Mitigating Esophageal Injury after Atrial Fibrillation Ablation Guided by Ablation Index; CLOSEr to goalJason S. Chinitz, MD1 and Eli Q. Harris, MD21.South Shore University HospitalNorthwell HealthBay Shore, NY2. Nassau University Medical CenterEast Meadow, NYFinancial support : none.Disclosures : Dr. Chinitz serves on the scientific advisory board for Biosense Webster and has received consulting fees
Abstract: After several years with sobering experiences with electrogram-based AF ablation approaches, Seitz et al present with the VX1 software a reliable tool to map and ablate spatio-temporal dispersion. The presented multicenter study in persistent AF patients was conducted in 1 expert and 7 satellite centers with a total of 17 operators, using the VX1 software to detect and subsequently ablate spatiotemporal dispersion. While the AF termination rate (88%) and the freedom from AF in 12 months FU (82%) was very encouraging, the VX1 software, using AI enhanced electrogram adjudication, achieved very similar results in all centers, regardless of the centre’s or the operator’s experience. Thus, the biggest criticism of electrogram-based ablation strategies, i.e. the lack of reproducibility in “non-expert” centers, seems to be finally addressed.
CT-imaging vs. high-density mapping in ischemic cardiomyopathy VT ablation: in whom do we trust?Thomas Fink, MD1, Vanessa Sciacca, MD1, Philipp Sommer, MD11Clinic for Electrophysiology, Herz- und Diabeteszentrum NRW, Ruhr-Universität Bochum, Bad Oeynhausen, Germany.Disclosures: PS is advisory board member of Abbott, Biosense Webster, Boston Scientific and Medtronic.Funding: (None)
Employing New Criteria for Confirmation of Conduction Pacing – Achieving True Left Bundle Branch Pacing May Be Harder Than Meets the EyeJoshua Sink, MD1, Nishant Verma, MD, MPH2Northwestern University, Feinberg School of Medicine, Department of Internal MedicineNorthwestern University, Feinberg School of Medicine, Division of CardiologyCorresponding Author:Nishant Verma, MD, MPH251 East Huron Street, Feinberg 8-503Chicago, IL 60611312-926-2148Nishant.Verma@nm.orgFunding: NoneDisclosures: Dr. Sink has nothing to disclose. Dr. Verma receives speaker honoraria from Medtronic, Biotronik and Baylis Medical and consulting fees from Boston Scientific, Biosense Webster, AltaThera Pharmaceuticals and Knowledge 2 Practice.Word Count: 1200In recent years, conduction system pacing (CSP) has garnered significant attention from the electrophysiology (EP) community. This movement has been driven by the hypothesis that using the natural conduction system activation is desirable and clinically beneficial in patients with advanced conduction disease and ventricular desynchrony. Permanent His-bundle pacing (PHBP) is generally seen as the purest form of conduction system activation. (Figure 1) PHBP was first described over 20 years ago but the idea has attracted substantial investigative effort in recent years. When successfully achieved, His bundle pacing has been associated with reduction in mortality, reduction in heart failure (HF) admissions, and improvement in left ventricular (LV) function compared to right ventricular (RV) pacing.1 Despite this, consistent achievability in real-world practice remains limited due to a variety of factors including narrow anatomic targetability, lead stability, high pacing thresholds, low ventricular sensing, and inability to correct the QRS in bundle branch block.2Thus, while waiting for the next iteration of improved delivery techniques, pacing leads and programming algorithms,, alternative methods of conductive system pacing have emerged, with the potential to surmount the challenges described.Left bundle branch pacing (LBBP) has recently emerged as an alternative method of CSP. The technique was first described by Huang et al. in 2017 and has seen a momentous rise in interest since.3 In 2019, Huang et al. produced a user manual for a successful LBBP procedure, and in it they attempted to develop the first iteration of criteria for the confirmation of LBBP.4 Utilizing these criteria, or close variations of them, a number of studies were published afterwards that demonstrated preliminary safety, feasibility, and efficacy of LBBP.5,6,7 LBBP became an attractive alternative to His bundle pacing because of the lower thresholds, improved lead stability, and higher procedural success rates. When compared against RV pacing in patients requiring a high burden of pacing, LBBP has demonstrated reduced mortality, HF admissions, and need for upgrade to a BiV device.8 In a small, non-randomized patient sample, LBBP showed