Functional substrate mapping of atrium in patients with atrial scar: A novel method to predict critical isthmus of atrial tachycardia.

Atrial tachycardia (AT) is a common rhythm disorder, especially in patients with atrial structural abnormalities. Although voltage mapping can provide a general picture of structural alterations which are mainly secondary to prior ablations, surgery or pressure/volume overload, data is scarce regarding the functional characteristics of low voltage regions in the atrium to predict critical isthmus of ATs. Recently, functional substrate mapping (FSM) emerged as a potential tool to evaluate the functionality of structurally altered regions in the atrium to predict critical sites of reentry. Current evidence suggested a clear association between deceleration zones of isochronal late activation mapping (ILAM) during sinus/paced rhythm and critical isthmus of reentry in patients with left AT. Therefore, these areas seem to be potential ablation targets even not detected during AT. Furthermore, abnormal conduction detected by ILAM may also have a role to identify the potential substrate and predict atrial fibrillation outcome after pulmonary vein isolation. Despite these promising findings, the utility of such an approach needs to be evaluated in large-scale comparative studies. In this review, we aimed to share our experience and review the current literature regarding the use of FSM during sinus/paced rhythm in the prediction of re-entrant ATs and discuss future implications and potential use in patients with atrial low-voltage areas.

Body Surface Potential Mapping during Ventricular Depolarization in Athletes with Prolonged PQ Interval after Exercise. / Mapeamento do Potencial da Superfície Corporal durante a Despolarização Ventricular em Atletas com Intervalo PQ Prolongado após Exercício.

BACKGROUND: Prolongation of the PQ interval, generally associated with an atrioventricular conduction delay, may be related to changes in intraventricular impulse spreading. OBJECTIVE: To assess, using body surface potential mapping (BSPM), the process of ventricular depolarization in athletes with prolonged PQ intervals at rest and after exercise. METHODS: The study included 7 cross-country skiers with a PQ interval of more than 200 ms (Prolonged-PQ group) and 7 with a PQ interval of less than 200 ms (Normal-PQ group). The BSPM from 64 unipolar torso leads was performed before (Pre-Ex) and after the bicycle exercise test (Post-Ex). Body surface equipotential maps were analyzed during ventricular depolarization. The significance level was 5%. RESULTS: Compared to Normal-PQ athletes, the first and second periods of the stable position of cardiac potentials on the torso surface were longer, and the formation of the "saddle" potential distribution occurred later, at Pre-Ex, in Prolonged-PQ athletes. At Post-Ex, the Prolonged-PQ group showed a shortening of the first and second periods of stable potential distributions and a decrease in appearance time of the "saddle" phenomenon relative to Pre-Ex (to the values near to those of the Normal-PQ group). Additionally, at Post-Ex, the first inversion of potential distributions and the total duration of ventricular depolarization in Prolonged-PQ athletes decreased compared to Pre-Ex and with similar values in Normal-PQ athletes. Compared to Normal-PQ athletes, the second inversion was longer at Pre-Ex and Post-Ex in Prolonged-PQ athletes. CONCLUSION: Prolonged-PQ athletes had significant differences in the temporal characteristics of BSPM during ventricular depolarization both at rest and after exercise as compared to Normal-PQ athletes.

