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Background: The circuit boundaries for reentrant ventricular tachycardia (VT) have been historically conceptualized within a 2-dimensional (2D) construct, with their fixed or functional nature unresolved. This study aimed to examine the correlation between localized lines of conduction block (LOB) evident during baseline rhythm with lateral isthmus boundaries that 3-dimensionally constrain the VT isthmus as a hyperboloid structure., Methods: A total of 175 VT activation maps were correlated with isochronal late activation maps during baseline rhythm in 106 patients who underwent catheter ablation for scar-related VT from 3 centers (42% nonischemic cardiomyopathy). An overt LOB was defined by a deceleration zone with split potentials (≥20 ms isoelectric segment) during baseline rhythm. A novel application of pacing within deceleration zone (≥600 ms) was implemented to unmask a concealed LOB not evident during baseline rhythm. LOB identified during baseline rhythm or pacing were correlated with isthmus boundaries during VT., Results: Among 202 deceleration zones analyzed during baseline rhythm, an overt LOB was evident in 47%. When differential pacing was performed in 38 deceleration zones without overt LOB, an underlying concealed LOB was exposed in 84%. In 152 VT activation maps (2D=53, 3-dimensional [3D]=99), 69% of lateral boundaries colocalized with an LOB in 2D activation patterns, and the depth boundary during 3D VT colocalized with an LOB in 79%. In VT circuits with isthmus regions that colocalized with a U-shaped LOB (n=28), the boundary invariably served as both lateral boundaries in 2D and 3D. Overall, 74% of isthmus boundaries were identifiable as fixed LOB during baseline rhythm or differential pacing., Conclusions: The majority of VT circuit boundaries can be identified as fixed LOB from intrinsic or paced activation during sinus rhythm. Analysis of activation while pacing within the scar substrate is a novel technique that may unmask concealed LOB, previously interpreted to be functional in nature. An LOB from the perspective of a myocardial surface is frequently associated with intramural conduction, supporting the existence of a 3D hyperboloid VT circuit structure. Catheter ablation may be simplified to targeting both sides around an identified LOB during sinus rhythm., Competing Interests: Disclosures Dr Tung has received consulting and speaking honoraria from Abbott, Biosense-Webster, and Boston Scientific.

Background: Catheter ablation strategies for ventricular fibrillation (VF) and polymorphic ventricular tachycardia (PMVT) are not established when spontaneous triggers are rare or absent., Objective: The purpose of this study was to report the feasibility and efficacy of a novel empiric ablation strategy of pacemapping to stored implantable cardioverter-defibrillator (ICD) template electrograms (SITE) of the clinical premature ventricular contraction (PVC) trigger., Methods: Fifteen patients with drug-refractory VF/PMVT receiving defibrillator shocks without identifiable and mappable PVC triggers were prospectively analyzed. The protocol incorporated systematic pacemapping from known arrhythmogenic sites (moderator band/right ventricular [RV] papillary muscles, left conduction system/Purkinje network, outflow tracts) with real-time comparison between the paced ICD electrogram (EGM) morphology and SITE., Results: Regions within the left Purkinje network yielded the best pacemap match for the SITE of the clinical PVC trigger in 55% of ablation targets (left posterior fascicle 6, left septal fascicle 1, left anterior fascicle 5), followed by the RV moderator band region in 14% (n = 3), RV papillary muscles in 13% (n = 3), periaortic region in 14% (n = 3), and left ventricular anterolateral papillary muscle in 4% (n = 1). Freedom from ICD therapies off antiarrhythmic drug (AAD) was 64% at 6 months and 48% at 12 months. Shock burden was reduced from 4 (2-6) to 0 (0-1) (P = .001), and use of AADs was reduced from 2 (1-2) to 0 (0-1) (P = .001)., Conclusion: In the absence of a mappable trigger, an empiric strategy of interrogating the Purkinje network, papillary muscles, and outflow tract regions by pacemap matching with SITE of the clinical PVC is feasible to guide ablation. A significant reduction in VF/PMVT therapy burden and AAD utilization was observed after a single procedure., (Copyright © 2021 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: While advances in the characterization of the structural substrate in arrhythmogenic right ventricular cardiomyopathy (ARVC) have been made, the ventricular tachycardia (VT) circuit remains incompletely described., Objective: The purpose of this study was to delineate the reentrant VT circuit with simultaneous epicardial and endocardial mapping (SEEM) in ARVC., Methods: Twenty-three consecutive patients with ARVC and VT underwent SEEM at 4 centers between 2014 and 2020. Retrospective analysis was performed on combined isochronal activation maps., Results: Of the 30 VT circuits, 24 were delineated with SEEM (956 [341-1843] endocardial points and 1763 [882-3054] epicardial points). The apex and outflow tract rarely harbored VT circuits, with 50% distributed in the inferior wall and 43% in the free wall. The entire tachycardia cycle length was recorded from the epicardium in 71% of circuits. In all circuits, a large proportion of the tachycardia cycle length was recorded from the epicardium relative to the endocardium. Localized epicardial reentry was observed in 35% of patients (14 mm × 15 mm), which was associated with smaller endocardial low voltage area (39 cm 2 vs 104 cm 2 ; P = .002) and preserved right ventricular ejection fraction (35% vs 25%; P = .046) compared with those with larger circuit dimensions. Seventy percent of termination sites were achieved from the epicardium., Conclusion: High-resolution recordings from both myocardial surfaces confirm a consistent predominance of epicardial participation during reentry in ARVC. Only the perivalvular inflow region of the "triangle of dysplasia" had a strong propensity to harbor VT circuits, with the greatest proportion located in the inferior wall. Localized epicardial reentry may be a manifestation of earlier stage disease with a relative paucity of endocardial substrate., (Copyright © 2021 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Objectives: This study sought to describe arrhythmia characteristics using ultra-high density (UHD) mapping of macro-re-entrant left atrial flutter (LAFL) which propagate via epicardial bridging (EB), and highlight regional anatomy that poses challenges to ablation., Background: Three-dimensional propagation via EB may contribute to the maintenance and complexity of LAFL., Methods: UHD activation maps of macro-re-entrant LAFL created with a mini-electrode basket catheter were analyzed between June 2015 and March 2020. EB was defined as a region of wave front discontinuity with focal activation distal to an activation gap. Regions of EB were correlated with anatomic structures known to have specialized epicardial bundles. Direct evidence of EB was obtained via percutaneous epicardial access (n = 22) with simultaneous epicardial recordings during endocardial activation gaps., Results: Among 159 patients who underwent LA endocardial procedures with UHD mapping, 43 patients with 47 macro-re-entrant LAFLs were included in this analysis. Evidence of EB was present in 38% of LAFLs. Four anatomic areas of EB were observed: coronary sinus (17%), vein of Marshall (28%), Bachmann's region (33%), and region of the septopulmonary bundle (22%). All 47 LAFLs were successfully ablated. Percutaneous epicardial mapping yielded direct evidence for EB in 9 patients with LAFL (41%). At 23 ± 13 months, 70% remained free from recurrent LAFL., Conclusions: In a selected population, UHD mapping demonstrates evidence of EB in 38% of cases of LAFL involving 4 distinct epicardial anatomic regions. Identification of discontinuous 3-dimensional activation patterns with attention to correlative regional LA anatomy may reduce the incidence of ablation failures for complex re-entry., Competing Interests: Author Disclosures Drs. Nayak and Tung have received speaker honoraria from Boston Scientific. Ms. Kwasnik and Mr. Lee are employees of Boston Scientific. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2020 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Objectives: This study aimed to evaluate the feasibility and accuracy of using a novel grid mapping catheter during scar-related ventricular tachycardia (VT) ablation., Background: Ultra-high-density (UHD) mapping improves identification of local abnormal ventricular activities (LAVAs) and characterization of scar substrates., Methods: Consecutive patients underwent endocardial and/or epicardial ablation guided by a HD grid mapping catheter. A linear duodecapolar catheter was used in the initial cases for systematic correlation. Isochronal late activation mapping was performed during sinus rhythm to identify deceleration zones, and activation mapping of VT was performed when tolerated., Results: In 38 patients, 51 electroanatomic maps (left ventricle: 26, epicardium: 21, right ventricle: 4) were created using a grid catheter. LAVAs were identified in 98% of cases and deceleration zones were observed in 86%. High-frequency electrograms with diastolic activation were identified during 44 sustained monomorphic VTs, and the critical isthmus was colocalized to deceleration zones during sinus rhythm in 96% of cases. In 17 cases that underwent sequential mapping with both grid and linear catheters, the low voltage area detected using the grid (HD wave) was significantly smaller, with ratios of 0.61 (<0.5 mV) and 0.81 (<1.5 mV) relative to the duodecapolar catheter., Conclusions: VT ablation guided by a novel HD grid catheter is safe and feasible for clinical use in human scar-related VT via both endocardial and epicardial approaches. Automated selection of larger bipolar amplitudes among orthogonal pairs consistently displayed smaller low voltage areas than a previously validated linear catheter., (Copyright © 2020 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Recurrences of atrial fibrillation (AF) after ablation have been attributed to conduction gaps and nontransmural ablation lesions., Objective: The purpose of this study was to assess the feasibility of adjunctive percutaneous mapping of the epicardial regions of the left atrium to characterize the transmural extent of substrate and ablation lesions., Methods: Between 2014 and 2018, combined epicardial and endocardial mapping of AF was performed in 18 patients via an inferior subxiphoid percutaneous approach (16 with previously failed ablation procedures and 2 patients with long-standing persistent AF) at 2 centers. Epicardial substrate mapping was compared with endocardial mapping to assess transmural uniformity., Results: Of 18 patients, 4 (22%) demonstrated nontransmural atrial low-voltage regions with relative epicardial sparing in the left atrial posterior wall. Transmural isolation of the posterior wall was achieved after an endocardial "box" lesion set in 6/9 (67%), guided by epicardial voltage data, while epicardial and endocardial dissociation during AF was observed in 1 patient. In 3 patients, epicardial capture along the endocardial pulmonary vein lesion set despite endocardial capture loss and bidirectional block was observed. Two cases of mitral flutter were terminated from the epicardium. A balloon was positioned in the pericardial space in 6 patients for esophageal protection during ablation., Conclusion: A percutaneous epicardial approach for mapping and ablation of the left atrium is feasible in the electrophysiology laboratory during endocardial catheter ablation for AF and may be useful as an adjunctive approach in refractory cases. High-density epicardial mapping can provide direct evidence of nonuniform lesion and substrate transmurality of the human left atrium before and after ablation., (Copyright © 2019 Heart Rhythm Society. Published by Elsevier Inc. All rights reserved.)

Background: While early precordial electrocardiographic (ECG) characteristics are useful to differentiate left-sided from the right-sided outflow tract ventricular arrhythmia (OTVA), few patterns predict an origin from the septal margin of the left ventricular (LV) summit.Objective: The purpose of this study was to report mapping and ablation characteristics of a new ECG pattern with left bundle branch morphology and an abrupt R-wave transition in lead V3 (ATV3).Methods: Over a 3-year period, 78 consecutive patients (mean age 57±15 years; 35% female) with OTVA were referred for mapping and ablation. Twenty patients (26%) exhibited an ATV3 pattern, of whom 65% failed prior ablation.Results: Ninety-two percent of patients with ATV3 that underwent simultaneous epicardial and endocardial mapping demonstrated an intramural or epicardial site of origin. Eighty percent of OTVA with ATV3 was eliminated by ablation from the vantage point of the interleaflet triangle below the right-left coronary junction. The ATV3 pattern showed higher sensitivity, specificity, predictive value, and accuracy than validated ECG criteria (notch or "w" pattern in lead V1, qrS pattern in leads V1 through V3, and pattern break V2) for predicting successful ablation in the region of the anterior LV ostium. At 12±11 months, freedom from ventricular arrhythmia recurrence was 89% and 82% in the ATV3 and control groups, respectively.Conclusion: ATV3 is a simple and distinct ECG pattern indicative of a site of origin from the septal margin of the LV summit. The right-left aortic interleaflet triangle vantage point was effective to eliminate OTVA with ATV3 that overwhelmingly exhibited the earliest activation from the epicardium or mid-myocardium. Test characteristics for ATV3 were superior to ECG patterns validated for the anterior LV ostium. [ABSTRACT FROM AUTHOR]

Background: The mechanisms for scar-related ventricular tachycardia (VT) originating from the periaortic region remain incompletely characterized.Objective: The purpose of this study was to map the circuits responsible for periaortic VT in high resolution.Methods: Cases with periaortic VT (2016-2020) were analyzed to characterize the substrate and mechanisms with multielectrode mapping. Periaortic VT was defined as low-voltage and/or deceleration zones within 2 cm of the left ventriculoaortic junction with a corresponding critical site during VT.Results: Forty-nine periaortic monomorphic VTs were analyzed in 30 patients (25% of all patients with nonischemic cardiomyopathy). Isolated periaortic substrate was observed in 27% of patients, with 73% having concomitant scar, most commonly in the mid-septum (47%). Deceleration zones were equally prevalent on the septal and lateral portions of the periaortic region (87% vs 73%; P = .19). During activation mapping of VT (tachycardia cycle length 392 ± 105 ms), localized reentrant patterns of activation (14 mm [10-17 mm] × 10 mm [7-14 mm]) were demonstrated in 63% and 37% of VTs showed centrifugal activation, consistent with a focal breakout pattern. Ninety-three percent of VTs fulfilled criteria for a reentrant mechanism. Sixty-five percent of reentrant circuits had endocardial activation gaps within the tachycardia cycle length (3-dimensional circuitry), which were associated with higher rates of recurrence as compared with 2-dimensional complete circuits at 1 year (73% vs 37%; P = .028).Conclusion: Periaortic VTs were observed in 25% of patients with nonischemic cardiomyopathy and scar-related VT. For the first time, localized reentry confined to this anatomically challenging region was demonstrated as the predominant mechanism by high-resolution circuit activation mapping. [ABSTRACT FROM AUTHOR]

