Functional nature of electrogram fractionation demonstrated by left atrial high-density mapping

Peak frequency analysis and functional substrate mapping to predict critical isthmus of atypical atrial tachycardia: Findings from a novel automated annotation algorithm to detect near-field signals

BACKGROUND

Atypical atrial tachycardia (AT) is a commonly encountered rhythm disorder, especially in patients with underlying atrial scar. Peak frequency (PF) annotation of bipolar electrograms is a novel method that mainly aims to discriminate near-field and far-field signals.

OBJECTIVE

This study aimed to evaluate the PF annotation of low-voltage zones and deceleration zones during sinus/paced rhythm and their role in predicting the critical isthmus (CI) and termination sites of atypical ATs.

METHODS

We retrospectively included a total of 25 patients (mean age, 60 ± 12 years; 13 [52%] male) who underwent high-density mapping during both sinus/paced rhythm and AT. Omnipolar voltage and isochronal late activation maps of the left atrium were created on the basis of PF annotation. The CI of the AT was defined on the basis of both activation mapping and successful termination site/change in AT during ablation.

RESULTS

A total of 30 ATs were mapped in the left atrium (22 [73.3%], localized reentry; 8 [26.7%], macroreentry). Median PF of the termination site was significantly higher compared with low-voltage zones alone (345 [209-530] Hz vs 235 (47-417] Hz; P < .001). PF had a significant predictive value for the termination site (area under the curve, 0.83; 95% confidence interval, 0.719-0.950; P < .001). When the cutoff value for PF was taken as 280 Hz, the sensitivity of the test was determined to be 80.0% and the specificity was determined to be 78.3%.

CONCLUSION

A PF annotation algorithm with a cutoff of 280 Hz accurately detects the CI of atypical ATs and accurately predicts deceleration zones during isochronal late activation mapping.

Atrial Cardiomyopathy: From Diagnosis to Treatment

With a better understanding of the susceptibility to atrial fibrillation (AF) and the thrombogenicity of the left atrium, the concept of atrial cardiomyopathy (ACM) has emerged. The conventional viewpoint holds that AF-associated hemodynamic disturbances and thrombus formation in the left atrial appendage are the primary causes of cardiogenic embolism events. However, substantial evidence suggests that the relationship between cardiogenic embolism and AF is not so absolute, and that ACM may be an important, underestimated contributor to cardiogenic embolism events. Chronic inflammation, oxidative stress response, lipid accumulation, and fibrosis leading to ACM form the foundation for AF. Furthermore, persistent AF can exacerbate structural and electrical remodeling, as well as mechanical dysfunction of the atria, creating a vicious cycle. To date, the relationship between ACM, AF, and cardiogenic embolism remains unclear. Additionally, many clinicians still lack a comprehensive understanding of the concept of ACM. In this review, we first appraise the definition of ACM and subsequently summarize the noninvasive and feasible diagnostic techniques and criteria for clinical practice. These include imaging modalities such as echocardiography and cardiac magnetic resonance imaging, as well as electrocardiograms, serum biomarkers, and existing practical diagnostic criteria. Finally, we discuss management strategies for ACM, encompassing "upstream therapy" targeting risk factors, identifying and providing appropriate anticoagulation for patients at high risk of stroke/systemic embolism events, and controlling heart rhythm along with potential atrial substrate improvements.

Identification of Critical Slowing of Conduction Using Unipolar Atrial Voltage and Fractionation Mapping

BACKGROUND

Ablation strategies targeting fractionated or low-voltage potentials have been widely used in patients with persistent types of atrial fibrillation (AF). However, recent studies have questioned their role in effectively representing sites of conduction slowing, and thus arrhythmogenic substrates.

OBJECTIVES

The authors studied the relationship between local conduction velocity (CV) and the occurrence of fractionated and/or low-voltage potentials in order to identify areas with critically slowing of conduction.

METHODS

Intraoperative epicardial mapping was performed during sinus rhythm. Unipolar potentials with an amplitude <1.0 mV were initially classified as low-voltage and potentials with ≥3 deflections as fractionation. A range of thresholds were also explored. Local CV was computed using discrete velocity vectors.

RESULTS

A total of 319 patients were included. Fractionated, low-voltage potentials were rare, accounting for only 0.36% (Q1-Q3: 0.15%-0.78%) of all atrial sites. Local CV at sites with fractionated, low-voltage potentials (46.0 cm/s [Q1-Q3: 22.6-72.7 cm/s]) was lowest compared with sites with either low-voltage, nonfractionated potentials (64.5 cm/s [Q1-Q3: 34.8-99.4 cm/s]) or fractionated, high-voltage potentials (65.9 cm/s [Q1-Q3: 41.7-92.8 cm/s]; P < 0.001). Slow conduction areas (CV <50 cm/s) could be most accurately identified by using a low voltage threshold (<1 mV) and a minimum of 3 deflections (positive predictive value: 54.2%-70.7%), although the overall sensitivity remained low (0.1%-1.9%).

CONCLUSIONS

Sites with fractionated, low-voltage potentials have substantially slower local CV compared with sites with either low-voltage, nonfractionated potentials or fractionated, high-voltage potentials. However, the strong inverse relationship between the positive predictive value and sensitivity of a combined voltage and fractionation threshold for slowed conduction is likely to complicate the use of these signal-based ablation approaches in AF patients.

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.

Influence of Heart Rate and Change in Wavefront Direction through Pacing on Conduction Velocity and Voltage Amplitude in a Porcine Model: A High-Density Mapping Study

BACKGROUND

Understanding the dynamics of conduction velocity (CV) and voltage amplitude (VA) is crucial in cardiac electrophysiology, particularly for substrate-based catheter ablations targeting slow conduction zones and low voltage areas. This study utilizes ultra-high-density mapping to investigate the impact of heart rate and pacing location on changes in the wavefront direction, CV, and VA of healthy pig hearts.

METHODS

We conducted in vivo electrophysiological studies on four healthy juvenile pigs, involving various pacing locations and heart rates. High-resolution electroanatomic mapping was performed during intrinsic normal sinus rhythm (NSR) and electrical pacing. The study encompassed detailed analyses at three levels: entire heart cavities, subregions, and localized 5-mm-diameter circular areas. Linear mixed-effects models were used to analyze the influence of heart rate and pacing location on CV and VA in different regions.

RESULTS

An increase in heart rate correlated with an increase in conduction velocity and a decrease in voltage amplitude. Pacing influenced conduction velocity and voltage amplitude. Pacing also influenced conduction velocity and voltage amplitude, with varying effects observed based on the pacing location within different heart cavities. Pacing from the right atrium (RA) decreased CV in all heart cavities. The overall CV and VA changes in the whole heart cavities were not uniformly reflected in all subregions and subregional CV and VA changes were not always reflected in the overall analysis. Overall, there was a notable variability in absolute CV and VA changes attributed to pacing.

CONCLUSIONS

Heart rate and pacing location influence CV and VA within healthy juvenile pig hearts. Subregion analysis suggests that specific regions of the heart cavities are more susceptible to pacing. High-resolution mapping aids in detecting regional changes, emphasizing the substantial physiological variations in CV and VA.

RETRO-mapping: A novel algorithm automating wavefront categorization using activation mapping during persistent atrial fibrillation demonstrates a reduction in wavefront collisions following pulmonary vein isolation

RETRO-mapping was developed to automate activation mapping of atrial fibrillation (AF). We used the algorithm to study the effect of pulmonary vein isolation (PVI) on the frequency of focal, planar, and colliding wavefronts in persistent AF. An AFocusII catheter was placed on the left atrial endocardium to record 3 s of AF at six sites pre and post-PVI in patients undergoing wide circumferential PVI for persistent AF. RETRO-mapping analyzed each segment in 2 ms time windows for evidence of focal, planar, and colliding waveforms and the automated categorizations manually validated. Ten patients were recruited. A total of 360 s of data in 120 segments of 3 s from 60 left atrial locations were analyzed. RETRO-map was highly effective at identifying focal waves and collisions during AF. PVI significantly reduced collision frequency but not focal and planar activation frequency. However, there was a significant reduction in the dispersion of activation directions. Larger studies may help determine factors associated with successful clinical outcome.

Identification of Atrial Transmural Conduction Inhomogeneity Using Unipolar Electrogram Morphology

(1) Background: Structural remodeling plays an important role in the pathophysiology of atrial fibrillation (AF). It is likely that structural remodeling occurs transmurally, giving rise to electrical endo-epicardial asynchrony (EEA). Recent studies have suggested that areas of EEA may be suitable targets for ablation therapy of AF. We hypothesized that the degree of EEA is more pronounced in areas of transmural conduction block (T-CB) than single-sided CB (SS-CB). This study examined the degree to which SS-CB and T-CB enhance EEA and which specific unipolar potential morphology parameters are predictive for SS-CB or T-CB. (2) Methods: Simultaneous endo-epicardial mapping in the human right atrium was performed in 86 patients. Potential morphology parameters included unipolar potential voltages, low-voltage areas, potential complexity (long double and fractionated potentials: LDPs and FPs), and the duration of fractionation. (3) Results: EEA was mostly affected by the presence of T-CB areas. Lower potential voltages and more LDPs and FPs were observed in T-CB areas compared to SS-CB areas. (4) Conclusion: Areas of T-CB could be most accurately predicted by combining epicardial unipolar potential morphology parameters, including voltages, fractionation, and fractionation duration (AUC = 0.91). If transmural areas of CB indeed play a pivotal role in the pathophysiology of AF, they could theoretically be used as target sites for ablation.