FUNDAMENTO: O prolongamento do intervalo PQ, geralmente associado a um atraso na condução atrioventricular, pode estar relacionado a alterações na propagação do impulso intraventricular. OBJETIVO: Avaliar, por meio do mapeamento do potencial de superfície corporal (BSPM), o processo de despolarização ventricular em atletas com intervalos PQ prolongados em repouso e após o exercício. MÉTODOS: O estudo incluiu 7 esquiadores cross-country com intervalo PQ superior a 200 ms (grupo PQ Prolongado) e 7 com intervalo PQ inferior a 200 ms (grupo PQ Normal). O BSPM de 64 derivações unipolares do tronco foi realizado antes (Pré-Ex) e após o teste ergométrico de bicicleta (Pós-Ex). Mapas equipotenciais da superfície corporal foram analisados durante a despolarização ventricular. O nível de significância foi de 5%. RESULTADOS: Comparado com atletas com PQ Normal, o primeiro e o segundo períodos de posição estável dos potenciais cardíacos na superfície do tronco foram mais longos, e a formação da distribuição de potencial "sela" ocorreu mais tarde, no Pré-Ex, nos atletas com PQ Prolongado. No Pós-Ex, o grupo PQ Prolongado apresentou um encurtamento do primeiro e segundo períodos de distribuições de potencial estáveis e uma diminuição no tempo de aparecimento do fenômeno "sela" em relação ao Pré-Ex (para valores próximos aos do Normal -Grupo PQ). Além disso, no Pós-Ex, a primeira inversão das distribuições de potencial e a duração total da despolarização ventricular em atletas com PQ Prolongado diminuíram em comparação com o Pré-Ex e com valores semelhantes em atletas com PQ Normal. Em comparação com atletas com PQ Normal, a segunda inversão foi mais longa no Pré-Ex e Pós-Ex em atletas com PQ Prolongado. CONCLUSÃO: Atletas com PQ prolongado apresentaram diferenças significativas nas características temporais do BSPM durante a despolarização ventricular, tanto em repouso quanto após o exercício, em comparação com atletas com PQ normal.

Quantitative comparison of the isolation lesions between conventional- and larger-sized visually guided laser balloon ablation.

BACKGROUND: The importance of a wider circumferential isolation of the pulmonary veins (PV), which includes a large portion of the left atrial posterior wall (LAPW), has been suggested in several studies. However, the extended isolation area using a larger inflated visually guided laser balloon (VGLB) ablation remains to be elucidated. METHODS: Seventy-eight patients with atrial fibrillation (AF) who underwent VGLB ablation were enrolled in this prospective study. An electroanatomic map of the left atrium was obtained before and after PV isolation (PVI) using a conventional-sized VGLB. The isolation areas were extended by the largest-sized VGLB ablation and remapped in the same manner. After the ablation, isolation areas were calculated with CARTO-3 system. The one-year atrial arrhythmia (Ata) recurrence was assessed.  RESULTS: The largest-sized VGLB ablation yielded statistically greater areas of isolation in left-sided PV antrum (PVA) (11.5 ± 2.3 cm2 vs. 15.9 ± 3.5 cm2, P < .001) and right-sided PVA (14.2 ± 3.3 cm2 vs. 20.6 ± 4.4 cm2, P < .001) than the conventional-sized VGLB. Further, non-ablated LAPW (12.3 ± 4.4 cm2 vs. 7.8 ± 3.9 cm2, P < .001) was significantly reduced after largest-sized VGLB ablation, compared to the conventional-sized VGLB ablation. The one-year Ata freedom was 83.7% in patients with paroxysmal AF and 96.4% in those with persistent AF. CONCLUSION: The largest-sized VGLB ablation technique can create a significantly wider isolation area of PVA and debulk a large amount of LAPW than the conventional-sized VGLB ablation. The one-year outcome was similarly high in paroxysmal and persistent AF.

Optimal cardiac rhythm during substrate mapping in scar-related ventricular tachycardia: Significance of wavefront direction on identifying critical sites.

BACKGROUND: A rotational activation pattern (RAP) around the localized line of a conduction block often correlates with sites specific to the critical zones of ventricular tachycardia (VT). The wavefront direction during substrate mapping affects manifestation of the RAP and line of block. OBJECTIVE: The purpose of this study was to investigate the most optimal cardiac rhythm for identifying RAP and line of block in substrate mapping. METHODS: We retrospectively evaluated 71 maps (median 3205 points/map) in 46 patients (65 ± 15 years; 33% with ischemic cardiomyopathy) who underwent high-density substrate mapping and ablation of scar-related VT. Appearance of a RAP during sinus, right ventricular (RV)-paced, left ventricular (LV)-paced, and biventricular-paced rhythms was investigated. RESULTS: RAP was identified in 24 of 71 maps (34%) in the region where wavefronts from a single direction reached but not in the region where wavefronts from multiple directions centripetally collided. The probability of identifying the RAP depended on scar location; that is, anteroseptal and inferoseptal, inferior and apical, and basal lateral RAPs were likely to be identified during sinus/atrial, RV-paced, and LV-paced rhythms, respectively. In 13 patients, the RAP was not evident in the baseline map but became apparent during remapping in the other rhythm, in which the wavefront reached the site earlier within the entire activation time. CONCLUSION: The optimal rhythm for substrate mapping depends on the spatial distribution of the area of interest. A paced rhythm with pacing sites near the scar may facilitate the identification of critical VT zones.

