The Effects of Fibrotic Cell Type and Its Density on Atrial Fibrillation Dynamics: An In Silico Study.

Remodeling in atrial fibrillation (AF) underlines the electrical and structural changes in the atria, where fibrosis is a hallmark of arrhythmogenic structural alterations. Fibrosis is an important feature of the AF substrate and can lead to abnormal conduction and, consequently, mechanical dysfunction. The fibrotic process comprises the presence of fibrotic cells, including fibroblasts, myofibroblasts and fibrocytes, which play an important role during fibrillatory dynamics. This work assesses the effect of the diffuse fibrosis density and the intermingled presence of the three types of fibrotic cells on the dynamics of persistent AF. For this purpose, the three fibrotic cells were electrically coupled to cardiomyocytes in a 3D realistic model of human atria. Low (6.25%) and high (25%) fibrosis densities were implemented in the left atrium according to a diffuse fibrosis representation. We analyze the action potential duration, conduction velocity and fibrillatory conduction patterns. Additionally, frequency analysis was performed in 50 virtual electrograms. The tested fibrosis configurations generated a significant conduction velocity reduction, where the larger effect was observed at high fibrosis density (up to 82% reduction in the fibrocytes configuration). Increasing the fibrosis density intensifies the vulnerability to multiple re-entries, zigzag propagation, and chaotic activity in the fibrillatory conduction. The most complex propagation patterns were observed at high fibrosis densities and the fibrocytes are the cells with the largest proarrhythmic effect. Left-to-right dominant frequency gradients can be observed for all fibrosis configurations, where the fibrocytes configuration at high density generates the most significant gradients (up to 4.5 Hz). These results suggest the important role of different fibrotic cell types and their density in diffuse fibrosis on the chaotic propagation patterns during persistent AF.

Protists and other organisms on a minute snail periostracum / Protistas e outros organismos em um pequeno periostracum de caracol

Abstract Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.

Resumo Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.

Entropy Mapping Approach for Functional Reentry Detection in Atrial Fibrillation: An In-Silico Study.

Catheter ablation of critical electrical propagation sites is a promising tool for reducing the recurrence of atrial fibrillation (AF). The spatial identification of the arrhythmogenic mechanisms sustaining AF requires the evaluation of electrograms (EGMs) recorded over the atrial surface. This work aims to characterize functional reentries using measures of entropy to track and detect a reentry core. To this end, different AF episodes are simulated using a 2D model of atrial tissue. Modified Courtemanche human action potential and Fenton-Karma models are implemented. Action potential propagation is modeled by a fractional diffusion equation, and virtual unipolar EGM are calculated. Episodes with stable and meandering rotors, figure-of-eight reentry, and disorganized propagation with multiple reentries are generated. Shannon entropy ( S h E n ), approximate entropy ( A p E n ), and sample entropy ( S a m p E n ) are computed from the virtual EGM, and entropy maps are built. Phase singularity maps are implemented as references. The results show that A p E n and S a m p E n maps are able to detect and track the reentry core of rotors and figure-of-eight reentry, while the S h E n results are not satisfactory. Moreover, A p E n and S a m p E n consistently highlight a reentry core by high entropy values for all of the studied cases, while the ability of S h E n to characterize the reentry core depends on the propagation dynamics. Such features make the A p E n and S a m p E n maps attractive tools for the study of AF reentries that persist for a period of time that is similar to the length of the observation window, and reentries could be interpreted as AF-sustaining mechanisms. Further research is needed to determine and fully understand the relation of these entropy measures with fibrillation mechanisms other than reentries.

