normal and ESRD,the time-domain indexes as well as Tpe/RR and Tpe/QT,which were corrected by RRI and QTI,were calculated to observe the influence of age and sex under normal physiological conditions,and the changes of the indexes under pathological conditions.Result:For the response of QTV to HRV analysis,there were significant diurnal differences both for LR and PI in Normal,but no significant diurnal variation of that was observed in ESRD,reflecting the loss of ANS reciprocal interaction in ESRD.When comparing the same indicators between Normal group and ESRD group in the same time period,there were no significant differences in LR values in low frequency band between two groups,while LR values in high frequency band in Normal were significant smaller than that in ESRD(Day:18.36%± 17.38%vs 39.37%±23.80%,P<0.05;Night:28.63%± 18.77%vs 42.31%±21.97%,P<0.05);PI on night was significantly higher in Normal compared with that in ESRD(0.310 ±0.155 vs 0.236 ±0.131,P<0.05),but no significant difference in PI was found between two groups in daytime.For the Tpe interval and its corrected indexes,the analysis of data from database Fantasia shows the Tpe interval has a significant difference between two age groups,and Tpe/RR has a significant difference between two sex groups,while no significant difference of Tpe/QT was found in the comparison of the different groups.When comparing the same indicators between Normal group and ESRD group in the same time period,the values of Tpe,Tpe/RR and Tpe/QT in Normal were smaller than those in ESRD,and those indexes were significantly different between the two groups at night.Conclusions:The linear parametric model and nonlinear prediction based on information decomposition have different sensitivity to autonomic nervous activity;The complexity of HRV in regulating QTV in population with high risk for cardiac arrhythmias and sudden cardiac death is reduced.Tpe interval showed prolongation under the condition of enhanced sympathetic nerve activity and pathology,Tpe/QT was less affected by age and sex. |
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