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Background: Ethanol infusion into the vein of Marshall (EIVoM) may increase mitral isthmus bidirectional block (MIBB) and cause local autonomic denervation that may improve outcome. Objective: This meta-analysis aimed to investigate whether the addition of EIVoM to atrial fibrillation (AF) ablation led to a better outcome. Methods: Systematic literature search was performed using PubMed, Scopus, ScienceDirect, and Europe PMC for studies that compared the addition of EIVoM during AF ablation with radiofrequency ablation. The primary outcome was atrial tachyarrhythmia (ATa) recurrence, defined as AF/atrial flutter/atrial tachycardia after the blanking period. Results: There were 2821 patients from 11 studies, and EIVoM was successful in 77% (95% confidence interval [CI] 62%–92%). ATa recurrence was 27% (95% CI 20%–34%) in the EIVoM group and 42% (95% CI 33%–51%) in ablation-only group. EIVoM reduced ATa recurrence (odds ratio [OR] 0.52; 95% CI 0.36–0.76; P < .001; I2 = 76.92). The rate of MIBB was 85% (95% CI 77%–94%) in the EIVoM group and 73% (95% CI 61%–85%) in the ablation-only group, which was significantly higher (OR 3.87; 95% CI 1.46–10.28; P < .001; I2 = 83.68). The mitral isthmus reconnection rate (OR 0.44; 95% CI 0.15–1.29; P = .14; I2 = 63.6) and repeat procedure rate (OR 0.76; 95% CI 0.53–1.08; P = .12; I2 = 48) were similar; however, a leave-one-out sensitivity analysis showed P < .05 for both. The benefits of EIVoM were not affected by age, left atrial diameter, and left ventricular ejection fraction (P > .05). Age (P = .029) and left atrial diameter (P = .042) were inversely associated with EIVoM benefits in terms of repeat ablation and mitral isthmus reconnection (age; P = .003). Conclusion: The addition of EIVoM to ablation increased MIBB and reduced ATa recurrence.

ABSTRACT A 58‐year‐old woman was referred for atrial flutter ablation after atrial fibrillation ablation. Linear and reinforcement mitral isthmus ablation failed to terminate the perimitral flutter. During vein of Marshall ethanol infusion (VOMEI), the flutter was terminated and followed by left atrial appendage (LAA) isolation. Voltage mapping showed that a large low voltage area was created in the superior and anterior wall of left atrium. During the waiting time, the LAA activation recovered. It would be necessary to keep in mind that VOMEI would lead to uncontrolled lesion of left atrium. [ABSTRACT FROM AUTHOR]

Background: Radiofrequency catheter ablation (RFA) targets the left atrial appendage isthmus (LAA isthmus) and mitral isthmus for treatment of atrial fibrillation. However, proximity of left circumflex artery (LCxA) and great cardiac vein (GCV) in the isthmuses poses fatal risks during ablation. Methods: This study investigated relationships of LCxA and GCV across three lines in the LAA and mitral isthmus, using 15 human cadaveric hearts. Distances between the vessels and the endocardium, myocardium, and perivascular fat thickness were measured. Results: The results showed that LCxA was mostly consistently located in lower atrial segments and GCV was in lower/upper atrial segments, with change of course mainly observed in the middle of the LAA. The LCxA was found as close as 3–5 mm from the lower border of the LAA isthmus in 80% of specimens, at a depth of 2–3 mm within the LAA isthmus, where 1 mm consisted of myocardium and the remainder was fat, which may not provide adequate protection due to the possibility of liquefaction of fat with heat application. The effective myocardial thickness was consistently 1 mm across all cases in both isthmuses. LCxA was 2 mm in second and third sections of LAA isthmus ("careful segment"). LCxA distances from left inferior pulmonary vein opening was 5 to 12 mm, occasionally dangerously close as <1 mm in 16% of cases. Conclusion: This study measured LCxA and GCV in the LAA and mitral isthmus across three lines for the first time in the Indian population, aiding surgeons in RFA planning. [ABSTRACT FROM AUTHOR]

Background: Achieving mitral isthmus (MI) block can be challenging. This prospective study evaluated the feasibility and efficacy of a systematic strategy comprising three consecutive steps to achieve MI block. Methods: Twenty consecutive patients (mean (± SD) age 71.4 ± 6.98 years) undergoing ablation of perimitral atrial tachycardia (PMAT) between December 2019 and November 2021 were included. MI was ablated using a systematic strategy comprising up to three consecutive steps: (1) endocardial ablation from the superolateral mitral annulus to the left pulmonary veins; (2) additional epicardial ablation in the coronary sinus (CS) on the opposite side of the endocardial line; and (3) ablation of early activation sites between endocardial and epicardial breakthroughs. Results: MI block was successfully achieved in 19/20 patients (95%). MI block after endocardial radiofrequency ablation alone (step 1) was observed in 7/20 patients (35%). Epicardial ablation within the CS on the other side of the endocardial line (step 2) resulted in bidirectional MI block in three more patients. Endocardial ablation of epicardial conduction was successful for nine additional patients (95% success). At the 12-month follow-up, five patients (25%) displayed recurrence of arrhythmia after a single procedure. One patient had electrical cardioversion for persistent atrial fibrillation. Four patients had a redo procedure for left atrial flutter and only two patients (10%) had conduction across the MI and showed recurrence of PMAT. No complications occurred. Conclusions: The three-step ablation strategy resulted in a high rate of acute and durable MI block. PMAT recurrence after a single procedure was 10% at 1-year follow-up. The three-step ablation strategy had a success rate of bidirectional MI conduction block of 95%. Recurrence of PMAT after a single procedure was 10% at 1-year follow-up. [ABSTRACT FROM AUTHOR]

BackgroundThis study examines the anatomical characteristics of the mitral isthmus (MI) and its spatial relationship with the esophagus in patients undergoing atrial fibrillation ablation, using cardiovascular computed tomographic angiography (CTA). Understanding this relationship is crucial to minimize the risk of esophageal injuries during ablation procedures.MethodsThe investigation included 300 participants, divided into 200 subjects in the experimental group undergoing atrial fibrillation ablation and 100 in the control group. Detailed CTA scans were used to assess the MI's structure and proximity to the esophagus, employing various measurements like the MI's endocardial length, depth, and its relation to adjacent esophageal anatomy.ResultsThe study revealed significant differences in the MI's length and distance measurements between the experimental and control groups, with the former showing greater dimensions, potentially influencing ablation strategies. A substantial proportion of patients exhibited close proximity or direct contact between the MI and the esophagus, emphasizing the importance of pre-procedural imaging in identifying risks for esophageal damage.ConclusionsPre-procedural cardiovascular CTA provides essential insights into the MI's anatomical details and its relation to the esophagus, aiding in the customization of ablation strategies to enhance procedural safety and efficacy. The findings highlight the significance of tailored imaging assessments to mitigate esophageal injury risks in atrial fibrillation ablation.

