Ablation Targets Research Articles

Non-invasive electrocardiographic imaging for the characterization of complex atrial tachyarrhythmias

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): This work was supported by the European Union NextGenerationEU/PRTR. Background – The non-invasive characterization of complex atrial tachyarrhythmias, including atrial flutter (AFL) and focal atrial tachycardia (AT) is challenging. Conventional 12-lead electrocardiogram (ECG) faces several limitations. Planning a precise and preprocedural strategy for complex tachyarrhythmias catheter ablation (CA) is not easy. Purpose To evaluate the diagnostic capacity of a novel electrocardiographic imaging (ECGI) system that does not require previous CT/MRI thoracic imaging. Methods – 42 patients (27 males, CHA2DS2-VASc score 2±1, LVEF 54.5 ± 11.0 % and LA area 31.3 ± 7.0 cm2) undergoing CA for focal AT or AFL were prospectively included in the study. A preprocedural ECGI was managed based on a 64-electrode vest, a torso reconstruction using a 3D real-time acquisition camera, and an artificial intelligence-based method to estimate the patient atrial geometry. The differential diagnostic capacities of non-invasive 12-lead ECG and ECGI were assessed compared with endocavity electroanatomical mapping (EAM) regarding three endpoints: 1) the identification of the involved atrial cavity, 2) the mechanism (focal/micro-reentry or macro-reentry), and (3) the ablation target site defined as the area where the earliest activation was located for focal/micro re-entrant arrhythmias, and the precise anatomical pathway for macro re-entrant tachyarrhythmias. Regarding the ECG, the three endpoints were assessed based on validated algorithms by 2 different observers blinded from the diagnosis. Results – 48 atrial tachyarrhythmias of which 59.5% occurred in the context of a history of CA were evaluated. The non-invasive characterization of complex atrial arrhythmias using this novel ECGI system was possible in 94% of the cases (Figure A): directly for 36 arrhythmias and after decreasing ventricular response using vagal maneuvers for 9. ECGI obtained global accuracy to identify the involved atrial cavity of 91.7%, the mechanism of 89.6%, and the ablation target of 83.3%. In challenging cases, such as in patients with history of CA for AF (n = 27) and in patients without a final diagnosis of counterclockwise typical AFL (n=38) the diagnosis capacity of ECGI is consistent compared to the whole study population. The ECGI diagnostic capacity significantly outclassed the ECG one regarding the identification of the involved cavity (p<0.001), the mechanism (p<0.05), and the ablation target (p<0.001). ECGI was able to prevent the totality of unnecessary transseptal punctures (n=7), representing 28% of the overall punctures. Conclusions (Figure B) – This novel non-invasive ECGI system that does not require CT/MRI thoracic imaging accurately characterizes complex atrial tachyarrhythmia and outclasses ECG, the current noninvasive diagnostic tool of reference.

Voltage characterization of abnormal conduction zones in patients affected by atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background In case of persistent atrial fibrillation (AF), atrial substrate assumes a dominant role in sustaining the arrhythmia. Recent studies prove that low voltage areas (LVA, Voltage Amplitude < 0,5 mV) represent an additional target for ablation of AF patients. Purpose The purpose of this study is to analyse whether structural atrial conduction abnormalities (i.e., pivot sites and slow conduction corridors) may occur outside low voltage areas. Methods The study is based on the retrospective analysis of 31 consecutive maps of patients undergoing AF ablation (16 paroxysmal and 15 persistent cases). The clinical procedures have been performed with the support of a mapping system. Sinus rhythm activation maps and bipolar maps used for this analysis have been created with a multipolar mapping catheter. Map points were only acquired when the electrode was in contact with the endocardial tissue to avoid misleading voltage amplitude information. Slow conduction corridors and pivot sites have been analysed. At these sites, EGMs characterization included voltage amplitude (mV), signal duration (ms) and fractionation. Results The average value of EGMs amplitude reported at pivot sites and slow conduction zones, respectively, amounted to 2,08 ± 0,63 mV and 2,1 ± 0,66 mV in paroxysmal cases. In persistent cases, there were slight decreased values to 1,95 ± 0,93 mV and 1,89 ± 0,89 mV. Characterization at pivot sites documented a mean duration value of 45,4 ± 4,64 ms and 49,93 ± 5,51 ms in paroxysmal and persistent patients, respectively, while in slow conduction zones 41,53 ± 7,94 ms and 49,04 ± 6,41 ms have been reported. As for fractionation, more than five deflections per signal have been identified in all abnormal conduction areas. Conclusion Our study proves that functional electrophysiological phenomena can occur outside low voltage areas, even in persistent cases. According to this analysis, not all LVA represent the correct target for catheter ablation, encouraging the development of further methods for investigation of atrial substrate.

Impact of cardiac magnetic resonance channels to localize deceleration zones during VT ablation

Abstract Funding Acknowledgements Type of funding sources: None. Background Cardiac magnetic resonance has demonstrated to accurately identify voltage conduction channels and it is nowadays an important tool to analyze the arrhythmic substrate, to predict ventricular tachycardia (VT) events and to aid VT ablation. The characteristics of CMR channels (CMR-CCs) that predicts the presence of deceleration zone (DZ) have not been explored. Methods Forty-four consecutive patients with scar-related VT undergoing ablation after CMR (October 2018-July 2021) were included (medium age 64.8±11.6 years; 95.5% male; 70.5% ischemic heart disease, mean ejection fraction of 32.3±7.8). Characteristics of CMR-CCs were analyzed and correlation with DZs both in baseline maps and remaps were performed. Patients were prospectively followed for VT recurrence for one year. Results Overall, 129 automatically detected CMR-CCs were analyzed (2.89±1.83 per patient; length: 52.72±65.44mm (0.18–376.73), CC mass: 1.76±2.46grams (0.01–14.59); protectedness 19.02±24.51% (0.01–143.51)). Overall, 73.6% of CMR-CCs were associated with a DZ: 58.1% CMR-CCs in baseline map and 15.5% with a DZs not observed initially but in remaps. The univariate analysis showed that channels associated with DZs were longer (61.83±73.43 vs. 29.96±32.55, OR 1.01, p0.004), with higher border zone mass (2.02±2.75 vs. 1.09±1.44, OR 1.28, p0.031) and more protectedness (21.90±27.23 vs. 11.46±14.20, OR1.02, p0.036). VT recurrence after one-year follow up was 21.95%. Conclusions Pre ablation CMR can accurately identify channels that correlates with DZs that could be targets for ablation, especially those CMR-CCs with higher length, border zone mass and protectedness. Additionally, some channels not related with DZ in the first map have a clear DZ after abolishing the first region of slow conduction, suggesting a very useful role of CMR to detect potential DZs.