greater improvement in LV ejection fraction (EF) compared to BiV pacing.9 Most notably, perhaps, is the astonishing rate of lead placement success, with achievement rates reported as high as 98% in sizable studies.6Differences between the two forms of CSP were apparent from the beginning, including in the appropriate QRS morphology after a successful case. Unlike PHBP, LBBP did not reproduce the native QRS and the QRS duration was often greater than at baseline (Figure 2). The arena of LBBP underwent a notable shift in the Fall of 2021 when Wu et al. proposed new criteria to prove LBBP.10 In this study, they presented an exquisite display of fundamental electrophysiologic principles by using mapping catheters positioned on the His and LV septum during LBB lead placement. Through this painstaking work, they clarified the difference between true LBBP and left bundle branch area pacing (LBBAP), which can incorporate both LBBP and left ventricular septal pacing (LVSP). In their proposed framework, without the presence of a His or LV septum mapping catheter, output dependent QRS transition from non-selective (NS-LBBP) to selective-LBBP (S-LBBP) or LVSP is necessary to prove LBBP and had a sensitivity and specificity of 100%.The present study by Shimeno et al, published in the current issue of the Journal of Cardiovascular Electrophysiology , is the first known effort to document achievement rates of LBBP by utilizing the modified criteria proposed by Wu et al.11 The primary finding of the study is that achieving true LBBP with an acceptable pacing threshold is likely harder than previously realized. As expected, there was improvement after a learning curve, but even in the last third of patients enrolled, the achievement rate of LBBP was only 50%. This is dramatically lower than previously reported achievement rates using the original Huang et al. criteria, and it suggests that not all patients in the previously described studies were actually achieving true LBBP. An unknown subset of patients in these studies was likely only achieving LVSP. This is probably due to a prior reliance on indicators such as a paced right bundle branch block (RBBB) pattern, identification of an intrinsic LBB potential, and/or use of V6 R-wave peak time cutoffs (RWPT) without clear output-dependent QRS transition. It is also worth noting that a variety of RWPT cutoffs have been used seemingly arbitrarily as ‘evidence of LBBP’. This presents a major dilemma and highlights the need for a clear set of LBBP criteria to be defined by the collective EP community. Despite these caveats, many of these previous studies did not fully confirm LBBP in their patients, yet the outcomes from these studies were still clinically promising. This raises the obvious question, does obtaining true LBBP matter? Future studies will need to explore the differences in clinical outcomes between true LBBP and LVSP.Secondarily, Shimeno et al. have provided a useful tool in identifying that LBB potential to QRS-onset ≥ 22ms had a specificity of 98% in predicting LBBP.11 This target measure can help future operators ensure proximal enough engagement of the LBB conduction system. Additionally, the group took a close look at validating a RWPT cutoff time for the prediction of LBBP. Unfortunately, a RWPT cutoff of 68 ms (in non-LBBB patients), determined by the ROC curve, was not highly predictive. This runs contrary to previous reports by Wu et al. and Jastrzebski et al., which reported higher predictive value of RWPT cutoffs10,12 Looking at the data surrounding RWPT cutoffs as a collective, it likely should not be used as a primary metric for confirming LBBP due to imperfect sensitivity and specificity, but it may be an alternative if output dependent QRS transition or change in RWPT of ≥10 ms is not observed. Additionally, in the event that capture thresholds are similar between the LBB and the adjacent myocardium, programmed stimulation is an option to try to reveal a QRS transition by exploiting differences in refractory periods.This study also highlighted one of the unique complications of LBBP by demonstrating a high rate of septal perforation. Paradoxically, more perforations were seen with increased experience, likely highlighting that deeper penetration into the septum is often sought as operators become more familiar with the procedure. The long-term clinical implications of this complication are, thus far, unknown.Looking forward, clear guidelines for confirmation of LBBP need to be defined. This is necessary to ensure quality before undertaking multi-center randomized controlled trials to