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.

Posterior Wall Isolation Improves Outcomes for Persistent AF With Rapid Posterior Wall Activity: CAPLA Substudy

BACKGROUND

Pulmonary vein isolation (PVI) is less effective in persistent atrial fibrillation (PerAF) than in paroxysmal atrial fibrillation (AF). However, the CAPLA (Effect of Catheter Ablation Using Pulmonary Vein Isolation With vs Without Posterior Left Atrial Wall Isolation on Atrial Arrhythmia Recurrence in Patients With Persistent Atrial Fibrillation: The CAPLA randomized clinical trial) of PVI vs posterior wall isolation (PWI) did not support empiric PWI in PerAF. We examined pulmonary vein (PV) and posterior wall (PW) electrical characteristics to determine if select patients may benefit from additional PWI.

OBJECTIVES

This study sought to determine the impact of PV and PW electrical characteristics on AF ablation outcomes in the CAPLA randomized study.

METHODS

Participants in spontaneous AF at the time of ablation were included from the CAPLA study. The mean, shortest, and longest PV, PW, and left atrial (LA) appendage cycle length measurements were annotated preablation using a multipolar catheter for 100 consecutive cycles. Next, cardioversion was performed with a high-density LA voltage map completed. Cox proportional hazards regression was utilized to determine clinical and electroanatomic predictors of AF recurrence overall and according to ablation strategy. Follow-up included twice daily single-lead electrocardiograms or continuous monitoring for 12 months.

RESULTS

A total of 151 patients (27% female, age 65 ± 9 years, 18% long-standing PerAF, LA volume index 52 ± 16 mL/m2, median AF duration 5 months [IQR: 2-10 months]) were in AF on the day of procedure and were randomized to PVI alone (50%) or PVI+PWI (50%) according to the CAPLA randomized clinical trial protocol. Baseline clinical, echocardiographic, and electroanatomic parameters were comparable between groups (all P > 0.05) including PV and PW characteristics. After 12 months, freedom from AF off antiarrhythmic drug therapy was 51.7% in PVI and 49.7% in PVI+PWI (log-rank P = 0.564). Rapid PW activity was defined as less than the median of the shortest PW cycle length (140 ms) and rapid PV activity was defined as less than the median of the shortest PV cycle length (126 ms). In those with rapid PW activity, the addition of PWI was associated with greater arrhythmia-free survival (56.4%) vs PVI alone (38.6%) (HR: 0.78; 95% CI: 0.67-0.94; log-rank P = 0.030). Moreover, in those undergoing PVI only, the risk of AF recurrence was higher in those with rapid PW activity (55.3% vs 46.5% in slower PW activity; HR: 1.50, 95%CI 1.11-2.26; log-rank P = 0.036). Rapid PV activity and PV cycle length (individual PVs or average of all 4 PVs) were not associated with outcome (all P > 0.05) regardless of ablation strategy. There was no correlation between PW cycle length and posterior low voltage (r = -0.06, P = 0.496). The addition of PWI did not improve arrhythmia-free survival in subgroups with LA enlargement (LA volume index >34 mL/m2) (HR: 0.69; 95% CI: 0.39-1.25; P = 0.301), posterior low-voltage zone (HR: 1.06; 95% CI: 0.68-1.66; P = 0.807), or long-standing PerAF (HR: 1.10; 95% CI: 0.71-1.72; P = 0.669).

CONCLUSIONS

Rapid PW activity is associated with an increased risk of AF recurrence post-catheter ablation. The addition of PWI in this subgroup was associated with a significant improvement in freedom from AF compared with PVI alone. The presence of rapid PW activity may identify patients with PerAF likely to benefit from PWI.

Comparison of clinical outcomes of Ibutilide-guided cardioversion and direct current synchronized cardioversion after radiofrequency ablation of persistent atrial fibrillation

Backgroup

Ibutilide has already been used for cardioversion of persistent atrial fibrillation (PsAF) after radiofrequency catheter ablation (RFCA). The purpose of this study was to determine the effect of Ibutilide-guided cardioversion on clinical outcomes after individualized ablation of PsAF.

Methods

From October 2020 to September 2021, consecutive patients with PsAF accepted for RFCA were prospectively enrolled. After individualized ablation including pulmonary vein isolation plus left atrial roof line ablation and personalized linear ablation based on left atrial low-voltage zones, patients were divided into the spontaneous conversion (SCV) group, direct current synchronized cardioversion (DCC) group and Ibutilide group according to different cardioversion types during ablation. The rates of freedom from atrial tachyarrhythmia (ATT) among the three groups were evaluated after follow-up.

Results

In this study, 110 patients were enrolled, including 12 patients with SCV, 50 patients receiving DCC and 48 patients receiving Ibutilide cardioversion after individualized ablation. Among the three groups, the SCV group had shorter AF duration {12 months [interquartile range (IQR) 12-16], P = 0.042} and smaller left atrial diameter (LAD) [35 mm (IQR: 33-42), P = 0.023]. A 12-month freedom from ATT rate was 83.3% in SCV group, 69.4% in DCC group, and 79.2% in Ibutilide group, respectively (Log-rank, P = 0.745). During the follow-up [17 months (IQR: 15-19)], the rate of freedom from ATT of SCV group (83.3%), and Ibutilide group (72.9%) were both higher than that of DCC group (53.1%, P = 0.042). Moreover, Kaplan-Meier analysis showed a significantly higher sinus rhythm (SR) maintenance in Ibutilide group than in DCC group (Log-rank, P = 0.041). After adjusting for risk factors of AF recurrence, the hazard ratio for AF recurrence of the DCC group with reference to the Ibutilide group was 4.10 [95% confidence interval (CI) (1.87-8.98), P < 0.001]. Furthermore, subgroup analysis showed that freedom from ATT rate in effective Ibutilide subgroup was significantly higher than noneffective Ibutilide subgroup (Log-rank, P < 0.001).

Conclusion

For the treatment of the patients with PsAF, Ibutilide-guided cardioversion after individualized RFCA may be benefit for maintenance of SR compared to conventional DCC, especially for the patients who are effective for administration of Ibutilide.

Functional mapping to reveal slow conduction and substrate progression in atrial fibrillation

AIMS

The aim of our study was to analyse the response to short-coupled atrial extrastimuli to identify areas of hidden slow conduction (HSC) and their relationship with the atrial fibrillation (AF) phenotype.

METHODS AND RESULTS

Twenty consecutive patients with paroxysmal AF and persistent AF (10:10) underwent the first pulmonary vein isolation procedure. Triple short-coupled extrastimuli were delivered in sinus rhythm (SR), and the evoked response was analysed: sites exhibiting double or highly fragmented electrograms (EGM) were defined as positive for HSC (HSC+). The delta of the duration of the bipolar EGM was analysed, and bipolar EGM duration maps were built. High-density maps were acquired using a multipolar catheter during AF, SR, and paced rhythm. Spatial co-localization of HSC+ and complex fractionated atrial EGMs (CFAE) during AF was evaluated. Persistent AF showed a higher number and percentage of HSC+ than paroxysmal AF (13.9% vs. 3.3%, P < 0.001). The delta of EGM duration was 53 ± 22 ms for HSC+ compared with 13 ± 11 (10) ms in sites with negative HSC (HSC-) (P < 0.001). The number and density of HSC+ were lower than CFAE during AF (19 vs. 56 per map, P < 0.001). The reproducibility and distribution of HSC+ in repeated maps were superior to CFAE (P = 0.19 vs. P < 0.001). Sites with negative and positive responses showed a similar bipolar voltage in the preceding sinus beat (1.65 ± 1.34 and 1.48 ± 1.47 mV, P = 0.12).

CONCLUSION

Functional mapping identifies more discrete and reproducible abnormal substrates than mapping during AF. The HSC+ sites in response to triple extrastimuli are more frequent in persistent AF than in paroxysmal AF.

Impact of Posterior Left Atrial Voltage on Ablation Outcomes in Persistent Atrial Fibrillation: CAPLA Substudy

BACKGROUND

Pulmonary vein isolation (PVI) is less effective in patients with persistent atrial fibrillation (PsAF). Adjunctive ablation targeting low voltage areas (LVAs) may improve arrhythmia outcomes.

OBJECTIVES

This study aims to compare the outcomes of adding posterior wall isolation (PWI) to PVI, vs PVI alone in PsAF patients with posterior wall LVAs.

METHODS

The CAPLA (Effect of Catheter Ablation Using Pulmonary Vein Isolation With vs Without Posterior Left Atrial Wall Isolation on Atrial Arrhythmia Recurrence in Patients With Persistent Atrial Fibrillation) study was a multicenter, randomized trial involving PsAF patients randomized 1:1 to either PVI alone or PVI with PWI. Voltage mapping performed during pacing pre-ablation was reviewed offline, with LVA defined as bipolar voltage of <0.5 mV. The primary endpoint was freedom from any documented atrial arrhythmia of >30 seconds off antiarrhythmic medication at 12 months after a single ablation procedure in patients with posterior LVA.