Omnipolar technology in ventricular tachycardia ablation: activation and substrate mapping with late activation isochrone analysis under extrastimulus protocol

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The cornerstone of the ablation of eschar-related ventricular tachycardias (VT) is the circumscription of the scar dense zone (DZ)/border zone (BZ) and the identification of regions of slow decremental conduction. The anisotropy of the BZ generates depolarisation waves with rapid changes in their direction that may not be detected by bipolar electrodes, as their identification capacity is orientation-dependent. Omnipolar technology detects the direction and velocity of the wavefront regardless of its orientation. Purpose Describe the effectiveness of the use of omnipolar technology for the development of electroanatomical and activation maps during the study of VT related to scar. Methods Single-centre, observational, descriptive study of a serie of patients: - Patient 1- 72-year-old male with ischaemic heart disease. - Patient 2- 46-year-old male with left arrhythmogenic cardiomyopathy. - Patient 3- 60-year-old male with biventricular arrhythmogenic cardiomyopathy. - Patient 4- 28-year-old female with right arrhythmogenic cardiomyopathy. - Patient 5- 42-year-old male with non-ischemic dilated cardiomyopathy. - Patient 6 - 73-year-old male with arrhythmogenic right cardiomyopathy. Omnipolar technology was used for the creation, under sensed extrastimuli in right ventricular apex protocol, of a voltage map, isochrone late activation map (ILAM), slow decremental conduction (SDC) analysis and, in case of VT induction, activation map with real-time visualisation of conduction vectors ("Strategic-multielectrode-positioning" / StaMP-mapping). Results In patients 1, 2 and 3 ILAM was performed identifying SDC regions. After induction of VT, StaMP-mapping was performed in these regions with identification of the diastolic corridor (image 1A, 1B, 1C). The corridor was eliminated and, subsequently, arrhythmogenic substrate ablation of late potentials in DZ/BZ was performed. In patients 4, 5 and 6 an identical protocol was performed, but VT induction was not achieved, so substrate ablation strategy was performed (image 1D, 1E, 1F). Patient 6 has had a recurrence of sustained VT. Conclusions Omnipolar technology, associated with the extrastimulus protocol, allows a more accurate study of scar-related VT, through the identification of SDC regions. These locations are current targets for substrate ablation and, in many cases, the origin of the critical isthmus.

Microelectrode voltage mapping for substrate assessment in catheter ablation of ventricular tachycardia: a dual-center experience

Abstract Funding Acknowledgements Type of funding sources: None. Background The assessment of the ventricular myocardial substrate critically depends on the size of mapping electrodes, their orientation with respect to wavefront propagation, and interelectrode distance. Objective we conducted a dual-center study to evaluate the impact of microelectrode mapping in patients undergoing catheter ablation (CA) of ventricular tachycardia (VT). Methods We included 21 consecutive patients (median age, 68 [12], 95% male) with structural heart disease undergoing CA for electrical storm (n=14) or recurrent VT (n=7) using the QDOT Micro catheter and a multipolar catheter (PentaRay, n=9). The associations of peak-to-peak maximum standard bipolar (BVc) and minibipolar (PentaRay, BVp) with microbipolar (BVμMax) voltages were respectively tested in sinus rhythm with mixed effect models. Furthermore, we compared the features of standard bipolar (BE) and microbipolar (μBE) electrograms in sinus rhythm at sites of termination with radiofrequency energy. Results BVμMax was moderately associated with both BVc (β=0.85, p<0.01) and BVp (β=0.56, p<0.01). BVμMax was 0.98 (95% CI, 0.93-1.04, p<0.01) mV larger than corresponding BVc, and 0.27 (95% CI, 0.16-0.37, p<0.01) mV larger than matching BVp in sinus rhythm, with higher percentage differences in low voltage regions, leading to smaller endocardial dense scar (2.3 [2.7] vs. 12.1 [17] cm2, p<0.01) and border zone (3.2 [7.4] vs. 4.8 [20.1] cm2, p=0.03) regions in microbipolar maps compared to standard bipolar maps. At sites of VT termination (n=14), μBE were of higher amplitude (0.9 [0.8] mV versus 0.4 [0.2] mV, p<0.01), longer duration (117 [66] ms versus 74 [38] ms, p<0.01), and with greater number of peaks (4 [2] versus 2 [1], p<0.01) in sinus rhythm compared to BE. Conclusions Microelectrode mapping is more sensitive than standard bipolar mapping in the identification of viable myocytes in SR, and may facilitate recognition of targets for catheter ablation.

