Unipolar and bipolar electrograms to predict successful ablation site of premature ventricular contractions originating from the free wall of the tricuspid annulus.

INTRODUCTION: This study aimed to identify the characteristics of unipolar and bipolar electrogram (UniEGM and BiEGM) in guiding successful ablation of premature ventricular contractions (PVCs) originating from the free wall of the ventricular aspect of the tricuspid annulus (TA). We hypothesized that the negative concordance pattern (NCP) on the onset of UniEGM and BiEGM, together with the least value of the difference between the earliest BiEGM and UniEGM dV/dTmax, might improve the accuracy of conventional mapping. METHODS AND RESULTS: Thirty consecutive patients who underwent successful catheter ablation from February 2018 to July 2021 were retrospectively analyzed. The BiEGM and UniEGM for successful ablation sites were compared with those for non-successful ablation sites. Among the 30 patients, 30 successful and 26 nonsuccessful ablation sites were compared. The earliest activation time of the BiEGM (BiEGMoneset-QRS) was 25 ± 6 ms for the successful ablation sites and 21 ± 6 ms for the nonsuccessful ablation sites (p = .47). The value of the difference in the earliest BiEGM and UniEGM dV/dTmax differed between successful and nonsuccessful ablation sites (6.4 ± 3.6 ms vs. 10.4 ± 6.8 ms). NCP was observed at 90.0% and 42.3% of the successful and nonsuccessful ablation sites, respectively. Alignment of NCP and BiEGMonset-UniEGM ≤6 ms was applied as the mapping criterion for successful PVC suppression (73.1% sensitivity and 87.7% specificity). The area under the receiver-operating characteristic curve for this cutoff was 0.85. CONCLUSION: Mapping based on an NCP at the onset of the BiEGM and UniEGM and the least difference value of the earliest BiEGM and UniEGM dV/dTmax had an excellent predictive value for successful ablation. These strategies may reduce the number of radiofrequency catheter ablation (RFCA) applications for free-wall tricuspid annular PVCs.

Spatiotemporal approximation of cardiac activation and recovery isochrones.

BACKGROUND: The sequence of myocardial activation and recovery can be studied in detail by invasive catheter recordings of cardiac electrograms (EGMs), or noninvasive inverse reconstructions thereof with electrocardiographic imaging (ECGI). Local activation and recovery times are obtained from a unipolar EGM by the moment of maximum downslope of the QRS complex or maximum upslope of the T wave, respectively. However, both invasive and noninvasive recordings of intracardiac EGMs may suffer from noise and fractionation, making reliable detection of these deflections nontrivial. METHODS: Here, we introduce a novel method that benefits from the spatial coupling of these processes, and incorporate not only the temporal EGM deflection, but also the spatial gradients. We validated this approach in computer simulations, in animal data with ECGI and invasive electrode recordings, and illustrated its use in a clinical case. RESULTS: In the simulated data, the spatiotemporal approach was able to incorporate spatial information to better select the correct deflection in artificially fractionated EGMs and outperformed the traditional temporal-only method. In experimental data, the accuracy of time estimation from ECGI compared to invasive recordings significantly increased from R = 0.73 (activation) and R = 0.58 (recovery) with the temporal-only method to R = 0.79 (activation) and R = 0.72 (recovery) with the novel approach. Localization of the pacing origin of paced beats improved significantly from 36 mm mean error with the temporal-only approach to 23 mm with the spatiotemporal approach. CONCLUSION: The spatiotemporal method to compute activation and recovery times from EGMs outperformed the traditional temporal-only approach in which spatial information was not taken into account.

Unipolar voltage mapping criteria for right ventricular septum: Influence of the aortic root.