Protists and other organisms on a minute snail periostracum / Protistas e outros organismos em um pequeno periostracum de caracol

Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.(AU)

Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.(AU)

Ablación cardiaca auricular: estrategias guiadas por el mapeo de electrogramas / Catheter Ablation for Atrial Fibrillation: Electrogram-Guided Methods

Resumen La ablación por radiofrecuencia se ha constituido como la técnica más utilizada para el tratamiento intervencionista de la fibrilación auricular. El aislamiento eléctrico de venas pulmonares se ha convertido en el procedimiento convencional, principalmente en pacientes con fibrilación auricular paroxística. Sin embargo, la tasa de éxito mediante esta técnica en pacientes con fibrilación auricular persistente es alrededor del 50%. Aunque se han propuesto diversas estrategias para guiar al electrofisiólogo en los procedimientos de ablación, estudios recientes muestran que la generación de líneas de ablación adicionales guiadas anatómicamente o mediante mapeo de electrogramas complejos fragmentados, no mejora la tasa de éxito del procedimiento convencional de aislamiento de venas pulmonares. En esta revisión, se consideran las limitaciones que representan los métodos de mapeo electrofisiológicos actuales, las nuevas estrategias de evaluación de los electrogramas y los métodos de procesamiento de señales que se ven propuestos en el futuro más inmediato, para guiar los procedimientos de ablación particularmente en pacientes con fibrilación auricular persistente.

Abstract Radiofrequency catheter ablation has evolved into an effective treatment option for drug-resistant patients with atrial fibrillation. Electrical isolation of the pulmonary veins has become the standard ablation strategy mainly in patients with paroxysmal atrial fibrillation. However, the success rate of pulmonary veins isolation is about 50% in patients with persistent atrial fibrillation. Although different strategies to guide the electrophysiologist in ablation procedures have been proposed. Recent studies show that the generation of additional ablation lines guided anatomically or by fragmented complex electrograms mapping does not improve the success rate of the conventional pulmonary veins isolation procedure. In this review, we describe the limitations of current electrophysiological mapping methods, the new electrogram evaluation strategies and the signal processing methods that are proposed in the immediate future, to guide ablation procedures, particularly in patients with atrial fibrillation persistent.

The temporal stability of recurrence quantification analysis attributes from chronic atrial fibrillation electrograms

Abstract Introduction The temporal behavior of atrial electrograms (AEGs) collected during persistent atrial fibrillation (persAF) directly affects ablative treatment outcomes. We investigated different durations of AEGs collected during persAF using recurrence quantification analysis (RQA). Methods 797 bipolar AEGs with different durations (from 0.5 s to 8 s) from 18 patients were investigated. Four RQA-based attributes were evaluated based on AEG durations: determinism (DET); recurrence rate (RR); laminarity (LAM); and diagonal lines' entropy (ENTR). The Spearman correlation (ρ) between each duration versus 8 s was calculated. AEG classification was performed following the CARTO criteria (Biosense Webster) and receiving operating characteristic (ROC) curves were created for the RQA variables. Results The RQA variables successfully discriminated the AEGs: the area under the ROC curves were as high as 0.70 for AEGs with 3.5 s or greater. Three types of AEGs were found using these variables: normal, fractionated and temporally unstable. The number of unstable AEGs decreased with longer AEG segments. Different AEG durations significantly affected the RQA variables (P<0.0001), with no statistical difference between the durations 6 s, 7 s and 8 s for DET, LAM and ENTR, and no difference between 7 s and 8 s for RR (P<0.0001). AEGs with 3 s or longer have shown ρ ≥ 80% for all variables. Conclusion The RQA variables have been shown effective in the characterization of AEGs collected during persAF with a shorter duration than current recommendations, which motivates their use for the characterization of atrial substrate during persAF ablation.

Force Trends and Pulsatility for Catheter Contact Identification in Intracardiac Electrograms during Arrhythmia Ablation.