assess LBBP in comparison to current pacing methods. To date, Wu et al. seem to have provided the best framework to achieve this.10 That said, there are concerns given that this has only been validated in 30 patients (and only 9 with LBBB). In an ideal world, these criteria would be validated in a larger population, though the work to accomplish this would be meticulous given the current gold standard of using an LV septal mapping catheter to prove conduction system capture. Shimeno et al. should be congratulated for their effort in putting this framework to practice. In their work, they have demonstrated that achieving true LBBP as defined by Wu et al. may be harder than meets the eye, and this is very important in assessing the practicality of using LBBP as a widespread alternative to other pacing methods.References:Abdelrahman M, Subzposh FA, Beer D, et al. Clinical Outcomes of His Bundle Pacing Compared to Right Ventricular Pacing. J Am Coll Cardiol . 2018;71(20):2319-2330. doi:10.1016/j.jacc.2018.02.048Zanon F, Abdelrahman M, Marcantoni L, et al. Long term performance and safety of His bundle pacing: A multicenter experience. J Cardiovasc Electrophysiol . 2019;30(9):1594-1601. doi:10.1111/jce.14063Huang W, Su L, Wu S, et al. A Novel Pacing Strategy With Low and Stable Output: Pacing the Left Bundle Branch Immediately Beyond the Conduction Block. Can J Cardiol . 2017;33(12):1736.e1-1736.e3. doi:10.1016/j.cjca.2017.09.013Huang W, Chen X, Su L, Wu S, Xia X, Vijayaraman P. A beginner’s guide to permanent left bundle branch pacing. Heart Rhythm . 2019;16(12):1791-1796. doi:10.1016/j.hrthm.2019.06.016Padala SK, Master VM, Terricabras M, et al. Initial Experience, Safety, and Feasibility of Left Bundle Branch Area Pacing: A Multicenter Prospective Study. JACC Clin Electrophysiol . 2020;6(14):1773-1782. doi:10.1016/j.jacep.2020.07.004Su L, Wang S, Wu S, et al. Long-Term Safety and Feasibility of Left Bundle Branch Pacing in a Large Single-Center Study. Circ Arrhythm Electrophysiol . 2021;14(2):e009261. doi:10.1161/CIRCEP.120.009261Huang W, Wu S, Vijayaraman P, et al. Cardiac Resynchronization Therapy in Patients With Nonischemic Cardiomyopathy Using Left Bundle Branch Pacing. JACC Clin Electrophysiol . 2020;6(7):849-858. doi:10.1016/j.jacep.2020.04.011Sharma PS, Patel NR, Ravi V, et al. Clinical outcomes of left bundle branch area pacing compared to right ventricular pacing: Results from the Geisinger-Rush Conduction System Pacing Registry. Heart Rhythm . 2022;19(1):3-11. doi:10.1016/j.hrthm.2021.08.033Wu S, Su L, Vijayaraman P, et al. Left Bundle Branch Pacing for Cardiac Resynchronization Therapy: Nonrandomized On-Treatment Comparison With His Bundle Pacing and Biventricular Pacing. Can J Cardiol . 2021;37(2):319-328. doi:10.1016/j.cjca.2020.04.037Wu S, Chen X, Wang S, et al. Evaluation of the Criteria to Distinguish Left Bundle Branch Pacing From Left Ventricular Septal Pacing. JACC Clin Electrophysiol . 2021;7(9):1166-1177. doi:10.1016/j.jacep.2021.02.018Shimeno K, Tamura S, Hayashi Y, et al. Achievement Rate and Learning Curve of Left Bundle Branch Capture in Left Bundle Branch Area Pacing Procedure Performed to Demonstrate Output-Dependent QRS Transition.J Cardiovasc Electrophysiol . 2022Jastrzębski M, Kiełbasa G, Curila K, et al. Physiology-based electrocardiographic criteria for left bundle branch capture. Heart Rhythm . 2021;18(6):935-943. doi:10.1016/j.hrthm.2021.02.021Figure LegendsFigure 1: Permanent His Bundle PacingPanel A: A 12-lead electrocardiogram (EKG) shows baseline conduction in a patient with exertional intolerance. The PR interval is markedly prolonged and, with exercise, this patient developed AV block. A permanent His-bundle pacemaker was implantedPanel B: An EKG demonstrating permanent His-bundle pacing in the same patient as panel A. Selective His-bundle capture results in reproduction of the intrinsic QRS complex.Figure 2: Non-Selective Left Bundle Branch PacingA 12-Lead electrocardiogram showing non-selective left bundle branch pacing. The paced QRS morphology is not a direct match for native conduction and the QRS duration is longer than at baseline. However, conduction system capture was confirmed with an output dependent QRS morphology change.FiguresFigure 1: Permanent His-Bundle Pacing
