Short-term forecasting of life-threatening cardiac arrhythmias based on symbolic dynamics and finite-time growth rates

Abstract

Ventricular tachycardia or fibrillation (VT-VF) as fatal cardiac arrhythmias are the main factors triggering sudden cardiac death. The objective of this study is to find early signs of sustained VT-VF in patients with an implanted cardioverter-defibrillator (ICD). These devices are able to safeguard patients by returning their hearts to a normal rhythm via strong defibrillatory shocks; additionally, they store the 1000 beat-to-beat intervals immediately before the onset of a life-threatening arrhythmia. We study these 1000 beat-to-beat intervals of 17 chronic heart failure ICD patients before the onset of a life-threatening arrhythmia and at a control time, i.e., without a VT-VF event. To characterize these rather short data sets, we calculate heart rate variability parameters from the time and frequency domain, from symbolic dynamics as well as the finite-time growth rates. We find that neither the time nor the frequency domain parameters show significant differences between the VT-VF and the control time series. However, two parameters from symbolic dynamics as well as the finite-time growth rates discriminate significantly both groups. These findings could be of importance in algorithms for next generation ICD's to improve the diagnostics and therapy of VT-VF.

Nonlinear Methods of Cardiovascular Physics and Their Clinical Applicability

“…Applying our new measures to the HRV data of the pilot study, we were able to detect and quantify the laminar phases before the occurrence of life-threatening cardiac arrhythmia. The differences between VT and the control series were more significant for RQA parameters than for measures used in [Wessel et al, 2000c]. This study also demonstrated the importance of developing sophisticated nonlinear dynamical tools for the analysis (not only) of medical data.…”

“…15). The objective of the pilot study in 1998 [Wessel et al, 2000c] was to find early signs of sustained VT in patients with an implanted Fig. 15.…”

“…These parameters are based on linear techniques and statistically characterize HRV. To classify additionally dynamical changes, we use only one measure based on the concept of symbolic dynamics which has been recently successfully applied to other cardiological problems [Kurths et al, 1995;Wessel et al, 2000c]. The main finding in discriminating young healthy from CHF patients is that there are enormous discrepancies in heart rate regulation between both groups.…”

“…Eq. (10) in Chapter 2) based on symbolic dynamics [Wessel et al, 2000c], which detects intermittently decreased HRV (CHF: 0.68-0.90 inter-quartile range -IQR, young healthy: 0.05-0.13 IQR, p < 10 −8 , Mann-Whitney U-Test) and completely discriminates the young healthy and the CHF group. POLVAR20 characterizes short phases of low variability from successive symbols of a simple alphabet, consisting of only the symbols "0" and "1".…”

“…Therefore, we favor measures of complexityanother approach within nonlinear dynamicswhich are able to quantitatively characterize the dynamics even for rather short time series [Schwarz et al, 1993;Kurths et al, 1995;Voss et al, 1996b;Voss et al, 1998;Wessel et al, 2000c].…”