A new workflow including Coherent algorithm in sinus rhythm for the treatment of Ventricular Tachycardia in patients with scar related heart disease

Abstract Funding Acknowledgements Type of funding sources: None. Background Catheter ablation is a well establish therapy in patients with structural heart disease (SHD) and sustain ventricular tachycardia (VT). Scar substrate modification is one of the two endpoint of a VT ablation procedure. Dechanneling is one of the described successful techniques that shown to be effective for substrate modification Aim This is a pilot study aiming to evaluate the feasibility and the acute efficacy of a new mapping approach for VT ablation with the combination of high density (HD) mapping and Coherent mapping algorithm. Methods All enrolled patients underwent radio frequency catheter ablation (RFCA) for drug-refractory VT or VT storm. Before mapping, programmed ventricular stimulation was performed in all patients for the induction of clinical VT or any other ventricular arrhythmias (VA), if VA was inducible, then electrical cardioversion was conducted to restore sinus rhythm. After transseptal puncture, left ventricular (LV) HD mapping was conducted using a 3D mapping system aiming >5000 mapping points during sinus rhythm, intrinsic atrial rhythm, or ventricular pacing with a multielectrode catheter. During HD mapping, all late potentials (LPs) were tagged as double potentials (DP) and all potentials below 0,2 mV were tagged as scar. Then, Coherent mapping was used to visualize electrical propagation through the LV, based on velocity vector identification, highlighting how the electrical signal enters the scar and identifying the "entrance points" (EP). RFCA was delivered in a power-controlled mode on all the individuated EPs using an open, irrigated-tip ablation catheter with contact force sensor. After RFCA, a second remap was conducted to evaluate the LPs abolition. Then, a programmed ventricular stimulation was performed to validate non inducibility of any VAs. Results 10 consecutive patients (age 71,25±10,32 years, 100% male) undergoing RFCA for drug-refractory VT or VT storm (50%). Acute procedural end-point were: abolition of the LPs and non-inducibility of any VA at the end of the procedure. Abolition of LPs was reached in all cases while non inducibility was reached in 9 patients (90%). Mean procedural time was 214±33,81 min, mean mapping time was 89±15,40 min with mean number of acquired points of 5218±359,56. Mean fluoroscopy time and dose were 15±33,81 min and 5218±7149,8 µGm2, respectively. Mean entrance points identified was 2,6±0,84. In 5 patents (50%), after ablation a modification in the refractory period of the left ventricular myocardium was observed. Mean RF time was 1216±565,46 seconds, with mean number of Visitag of 33±29,98. No acute complication were reported. Conclusion High-density mapping in sinus rhythm combined with Coherent algorithm facilitates the understanding of the substrate and provides targets for effective ablation. This approach has been proven safe and with high acute success rates.

Pulsed-field- vs. cryo- vs. radiofrequency ablation: one-year recurrence rates after pulmonary vein isolation in patients with persistent atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background A multipolar pulsed-field ablation (PFA) catheter has recently been introduced and showed favorable data in terms of safety and procedural efficiency of pulmonary vein isolation (PVI) for atrial fibrillation (AF). Long-term outcome data in comparison to other ablation modalities however is lacking. Purpose To compare procedural and one-year recurrence data of patients with persistent AF (persAF) undergoing a first PVI using PFA, cryoballoon ablation (Cryo), or radiofrequency (RFA). Methods Consecutive patients with persAF undergoing a first PVI with PFA at our institution from May to December 2021 were included. For comparison, patients with persAF undergoing a first PVI with Cryo or RFA between May 2020 and March 2021 were included. A 3-D electro-anatomical mapping system was used in PFA and RFA, but not in Cryo. The following ablation protocols were used to achieve acute PVI: In the PFA group, the standard 32-applications lesion-set and supplementary applications at the discretion of the operator. In the Cryo group, a time-to-effect plus two minutes strategy and in the RFA group following to the CLOSE protocol. Patients were followed with 7d-Holter ECGs 3, 6, and 12 months after ablation. The primary endpoint was recurrence of any atrial arrhythmia following a blanking period of 3 months. Results A total of 177 patients were included (PFA: 65; Cryo: 63; RF: 49). Age, gender, CHA2DS2-VASc score, LVEF and LAVI did not differ among the groups (Table). Median procedure time was different among the groups (PFA: 109 [interquartile range 88-130] min, Cryo: 81 [62-96] min, RF: 177 [153-200] min, p < 0.01). Fluoroscopy dose was different among groups: RF (1.9 [0.7-4.9] Gycm2), PFA (8.3 [4.3-19.0] Gycm2), and Cryo (9.5 [4.8-19.1] Gycm2, p<0.01). Median follow-up time in patients without recurrence was 13 [11-13] months for the PFA group, 13 [12-13] months for the Cryo group and 12 [11-13] months for RFA group. Recurrence of atrial arrhythmias in the KM-analysis after 12 months was not different in all three groups (PFA 44%, Cryo: 33%, RFA: 51%, Figure). Conclusion In patients with persAF, recurrence of atrial arrhythmias 12 months after PFA-PVI only is high, regardless of ablation modality. Assessment of strategies including ablation of extra-PV targets in some patients with persAF is needed.