Title: Percutaneous Lead Extraction in Patients with Large Vegetations: Limiting our Aspirations.Robert D. Schaller, DO11The Section of Cardiac Electrophysiology, Cardiovascular Division, Department of Medicine, Hospital of the University of Pennsylvania, Philadelphia, PennsylvaniaFunding: This work was supported in part by the Mark Marchlinski EP Research & Education FundKey words: Lead extraction, vegetation, pulmonary embolism, thrombus, aspirationDisclosures: NoneWord count: 1547Transvenous lead extraction (TLE) in the 1960’s involved orthopedic-style pulley systems that joined the exposed portion of the lead to progressively heavier weights hanging from the bed. Sustained tension on the lead was maintained until the patient experienced discomfort, ventricular arrhythmias, or noticeable resistance developed, and was maintained for minutes to days. The location of the lead within the chest was monitored with daily chest radiographs and the ensuingbang of the weight hitting the floor of the intensive care unit signified case conclusion; at which point the patient was assessed. Complications were erratic and included lead laceration and possible migration, injury to the tricuspid valve (TV), myocardial avulsion, tamponade, and death.1 Due to the immature nature of the procedure at that time, it was relegated to infectious indications including lead-related endocarditis, at that time referred to as “catheter fever”.Contemporary TLE has evolved into a highly refined practice with a multitude of tools and predictable results, and procedural indications that now span infection, venous occlusion, management of redundant leads, and access to magnetic resonance imaging.2Procedural imaging with computed tomography (CT) and real-time ultrasound-based tools have similarly changed the TLE experience with identification of adhesions, thrombi, vegetations, and complications.3 Large lead-related masses have historically caused angst due to the possibility of being sheared off by the extraction sheath and embolizing to the lung, and still represent a relative contraindication to percutaneous TLE.2In this issue of the Journal of Cardiovascular Electrophysiology , Giacopelli, et al.4 present the outcomes of 25 consecutive patients (mean age 64 years, 68% male) including 5 with pacemakers, 10 with implantable cardioverter-defibrillators, and 10 with cardiac resynchronization therapy devices, who underwent TLE with vegetations ≥10 mm on transesophageal echocardiography (TEE). Contrast-enhanced CT was performed before and after TLE with 18 (72%) patients showing subclinical pulmonary embolism (PE). Vegetation size (median of 17.5 mm and maximum of 30 mm) did not differ in those with and without PE (20.0 mm vs. 14.0 mm, p=0.116). Complete TLE success was achieved in all patients with 76% requiring advanced tools and 2 needing femoral snaring, and there were no significant procedural complications. In the group with pre-TLE PE, a post-TLE scan confirmed the presence of PE in only 14/18 (78%) and there were no patients with new PE formation. During a median follow-up period of 19.4 months, no re-infection of the new implanted systems was reported and there were 5 deaths (20%); with no differences between the groups. The authors concluded that subclinical PE was common in this clinical scenario but did not influence the complexity or safety of the procedure.Several aspects of this paper warrant comment. No data are reported on the size or location of the PEs nor the time between the first and second CT. It is possible that small PEs would not be identified on subsequent studies days after antibiotics had already been started. Patients also received acute and chronic anticoagulation if PE was identified, which in the setting of vegetations, is generally not indicated and could potentially lead to bleeding. The authors did not provide information regarding infectious pathogens or the timing of culture clearance, which could influence treatment. Additionally, it is unclear which patients received new CIED systems including the type and timing of reimplantation, which might influence subsequent infectious risk. A vascular occlusion balloon was not used in any patients in this report. While this tool is associated with a reduced risk of death in the setting of a superior vena cava laceration when used properly, it has also been shown to be thrombogenic during long dwell times,5 and use could impact post-operative CTs in future studies. Despite utilizing transthoracic echocardiography during TLE, neither TEE nor intracardiac echocardiography were used intraoperatively and thus no information regarding the precise location of the vegetations within the heart is known. Importantly, no information regarding the characteristics of the vegetations other than size was reported.Not all lead-related masses are created equal with two distinct sub-types previously described.6 The first is composed of thickened