BACKGROUND: The circuit boundaries for reentrant ventricular tachycardia (VT) have been historically conceptualized within a 2-dimensional (2D) construct, with their fixed or functional nature unresolved. This study aimed to examine the correlation between localized lines of conduction block (LOB) evident during baseline rhythm with lateral isthmus boundaries that 3-dimensionally constrain the VT isthmus as a hyperboloid structure. METHODS: A total of 175 VT activation maps were correlated with isochronal late activation maps during baseline rhythm in 106 patients who underwent catheter ablation for scar-related VT from 3 centers (42% nonischemic cardiomyopathy). An overt LOB was defined by a deceleration zone with split potentials (≥20 ms isoelectric segment) during baseline rhythm. A novel application of pacing within deceleration zone (≥600 ms) was implemented to unmask a concealed LOB not evident during baseline rhythm. LOB identified during baseline rhythm or pacing were correlated with isthmus boundaries during VT. RESULTS: Among 202 deceleration zones analyzed during baseline rhythm, an overt LOB was evident in 47%. When differential pacing was performed in 38 deceleration zones without overt LOB, an underlying concealed LOB was exposed in 84%. In 152 VT activation maps (2D=53, 3-dimensional [3D]=99), 69% of lateral boundaries colocalized with an LOB in 2D activation patterns, and the depth boundary during 3D VT colocalized with an LOB in 79%. In VT circuits with isthmus regions that colocalized with a U-shaped LOB (n=28), the boundary invariably served as both lateral boundaries in 2D and 3D. Overall, 74% of isthmus boundaries were identifiable as fixed LOB during baseline rhythm or differential pacing. CONCLUSIONS: The majority of VT circuit boundaries can be identified as fixed LOB from intrinsic or paced activation during sinus rhythm. Analysis of activation while pacing within the scar substrate is a novel technique that may unmask concealed LOB, previously interpreted to be functional in nature. An LOB from the perspective of a myocardial surface is frequently associated with intramural conduction, supporting the existence of a 3D hyperboloid VT circuit structure. Catheter ablation may be simplified to targeting both sides around an identified LOB during sinus rhythm. [ABSTRACT FROM AUTHOR]

Background: Fast ventricular tachycardias (VTs) have historically been attributed to shorter path lengths with smaller reentrant circuit dimensions in animal models. The relationship between the dimensions of the reentrant VT circuit and tachycardia cycle length (TCL) has not been examined in humans. This study aimed to analyze the determinants of the rate of human VT with comparison of circuit dimensions and conduction velocity (CV) across a wide range of both stable and unstable VTs delineated by high-resolution mapping.Methods: Fifty-four VTs with complete circuit delineation (>90% TCL) by high-resolution multielectrode mapping were analyzed in 49 patients (men, 88%; age, 65 years [58-71 years]; nonischemic, 47%). Fast VT was defined as TCL <333 milliseconds (rate >180 bpm). Unstable VT was defined by hemodynamic deterioration with an intrinsic mean arterial pressure <60 mm Hg during a sustained episode.Results: The median TCL of VT was 365 milliseconds (306-443 milliseconds), and 24 fast VTs were characterized. A wide range of CVs was observed within the entrance (0.03-0.55 m/s), common pathway (0.03-0.77 m/s), exit (0.03-0.53 m/s), and outer loop (0.17-1.13 m/s). There were no significant differences in the median dimensions of the isthmus and path length between fast and slow VTs and between unstable and stable VTs. The outer loop CV was the only circuit component that correlated with TCL in both ischemic cardiomyopathy (r=-0.5, P=0.006) and nonischemic cardiomyopathy (r=-0.45, P=0.028). The duration of the longest diastolic electrogram was inversely correlated with the dimensions of common pathway (length: r=-0.46, P=0.001, width: r=-0.3, P=0.047) and predictive of rapid VT termination by a single radiofrequency application (r=-0.41, P=0.023).Conclusions: Because of a wide spectrum of CV observed within the reentrant path during human VT, the dimensions of the circuit were not predictive of VT cycle length. For the first time, we demonstrate that the CV of the outer loop, rather than isthmus, is the principal determinant of the rate of VT. The size of the circuit was similar between fast and slow VTs and between unstable and stable VTs. Long, continuous electrograms were indicative of spatially confined isthmus dimensions, confirmed by rapid termination of VT during radiofrequency delivery. [ABSTRACT FROM AUTHOR]