RESULTS

A total of 210 patients (average 64.6 ± 9.2 years,73.3% males, median atrial fibrillation duration 4.5 months [IQR: 2 to 8 months]) underwent multipolar left atrial mapping during coronary sinus pacing with posterior LVA present in 69 (32.9%). Patients with posterior LVA were more likely to have LVA in other atrial regions (91.7% vs 57.1%; P < 0.01), larger left atrial diameter (4.8 cm vs 4.4 cm; P < 0.01), and significantly increased risk of atrial arrhythmia recurrence at 12 months (LVA: 56.5% vs no LVA: 41.4%; HR: 1.51; 95% CI: 1.01-2.27; P = 0.04) compared to no posterior LVA. However, the addition of PWI to PVI did not significantly improve freedom from atrial arrhythmia recurrence over PVI alone (PVI with PWI: 44.8% vs PVI: 41.9%; HR: 0.95; 95% CI: 0.51-1.79; P = 0.95).

CONCLUSIONS

In patients with PsAF undergoing catheter ablation, posterior LVA was associated with a significant increase in atrial arrhythmia recurrence. However, the addition of PWI in those with posterior LVA did not reduce atrial arrhythmia recurrence over PVI alone.

High-density mapping of the average complex interval helps localizing atrial fibrillation drivers and predicts catheter ablation outcomes

Background

Persistent Atrial Fibrillation (PersAF) electrogram-based ablation is complex, and appropriate identification of atrial substrate is critical. Little is known regarding the value of the Average Complex Interval (ACI) feature for PersAF ablation.

Objective

Using the evolution of AF complexity by sequentially computing AF dominant frequency (DF) along the ablation procedure, we sought to evaluate the value of ACI for discriminating active drivers (AD) from bystander zones (BZ), for predicting AF termination during ablation, and for predicting AF recurrence during follow-up.

Methods

We included PersAF patients undergoing radiofrequency catheter ablation by pulmonary vein isolation and ablation of atrial substrate identified by Spatiotemporal Dispersion or Complex Fractionated Atrial Electrograms (>70% of recording). Operators were blinded to ACI measurement which was sought for each documented atrial substrate area. AF DF was measured by Independent Component Analysis on 1-minute 12-lead ECGs at baseline and after ablation of each atrial zone. AD were differentiated from BZ either by a significant decrease in DF (>10%), or by AF termination. Arrhythmia recurrence was monitored during follow-up.

Results

We analyzed 159 atrial areas (129 treated by radiofrequency during AF) in 29 patients. ACI was shorter in AD than BZ (76.4 ± 13.6 vs. 86.6 ± 20.3 ms; p = 0.0055), and mean ACI of all substrate zones was shorter in patients for whom radiofrequency failed to terminate AF [71.3 (67.5-77.8) vs. 82.4 (74.4-98.5) ms; p = 0.0126]. ACI predicted AD [AUC 0.728 (0.629-0.826)]. An ACI < 70 ms was specific for predicting AD (Sp 0.831, Se 0.526), whereas areas with an ACI > 100 ms had almost no chances of being active in AF maintenance. AF recurrence was associated with more ACI zones with identical shortest value [3.5 (3-4) vs. 1 (0-1) zones; p = 0.021]. In multivariate analysis, ACI < 70 ms predicted AD [OR = 4.02 (1.49-10.84), p = 0.006] and mean ACI > 75 ms predicted AF termination [OR = 9.94 (1.14-86.7), p = 0.038].

Conclusion

ACI helps in identifying AF drivers, and is correlated with AF termination and AF recurrence during follow-up. It can help in establishing an ablation plan, by prioritizing ablation from the shortest to the longest ACI zone.

In Atrial Fibrillation, Omnipolar Voltage Maps More Accurately Delineate Scar Than Bipolar Voltage Maps

BACKGROUND

Optimal method for voltage assessment in AF remains unclear.

OBJECTIVES

This study evaluated different methods for assessing atrial voltage and their accuracy in identifying pulmonary vein reconnection sites (PVRSs) in atrial fibrillation (AF).

METHODS

Patients with persistent AF undergoing ablation were included. De novo procedures: voltage assessment in AF with omnipolar voltage (OV) and bipolar voltage (BV) methodology and BV assessment in sinus rhythm (SR). Activation vector and fractionation maps were reviewed at voltage discrepancy sites on OV and BV maps in AF. AF voltage maps were compared with SR BV maps. Repeat ablation procedures: OV and BV maps in AF were compared to detect gaps in wide area circumferential ablation (WACA) lines that correlated with PVRS.

RESULTS

Forty patients were included: 20 de novo and 20 repeat procedures. De novo procedure: OV vs BV maps in AF; average voltage 0.55 ± 0.18 mV vs 0.38 ± 0.12 mV; P = 0.002, voltage difference of 0.20 ± 0.07 mV; P = 0.003 at coregistered points and proportion of left atrium (LA) area occupied by low-voltage zones (LVZs) was smaller on OV maps (42.4% ± 12.8% OV vs 66.7% ± 12.7% BV; P < 0.001). LVZs identified on BV maps and not on OV maps correlated frequently to wavefront collision and fractionation sites (94.7%). OV AF maps agreed better with BV SR maps (voltage difference at coregistered points 0.09 ± 0.03 mV; P = 0.24) unlike BV AF maps (0.17 ± 0.07 mV, P = 0.002). Repeat ablation procedure: OV was superior in identifying WACA line gaps that correlated with PVRS than BV maps (area under the curve = 0.89, P < 0.001).

CONCLUSIONS

OV AF maps improve voltage assessment by overcoming the impact of wavefront collision and fractionation. OV AF maps correlate better with BV maps in SR and more accurately delineate gaps on WACA lines at PVRS.

High Dominant Frequencies and Fractionated Potentials Do Not Indicate Focal or Rotational Activation During AF

BACKGROUND

Dominant frequencies (DFs) or complex fractionated atrial electrograms (CFAEs), indicative of focal sources or rotational activation, are used to identify target sites for atrial fibrillation (AF) ablation in clinical studies, although the relationship among DF, CFAE, and activation patterns remains unclear.

OBJECTIVES

This study sought to investigate the relationship between patterns of activation underlying DF and CFAE sites during AF.

METHODS

Epicardial high-resolution mapping of the right and left atrium including Bachmann's bundle was performed in 71 participants. We identified the highest dominant frequency (DF_max) and highest degree of CFAE (CFAE_max) with the use of existing clinical criteria and classified patterns of activation as focal or rotational activation and smooth propagation, conduction block (CB), collision and remnant activity, and fibrillation potentials as single, double, or fractionated potentials containing, respectively, 1, 2, or 3 or more negative deflections. Relationships among activation patterns, DF_max, and potential types were investigated.

RESULTS

DF_max were primarily located at the left atrioventricular groove and did not harbor focal activation (proportion focal waves: 0% [IQR: 0%-2%]). Compared with non-DF_max sites, DF_max were characterized by more frequent smooth propagation (22% [IQR: 7%-48%] vs 17% [IQR: 11%-24%]; P = 0.001), less frequent conduction block (69% [IQR: 51%-81%] vs 74% [IQR: 69%-78%]; P = 0.006), a higher proportion of single potentials (72% [IQR: 55%-84%] vs 6%1 [IQR: 55%-65%]; P = 0.003), and a lower proportion of fractionated potentials (4% [IQR: 1%-11%] vs 12% [IQR: 9%-15%]; P = 0.004). CFAE_max were mainly found at the pulmonary veins area, and only 1% [IQR: 0%-2%] of all CFAE_max contained focal activation. Compared with non-CFAE_max sites, CFAE_max sites were characterized by less frequent smooth propagation (1% [IQR: 0%-1%] vs 17% [IQR: 12%-24%]; P < 0.001) and more frequent remnant activity (20% [IQR: 12%-29%] vs 8% [IQR: 5%-10%]; P < 0.001), and harbored predominantly fractionated potentials (52% [IQR: 43%-66%] vs 12% [IQR: 9%-14%]; P < 0.001).

CONCLUSIONS

Focal or rotational patterns of activation were not consistently detected at DF_max domains and CFAE_max sites. These findings do not support the concept of targeting DF_max or CFAE_max according to existing criteria for AF ablation.

Functional substrate mapping characteristics during sinus rhythm predicts critical isthmus of reentrant atrial tachycardia

BACKGROUND

Atrial tachycardia (AT) is a commonly encountered rhythm disorder in patients with underlying atrial scar. The role of atrial late activation mapping during sinus rhythm to predict the critical isthmus (CI) of AT has yet to be systematically evaluated. We aimed to investigate the relationship between the functional substrate mapping (FSM) characteristics and the CI of reentrant ATs in patients with underlying atrial low-voltage areas.

METHODS

Patients with history of left AT who underwent catheter ablation with 3D mapping using high-density mapping were enrolled. Voltage map and isochronal late activation mapping were created during sinus/paced rhythm to detect deceleration zones (DZ). Electrograms with continuous-fragmented morphology were also tagged. After induction of AT, activation mapping was performed to detect CI of the tachycardia. Atrial tachyarrhythmia (ATa) recurrence was defined as detection of atrial fibrillation or AT (≥30 s) during the follow-up.