INTRODUCTION: Unipolar voltage mapping through its wider "field of view" can identify substrate deeper to the endocardium on the right ventricular (RV) free wall and left ventricle. The reference value(s) for normal endocardial (ENDO) unipolar voltage (UNI) for the septal aspect of the right ventricle (RV) and the effect of the aortic root that is directly opposed to the posterior septal plane of the RV outflow tract (RVOT) have not been established. METHODS AND RESULTS: We performed detailed (185 ± 70, range 127-342 points) RV ENDO UNI maps in 9 patients without structural heart disease; 6 had magnetic resonance (MR) imaging; 5 were males; the mean age was 49 ± 11 years. For MR analysis, the location of the aortic root was defined and its effect on unipolar voltage determined. The UNI voltage on posterior RVOT was lower (mean 6.56 ± 2.33 mV, 95% CI 6.08-7.05), compared to the rest of the septal aspect of RV (mean 8.33 ± 2.34 mV, P < 0.001, 95% CI 7.84-8.84). MR analysis confirmed that the lowest voltage region was opposite to MR-defined aortic root. Using a cutoff for UNI abnormality of 6.0 mV for the posterior aspect of the RVOT opposite to the aortic root and 7.5 mV for the rest of the septal aspect of the RV, there was no confluent area of unipolar abnormality in any patient. CONCLUSION: We defined normal ENDO UNI cutoffs as 7.5 mV for the septal aspect of the RV with adjustment to 6.0 mV over the posterior RVOT opposite to the aortic root.

A novel diagnostic tool to identify atrial endo-epicardial asynchrony using signal fingerprinting.

OBJECTIVE: Patients with persistent atrial fibrillation (AF) have more electrical endo-epicardial asynchrony (EEA) during sinus rhythm (SR) than patients without AF. Prior mapping studies indicated that particularly unipolar, endo- and/or epicardial electrogram (EGM) morphology may be indicators of EEA. This study aim to develop a novel method for estimating the degree of EEA by using unipolar EGM characteristics recorded from either the endo- and/or epicardium. METHODS: Simultaneous endo-epicardial mapping during sinus rhythm was performed in 86 patients. EGM characteristics, including unipolar voltages, low-voltage areas (LVAs), potential types (single, short/long double and fractionated potentials: SP, SDP, LDP and FP) and fractionation duration (FD) of double potentials (DP) and FP were compared between EEA and non-EEA areas. Asynchrony Fingerprinting Scores (AFS) containing quantified EGM characteristics were constructed to estimate the degree of EEA. RESULTS: Endo- and epicardial sites of EEA areas are characterized by lower unipolar voltages, a higher number of LDPs and FPs and longer DP and FP durations. Patients with AF have lower potential voltages in EEA areas, along with alterations in the potential types. The EE-AFS, containing the proportion of endocardial LVAs and FD of epicardial DPs, had the highest predictive value for determining the degree of EEA (AUC: 0.913). Endo- and epi-AFS separately also showed good predictive values (AUC: 0.901 and 0.830 respectively). CONCLUSIONS: EGM characteristics can be used to identify EEA areas. AFS can be utilized as a novel diagnostic tool for accurately estimating the degree of EEA. These characteristics potentially indicate AF related arrhythmogenic substrates.

EDEN (Electrocardiographic Radial Depth Navigation): A Novel Approach to Navigate Inside Heart Muscle.

BACKGROUND: Intramyocardial guidewire navigation is a novel technique that allows free transcatheter movement within ventricular muscle. Guidewire radial depth, between endocardial and epicardial surfaces, is ambiguous by x-ray and echocardiography. OBJECTIVES: The aim of this study was to develop a simple tool, EDEN (Electrocardiographic Radial Depth Navigation), to indicate radial depth during intramyocardial guidewire navigation. Combined with routine imaging, EDEN facilitates a new family of intramyocardial catheter procedures to slice, reshape, pace, and ablate the heart. METHODS: We mapped intramyocardial electrograms of left and right ventricular walls and septum during open- and closed-chest swine procedures (N = 53), including MIRTH (Myocardial Intramural Remodeling by Transvenous Tether) ventriculoplasty. We identified radial depth-dependent features on unipolar electrograms. We developed a machine learning-based classifier to indicate categorical position, and modeled the findings in silico to test understanding of the physiology. RESULTS: EDEN signatures distinguished 5 depth zones throughout left and right ventricular free walls and interventricular septum. Relative ST-segment elevation magnitude best discriminated position and was maximum (40.1 ± 6.5 mV) in the midmyocardium. Subendocardial positions exhibited dominant Q waves with lower-amplitude ST segments (16.8 ± 5.8 mV), whereas subepicardial positions exhibited dominant R waves with lower-amplitude ST segments (15.7 ± 4.8 mV). EDEN was unaffected by pacing-induced left bundle branch block. ST-segment elevation declined over minutes and reappeared after submillimeter guidewire manipulation. Modeling recapitulated EDEN features. The machine learning-based classifier was 97% accurate. EDEN successfully guided MIRTH ventriculoplasty. CONCLUSIONS: EDEN provides a simple and reproducible real-time reflection of categorical guidewire-tip radial depth during intramyocardial guidewire navigation. Used in tandem with x-ray, EDEN enables novel, transcatheter, intramyocardial therapies such as MIRTH, SESAME (Septal Surfing Along Midline Endocardium), and cerclage ventriculoplasty.

