Vector Field Heterogeneity for the Assessment of Locally Disorganised Cardiac Electrical Propagation Wavefronts From High-Density Multielectrodes

High-density multielectrode catheters are becoming increasingly popular in cardiac electrophysiology for advanced characterisation of the cardiac tissue, due to their potential to identify impaired sites. These are often characterised by abnormal electrical conduction, which may cause locally disorganised propagation wavefronts. To quantify it, a novel heterogeneity parameter based on vector field analysis is proposed, utilising finite differences to measure direction changes between adjacent cliques. The proposed Vector Field Heterogeneity metric has been evaluated on a set of simulations with controlled levels of organisation in vector maps, and a variety of grid sizes. Furthermore, it has been tested on animal experimental models of isolated Langendorff-perfused rabbit hearts. The proposed parameter exhibited superior capturing ability of heterogeneous propagation wavefronts compared to the classical Spatial Inhomogeneity Index, and simulations proved that the metric effectively captures gradual increments in disorganisation in propagation patterns. Notably, it yielded robust and consistent outcomes for [Formula: see text] grid sizes, underscoring its suitability for the latest generation of orientation-independent cardiac catheters.

Evaluation and assessment of clique arrangements for the estimation of omnipolar electrograms in high density electrode arrays: an experimental animal model study

High-density catheters combined with Orientation Independent Sensing (OIS) methods have emerged as a groundbreaking technology for cardiac substrate characterisation. In this study, we aim to assess the arrangements and constraints to reliably estimate the so-called omnipolar electrogram (oEGM). Performance was evaluated using an experimental animal model. Thirty-eight recordings from nine retrospective experiments on isolated perfused rabbit hearts with an epicardial HD multielectrode were used. We estimated oEGMs according to the classic triangular clique (4 possible orientations) and a novel cross-orientation clique arrangement. Furthermore, we tested the effects of interelectrode spacing from 1 to 4 mm. Performance was evaluated by means of several parameters that measured amplitude rejection ratios, electric field loop area, activation pulse width and morphology distortion. Most reliable oEGM estimations were obtained with cross-configurations and interelectrode spacings [Formula: see text] mm. Estimations from triangular cliques resulted in wider electric field loops and unreliable detection of the direction of the propagation wavefront. Moreover, increasing interelectrode distance resulted in increased pulse width and morphology distortion. The results prove that current oEGM estimation techniques are insufficiently accurate. This study opens a new standpoint for the design of new-generation HD catheters and mapping software.

Assessment of the Interelectrode Distance Effect over the Omnipole with High Multielectrode Arrays

The development of high-density multielectrode catheters has significantly advanced cardiac electrophysiology mapping. High-density grid catheters have enabled the creation of a novel technique for reconstructing electrogram (EGM) signals known as "omnipole," which is believed to be more reliable than other methods, especially in terms of orientation independence. This study aims to evaluate how distance affects the omnipolar reconstruction of EGMs by comparing different configurations. Using an animal set up of perfused isolated rabbit hearts, recordings were taken using an ad hoc high-density epicardial multielectrode catheter. Inter-electrode distances ranging from 1 to 4 mm were analysed for their effect on the quality of resulting EGMs. Two biomarkers were computed to evaluate the robustness of the reconstructions: the areas contained within the bipolar loops and the amplitudes of the omnipoles. We hypothesised that both bipolar and omnipolar electrograms would be more robust at shorter inter-electrode distances. The results showed that an increase in distance triggers an increase in loop areas and amplitudes, which supports the hypothesis. This finding provides a more reliable estimate of wavefront propagation for the cross-omnipolar reconstruction method. These results emphasise the importance of distance in cardiac electrophysiology mapping and provide valuable insights into the use of high-density multielectrode catheters for EGM reconstruction.Clinical Relevance- The results of this study have direct clinical relevance in the application of the described techniques to recording systems in the cardiac electrophysiology laboratory, enabling clinicians to obtain more precise characterisation of signals in the myocardium.

Performance assessment of electrode configurations for the estimation of omnipolar electrograms from high density arrays

OBJECTIVE

The aim of this study is to propose a method to reduce the sensitivity of the estimated omnipolar electrogram (oEGM) with respect to the angle of the propagation wavefront.

METHODS

A novel configuration of cliques taking into account all four electrodes of a squared cell is proposed. To test this approach, simulations of HD grids of cardiac activations at different propagation angles, conduction velocities, interelectrode distance and electrogram waveforms are considered.

RESULTS

The proposed approach successfully provided narrower loops (essentially a straight line) of the electrical field described by the bipole pair with respect to the conventional approach. Estimation of the direction of propagation was improved. Additionally, estimated oEGMs presented larger amplitude, and estimations of the local activation times were more accurate.

CONCLUSIONS

A novel method to improve the estimation of oEGMs in HD grid of electrodes is proposed. This approach is superior to the existing methods and avoids pitfalls not yet resolved.

RELEVANCE

Robust tools for quantifying the cardiac substrate are crucial to determine with accuracy target ablation sites during an electrophysiological procedure.

From 12 to 1 ECG lead: multiple cardiac condition detection mixing a hybrid machine learning approach with a one-vs-rest classification strategy

OBJECTIVE

Detecting different cardiac diseases using a single or reduced number of leads is still challenging. This work aims to provide and validate an automated method able to classify ECG recordings. Performance using complete 12-lead systems, reduced lead sets, and single-lead ECGs is evaluated and compared.

APPROACH

Seven different databases with 12-lead ECGs were provided during the PhysioNet/Computing in Cardiology Challenge 2021, where 88,253 annotated samples associated with none, one, or several cardiac conditions among 26 different classes were released for training, whereas 42,896 hidden samples were used for testing. After signal preprocessing, 81 features per ECG-lead were extracted, mainly based on heart rate variability, QRST patterns and spectral domain. Next, a One-vs-Rest classification approach made of independent binary classifiers for each cardiac condition was trained. This strategy allowed each ECG to be classified as belonging to none, one or several classes. For each class, a classification model among two binary Supervised Classifiers and one Hybrid Unsupervised-Supervised classification system was selected. Finally, we performed a 3-fold cross-validation to assess the system's performance.