endocardium and fibrous tissue covering the leads and ultimately forming into connective tissue. These masses, commonly found on leads behind the TV, are caused by a vortical flow pattern leading to low shear stress on the lead surface and provoking neointimal hyperplasia,7 and range from small fibrous strands to large, smooth organized thrombus (Figure, left column). Despite their sterile nature, TLE in the setting of a large, mature thrombus could result in embolization and obstruction of the pulmonary artery resulting in symptomatic PE. The second type, frequently seen in the setting of infective endocarditis, is composed of inflammatory cells, platelets, adhesion molecules, fresh fibrin, and bacteria binding to coagulum and forming vegetations. They are typically longer, more likely to be multi-lobular, and commonly span several chambers of the heart (Figure, right column). These vegetations that are typically acute, with friable finger-like projections, characteristically break apart upon being sheared off during TLE, with reports showing low risk of symptomatic PE.8 Vegetations that are lobular, however, have been associated with worse outcomes.9Despite acute procedural success in the setting of lead-related vegetations, mortality rates at 1 year approach 25%.10 Indeed, despite successful TLE in this report, 20% of patients were dead at 1.5 years. Although complete understanding of the mechanism of these poor outcomes remains unknown, septic emboli, lung abscesses, and infected lead “ghosts” have been implicated.11 Vegetation removal prior to TLE has thus represented an appealing therapeutic option with reports of successful percutaneous aspiration prior to TLE showing promising results, albeit with unknown long-term benefit.12,13 Although the lack of new PEs after TLE in this report does not directly support the effort, cost, and added risk of such a strategy, “debulking” of infectious burden remains a tempting complementary treatment. Importantly, the acute safety of TLE with large vegetations in this study should not be extrapolated to chronic, large lead-related masses, which are more like to cause acute PE if embolized. While aspiration of these sterile masses prior to TLE is appealing from a procedural outcome perspective, their morphologic characteristics, and the imperfect, but evolving, aspiration sheaths currently available are limiting, and requires consideration of surgical extraction. Further advancements in aspiration catheter technology and the development of right ventricular outflow track filters might influence future management.TLE continues to represent the gold standard for the management of lead-related infection.2 Due to the extensive work of the pathfinders in the vanguard of procedural development, the sound of crashing weights has been supplanted by those that power advancing sheaths. Yet despite the safe and predictable nature of modern-day TLE, the sobering long-term mortality of patients with infectious indications remains out of proportion to acute procedural success. While infectious “debulking” continues to represent the most attractive and practical complementary option to address this incongruity, future studies should concentrate both on identification of mass characteristics that suggest success, as well as determining if long-term benefits exist above and beyond lead removal. However, if improvement in clinical outcomes that warrant this added cost and effort are not identified, we should likely limit our aspirations.
A 13-year-old boy was hospitalized after a syncopal episode that occurred during exercise. He suddenly felt chest tightness, sweating and palpitations, followed by a transient loss of conciseness. Upon emergency medical team arrival, he was awake and oriented. Baseline ECG showed sinus rhythm at a rate of 98 bpm, with narrow QRS, and no signs of long QT, Brugada, or pre-excitation. Physical examination, blood tests, 24 hours Holter monitoring, transthoracic echocardiography and stress test were all within normal limits. Eight days later he experienced a second episode of palpitations while walking to school. ECG revealed regular wide complex tachycardia (WCT) at a rate of 200 bpm, with LBBB morphology that terminated with Adenosine (Figure 1). The clinical tachycardia was easily induced by programmed electrical stimulation (Figure 2A). Diagnostic electrophysiological maneuver (Figure 2B) was followed by successful ablation, during which a unique phenomenon was noted (Figure 3). What is the diagnosis of the tachycardia and what are the unique findings noted during and after ablation?
