Multicenter Study of Dynamic High-Density Functional Substrate Mapping Improves Identification of Substrate Targets for Ischemic Ventricular Tachycardia Ablation

ISS Fro Kin mo Bio Tra the in tha Th ins vis Ma OBJECTIVES The goal of this study was to evaluate the role of dynamic substrate changes in facilitating conduction delay and re-entry in ventricular tachycardia (VT) circuits. BACKGROUND The presence of dynamic substrate changes facilitate functional block and re-entry in VT but are rarely studied as part of clinical VT mapping. METHODS Thirty patients (age 67 9 years; 27 male subjects) underwent ablation. Mapping was performed with the Advisor HD Grid multipolar catheter. A bipolar voltage map was obtained during sinus rhythm (SR) and right ventricular sensed protocol (SP) single extra pacing. SR and SP maps of late potentials (LP) and local abnormal ventricular activity (LAVA) were made and compared with critical sites for ablation, defined as sites of best entrainment or pace mapping. Ablation was then performed to critical sites, and LP/LAVA identified by the SP. RESULTS At a median follow-up of 12 months, 90% of patients were free from antitachycardia pacing (ATP) or implantable cardioverter-defibrillator shocks. SP pacing resulted in a larger area of LP identified for ablation (19.3 mm vs. 6.4 mm) during SR mapping (p 1⁄4 0.001), with a sensitivity of 87% and a specificity of 96%, compared with 78% and 65%, respectively, in SR. CONCLUSIONS LP and LAVA observed during the SP were able to identify regions critical for ablation in VT with a greater accuracy than SRmapping. This may improve substrate characterization in VT ablation. The combination of ablation to critical sites and SP-derived LP/LAVA requires further assessment in a randomized comparator study. (J Am Coll Cardiol EP 2020;-:-–-) © 2020 The Authors. Published by Elsevier on behalf of the American College of Cardiology Foundation. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). N 2405-500X https://doi.org/10.1016/j.jacep.2020.06.037 m the Department of Cardiac Electrophysiology, The Barts Heart Center, St. Bartholomew’s Hospital, London, United gdom; Institute of Cardiovascular Science, University College London, London, United Kingdom; and the Royal Bourneuth and Christchurch Hospitals, United Kingdom. This work was supported by University College London Hospitals medicine National Institute for Health Research. Dr. Srinivasan was supported by a British Heart Foundation Clinical Research ining Fellowship (FS/14/9/30407). Dr. Lambiase was supported by the Medical Research Council (G0901819), Barts BRC, and Stephen Lyness Research Fund. Drs. Srinivasan, Chow, Lowe, Schilling, and Lambiase have received speaker fees from Abbott the last 10 years. Dr. Lambiase has received research grants from Boston Scientific and Abbott. All other authors have reported t they have no relationships relevant to the contents of this paper to disclose. e authors attest they are in compliance with human studies committees and animal welfare regulations of the authors’ titutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, it the JACC: Clinical Electrophysiology author instructions page. nuscript received September 10, 2019; revised manuscript received June 26, 2020, accepted June 29, 2020. ABBR EV I A T I ON S

V entricular tachycardia (VT) is classically associated with re-entrant arrhythmia over a fixed anatomical structure. Activation and entrainment mapping of VT remain the gold standard for identifying critical sites for ablation of VT (1); however, this method is limited by poorly tolerated or nonsustained VT. Several substrate-guided approaches have been developed to overcome this, including scar homogenization (2) and late potentials (LP) mapping (3)(4)(5). However, outcomes when comparing both methods are similar (6), and procedure success can be as low as 47% (7).
A key element in facilitating VT is the presence of dynamic changes within the substrate that may not be evident during sinus rhythm substrate mapping but may form a critical aspect of the tachycardia mechanism when conduction velocity slows dynamically and tissue refractory periods lengthen. We have previously described dynamic substrate changes within regions of myocardial scar and LP (8). Several methods have been studied to invoke dynamic substrate changes in critical regions for ablation, including decrement-evoked potential (DEEP) mapping (9,10), which involves a drive train and S2 pacing protocol, and evoked delayed potential mapping, in which electrogram changes during right ventricular (RV) drive train pacing and S1 to S2 pacing are examined (11). However, VT on device traces is often seen to be initiated by single extrasystolic beats (12,13).
The current study aimed to investigate dynamic substrate changes to local abnormal ventricular activity (LAVA) and LP, in relation to critical sites for VT ablation using high-resolution mapping of the ventricle with the Advisor HD Grid (Abbott, Inc., Abbott Park, Illinois), during short coupled single extrastimuli from the right ventricle ( Figure 1C).
LP were defined, as per published literature (3,5), as isolated high-frequency local electrograms after the offset of the terminal portion of the QRS. To assess local activation time of LP, the window of interest was set at þ500 ms from reference.
Following this, activation complemented by entrainment mapping of induced VTs were performed in 21 patients, 9 of whom also had pace mapping performed for additional conformation. The critical isthmus during entrainment mapping was considered according to established criteria (1). Where mapping/ entrainment in VT was not possible, a pace map strategy was used (9 of 30 patients); we aimed for a match >96% to the clinical VT, as previously described (14). A total of 75 VTs were entrained (n ¼ 45) or pace mapped (n ¼ 30) in 30 patients.
Ablation was then performed to sites of best entrainment/pace map and all LP and LAVA substrates defined by the Barts SP, using the TactiCath Ablation Catheter (Abbott Inc.), irrigated at a power of 50 W, targeting a lesion size index of 7 for each lesion.
Procedure endpoint was VT noninducibility. Noninducibility was confirmed by programmed electrical stimulation, with a drive at 600 ms and 400 ms performed until ERP at S4 from the RV apex and base.
Nonclinical VTs were not ablated.
DATA COLLECTION AND ANALYSIS. Substrate maps were collected by using the Advisor HD Grid Subsequently, a new window of interest was set within the mapping system that contained the entire diastolic interval, and the TurboMap feature was used to identify the latest LP from the Barts SP data. The system was set to annotate the latest LP identified within the diastolic window, and these were then individually checked and manually corrected ( Figure 1C).        Our findings differ significantly from the DEEP mapping (9)