MAIN RESULTS

Our classifiers received scores of 0.39, 0.38, 0.39, 0.38, and 0.37 for the 12, 6, 4, 3 and 2-lead versions of the hidden test set with the Challenge evaluation metric (CM). Also, we obtained a mean G-score of 0.80, 0.78, 0.79, 0.79, 0.77 and 0.74 for the 12, 6, 4, 3, 2 and 1-lead subsets with the public training set during our 3-fold cross-validation.

SIGNIFICANCE

We proposed and tested a machine learning approach focused on flexibility for identifying multiple cardiac conditions using one or more ECG leads. Our minimal-lead approach may be beneficial for novel portable or wearable ECG devices used as screening tools, as it can also detect multiple and concurrent cardiac conditions.

Simultaneous atrial and ventricular restitution and fibrillation analyses using a low-cost scalable panoramic whole-heart optical mapping configuration for whole-heart imaging of translational models

Introduction

Optical mapping (OM) is the primary method for imaging electrophysiologically relevant parameters from the outer surface of Langendorff-perfused hearts. However, current panoramic OM systems are financially challenging, require multiple sensors to map wide areas of the surface with overlapping regions and missing areas of interest due to the intrinsic shape of the heart. We proposed different panoramic configurations to dynamically characterize atrial and ventricular function during arrhythmia and, in presence of a coronary occlusion.

Methods

We devised both a multi-sensor and a single sensor system integrated with the perfusion circuit comprising sensor elements, a control system for led illumination, electrical stimulation and sensing of physiological variables. Two configurations were tested: A multi-sensor panoramic approach including different camera views and, a precision near-ellipsoidal curved mirror (highly concentrated reflectance in the range 380nm-800nm), with exponential profile and diameter to harbor small to large hearts was used. Twelve-rabbits and two pig hearts were included in the study. OM was performed using di-4 ANDBQPQ near-infrared dye and 5–10uM blebbistatine. Initial camera calibration was done using a fishnet-like pattern and nylon landmarks. We characterized signal-tonoise ratios (SNR) of reconstructed action potentials (AP) and obtained parametric maps of the activation process. A custom-built computational pipeline for accurate motion compensation and AP reconstructions was used. Hearts were stimulated until ventricular fibrillation (VF) was induced with and without presence of a coronary occlusion in the LADartery (LADCO).

Results

High SNRs spatial maps were obtained after AP reconstruction (42.24±4.23dB,stimulated; 23.31±5.24dB,VF) in the most restrictive set-up, the single-sensor near-ellipsoidal configuration. Quantified activation and repolarization dynamic restitution properties were assigned to anatomically labelled scale-invariant areas in the atrium and ventricles during the induction process. Atrial and ventricular restitution dynamics could be reconstructed and analyzed simultaneously. Slower conduction (CT) and higher dispersion in repolarization (DoR) was observed after LADCO in LV (CT: 13.4±5.31ms-vs-22.42±6.82ms,DoR:23.24±4.23ms-vs-38.03±9.17ms,p<0.05). During VF, more heterogeneous activation patterns, enhanced left-to-right VV spectral gradient profiles, and spatially constraint shorter-lived filaments, partially explained the disturbances observed during LADCO. Results obtained with a direct multiple sensor configuration allowed for complete tracking of dominant sources, yet presenting overlapped information.

Conclusion

Hereby results comparing two low-cost configurations for panoramic imaging are presented and validated for the study of cardiac propagation throughout the whole epicardial surface for the study of arrhythmia, drug interventions and cardiovascular disease.

Funding Acknowledgement

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): CIBERcv

Non-invasive characterisation of macroreentrant atrial tachycardia types from a vectorcardiographic approach with the slow conduction region as a cornerstone

BACKGROUND AND OBJECTIVES

Macroreentrant atrial tachyarrhythmias (MRATs) can be caused by different reentrant circuits. The treatment for each MRAT type may require ablation at different sites, either at the right or left atria. Unfortunately, the reentrant circuit that drives the arrhythmia cannot be ascertained previous to the electrophysiological intervention.

METHODS

A noninvasive approach based on the comparison of atrial vectorcardiogram (VCG) loops is proposed. An archetype for each group was created, which served as a reference to measure the similarity between loops. Methods were tested in a variety of simulations and real data obtained from the most common right (peritricuspid) and left (perimitral) macroreentrant circuits, each divided into clockwise and counterclockwise subgroups. Adenosine was administered to patients to induce transient AV block, allowing the recording of the atrial signal without the interference of ventricular signals. From the vectorcardiogram, we measured intrapatient loop consistence, similarity of the pathway to archetypes, characterisation of slow velocity regions and pathway complexity.

RESULTS

Results show a considerably higher similarity with the loop of its corresponding archetype, in both simulations and real data. We found the capacity of the vectorcardiogram to reflect a slow velocity region, consistent with the mechanisms of MRAT, and the role that it plays in the characterisation of the reentrant circuit. The intra-patient loop consistence was over 0.85 for all clinical cases while the similarity of the pathway to archetypes was found to be 0.85 ± 0.03, 0.95 ± 0.03, 0.87 ± 0.04 and 0.91 ± 0.02 for the different MRAT types (and p<0.02 for 3 of the 4 groups), and pathway complexity also allowed to discriminate among cases (with p<0.05).

CONCLUSIONS

We conclude that the presented methodology allows us to differentiate between the most common forms of right and left MRATs and predict the existence and location of a slow conduction zone. This approach may be useful in planning ablation procedures in advance.

Classification model based on strain measurements to identify patients with arrhythmogenic cardiomyopathy with left ventricular involvement

BACKGROUND AND OBJECTIVE

A heterogenous expression characterizes arrhythmogenic cardiomyopathy (AC). The evaluation of regional wall movement included in the current Task Force Criteria is only qualitative and restricted to the right ventricle. However, a strain-based approach could precisely quantify myocardial deformation in both ventricles. We aim to define and modelize the strain behavior of the left ventricle in AC patients with left ventricular (LV) involvement by applying algorithms such as Principal Component Analysis (PCA), clustering and naïve Bayes (NB) classifiers.

METHODS

Thirty-six AC patients with LV involvement and twenty-three non-affected family members (controls) were enrolled. Feature-tracking analysis was applied to cine cardiac magnetic resonance imaging to assess strain time series from a 3D approach, to which PCA was applied. A Two-Step clustering algorithm separated the patients' group into clusters according to their level of LV strain impairment. A statistical characterization between controls and the new AC subgroups was done. Finally, a NB classifier was built and new data from a small evolutive dataset was predicted.

