Examinando por Autor "Alonso Atienza, Felipe"
Mostrando 1 - 20 de 24
- Resultados por página
- Opciones de ordenación
Ítem A Review on Recent Patents in Digital Processing for Cardiac Electric Signals (I): From Basic Systems to Arrhythmia Analysis(2009-07-14T11:06:21Z) Goya Esteban, R; Barquero Pérez, Óscar; Alonso Atienza, Felipe; Everss, E; Requena Carrión, Jesús; García Alberola, Arcadi; Rojo-Álvarez, José LuisCardiac electric signals are currently the most informative source about the heart rhythm and its disorders, and hence, the use of adequate digital signal processing techniques is necessary to yield reliable diagnostic parameters, either to the clinician or to automatic monitoring systems. A number of systems have been patented during the last years, which are grouped in this review according to their application scope. In this first part, techniques for electrocardiogram and intracardiac electrogram filtering, and for feature extraction, are first examined, then patents on arrhythmia analysis are then summarized. The wide number of basic systems for cardiac signal processing analysis that have been disclosed indicates that this field represents a main scenario in the near and middle future of cardiac health.Ítem A Review on Recent Patents in Digital Processing for Cardiac Electric Signals (II): Advanced Systems and Applications(2009-07-14T11:13:08Z) Barquero Pérez, Óscar; Goya Esteban, R; Alonso Atienza, Felipe; Requena Carrión, Jesús; Everss, E; García Alberola, Arcadi; Rojo-Álvarez, José LuisDigital signal processing algorithms for cardiac recordings have been paid much attention in recently disclosed patents. In this second part of our review of the state-of-art patents, systems for sudden cardiac death prediction, as well as for apnea analysis, are summarized. Advanced digital signal processing algorithms for cardiac electric signals are specifically reviewed, including independent component decompositions, and nonlinear methods (chaos, fractals, and entropies). Finally, systems aiming to solve the inverse problem in electrocardiography are presented. Concluding remarks on these systems and on the whole review are discussed.Ítem Action Potential Alternans in LQT3 Syndrome: A Simulation Study(2009-06-15T09:26:47Z) Alonso Atienza, Felipe; Requena Carrión, J; Rojo-Álvarez, José Luis; Berenfeld, O; Jalife, JThe long QT syndrome type-3 (LQT3) is an inherited cardiac disorder caused by mutations in the sodium channel gene SCN5A. LQT3 has been associated with ventricular arrhythmias and sudden cardiac death, specially at low heart rates. Based on computer simulations and experimental investigations, analysis of the morphology of the Action Potential (AP) has shown that it undergoes early afterdepolarizations (EADs) and spontaneous discharges, which are thought to be the trigger for reentry like-activity. However, dynamic characteristics of cardiac tissue are also important factors of arrhythmia mechanisms. In this work, we propose a dynamical analysis of the LQT3 at cellular level. We use a detailed Markovian model of the DKPQ mutation, which is associated with LQT3, and we study beat-to-beat AP Duration (APD) variations by using a long-term stimulation protocol. Compared to wild-type (WT) cells, DKPQ mutant cells are found to develop APD alternans over a narrow range of stimulation frequencies. Moreover, the interval of frequency dependence of APD alternans is related to the degree of severity of the EADs present in the AP. In conclusion, dynamical analysis of paced cells is a useful approach to understand the mechanisms of rate dependent arrhythmias.Ítem AKPQ mutation in LQT3 results in increased frequency and stability of reentry(2009-07-28T10:25:27Z) Alonso Atienza, Felipe; Requena Carrión, Jesús; Rojo-Álvarez, José Luis; Berenfeld, O; Jalife, JÍtem Analysing Effects of Implant Dimensions on Electrocardiograph: A Modeling Approach(2009-06-15T09:22:13Z) Väisänen, J; Requena Carrión, J; Alonso Atienza, Felipe; Rojo-Álvarez, José Luis; Hyttinen, JModeling offers effective means of studying the effects of implant dimensions on the measured electrocardiograph (ECG) prior to any in vivo tests, and thus provides the designer with valuable information. Finite difference (FDM) and lead field approaches combined with cardiac activation models offer straightforward and effective methods for analyzing different ECG measurement configurations. In the present study such methods are applied in studying the effects of implant dimensions on the simulated ECG which describes an ectopic beat originating from the apex. The results indicated that the change in interelectrode distance has the largest effects on the ECG. Other parameters related implant dimensions have minor effect on the ECG.