RESULTS

Among 35 patients [mean age: 62 ± 9, gender: 25 (71.5%) female] with left AT, a total of 42 reentrant ATs induced. Voltage mapping during sinus rhythm revealed low-voltage area of 37.1 ± 23.8% of the left atrium. The mean value of bipolar voltage, EGM duration, and conduction velocity during sinus rhythm corresponding to CI of ATs were 0.18 ± 0.12 mV, 133 ± 47 ms, and 0.12 ± 0.09 m/s, respectively. Total number of DZs per chamber was 1.5 ± 0.6, which were located in the low-voltage zone (<0.5 mV) detected by high-density mapping. All CIs of reentry were colocalized with DZs detected during FSM. The positive predictive value of DZs to detect CI of inducible ATs is 80.4%. Freedom from ATa after the index procedure was 74.3% during a mean follow-up of 12.2 ± 7.5 months.

CONCLUSION

Our findings demonstrated the utility of FSM during sinus rhythm to predict the CI of AT. DZs displayed continuous-fragmented signal morphology with slow conduction which may guide to tailor ablation strategy in case of underlying atrial scar.

Construction and integrated analysis of the ceRNA network hsa_circ_0000672/miR-516a-5p/TRAF6 and its potential function in atrial fibrillation

Atrial fibrosis is a crucial contributor to initiation and perpetuation of atrial fibrillation (AF). This study aimed to identify a circRNA-miRNA-mRNA competitive endogenous RNA (ceRNA) regulatory network related to atrial fibrosis in AF, especially to validate hsa_circ_0000672/hsa_miR-516a-5p/TRAF6 ceRNA axis in AF preliminarily. The circRNA-miRNA-mRNA ceRNA network associated with AF fibrosis was constructed using bioinformatic tools and literature reviews. Left atrium (LA) low voltage was used to represent LA fibrosis by using LA voltage matrix mapping. Ten controls with sinus rhythm (SR), and 20 patients with persistent AF including 12 patients with LA low voltage and 8 patients with LA normal voltage were enrolled in this study. The ceRNA regulatory network associated with atrial fibrosis was successfully constructed, which included up-regulated hsa_circ_0000672 and hsa_circ_0003916, down-regulated miR-516a-5p and five up-regulated hub genes (KRAS, SMAD2, TRAF6, MAPK11 and SMURF1). In addition, according to the results of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, these hub genes were clustered in TGF-beta and MAPK signaling pathway. In the patients with persistent AF, hsa_circ_0000672 expression in peripheral blood monocytes was significantly higher than those in controls with SR by quantitative real-time polymerase chain reaction (p-value < 0.001). Furthermore, hsa_circ_0000672 expression was higher in peripheral blood monocytes of persistent AF patients with LA low voltage than those with LA normal voltage (p-value = 0.002). The dual-luciferase activity assay confirmed that hsa_circ_0000672 exerted biological functions as a sponge of miR-516a-5p to regulate expression of its target gene TRAF6. Hsa_circ_0000672 expression in peripheral blood monocytes may be associated with atrial fibrosis. The hsa_circ_0000672 may be involved in atrial fibrosis by indirectly regulating TRAF6 as a ceRNA by sponging miR-516a-5p.

Characterization and identification of atrial fibrillation drivers in patients with nonparoxysmal atrial fibrillation using simultaneous amplitude frequency electrogram transform

INSTRUCTION

We hypothesized that real-time simultaneous amplitude frequency electrogram transform (SAFE-T) during sinus rhythm (SR) is able to identify and characterize the drivers of atrial fibrillation (AF) in nonparoxysmal (NP) AF.

METHODS

Twenty-one NPAF patients (85.71% males, mean age 52 years old) underwent substrate mapping during SR (SAFE-T and voltage) and during AF (complex fractionated atrial electrograms [CFAE] and similarity index [SI]). After pulmonary veins isolation, extensive substrate ablation was performed with the endpoint of procedural termination or elimination of all SI sites (>63% similarities). Sites with procedural termination and non-termination sites were tagged for postablation SR analysis using SAFE-T.

RESULTS

In 74 CFAE sites identified (average of 3 ± 2 sites per person), 28 (37.84%) were identified as termination sites demonstrating a high SI compared with the non-termination sites (80.11 ± 9.57% vs. 45.96 ± 13.38%, p < .001) during AF. During SR, these termination sites have high SAFE-T values and harbor a highly resonant, localized, repetitive high frequency components superimposed in the low frequency components compared with non-termination sites (5.70 ± 3.04 vs. 1.49 ± 1.66 Hz·mV, p < .001). In the multivariate analysis, the termination sites have higher SAFE-T and SI value (p < .001).

CONCLUSION

AF procedural termination sites harbored signal characteristics of repetitive, high frequency component of individualized electrogram during SR, which can be masked by the low frequency fractionated electrogram and are difficult to see from the bipolar electrogram. Thus, SAFE-T mapping is feasible in identifying and characterizing sites of AF drivers.

Repeat ablation strategy for recurrent persistent atrial fibrillation: A propensity-matched score comparison between "2C3L" and "extensive ablation" approach

BACKGROUND

Debates exist in the repeat ablation strategy for patients with recurrence presenting as persistent atrial fibrillation (AF) after initial persistent AF ablation.

OBJECTIVE

To compare the outcome between the "2C3L" and "extensive ablation" approach in patients undergoing repeat procedures for recurrent persistent AF.

METHODS

Propensity-score matching was performed in 196 patients with AF recurrence undergoing repeat ablation, and 79 patients treated with "2C3L" strategy were matched to 79 patients treated with "extensive ablation" strategy. The "2C3L" approach included pulmonary vein isolation, mitral isthmus, left atrial roof, and cavotricuspid isthmus ablation, while the "extensive ablation" strategy included extensive ablation of a variety of other targets aiming to terminate the AF. The primary outcome was freedom from any atrial tachyarrhythmia after 24-h ambulatory monitoring follow-up for 12 months.

RESULTS

No statistically significant difference was found between the primary outcome between the "2C3L" and the "extensive ablation" group [70.9% vs. 69.6%, p = .862; 95% confidence interval (CI) -12.8 to 15.3], although the "extensive ablation" group had a significantly high proportion of AF termination (19.0% for "2C3L" vs. 41.8% for "extensive ablation" group, p = .002; 95% CI 8.5-35.9). And AF termination was not related to the primary outcome in multifactorial regression. At 40 ± 22 months after the repeat procedure, the primary outcome was also comparable (57.0 % for "2C3L" vs. 48.1% for "extensive ablation" group, p = .265; 95% CI -6.6 to 23.7).

CONCLUSION

The outcome between the "2C3L" and "extensive ablation" approaches was comparable in patients undergoing repeat procedures for recurrent persistent AF.

Comparing the efficacy of catheter ablation strategies for persistent atrial fibrillation: a Bayesian analysis of randomized controlled trials

BACKGROUND

Catheter ablation has been recommended as the first-line treatment option for selected patients with atrial fibrillation (AF). However, a widely accepted ablation strategy for persistent AF (perAF) has not yet been established. The benefits of ablation strategies are not conclusive for perAF. There is an urgent need to systematically analyze the results of previous studies and rank these treatment strategies to guide clinical practice.

METHODS

Randomized controlled trials (RCTs) on ablation for perAF were included. The primary outcome was recurrence of atrial tachyarrhythmia (AT) after a single ablation procedure. A Bayesian random-effects network meta-analysis model was fitted.

RESULTS

Twenty-three studies were included in the analysis. A total of 3394 patients and 22 ablation strategies were found in the involved studies. The ablation strategy of pulmonary vein isolation (PVI) + electrical box isolation of the left atrial posterior wall (PBOX) + non-PV trigger ablation (NPV) showed the best treatment effect in terms of the primary outcome. The individualized ablation strategies of mapping and ablation combined with PVI, such as PVI + rotors, PVI + dispersion areas, and PVI + low voltage zone (LVZ) also showed a better ablation effect in perAF.

CONCLUSIONS

PVI ablation is a widely used strategy in perAF and is recognized as a cornerstone procedure for perAF. The PVI + PBOX + NPV strategy showed the highest rank in our analysis. Mapping and ablation strategies that could provide individualized substrate modification also showed a better rank in our analysis and are believed to be a promising direction for the treatment of perAF.