The intracardiac electrical activation maps are commonly used as a guide in the ablation of cardiac arrhythmias. The use of catheters with force sensors has been proposed in order to know if the electrode is in contact with the tissue during the registration of intracardiac electrograms (EGM). Although threshold criteria on force signals are often used to determine the catheter contact, this may be a limited criterion due to the complexity of the heart dynamics and cardiac vorticity. The present paper is devoted to determining the criteria and force signal profiles that guarantee the contact of the electrode with the tissue. In this study, we analyzed 1391 force signals and their associated EGM recorded during 2 and 8 s, respectively, in 17 patients (82 ± 60 points per patient). We aimed to establish a contact pattern by first visually examining and classifying the signals, according to their likely-contact joint profile and following the suggestions from experts in the doubtful cases. First, we used Principal Component Analysis to scrutinize the force signal dynamics by analyzing the main eigen-directions, first globally and then grouped according to the certainty of their tissue-catheter contact. Second, we used two different linear classifiers (Fisher discriminant and support vector machines) to identify the most relevant components of the previous signal models. We obtained three main types of eigenvectors, namely, pulsatile relevant, non-pulsatile relevant, and irrelevant components. The classifiers reached a moderate to sufficient discrimination capacity (areas under the curve between 0.84 and 0.95 depending on the contact certainty and on the classifier), which allowed us to analyze the relevant properties in the force signals. We conclude that the catheter-tissue contact profiles in force recordings are complex and do not depend only on the signal intensity being above a threshold at a single time instant, but also on time pulsatility and trends. These findings pave the way towards a subsystem which can be included in current intracardiac navigation systems assisted by force contact sensors, and it can provide the clinician with an estimate of the reliability on the tissue-catheter contact in the point-by-point EGM acquisition procedure.

Protists and other organisms on a minute snail periostracum

Abstract Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.

Resumo Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.

Protists and other organisms on a minute snail periostracum

Abstract Since the foundation of the Malacological Center in 1980, Universidad Centro Americana (UCA), Managua-Nicaragua, has been monitoring and collecting the marine, terrestrial, fluvial and lake mollusk population of the country. Many specimens have been photographed by Scanning Electronic Microscope (SEM), and in one of these, observation of the hairy periostracum reveals a seemingly thriving population of minute protists in possible symbiosis with their host. Adequate magnification and comparison with previous studies allowed the determination of these hosts as diatoms, testaceous amoebae, yeast, phacus, spores and other undetermined organisms which occur in tropical forests on rocks, trees and leaves. Here illustrated are diatoms and other organisms detected for the first time on the periostracum of a tropical rainforest mollusk.

Resumo Desde a fundação do Centro Malacológico em 1980, a Universidad Central Americana (UCA), Manágua-Nicarágua, vem acompanhando e coletando a população de moluscos marinhos, terrestres, fluviais e lagoas do país. Muitos espécimes foram fotografados pelo microscópio eletrônico de varredura (SEM) e, em um deles, a observação do periostracum peludo revela uma população aparentemente próspera de protistas de minuto em possível simbiose com o hospedeiro. A ampliação adequada e a comparação com estudos anteriores permitem a determinação dessas diatomáceas, amebas testaceas, leveduras, phacus, esporos e outros organismos indeterminados que ocorrem em florestas tropicais em rochas, árvores e folhas. Aqui estão as diatomeas e outros organismos pela primeira vez detectados no periostracum de um molusco tropical.

IDENTIFICACIÓN DE ZONAS SUSCEPTIBLES DE ABLACIÓN EN FIBRILACIÓN AURICULAR PERMANENTE IMPLEMENTANDO ENTROPÍA APROXIMADA EN UN MODELO 2D / IDENTIFICATION OF TARGET SITES FOR ABLATION DURING PERMANENT ATRIAL FIBRILLATION IMPLEMENTING APPROXIMATE ENTROPY IN A 2D MODEL / IDENTIFICAÇÃO DE ÁREAS SUSCETÍVEIS DE ABLAÇÃO PERMANENTE DE FIBRILAÇÃO ATRIAL NA IMPLEMENTAÇÃO ENTROPY APROXIMADO UM MODELO 2D

