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.

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.

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.

Granger Causality and Jensen-Shannon Divergence to Determine Dominant Atrial Area in Atrial Fibrillation.

Atrial fibrillation (AF) is already the most commonly occurring arrhythmia. Catheter pulmonary vein ablation has emerged as a treatment that is able to make the arrhythmia disappear; nevertheless, recurrence to arrhythmia is very frequent. In this study, it is proposed to perform an analysis of the electrical signals recorded from bipolar catheters at three locations, pulmonary veins and the right and left atria, before to and during the ablation procedure. Principal Component Analysis (PCA) was applied to reduce data dimension and Granger causality and divergence techniques were applied to analyse connectivity along the atria, in three main regions: pulmonary veins, left atrium (LA) and right atrium (RA). The results showed that, before the procedure, patients with recurrence in the arrhythmia had greater connectivity between atrial areas. Moreover, during the ablation procedure, in patients with recurrence in the arrhythmial both atria were more connected than in patients that maintained sinus rhythms. These results can be helpful for procedures designing to end AF.

Refined Multiscale Fuzzy Entropy to Analyse Post-Exercise Cardiovascular Response in Older Adults With Orthostatic Intolerance.

Orthostatic intolerance syndrome occurs when the autonomic nervous system is incapacitated and fails to respond to the demands associated with the upright position. Assessing this syndrome among the elderly population is important in order to prevent falls. However, this problem is still challenging. The goal of this work was to determine the relationship between orthostatic intolerance (OI) and the cardiovascular response to exercise from the analysis of heart rate and blood pressure. More specifically, the behavior of these cardiovascular variables was evaluated in terms of refined composite multiscale fuzzy entropy (RCMFE), measured at different scales. The dataset was composed by 65 older subjects, 44.6% (n = 29) were OI symptomatic and 55.4% (n = 36) were not. Insignificant differences were found in age and gender between symptomatic and asymptomatic OI participants. When heart rate was evaluated, higher differences between groups were observed during the recovery period immediately after exercise. With respect to the blood pressure and other hemodynamic parameters, most significant results were obtained in the post-exercise stage. In any case, the symptomatic OI group exhibited higher irregularity in the measured parameters, as higher RCMFE levels in all time scales were obtained. This information could be very helpful for a better understanding of cardiovascular instability, as well as to recognize risk factors for falls and impairment of functional status.

Entropy at the right atrium as a predictor of atrial fibrillation recurrence outcome after pulmonary vein ablation.

Atrial fibrillation (AF) recurrence rates after successful ablation procedures are still high and difficult to predict. This work studies the capability of entropy measured from intracardiac recordings as an indicator for recurrence outcome. Intra-atrial recordings from 31 AF patients were registered previously to an ablation procedure. Four electrodes were located at the right atrium (RA) and four more at the left atrium (LA). Sample entropy measurements were applied to these signals, in order to characterize different non-linear AF dynamics at the RA and LA independently. In a 3 months follow-up, 19 of them remained in sinus rhythm, whereas the other 12 turned back to AF. Entropy values can be associated to a proarrhythmic indicator as they were higher in patients with AF recurrence (1.11±0.15 vs. 0.91±0.13), in persistent patients (1.03±0.19 vs. 0.96±0.15), and at the LA with respect to the RA (1.03±0.23 vs. 0.89±0.15 for paroxysmal AF patients). Furthermore, entropy values at the RA arose as a more reliable predictor for recurrence outcome than at the LA. Results suggest that high entropy values, especially at the RA, are associated with high risk of AF recurrence. These findings show the potential of the proposed method to predict recurrences post-ablation, providing additional insights to the understanding of arrhythmia.

On the preprocessing of atrial electrograms in atrial fibrillation: understanding Botteron's approach.

BACKGROUND: The dominant atrial frequency is a key parameter for the analysis of atrial fibrillation (AF) from intracardiac recordings. The preprocessing approach employed by Botteron et al. in an early work is able to retrieve this frequency. The preprocessing steps are: (1) 40-250-Hz band-pass filtering, (2) rectification, and (3) 20 Hz low-pass filtering. METHODS AND RESULTS: The theoretical aspects of this process are addressed. Moreover, its time-domain and frequency-domain properties are evaluated using both simulations and real electrogram (EGM) recordings. The fundamental frequency is emphasized, due to the rectification step. As the interval between consecutive activations becomes more irregular, fundamental frequency detection becomes less robust. In the case of fractionated EGM, this approach fails. In time-domain, the waveform of the atrial beats are dramatically modified, hence hindering any further analysis on the morphology of the activations. CONCLUSIONS: Botteron preprocessing succeeds in estimating the dominant atrial rate in most EGMs during AF. However, this approach presents some limitations and improved methods are required.

Profound sedation with propofol modifies atrial fibrillation dynamics.

During atrial fibrillation (AF), multiple wandering propagation wavelets at high rates drift around both atria under controversial hierarchical models. Antiarrhythmic drugs modify the cardiac ionic currents supporting the fibrillation process within the atria, and can alter AF propagation dynamics and even terminate the arrhythmia. However, some other drugs, theoretically nonantiarrhythmic, may slightly block particular cardiac ionic currents through uncertain mechanisms in such a subtle way at regular heart rates that may have been pharmacologically overlooked. These potential effects might be better exposed at much higher activation rates as in AF, where atrial cells depolarize over 400 times per second. In this review, we aimed to compile and discuss results from several studies evaluating the net effect of profound sedation with propofol on atrial cells and atrioventricular (AV) conduction. Propofol is a very commonly used anesthetic agent, and its possible effect on AF dynamics has systematically not been taken into account in the myriad of clinical studies dealing with AF intracardiac recordings. The possible effect of sedation with propofol on AF was evaluated through the analysis of AF propagation patterns before and after its infusion in a series of patients submitted to pulmonary vein ablation. Effect on AV conduction will be discussed as well.