Fixed complex electrograms during sinus rhythm and local pacing: potential ablation targets for persistent atrial fibrillation

In atrial fibrillation (AF) patients, complex electrograms during sinus rhythm (C-EGMs) could be pathological or not. We aimed to demonstrate whether local pacing was helpful to discern pathological C-EGMs. 126 persistent AF patients and 27 patients with left-side accessory pathway (LAP) underwent left atrial mapping during sinus rhythm. If C-EGMs were detected, local pacing was performed. If the electrograms turned normal, we defined them as non-fixed C-EGMs, otherwise as fixed C-EGMs. No difference was detected in the incidence and proportion of non-fixed C-EGMs between AF patients and LAP patients (101/126 vs. 19/27, P = 0.26; 9.1 ± 6.0% vs. 7.7 ± 5.7%, P = 0.28). However, the incidence and proportion of fixed C-EGMs were higher in persistent AF patients (87/126 vs. 1/27, P < 0.01; 4.3 ± 3.4% vs. 0.1 ± 0.5%, P < 0.01). Compared with non-fixed C-EGMs, fixed C-EGMs had lower amplitudes, longer electrogram durations and longer Stimuli-P wave internals. All AF patients received circumferential pulmonary vein isolation. Among AF patients with fixed C-EGMs, 45 patients received fixed C-EGMs ablation and 42 patients underwent linear ablation. Compared with linear ablation, fixed C-EGMs ablation reduced recurrence (HR: 0.43; 95% CI 0.21‐0.81; P = 0.011). Among patients without fixed C-EGMs ablation, the proportion of fixed C-EGMs was an independent predictor of ablation outcomes (HR for per percent: 1.13, 95% CI 1.01–1.28, P = 0.038). C-EGMs could be classified into fixed and non-fixed C-EGMs through local pacing. Fixed rather than non-fixed C-EGMs might indicate abnormal atrial substrates and fixed C-EGMs ablation improve outcomes of persistent AF ablation.

Atrial Fibrillation and Acute Ischemic Stroke: Evaluation of the Contemporary 2018 National Inpatient Sample Database

Background

Atrial fibrillation (AF) in acute ischemic stroke (AIS) is considered a binary entity regardless of AF type. We aim to investigate in-hospital morbidity and mortality among patients with nonparoxysmal AF-related AIS.

Methods

Patients hospitalized for AIS with associated paroxysmal or persistent AF were identified from the 2018 national inpatient sample database. We compared in-hospital mortality, stroke-related morbidity, hospital cost, length of stay, and discharge disposition in patients hospitalized with paroxysmal or persistent AF.

Results

A total of 26,470 patients were hospitalized for AIS with paroxysmal or persistent AF. Patient with AIS with persistent AF had a longer hospital length of stay (paroxysmal AF, mean [M] 5.7 days, standard deviation [SD] ±6.8 days; persistent AF, M 7.4 days, SD ±11.9 days, P < 0.001) and in-hospital costs (paroxysmal AF, M $15,449, SD ±$18,320; persistent AF, M $19,834 SD ±$23,312, P < 0.001). Patients with AIS with permanent AF had higher in-hospital mortality (paroxysmal AF, 4.6%, vs permanent AF, 6.2%, P < 0.001). Indirect markers of stroke-related disability, like intracranial hemorrhage (odds ratio [OR]: 1.9, 95% confidence interval (CI): 1.6-2.2), need for gastrostomy (OR: 2.1, 95% CI: 1.8-2.4), and tracheostomy (OR: 3.1, 95% CI: 2.1-4.4) were more associated with AIS from persistent AF.

Conclusions

Persistent AF is associated with poor in-hospital stroke-related outcome, possibly due to a worse thrombo-embolic phenomenon. AF pattern may be a harbinger of worse stroke-related morbidity.

Left Atrial Localized Low-Voltage Areas Indicate Whole Left Atrial Electrophysiological Degeneration in Atrial Fibrillation Patients

BACKGROUND

The efficacy of ablation targeting low-voltage areas (LVAs) is controversial, although LVA presence is well known to be associated with atrial fibrillation (AF) recurrence after ablation. AF substrate may not localize within LVAs.

METHODS AND RESULTS

This observational study enrolled 405 consecutive patients who underwent an initial AF ablation procedure. The left atrial (LA) voltage map was obtained after pulmonary vein isolation. LVAs were defined as areas with voltage <0.5 mV. To estimate whole LA electrophysiological degeneration, mean regional voltage at each of the 6 regions and LA total conduction velocity were measured. LVAs existed in 143 of 405 (35.3%) patients. Patients with LVAs demonstrated lower mean regional voltages throughout all 6 regions compared to those without LVAs (1.3 [1.8, 0.8] vs. 0.6 [1.0, 0.2] mV for the anterior wall, P<0.001). In contrast, LA conduction velocity was lower in patients with LVAs than in those without (0.89 [1.01, 0.74] vs. 0.93 [1.03, 0.87] m/s, P<0.001). Multivariate analysis revealed that low LA total conduction velocity and a higher number of regions with mean voltage reduction were independently associated with AF recurrence, although LVA presence was not.

CONCLUSIONS

Patients with localized LA LVAs were characterized by whole LA electrophysiological degeneration as assessed by mean regional voltage and conduction velocity. In addition, whole LA electrophysiological degeneration parameters were well associated with AF recurrence.

Association Between the Coronary Sinus Ostial Size and Atrioventricular Nodal Reentrant Tachycardia in Patients With Pulmonary Arterial Hypertension

Aims

The incidence of atrioventricular nodal reentrant tachycardia (AVNRT) is higher in pulmonary arterial hypertension (PAH) patients than in the general population. AVNRT is reportedly associated with a larger coronary sinus (CS) ostium (CSo). However, the correlation between AVNRT and CSo size in PAH patients is poorly investigated. We aimed to investigate the impact of CSo size on AVNRT and identify its risk factors in PAH.

Methods and Results

Of 102 PAH patients with catheter ablation of supraventricular tachycardia (SVT), twelve with a confirmed AVNRT diagnosis who underwent computed tomographic angiography were retrospectively enrolled as the study group. The control group (PAH without SVT, n = 24) was matched for sex and BMI at a 2:1 ratio. All baseline and imaging data were collected. Mean pulmonary artery pressure was not significantly different between the two groups (65.3 ± 16.8 vs. 64.5 ± 17.6 mmHg, P = 0.328). PAH patients with AVNRT were older (45.9 ± 14.8 vs. 32.1 ± 7.6 years, P = 0.025), had a larger right atrial volume (224.4 ± 129.6 vs. 165.3 ± 71.7 cm3, P = 0.044), larger CSo in the left anterior oblique (LAO) plane (18.6 ± 3.3 vs. 14.8 ± 4.0 mm, P = 0.011), and larger CSo surface area (2.08 ± 1.35 vs. 1.45 ± 0.73 cm2, P = 0.039) and were more likely to have a windsock-shape CS (75% vs. 16.7%, P = 0.001) than those without AVNRT. A linear correlation was shown between CSo diameter in the LAO-plane and the atrial fractionation of the ablation target for AVNRT (R2 = 0.622, P = 0.012).

Conclusion

Anatomical dilation of the CSo is a risk factor for AVNRT development in patients with PAH.

Catheter Ablation in Persistent AF, the Evolution towards a More Pragmatic Strategy

Atrial fibrillation (AF) is the most common cardiac arrhythmia worldwide and represents a heterogeneous disorder with a complex pathological basis. While significant technological advances have taken place over the last decade in the field of catheter ablation of AF, response to ablation varies and long-term success rates in those with persistent AF remain modest. Mechanistic studies have highlighted potentially different sustaining factors for AF in the persistent AF population with substrate-driven focal and re-entrant sources in the body of the atria identified on invasive and non-invasive mapping studies. Translation to clinical practice, however, remains challenging and the application of such mapping techniques to clinical ablation has yet to demonstrate a significant benefit beyond pulmonary vein isolation (PVI) alone in the persistent AF cohort. Recent advances in catheter and ablation technology have centered on improving the durability of ablation lesions at index procedure and although encouraging results have been demonstrated with early studies, large-scale trials are awaited. Further meaningful improvement in clinical outcomes in the persistent AF population requires ongoing advancement in the understanding of AF mechanisms, coupled with continuing progress in catheter technology capable of delivering durable transmural lesions.

Characterization of cardiac electrogram signals in atrial arrhythmias

Despite significant advancements in 3D cardiac mapping systems utilized in daily electrophysiology practices, the characterization of atrial substrate remains crucial for the comprehension of supraventricular arrhythmias. During mapping, intracardiac electrograms (EGM) provide specific information that the cardiac electrophysiologist is required to rapidly interpret during the course of a procedure in order to perform an effective ablation. In this review, EGM characteristics collected during sinus rhythm (SR) in patients with paroxysmal atrial fibrillation (pAF) are analyzed, focusing on amplitude, duration and fractionation. Additionally, EGMs recorded during atrial fibrillation (AF), including complex fractionated atrial EGMs (CFAE), may also provide precious information. A complete understanding of their significance remains lacking, and as such, we aimed to further explore the role of CFAE in strategies for ablation of persistent AF. Considering focal atrial tachycardias (AT), current cardiac mapping systems provide excellent tools that can guide the operator to the site of earliest activation. However, only careful analysis of the EGM, distinguishing low amplitude high frequency signals, can reliably identify the absolute best site for RF. Evaluating macro-reentrant atrial tachycardia circuits, specific EGM signatures correspond to particular electrophysiological phenomena: the careful recognition of these EGM patterns may in fact reveal the best site of ablation. In the near future, mathematical models, integrating patient-specific data, such as cardiac geometry and electrical conduction properties, may further characterize the substrate and predict future (potential) reentrant circuits.