Electric Field-Based Spatial Analysis of Noncontact Unipolar Electrograms to Map Regional Activation-Repolarization Intervals.

BACKGROUND: Spatial heterogeneity in repolarization plays an important role in generating and sustaining cardiac arrhythmias. Reliable determination of repolarization times remains challenging. OBJECTIVES: The goal of this study was to improve processing of densely sampled noncontact unipolar electrograms to yield reliable high-resolution activation and repolarization maps. METHODS: Endocardial noncontact unipolar electrograms were both simulated and recorded in pig left ventricle. Electrical activity on the endocardial surface was processed in terms of a pseudo-electric field. Activation and repolarization times were calculated by using an amplitude-weighted average on QRS and T waves (ie, the E-field method). This was compared vs the conventional Wyatt method on unipolar electrograms. Timing maps were validated against timing on endocardial action potentials in a simulation study. In vivo, activation and repolarization times determined by using this alternative E-field method were validated against simultaneously recorded endocardial monophasic action potentials (MAPs). RESULTS: Simulation showed that the E-field method provides viable measurements of local endocardial action potential activation and repolarization times. In vivo, correlation of E-field activation times with MAP activation times (rE = 0.76; P < 0.001) was similar to those of Wyatt (rWyatt = 0.80, P < 0.001; P[h1:rE > rWyatt] = 0.82); for repolarization times, correlation improved significantly (rE = 0.96, P < 0.001; rWyatt = 0.82, P < 0.001; P[h1:rE > rWyatt] < 0.00001). This resulted in improved correlations of activation-repolarization intervals to endocardial action potential duration on MAP (rE = 0.96, P < 0.001; rWyatt = 0.86, P < 0.001; P[h1:rE > rWyatt] < 0.00001). Spatial beat-to-beat variation of repolarization could only be calculated by using the E-field methodology and correlated well with the MAP beat-to-beat variation of repolarization (rE = 0.76; P = 0.001). CONCLUSIONS: The E-field method substantially enhances information from endocardial noncontact electrogram data, allowing for dense maps of activation and repolarization times and derived parameters.

How to use bipolar and unipolar electrograms for selecting successful ablation sites of ventricular premature contractions.

BACKGROUND: Local activation time is often determined by the maximal negative of the extracellular unipolar potential (-dV/dTmax). While this is accurate in 2-dimensional uniform tissue, propagation through nonuniform or 3-dimensional structures have shown discordance between -dV/dTmax and local activation time. OBJECTIVE: The purpose of this study was to examine the relationship between bipolar and unipolar electrograms for selecting successful ablation sites of endocardial (superficial) vs intramural (deep) ventricular premature contractions (VPCs). METHODS: This cohort consisted of 66 patients with VPCs presenting for ablation in a bigeminy, trigeminy, or quadrigeminy pattern. VPCs were classified as endocardial if ablation at the earliest endocardial site resulted in immediate suppression (<10 seconds) or as intramural if ablation resulted in delayed suppression (≥10 seconds), required multiple applications, or was not achieved. Unipolar and bipolar electrograms were analyzed. RESULTS: In endocardial VPCs, the first rapid bipolar deflection corresponded with unipolar -dV/dTmax, occurring 20.5 ms (17.8-26.0 ms) and 16.0 ms (6.8-22.0 ms), respectively, before the QRS onset. In successfully ablated intramural VPCs, the first rapid bipolar deflection preceded the QRS onset by 14.0 ms (11.2-22.6 ms) and coincided with the first rapid unipolar deflection, although -dV/dTmax occurred 10.5 ms (0.0-20.8 ms) after the QRS onset and often coincided with far-field activity. In unsuccessfully ablated intramural VPCs, the first rapid bipolar deflection to QRS onset interval was shorter in comparison to successfully ablated intramural VPCs (1.5 ms vs 14.0 ms; P < .001) while the unipolar -dV/dTmax to QRS onset interval was similar (P = .095). CONCLUSION: Mapping of VPCs should be guided by the first rapid bipolar deflection that corresponds to a similarly early unipolar deflection but not with -dV/dTmax.