RESULTS

60% of AC-LV patients showed mildly affected strain and 40% severely affected strain. Both groups and controls exhibited statistically significant differences, especially when comparing controls and severely affected AC-LV patients. The classification accuracy of the strain NB classifier reached 82.76%. The model performance was as good as to classify the individuals with a 100% sensitivity and specificity for severely impaired strain patients, 85.7% and 81.1% for mildly impaired strain patients, and 69.9% and 91.4% for normal strain, respectively. Even when the severely affected LV-AC group was excluded, LV strain showed a good accuracy to differentiate patients and controls. The prediction of the evolutive dataset revealed a progressive alteration of strain in time.

CONCLUSIONS

Our LV strain classification model may help to identify AC patients with LV involvement, at least in a setting of a high pretest probability, such as family screening.

Implementación de un sistema de detección de señales débiles de futuro mediante técnicas de minería de textos

Actualmente, una de las mayores amenazas para las empresas es no ser capaces de hacer frente a los cambios constantes que se dan en el mercado, por no predecirlos con la suficiente antelación. Por ello, el desarrollo de nuevos procesos que faciliten la detección de fenómenos y cambios futuros significativos es una componente clave para una correcta toma de decisiones que marque un rumbo correcto para la empresa. Por esta razón, se propone un sistema basado en una arquitectura de inteligencia de negocio que permite detectar cambios discretos o señales débiles (weak signals) en el presente, pero que son indicativos de fenómenos más significativos y cambios trascendentales en el futuro. Frente a los trabajos actuales que se centran en fuentes de información estructuradas, o como mucho, con un único tipo de fuente de datos, en este trabajo la detección de estas señales se realiza de forma cuantitativa a partir de documentos heterogéneos y no estructurados de diversa índole (artículos científicos, periodísticos y redes sociales) sobre los que se aplican técnicas de minería de textos. El sistema ha sido testeado para estudiar el futuro del sector de los paneles solares, habiéndose obtenido resultados prometedores para ayudar a expertos en el reconocimiento de nuevos factores de peso en sus mercados y en el desarrollo de nuevas oportunidades.

Modifications of short-term intrinsic pacemaker variability in diet-induced metabolic syndrome: a study on isolated rabbit heart

Metabolic syndrome (MetS) describes a condition associated with multiple diseases concomitantly such as diabetes, hypertension, obesity, and dyslipidemia. It has been linked with higher prevalence of cardiovascular disease, atrial fibrillation, and sudden cardiac death. One of the underlying mechanisms could be altered automaticity, which would reflect modifications of sinus node activity. These phenomena can be evaluated analyzing the components of heart rate variability (HRV). Our aim was to examine the modifications of sinus node variability in an isolated heart model of diet-induced obesity and MetS. Male NZW rabbits were randomly assigned to high-fat (HF, n = 8), control (HF-C, n = 7), high-fat, high-sucrose (HFHS, n = 9), and control (HFHS-C, n = 9) groups, fed with their respective diets during 18/28 weeks. After euthanasia, their hearts were isolated in a Langendorff system. We recorded 10-15 min of spontaneous activity. Short RR time series were analyzed, and standard HRV parameters were determined. One-way ANOVA, Kruskal-Wallis test, and bivariate correlation were used for statistical analysis (p < 0.05). We did find an increase in the complexity and irregularity of intrinsic pacemaker activity as shown by modifications of approximate entropy, sample entropy, minimum multiscale entropy, and complexity index in HFHS animals. Even though no differences were found in standard time and frequency-domain analyses, spectral heterogeneity increased in HFHS group. Animal weight and glucose intolerance were highly correlated with the modifications of intrinsic pacemaker variability. Finally, modifications of intrinsic HRV seemed to be reliant on the number of components of MetS present, given that only HFHS group showed significant changes towards an increased complexity and irregularity of intrinsic pacemaker variability.

The Antithrombotic Potential of Dalteparin in Man Assessed Indirectly by Wessler’s Technique

The aim of this study was to demonstrate the effectiveness of a new experimental approach for assessing the antithrombotic potential of low molecular weight heparins (LMWH) such as dalteparin. In this approach, sera obtained from healthy volunteers treated with various i.v. doses of dalteparin (30, 60 or 120 anti-Xa IU/kg) or placebo (physiological saline) were used as the thrombogenic challenge in a Wessler’s stasis model of experimental venous thrombosis in the rat. Sera from placebo-treated volunteers showed a stable thrombogenic activity (0.25 ml/kg of serum producing thrombi of about 50 mg wet weight). Sera from healthy volunteers having previously received dalteparin however demonstrated dose- and time-related reductions in their thrombogenic activity. Half-lives of these effects were 300, 444 and >480 min for 30,60 and 120 anti-Xa IU/kg dalteparin respectively. These values were significantly higher than the corresponding anti-Xa and anti-IIa half-lives.

Further Studies on the Mechanism for the Antithrombotic Effects of Naroparcil, an Orally Active Thioxyloside Compound

The antithrombotic β-D-xyloside, naroparcil, has previously been shown to induce a dose-related increase of circulating glycosaminoglycans (GAGs) together with an antithrombin activity (anti-IIa) via heparin cofactor II (HCII) in the rabbit. In order to go further in the mechanisms, the relationship between the antithrombotic activity, the HCII-mediated anti-IIa activity and the plasma GAG content was investigated. We showed that the in vitro specific activity on the inhibition of thrombin by HCII of the plasma GAG extract from naroparcil-treated rabbits was increased by a factor of 60 when compared to controls. In addition, the fractionation of the plasma GAG extract by affinity chromatography on immobilized HCII led to a more potent material whereas the low-affinity fraction was shown to be inactive in thrombin inhibition by HCII.

The qualitative analysis of GAGs showed the presence of the ΔDi-4S DS disaccharide, undetectable in control, which accounted for 22% in the unfractionated GAG extract and for 60% in the high affinity fraction. In vitro experiments using immuno-depleted plasma in antithrombin III (ATIII), HCII or both, indicated that the anti-IIa activity of the plasma GAG extract from naroparcil-treated rabbits was mainly due to HCII potentialisation. The unfractionated GAG extract and the high affinity fraction were shown to be antithrombotic in a Wessler-based model in the rat, giving ED80 values of 610 UA/kg and 56 UA/kg respectively whereas the low-affinity fraction was devoid of any antithrombotic activity. These results show that the antithrombotic activity of naroparcil is dependent on modification in the plasma GAG profile which inactivates thrombin via the HCII.