Background: Mitral isthmus (MI) conduction block is a fundamental step in anatomical approach treatment for persistent atrial fibrillation (PeAF). However, MI block is hardly achievable with endocardial ablation only. Retrograde ethanol infusion (EI) into the vein of Marshall (VOM) facilitates MI block. Fluorographic myocardial staining (MS) during VOM-EI could be helpful in predicting procedural alcoholization outcome even if its role is qualitatively assessed in the routine. The aim was to quantitatively assess MS during VOM-EI and to evaluate its association with MI block achievement. Methods: Consecutive patients undergoing catheter ablation for PeAF at Fondazione Toscana Gabriele Monasterio (Pisa, Italy) from February 2022 to May 2023 were considered. Patients with identifiable VOM were included. A proposed index of MS (MSI) was retrospectively calculated in each included patient. Correlation of MSI with low-voltage zones (LVZ) extension after VOM-EI and its association with MI block achievement were assessed. Results: In total, 42 patients out of 49 (85.8%) had an identifiable VOM. MI block was successfully achieved in 35 patients out of 42 (83.3%). MSI was significantly associated with the occurrence of MI block (OR 1.24 (1.03–1.48); p = 0.022). A higher MSI resulted in reduced ablation time (p = 0.014) and reduced radiofrequency applications (p = 0.002) to obtain MI block. MSI was also associated with MI block obtained by endocardial ablation only (OR 1.07 (1.02–1.13); p = 0.002). MSI was highly correlated with newly formed LVZ extension (r = 0.776; p = 0.001). Conclusions: In our study cohort, optimal MSI predicts MI block and facilitates its achievement with endocardial ablation only. [ABSTRACT FROM AUTHOR]

Introduction: Some previous studies have reported that a first‐step ethanol infusion into the vein of Marshall (EIVOM) with touch‐up radiofrequency (RF) ablation can facilitate mitral isthmus (MI) block and improves the ablation outcomes in persistent atrial fibrillation (PeAF) patients. However, the effect of an initial RF ablation with an adjunctive EIVOM has not been fully investigated. Methods: This study enrolled 233 PeAF patients undergoing pulmonary vein isolation and linear ablation including an MI, roof line, and cavotricuspid isthmus ablation. An EIVOM was performed when endocardial ablation with or without coronary sinus ablation failed to create MI block. Results: Bidirectional MI block was achieved in 224 patients (96.1%). Among them, MI block was obtained by only RF ablation in 174/224 patients (77.7%) (RF group) and an adjunctive EIVOM was needed in 50/224 (22.3%) (EIVOM group). During the follow‐up, 113 (64.9%) RF group patients were free from AF/atrial tachycardia compared to 41 (82.0%) EIVOM group patients (log‐rank p =.045). In a multivariate Cox regression analysis, an adjunctive EIVOM was associated with a lower recurrence rate (hazard ratio = 0.39, 95% confidence interval = 0.17–0.78, p =.006). Conclusion: An initial RF ablation with an adjunctive EIVOM strategy improved MI ablation's acute success rate and was associated with better clinical outcomes. [ABSTRACT FROM AUTHOR]

A 62‐year‐old man with a history of catheter ablation for atrial fibrillation and atrial tachycardia (AT) received a line of block of the mitral isthmus (MI) and electrical isolation of the left atrial appendage (LAA). Upon entrainment pacing, AT recurred and was diagnosed as peri‐mitral AT (PMAT) with electrical irrelevance of MI, LAA, and left pulmonary vein, having a critical isthmus identified as Marshall bundle (MB). MB was then infused with ethanol, leading to the successful treatment of the PMAT. [ABSTRACT FROM AUTHOR]

Background: The block methods and predictors of acute mitral isthmus (MI) have previously been well described. However, the predictors of the long-term MI block durability have not been fully investigated. Methods: One hundred and ninety patients with persistent atrial fibrillation underwent pulmonary vein isolation and linear ablation, including a MI ablation during the first procedure. Among them, acute MI block was achieved in 185 patients (97.4%). A repeat procedure was performed in 42 patients, and the lesion durability including of the MI block was investigated. Results: In 42 patients with a repeat ablation, MI reconnections were observed in 18 patients (42.9%). In patients in who achieved complete MI block solely through endocardial linear ablation during the first procedure, the MI reconnection rate in the second procedure was significantly lower when compared to the others (22.2% vs. 58.3%, P=0.017). MI reconnection gaps were mainly observed at sites close to the ridge and coronary sinus. Conclusions: If complete MI block was obtained by only endocardial linear ablation in the first procedure, the MI reconnection rate in the second procedure was significantly lower. Necessitating additional MI ablation using an epicardial approach is an indicator of a higher risk of MI reconnection on follow up. [ABSTRACT FROM AUTHOR]

The exponential rise in the incidence of peri‐mitral flutter has paralleled the increasing use of more extensive atrial substrate ablation for atrial fibrillation (AF). Given the relative paucity of randomized evidence to support its role in AF management, mitral isthmus ablation should largely be reserved for patients with peri‐mitral flutter. Catheter ablation for peri‐mitral flutter is challenging due to complex anatomic relationships. The aim of this report is to review the anatomic considerations and approaches to catheter ablation for peri‐mitral flutter. [ABSTRACT FROM AUTHOR]