Identification of atrial complex electrograms by short-coupled extrastimuli in paroxysmal and persistent atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): - Health Council of the Andalusian Regional Government through the project "PI-0057-2017". - European Regional Development Fund/European Social Fund. Introduction Electrogram fractionation during atrial fibrillation (AF) and sinus rhythm have been studied as marker of atrial remodeling and potential target for ablation. Objective The aim of our study was to analyze the response to closely coupled atrial extrastimuli and try to identify areas of hidden slow conduction (HSC) that can promote reentry and AF maintenance in paroxysmal and persistent AF. Methods Twenty consecutive patients with paroxysmal AF and persistent AF (10:10) underwent first PVI procedure. During sinus rhythm triple short coupled extrastimuli was delivered. Locations showing double or highly fragmented electrograms in response to triple extrastimuli were defined as positive electrogram (HSC-EGM) (Figure 1). Increase in duration (delta) of the bipolar EGM was recorded. Two consecutive high-density maps were acquired using a multipolar catheter during AF, sinus and paced rhythms. Spatial correlation of HSC-EGM and complex atrial fractionation (CFAEs) during AF were evaluated. Results Patients with persistent AF showed a higher number and percentage of HSC-EGM than paroxysmal AF (13,9% vs 3,3%, p<0.001) (Figure 2). Delta of EGM duration was 53 ± 22 ms compared to 16 ± 14 ms in sites with a negative response (p<0.001). The number of HSC-EGM distinguished with extrastimuli was lower than that of CFAEs during AF (19 vs 56 per map, p<0.01). The reproducibility of the extension and distribution of HSC-EGM in the repeated maps was superior to that of the CFAEs. The distribution of the HSC-EGM was comparable with those found in the initial map (p=0,32), however, there were significant differences in the distribution of CFAEs between the first map and the remap (p=0.003). Conclusion HSC-EGM in response to triple extrastimuli are more frequent in persistent AF. This type of evoked response could reveal the presence of slow conduction areas and could be considered a potential target for ablation of persistent atrial fibrillation. More studies are needed to confirm this hypothesis.

Determining physiological VT ablation targets in the era of early VT ablation

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Professor Nanthakumar is a recipient of the Mid-career Investigator Award from the Heart & Stroke Foundation of Ontario. Background Ablation targets in the era of early ventricular tachycardia (VT) ablation will likely be driven by substrate-based physiological target approaches rather than activation mapping. Decrement evoked potentials (DeEP) have been co-localized to the diastolic VT circuit and are used as a method to perform VT ablation when VT cannot or should not be induced.1 Traditionally these potentials are evoked by a single extrastimulus. The incremental utility of a second extrastimulus in detecting these potentials has not been evaluated. Purpose We studied the utility of the second extra stimulus (S3) in detecting substrate ablation over the first extra stimulus (S2) following a drivetrain (S1) of 8 beats at 600ms. Methods DeEP was measured as the time difference between the pacing stimulus and the nearfield local activation delay on the bipolar electrogram during the S1 drivetrain and after the S2 or S3 respectively. Decrement of ≥10ms was considered a positive DeEP site. A total of 157 sites from 6 patients with VT were analysed. The incremental value of S3-induced DeEP was compared to the S2-induced DeEP. Results The mean decrement was significantly greater on the S3 compared to the S2 (41.8±35.6ms for S3 vs 25.8±20.4ms for S2, P <0.0001). The mean incremental value of the S3 was 15.9ms (95% CI, 11.5-20.3ms). From the 157 intracardiac electrograms studied, 79.1% had a positive DeEP with S2 alone. At the same electrode locations, an additional S3 evoked DeEP in 82.2% of sites. Conclusion When physiological substrate is present on the first extra stimulus, the second extra stimulus magnifies the identification of the target. However, we found in our study that the second extrastimulus uncovered a hidden arrhythmogenic substrate in only 3.1% additional mapped sites. Consequently, the utility of the second extrastimulus in identification of hidden substrate needs to be balanced with the risk of induction of potentially unstable rhythms.

The effect of scar imaging quality on in-silico pace-mapping of post-infarction ventricular tachycardia

Abstract Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Wellcome Trust and British Heart Foundation. Background In-silico pacing mapping is a technique which involves using an anatomically-personalised image-based computational model to generate a ‘virtual’ clinical pace map for enhanced pre-procedural ablation planning of post-infarction ventricular tachycardia (VT). Utilising, as it does, a direct clinical ECG (or implanted device) recording of the clinical VT in order to construct the map, it has a number of advantages over other computational methods which attempt to simulate patient-specific VTs to identify ablation targets. However, accurate model construction relies on adequate scar imaging data, which may not be available with current clinical cardiac MR (CMR) sequences. Purpose To investigate the impact of scar imaging quality on the ability of in-silico pace-mapping to determine the VT origin. Methods VTs were simulated in three post-infarction porcine heart models reconstructed from high resolution (1mm isotropic) contrast-enhanced CMR data. Visual analysis of the VT circuits was performed to identify the VT site of origin (exit site) in each case (as the gold standard). The ECG of each simulated VT was computed and used as input for the construction of the in-silico virtual pace-mapping approach. Prior to pace map construction, the scar anatomy was modified to represent three different levels of imaging resolution: high resolution scar mapping (default); low resolution scar (representing standing clinical CMR sequences), obtained by performing dilation and erosion in the scar to close all inner pathways; and, finally, no scar (cardiac anatomy only, representing CT-based reconstructions). In-silico pace-mapping was performed by pacing the heart in N = 1000 sites from randomly chosen locations, on both surfaces and intramurally, within close proximity (<5mm) from the infarct. ECG signals computed following each paced activation wavefront were compared to the VT ECG through correlation analysis to construct the virtual pace map. The distance d between the VT exit site and the pacing location with the strongest correlation was also computed. Results As can be seen in Figure 1, correlation between VT and paced ECGs was found to be strongest at pacing locations near the VT exit site in all models. Correlation coefficients were similar in value and distribution in models with high- (min: -0.49±0.27 and max: 0.92±0.05) and low-resolution scars (min: -0.46±0.29 and max: 0.93±0.05). While the correlation map in the absence of scar had smaller values when compared to the other two models (min: -0.50±0.24 and max: 0.71±0.09), the VT exit was still located near the pacing location with the strongest correlation: d = 9.47±2.83 (high-res), d = 6.63±6.35mm (low-res) and d = 18.60±7.10mm (no scar). Conclusion In-silico pace-mapping successfully detected the VT exit sites regardless the resolution of the scar. This finding suggest that the level of infarct anatomical detail has a minor effect on simulated paced activation to localize VT ablation.