Antithrombotic and Anticoagulant Activities of a Low Molecular Weight Fucoidan by the Subcutaneous Route

Fucoidans (high-molecular-weight sulfated polysaccharides extracted from brown seaweeds) have anticoagulant and antithrombotic effects. They inhibit thrombin by catalyzing both serpins (antithrombin and heparin cofactor II) according to their chemical structures and origins. In this study, a low-molecular-weight (LMW) fucoidan of 8 kDa was obtained by chemical degradation of a high-molecular-weight fraction. The antithrombotic and anticoagulant activities of this new compound were compared to those of a low-molecular-weight heparin (LMWH), dalteparin, following subcutaneous administration to rabbits. This LMW fucoidan exhibited dose-related venous antithrombotic activity, with an ED80 of about 20 mg/kg, 2 h after a single subcutaneous injection. Its activity was comparable to that of dalteparin (close to 200 anti-Xa IU/kg) and was maximal 30 min after a single subcutaneous injection. The activity remained stable (about 70%) from 1 to 4 h after injection, but disappeared by 8 h. The antithrombotic activity was not associated with either a prolongation of the thrombin clotting time (TCT) or an increase in anti-Xa activity, contrary to dalteparin. A slight prolongation of APTT occurred with both compounds. This venous antithrombotic activity was associated with a decrease in ex vivo thrombin generation and with a significant increase in the lag phase in a thrombin generation test. LMW fucoidan thus has potent antithrombotic activity and a potentially weaker haemorrhagic effect (i.e. a smaller effect on coagulation tests and a smaller prolongation of the bleeding time) than dalteparin.

Hydrogen Sulfide Improves Cardiomyocyte Function in a Cardiac Arrest Model

Background

Cardioplegic arrest is a common procedure for many types of cardiac surgery, and different formulations have been proposed to enhance its cardio-protective effect. Hydrogen sulfide is an important signaling molecule that has cardio-protective properties. We therefore studied the cardio-protective effect of hydrogen sulfide in cardiac cell culture and its potential therapeutic use in combination with cardioplegia formulations.

Materials/Methods

We added hydrogen sulfide donor GYY4137 to HL-1 cells to study its protective effect in nutrient starved conditions. In addition, we tested the potential use of GYY4137 when it is added into two different cardioplegia formulations: Cardi-Braun^® solution and del Nido solution in an ex vivo Langendorff perfused rat hearts model.

Results

We observed that eight-hour pre-treatment with GYY4137 significantly suppressed apoptosis in nutrient-starved HL-1 cells (28% less compared to untreated cells; p<0.05), maintained ATP content, and reduced protein synthesis. In ex vivo experiments, Cardi-Braun^® and del Nido cardioplegia solutions supplemented with GYY4137 significantly reduced the pro-apoptotic protein caspase-3 content and preserved ATP content. Furthermore, GYY4137 supplemented cardioplegia solutions decreased the S-(5-adenosyl)-L-methionine/S-(adenosyl)-L-homocysteine ratio, reducing the oxidative stress in cardiac tissue. Finally, heart beating analysis revealed the preservation of the inter-beat interval and the heart rate in del Nido cardioplegia solution supplemented with GYY4137.

Conclusions

GYY4137 preconditioning preserved energetic state during starved conditions, attenuating the cardiomyocytes apoptosis in vitro. The addition of GYY4137 to cardioplegia solutions prevented apoptosis, ATP consumption, and oxidative stress in perfused rat hearts, restoring its electrophysiological status after cardiac arrest. These findings suggested that GYY4137 sulfide donor may improve the cardioplegia solution performance during cardiac surgery.

Spatiotemporal Characteristics of QRS Complexes Enable the Diagnosis of Brugada Syndrome Regardless of the Appearance of a Type 1 ECG

INTRODUCTION

The diagnosis of Brugada syndrome based on the ECG is hampered by the dynamic nature of its ECG manifestations. Brugada syndrome patients are only 25% likely to present a type 1 ECG. The objective of this study is to provide an ECG diagnostic criterion for Brugada syndrome patients that can be applied consistently even in the absence of a type 1 ECG.

METHODS AND RESULTS

We recorded 67-lead body surface potential maps from 94 Brugada syndrome patients and 82 controls (including right bundle branch block patients and healthy individuals). The spatial propagation direction during the last r' wave and the slope at the end of the QRS complex were measured and compared between patients groups. Receiver-operating characteristic curves were constructed for half of the database to identify optimal cutoff values; sensitivity and specificity for these cutoff values were measured in the other half of the database. A spontaneous type 1 ECG was present in only 30% of BrS patients. An orientation in the sagittal plane < 101º during the last r' wave and a descending slope < 9.65 mV/s enables the diagnosis of the syndrome with a sensitivity of 69% and a specificity of 97% in non-type 1 Brugada syndrome patients.

CONCLUSION

Spatiotemporal characteristics of surface ECG recordings can enable a robust identification of BrS even without the presence of a type 1 ECG.

Noninvasive Estimation of Epicardial Dominant High-Frequency Regions During Atrial Fibrillation

INTRODUCTION

Ablation of high dominant frequency (DF) sources in patients with atrial fibrillation (AF) is an effective treatment option for paroxysmal AF. The aim of this study was to evaluate the accuracy of noninvasive estimation of DF and electrical patterns determination by solving the inverse problem of the electrocardiography.

METHODS

Four representative AF patients with left-to-right and right-to-left atrial DF patterns were included in the study. For each patient, intracardiac electrograms from both atria were recorded simultaneously together with 67-lead body surface recordings. In addition to clinical recordings, realistic mathematical models of atria and torso anatomy with different DF patterns of AF were used. For both mathematical models and clinical recordings, inverse-computed electrograms were compared to intracardiac electrograms in terms of voltage, phase, and frequency spectrum relative errors.