Background : We describe our initial experience using a multipolar pulsed-field ablation catheter for the treatment of left atrial (LA) reentry tachycardia. Methods: We included all patients with LA reentry tachycardia treated with PFA at our institution between September 2021 and March 2022. The tachycardia mechanism was identified using 3D electro-anatomical mapping (3D-EAM). Subsequently, a roof line, anterior line, or mitral isthmus line was ablated as appropriate. Roof line ablation was always combined with LA posterior wall (LAPW) ablation. Positioning of the PFA catheter was guided by a 3D-EAM system and by fluoroscopy. Bidirectional block across lines was verified using standard criteria. Additional radiofrequency ablation (RFA) was used to achieve bidirectional block as necessary. Results: Among 22 patients (median age 70 (59–75) years; 9 females), we identified 27 LA reentry tachycardia: seven roof dependent macro-reentries, one posterior-wall micro-reentry, twelve peri-mitral macro-reentries, and seven anterior-wall micro-reentries. We ablated a total of 20 roof lines, 13 anterior lines, and 6 mitral isthmus lines. Additional RFA was necessary for two anterior lines (15%) and three mitral isthmus lines (50%). Bidirectional block was achieved across all roof lines, 92% of anterior lines, and 83% of mitral isthmus lines. We observed no acute procedural complications. Conclusion: Ablation of a roof line and of the LAPW is feasible, effective, and safe using this multipolar PFA catheter. However, the catheter is less suited for ablation of the mitral isthmus and the anterior line. A focal pulsed-field ablation catheter may be more effective for ablation of these lines. This study shows the feasibility to ablate linear lesions with a multipolar pulsed-field ablation catheter. 27 left atrial reentry tachycardia were treated in 22 patients. [ABSTRACT FROM AUTHOR]

BackgroundMarshall vein ethanol infusion (MVEI) as an additional therapy to conventional catheter ablation (CA) has been proved to be efficacious in patients with persistent atrial fibrillation (PeAF). However, whether empirical MVEI could be the first-line strategy in mitral isthmus (MI) ablation has seldom been investigated. Here, we aim to compare the efficacy, safety, and long-term outcomes between provisional and empirical MVEI in PeAF patients undergoing the index MI ablation procedure.MethodsWe enrolled 133 patients with PeAF either in the provisional group (n = 38, MVEI was performed when conventional endocardial and/or epicardial ablation procedures were inadequate to achieve bidirectional MI block) or in the empirical group (n = 95, MVEI was performed empirically before MI CA).ResultsAll of the baseline characteristics were comparable. Less spontaneous or inducible atrial tachycardias (ATs) were encountered in the empirical group of patients (P

We here present a case of a perimitral flutter occurring after a prior atrial fibrillation cryoballoon ablation and a second ablation procedure using radiofrequency with Marshall-PLAN study protocol (ethanol infusion in the vein of Marshall plus endocardial mitral isthmus, roof, and cavotricuspid isthmus lines). Activation mapping revealed mitral isthmus and roof reconnection. However, endocardial ablation at these sites failed to terminate the arrhythmia. Complete mitral isthmus block occurred only after radiofrequency applications at the great cardiac vein level. Epicardial connections at mitral isthmus sustained the arrhythmia and prevented block. This case underlies the importance of evaluation of mitral isthmus block with proper validation of ablation lines to prevent future tachyarrhythmias recurrences. [ABSTRACT FROM AUTHOR]

Aims: Bidirectional and durable block of mitral isthmus (MI) is essential for catheter ablation of persistent atrial fibrillation (PeAF) and perimitral flutter (PMF), but it remains a challenge. The aim of this study was to create a simple anatomical ablation strategy with minimal fluoroscopy that would yield a high success rate for MI block.Methods and Results: Patients with PeAF or PMF were included. Mitral isthmus was ablated in a stepwise strategy. In Step 1, endocardial MI linear ablation was performed; in Step 2, ablation was targeted to the posterolateral portion of the left atrium along the MI line; in Step 3, epicardial ablation within the coronary sinus (CS) was performed across the MI line to the ostium of the vein of Marshall (VOM) or performed within the VOM if available; in Step 4, the catheter was rotated and ablated in the CS to isolate the CS; and in Step 5, the early activation site with complex component potential above the MI line during distal CS pacing was considered as the ablation target. All patients were followed up. A total of 178 (17 patients with mechanical prosthetic mitral valve) were included. One hundred and sixty-six patients achieved a confirmed MI bidirectional conduction block (93%). One patient had cardiac tamponade. Four patients showed re-conduction across the MI line during a repeated ablation. In the latest follow-up [12 (7, 16) months], 161 of 178 (90%) patients maintained their sinus rhythm.Conclusion: A simple stepwise anatomical ablation strategy for MI shows a high success rate with low fluoroscopy exposure. [ABSTRACT FROM AUTHOR]

Background: Achieving a durable mitral line block using radiofrequency as a part of an anatomical approach for ablation in patients with persistent atrial fibrillation or for treating peri-mitral flutter has always been challenging due to the complex anatomy of the mitral isthmus. Epicardial ablation via the coronary sinus and the vein of Marshall has been proposed to help create durable lesions. Recently, a novel lattice-tip catheter using pulsed field ablation has shown promising results for creating mitral lines, despite limited data., Methods and Results: We present a case demonstrating the recovery of connection through the mitral isthmus after a waiting period, despite initial clear isolation achieved by creating an endocardial linear lesion. This necessitated further epicardial lesions, performed via ethanol infusion into the vein of Marshall, due to the presence of a coronary sinus CRT lead in this patient., Conclusion: Despite the high rates of acute mitral line block with PFA the rate of recurrence might be significant. Considering its novelty, our experience with point-by-point PFA is more limited. The present case report highlights the risk of delayed reconnection treated with EI-VOM. Further studies are warranted to explore additional outcomes and recurrence patterns among these patients., (© 2025 Wiley Periodicals LLC.)