CT- und MRT-Bildgebung in der Rhythmologie

Die Anwendung bildgebender Verfahren gewinnt in der interventionellen Elektrophysiologie entgegen der geringen Beachtung in den aktuell geltenden nationalen und internationalen Leitlinien zur Behandlung von Patienten mit Vorhofflimmern und ventrikulären Tachykardien auch über die reine Diagnostik zugrunde liegender struktureller Herzerkrankungen hinaus immer mehr an Bedeutung. Die breite Anwendung der Computertomografie (CT) und der Magnetresonanztomografie (MRT) ergibt sich aus den spezifischen Möglichkeiten dieser bildgebenden Techniken heraus: Gewebecharakterisierung des Myokards auf Vorhof- und Kammerebene mit präziser Darstellung von Infarktnarben, Grenzzonen und vitalem Myokard (MRT inklusive Late-Gadolinium-Enhancement-Darstellung); hochauflösende Darstellung wichtiger anatomischer Strukturen inklusive der Koronararterien und präzise Identifizierung von kritischer ventrikulärer Wandausdünnung im Infarktareal (CT); Identifizierung potenzieller Komplikationen nach Vorhofflimmerablation (Pulmonalvenenstenosen, Ösophagusruptur oder -fistel). Stärken und Schwächen sowie mögliche relative und absolute Kontraindikationen bei der Anwendung dieser beiden Methoden müssen jedoch berücksichtigt werden. Generell kann die Anwendung bildgebender Verfahren insbesondere für die Therapieplanung und -steuerung als wertvolle Ergänzung mit der Möglichkeit der Steigerung von Effektivität und Sicherheit gesehen werden. Prospektive randomisierte Studien liegen jedoch zu wichtigen aktuellen Anwendungsbereichen der CT und MRT noch nicht vor. Wichtigste Grundlage der interventionellen Elektrophysiologie in der Therapie supraventrikulärer und ventrikulärer Arrhythmien wird noch auf lange Sicht die Anwendung klassischer elektrophysiologischer Manöver und Strategien sowie die Verwendung sich immer weiter entwickelnder elektroanatomischer Mappingsysteme bleiben.

Atrial Fibrillation Structural Substrates: Aetiology, Identification and Implications

Atrial remodelling in AF underlines the electrical, structural and mechanical changes in the atria of patients with AF. Several risk factors for AF contribute to the development of the atrial substrate, with some evidence that atrial remodelling reversal is possible with targeted intervention. In this article, the authors review the electrophysiological changes that characterise the atrial substrate in patients with AF risk factors. They also discuss the pitfalls of mapping the atrial substrate and the implications for developing tailored ablation strategies to improve outcomes in patients with AF.

New developments in catheter ablation for patients with congenital heart disease

Introduction: There are numerous challenges to catheter ablation in patients with congenital heart disease (CHD), including access to cardiac chambers, distorted anatomies, displaced conduction systems, multiple and/or complex arrhythmia substrates, and excessively thickened walls, or interposed material. Areas covered: Herein, we review recent developments in catheter ablation strategies for patients with CHD that are helpful in addressing these challenges. Expert opinion: Remote magnetic navigation overcomes many challenges associated with vascular obstructions, chamber access, and catheter contact. Patients with CHD may benefit from a range of ablation catheter technologies, including irrigated-tip and contact-force radiofrequency ablation and focal and balloon cryoablation. High-density mapping, along with advances in multipolar catheters and interpolation algorithms, is contributing to new mechanistic insights into complex arrhythmias. Ripple mapping allows the activation wave front to be tracked visually without prior assignment of local activation times or window of interest, and without interpolations of unmapped regions. There is growing interest in measuring conduction velocities to identify arrhythmogenic substrates. Noninvasive mapping with a multielectrode-embedded vest allows prolonged bedside monitoring, which is of particular interest in those with non-sustained or multiple arrhythmias. Further studies are required to assess the role of radiofrequency needle catheters and stereotactic radiotherapy in patients with CHD.

Multilayer fabrication of durable catheter-deployable soft robotic sensor arrays for efficient left atrial mapping

Devices that perform cardiac mapping and ablation to treat atrial fibrillation provide an effective means of treatment. Current devices, however, have limitations that either require tedious point-by-point mapping of a cardiac chamber or have limited ability to conform to the complex anatomy of a patient's cardiac chamber. In this work, a detailed, scalable, and manufacturable technique is reported for fabrication of a multielectrode, soft robotic sensor array. These devices exhibit high conformability (~85 to 90%) and are equipped with an array of stretchable electronic sensors for voltage mapping. The form factor of the device is intended to match that of the entire left atrium and has a hydraulically actuated soft robotic structure whose profile facilitates deployment from a 13.5-Fr catheter. We anticipate that the methods described in this paper will serve a new generation of conformable medical devices that leverage the unique characteristics of stretchable electronics and soft robotics.

Direction- and rate-dependent fractionation during atrial fibrillation persistence: Unmasking cardiac anisotropy?

This human case is the first to illustrate morphological manifestations of direction‐ and rate‐dependent anisotropic conduction in high‐resolution unipolar atrial potentials. Premature impulses induced low‐amplitude, fractionated extracellular potentials with exceptionally prolonged durations in a 76‐year old longstanding persistent patient with atrial fibrillation (AF), demonstrating direction‐dependency of anisotropic conduction. An increased pacing frequency induced presence of similar fractionated potentials, reflecting rate‐dependent anisotropy and inhomogeneous, slow conduction. Pacing with different rates and from different sites could aid in identifying nonuniform anisotropic tissue and thus the substrate of AF.

How, When, and Why: High-Density Mapping of Atrial Fibrillation

High-density (HD) mapping presents opportunities to enhance delineation of atrial fibrillation (AF) substrate, improve efficiency of the mapping procedure without sacrificing safety, and afford new mechanistic insights regarding AF. Innovations in hardware, software algorithms, and development of novel multielectrode catheters have allowed HD mapping to be feasible and reliable. Patients to particularly benefit from this technology are those with paroxysmal AF in setting of preexisting atrial scar, persistent AF, and AF in the setting of complex congenital heart disease. The future will bring refinements in automated HD mapping including evolution of noncontact methodologies and artificial intelligence to supplant current techniques.

Impact of pulmonary vein isolation on mechanisms sustaining persistent atrial fibrillation: Predicting the acute response

BACKGROUND

Noninvasive mapping identifies potential drivers (PDs) in atrial fibrillation (AF). We analyzed the impact of pulmonary vein isolation (PVI) on PDs and whether baseline PD pattern predicted termination of AF.

METHODS

Patients with persistent AF less than 2 years underwent electrocardiographic imaging mapping before and after cryoballoon PVI. We recorded the number of PD occurrences, characteristics (rotational wavefronts ≥ 1.5 revolutions or focal activations), and distribution using an 18-segment atrial model.

RESULTS

Of 100 patients recruited, PVI terminated AF in 15 patients; 21.3% ± 9.1% (8.7 ± 4.8) of PDs occurred at the pulmonary veins (PVs) and posterior wall. PVI had no impact on PD occurrences outside the PVs and posterior wall (33.2 ± 12.9 vs 31.6 ± 12.5; P = .164), distribution over the remaining 13 segments (9 [8-11] vs 9 [8-10]; P = .634), the proportion of PDs that was rotational (82.9% ± 9.7% vs 83.6% ± 10.1%; P = .496), or temporal stability (2.4 ± 0.4 vs 2.4 ± 0.5 rotations; P = .541). Fewer focal PDs (area under the curve, 0.683; 95% CI, 0.528-0.839; P = .024) but not rotational PDs (P = .626) predicted AF termination with PVI.

CONCLUSIONS

PVI did not have a global impact on PDs outside the PVs and posterior wall. Although fewer focal PDs predicted termination of AF with PVI, the burden of rotational PDs did not. It is accepted though not all PDs are necessarily real or important. Outcome data are needed to confirm whether noninvasive mapping can predict patients likely to respond to PVI.

Challenges Associated with Interpreting Mechanisms of AF

Determining optimal treatment strategies for complex arrhythmogenesis in AF is confounded by the lack of consensus regarding the mechanisms causing AF. Studies report different mechanisms for AF, ranging from hierarchical drivers to anarchical multiple activation wavelets. Differences in the assessment of AF mechanisms are likely due to AF being recorded across diverse models using different investigational tools, spatial scales and clinical populations. The authors review different AF mechanisms, including anatomical and functional re-entry, hierarchical drivers and anarchical multiple wavelets. They then describe different cardiac mapping techniques and analysis tools, including activation mapping, phase mapping and fibrosis identification. They explain and review different data challenges, including differences between recording devices in spatial and temporal resolutions, spatial coverage and recording surface, and report clinical outcomes using different data modalities. They suggest future research directions for investigating the mechanisms underlying human AF.

Association of Left Atrial High-Resolution Late Gadolinium Enhancement on Cardiac Magnetic Resonance With Electrogram Abnormalities Beyond Voltage in Patients With Atrial Fibrillation

BACKGROUND

Conflicting data have been reported on the association of left atrial (LA) late gadolinium enhancement (LGE) with atrial voltage in patients with atrial fibrillation. The association of LGE with electrogram fractionation and delay remains to be examined. We sought to examine the association between LA LGE on cardiac magnetic resonance and electrogram abnormalities in patients with atrial fibrillation.

