The knowledge of transitions between regular, laminar or chaotic behaviors is essential to understand the underlying mechanisms behind complex systems. While several linear approaches are often insufficient to describe such processes, there are several nonlinear methods that, however, require rather long time observations. To overcome these difficulties, we propose measures of complexity based on vertical structures in recurrence plots and apply them to the logistic map as well as to heart-rate-variability data. For the logistic map these measures enable us not only to detect transitions between chaotic and periodic states, but also to identify laminar states, i.e., chaos-chaos transitions. The traditional recurrence quantification analysis fails to detect the latter transitions. Applying our measures to the heart-rate-variability data, we are able to detect and quantify the laminar phases before a life-threatening cardiac arrhythmia occurs thereby facilitating a prediction of such an event. Our findings could be of importance for the therapy of malignant cardiac arrhythmias.

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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.

Compression entropy might be a suitable parameter for short-term forecasting of life-threatening tachycardia in ICD.

Background— The incidence of silent cerebral lesions (SCL) after atrial fibrillation (AF) ablation is highly variable, depending on the technology used. Recently, an increased risk for SCL has been described for a novel, nonirrigated ablation tool using multielectrode phased radiofrequency (PVAC). The aim of this prospective study was to evaluate the incidence and long-term follow-up of SCL in patients undergoing robotically assisted pulmonary vein isolation (RA-PVI) as compared with manual PVI. Methods and Results— Circumferential PVI using irrigated radiofrequency current was performed on 70 patients (41 patients with paroxysmal AF, 59%). Fifty patients underwent RA-PVI and 20 patients underwent a manual approach. Cerebral MRI was performed the day before and the day after the ablation procedure; follow-up MRI was performed on 9 of 12 (75%) patients after a follow-up period of 21 months. SCLs were found in 12 of 70 (17%) patients in this study; the incidence of SCLs was similar in patients undergoing RA-PVI as compared with manually ablated patients (n=9, 18% versus n=3, 15%; probability value=1.0). In 1 patient undergoing manual PVI (1%), an SCL with asymptomatic subarachnoid hemorrhage was detected; the bleeding completely resolved within 1 month. Transient ischemic attack occurred in 1 (1%) patient 2 days after manual PVI. After a median follow-up period of 21 months, no residual SCLs were detected. Conclusions— The incidence of SCL using the robotic navigation system was 18% in this study. Incidence and size of SCL appears to be similar after RA-PVI as compared with manual PVI. Repeat MRI showed no residual SCLs at long-term follow-up.