Morphology quantification of atrial fibrillation under propofol using principal components analysis.

The effect of the most useful anaesthetic in cardiovascular therapy, called propofol, was evaluated in patients with atrial fibrillation (AF). In order to represent the electrogram recordings in a more efficient manner Principal component analysis (PCA) has been applied. Moreover, to reduce the data set to a few representative activations PCA was applied again to measure the average dissimilarity between consecutive activations of an intracardiac signal. In addition PCA was applied directly to the activations extracted from each dipole to analysis temporal varibility, and spatial variability with the comparation of the signals from different dipoles. The proposed indexes show different behaviour patterns along the atrial area during the anaesthetic effects.

Skeletal myoblast implants induce minor propagation delays, but do not promote arrhythmias in the normal swine heart.

AIMS: Whether skeletal myoblast (SM) implants are proarrhythmic is still controversial due to conflicting pre-clinical and clinical data. We hypothesized that if SM implants are arrhythmogenic, they will facilitate the induction of ventricular tachyarrhythmias by promoting heterogeneous propagation of activation wavefronts. METHODS: Skeletal myoblast cells were harvested from 10 pigs. A month later, 125 ± 37 × 10(6) cells were subepicardially injected in an area of ∼2 cm(2) at the anterolateral aspect of the left ventricle. Four weeks later, a ventricular stimulation protocol was conducted. Once explanted, epicardial wavefronts over SM and adjacent control areas were optically mapped. Eight saline-injected animals were used as controls. To compare with clear arrhythmogenic substrates, propagation patterns were also evaluated in infarcted hearts and on a SM-implanted heart following amiodarone infusion. RESULTS: In SM hearts, fibrosis and differentiated SM cells were consistently found and no tachyarrhythmias were induced. Wavefronts propagated homogeneously over SM and adjacent areas, with no late activation zones, as opposed to the infarcted hearts. The time required for the wavefronts to depolarize both areas were similar, becoming only slightly longer at SM areas after an extra-stimulus (P = 0.025). Conduction velocities and APD(90) were also similar. Saline hearts showed similar results. The extent of the conduction delay was not related to the number of injected SM cells. CONCLUSION: In normal swine hearts, myoblast implants promote localized fibrosis and slightly retard epicardial wavefront propagation only after extra-stimuli. However, SM implants are not associated with local re-entry and do not facilitate ventricular tachyarrhythmias in the whole normal heart.

Propofol effects on atrial fibrillation wavefront delays.

Since the cardiac activity during atrial fibrillation (AF) may be influenced by autonomic modulations, in this study, a novel method to quantify the effects of the most common anesthetic agent (propofol) in AF ablation procedures is introduced. This study has two main objectives: first, to assess whether the sedation earlier to radio frequency ablation affects the arrhythmia itself, and second, to provide new information that contributes to a better understanding of the influence of the autonomic nervous system on AF. The methodology presented is based on the measurement of synchronization and delay indexes between two atrial activations at adjacent intracavitary electrodes. These parameters aim to estimate whether two activations at different sites may be caused by the same propagating wavefront, or otherwise, are the consequence of independent wavefronts. The results showed that the mentioned indexes have a different behavior at both atria: the right atrium becomes more synchronized with propofol administration, whereas the synchronization index decreases at the left atrium.

Ablation of atrioventricular nodal reentrant tachycardia using remote magnetic guidance (stereotaxis) requires lower temperature and power settings because of improved local contact.

INTRODUCTION AND OBJECTIVES: The Stereotaxis(R) remote magnetic navigation system provides a new approach to ablation that could increase catheter stability. The aim was to determine whether improved tissue contact necessitates a change in traditional radiofrequency ablation parameters. METHODS: The study compared ablation of atrioventricular nodal reentrant tachycardia (AVNRT) using remote navigation (4-mm catheter) in 19 patients with conventional ablation in 18 patients (4-mm catheter, temperature 60-65 degrees C, power 50 W). The radiofrequency energy needed to ensure that no more than a single nodal echo beat could be induced was measured. RESULTS: Charring was observed with traditional parameters on the first applications of the remotely navigated catheter. Hence, the energy was subsequently reduced (to 50 degrees C and 40 W). There was no difference in the number of applications between remote navigation and conventional groups (median: 6 vs. 8.5; interquartile range [IQR]: 11 vs. 9). Applications lasting

Atrial fibrillation organization: quantification of propofol effects.

The effect of conventional i.v. anaesthetic agents on atrial fibrillation (AF) dynamics has not been fully addressed. We aim to evaluate whether the most frequently used intravenous anaesthetic agent, propofol, modifies AF organization parameters. Multiple and simultaneous intraatrial bipolar recordings from 27 patients in AF were analyzed before and after infusing a propofol bolus. Signal organization parameters were determined using time and frequency domain analysis. Non-linear analysis was also performed to determine signal entropy. Linear analysis showed that AF becomes more organized in right atrial recordings after infusing propofol, increasing interelectrode correlation (difference of 0.017 +/- 0.005), with the contrary effect on the left atrial dipoles (difference of -0.015 +/- 0.009, p = 0.008). Entropy analysis showed similar findings, achieving a statistical significance of p = 0.001 with Shannon Entropy.