La fibrilación auricular (FA) es la arritmia cardiaca más común. La ablación con catéter se ha convertido en la principal estrategia terapéutica para el tratamiento de la FA paroxística, sin embargo, los resultados en FA permanente no son completamente satisfactorios. Se propone la ablación de los electrogramas auriculares complejos fragmentados (CFAE) para la terminación de un rotor como mecanismo de mantenimiento de FA permanente. El objetivo de este trabajo es caracterizar los CFAE mediante la implementación de entropía aproximada (ApEn) y correlacionarlos con el tip de un rotor simulado. Para esto, se desarrolló un modelo 2D de tejido de aurícula humana bajo condiciones de FA permanente; se registraron electrogramas unipolares durante la actividad del rotor y se desarrolló un algoritmo para la medida de ApEn. La ApEn permitió localizar los CFAE con una alta precisión y relacionarlos con el tip del rotor. Por lo que este índice podría ser muy eficaz en la identificación de zonas susceptibles de ablación.

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Catheter ablation has become the main therapeutic strategy for the treatment of paroxysmal AF, however, results in permanent AF are not completely satisfactory. Ablation of complex fractionated atrial electrograms (CFAE) is proposed for the termination of a rotor as mechanism of permanent AF maintenance. The aim of this work is to characterize the CFAE by implementing approximate entropy (ApEn) and to correlate with the tip of a simulated rotor. For this, a 2D model of human atrial tissue under permanent FA conditions was developed. Unipolar electrograms were recorded during the rotor activity and an algorithm to measure ApEn was developed. The ApEn allowed locate the CFAE with high precision and relate them to the tip of the rotor. So this index could be very effective in identifying target sites for ablation.

A fibrilação atrial (FA) é a arritmia cardíaca mais comum. A ablação por cateter tornou-se a principal estratégia terapêutica para o tratamento da fibrilação atrial paroxística, no entanto, resulta em FA permanente não são completamente satisfatórios. Ablação de fones de ouvido eletrocardiogramas complexos fragmentada (CFAE) para a conclusão de um rotor como um mecanismo de manutenção da FA permanente, é proposto. O objetivo deste trabalho é caracterizar o CFAE através da implementação de entropia aproximada (ApEn) e correlacioná-los com a ponta de um rotor simulado. Para isso, um modelo em 2D do tecido atrial humano sob condições de FA permanente desenvolvido; unipolares electrogramas foram registados durante a actividade do rotor e um algoritmo para medir ApEn desenvolvido. O ApEn permitido CFAE localizar com precisão elevada e relacioná-los com a ponta do rotor. Portanto, esta taxa pode ser muito eficaz na identificação de áreas suscetíveis a ablação.

Electrogramas intracardíacos en tiempo real en el diagnóstico de fallas de marcapasos / Real time intracardiac electrograms for the diagnosis of pacemaker malfunction

El desplazamiento crónico del catéter ventricular es una complicación infrecuente del implante de marcapasos. Es infrecuente que un catéter desplazado sense y capture en una cámara donde no fue implantado originalmente. Se presenta el caso de un paciente con marcapasos doble cámara en el que el catéter ventricular se desplazó hacia la aurícula derecha. El catéter desplazado permite sensar y capturar la aurícula. El diagnóstico inicial se realizó mediante el análisis deductivo conjunto de los electrogramas en tiempo real y los eventos en los canales de registro ("marker channel"). La radiografía de tórax confirmó el diagnóstico presuntivo.

Chronic ventricular lead dislodgement is an infrequent complication of pacemaker implantation. Occasionally, the dislodged lead may sense and capture a chamber in which the lead was not originally positioned. Intracardiac real time electrograms and channel markers are useful tools for the diagnosis of pacemaker malfunction. We present the case of a patient with a ventricular lead dislodgement into the atrium. The ventricular lead was able to sense and capture the atrium. Initial diagnosis was performed based on the deductive analysis of intracardiac real time electrograms and channel markers and confirmed by chest X-ray.