Atrial fibrosis identification with unipolar electrogram eigenvalue distribution analysis in multi-electrode arrays.

Atrial fibrosis plays a key role in the initiation and progression of atrial fibrillation (AF). Atrial fibrosis is typically identified by a peak-to-peak amplitude of bipolar electrograms (b-EGMs) lower than 0.5 mV, which may be considered as ablation targets. Nevertheless, this approach disregards signal spatiotemporal information and b-EGM sensitivity to catheter orientation. To overcome these limitations, we propose the dominant-to-remaining eigenvalue dominance ratio (EIGDR) of unipolar electrograms (u-EGMs) within neighbor electrode cliques as a waveform dispersion measure, hypothesizing that it is correlated with the presence of fibrosis. A simulated 2D tissue with a fibrosis patch was used for validation. We computed EIGDR maps from both original and time-aligned u-EGMs, denoted as [Formula: see text] and [Formula: see text], respectively, also mapping the gain in eigenvalue concentration obtained by the alignment, [Formula: see text]. The performance of each map in detecting fibrosis was evaluated in scenarios including noise and variable electrode-tissue distance. Best results were achieved by [Formula: see text], reaching 94% detection accuracy, versus the 86% of b-EGMs voltage maps. The proposed strategy was also tested in real u-EGMs from fibrotic and non-fibrotic areas over 3D electroanatomical maps, supporting the ability of the EIGDRs as fibrosis markers, encouraging further studies to confirm their translation to clinical settings. Upper panels: map of [Formula: see text] from 3×3 cliques for Ψ= 0∘ and bipolar voltage map Vb-m, performed assuming a variable electrode-to-tissue distance and noisy u-EGMs (noise level σv = 46.4 µV ). Lower panels: detected fibrotic areas (brown), using the thresholds that maximize detection accuracy of each map.

Detection of Endo-epicardial Asynchrony in the Atrial Wall Using One-Sided Unipolar and Bipolar Electrograms.

Endo-epicardial asynchrony (EEA) is a new mechanism possibly maintaining atrial fibrillation. We aimed to determine the sensitivity and best recording modus to detect EEA on electrograms recorded from one atrial side using electrogram fractionation. Simultaneously obtained right atrial endo- and epicardial electrograms from 22 patients demonstrating EEA were selected. Unipolar and (converted) bipolar electrograms were analyzed for presence and characteristics of fractionation corresponding to EEA. Sensitivity of presence of EEA corresponding fractionation was high in patients (86-96%) and moderately high (65-78%) for the asynchronous surface area for unipolar and bipolar electrograms equally. In bipolar electrograms, signal-to-noise ratio of EEA corresponding fractionation decreased and additional fractionation increased for electrograms recorded at the endocardium. Sensitivity of fractionation corresponding to EEA is high for both unipolar and bipolar electrograms. Unipolar electrograms are more suited for detection of EEA due to a larger signal-to-noise ratio and less disturbance of additional fractionation. Unipolar electrograms are more suited than bipolar electrograms to detect endo-epicardial asynchrony on one side of the atrial wall using electrogram fractionation.

Characterization of Atrial Propagation Patterns and Fibrotic Substrate With a Modified Omnipolar Electrogram Strategy in Multi-Electrode Arrays.