This article reviews the structure of the atrial chambers to consider the anatomic bases for obstacles and barriers in atrial flutter. In particular, the complex myocardial arrangement and composition of the cavotricuspid isthmus could account for a slow zone of conduction. Prominent muscle bundles within the atria and interatrial, and myoarchitecture of the walls, could contribute to preferential conduction pathways. Alterations from tissue damage as part of aging, or from surgical interventions could lead to re-entry. [ABSTRACT FROM AUTHOR]

Abstract Background The termination of bi‐atrial tachycardia (BiAT) via the ablation of the Bachmann's bundle (BB) and mitral isthmus (MI) has been previously reported; however, the strategy and long‐term results of catheter ablation for BiAT remain unclear. Methods The data of nine patients with BiAT who underwent low voltage zone (LVZ) ablation of the left atrial anterior wall (LAAW) after pulmonary vein isolation were reviewed. Patients with a P wave duration 100 ms underwent BB ablation. Results MI ablation was performed in three patients and six patients underwent BB ablation. The difference in the P wave duration before and after ablation was significantly different between the ablation sites (MI group: 5.0 ms difference; BB group; 38.5 ms difference; P = .024). The P wave duration was prolonged by >20 ms and was 120 ms or more after ablation in 5/6 patients who underwent BB ablation. The total recurrence rate was 11.0% (mean: 26.9 months). Conclusion The recurrence of BiAT after MI or BB ablation is low. When BB ablation was performed, the P wave duration was prolonged by >20 ms and was at least 120 ms after the ablation, which may be an endpoint that can be used to measure the success of the ablation.

Abstract Introduction After mitral isthmus (ΜΙ) catheter ablation, perimitral atrial flutter (PMF) circuits can be maintained due to the preservation of residual myocardial connections, even if conventional pacing criteria for complete MI block are apparently met (MI pseudo‐block). We aimed to study the incidence, the electrophysiological characteristics, and the long‐term outcome of these patients. Methods Seventy‐two consecutive patients (mean age 62.4 ± 10.2, 62.5% male) underwent MI ablation, either as part of an atrial fibrillation (AF) ablation strategy (n = 35), or to treat clinical reentrant atrial tachycardia (AT) (n = 32), or to treat AT that occurred during ablation for AF (n = 5). Ιn all patients, the electrophysiological characteristics of PMF circuits were studied by high‐density mapping. Results Mitral isthmus block was successfully achieved in 69/72 patients (95.6%). Five patients developed PMF after confirming MI block. In these patients, high‐density mapping during the PMF showed a breakthrough in MI with extremely low impulse conduction velocity (CV). In contrast, in usual PMF circuits that occurred after AF ablation, the lowest CV of the reentrant circuit was of significantly higher value (0.07 ± 0.02 m/s vs 0.25 ± 0.07 m/s, respectively; P

Background: The vein of Marshall (VOM), which is surrounded by the Marshall bundle (MB), behaves as an epicardial connection bypassing the mitral isthmus. The influence of radiofrequency ablation and VOM ethanol infusion (VOM-EI) on epicardial MB conduction remains unclear.Objective: The purpose of this study was to evaluate MB conduction status during mitral isthmus ablation.Methods: Of 57 consecutive patients undergoing mitral isthmus ablation, 50 with electrode catheter cannulation into the VOM were analyzed. MB conduction was investigated by evaluating electrograms inside the VOM. Endocardial ablation was initially performed, followed by ablation inside the coronary sinus (CS), if required. Selective VOM-EI was performed if the MB potentials still exhibited early activation after radiofrequency ablation, suggesting the presence of MB connection bridging the mitral isthmus.Results: VOM electrograms composed of near-field MB and far-field left atrial potentials were recorded in all patients. Solely with endocardial ablation, 33 patients (66%) achieved entire mitral isthmus block, and 43 patients (86%) achieved an epicardial MB conduction block. MB potentials exhibited early activation in the remaining 7 (14%), even after requiring CS ablation. VOM-EI then was performed. Elimination of MB potentials was verified by electrode catheter reinsertion after VOM-EI. Mitral isthmus conduction was successfully blocked during VOM-EI in 4 patients and during additional radiofrequency ablation in the remaining 3. All patients finally achieved entire mitral isthmus block.Conclusion: MB is effectively ablated by radiofrequency ablation. Continuous evaluation of MB conduction can reveal epicardial conduction and ablation effect. A residual MB epicardial connection is relatively rare but can be ablated by VOM-EI. [ABSTRACT FROM AUTHOR]

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A 57-year-old man underwent his seventh ablation session for atrial tachycardia (AT). His previous ablations involved several regions of the right atrium (RA) and left atrium (LA). The AT was characterized as biatrial tachycardia with a circuit involving the mitral annulus and septal RA. The AT was terminated by ablation through the insertion site of Bachmann’s bundle (BB) in both atria. After 3 months, the patient underwent his eighth ablation session because of AT recurrence. Activation maps showed that the connection from the RA to LA and vice versa was maintained via BB and the coronary sinus, respectively. The ablation target to interrupt the AT circuit was the mitral isthmus (MI), not BB, because BB supplied the electrical activation of the left atrial appendage (LAA) via a unidirectional electrical connection from the RA to LA. Ablation attempts from within the coronary sinus were performed to target the epicardial connection in the MI and led to complete blockage of the connection from the LA to RA. Otherwise, the connection from the RA to LA was preserved via BB. The patient was free of symptoms and anti-arrhythmic drugs at the 4-month follow-up. However, he had a high risk of electrical isolation of the LAA because extensive ablations had been performed; the strategy of targeting the MI contributed to the balance between preserving the electrical activation of the LAA and treating the biatrial tachycardia. Verification of the connective pathway between the two atria might be helpful to determine the optimal target.

Purpose: It is It is widely accepted that atrial fibrillation (AF) accounts for half of arrhythmia recurrences following endocardial catheter ablation of AF. An epicardial-endocardial approach (hybrid) has emerged as an alternative to endocardial ablation alone for the treatment of AF, yet recurrence after a hybrid procedure has not been well characterized. This retrospective study is aimed at characterizing recurrence following hybrid ablation for patients with persistent AF. Methods: Patients with persistent AF (N = 108) received both endocardial and epicardial ablation of the posterior left atrial wall using catheter ablation and a small midline surgical approach (hybrid). Presence of atrial flutter or AF was determined with ambulatory monitoring (n = 22) or electrocardiogram analysis (n = 86) at each follow-up visit. Recurrence mode was confirmed by electrophysiology study for those patients undergoing subsequent catheter ablation after hybrid ablation. Results: Patients were followed for a mean ± standard deviation of 25 ± 14 months. Of patients who had a recurrence, 53% (n = 33) were in atrial flutter and 47% (n = 29) were in AF. Of those who had a recurrence with atrial flutter, 14 received repeat ablation for either left (n = 11) or left/right (n = 3) atrial flutter and 3 received AF ablation. Half of ablations for atrial flutter recurrence following the hybrid procedure involved the mitral isthmus. Conclusions: Atrial flutter accounts for about half of arrhythmia recurrences post-hybrid ablation. If catheter ablation of the mitral isthmus is considered during the hybrid procedure to prevent subsequent occurrence of perimitral flutter, bidirectional block must be performed to ensure a complete line of block.