RESULTS

Comparison between intracardiac and inverse computed electrograms for AF patients showed 8.8 ± 4.4% errors for DF, 32 ± 4% for voltage, and 65 ± 4% for phase determination. These results were corroborated by mathematical simulations showing that the inverse problem solution was able to reconstruct the frequency spectrum and the DF maps with relative errors of 5.5 ± 4.1%, whereas the reconstruction of the electrograms or the instantaneous phase presented larger relative errors (i.e., 38 ± 15% and 48 ± 14 % respectively, P < 0.01).

CONCLUSIONS

Noninvasive reconstruction of atrial frequency maps can be achieved by solving the inverse problem of electrocardiography with a higher accuracy than temporal distribution patterns.

Attraction of rotors to the pulmonary veins in paroxysmal atrial fibrillation: a modeling study

Maintenance of paroxysmal atrial fibrillation (AF) by fast rotors in the left atrium (LA) or at the pulmonary veins (PVs) is not fully understood. To gain insight into this dynamic and complex process, we studied the role of the heterogeneous distribution of transmembrane currents in the PVs and LA junction (PV-LAJ) in the localization of rotors in the PVs. We also investigated whether simple pacing protocols could be used to predict rotor drift in the PV-LAJ. Experimentally observed heterogeneities in IK1, IKs, IKr, Ito, and ICaL in the PV-LAJ were incorporated into two- and pseudo three-dimensional models of Courtemanche-Ramirez-Nattel-Kneller human atrial kinetics to simulate various conditions and investigate rotor drifting mechanisms. Spatial gradients in the currents resulted in shorter action potential duration, minimum diastolic potential that was less negative, and slower upstroke and conduction velocity for rotors in the PV region than in the LA. Rotors under such conditions drifted toward the PV and stabilized at the shortest action potential duration and less-excitable region, consistent with drift direction under intercellular coupling heterogeneities and regardless of the geometrical constraint in the PVs. Simulations with various IK1 gradient conditions and current-voltage relationships substantiated its major role in the rotor drift. In our 1:1 pacing protocol, we found that among various action potential properties, only the minimum diastolic potential gradient was a rate-independent predictor of rotor drift direction. Consistent with experimental and clinical AF studies, simulations in an electrophysiologically heterogeneous model of the PV-LAJ showed rotor attraction toward the PV. Our simulations suggest that IK1 heterogeneity is dominant compared to other currents in determining the drift direction through its impact on the excitability gradient. These results provide a believed novel framework for understanding the complex dynamics of rotors in AF.

Body surface localization of left and right atrial high-frequency rotors in atrial fibrillation patients: a clinical-computational study

BACKGROUND

Ablation is an effective therapy in patients with atrial fibrillation (AF) in which an electrical driver can be identified.

OBJECTIVE

The aim of this study was to present and discuss a novel and strictly noninvasive approach to map and identify atrial regions responsible for AF perpetuation.

METHODS

Surface potential recordings of 14 patients with AF were recorded using a 67-lead recording system. Singularity points (SPs) were identified in surface phase maps after band-pass filtering at the highest dominant frequency (HDF). Mathematical models of combined atria and torso were constructed and used to investigate the ability of surface phase maps to estimate rotor activity in the atrial wall.

RESULTS

The simulations show that surface SPs originate at atrial SPs, but not all atrial SPs are reflected at the surface. Stable SPs were found in AF signals during 8.3% ± 5.7% vs. 73.1% ± 16.8% of the time in unfiltered vs. HDF-filtered patient data, respectively (P < .01). The average duration of each rotational pattern was also lower in unfiltered than in HDF-filtered AF signals (160 ± 43 ms vs. 342 ± 138 ms; P < .01), resulting in 2.8 ± 0.7 rotations per rotor. Band-pass filtering reduced the apparent meandering of surface HDF rotors by reducing the effect of the atrial electrical activity occurring at different frequencies. Torso surface SPs representing HDF rotors during AF were reflected at specific areas corresponding to the fastest atrial location.

CONCLUSION

Phase analysis of surface potential signals after HDF filtering during AF shows reentrant drivers localized to either the left atrium or the right atrium, helping in localizing ablation targets.

[Resistance to first-line drugs and major genotypic lineages of Mycobacterium tuberculosis in the 3 French Department of the Americas: Profiles, evolution, and trends (1995-2011)]

This is the first overview on resistant and multidrug resistant isolates of Mycobacterium tuberculosis circulating in the French Department of the Americas (Guadeloupe, Martinique, and French Guiana) over 17 years (January 1995-December 2011). A total of 1,239 cases were studied: 1,199 new cases (primary and multidrug resistance of 11.8 and 1.6% respectively), and 40 persistent (defined as cases with a previous history of positive culture over 6 months interval and whose spoligotypes remain unchanged), in which significantly higher proportions of resistance to at least isoniazid (22.5%, P = 0.002), rifampicin (20.0%, P < 0.001), and multidrug resistance (17.5%, P < 0.001) were observed as compared to new cases. The 281 spoligotypes obtained showed the presence of five major lineages, T (29.9%), LAM (23.9%), Haarlem (22.1%), EAI (7.1%), and X (6.7%). Two of these lineages, X and LAM, predominate among resistant and multidrug resistant isolates respectively (X: 10.5% of resistant isolates, P = 0.04; LAM: 42.3% of multidrug resistant isolates, P = 0.02). Four of the 19 major spoligo-profiles, corresponding to SIT 20, 64, 45, and 46, were significantly associated with drug resistance. Among them, genotype SIT 20, associated with monoresistance to isoniazid and multidrug resistance, would be actively and persistently in circulation, since 1999, in French Guiana, department in which one may also observe the presence of strains of M. tuberculosis phylogeographically associated to Guiana and Suriname (SIT 131 and SIT 1340).

Adaptive step ODE algorithms for the 3D simulation of electric heart activity with graphics processing units

In this paper we studied the implementation and performance of adaptive step methods for large systems of ordinary differential equations systems in graphics processing units, focusing on the simulation of three-dimensional electric cardiac activity. The Rush-Larsen method was applied in all the implemented solvers to improve efficiency. We compared the adaptive methods with the fixed step methods, and we found that the fixed step methods can be faster while the adaptive step methods are better in terms of accuracy and robustness.