Characterization of conduction system activation in the postinfarct ventricle using ripple mapping.

BACKGROUND: Three-dimensional (3D) mapping of the ventricular conduction system is challenging. OBJECTIVE: The purpose of this study was to use ripple mapping to distinguish conduction system activation to that of adjacent myocardium in order to characterize the conduction system in the postinfarct left ventricle (LV). METHODS: High-density mapping (PentaRay, CARTO) was performed during normal rhythm in patients undergoing ventricular tachycardia ablation. Ripple maps were viewed from the end of the P wave to QRS onset in 1-ms increments. Clusters of >3 ripple bars were interrogated for the presence of Purkinje potentials, which were tagged on the 3D geometry. Repeating this process allowed conduction system delineation. RESULTS: Maps were reviewed in 24 patients (mean 3112 ± 613 points). There were 150.9 ± 24.5 Purkinje potentials per map, at the left posterior fascicle (LPF) in 22 patients (92%) and at the left anterior fascicle (LAF) in 15 patients (63%). The LAF was shorter (41.4 vs 68.8 mm; P = .0005) and activated for a shorter duration (40.6 vs 64.9 ms; P = .002) than the LPF. Fourteen of 24 patients had left bundle branch block (LBBB), with 11 of 14 (78%) having Purkinje potential-associated breakout. There were fewer breakouts from the conduction system during LBBB (1.8 vs 3.4; 1.6 ± 0.6; P = .039) and an inverse correlation between breakout sites and QRS duration (P = .0035). CONCLUSION: We applied ripple mapping to present a detailed electroanatomic characterization of the conduction system in the postinfarct LV. Patients with broader QRS had fewer LV breakout sites from the conduction system. However, there was 3D mapping evidence of LV breakout from an intact conduction system in the majority of patients with LBBB.

A novel automated peak frequency annotation algorithm for identifying deceleration zones and ventricular tachycardia ablation sites.

BACKGROUND: Current annotation of local fractionated signals during ventricular electroanatomic mapping (EAM) requires manual input subject to variability and error. OBJECTIVES: The purpose of this study was to evaluate a novel peak frequency (PF) annotation software for its ability to automatically detect late potentials (LPs) and local abnormal ventricular activity (LAVA), determine an optimal range for display, and assess its impact on isochronal late activation mapping (ILAM). METHODS: EAM data from 25 patients who underwent ventricular tachycardia (VT) ablation were retrospectively analyzed. Samplings of electrogram PFs from areas of normal bipolar voltage, areas of low voltage, and areas of low voltage with fractioned signals were performed. An optimal range of frequency display was identified from these patients and applied to a validation cohort of 10 prospective patients to assess high PF within scar as a predictor of VT ablation target sites, in particular deceleration zones (DZs) identified by ILAM, LP, and LAVA. RESULTS: Voltage and PF ranges of normal endocardial tissue varied widely. Using 220 Hz as a frequency cutoff value in areas of low bipolar voltage, areas of high fractionation were identified with sensitivity of 91% and specificity of 85% There was no significant reduction in targeted DZ surface areas, and colocalization with DZs was observed in all cases. Applied to the prospective cohort, PF predicted fractionated areas and DZ in 9 of 10 patients. CONCLUSION: A PF annotation algorithm with a cutoff of 220 Hz accurately identifies areas of fractioned signals and accurately predicts DZs during ILAM.

A reduced complexity ECG imaging model for regularized inversion optimization.