Background: Reconnection of the mitral isthmus (MI) is common after radiofrequency ablation (RFA). Vein of Marshall ethanol infusion (VOMEI) expedites MI ablation, but long-term results are unclear., Objectives: This study sought to determine anatomic substrates of failed MI ablation, with and without VOMEI., Methods: Consecutive VOMEI procedures were included (n = 231; of which 140 were de novo ablations and 91 were prior RFA failures (rescue VOMEI). MI conduction mechanisms were studied with vein of Marshall (VOM) electrograms obtained with a 2-F octapolar catheter, mapping, and differential pacing., Results: In rescue VOMEI, intact VOM electrograms showed epicardial connections, epi-endocardial dissociation, and VOM conduction in pseudo-MI block. After VOMEI, after a follow-up of 725 ± 455 days, 78 patients (33.7%) experienced recurrence. Of those, 36 (46%) had evidence of MI reconnection and 42 had other mechanisms. Of the 36 patients with MI reconnection, endocardial radiofrequency (RF) at the annular MI restored block in 16 (45%), and coronary sinus (CS) RF was required in 20 (55%). Post-VOMEI recurrence mechanisms included CS connection-dependent arrhythmias: CS-mediated perimitral flutter, CS-to-left atrium (LA) and CS ostial re-entry, and CS focal activity. Intraprocedural factors associated with MI reconnection included volume of ethanol delivered ≥4 mL (OR: 0.74; P = NS), CS ablation at VOMEI (OR: 4.05; P = 0.003), and age (OR: 1.06; P = 0.011)., Conclusions: MI reconnections after RFA are due to epicardial connections from VOM. Recurrences after VOMEI are due to incomplete annular MI RFA and CS arrhythmogenesis including CS-mediated perimitral flutter, CS-to-LA re-entry and CS focal activity. Adding complete CS disconnection to VOMEI may prevent recurrences., Competing Interests: Funding Support and Author Disclosures This study was funded by National Institutes of Health grants R61HL164873 and R01HL168277 and the Lois and Carl Davis and Charles Burnett III endowments (to Dr Valderrábano). The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Purpose: Diagnosis of atrial tachycardia (AT) with 3D mapping system remains challenging due to fibrosis or previous ablation. This study aims to evaluate a new electroanatomical mapping annotation setting using a window of interest adjusted at the end of the P wave (WOIp wave) to identify the AT mechanism more accurately. Methods: Twenty patients with successful ablation of left AT using navigation system CARTO3 were evaluated. Two maps for each patient were generated offline using either conventional settings of WOI (WOIconv.) or WOIp wave. Three investigators from two centres analysed the maps blindly. Results: Mechanisms of AT were macroreentrant in 14/20 patients (70%) and focal in 6/20 (30%). WOIp wave resulted in a significant increase in the percentage of correct identification of the mechanism based on mapping alone (93.3 ± 13.7% vs 58.3 ± 33.9%; p = 0.0003) compared with WOIconv.. Diagnoses based on mapping were arrived at faster (27.8 ± 16.4 s vs 38.97 ± 13.64 s, respectively; p = 0.0231) and with a greater confidence in the diagnosis (confidence index 2.57 ± 0.45 vs 2.12 ± 0.45, respectively; p = 0.0024). With perimitral re-entry specifically "early meets late" was closer to the anatomical region of the mitral isthmus (15.9 ± 20.9 mm vs 48.77 ± 23.23 mm, respectively; p = 0.0028). Conclusions: This study found that electroanatomical mapping acquisition with a window of interest set at the end of the P wave improves the ability to diagnose the arrhythmia mechanism based on the initial map. It is particularly beneficial in identifying area of interest for ablation in perimitral AT. [ABSTRACT FROM AUTHOR]

Introduction: Catheter ablation for perimitral atrial tachycardia (PMAT) that persists despite lateral mitral isthmus (LMI) ablation is challenging. The aim of this study was to identify the role of the ligament of Marshall (LOM) in PMATs that persist after LMI conduction block has been created, and evaluate the validity of ethanol infusion into the vein of Marshall (VOM) as treatment. Methods and Results: Sixteen consecutive PMATs in 13 patients that persisted despite apparent LMI conduction block, which was confirmed by ultrahigh‐resolution mapping and entrainment pacing along the mitral annulus, were analyzed. PMATs were classified into two types based on the location of the endocardial breakthrough site: those utilizing the LOM (n = 13), which had a breakthrough site along with the LOM, and those not utilizing the LOM (n = 3), which had a breakthrough site at an anterior or posterior side of the LOM. Of the 16 PMATs, 5 PMATs (31%) were not suitable for ethanol infusion into the VOM because the LOM was not involved in the tachycardia circuit or because of the anatomy of the VOM. Fourteen PMATs (88%) were successfully terminated solely by breakthrough site ablation. At a mean follow‐up period of 12 ± 9 months, 10 (77%) patients have remained free from atrial tachyarrhythmias. Conclusion: In cases of PMAT following LMI ablation, epicardial conduction over the LMI can occur independently of the LOM. Ethanol infusion into the VOM in such cases would not abolish residual epicardial conduction. The anatomy of the VOM can also preclude the use of this method. [ABSTRACT FROM AUTHOR]

Background: Mitral isthmus gaps have been ascribed to an epicardial musculature anatomically related to the great cardiac vein (GCV) and the vein of Marshall (VOM). Their lumen offers an access for radiofrequency application or ethanol infusion, respectively.Objective: The purpose of this study was to evaluate the frequency of mitral isthmus gaps accessible via the GCV lumen, to assess their location around the GCV circumference, and to propose an efficient ablation strategy when present.Methods: One hundred consecutive patients underwent VOM ethanol infusion (step 1) and endocardial linear ablation from the mitral annulus to the left inferior pulmonary vein (step 2). In cases of mitral isthmus gap, endovascular ablation of the GCV anchored wall facing the left atrium was systematically performed (step 3), while the opposite GCV free wall was targeted in case of block failure only (step 4).Results: After VOM ethanol infusion and endocardial ablation, mitral isthmus block occurred in 51 patients (51%). Pacing maneuvers and activation sequences demonstrated an epicardial gap via the VOM in 2 patients (2%) and via the GCV in 47 patients (47%). In the latter case, block was achieved at the GCV anchored wall in 42 patients (89%) and the GCV free wall in 5 patients (11%). Global success rate of mitral isthmus block was 98%. No tamponade occurred.Conclusion: With the advent of VOM ethanol infusion, residual mitral isthmus gaps are mostly eliminated within the first centimeter of the GCV. Thorough mapping of the entire circumference of the GCV wall can help identify these epicardial gaps. [ABSTRACT FROM AUTHOR]