Characterization of typical and atypical atrial flutter loops from the vectorcardiogram

Current techniques for atrial flutter (AFL) treatment involve radiofrequency ablation. This is a relatively simple and short procedure for typical AFL, whereas becomes more complex and unpredictable in the case of atypical AFL. Therefore, non-invasive characterization of AFL would be helpful for the management of ablation procedures. In this study the behavior of typical and atypical AFL groups is characterized from the vectorcardiographic AFL loops. The initial hypothesis is that typical AFL loops resemble each other, whereas atypical AFL loops differ from typical AFL ones. All patient loops were compared to a reference, by analyzing the global trajectory, pathway complexity and distance to the reference loop. The distance was the most significative parameter, being 0.445 ± 0.135 and 0.799 ± 0.144 for typical and atypical AFL (p = 8.00 e-5). In addition, an intrapatient analysis revealed a higher stability of typical AFL loops than in the case of atypical AFL.

Modifications in ventricular fibrillation and capture capacity induced by a linear radiofrequency lesion

INTRODUCTION AND OBJECTIVES

An analysis was made of the effects of a radiofrequency-induced linear lesion during ventricular fibrillation and the capacity to capture myocardium through high-frequency pacing.

METHODS

Using multiple epicardial electrodes, ventricular fibrillation was recorded in 22 isolated perfused rabbit hearts, analyzing the activation maps upon applying trains of stimuli at 3 different frequencies close to that of the arrhythmia: a) at baseline; b) after radio-frequency ablation to induce a lesion of the left ventricular free wall (length=10 [1] mm), and c) after lengthening the lesion (length=23 [2] mm).

RESULTS

Following lesion induction, the regularity of the recorded signals decreased and significant variations in the direction of the activation fronts were observed. On lengthening the lesion, there was a slight increase in the episodes with at least 3 consecutive captures when pacing at cycles 10% longer than the arrhythmia (baseline: 0.6 [0.7]; initial lesion: 1 [1], no significant differences; lengthened lesion: 3 [2.8]; P<.001), while a decrease was observed in those obtained upon pacing at cycles 10% shorter than the arrhythmia.

CONCLUSIONS

The radio-frequency -induced lesion increases the heterogeneity of myocardial activation during ventricular fibrillation and modifies arrival of the activation fronts in the adjacent zones. High-frequency pacing during ventricular fibrillation produces occasional captures during at least 3 consecutive stimuli. The lengthened lesion in turn slightly increases capture capacity when using cycles slightly longer than the arrhythmia.

Functional mathematical model of dual pathway AV nodal conduction

Dual atrioventricular (AV) nodal pathway physiology is described as two different wave fronts that propagate from the atria to the His bundle: one with a longer effective refractory period [fast pathway (FP)] and a second with a shorter effective refractory period [slow pathway (SP)]. By using His electrogram alternance, we have developed a mathematical model of AV conduction that incorporates dual AV nodal pathway physiology. Experiments were performed on five rabbit atrial-AV nodal preparations to develop and test the presented model. His electrogram alternances from the inferior margin of the His bundle were used to identify fast and slow wave front propagations. The ability to predict AV conduction time and the interaction between FP and SP wave fronts have been analyzed during regular and irregular atrial rhythms (e.g., atrial fibrillation). In addition, the role of dual AV nodal pathway wave fronts in the generation of Wenckebach periodicities has been illustrated. Finally, AV node ablative modifications have been evaluated. The model accurately reproduced interactions between FP and SP during regular and irregular atrial pacing protocols. In all experiments, specificity and sensitivity higher than 85% were obtained in the prediction of the pathway responsible for conduction. It has been shown that, during atrial fibrillation, the SP ablation significantly increased the mean HH interval (204 ± 39 vs. 274 ± 50 ms, P < 0.05), whereas FP ablation did not produce significant slowing of ventricular rate. The presented mathematical model can help in understanding some of the intriguing AV node mechanisms and should be considered as a step forward in the studies of AV nodal conduction.

Characteristics of inverse-computed epicardial electrograms of Brugada syndrome patients

Brugada syndrome (BrS) causes sudden death in patients with structurally normal hearts. Manifestation of BrS in the ECG is dynamic and most patients do not show unequivocal signs of the syndrome during ECG screening. Electrograms (EGMs) of BrS patients show conduction delay and fractionation at the right ventricular outflow tract area (RVOT) and thus could be used for diagnosis, but their recording requires an invasive procedure. We have obtained 67-lead body surface potential mapping recordings (BSPM) of 6 BrS patients and 6 controls and computed their EGMs by solving the inverse problem of electrocardiography by using Tikhonov's regularization method. Inverse-computed EGMs presented similar activation times and durations in controls and BrS patients for apex and septum. However, RVOT EGMs showed a later activation in BrS patients than in controls (58 ± 7 vs. 39 ± 5 ms, p<0.01) and EGMs were longer (122 ± 22 vs. 85 ± 8 ms, p<0.01). Inverse-computed EGMs of BrS patients showed abnormalities consistent with those observed in electrophysiological studies and could be used for a non-invasive diagnosis and characterization of Brugada syndrome.

Impact of immigration on tuberculosis epidemiology in a low-incidence country

Mycobacterium tuberculosis strains from 349 patients were isolated in western Sweden during the years 2001-2005. Only 26% of the tuberculosis (TB) patients were born in Sweden. All the others were born in any of 42 different countries; 17% in other European countries, 28% in Africa, 16% in Asia, 11% in the Middle East, and 2% in South America. The mean age of the Swedish-born patients was 67 years, while the mean age among the foreign-born patients was 37 years. The male/female ratio was 1.6 among the Swedes and 0.9 among those born abroad. Extrapulmonary manifestations of TB were most common among patients born in Africa while lung infections without extrapulmonary manifestations were most common in patients born in Europe, including Sweden. Spoligotyping showed that patients with T or Beijing strains had more pulmonary TB than extrapulmonary TB, while patients with EAI and CAS strains had a high proportion of extrapulmonary TB. The ancestral and/or evolutionary older PGG1 strains were more often isolated from the foreign-born patients than from the Swedish-born patients, who had strains generally being of the evolutionary recent genogroups PGG2/PGG3. We conclude that immigration from countries with a high incidence of TB has a strong impact on the TB epidemiology in western Sweden, a finding that should be taken into account by TB control strategists when developing programmes for eradication of TB in low prevalence settings.