The thinning of the skin over the pocket is an occasional phenomenon in patients with cardiac implantable electronic devices (CIEDs) most often associated with the technique of implantation of the device. It is likely that the thinning of the skin over the generator is a risk factor for the development of infectious complications in patients with CIED. Analysis of large database of 3706 patients undergoing transvenous lead extraction (TLE) showed higher number of points of PADIT score and more often previous pocket plastic surgery in patients with too shallow pocket. Most likely, diagnosing only a too shallow CIED pocket is often an early symptom of infection.
Introduction: Increasing evidence has suggested improved outcomes in atrial fibrillation (AF) patients with heart failure (HF) undergoing catheter ablation (CA) as compared to medical therapy. We sought to investigate the benefit of CA on outcomes of patients with AF and HF as compared to medical therapy. Methods and Results: A systematic review of PubMed, Embase, and Cochrane Central Register of Clinical Trials was performed for clinical studies evaluating the benefit of CA for patients with AF and HF. Primary endpoint was all-cause mortality. Secondary endpoints included atrial-arrhythmia recurrence and improvement in left ventricular ejection fraction (LVEF). Eight randomized controlled trials were included with a total of 2121 patients (mean age: 65 ± 5 years; 72% male). Mean follow-up duration was 32.9 ± 14.5 months. All-cause mortality in patients who underwent CA was significantly lower than in the medical treatment group (8.8% vs. 13.5%, RR 0.65, 95% CI 0.51-0.83, P=0.0005). A 35% relative risk reduction and 4.7% absolute risk reduction in all-cause mortality was observed with CA. Rates of atrial-arrhythmia recurrence were significantly lower in the CA group (39.9% vs 69.6%, RR 0.55, 95% CI 0.40-0.76, P=0.0003). Improvement in LVEF was significantly higher in patients undergoing CA (+9.4 ±7.6%) as compared to conventional treatment (+3.3±8%) (Mean difference 6.2, 95% CI 3.6-8.8, P<0.00001). Conclusion: CA for AF in patients with HF decreases all-cause mortality, improves atrial-arrhythmia recurrence rate and LVEF when compared to medical management. CA should be considered the treatment of choice to improve survival in this select group of patients.
Bipolar Ablation for Outflow Tract Ventricular Arrhythmias: When the Going gets Tough, Two Catheters may be Better than One Anurut Huntrakul, MD1,2 and Jackson J. Liang, DO11 Electrophysiology Section, Division of Cardiology, Cardiovascular Center, University of Michigan Medical Center, Ann Arbor, MI 48109, USA.2 Division of Cardiovascular Medicine, Department of Medicine, Faculty of Medicine, Chulalongkorn University, King Chulalongkorn Memorial Hospital, Bangkok 10330, ThailandFunding: NoneDisclosures: None
High Density Pace-Mapping for Scar-related Ventricular Tachycardia AblationTravis D. Richardson MD and William G. Stevenson MD.1 Division of Cardiovascular Medicine, Vanderbilt University Medical Center, Nashville, TN, USARunning Title: High Density Pace MappingCorresponding Author:Travis D. Richardson, MDDivision of Cardiovascular MedicineVanderbilt University Medical Center1211 Medical Center DrNashville, TN 37232USAEmail: email@example.comWord Count: 2,225Conflicts of Interest :Dr. Stevenson has received speaking Honoria from: Boston Scientific, Medtronic, Abbott, Johnson and Johnson, and Biotronik; he is co-holder of a patent for irrigated needle ablation that is consigned to Brigham and Women’s Hospital.Dr. Richardson has received research funding from Medtronic Inc, Abbott Inc and served as a consultant for Philips Inc and Johnson and Johnson.This work did not receive any funding.Despite advances in medical and interventional therapies, ventricular tachycardia (VT) due to reentrant activity within complex regions of myocardial scar remains a common late complication of myocardial infarction.1 While implantable defibrillators (ICD) may prevent sudden death, ICD shocks are painful and impact quality of life2. Catheter ablation reduces the likelihood of ICD therapies and it’s role early in the course of disease is expanding3–5. However, several factors limit the success and safety of catheter ablation procedures. Scar-related reentry circuits can be large with a critical isthmus shared by multiple loops. Ablation of the isthmus is associated with a low risk of recurrence of that VT6,7. The critical isthmus can be identified during VT by detailed activation mapping and entrainment. However, prolonged mapping during VT is often not feasible or desired. Patients undergoing VT ablation often have severe systolic heart