Background: The clinical anatomy of the left atrium is of special interest since many invasive procedures are performed within this chamber. Pulmonary vein isolation, linear transcatheter ablations, transcatheter mitral valve repair procedures and left atrial appendage occlusions are examples of highly effective procedures done within the left atrial chamber. Methods: This narrative literature review seeks to discuss the latest articles about the anatomy of left atrial structures. Results: This article reviews recent morphological studies about the pulmonary venous ostia, the myocardial sleeves of the pulmonary veins, the mitral isthmus, the left atrial appendage isthmus, the left atrial medial isthmus and the other left atrial isthmuses together with spatial relationships of blood vessels within the isthmus lines. This review touch upon the clinical relevance of the left lateral ridge and the left atrial appendage. Conclusion: A thorough understanding of local anatomy is essential for safe electrophysiologic invasive procedures. Clinical anatomy of the left atrium is treacherous, difficult and its unfamiliarity can cause serious intraoperative complications. Some anatomical features of the left atrium may significantly impede invasive transcatheter interventions, especially ablation procedures.

Introduction: Ethanol infusion in the vein of Marshall (EIVOM) effectively creates a linear ablation lesion in the mitral isthmus (MI). However, data on the long‐term success rates of MI ablation is limited. Methods and Results: Our cohort consisted of 560 patients with nonparoxysmal atrial fibrillation (AF) who underwent an initial MI ablation. Ablations were performed by only radiofrequency (RF) in 384 (RF group) or by RF and EIVOM in 176 (EIVOM/RF group) patients; 5 ml anhydrous ethanol was used to perform EIVOM in advance of RF. Following EIVOM, RF pulses were delivered to the lateral MI line. Bidirectional MI block was fully achieved in 353/384 (92%) (First 318, Re‐do 35) patinents in the RF group and 171/176 (97%) (First 128, Re‐do 43) patients in the EIVOM/RF group (p =.09 in the first, p =.10 in the re‐do ablation cases). In cases with complete MI line block, recurrent AF or atrial tachycardia was observed in 130/353 (37%) patients in the RF group and in 64/171 (37%) patients in the EIVOM/RF group (log‐rank p =.12 in the first, and p =.30 in the re‐do ablation cases). Of the total 560 patients, 123 proceeded to the subsequent ablation session. Reconduction across MI line block was observed in 39/80 (49%) patients in the RF group and 25/43 (58%) patients in the EIVOM/RF group (p =.32). Conclusion: EIVOM effectively ensures MI line block; however, the reconduction rate was similar between the two groups. [ABSTRACT FROM AUTHOR]

Background: The termination of bi‐atrial tachycardia (BiAT) via the ablation of the Bachmann's bundle (BB) and mitral isthmus (MI) has been previously reported; however, the strategy and long‐term results of catheter ablation for BiAT remain unclear. Methods: The data of nine patients with BiAT who underwent low voltage zone (LVZ) ablation of the left atrial anterior wall (LAAW) after pulmonary vein isolation were reviewed. Patients with a P wave duration <100 ms during sinus rhythm underwent MI ablation and those with a P wave duration >100 ms underwent BB ablation. Results: MI ablation was performed in three patients and six patients underwent BB ablation. The difference in the P wave duration before and after ablation was significantly different between the ablation sites (MI group: 5.0 ms difference; BB group; 38.5 ms difference; P =.024). The P wave duration was prolonged by >20 ms and was 120 ms or more after ablation in 5/6 patients who underwent BB ablation. The total recurrence rate was 11.0% (mean: 26.9 months). Conclusion: The recurrence of BiAT after MI or BB ablation is low. When BB ablation was performed, the P wave duration was prolonged by >20 ms and was at least 120 ms after the ablation, which may be an endpoint that can be used to measure the success of the ablation. [ABSTRACT FROM AUTHOR]

Background: The Vein of Marshall Ethanol for Untreated Persistent AF (VENUS) trial demonstrated that adding vein of Marshall (VOM) ethanol infusion to catheter ablation (CA) improves ablation outcomes in persistent atrial fibrillation (AF). There was significant heterogeneity in the impact of VOM ethanol infusion on rhythm control.Objective: The purpose of this study was to assess the association between outcomes and (1) achievement of bidirectional perimitral conduction block and (2) procedural volume.Methods: The VENUS trial randomized patients with persistent AF (N = 343) to CA combined with VOM ethanol or CA alone. The primary outcome (freedom from AF or atrial tachycardia [AT] lasting longer than 30 seconds after a single procedure) was analyzed by 2 categories: (1) successful vs no perimitral block and (2) high- (>20 patients enrolled) vs low-volume centers.Results: In patients with perimitral block, the primary outcome was reached 54.3% after VOM-CA and 37% after CA alone (P = .01). Among patients without perimitral block, freedom from AF/AT was 34.0% after VOM-CA and 37.0% after CA (P = .583). In high-volume centers, the primary outcome was reached in 56.4% after VOM-CA and 40.2% after CA (P = .01). In low-volume centers, freedom from AF/AT was 30.77% after VOM-CA and 32.61% after CA (P = .84). In patients with successful perimitral block from high-volume centers, the primary outcome was reached in 59% after VOM-CA and 39.1% after CA (P = .01). Tests for interaction were significant (P = .002 for perimitral block and P = .04 for center volume).Conclusion: Adding VOM ethanol infusion to CA has a greater impact on outcomes when associated with perimitral block and performed in high-volume centers. Perimitral block should be part of the VOM procedure. [ABSTRACT FROM AUTHOR]