Cellulose Fermentation by an Asporogenous Mutant and an Ethanol-Tolerant Mutant of Clostridium thermocellum

Two mutants of Clostridium thermocellum were isolated after UV light mutagenesis. Mutant A1, selected as asporogenous, exhibited a fermentation pattern similar to that of the wild type. However, at pH 6.5, the mutant degraded 12% more cellulose than did the wild type, leading to enhanced ethanol production. Mutant 647, selected as ethanol tolerant, was able to grow in medium containing 4% ethanol. During the early stage of the exponential growth phase, ethanol was produced as the main product, up to a concentration of about 9 g/liter. After 3 days of culture, 48.3 g (89% of the initial amount) of degraded cellulose per liter was fermented into 12.7 g of ethanol per liter.

Enhanced Cellulose Fermentation by an Asporogenous and Ethanol-Tolerant Mutant of Clostridium thermocellum

A mutant of Clostridium thermocellum isolated after UV mutagenesis and selection for resistance to fluoropyruvate was found to be asporogenous and ethanol tolerant. The mutant was also an ethanol hyperproducer, able to ferment 63 g of cellulose into 14.5 g of ethanol per liter of medium. The ratio of ethanol to total organic acids produced by the mutant was increased, and H(2) production was decreased. Culture conditions were optimized for ethanol production by the new strain.

Entropy measurements in paroxysmal and persistent atrial fibrillation

Recent studies on atrial fibrillation (AF) have identified different activation patterns in paroxysmal and persistent AF. In this study, bipolar intra-atrial registers from 28 patients (14 paroxysmal AF and 14 persistent AF) were analyzed in order to find out regional differences in the organization in both types of arrhythmias. The organization of atrial electrical activity was assessed in terms of nonlinear parameters, such as entropy measurements. Results showed differences between the atrial chambers with a higher disorganization in the left atrium in paroxysmal AF patients and a more homogenous behavior along the atria in persistent AF patients.

Limitations of Dower's inverse transform for the study of atrial loops during atrial fibrillation

INTRODUCTION

Spatial characteristics of atrial fibrillatory waves have been extracted by using a vectorcardiogram (VCG) during atrial fibrillation (AF). However, the VCG is usually not recorded in clinical practice and atrial loops are derived from the 12-lead electrocardiogram (ECG). We evaluated the suitability of the reconstruction of orthogonal leads from the 12-lead ECG for fibrillatory waves in AF.

METHODS

We used the Physikalisch-Technische Bundesanstalt diagnostic ECG database, which contains 15 simultaneously recorded signals (12-lead ECG and three Frank orthogonal leads) of 13 patients during AF. Frank leads were derived from the 12-lead ECG by using Dower's inverse transform. Derived leads were then compared to true Frank leads in terms of the relative error achieved. We calculated the orientation of AF loops of both recorded orthogonal leads and derived leads and measured the difference in estimated orientation. Also, we investigated the relationship of errors in derivation with fibrillatory wave amplitude, frequency, wave residuum, and fit to a plane of the AF loops.

RESULTS

Errors in derivation of AF loops were 68 +/- 31% and errors in the estimation of orientation were 35.85 +/- 20.43 degrees . We did not find any correlation among these errors and amplitude, frequency, or other parameters.

CONCLUSIONS

In conclusion, Dower's inverse transform should not be used for the derivation of orthogonal leads from the 12-lead ECG for the analysis of fibrillatory wave loops in AF. Spatial parameters obtained after this derivation may differ from those obtained from recorded orthogonal leads.

Effects of chronic exercise on myocardial refractoriness: a study on isolated rabbit heart

AIM

To determine whether chronic physical training increases atrial and ventricular refractoriness in isolated rabbit heart.

METHODS

Trained rabbits were submitted to a protocol of treadmill running. The electrophysiological parameters of refractoriness investigated in an isolated heart preparation were: (1) atrial effective refractory period (AERP) and atrial functional refractory period and ventricular effective and functional refractory periods (VERP and VFRP) using the extrastimulus technique at four different pacing cycle lengths; (2) the dominant frequency (DF) of ventricular fibrillation (VF). A multi-electrode plaque containing 256 electrodes and a spectral method were used to obtain the mean, maximum and minimum DF of VF. Sinus cycle length of the isolated hearts was determined as an electrophysiological parameter of training. In vivo heart rate, myocardial heat shock proteins (HSP60) and inducible nitric oxide synthase were also determined in some animals as electrophysiological and biochemical markers of training respectively.

RESULTS

VERP and VFRP were longer in the trained group than in the control group. The mean DF of VF was lower in the trained group than in the control group. Despite the fact that training did not significantly modify the AERP, it tended to be longer in the trained group (P = 0.09).

CONCLUSION

Training seems to increase the electrical stability of ventricular myocardium. As the electrophysiological modifications were exhibited in hearts not submitted to extrinsic nervous system or humoral influences, they are, at least in part, intrinsic modifications. These electrophysiological data also suggest that training could protect against reentrant ventricular arrhythmias.

Analyzing the electrophysiological effects of local epicardial temperature in experimental studies with isolated hearts

As a result of their modulating effects upon myocardial electrophysiology, both hypo- and hyperthermia can be used to study the mechanisms that generate or sustain cardiac arrhythmias. The present study describes an original electrode developed with thick-film technology and capable of controlling regional temperature variations in the epicardium while simultaneously registering its electrical activity. In this way, it is possible to measure electrophysiological parameters of the heart at different temperatures. The results obtained with this device in a study with isolated and perfused rabbit hearts are reported. An exploration has been made of the effects of local temperature changes upon the electrophysiological parameters implicated in myocardial conduction. Likewise, an analysis has been made of the influence of local temperature upon ventricular fibrillation activation frequency. It is concluded that both regional hypo- and hyperthermia exert reversible and opposite effects upon myocardial refractoriness and conduction velocity in the altered zone. The ventricular activation wavelength determined during constant pacing at 250 ms cycles is not significantly modified, however. During ventricular fibrillation, the changes in the fibrillatory frequency do not seem to be transmitted to normal temperature zones.