Ítem Analysis of the Scope of Unipolar and Bipolar Electrograms in Implantable Cardioverter Defibrillators(2009-07-23T10:51:41Z) Requena Carrión, Jesús; Väisänen, J; Hyttinen, J; Rojo-Álvarez, José Luis; Alonso Atienza, Felipe; Malmivuo, JÍtem Bootstrap Feature Selection in Support Vector Machines for Ventricular Fibrillation Detection(2009-07-23T11:01:23Z) Alonso Atienza, Felipe; Rojo-Álvarez, José Luis; Camps Valls, Gustavo; Rosado Muñoz, A; García Alberola, ASupport Vector Machines (SVM) for classification are being paid special attention in a number of practical applications. When using nonlinear Mercer kernels, the mapping of the input space to a highdimensional feature space makes the input feature selection a difficult task to be addressed. In this paper, we propose the use of nonparametric bootstrap resampling technique to provide with a statistical, distribution independent, criterion for input space feature selection. The confidence interval of the difference of error probability between the complete input space and a reduced-in-one-variable input space, is estimated via bootstrap resampling. Hence, a backward variable elimination procedure can be stated, by removing one variable at each step according to its associated confidence interval. A practical example application to early stage detection of cardiac Ventricular Fibrillation (VF) is presented. Basing on a previous nonlinear analysis based on temporal and spectral VF parameters, we use the SVM with Gaussian kernel and bootstrap resampling to provide with the minimum input space feature set that still holds the classification performance of the complete data. The use of bootstrap resampling is a powerful input feature selection procedure for SVM classifiers.Ítem Changes in Cardiac Indices from Implanted Defibrillator-Stored Electrograms Due to Acquisition and Preprocessing Conditions(2009-06-15T09:41:57Z) Requena Carrión, J; Rojo-Álvarez, José Luis; Everss, E; Alonso Atienza, Felipe; Sánchez Muñoz, JJ; Ortiz, M; García Alberola, AA wide number of cardiac indices have been proposed to describe electrocardiograms (ECG) during ventricular Fibrillation (VF), and they can be useful when analyzing electrograms (EGM) stored in Implantable Cardioverter Defibrillator (ICD) during spontaneous VF. However, the dependence of their measurement on acquisition and preprocessing conditions has not been so far statistically quantified. We propose a systematic procedure based on nonparametric bootstrap resampling methods to obtain standard errors and confidence intervals for a test. This test detects changes in the statistical distribution of cardiac indices from ICD-stored EGM during VF, due to discrepancies in acquisition and preprocessing conditions. As an application example, significant changes in the distributions of selected spectral indices due to lead configuration were found by comparing measurements obtained from simultaneo usly recorded unipolar and bipolar EGM during VF. Our nonparametric bootstrap approach can be readily applied to the measurement of cardiac indices, allowing us to study their changes under a diversity of conditions in a systematic way.Ítem Contribution of the Left Anterior Myocardium to the Body Surface Potentials in Case of Apical Ectopic Beat(2009-06-15T09:36:55Z) Väisänen, J; Requena Carrión, J; Alonso Atienza, Felipe; Rojo-Álvarez, José Luis; Malmivuo, J; Hyttinen, JThe present paper describes a study where effects of anterior myocardium on body surface potentials were investigated. The study combines numerical lead field analysis combined with cardiac automata model. Electric fields are calculated with finite difference method in a 3-D model of male thorax. The cardiac activation applied in the study is an ectopic beat originating in the apex. The correlations and mean differences between signal generated by anterior segments of left ventricle and signal generated by both ventricles were analysed for 117 leads. The results show that there are leads which have high correlation (>0.9) with low the relative mean difference (<0.2) between the signals generated by anterior segments and signals generated by whole ventricles. These electrode locations would be optimal to monitor the activation of anterior segments when ectopic beats originate in apex.Ítem Contributions of the 12 Segments of Left Ventricular Myocardium to the Body Surface Potentials(2009-07-23T11:39:20Z) Väisänen, J; Requena Carrión, Jesús; Alonso Atienza, Felipe; Hyttinen, J; Rojo-Álvarez, José Luis; Malmivuo, JExperimental and inverse approaches have been applied in studying the contributions of different parts of the myocardium to the ECG measurements. Also optimal electrode locations for different clinical purposes have been studied by applying body surface maps. It is valuable to know where the measured ECG is actually generated. Thus the measurements can be designed to be most optimal to measure certain myocardial sources. Here we assess the contributions of 12 left ventricular segments to the potentials of 117 surface leads. The study is based on the numerical lead field analysis combined with the cardiac activation modeling. We analyzed the contributions of the signals generated by different segments to the total signal generated by the left ventricle. It was found that anterior segments have high contributions to the leads on the lower left thorax and inferior segments on the leads on the lower left back. These results were expected based on the previous clinical studies.