Introduction: After mitral isthmus (ΜΙ) catheter ablation, perimitral atrial flutter (PMF) circuits can be maintained due to the preservation of residual myocardial connections, even if conventional pacing criteria for complete MI block are apparently met (MI pseudo‐block). We aimed to study the incidence, the electrophysiological characteristics, and the long‐term outcome of these patients. Methods: Seventy‐two consecutive patients (mean age 62.4 ± 10.2, 62.5% male) underwent MI ablation, either as part of an atrial fibrillation (AF) ablation strategy (n = 35), or to treat clinical reentrant atrial tachycardia (AT) (n = 32), or to treat AT that occurred during ablation for AF (n = 5). Ιn all patients, the electrophysiological characteristics of PMF circuits were studied by high‐density mapping. Results: Mitral isthmus block was successfully achieved in 69/72 patients (95.6%). Five patients developed PMF after confirming MI block. In these patients, high‐density mapping during the PMF showed a breakthrough in MI with extremely low impulse conduction velocity (CV). In contrast, in usual PMF circuits that occurred after AF ablation, the lowest CV of the reentrant circuit was of significantly higher value (0.07 ± 0.02 m/s vs 0.25 ± 0.07 m/s, respectively; P <.001). Patients presented with clinical AT had better prognosis in maintaining sinus rhythm after MI ablation compared with patients presented with AF. Conclusion: Perimitral atrial flutter with MI pseudo‐block may be present after MI ablation and has specific electrophysiological features characterized by remarkably slow CV in the MI. Thus, even after MI block is achieved, a more detailed mapping in the boundaries of the ablation line or reinduction attempts may be needed to exclude residual conduction. [ABSTRACT FROM AUTHOR]

Purpose: Although experimental data have suggested that temporary occlusion of the coronary sinus (CS) can facilitate the creation of transmural lesions across the atrial wall (AW) during mitral isthmus radiofrequency (RF) ablation, no computer modeling study has yet been made on the effect of the blood flow inside the epicardial vessels and its stoppage by an occlusion balloon. Methods: Computer simulations using constant power were conducted to study these phenomena by two methods: (1) by setting blood velocity in the CS to zero, which mimics a distal occlusion; and (2) by including a balloon filled with air in the model just below the ablation site, which mimics a proximal occlusion. Results: For short ablations (15 s) and perpendicular electrode/tissue orientation, lesion size was smaller with proximal occlusion compared to distal or no occlusion, regardless of the AW-CS distance (from 0.5 mm to 3.4 mm). For other angulations (0 and 45°) lesion size was almost the same in all cases. For longer ablations (60 s), the internal CS blood flow (no occlusion) considerably reduced lesion size, while stoppage combined with the proximal presence of a balloon produced the largest lesions. This performance was similar for different catheter angulations (0, 45 and 90°). Balloon length (from 10 to 40 mm) was found to be an irrelevant parameter when proximal occlusion was modeled. Conclusions: Using an air-filled balloon to occlude CS facilitates mitral isthmus ablation in long ablations, while proximal occlusion could impede transmural lesions in the case of short ablations (15 s).

Background: Perimitral atrial tachycardias (PMATs) are common atrial tachycardias (ATs), yet their mechanisms vary.Objective: The purpose of this study was to characterize clinical spontaneous PMATs using an ultra-high-resolution (UHR) mapping system.Methods: The study included 32 consecutive PMATs in 31 patients who had undergone AT mapping/ablation using a UHR mapping system.Results: Six, 10, 11, and 5 PMATs occurred in cardiac intervention-naïve (group A), post-lateral/posterior mitral isthmus linear ablation (group B), post-atrial fibrillation ablation without mitral isthmus linear ablation (group C), and post-cardiac surgery (group D) patients, respectively. Group A patients tended to be older, more likely were female, and had sinus node or atrioventricular conduction disturbances more frequently. A 12-lead synchronous isoelectric interval was observed in 15 PMATs (46.9%). Coronary sinus activation was proximal to distal or distal to proximal except in 3 PMATs with straight patterns due to epicardial gaps. Left atrial anterior/septal wall (LAASW) low-voltage areas were smallest in group B. Slow conduction areas (SCAs) were identified in 26 PMATs (81.2%) and were located on the LAASW in all group A and group D patients. Conduction velocity in the SCAs was slowest in group B. In group B, all PMATs were terminated by single applications, and the gaps were located epicardially in 5 of 10 (50%). Anterior (n = 23) or lateral/posterior (n = 9) mitral isthmus linear block was successfully created without any complications in all. Twenty-five concomitant ATs among 18 patients (58.1%) also were eliminated. During a median of 20.0 (11.0-40.0) months of follow-up, 28 patients (90.3%) were free from any atrial tachyarrhythmias.Conclusion: An UHR mapping-guided approach with identification of the individual tachycardia mechanism should be the preferred strategy given the distinct and complex arrhythmia mechanisms. [ABSTRACT FROM AUTHOR]

Mitral isthmus (MI) ablation is commonly performed as an adjunct therapy to pulmonary isolation during the treatment for persistent atrial fibrillation. Confirmation of complete MI block is essential because an incomplete MI block may result in iatrogenic atrial tachycardia. However, there are several pitfalls in the diagnosis of an MI line block. We herein report a case of transient pause‐dependent MI block during MI ablation. [ABSTRACT FROM AUTHOR]

Background: Data on the incidence, clinical characteristics, and implications of acute conduction recurrence during mitral isthmus (MI) ablation are scarce. Methods: MI ablation was performed in patients with atrial fibrillation. After confirming bidirectional conduction block, the acute conduction recurrence of MI was systematically evaluated. Clinical and electrophysiological characteristics were analyzed. Results: A total of 66 consecutive patients in whom bidirectional conduction block of MI was achieved were prospectively enrolled in a single center. Acute conduction recurrence of MI developed in 12 (18.2%) patients within 14.2 ± 11.5 minutes after the confirmation of bidirectional conduction block. There were two recurrent conduction breakthrough sites of MI along the course of the great cardiac vein (4.5 ± 3.5 min) in two patients and 11 along the course of the ligament of Marshall (LOM) (16.0 ± 11.6 min, P =.035) in 11 patients. LOM accounted for most (84.6%, 11/13) acute MI conduction recurrence. MI length, total ablation time, and procedure time for MI were greater in patients with acute conduction recurrence than in those without acute conduction recurrence. During follow‐up, arrhythmia recurrences were less observed in patients with acute conduction when compared to patients without acute conduction recurrence (0% vs 26.4%, P =.055). Conclusion: Acute conduction recurrence, predominantly due to recurrent LOM conduction, was a common phenomenon during MI ablation, and its evaluation should therefore be the focus to improve MI ablation efficacy and durability. [ABSTRACT FROM AUTHOR]