METHODS

High-resolution LGE cardiac magnetic resonance was performed before electrogram mapping and ablation in atrial fibrillation patients. Cardiac magnetic resonance features were quantified using LA myocardial signal intensity Z score (SI-Z), a continuous normalized variable, as well as a dichotomous LGE variable based on previously validated methodology. Electrogram mapping was performed pre-ablation during sinus rhythm or LA pacing, and electrogram locations were coregistered with cardiac magnetic resonance images. Analyses were performed using multilevel patient-clustered mixed-effects regression models.

RESULTS

In the 40 patients with atrial fibrillation (age, 63.2±9.2 years; 1312.3±767.3 electrogram points per patient), lower bipolar voltage was associated with higher SI-Z in patients who had undergone previous ablation (coefficient, -0.049; P<0.001) but not in ablation-naive patients (coefficient, -0.004; P=0.7). LA electrogram activation delay was associated with SI-Z in patients with previous ablation (SI-Z: coefficient, 0.004; P<0.001 and LGE: coefficient, 0.04; P<0.001) but not in ablation-naive patients. In contrast, increased LA electrogram fractionation was associated with SI-Z (coefficient, 0.012; P=0.03) and LGE (coefficient, 0.035; P<0.001) only in ablation-naive patients.

CONCLUSIONS

The association of LA LGE with voltage is modified by ablation. Importantly, in ablation-naive patients, atrial LGE is associated with electrogram fractionation even in the absence of voltage abnormalities.

Intra-Atrial Conduction Delay Revealed by Multisite Incremental Atrial Pacing is an Independent Marker of Remodeling in Human Atrial Fibrillation

Objectives

This study sought to characterize direction-dependent and coupling interval–dependent changes in left atrial conduction and electrogram morphology in uniformly classified patients with paroxysmal atrial fibrillation (AF) and normal bipolar voltage mapping.

Background

Although AF classifications are based on arrhythmia duration, the clinical course, and treatment response vary between patients within these groups. Electrophysiological mechanisms responsible for this variability are incompletely described.

Methods

Intracardiac contact mapping during incremental atrial pacing was used to characterize atrial conduction, activation dispersion, and electrogram morphology in 15 consecutive paroxysmal AF patients undergoing first-time pulmonary vein isolation. Outcome measures were vulnerability to AF induction at electrophysiology study and 2-year follow-up for arrhythmia recurrence.

Results

Conduction delay showed a bimodal distribution, occurring at either long (high right atrium pacing: 326 ± 13 ms; coronary sinus pacing: 319 ± 16 ms) or short (high right atrium pacing: 275 ± 11 ms; coronary sinus pacing: 271 ± 11 ms) extrastimulus coupling intervals. Arrhythmia recurrence was found only in patients with conduction delay at long extrastimulus coupling intervals, and patients with inducible AF were characterized by increased activation dispersion (activation dispersion time: 168 ± 29 ms vs. 136 ± 11 ms). Electrogram voltage and duration varied throughout the left atrium, between patients, and with pacing site but were not correlated with AF vulnerability or arrhythmia recurrence.

Conclusions

Within the single clinical entity of paroxysmal AF, incremental atrial pacing identified a spectrum of activation patterns correlating with AF vulnerability and arrhythmia recurrence. In contrast, electrogram morphology (characterized by electrogram voltage and duration) was highly variable and not associated with AF vulnerability or recurrence. An improved understanding of the electrical phenotype in AF could lead to improved mechanistic classifications.

Left atrial voltage mapping: defining and targeting the atrial fibrillation substrate

Low atrial endocardial bipolar voltage, measured during catheter ablation for atrial fibrillation (AF), is a commonly used surrogate marker for the presence of atrial fibrosis. Low voltage shows many useful associations with clinical outcomes, comorbidities and has links to trigger sites for AF. Several contemporary trials have shown promise in targeting low voltage areas as the substrate for AF ablation; however, the results have been mixed. In order to understand these results, a thorough understanding of voltage mapping techniques, the relationship between low voltage and the pathophysiology of AF, as well as the inherent limitations in voltage measurement are needed. Two key questions must be answered in order to optimally apply voltage mapping as the road map for ablation. First, are the inherent limitations of voltage mapping small enough as to be ignored when targeting specific tissue based on voltage? Second, can conventional criteria, using a binary threshold for voltage amplitude, truly define the extent of the atrial fibrotic substrate? Here, we review the latest clinical evidence with regard to voltage-based ablation procedures before analysing the utility and limitations of voltage mapping. Finally, we discuss omnipole mapping and dynamic voltage attenuation as two possible approaches to resolving these issues.

Catheter Ablation of Long-standing Persistent Atrial Fibrillation: a Reckless Challenge or a Way to Real Cure?

Long-standing persistent atrial fibrillation (L-PeAF) is a category in which rhythm control is attempted while atrial fibrillation (AF) is maintained for more than 1 year. Because AF is a progressive disease and L-PeAF accompanies significant electrical and structural remodeling of atria, it is difficult to restore and maintain sinus rhythm in patients with L-PeAF. Nonetheless, the rhythm outcome is being increasingly improved by the development of sophisticated mapping devices, highly efficient catheters, and evidence-based ablation strategies, and the rational choice of patient selection criteria. This review discusses the evolution of the rhythm control outcome of L-PeAF and its future direction of development.

Coronary Sinus Electrograms May Predict New-onset Atrial Fibrillation After Typical Atrial Flutter Radiofrequency Ablation (CSE-AF)

Background

Complex fractionated electrograms (EGMs) of the coronary sinus electrograms (CSEs) are employed as a target during radiofrequency ablations (RFA) of atrial fibrillation (AF). Anatomically, CSEs includes both of left atrium (LA), coronary sinus musculature and right atrium (RA) electrograms.

Aim

To determine the significance of fractionated CSE and delayed potentials as a predictor of new-onset AF after radiofrequency ablation (RFA) of isolated atrial flutter (AFL).

Methods

Consecutive patients underwent AFL ablation. Fractionated and/or continuous discrete activities were recorded from coronary sinus electrograms during sinus rhythm and during pacing. Earliest CSE to the S nadir or peak R in milliseconds was recorded and considered as propagation delay for EGMs.

Results

Forty patients were included during a mean follow-up period of 55.1± 15.8 months. Twenty patients (50 %) developed AF while the remaining 20 patients maintained sinus rhythm(SR) during the follow-up period. Proximal and mid CSEs were significantly fractionated in AF group compared to group with no AF development (65 % and 60% Vs. 35 % and 30 %, p = 0.03, respectively). However, during pacing from distal duo-decapolar catheter (pole 1-2), distal CSEs alone were significantly fractionated (p < 0.05) compared to SR group. Significant delayed propagation of proximal CSE during pacing and in sinus rhythm were observed in AF group (12.3 ± 9.2 ms vs 7.1 ± 3.6 ms, p = 0.03) and (7.2 ± 2.9 ms Vs 8.1 ± 4.6 ms, p= 0.02) in the same order.

Conclusion

Incidence of AF is associated with fractionated proximal and mid CSE in sinus rhythm and distal CSE during paced rhythm after isolated AFL ablation. Delayed proximal CSE propagation is correlated with AF incidence.

Atrial Fibrillation Mechanisms and Implications for Catheter Ablation

AF is a heterogeneous rhythm disorder that is related to a wide spectrum of etiologies and has broad clinical presentations. Mechanisms underlying AF are complex and remain incompletely understood despite extensive research. They associate interactions between triggers, substrate and modulators including ionic and anatomic remodeling, genetic predisposition and neuro-humoral contributors. The pulmonary veins play a key role in the pathogenesis of AF and their isolation is associated to high rates of AF freedom in patients with paroxysmal AF. However, ablation of persistent AF remains less effective, mainly limited by the difficulty to identify the sources sustaining AF. Many theories were advanced to explain the perpetuation of this form of AF, ranging from a single localized focal and reentrant source to diffuse bi-atrial multiple wavelets. Translating these mechanisms to the clinical practice remains challenging and limited by the spatio-temporal resolution of the mapping techniques. AF is driven by focal or reentrant activities that are initially clustered in a relatively limited atrial surface then disseminate everywhere in both atria. Evidence for structural remodeling, mainly represented by atrial fibrosis suggests that reentrant activities using anatomical substrate are the key mechanism sustaining AF. These reentries can be endocardial, epicardial, and intramural which makes them less accessible for mapping and for ablation. Subsequently, early interventions before irreversible remodeling are of major importance. Circumferential pulmonary vein isolation remains the cornerstone of the treatment of AF, regardless of the AF form and of the AF duration. No ablation strategy consistently demonstrated superiority to pulmonary vein isolation in preventing long term recurrences of atrial arrhythmias. Further research that allows accurate identification of the mechanisms underlying AF and efficient ablation should improve the results of PsAF ablation.

Compass Mapping, Double Potentials, Activation Patterns Can Identify and Track Rotational Activity Sites in the Left Atrium of Humans with Persistent Atrial Fibrillation

BACKGROUND

Rotational circuits that occur between bipolar electrodes exhibit double potentials (DPs). It had been previously surmised that rotors could not be electrically tracked directly.