Integration of electroanatomical mapping data with whole human heart histology to identify the morphological characteristics of VT substrate in patients with NICM

Abstract Funding Acknowledgements Type of funding sources: None. Introduction The dominant mechanism of ventricular tachycardia (VT) in patients with non-ischemic cardiomyopathy (NICM) is re-entry related to fibrosis. Fibrosis in NICM is fundamentally different from post-infarct scars. Fibrosis does not equal VT substrate. The amount and characteristics of fibrosis related to VT in NICM are unknown. Aim To describe histological characteristics associated with VT substrate in patients with NICM using integration of electroanatomical mapping (EAM) data and whole human heart histology. Methods EAM data of 10 patients with NICM who died or underwent heart transplantation after catheter ablation (CA) for VT were reviewed. VT related sites were categorized as class I (entrainment response/VT termination during CA), or class II (other ablation target sites). Explanted hearts were sliced and stained. Ablation lesions were identified and excluded from histological analysis. EAM and whole heart histology were integrated and class I/II sites projected onto the slices using reversed registration and assigned to a segment (32 segment model). VT exit sites (based on 12 lead VT-ECG) were indicated on a 16-segment model (fig 1). The amount and homogeneity of fibrosis was determined. A new method to measure pattern and inhomogeneity of fibrosis was developed with scores between 0 (inhomogeneous confluent) and 0.5 (homogeneous diffuse). Results In 10 patients (9 with a class IV/V mutation) a median of 11 (range 3-18) VTs were induced. A total of 37 class I sites could be identified and 182/320 segments contained class II sites. After exclusion of ablation lesions, the LV had a median of 24.7% fibrosis (range 11.3-39.3%). Higher percentages of fibrosis were found in the basal anteroseptal ring which also contained the majority of class 1 (21/37) sites. In contrast, VT exit areas were clustered in the apico-septal and basal anterolateral segments. Class 1 VT related site segments contained more fibrosis (median 35.3% IQR [29.1-48.7] vs 22.1% [13.2-32.8], p<0.001) and were more inhomogeneous confluent (median 0.22 IQR [0.185-0.257] vs 0.27 [0.217-0.312], p=0.003) compared to segments without class 1 sites (fig 2). These findings were true for class 2 sites (p<0.004). ROC analysis determined a cut-off of >31% fibrosis for the identification of class I VT related sites (AUC: 0.75, sensitivity 72% specificity 72%). Of note, in segments with <31% fibrosis and class 1 related VT sites, there was a tendency towards inhomogeneous confluent fibrosis compared to those without VT related sites (median score 0.27 vs 0.29). Conclusion In human hearts with NICM and VT, fibrosis clusters in the basal anteroseptal ring. The majority of VT related sites are located in segments with >31% fibrosis and a higher degree of inhomogeneity but they are also found in segments with less fibrosis, but with inhomogeneous confluent fibrosis. This data suggest that location, amount and inhomogeneous confluence of fibrosis contribute to arrhythmogeneity.

Pulsed-field ablation for redo procedures after failed radiofrequency or cryo ablation for atrial fibrillation

Abstract Funding Acknowledgements Type of funding sources: None. Background Pulsed-field ablation (PFA) has recently been introduced for pulmonary vein isolation (PVI). It might also be of potential value for redo procedures after failed radiofrequency or cryo ablation for atrial fibrillation (AF). Purpose To describe our initial experience using a multipolar PFA catheter for redo procedures after failed AF ablation. Methods Consecutive patients undergoing a redo procedure for recurrent atrial arrhythmias at our institution using a multipolar PFA catheter from Mai 2021 until October 2022 were included. A 3D electro-anatomical bipolar voltage map was generated to identify pulmonary vein (PV) reconnection, quantify the level of isolation (antral vs. ostial isolation), and characterize the extent of extra-PV low-voltage tissue. In case of PV reconnection, re-isolation was performed using PFA, with at least four applications in both basket and flower configuration. In case of only ostial PV isolation, additional PFA applications in flower configuration were delivered to widen the isolation to a more antral level. If all veins were already isolated on an antral level and/or if low-voltage areas were found on the posterior wall, a posterior wall ablation was added with the same PFA device at the discretion of the operator. Results We identified 170 patients (mean age: 64 ±11years, 45 (27%) women), undergoing a redo procedure using PFA. The median number of previous ablations was 1 (range 1-6), the most recent ablation was performed using radiofrequency in 122 (72%), cryo in 42 (25%), and surgery in 5 (3%) patients. In 104 (61%) patients, at least one reconnected PV was found. In total, 244 of 680 PV (36%) showed reconnection. In addition to PV reisolation, additional antral applications were delivered in 205 of 436 still isolated veins (47%). Posterior wall ablation was added in 112 (66%) patients (43% in paroxysmal AF, 78% in persistent AF, Figure). Median procedure duration was 101 minutes (IQR 80-137). There was no cardiac tamponade, no stroke, and no esophageal fistula observed in this cohort. Conclusion For patients with recurrence after catheter ablation of atrial fibrillation, re-ablation using PFA is feasible and safe. Most common ablation targets were the pulmonary veins and the posterior wall. Whether the complementary effect of a different technology improves outcome needs further investigation.