Introduction: The omnipolar electrogram method was recently proposed to try to generate orientation-independent electrograms. It estimates the electric field from the bipolar electrograms of a clique, under the assumption of locally plane and homogeneous propagation. The local electric field evolution over time describes a loop trajectory from which omnipolar signals in the propagation direction, substrate and propagation features, are derived. In this work, we propose substrate and conduction velocity mapping modalities based on a modified version of the omnipolar electrogram method, which aims to reduce orientation-dependent residual components in the standard approach. Methods: A simulated electrical propagation in 2D, with a tissue including a circular patch of diffuse fibrosis, was used for validation. Unipolar electrograms were calculated in a multi-electrode array, also deriving bipolar electrograms along the two main directions of the grid. Simulated bipolar electrograms were also contaminated with real noise, to assess the robustness of the mapping strategies against noise. The performance of the maps in identifying fibrosis and in reproducing unipolar reference voltage maps was evaluated. Bipolar voltage maps were also considered for performance comparison. Results: Results show that the modified omnipolar mapping strategies are more accurate and robust against noise than bipolar and standard omnipolar maps in fibrosis detection (accuracies higher than 85 vs. 80% and 70%, respectively). They present better correlation with unipolar reference voltage maps than bipolar and original omnipolar maps (Pearson's correlations higher than 0.75 vs. 0.60 and 0.70, respectively). Conclusion: The modified omnipolar method improves fibrosis detection, characterization of substrate and propagation, also reducing the residual sensitivity to directionality over the standard approach and improving robustness against noise. Nevertheless, studies with real electrograms will elucidate its impact in catheter ablation interventions.

Real-Time Ventricular Cancellation in Unipolar Atrial Fibrillation Electrograms.

Unipolar atrial fibrillation (AF) electrograms (EGMs) require far-field ventricle cancellation to recover hidden atrial activations. Current methods cannot achieve real-time cancellation because of the temporal delay they introduce. We propose a new real-time ventricular cancellation (RVC) method based on causal implementation optimized for real-time functioning. The method is similar to the classical average beat subtraction (ABS) method but it computes the ventricular contribution before the ventricular activation finishes. We compare the proposed method to the ABS on synthetic and real EGM databases for the time and frequency domains. All parameters and their optimal values are analyzed and validated. The RVC method provides a good reconstruction of the unipolar EGMs and a better local activation time detection than the classical approach with average F1scores 0.7307 and 0.7125, respectively. The spectral analysis shows that the average power after ventricular cancellation is reduced for frequency bands between 3 and 5.5 Hz, demonstrating that the proposed method removes the ventricular component present in the unipolar EGM signals compared to the ABS method. The phase mapping analysis on the RVC method presented lower error when comparing the annotated EGM cycles with the phase inversion intervals. In terms of performance ABS and RVC behave similarly, but the real-time capability of the latter justifies its preference over the offline implementations. In the clinical environment other online investigations, e.g., rotational activity assessment, dominant frequency or local activation time mapping, might benefit from the real-time potential of the proposed cancellation method.

Monitoring the dynamics of acute radiofrequency ablation lesion formation in thin-walled atria - a simultaneous optical and electrical mapping study.

Background Radiofrequency ablation (RFA) is a common approach to treat cardiac arrhythmias. During this intervention, numerous strategies are applied to indirectly estimate lesion formation. However, the assessment of the spatial extent of these acute injuries needs to be improved in order to create well-defined and durable ablation lesions. Methods We investigated the electrophysiological characteristics of rat atrial myocardium during an ex vivo RFA procedure with fluorescence-optical and electrical mapping. By analyzing optical data, the temporal growth of punctiform ablation lesions was reconstructed after stepwise RFA sequences. Unipolar electrograms (EGMs) were simultaneously recorded by a multielectrode array (MEA) before and after each RFA sequence. Based on the optical results, we searched for electrical features to delineate these lesions from healthy myocardium. Results Several unipolar EGM parameters were monotonically decreasing when distances between the electrode and lesion boundary were smaller than 2 mm. The negative component of the unipolar EGM [negative peak amplitude (Aneg)] vanished for distances lesser than 0.4 mm to the lesion boundary. Median peak-to-peak amplitude (Vpp) was decreased by 75% compared to baseline. Conclusion Aneg and Vpp are excellent parameters to discriminate the growing lesion area from healthy myocardium. The experimental setup opens new opportunities to investigate EGM characteristics of more complex ablation lesions.

Simultaneous Comparison of Electrocardiographic Imaging and Epicardial Contact Mapping in Structural Heart Disease.

