José Luis Rojo Álvarez

A Probabilistic Model of Cardiac Electrical Activity Based on a Cellular Automata System

Introduction 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.

Desarrollo de un modelo probabilístico de la actividad eléctrica cardíaca basado en un autómata celular

Introduccion y objetivos La utilizacion de modelos matematicos de activacion y propagacion del impulso ha mejorado la comprension de diversos mecanismos electrofisiologicos involucrados en la genesis de las arritmias. Las simulaciones mas realistas se basan en los modelos de reaccion-difusion e implican una carga computacional muy elevada. El objetivo del estudio es desarrollar un modelo de activacion electrica cardiaca por ordenador que permita simular fenomenos electrofisiologicos complejos y que no requiera la carga computacional necesaria en otros modelos habitualmente empleados. Material y metodo Se ha modelado el tejido cardiaco como un automata celular, cada uno de cuyos elementos adopta estados discretos en funcion de su estado previo y del de las celulas vecinas siguiendo unas reglas sencillas. La activacion se contempla como un proceso probabilistico y se ajusta mediante el fenomeno de restitucion, mientras la repolarizacion se modela como un proceso determinista. Finalmente, las corrientes celulares se calculan utilizando un potencial de accion prototipo, lo que permite simular los electrogramas virtuales monopolares y bipolares en cualquier punto del espacio. Resultados Se ha conseguido reproducir frentes planos de activacion, propagacion de un estimulo focal y reentradas estables e inestables en 2 dimensiones, con sus electrogramas correspondientes. El modelo es particularmente adecuado para simular los fenomenos asociados a la curvatura de los frentes, y permite reproducir la conduccion fibrilatoria y los rotores estables en 2 y 3 dimensiones. Conclusiones Aunque el modelo de automata celular probabilistico desarrollado es sencillo y no requiere cargas computacionales elevadas, es capaz de simular de forma realista fenomenos complejos de gran interes en electrofisiologia.

Early Heart Rate Increase Does Not Predict the Result of the Head-Up Tilt Test Potentiated With Nitroglycerin

INTRODUCTION AND OBJECTIVES The magnitude of the change in heart rate during the first few minutes of the head-up tilt test has been used to predict the tests result. The aim of this study was to investigate whether the heart rate increase during the head-up tilt test potentiated with nitroglycerin is related to the development of syncope. PATIENTS AND METHOD The study included 158 consecutive patients with syncope, with stable sinus rhythm, and without structural cardiac disease who were undergoing a head-up tilt test with nitroglycerin. The heart rate increment induced by the tilt maneuver and by nitroglycerin administration was calculated, and its relationship to clinical variables and to the tests results was analyzed. RESULTS The head-up tilt test gave positive results in 117 patients (74%). The heart rate was 68.7 (11.3) bpm in the decubitus position and 85.1 (15.4) bpm during the first 6 min of tilting. There was strong inverse correlation between the heart rate increase induced by tilting and age (r=--0.63; P<.001), but the increase (16.8 [9.3] bpm in patients with syncope versus 14.9 [11.3] bpm in those without; P=.3) did not predict the result of the test. The heart rate increase induced by nitroglycerin was also similar for patients with and without syncope during the pharmacologic phase of the test (27.3 [12.6] bpm and 26.7 (13.4) bpm, respectively; P=.8). CONCLUSIONS The magnitude of the heart rate increase during the first few minutes of tilt-testing and after nitroglycerin administration is inversely related to age but does not predict the result of the head-up tilt test with nitroglycerin.

A Review on Recent Patents in Digital Processing for Cardiac Electric Signals (I): From Basic Systems to Arrhythmia Analysis

Cardiac 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.

Requirements Quality Analysis: A Successful Case Study in the Industry

This case study analyses the applicability of a Quality Improvement Process that will enhance the quality of the requirements using an existing requirement specification to seed the Knowledge Base with the organization know–how. This Knowledge Base drives the quality assessment and directs the requirement authors to the areas that can be improved. The updated specification feeds back into the Knowledge Base thereby institutionalizing continuous process improvement into Alstom. The case study has been developed by means of a Proof of Concepts using the RQS suit tools to gather the knowledge (KM), analyse the quality (RQA) and authoring requirements (RAT).

Analysis of the INCOSE Rules for Writing Good Requirement in Industry: A Tool Based Study

The Requirements Engineering (RE) discipline has been promoted, implemented and deployed for more than 20 years through standardization agencies (ISO/IEC, IEEE) and national/international organizations (such as INCOSE). Ever since, despite an increasing maturity, RE remains a discipline unequally understood and implemented, even within the same organization. Problems found in current Systems Engineering projects with focus in RE could be mitigated using quality metrics in the process. Quality metrics aids in the process of writing good requirements by following a reference guide. INCOSE has promoted and published a guide for writing good requirements, with support of several industrial and academic partners. The more correct, complete and consistent a requirement is, the best performance it will have, and fewer errors will occur in system developments and operation. This paper presents a study where a set of the published INCOSE rules have been implemented in a tool for assessing requirements quality.