failure as well as other comorbid conditions. VT is often not hemodynamically tolerated and even when tolerated, prolonged time in VT may lead to decompensation. Strategies to limit initiation and mapping of VT may improve procedural safety8. Methods to guide ablation based on characterization of the sinus rhythm substrate alone have generally shown good results9. A number of approaches have been applied, including ablation over the entire low voltage area (scar homogenization)10. While this is often successful, areas of scar can be quite extensive, and undoubtedly this technique leads to ablation of more areas than absolutely necessary for success. This approach is also more effective if epicardial ablation is routinely included, which has the potential to increase procedural risk. A strategy to focus on the critical regions, particularly when a clinically relevant VT is known, remains a reasonable first step in the procedure. A variety of electrogram markers of critical regions have been described including late potentials, potentials that display variable coupling to surrounding tissue during programmed stimulation11 , and areas of slow conduction identified by high density mapping 12,13. While these are likely to increase the specificity of ablation targets compared to electrogram voltage alone, they are also seen at bystander areas14.Pace-mapping during sinus rhythm is useful to help identify the general location of focal arrhythmia sources,15 and can also be used in scar related reentry.16,17 At the reentry circuit exit region the paced QRS morphology often resembles the VT QRS, and this will also occur at sites proximal to the exit provided that the stimulated wavefront follows the reentry path to the exit. A stimulus – QRS > 40 ms is also consistent with slow conduction away from the pacing site, that can be a marker for reentry substrate17.In this issue of the Journal of Cardiovascular Electrophysiology,Guenancia et al. review their technique of using high density pace mapping to guide VT ablation18. Their method takes advantage of software available in electroanatomic mapping systems that assigns a measure of correlation between two different QRS morphologies; in this case the VT and the paced QRS morphology.19 A pacing correlation map is generated by pacing multiple sites within the ventricle and color coding the algorithmically derived score for display at each point on the anatomic map. Sites near the exit from the reentry circuit isthmus, typically along the border of a scar, will display good correlation with induced VT. As one moves along the isthmus deeper into the low voltage scar the S-QRS prolongs due to the conduction time between the pacing site and the exit region. If the isthmus is anatomically defined, such that it is present during VT and sinus rhythm, the QRS morphology remains similar to the VT as long as the paced wavefront follows the isthmus out to the exit. Moving to the entrance or adjacent sites outside the isthmus can produce an abrupt transition to a markedly different paced QRS because the wavefront can propagate away without following the path of the isthmus.20 Thus, the pace-map correlation maps can outline the location of a reentry circuit isthmus during sinus rhythm, as they illustrate.Their method can also help identify cases in which the critical isthmus is not located on the surface being mapped. When the VT circuit is epicardial or intramural, the earliest endocardial activation may appear focal. Similarly, the pace-map correlation maps may reveal a concentric or focal pattern of matching, potentially allowing recognition of this situation without the need for activation mapping during VT.We agree with the fundamental principles described, and feel this technique can be a helpful substrate mapping approach. There are several caveats. Evaluation to clarify its specificity and sensitivity is limited. The authors report that in their unpublished experience an abrupt transition is seen in the majority of post-infarct cases, they have also published a series of 10 post-infarct patients undergoing VT ablation during which the pacing correlation maps visually matched VT activation maps.21This technique is likely to be effective in cases where the VT isthmus is confined to the ventricular surface being mapped. Pacing can capture deep to the endocardium depending on current strength.22 Whether this technique can detect intramural isthmuses and whether deep tissue that can be captured with pacing can also be ablated from the pacing site is not clear.It is important to point out that very good correlations with VT can be observed pacing in an outer loop immediately adjacent to the exit where one would