The effects of catheter choice on accessory pathway mapping efficiency

Abstract Funding Acknowledgements: Type of funding sources: None. Recent studies have assessed the use of a novel high density (HD) mapping catheter in pediatric patients, finding that the catheter is safe and effective in this population. However, there is a lack of understanding on use patterns of HD mapping technologies in this population and how these patterns affect intraprocedural workflows. The objective of this analysis was to assess the role of mapping catheter choice on the efficiency of accessory pathway localization and ablation in patients with structurally normal hearts treated in a pediatric EP setting. Acute data from 61 accessory pathway ablation cases in patients treated in a pediatric EP setting were prospectively collected from 14 hospitals in 6 countries in Europe and the US. Choice of mapping tools and strategy was left to physician discretion. Procedure data such as map collection duration and statistics were compared across three mapping catheter choices: Ablation Catheter (AC) (n=42), Linear Catheter (LC) (n=9), and HD Grid Catheter (HDC) (n=10). Of the 61 procedures, 16 cases were patients aged 0-12 years (26%), 34 aged 13-17 years (56%), and 5 aged 18+ years (18%). Distribution of catheter use was similar across age groups with HDC use of 13%, 15%, and 27%, respectively. Pathway location did not correlate with catheter choice. There was 0% incidence of congenital heart disease. Mean mapping times in the AC, LC, and HDC groups were 20.6±15.8, 18.8±12.9, and 14.2±13.8 minutes, respectively; differences in mapping times were not statistically significant but trended lower with higher density mapping. The mean number of mapping points used in each group was 44±46, 101±62, and 1521±908 points, respectively (p<.01). Ablation was attempted in 57 (93%) of cases with 100% acute success eliminating accessory pathway conduction. Ablation time was analyzed in patients receiving RF ablation (93% of treated; n=53); mean RF time was 526s in the AC group, 369s in the LC group, and 367s in the HDC group; differences were not statistically significant (p>.05). All groups had similar ablation target technique distributions including timing map and signal morphology. Mean procedure time was 2:11 (h:mm) in the AC group, 1:56 in the LC group, and 1:44 in the HDC group; differences were not statistically significant. Analysis of this cohort of pathways in a pediatric setting shows multipolar catheters may provide more mapping information in shorter times. RF ablation and procedure times also trend shorter in procedures with HD Grid used for mapping, regardless of anatomic location of pathway. Further analysis in a larger cohort may be warranted to validate these findings and explore use of open window mapping described elsewhere.

Optimisation of decrementing evoked potential mapping for functional substrate identification in ischaemic ventricular tachycardia ablation

Abstract Funding Acknowledgements Type of funding sources: None. Background Decrement evoked potential (DeEP) mapping has been shown to identify the functional substrate critical to the Ventricular Tachycardia (VT) circuit with a higher specificity than late potential mapping.[1] However, there is limited data on methodological optimisation of this technique which could identify more relevant regions of conduction delay and functional block that occurs during clinical VT by activating the substrate at coupling intervals closer to the VT cycle length (CL). Purpose The goal of this study was to investigate a range of short coupled extra-stimuli and decrement thresholds to improve DeEP mapping target identification in patients with ischaemic cardiomyopathy. Methods Thirteen patients (70±12 years) underwent VT ablation. Mapping was performed with the Advisor HD Grid multipolar catheter. Maps were generated using omnipolar electrograms (EGMs). DeEP mapping was performed using 3 different extra-stimuli (S2) sequentially in each case: (1) 400 ms (DeEP-400); (2) VT cycle length (VTCL); (3) ventricular effective refractory period (VERP) + 20 ms. For each of the DeEP-400, DeEP-VTCL and DeEP-VERP maps, the definition of a DeEP was altered from the standard 10 ms decrement to multiple thresholds of 10 ms to 50 ms in 10 ms increments (figure 1). DeEP maps were compared to the VT exit site identified with VT activation maps. All patients underwent DeEP-400 focused ablation. Results All patients had 1 clinical VT (VTCL = 353 ± 48 ms; VERP + 20 ms = 300 ± 20 ms). Mean left ventricular ejection fraction was 30 ± 12 %. Sensitivity and specificity analyses (figure 2) show the optimal threshold for defining a DeEP is with an EGM prolongation of ≥ 20 ms for the DeEP-400 (sens. 77%, spec. 79%, ROC AUC 0.84), DeEP-VTCL (sens. 77%, spec. 79%, ROC AUC 0.83) and DeEP-VERP (sens. 69%, spec. 74%, ROC AUC 0.76) maps. Proportional to total mapped area, the DeEP-400 map area was significantly smaller than DeEP-VERP map area (19.0 ± 7.6 % vs 26.4 ± 14.3%; p=0.02). Delivering the S2 at the conventional VERP + 20 ms using a 10 ms decrement definition yielded a sensitivity of 84.6% and a specificity of 62.0% with a target ablation area of 33.9 cm2. With the optimised protocol of delivering the S2 at 400 ms using a 20 ms decrement definition, the sensitivity remains high at 76.9% with an improved specificity of 79.0%, thus reducing the ablation target area by 50% to 16.8 cm2. 92% patients were free of any VT after DeEP-400 guided ablation at 6-month median follow-up. Conclusion In this prospective, mechanistic study utilising omnipolar technology to explore a range of S2 extra-stimuli and decrement thresholds, DeEPs were optimally defined by a conduction delay of ≥ 20 ms with an S2 extra-stimulus coupling interval of 400 ms or VTCL to more accurately localise the VT exit site. This optimised DeEP mapping protocol further refines identification of the critical myocardial sites involved in the initiation and maintenance of VT.