Ítem Deconvolution and Causality for 1:1 Arrhythmia Discrimination in Dual Chamber Defibrillator(2009-06-15T08:38:10Z) Rojo-Álvarez, José Luis; Alonso Atienza, Felipe; Martínez Alzamora, N; Arenal Maíz, Ángel; Piñeiro Ave, J; Artés Rodríguez, AÍtem Denoising of Heart Rate Variability Signals During Tilt Test Using Independent Component Analysis and Multidimensional Recordings(2009-07-14T11:55:00Z) Gimeno Blanes, FJ; Rojo-Álvarez, José Luis; Requena Carrión, Jesús; Everss, E; Hernández Ortega, J; Alonso Atienza, Felipe; García Alberola, ArcadiÍtem Desarrollo de un modelo probabilístico de la actividad eléctrica cardíaca basado en un autómata celular(2005-01) Alonso Atienza, Felipe; Requena Carrión, Jesús; García Alberola, Arcadi; Rojo-Álvarez, José Luis; Sánchez Muñoz, Juan J.; Martínez Sánchez, Juan; Valdés Chávarri, MarianoIntroduction and objectives. Mathematical models of cardiac electrical activity may help to elucidate the electrophysiological mechanisms involved in the genesis of arrhythmias. The most realistic simulations are based on reaction-diffusion models and involve a considerable computational burden. The aim of this study was to develop a computer model of cardiac electrical activity able to simulate complex electrophysiological phenomena but free of the large computational demands required by other commonly used models. Material and method. A cellular automata system was used to model the cardiac tissue. Each individual unit had several discrete states that changed according to simple rules as a function of the previous state and the state of the neighboring cells. Activation was considered as a probabilistic process and was adjusted using restitution curves. In contrast, repolarization was modeled as a deterministic phenomenon. Cell currents in the model were calculated with a prototypical action potential that allowed virtual monopolar and bipolar electrograms to be simulated at any point in space. Results. Reproducible flat activation fronts, propagation from a focal stimulus, and reentry processes that were stable and unstable in two dimensions (with their corresponding electrograms) were obtained. The model was particularly suitable for the simulation of the effects observed in curvilinear activation fronts. Fibrillatory conduction and stable rotors in two- and three-dimensional substrates were also obtained. Conclusions. The probabilistic cellular automata model was simple to implement and was not associated with a high computational burden. It provided a realistic simulation of complex phenomena of interest in electrophysiology.Ítem Effects of the Location of Myocardial Infarction on the Spectral Characteristics of Ventricular Fibrillation(2009-07-23T10:00:40Z) Sánchez Muñoz, Juan J; Rojo-Álvarez, José Luis; García Alberola, A; Everss, E; Requena Carrión, Jesús; Ortiz, M; Alonso Atienza, Felipe; Valdés, MÍtem Estimation of the Scope of Transvenous Lead Systems in Implantable Cardioverter Defibrillators(2009-06-15T09:32:29Z) Requena Carrión, J; Väisänen, J; Alonso Atienza, Felipe; Rojo-Álvarez, José Luis; Hyttinen, J; García Alberola, AThe analysis of intracardiac Electrograms (EGM) recorded by transvenous lead systems in Implantable Cardioverter Defibrillators (ICD) often entails assumptions on the scope of the lead system. Based on bioelectric signal modeling and on numerical analysis, we studied quantitatively the scope of unipolar and bipolar lead configurations in ICD. We defined the scope in terms of the Mean Square Difference (MSD) between EGM generated by the whole myocardium, and EGM generated by different families of regions within the myocardium. For unipolar and bipolar lead systems, simulations showed that the smallest myocardial region involving a given value of MSD is characterized by the highest measurement sensitivity. Furthermore, the scope in the ventricles was found to be an order of magnitude smaller for bipolar leads than for unipolar leads. Bioelectric signal modeling combined with numerical analysis constitutes a powerful method to study quantitatively the scope of transvenous lead systems.