not anticipate RF ablation delivery would be effective. If a focal pattern is seen on both the endocardial and epicardial surfaces very little can be inferred about the VT circuit; the site with better correlation would be expected to be closer to the exit. In this setting entrainment during a brief episode of induced VT with assessment of the post-pacing interval can potentially clarify the proximity to the reentry circuit.During VT, areas of functional conduction block may be present that are absent during sinus rhythm. Functional block can also occur remote from the reentry isthmus and alter activation wavefronts during VT changing the QRS morphology. Theoretically it is then possible to have poor correlation between the VT and paced QRS at its exit. In animal models of post-infarction VT exit regions have been shown to harbor very slow areas of conduction which could be prone to altering total ventricular activation during VT.23.We would caution against generalizing these techniques to patients with dilated cardiomyopathies where confluent regions of low voltage scar are absent. Diffuse interstitial fibrosis may play a greater role in some of these VT circuit and anatomically fixed isthmus sites are less likely to be present.Further study is needed before utilizing this technique when anatomical structures within the ventricle are involved in the VT circuit. Structures such as the moderator band may by definition have multiple exits and varied QRS morphologies24, and papillary muscles may display large areas of similar paced morphology25, potentially distorting pacing correlation maps.This technique is unlikely to correctly characterize VT circuits that involve a portion of the cardiac conduction system as occurs in some scar-related VTs and in bundle-branch reentry.26 These circuits may demonstrate a focal pattern at the left or right ventricular apical septum on pacing correlation maps due to the long, insulated nature of the reentrant circuit itself, and ablation at the exit site is very unlikely to be effective.This strategy of high density pace mapping adds to the available substrate mapping methods for guiding VT ablation while limiting VT induction. This strategy does not rely on electrogram interpretation, making it of particular interest in regions of very low voltage. Indeed, when utilizing larger recording electrodes, such as an ablation catheter, pacing will often reveal the presence of excitable tissue where a local electrogram is not always apparent. In post-infarct ventricular tachycardia circuits with a well-defined scar and a short anatomically bounded isthmus, pacing correlation maps are likely to be revealing. More study is warranted to further assess this method in relation to other substrate mapping methods, in complex substrate with intramural components, and in other disease substrates. It is useful to have multiple tools in the tool box. More studies are needed to further define which tools work best for which substrate.References:1. Stevenson WG: Ventricular Tachycardia After Myocardial Infarction: From Arrhythmia Surgery to Catheter Ablation. J Cardiovasc Electrophysiol 1995; 6:942–950.2. Moss AJ, Schuger C, Beck CA, et al.: Reduction in inappropriate therapy and mortality through ICD programming. N Engl J Med 2012; 367:2275–2283.3. Sapp JL, Wells GA, Parkash R, et al.: Ventricular Tachycardia Ablation versus Escalation of Antiarrhythmic Drugs. N Engl J Med 2016; 375:111–121.4. Cronin EM, Bogun FM, Maury P, et al.: 2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias: Executive summary. Heart Rhythm 2020; 17:e155–e205.5. Della Bella P, Baratto F, Vergara P, et al.: Does Timing of Ventricular Tachycardia Ablation Affect Prognosis in Patients With an Implantable Cardioverter Defibrillator? Results From the Multicenter Randomized PARTITA Trial. Circulation 2022; .6. Hadjis A, Frontera A, Limite LR, et al.: Complete Electroanatomic Imaging of the Diastolic Pathway Is Associated With Improved Freedom From Ventricular Tachycardia Recurrence. Circ Arrhythm Electrophysiol 2020; 13:e008651.7. Tokuda M, Kojodjojo P, Tung S, et al.: Characteristics of Clinical and Induced Ventricular Tachycardia Throughout Multiple Ablation Procedures. 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The study by Worck et al. raises interesting findings with regard to left atrial posterior wall ablation. The utility of ablation at the CRZ -- which may represent epicardial connection via the septopulmonary bundle -- warrants future research. Upcoming trials utilising existing technology, along with increased availability of pulsed field ablation, will advance our knowledge of the impact of left atrial posterior wall isolation.