La microscopie confocale: interet pour l'analyse du relief cutané. Un outil d'évaluation dermo-cosmétique

Nowadays, the determination of human skin microtopography is usually carried out by methods based on mechanical techniques (profilometry and surfometry), or founded on optical conception (shadowing method and profilometry). Negative skin replicas made of a silicone rubber material (Silflo((R))) or positive casts performed from an epoxy resin (Araldite((R))), are used to assess the skin microstructure. Skin surface microtopography is quantified by measuring furrows depths and spaces between them. An original application using confocal scanning laser microscope (CLSM) is described in this paper. The CLSM gives simultaneously images of the skin surface associated with quantitative measurements of the microtopography. With this apparatus, it is easy to achieve perfect skin replica images with assessment of its microstructure, before and after applications of topical medicines or cosmetic products to evaluate the skin surface restoration. It is worth to mention that it is indispensable to analyse the same skin surface (same plateaux and same furrows). For this reason, it is necessary to localize exactly and to replicate the same skin surface area (4 mm(2)) before and after the cosmetic use, whatever the extended period of the topical application.

Prognostic and therapeutic implications of dipyridamole stress cardiovascular magnetic resonance on the basis of the ischaemic cascade

OBJECTIVE

To determine the prognostic and therapeutic implications of stress perfusion cardiovascular magnetic resonance (CMR) on the basis of the ischaemic cascade.

SETTING

Single centre study in a teaching hospital in Spain.

PATIENTS

Dipyridamole stress CMR was performed on 601 patients with ischaemic chest pain and known or suspected coronary artery disease. On the basis of the ischaemic cascade, patients were categorised in C1 (no evidence of ischaemia, n = 354), C2 (isolated perfusion deficit at stress first-pass perfusion imaging, n = 181) and C3 (simultaneous perfusion deficit and inducible wall motion abnormalities, n = 66). CMR-related revascularisation (n = 102, 17%) was defined as the procedure prompted by the CMR results and carried out within the next three months.

RESULTS

During a median follow-up of 553 days, 69 major adverse cardiac events (MACE), including 21 cardiac deaths, 14 non-fatal myocardial infarctions and 34 admissions for unstable angina with documented abnormal angiography were detected. In non-revascularised patients (n = 499), the MACE rate was 4% (14/340) in C1, 20% (26/128) in C2 and 39% (12/31) in C3 (adjusted p value = 0.004 vs C2 and <0.001 vs C1). CMR-related revascularisation had neutral effects in C2 (20% vs 19%, 1.1 (0.5 to 2.4), p = 0.7) but independently reduced the risk of MACE in C3 (39% vs 11%, 0.2 (0.1 to 0.7), p = 0.01).

CONCLUSIONS

Dypiridamole stress CMR is able to stratify risk on the basis of the ischaemic cascade. A small group of patients with severe ischaemia-simultaneous perfusion deficit and inducible wall motion abnormalities-are at the highest risk and benefit most from MACE reduction due to revascularisation.

Evaluation of lead selection methods for optimal reconstruction of body surface potentials

In this study, several methods for optimal lead selection from multilead electrocardiographic recordings are analyzed. Two different lead selection methods have been implemented. For their evaluation, a linear transformation that reconstructs nonselected leads from selected leads is computed according to the least squares optimization, and the performance is evaluated in terms of the mean square error of the derived potentials and correlation. The algorithms were tested on a database of 72 body surface potential recordings: 18 controls, 18 bundle-branch block, 18 myocardial infarction, and 18 ventricular hypertrophy. Each data set was divided into a study and test subsets. Two experiments were carried out: (1) The lead selection, transformation matrix, and performance evaluation is carried out over the test data set (ideal case), and (2) the lead selection and transformation matrix is carried out over the study data set, but the performance is evaluated over the test data set (real case). Our results show important reconstruction errors with either lead selection methods, and only increasing the number of leads reduces the error in reconstruction. However, if a reduced number of leads are to be selected outside the standard 12-lead electrocardiogram, the method proposed by Lux has been shown to be the best option.

In vitro antimicrobial activity of the leaf extract of Harungana madagascariensis Lam. Ex Poir. (Hypericaceae) against strains causing otitis externa in dogs and cats

Otitis externa in dogs and cats is always caused by a combination of yeasts and bacteria, among which the most important are Malassezia pachydermatis, Staphylococcus intermedius and Pseudomonas species. These organisms often develop resistance to classical antimicrobial agents. Therefore, the aim of this study was to investigate the antimicrobial activities of an ethyl acetate leaf extract of Harungana madagascariensis against the organisms cited, to carry out the phytochemical investigation of this extract and to determine its bioactive chemical class using dilution techniques, the bioautography method and the standard phytochemical method described by Harborne (1973). Phytochemical analysis revealed the presence of saponins, tannins, flavonoids, alkaloids and anthracenic derivatives. The bioassay showed that the antimicrobial properties may be attributed to astilbin, a flavanone derivative identified on the basis of its spectroscopic data. The results suggest that the extract could be used in an antimicrobial preparation effective against the whole range of organisms incriminated in otitis externa in dogs and cats, with a minimal inhibitory concentration (MIC) of 250 microg/ml.

The role of independent component analysis in the signal processing of ECG recordings

Independent component analysis (ICA) is an emerging technique for multidimensional signal processing. In recent years, these techniques have been proposed for solving a large number of biomedical applications. This work reviews current knowledge on ICA in electrocardiographic (ECG) analysis. The benefits that ICA can bring to clinical practice are illustrated with four relevant clinical applications: foetal ECG extraction from maternal ECG recordings, analysis of atrial fibrillation, ECG denoising and removal of pacemaker artefacts.

Implantable cardioverter defibrillator algorithms: status review in terms of computational cost

In recent decades, implantable cardioverter defibrillators (ICDs) have improved substantially, becoming the treatment of choice for patients at high risk of life-threatening arrhythmias. Nevertheless, inappropriate shock therapy for non-ventricular arrhythmias is still a problem. Extending the ICD battery lifetime demands very low power consumption, which is obtained at very low microprocessor clock frequencies. Currently, some high-performance algorithms remain beyond the computational capabilities of ICDs. Future ICDs with higher computing power will permit the implementation of computationally intensive algorithms, enhancing the discrimination performance and preventing inappropriate shock therapies. An ICD algorithm status review is presented from the point of view of signal processing techniques and their computational costs. Several examples of discrimination algorithms with increasing computational cost are analyzed. Whereas some of them are already used in commercial ICDs, other algorithms cannot be implemented yet in current ICDs. A solution based on dynamic adaptation of microprocessor power consumption to meet algorithm computational requirements is proposed. This solution allows implementation of complex discrimination algorithms in ICDs without significantly increasing the power consumption.