The resolution of the inverse problem of electrocardiography represents a major interest in the diagnosis and catheter-based therapy of cardiac arrhythmia. In this context, the ability to simulate several cardiac electrical behaviors was crucial for evaluating and comparing the performance of inversion methods. For this application, existing models are either too complex or do not produce realistic cardiac patterns. In this work, a low-resolution heart-torso model generating realistic whole heart cardiac mappings and electrocardiograms in healthy and pathological cases is designed. This model was built upon a simplified heart-torso geometry and implements the monodomain formalism by using the finite element method. In addition, a model reduction step through a sensitivity analysis was proposed where parameters were identified using an evolutionary optimization approach. Finally, the study illustrates the usefulness of the proposed model by comparing the performance of different variants of Tikhonov-based inversion methods for the determination of the regularization parameter in healthy, ischemic and ventricular tachycardia scenarios. First, results of the sensitivity analysis show that among 58 parameters only 25 are influent. Note also that the level of influence of the parameters depends on the heart region. Besides, the synthesized electrocardiograms globally present the same characteristic shape compared to the reference once with a correlation value that reaches 88%. Regarding inverse problem, results highlight that only Robust Generalized Cross Validation and Discrepancy Principle provide best performance, with a quasi-perfect success rate for both, and a respective relative error, between the generated electrocardiograms to the reference one, of 0.75 and 0.62.

Comparison of Gastric Alimetry® body surface gastric mapping versus electrogastrography spectral analysis.

Electrogastrography (EGG) non-invasively evaluates gastric motility but is viewed as lacking clinical utility. Gastric Alimetry® is a new diagnostic test that combines high-resolution body surface gastric mapping (BSGM) with validated symptom profiling, with the goal of overcoming EGG's limitations. This study directly compared EGG and BSGM to define performance differences in spectral analysis. Comparisons between Gastric Alimetry BSGM and EGG were conducted by protocolized retrospective evaluation of 178 subjects [110 controls; 68 nausea and vomiting (NVS) and/or type 1 diabetes (T1D)]. Comparisons followed standard methodologies for each test (pre-processing, post-processing, analysis), with statistical evaluations for group-level differences, symptom correlations, and patient-level classifications. BSGM showed substantially tighter frequency ranges vs EGG in controls. Both tests detected rhythm instability in NVS, but EGG showed opposite frequency effects in T1D. BSGM showed an 8× increase in the number of significant correlations with symptoms. BSGM accuracy for patient-level classification was 0.78 for patients vs controls and 0.96 as compared to blinded consensus panel; EGG accuracy was 0.54 and 0.43. EGG detected group-level differences in patients, but lacked symptom correlations and showed poor accuracy for patient-level classification, explaining EGG's limited clinical utility. BSGM demonstrated substantial performance improvements across all domains.

Body surface potential mapping detects early disease onset in plakophilin-2-pathogenic variant carriers.

AIMS: Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a progressive inherited cardiac disease. Early detection of disease and risk stratification remain challenging due to heterogeneous phenotypic expression. The standard configuration of the 12 lead electrocardiogram (ECG) might be insensitive to identify subtle ECG abnormalities. We hypothesized that body surface potential mapping (BSPM) may be more sensitive to detect subtle ECG abnormalities. METHODS AND RESULTS: We obtained 67 electrode BSPM in plakophilin-2 (PKP2)-pathogenic variant carriers and control subjects. Subject-specific computed tomography/magnetic resonance imaging based models of the heart/torso and electrode positions were created. Cardiac activation and recovery patterns were visualized with QRS- and STT-isopotential map series on subject-specific geometries to relate QRS-/STT-patterns to cardiac anatomy and electrode positions. To detect early signs of functional/structural heart disease, we also obtained right ventricular (RV) echocardiographic deformation imaging. Body surface potential mapping was obtained in 25 controls and 42 PKP2-pathogenic variant carriers. We identified five distinct abnormal QRS-patterns and four distinct abnormal STT-patterns in the isopotential map series of 31/42 variant carriers. Of these 31 variant carriers, 17 showed no depolarization or repolarization abnormalities in the 12 lead ECG. Of the 19 pre-clinical variant carriers, 12 had normal RV-deformation patterns, while 7/12 showed abnormal QRS- and/or STT-patterns. CONCLUSION: Assessing depolarization and repolarization by BSPM may help in the quest for early detection of disease in variant carriers since abnormal QRS- and/or STT-patterns were found in variant carriers with a normal 12 lead ECG. Because electrical abnormalities were observed in subjects with normal RV-deformation patterns, we hypothesize that electrical abnormalities develop prior to functional/structural abnormalities in ARVC.