BACKGROUND: The accuracy of ECG imaging (ECGI) in structural heart disease remains uncertain. This study aimed to provide a detailed comparison of ECGI and contact-mapping system (CARTO) electrograms. METHODS: Simultaneous epicardial mapping using CARTO (Biosense-Webster, CA) and ECGI (CardioInsight) in 8 patients was performed to compare electrogram morphology, activation time (AT), and repolarization time (RT). Agreement between AT and RT from CARTO and ECGI was assessed using Pearson correlation coefficient, ρ AT and ρ RT, root mean square error, E AT and E RT, and Bland-Altman plots. RESULTS: After geometric coregistration, 711 (439-905; median, first-third quartiles) ECGI and CARTO points were paired per patient. AT maps showed ρ AT=0.66 (0.53-0.73) and E AT=24 (21-32) ms, RT maps showed ρ RT=0.55 (0.41-0.71) and E RT=51 (38-70) ms. The median correlation coefficient measuring the morphological similarity between the unipolar electrograms was equal to 0.71 (0.65-0.74) for the entire signal, 0.67 (0.59-0.76) for QRS complexes, and 0.57 (0.35-0.76) for T waves. Local activation map correlation, ρ AT, was lower when default filters were used (0.60 (0.30-0.71), P=0.053). Small misalignment of the ECGI and CARTO geometries (below ±4 mm and ±4°) could introduce variations in the median ρ AT up to ±25%. Minimum distance between epicardial pacing sites and the region of earliest activation in ECGI was 13.2 (0.0-28.3) mm from 25 pacing sites with stimulation to QRS interval <40 ms. CONCLUSIONS: This simultaneous assessment demonstrates that ECGI maps activation and repolarization parameters with moderate accuracy. ECGI and contact electrogram correlation is sensitive to electrode apposition and geometric alignment. Further technological developments may improve spatial resolution.

Non-contact mapping in cardiac electrophysiology.

Catheter ablation of atrial and ventricular arrhythmias is now considered a standard technology for selected patients. In some patients, however, cure of the arrhythmia is hampered by the complexity of the arrhythmia or the way the arrhythmia presents in the electrophysiological laboratory: some focal atrial and ventricular arrhythmias are difficult to induce using electrical stimulation or medical provocation. Precise mapping of these arrhythmias is challenging or even impossible by contact mapping, while other arrhythmias are poorly tolerated and need early termination.In these scenarios, use of non-contact mapping technology can be an alternative to conventional mapping, since isopotential maps may require no more than one ectopic beat identical with the clinical focal arrhythmia to reconstruct its endocardial origin. This review article presents the technology of non-contact cardiac mapping, as well as various arrhythmias that have been successfully treated using this technology in the past. The possibilities and limitations of using non-contact cardiac mapping under various conditions are also presented.

Novel methods for characterization of paroxysmal atrial fibrillation in human left atria.

INTRODUCTION: More effective methods for characterizing 3D electrical activity in human left atrium (LA) are needed to identify substrates/triggers and microreentrant circuit for paroxysmal atrial fibrillation (PAF). We describe a novel wavelet-based approach and wave-front centroid tracking that have been used to reconstruct regional activation frequency and electrical activation pathways from non-contact multi-electrode array. METHODS: Data from 13 patients acquired prior to ablation for PAF with a 64 electrode noncontact catheter positioned in the LA were analysed. Unipolar electrograms were reconstructed at 2048 locations across each LA endocardial surface. Weighted fine- and coarse-scale electrograms were constructed by wavelet decomposition and combined with peak detection to identify atrial fibrillation (AF) activation frequency and fractionated activity at each site. LA regions with upper quartile AF frequencies were identified for each patient. On the other hand, a wave-front centroid tracking approach was introduced for this first time to detect macro-reentrant circuit during PAF. RESULTS: The results employing wavelet-based analysis on atrial unipolar electrograms are validated by the signals recorded simultaneously via the contacted ablation catheter and visually tracking the 3D spread of activation through the interest region. Multiple connected regions of high frequency electrical activity were seen; most often in left superior pulmonary vein (10/12), septum (9/12) and atrial roof (9/12), as well as the ridge (8/12). The wave-front centroid tracking approach detects a major macro circuit involving LPVs, PLA, atrial floor, MV, septum, atrial roof and ridge. The regions with high frequency by wave-front tracking are consistent with the results using wavelet approach and our clinical observations. CONCLUSIONS: The wavelet-based technique and wave-front centroid tracking approach provide a robust means of extracting spatio-temporal characteristics of PAF. The approach could facilitate accurate identification of pro-arrhythmic substrate and triggers, and therefore, to improve success rate of catheter ablation for AF.