Mapping Technologies for Catheter Ablation of Atrial Fibrillation Beyond Pulmonary Vein Isolation

Radiation therapy for ventricular arrhythmias

Ventricular arrhythmias (VA) can be life-threatening arrhythmias that result in significant morbidity and mortality. Catheter ablation (CA) is an invasive treatment modality that can be effective in the treatment of VA where medications fail. Recurrence occurs commonly following CA due to an inability to deliver lesions of adequate depth to cauterise the electrical circuits that drive VA or reach areas of scar responsible for VA. Stereotactic body radiotherapy is a non-invasive treatment modality that allows volumetric delivery of energy to treat circuits that cannot be reached by CA. It overcomes the weaknesses of CA and has been successfully utilised in small clinical trials to treat refractory VA. This article summarises the current evidence for this novel treatment modality and the steps that will be required to bring it to the forefront of VA treatment.

Electrographic flow mapping of persistent atrial fibrillation: intra- and inter-procedure reproducibility in the absence of 'ground truth'

AIMS

Validating mapping systems that identify atrial fibrillation (AF) sources (focal/rotational activity) is confounded by the absence of ground truth. A key concern of prior mapping technologies is spatiotemporal instability, manifesting as poor map reproducibility. Electrographic flow (EGF) employs a novel algorithm that visualizes atrial electrical wavefront propagation to identify putative AF sources. We analysed both intra- (3 min) and inter- (>3 months) procedure EGF map reproducibility.

METHODS AND RESULTS

In 23 persistent AF patients, after pulmonary vein isolation (PVI), EGF maps were generated from 3 serial 1 min recordings using a 64-electrode basket mapping catheter (triplets) at right and left atrial locations. Source prevalence from map triplets was compared between recordings. Per protocol, 12 patients returned for 3-month remapping (1 non-inducible): index procedure post-PVI EGF maps were compared with initial EGF remapping at 3-month redo. Intra-procedure reproducibility: analysing 224 map triplets (111 right atrium, 113 left atrium) revealed a high degree of map consistency with minimal min-to-min shifts: 97 triplets (43%), exact match of leading sources on all 3 maps; 95 triplets (42%), leading source within 1 electrode space on 2 of 3 maps; and 32 triplets (14%), chaotic leading source pattern. Average deviation in source prevalence over 60 s was low (6.4%). Inter-procedure reproducibility: spatiotemporal stability of EGF mapping >3 months was seen in 16 of 18 (89%) sources mapped in 12 patients with (re)inducible AF.

CONCLUSION

Electrographic flow mapping generates reproducible intra- and inter-procedural maps, providing rationale for randomized clinical trials targeting these putative AF sources.

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.

Electrographic flow mapping for atrial fibrillation: theoretical basis and preliminary observations

Ablation strategies remain poorly defined for persistent atrial fibrillation (AF) patients with recurrence despite intact pulmonary vein isolation (PVI). As the ability to perform durable PVI improves, the need for advanced mapping to identify extra-PV sources of AF becomes increasingly evident. Multiple mapping technologies attempt to localize these self-sustained triggers and/or drivers responsible for initiating and/or maintaining AF; however, current approaches suffer from technical limitations. Electrographic flow (EGF) mapping is a novel mapping method based on well-established principles of optical flow and fluid dynamics. It enables the full spatiotemporal reconstruction of organized wavefront propagation within the otherwise chaotic and disorganized electrical conduction of AF. Given the novelty of EGF mapping and relative unfamiliarity of most clinical electrophysiologists with the mathematical principles powering the EGF algorithm, this paper provides an in-depth explanation of the technical/mathematical foundations of EGF mapping and demonstrates clinical applications of EGF mapping data and analyses. Starting with a 64-electrode basket catheter, unipolar EGMs are recorded and processed using an algorithm to visualize the electrographic flow and highlight the location of high prevalence AF "source" activity. The AF sources are agnostic to the specific mechanisms of source signal generation.

Electrogram Morphology Recurrence for Mapping Persistent Atrial Fibrillation: Initial vs Redo Catheter Ablation

BACKGROUND

Electrogram (EGM) morphology recurrence (EMR) mapping of persistent atrial fibrillation (AF) quantifies consistency of activation and is expected to be high and rapid near AF drivers.

OBJECTIVES

The purpose of this study was to compare EMR in left atria (LA) and right atria (RA) in patients undergoing first vs redo ablation for persistent AF.

METHODS

Multisite LA/RA mapping (LA: 281 ± 176 sites/patient; RA: 239 ± 166 sites/patient) before persistent AF ablation was performed in 42 patients (30 males, age 63 ± 9 years) undergoing first (Group 1, n = 32) or redo ablation (Group 2, n = 10). After cross-correlation of each automatically detected EGM with every other EGM per recording, the most recurrent electrogram morphology was identified and its frequency (Rec%) and recurrence cycle length (CLR) were computed.