A method for noninvasive beat-by-beat visualization of His bundle signals.

BACKGROUND: Invasive recording of His bundle signals (HBS) in electrophysiological study (EPS) is important in determining HV interval, the time taken to activate the ventricles from the His bundle. Noninvasive surface measurements of HBS are attempted by averaging typically 100-200 cardiac cycles of ECG time series in body surface potential mapping (BSPM) and in magnetocardiography (MCG) which records weak cardiac magnetic fields by highly sensitive detectors. However, noninvasive beat-by-beat extraction of HBS is challenged by ramp-like atrial signals and noise in PR segment of the cardiac cycle. METHODS: By making use of a signal-averaged trace showing prominent HBS as a guide trace, we developed a method combining interval-dependent wavelet thresholding (IDWT) and signal space projection (SSP) technique to eliminate artifacts from single beats. The method was applied on MCG recorded on 21 subjects with known HV intervals based on EPS and noninvasive signal-averaging, including five subjects with BSPM recorded subsequently. The method was also applied on stress-MCG of a subject featuring autonomic dynamics. RESULTS: HBS could be extracted from 19 out of 21 subjects by signal-averaging whose timing differed from EPS between -8 and 11 ms as tested by 2 observers. HBS in single beats were seen as aligned patterns in inter-beat contours and were appreciable in stress-MCG and conspicuous than BSPM. The performance of the method was evaluated on simulated and measured MCG to be adequate if the signal-to-noise ratio was at least 20 dB. CONCLUSIONS: These results suggest the use of this method for noninvasive assessments on HBS.

An expert review of the inverse problem in electrocardiographic imaging for the non-invasive identification of atrial fibrillation drivers.

BACKGROUND AND OBJECTIVE: Electrocardiographic imaging (ECGI) has emerged as a non-invasive approach to identify atrial fibrillation (AF) driver sources. This paper aims to collect and review the current research literature on the ECGI inverse problem, summarize the research progress, and propose potential research directions for the future. METHODS AND RESULTS: The effectiveness and feasibility of using ECGI to map AF driver sources may be influenced by several factors, such as inaccuracies in the atrial model due to heart movement or deformation, noise interference in high-density body surface potential (BSP), inconvenient and time-consuming BSP acquisition, errors in solving the inverse problem, and incomplete interpretation of the AF driving source information derived from the reconstructed epicardial potential. We review the current research progress on these factors and discuss possible improvement directions. Additionally, we highlight the limitations of ECGI itself, including the lack of a gold standard to validate the accuracy of ECGI technology in locating AF drivers and the challenges associated with guiding AF ablation based on post-processed epicardial potentials due to the intrinsic difference between epicardial and endocardial potentials. CONCLUSIONS: Before performing ablation, ECGI can provide operators with predictive information about the underlying locations of AF driver by non-invasively and globally mapping the biatrial electrical activity. In the future, endocardial catheter mapping technology may benefit from the use of ECGI to enhance the diagnosis and ablation of AF.

Principles and clinical methods of body surface gastric mapping: Technical review.

BACKGROUND AND PURPOSE: Chronic gastric symptoms are common, however differentiating specific contributing mechanisms in individual patients remains challenging. Abnormal gastric motility is present in a significant subgroup, but reliable methods for assessing gastric motor function in clinical practice are lacking. Body surface gastric mapping (BSGM) is a new diagnostic aid, employs multi-electrode arrays to measure and map gastric myoelectrical activity non-invasively in high resolution. Clinical adoption of BSGM is currently expanding following studies demonstrating the ability to achieve specific patient subgrouping, and subsequent regulatory clearances. An international working group was formed in order to standardize clinical BSGM methods, encompassing a technical group developing BSGM methods and a clinical advisory group. The working group performed a technical literature review and synthesis focusing on the rationale, principles, methods, and clinical applications of BSGM, with secondary review by the clinical group. The principles and validation of BSGM were evaluated, including key advances achieved over legacy electrogastrography (EGG). Methods for BSGM were reviewed, including device design considerations, patient preparation, test conduct, and data processing steps. Recent advances in BSGM test metrics and reference intervals are discussed, including four novel metrics, being the 'principal gastric frequency', BMI-adjusted amplitude, Gastric Alimetry Rhythm Index™, and fed: fasted amplitude ratio. An additional essential element of BSGM has been the introduction of validated digital tools for standardized symptom profiling, performed simultaneously during testing. Specific phenotypes identifiable by BSGM and the associated symptom profiles were codified with reference to pathophysiology. Finally, knowledge gaps and priority areas for future BSGM research were also identified by the working group.