Ítem Estudio de los mecanismos de las arritmias cardíacas mediante modelado y procesado robusto digital de señal(2008-05) Alonso Atienza, FelipeÍtem Identificación de Artefactos en Registros Multidimensionales de Parámetros Hemodinámicos mediante Análisis de Componentes Independientes(2009-07-14T11:42:52Z) Requena Carrión, Jesús; González Serrano, F; Everss, E; Alonso Atienza, Felipe; García Alberola, Arcadi; Rojo-Álvarez, José LuisLos parámetros hemodinámicas monitorizados durante la Prueba de Basculación (PB) sufren perturbaciones que pueden degradar considerablemente los resultados de su análisis. Asumiendo independencia estadística entre las fuentes de interés y los artefactos, en este artículo se propone un procedimiento de identificación de artefactos basado en la teoría del Análisis de Componentes Independientes (ACI). Registros de Frecuencia Cardiaca, Presión Arterial Sistólica, Presión Arterial Diastólica y Volumen de Expulsión Cardiaco monitorizados en pacientes sometidos a la PB, se procesaron mediante el método de ACI. Este procedimiento permitió identificar satisfactoriamente artefactos debidos a extrasístoles cuando no existían perturbaciones de otra naturaleza, si bien su capacidad de identificación resultó ser menor en presencia de artefactos debidos a errores en la estimación de intervalos RR. La identificación de artefactos en registros hemodinámicos multidimensionales es potencialmente abordable mediante esquemas de ACI.Ítem Nonuniform Interpolation of Noisy Signals Using Support Vector Machines(2007-08-01) Rojo-Álvarez, José Luis; Figuera Pozuelo, Carlos; Camps Valls, Gustavo; Alonso Atienza, Felipe; Martínez Ramón, ManelThe problem of signal interpolation has been intensively studied in the Information Theory literature, in conditions such as unlimited band, nonuniform sampling, and presence of noise. During the last decade, support vector machines (SVM) have been widely used for approximation problems, including function and signal interpolation. However, the signal structure has not always been taken into account in SVM interpolation. We propose the statement of two novel SVM algorithms for signal interpolation, specifically, the primal and the dual signal model based algorithms. Shift-invariant Mercer¿s kernels are used as building blocks, according to the requirement of bandlimited signal. The sinc kernel, which has received little attention in the SVM literature, is used for andlimited reconstruction. Well-known properties of general SVM algorithms (sparseness of the solution, robustness, and regularization) are explored with simulation examples, yielding improved results with respect to standard algorithms, and revealing good characteristics in nonuniform interpolation of noisy signals.Ítem Numerical Analysis of the Resolution of Surface Electrocardiographic Lead Systems(2009-07-23T11:45:29Z) Requena Carrión, Jesús; Väisänen, J; Rojo-Álvarez, José Luis; Hyttinen, J; Alonso Atienza, Felipe; Malmivuo, JNon-invasive electrocardiographic (ECG) techniques for assessing the electrical activity of selected regions within the cardiac muscle can benefit from suitable positioning of surface electrodes. This positioning is usually guided heuristically and complemented by clinical and experimental studies, but there is a lack of general methods to characterize quantitatively the ability of a given electrode configuration to focus on selected regions of the heart. In this study we explore an approach to the characterization of the resolution of surface ECG systems based on the concept of Resolution Mass (RM). By integrating bioelectric signal modeling and numerical methods, we explore, in an application example, the location and size of the RM for a multielectrode ECG system. The concept of RM combined with bioelectric signal modeling and numerical methods constitutes a powerful tool to investigate the resolution properties of surface ECG systems.Ítem Reconstruction of Transmembrane Currents Using Support Vector Machines and Its Application to Endocardial Mapping: A Model Study(2009-06-15T09:13:32Z) Alonso Atienza, Felipe; Rojo-Álvarez, José Luis; Álvarez, D; Moscoso, M; García Alberola, ARecent endocardial mapping systems reconstruct an instantaneous image of the endocardial electrical activity performing the inverse problem of electrocardiography (IPE), which consists of estimating the endocardial surface potentials from intracavitary probe potentials. Even though the IPE has been long studied, it still being paid attention due to its ill-posed nature, and many different regularization techniques have been explored in this setting. In this study we analyzed Support Vector machines (SVM) as an alternative regularization technique regarding their robustness against ill-posed problems. We propose here two new SVM algorithms, specifically adapted to the ill-posing issues of the IPE, and develop the equations for endocardial mapping of transmembrane currents. We show, both in simple simulations and in a previously developed cellular automata, that the ill-posing robustness of the SVM is higher when compared to regularized approaches during the depolarization phase. In conclusion, the properties of the developed SVM algorithms stand for an appropriate framework for addressing the IPE