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

Ventricular tachycardia or fibrillation (VT-VF) as fatal cardiac arrhythmia s are the main factors triggering sudden cardiac death. The objective of th is study is to find early signs of sustained VT-VF in patients with an impl anted cardioverter-defibrillator (ICD). These devices are able to safeguard patients by returning their hearts to a normal rhythm via strong defibrill atory shocks; additionally, they store the 1000 beat-to-beat intervals imme diately before the onset of a life-threatening arrhythmia. We study these 1 000 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., wit hout a VT-VF event. To characterize these rather short data sets, we calcul ate heart rate variability parameters from the time and frequency domain, f rom symbolic dynamics as well as the finite-time growth rates. We find that neither the time nor the frequency domain parameters show significant diff erences between the VT-VF and the control time series. However, two paramet ers from symbolic dynamics as well as the finite-time growth rates discrimi nate significantly both groups. These findings could be of importance in al gorithms for next generation ICD's to improve the diagnostics and therapy o f VT-VF.