Robustness of imageless electrocardiographic imaging against uncertainty in atrial morphology and location.

INTRODUCTION: Electrocardiographic Imaging is a non-invasive technique that requires cardiac Imaging for the reconstruction of cardiac electrical activity. In this study, we explored imageless ECGI by quantifying the errors of using heart meshes with either an inaccurate location inside the thorax or an inaccurate geometry. METHODS: Multiple­lead body surface recordings of 25 atrial fibrillation (AF) patients were recorded. Cardiac atrial meshes were obtained by segmentation of medical images obtained for each patient. ECGI was computed with each patient's segmented atrial mesh and compared with the ECGI obtained under errors in the atrial mesh used for ECGI estimation. We modeled both the uncertainty in the location of the atria inside the thorax by artificially translating the atria inside the thorax and the geometry of the atrial mesh by using an atrial mesh in a reference database. ECGI signals obtained with the actual meshes and the translated or estimated meshes were compared in terms of their correlation coefficients, relative difference measurement star, and errors in the dominant frequency (DF) estimation in epicardial nodes. RESULTS: CC between ECGI signals obtained after translating the actual atrial meshes from the original position by 1 cm was above 0.97. CC between ECGIs obtained with patient specific atrial geometry and estimated atrial geometries was 0.93 ± 0.11. Mean errors in DF estimation using an estimated atrial mesh were 7.6 ± 5.9%. CONCLUSION: Imageless ECGI can provide a robust estimation of cardiac electrophysiological parameters such as activation rates even during complex arrhythmias. Furthermore, it can allow more widespread use of ECGI in clinical practice.

A Patchwork Method to Improve the Performance of Current Methods for Solving the Inverse Problem of Electrocardiography.

OBJECTIVE: Noninvasive electrocardiographic imaging (ECGI) reconstructs cardiac electrical activity from body surface potential measurements. However, current methods have demonstrated inaccuracies in reconstructing sinus rhythm, and in particular breakthrough sites. This study aims to combine existing inverse algorithms, making the most of their advantages while minimizing their limitations. METHOD: The "patchwork method" (PM) combines two classical numerical methods for ECGI: the method of fundamental solutions (MFS) and the finite-element method (FEM). We assume that the method with the smallest residual in the predicted torso potentials, computed using the boundary element method (BEM), provides the most accurate solution. The PM selects for each heart node and time step the method whose estimated reconstruction error is smallest. The performance of the PM was evaluated using simulated ectopic and normal ventricular beats. RESULTS: Cardiac potentials and activation maps obtained with the PM (CC = 0.63 ± 0.01 and 0.61 ± 0.05 respectively) were more accurate than MFS (CC = 0.61 ± 0.01 and 0.48 ± 0.05 respectively), FEM (CC = 0.58 ± 0.01 and 0.51 ± 0.02 respectively) or BEM (CC = 0.57 ± 0.02 and 0.49 ± 0.02 respectively). The PM also located all epicardial breakthrough sites, whereas the traditional numerical methods usually missed one. Furthermore, the PM showed its robustness and stability in the presence of Gaussian noise added to the torso potentials. CONCLUSION: The PM overcomes some of the limitations of classical numerical methods, improving the accuracy of mapping important features of activation during sinus rhythm and paced beats. SIGNIFICANCE: This novel method for optimizing ECGI solutions opens a new avenue for improving not only ECGI but also other inverse problems.