RESULTS

In Groups 1 and 2, minimum CLR was 172.8 ± 26.0 milliseconds (LA: 178.2 ± 37.6 milliseconds, RA: 204.4 ± 34.0 milliseconds, P = 0.0005) and 186.5 ± 28.3 milliseconds (LA: 196.1 ± 38.1 milliseconds vs RA: 199.0 ± 30.2 milliseconds, P = 0.75), with Rec% 94.7% ± 10% and 93.8% ± 9.2%. Group 2 minimum CLR was not different from Group 1 (P = 0.20). Shortest CLR was in the LA in 84% of Group 1 and 50% of Group 2 patients (P = 0.04). Only 1 of 10 patients in Group 2 had the shortest CLR in the pulmonary veins (PVs) compared with 19 of 32 in Group 1 (P = 0.01). Most sites (77.6%) had Rec% <50%.

CONCLUSIONS

EMR identified the shortest CLR sites in the PVs in 59% of patients undergoing initial persistent AF ablation, consistent with reported success rates of ∼50% for PV isolation. The majority of sites have low recurrence and may reflect bystander sites not critical for maintaining AF. EMR provides a robust new method for quantifying consistency and rapidity of activation direction at multiple atrial sites.

A novel approach for quantitative electrogram analysis for driver identification: Implications for ablation in persistent atrial fibrillation

Objective

This study sought to study the feasibility, efficacy, and safety of using multiscale entropy (MSE) analysis to guide catheter ablation for persistent atrial fibrillation (PsAF) and predict ablation outcomes.

Methods

We prospectively enrolled 108 patients undergoing initial ablation for PsAF. MSE was calculated based on bipolar intracardiac electrograms (iEGMs) to measure the dynamical complexity of biological signals. The iEGMs data were exported after pulmonary vein isolation (PVI), then calculated in a customed platform, and finally re-annotated into the CARTO system. After PVI, regions of the highest mean MSE (mMSE) values were ablated in descending order until AF termination, or three areas had been ablated.

Results

Baseline characteristics were evenly distributed between the AF termination (n = 38, 35.19%) and the non-termination group. The RA-to-LA mean MSE (mMSE) gradient demonstrated a positive gradient in the non-termination group and a negative gradient in the termination group (0.105 ± 0.180 vs. −0.235 ± 0.256, P &lt; 0.001). During a 12-month follow-up, 29 patients (26.9%) had arrhythmia recurrence after single ablation, and 18 of them had AF (62.1%). The termination group had lower rates of arrhythmia recurrence (15.79 vs. 32.86%, Log-Rank P = 0.053) and AF recurrence (10.53 vs. 20%, Log-Rank P = 0.173) after single ablation and a lower rate of arrhythmia recurrence (7.89 vs. 27.14%, Log-Rank P = 0.018) after repeated ablation. Correspondingly, subjects with negative RA-to-LA mMSE gradient had lower incidences of arrhythmia (16.67 vs. 35%, Log-Rank P = 0.028) and AF (16.67 vs. 35%, Log-Rank P = 0.032) recurrence after single ablation and arrhythmia recurrence after repeated ablation (12.5 vs. 26.67%, Log-Rank P = 0.062). Marginal peri-procedural safety outcomes were observed.

Conclusion

MSE analysis-guided driver ablation in addition to PVI for PsAF could be feasible, efficient, and safe. An RA &lt; LA mMSE gradient before ablation could predict freedom from arrhythmia. The RA-LA MSE gradient could be useful for guiding ablation strategy selection.

Convolutional Neural Networks for Mechanistic Driver Detection in Atrial Fibrillation

The maintaining and initiating mechanisms of atrial fibrillation (AF) remain controversial. Deep learning is emerging as a powerful tool to better understand AF and improve its treatment, which remains suboptimal. This paper aims to provide a solution to automatically identify rotational activity drivers in endocardial electrograms (EGMs) with convolutional recurrent neural networks (CRNNs). The CRNN model was compared with two other state-of-the-art methods (SimpleCNN and attention-based time-incremental convolutional neural network (ATI-CNN)) for different input signals (unipolar EGMs, bipolar EGMs, and unipolar local activation times), sampling frequencies, and signal lengths. The proposed CRNN obtained a detection score based on the Matthews correlation coefficient of 0.680, an ATI-CNN score of 0.401, and a SimpleCNN score of 0.118, with bipolar EGMs as input signals exhibiting better overall performance. In terms of signal length and sampling frequency, no significant differences were found. The proposed architecture opens the way for new ablation strategies and driver detection methods to better understand the AF problem and its treatment.