The impact of electroanatomical mapping and VT substrate ablation on primary and secondary prevention ICD indication in patients with repaired Tetralogy of Fallot

Abstract Funding Acknowledgements Type of funding sources: None. Background Patients with repaired tetralogy of Fallot (rTOF) remain at risk for monomorphic ventricular tachycardia (MVT) and sudden cardiac death. Primary prevention ICD implantation studies report annualized rates of appropriate ICD therapy of ≈7% mainly for MVT. Slow conducting anatomical isthmus (SCAI) is the dominant MVT substrate, and SCAI transection by ablation has been associated with favorable long-term outcomes. Electroanatomical mapping (EAM) is the gold standard to identify SCAI. The impact of a systematic approach of EAM and ablation of SCAI on patient selection for ICD implantation is unknown. Objective The study aimed to evaluate the long-term arrhythmic outcome of rTOF patients who underwent EAM and ablation for primary and secondary prevention of MVT. Methods Consecutive patients with rTOF who underwent EAM for VT substrate identification between 2005 and 2020 were included. Indication for EAM were (A) spontaneous VT/cardiac arrest or (B) before re-valving or for risk stratification. In patients with SCAI, catheter or surgical transection was attempted. The risk score for VT/SCD proposed by Khairy et. al was calculated. After successful ablation of SCAI, ICD implantation was offered but subject to shared decision making. Patients were followed for VT and all-cause mortality. Results A total of 125 pts (Group A=28; Group B=97) were included (37±17 years, 62% men, QRS 155±32ms, preserved/mildly reduced LV and RV function 96% and 81%, respectively). A SCAI was present in 59 patients (47%) (A=26, B=33). In 45 patients, 67 MVTs were induced (CL 271±54 ms), of which 63 (94%) were related to SCAI. In 44/61 patients (72%) who underwent ablation, procedural success could be achieved (A 16/27, B 28/34). During a median follow-up of 58 (IQR 27-105) months (36 pts with ICDs), 7 patients died (5 heart failure; 2 non-cardiac cause), and 13 had VT (A=9, B=4). In 12/13 pts with VT, SCAI could not be transected (A=8, B=4), and the remaining patient, who had impaired LV/RV function, recurred with a different VT. In patients without SCAI or successful SCAI transection and preserved/mildly reduced function, no VT occurred (figure). According to the risk score, 22, 27, and 48 of group B patients were classified as high (predicted annualized VT 0%), intermediate (3.8%), and low risk (17.5%). Accordingly, 77/125 (62%) (all 28 pts of group A and 49 patients [intermediate or high risk] of group B) would have been considered candidates for ICD. After implementing the EAM-based approach, 39 patients (18 patients in group A and 21 patients in group B) may remain candidates for ICD implantation, indicating a potential 49% reduction in ICD implantation. Conclusion Patients with successful transection of SCAI had excellent long-term outcome. EAM-based risk stratification and (preventive) ablation targeting SCAI may significantly reduce ICD implantation rates for primary and secondary preventions in rTOF.

Adaptable platform for trapped cold electrons, hydrogen and lithium anions and cations

Cold cations, electrons and anions are ubiquitous in space, participate in star formation chemistry and are relevant to studies on the origin of molecular biology homochirality. We report on a system to generate and trap these species in the laboratory. Laser ablation of a solid target (LiH) facing a sublimating Ne matrix generates cold electrons, anions, and cations. Axial energy distributions (of {{{{{{rm{e}}}}}}}^{-}, {{{{{{rm{H}}}}}}}^{pm } and {{{{{{rm{Li}}}}}}}^{pm }) peaked at 0–25 meV are obtained in a Penning trap at 90 mT and 0.5 eV barrier. Anions can be guided and neutralized with low recoil energy by near–threshold photodetachment. An immediate prospect for this {{{{{{rm{H}}}}}}}^{-} source is to load hydrogen atoms into the ALPHA antihydrogen trap at CERN toward direct spectroscopic comparison of both conjugated species beyond 13 significant figures. The production is potentially scalable and adaptable to different species including deuterium and tritium, relevant for neutrino mass and fusion research.

P57 VOLTAGE CHARACTERIZATION OF ABNORMAL CONDUCTION ZONES IN PATIENTS AFFECTED BY ATRIAL FIBRIALLATION

Abstract Background In case of persistent atrial fibrillation (AF), atrial substrate assumes a dominant role in sustaining the arrhythmia. Recent studies prove that low voltage areas (LVA, Voltage Amplitude < 0,5 mV) represent an additional target for ablation of AF patients. Purpose. The purpose of this study is to analyse whether structural atrial conduction abnormalities (i.e., pivot sites and slow conduction corridors) may occur outside low voltage areas. Methods The study is based on the retrospective analysis of 31 consecutive maps of patients undergoing AF ablation (16 paroxysmal and 15 persistent cases). The clinical procedures have been performed with the support of a mapping system. Sinus rhythm activation maps and bipolar maps used for this analysis have been created with a multipolar mapping catheter. Map points were only acquired when the electrode was in contact with the endocardial tissue to avoid misleading voltage amplitude information. Slow conduction corridors and pivot sites have been analysed. At these sites, EGMs characterization included voltage amplitude (mV), signal duration (ms) and fractionation. Results The average value of EGMs amplitude reported at pivot sites and slow conduction zones, respectively, amounted to 2,08 ± 0,63 mV and 2,1 ± 0,66 mV in paroxysmal cases. In persistent cases, there were slight decreased values to 1,95 ± 0,93 mV and 1,89 ± 0,89 mV. Characterization at pivot sites documented a mean duration value of 45,4 ± 4,64 ms and 49,93 ± 5,51 ms in paroxysmal and persistent patients, respectively, while in slow conduction zones 41,53 ± 7,94 ms and 49,04 ± 6,41 ms have been reported. As for fractionation, more than five deflections per signal have been identified in all abnormal conduction areas. Conclusion Our study proves that functional electrophysiological phenomena can occur outside low voltage areas, even in persistent cases. According to this analysis, not all LVA represent the correct target for catheter ablation, encouraging the development of further methods for investigation of atrial substrate.

The spatiotemporal electrogram dispersion ablation targeting rotors is more effective for elderly patients than non-elderly population.