PURPOSE

Our purpose was twofold; first, to show that the use of compass mapping, one can regionally identify rotational activity; and second, to show that by combining simultaneous compass map recordings, standard narrow-adjacent bipolar, and unipolar recordings, that specific signature recording patterns emerge that allow one to identify the accurate time, location, and path of a rotational mechanism.

METHODS

This was an observational study in 20 patients with persistent atrial fibrillation in which the electrode configuration of a circular mapping catheter was changed to wide cross-circle electrode pairing (compass mapping). DPs were recorded and analyzed from 12 left atrial (LA) sites and identified electrical wavefront patterns and direction. A substudy analyzed transitions patterns with simultaneous narrow-adjacent bipolar and unipolar recordings.

RESULTS

Four wavefront patterns were identified: DPs, peripheral waves (PWs), distal peripheral waves and fibrillatory activity. DP wavefront patterns exhibited significantly shorter cycle lengths than PWs in 8 of 12 LA sites. Patients had 2.9± 2.1 regions that exhibited DPs. DPs of varying duration were found, few (25%) were of stable duration and location. Detailed electrical examination at the transition between a PW to a DP identified a highly consistent pattern of simultaneous reversal of activation sequence, a special form of Doppler effect for spiral waves as a rotor passes between 2 electrodes, and a ½ cycle drop-off of activation signals along the line of electrodes.

CONCLUSION

DP recordings in compass mode can provide a regional assessment for the existence of rotational activity. Simultaneous DP recordings in compass mode, narrow-adjacent bipolar, and unipolar recording provide an accurate assessment of the time, location, and path that a rotational mechanism breaches a perimeter of electrodes. Accurate time, location and path of perimeter breaches can be used to electrically track rotational mechanisms during atrial fibrillation.

The effect of activation rate on left atrial bipolar voltage in patients with paroxysmal atrial fibrillation

INTRODUCTION

Bipolar voltage is used during electroanatomic mapping to define abnormal myocardium, but the effect of activation rate on bipolar voltage is not known. We hypothesized that bipolar voltage may change in response to activation rate. By examining corresponding unipolar signals we sought to determine the mechanisms of such changes.

METHODS AND RESULTS

LA extrastimulus mapping was performed during CS pacing in 10 patients undergoing first time paroxysmal atrial fibrillation ablation. Bipolar and unipolar electrograms were recorded using a PentaRay catheter (4-4-4 spacing) and indifferent IVC electrode, respectively. An S1S2 pacing protocol was delivered with extrastimulus coupling interval reducing from 350 to 200 milliseconds. At each recording site (119 ± 37 per LA), bipolar peak-to-peak voltage, unipolar peak to peak voltage and activation delay between unipole pairs was measured. Four patterns of bipolar voltage/extrastimulus coupling interval curves were seen: voltage attenuation with plateau voltage >1 mV (48 ± 15%) or <1 mV (22 ± 15%), and voltage unaffected by coupling interval with plateau voltage >1 mV (17 ± 10%) or <1 mV (13 ± 8%). Electrograms showing bipolar voltage attenuation were associated with significantly greater unipolar voltage attenuation at low (25 ± 28 mV/s vs. 9 ± 11 mV/s) and high (23 ± 29 mV/s vs. 6 ± 12 mV/s) plateau voltage sites (P < 0.001). There was a small but significant increase in conduction delay between unipole pairs at sites showing bipolar voltage attenuation (P = 0.026).

CONCLUSIONS

Bipolar electrogram voltage is dependent on activation rate at a significant proportion of sites. Changes in unipolar voltage and timing underlie these effects. These observations have important implications for use of voltage mapping to delineate abnormal atrial substrate.

Electrogram signature of specific activation patterns: Analysis of atrial tachycardias at high-density endocardial mapping

BACKGROUND

The significance of fractionated electrograms (EGMs) is object of debate, with multiple mechanisms described.

OBJECTIVE

Using Rhythmia, a high-density mapping system, we sought to investigate the relationship between specific electrophysiological phenomena and EGM characteristics at those sites.

METHODS

Twenty-five consecutive patients underwent high-density atrial mapping during atrial tachycardias. Bipolar EGMs were recorded with a 64-electrode basket catheter. The following atrial phenomena were identified: slow conduction (SC) areas, lines of block (LB), wavefront collisions (WFC), pivot sites (PS), and gaps. EGMs collected at these predefined areas were analyzed in terms of amplitude, duration, and morphology.

RESULTS

Twenty-five atrial maps with 195 sites of interest (1755 EGMs) were object of our analysis. Thirty-five percent were sites of SC: fractionation had low amplitude (0.16 ± 0.07 mV) and long duration (87.8 ± 10.7 ms); wavefront collisions were seen in 38% of sites with EGMs shorter in duration (46.5 ± 4.5 ms) and higher in voltage (0.58 ± 0.13 mV); 17% were lines of block, never responsible for fractionation (0.13 ± 0.05 mV; 122.4 ms ± 24.8 ms); 9% were PS with a high degree of fractionation (0.55 ± 0.15 mV; 85.8 ± 7.9 ms). Two gaps were identified (1%) with a low degree of fractionation.

CONCLUSION

Specific EGM characteristics in atrial tachycardia can be reproducibly linked to electrophysiological mechanisms. High-voltage and short-duration EGMs are associated with collision sites and PS that are unlikely to form critical sites for ablation; long-duration, low-voltage EGMs are associated with SC. However, not all SC regions will lie within the critical circuit and identification by only EGM characteristics cannot guide ablation.

Wavefront direction and cycle length affect left atrial electrogram amplitude

BACKGROUND

The relationship between atrial electrogram (EGM) characteristics in atrial fibrillation (AF) and those in sinus rhythm (SR) are generally unknown. The activation rate and direction may affect EGM characteristics. We examined characteristics of left atrial (LA) EGMs obtained during pacing from different sites.

METHODS

The study included 10 patients undergoing pulmonary vein isolation for AF. Atrial EGMs were recorded from a 64-pole basket catheter placed in the LA, and bipolar EGM amplitudes from the distal electrode pair (1-2) and proximal electrode pair (6-7) from 8 splines were averaged. The high right atrium (HRA), proximal coronary sinus (CSp), and distal coronary sinus (CSd) were paced at 600 ms and 300 ms.

RESULTS

When the LA voltage at SR was ≥1.5 mV, bipolar voltages of the HRA were greater than those of the CSp, which were greater than those of the CSd, regardless of the pacing cycle length. The shorter pacing cycle length resulted in a reduction of the LA EGM voltage at sites of SR voltage ≥1.5 mV, but no significant difference was seen at sites where the SR EGM amplitude was between >0.5 and <1.5 mV. No significant differences were seen in intra-basket conduction times between pacing cycle lengths of 600 ms and 300 ms at any pacing site.

CONCLUSION

The rate and direction-dependent reduction of the amplitude of atrial EGMs may explain, in part, the voltage discordance during SR and AF.

Influence of the left atrial contact areas on fixed low-voltage zones during atrial fibrillation and sinus rhythm in persistent atrial fibrillation

BACKGROUND

Atrial low-voltage zones (LVZ) are suggested as important factors for maintaining persistent atrial fibrillation (PsAF). The relationship between LVZs and left atrial (LA) contact areas (CoAs) is still unclear.

OBJECTIVE

To assess whether CoA regions were involved in atrial substrate properties maintaining PsAF.

METHODS

A total of 50 patients with PsAF (36 long-lasting) were analyzed. Three representative CoA detection areas (ascending aorta-anterior-LA, descending aorta-left pulmonary vein antrum, and vertebrae-posterior-LA) were registered on the mapping geometry. Electrograms during AF and sinus rhythm (SR) were acquired, and the fractionated electrograms (CFE; < 80milliseconds) and voltages were analyzed regarding the CoAs.

RESULTS

After SR conversion, 76% (38/50) had a significant LVZ (>5% of the total LA surface area). Patients with long-lasting PsAF versus PsAF had larger CoA areas (7.7 ± 3.0 vs. 4.5 ± 2.5cm² , P < 0.05) and overlapped-LVZs (8.2 [3.2-11.0] vs. 2.1 [0.7-3.7] cm² , P = 0.0126) between the SR-LVZs (<0.5 mV) and AF-LVZs (<0.2 mV). Overlapped-LVZs were frequently observed in CoA regions (anterior 76.4%; LIPV antrum 78.8%, and vertebrae 39.2%), and those LVZs had smaller unipolar voltages than those distant from the CoA regions (0.64 ± 0.16 vs. 2.5 ± 1.5 mV, P < 0.0001). SR-LVZ targeted ablation, including of CoA regions, rendered AF termination (n = 8, 21%), and 88% of the sites were not located immediately above, but adjacent to, the overlapped-LVZs. Significant AF slowing (6.0 ± 0.6 to 5.6 ± 0.6 Hz; P < 0.05) accompanied by unintentional CFE elimination (9.8-1.8 cm² ; P < .0001) was achieved in patients without termination.

CONCLUSION

Our data suggested that external structures in contact with the LA are involved in the creation of localized diseased myocardium necessary for PsAF maintenance.