Modulating atrial fibrillation (AF) drivers has been proposed as one of the effective ablation strategies for non-paroxysmal AF (non-PAF). However, the optimal non-PAF ablation strategy is still under debate because the exact mechanisms of AF persistence including focal activity and/or rotational activity, are not well-understood. Recently, spatiotemporal electrogram dispersion (STED) assumed to indicate rotors in the form of rotational activity is proposed as an effective target for non-PAF ablation. We aimed to clarify the effectiveness of STED ablation for modulating AF drivers. STED ablation plus pulmonary vein isolation was applied in 161 consecutive non-PAF patients not undergoing previous ablation. STED areas within the entire left and right atria were identified and ablated during AF. After the procedures, the STED ablation's acute and long-term outcomes were investigated. (1) Despite a more effective acute outcome of the STED ablation for both AF termination and non-inducibility of atrial tachyarrhythmias (ATAs), Kaplan-Meier curves showed that the 24-month freedom ratio from ATAs was 49%, which resulted from the higher recurrence ratio of atrial tachycardia (AT) rather than AF. (2) A multivariate analysis showed that the determinant of ATA recurrences was only a non-elderly age, not long-standing persistent AF, and an enlarged left atrium, which were conventionally considered as key factors. STED ablation targeting rotors was effective in elderly non-PAF patients. Therefore, the main mechanism of AF persistency and the component of the fibrillatory conduction might vary between elders and non-elders. However, we should be careful about post-ablation ATs following substrate modification.

PO-05-037 EFFICACY AND CLINICAL CHARACTERISTICS OF AVERT-VT: ABLATION AT VIRTUAL-HEART PREDICTED VT

We have previously demonstrated the feasibility of virtual-heart simulations in determining noninvasively the optimal infarct-related ventricular tachycardia (VT) ablation targets and guiding the clinical ablation. We are now proceeding with AVERT-VT, an FDA-approved study for ten prospective patients. To develop the end-to-end personalized computational modeling prediction pipeline enabling AVERT-VT and to assess the corresponding clinical characteristics of the predicted virtual-heart ablation targets. We developed a comprehensive end-to-end computational pipeline enabling AVERT-VT (Fig). 3D LGE-MRI scans with 1.5x1.5mm in-plane spatial resolution and slice thickness <2mm were used to reconstruct the 3D left ventricular (LV) model incorporating deep scar, border (gray) zone, and non-infarcted tissue. In silico rapid pacing from 7 LV regions were performed to induce VTs. The optimal ablation targets were determined by thorough analyses of the wavefront propagation of the induced in silico VTs. A linear ablation connecting a VT ablation target to a transmural deep scar region, the basal region, or the other VT target was performed to eliminate the potential VT pathway formed by the target ablation. Potential emergent VTs in the post-ablation substrate were investigated by repeating the VT induction pacing protocol. This process was iterated until complete VT non-inducibility was achieved. The initial and repeat ablation targets, linear ablations, as well as the LV, right ventricle, infarct area, aortic arch, and left and right coronary cusp geometries, were exported as an ablation strategy plan compatible with the clinical mapping system. The figure presents results from one patient in the clinical study. The ablation plan was successfully imported and co-registered to the patient’s heart. The extent of the model infarct corresponded to the bipolar low-voltage regions. Abnormal electrograms were observed at the proposed targets. 2 VTs were observed during the procedure. Areas of latest activation in sinus rhythm and best pace maps, with a long stimulus to QRS, were found at 2 of the proposed targets. One of the seven proposed targets was not ablated due to the proximity to the left sided His potential. The patient was not inducible of any VT at the end of the procedure. AVERT-VT proposed targets corresponded to abnormal electrograms, and ablating at the targets led to VT non-inducibility.

PO-03-090 NOVEL HIGH RESOLUTION MR IMAGING IMPROVES PRE-PROCEDURE IDENTIFICATION OF ABLATION TARGETS IN POST-INFARCT VENTRICULAR TACHYCARDIA

MRI-based personalized virtual heart models (VHM) are a useful tool for reconstructing scar distribution and identifying VT circuits for planning catheter ablation procedure, an effective therapy for preventing sudden cardiac death from VT in patients with myocardial infarction. However, the MRI resolution used to reconstruct VHMs may not be sufficient to accurately detect all VT circuits, possibly leading to erroneous predictions. To predict catheter ablation targets in the arrhythmogenic substrate using VHMs reconstructed from both clinical and high-resolution 2D MRI datasets and compare the predictions. High-resolution (1.352 x 3mm) short-axis cardiac MRI were acquired by combining two subsequent clinical resolution (1.352 x 6mm) short-axis MRI from nine post-infarct patients undergoing VT ablation. The high-resolution and two clinical MRI were used to reconstruct a total of three personalized VHMs for each patient that represented the patient-specific infarct remodeling. Rapid pacing was used to assess the VT circuits and identify ablation targets in each VHM. Differences in VT inducibility and location were assessed between the high and clinical resolution VHM reconstructions, as well as between the two clinical resolution VHM reconstructions. Virtual ablations were performed to identify emergent VTs and were also compared between the VHMs for each patient. The amount of fibrotic remodeling changed by 12.6 ± 3.3% between the high-resolution and two clinical MRI VHMs for each patient, while the distribution was only moderately affected (Fig 1). The heterogeneity of the myocardium and the fractal dimension (complexity) of the scar tissue was not statistically different between the VHMs for each patient (Fig 1). VT inducibility was observed in all VHMs with an average of 2.7 [1-4] unique VT morphologies induced in each VHM. In two patients, only one clinical VHM was able to identify all the unique VT morphologies observed in the high-resolution VHM. VT exit sites in the clinical MRI VHMs were within 5mm of the exit sites observed in the high-resolution VHMs in 72.2% of cases. Virtual ablations uncovered emergent VT circuits in two of the high-resolution VHMs, compared to only one of the corresponding clinical MRI VHMs. The distribution of ablation targets required to terminate VT was statistically different in 44.4% of cases (Fig 1). VHMs reconstructed from high-resolution MRI more accurately identify VT circuits and may improve catheter ablation outcomes.