Mitral isthmus block during left lateral accessory pathway ablation has been reported in the past. Here, we document for the first time an irregular atrioventricular reciprocating tachycardia due to alternating mitral isthmus block and mitral isthmus delay, resulting in different atrioventricular node conduction times and tachycardia cycle length. [ABSTRACT FROM AUTHOR]

BACKGROUND: Bidirectional mitral isthmus (MI) block is conventionally verified by differential pacing from the coronary sinus (CS) and its sequence change. This study aimed to evaluate the ability of differential pacing from the vein of Marshall (VOM) to detect epicardial MI connections. METHODS: Radiofrequency and VOM ethanol MI ablation were performed with a VOM electrode catheter inserted to the septal side of the ablation line. MI block was verified using conventional CS pacing. To perform differential VOM pacing analysis, initial pacing was delivered from a distal VOM bipole closer to the block line, and then from a proximal VOM bipole. The intervals from pacing stimulus during different VOM pacing sites to the electrogram recorded through the CS catheter on the opposite side of the line were compared. When the interval during distal VOM pacing was longer than that during proximal VOM pacing, it indicated a VOM connection block; however, if the former interval was shorter, the connection through the VOM was considered persistent. RESULTS: Overall, 50 patients were evaluated. According to CS pacing, MI ablation was incomplete in 9 patients, in whom the analysis indicated persistent VOM connection. Among 41 patients with complete MI block, confirmed by CS finding, in 30 (73%) patients, the interval during distal VOM pacing was longer than that during proximal VOM pacing by 11±5 ms. However, in 11 patients (27%) the former interval was revealed to be shorter than the latter by 16±8 ms, indicating residual VOM connection. Conduction time across the line was significantly shorter in 11 patients than in the other 30 (166±21 versus 197±36 ms; P <0.01). Ten successful reevaluated analyses after VOM ethanol and further radiofrequency ablation of the connection indicated VOM block achievement. CONCLUSIONS: Differential VOM pacing maneuver reflects the VOM conduction status. This maneuver can uncover residual epicardial connections that are missing with CS pacing. [ABSTRACT FROM AUTHOR]

Background: Reconnection after mitral isthmus (MI) block with radiofrequency ablation is common., Objectives: The aim of this study was to investigate the effects of ethanol infusion in the vein of Marshall (EIVOM) on acute reconnection after MI bidirectional block., Methods: Patients with persistent atrial fibrillation who were scheduled to receive radiofrequency ablation for the first time were randomly assigned to the radiofrequency catheter ablation (RFCA) group (n = 44) or the EIVOM group (n = 45). The RFCA group's strategy was bilateral pulmonary vein ablation and linear ablation; in the EIVOM group, EIVOM was performed first. The primary endpoint was acute reconnection 30 minutes after MI bidirectional block., Results: A total of 89 patients (average age 62.9 years; 57.3% male) were enrolled. The average duration for persistent atrial fibrillation was 2.3 years. Before observation, all patients in the EIVOM group achieved MI bidirectional block (45 of 45 [100%]), compared with 84.1% (37 of 44) in the RFCA group. After the observation, 3 cases of MI reconnection occurred in the EIVOM group and 13 cases in the RFCA group (6.7% vs 35.1%; P < 0.05). After additional ablation, the final MI block rates in the EIVOM and RFCA groups were 97.8% (44 of 45) and 72.7% (32 of 44), respectively. During a 1-year follow-up, 8 of 45 patients who underwent EIVOM had recurrent atrial fibrillation, compared with 14 of 44 in the RFCA group (17.8% vs 31.8%; P < 0.01)., Conclusions: EIVOM can reduce acute reconnection after MI bidirectional block and significantly increase first-pass MI block., Competing Interests: Funding Support and Author Disclosures This study was funded by the following: National Key Research and Development Program of China (2020YFC2004803); Beijing Municipal Commission of Science and Technology (D171100006817001); National Natural Science Foundation of China (82000322); and Zhongnanshan Medical Foundation of Guangdong Province (ZNSA-2020017); the National Key Research and Development Program of China (2022YFC3601303); and a grant from the Science and Technology Program of Guangdong Province (No. 2019B020230004). The authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2024. Published by Elsevier Inc.)

Background and objectives: Macroreentrant atrial tachycardias often occur following atrial fibrillation ablation, most commonly due to nontransmural lesions in prior ablation lines. Perimitral atrial flutter is one such arrhythmia which requires ablation of the mitral isthmus. Our objectives were to review the literature regarding ablation of the mitral isthmus and to provide our approach for assessment of mitral isthmus block. Methods: We review anatomical considerations, ablation strategies, and assessment of conduction block across the mitral isthmus, which is subject to several pitfalls. Activation sequence and spatial differential pacing techniques are discussed for assessment of both endocardial and epicardial bidirectional mitral isthmus block. Results: Traditional methods for verifying mitral isthmus block include spatial differential pacing, activation mapping, and identification of double potentials. Up to 70% of cases require additional ablation in the coronary sinus (CS) to achieve transmural block. Interpretation of transmural block is subject to six pitfalls involving pacing output, differentiation of endocardial left atrial recordings from epicardial CS recordings, identification of a slowly conducting gap in the line, and catheter positioning during spatial differential pacing. Interpretation of unipolar electrograms can identify nontransmural lesions. We employ a combined epicardial and endocardial assessment of mitral isthmus block, which involves using a CS catheter for epicardial recording and a duodecapolar Halo catheter positioned around the mitral annulus for endocardial recording. Conclusions: The assessment of transmural mitral isthmus block can be challenging. Placement of an endocardial mapping catheter around the mitral annulus can provide a precise assessment of conduction across the mitral isthmus. [ABSTRACT FROM AUTHOR]

Background: The left atrial myocardium (LAM) and coronary sinus (CS) musculature (CSM) generate atrial electrograms recorded inside the CS (AECSs). The vein of Marshall (VOM) courses the mitral isthmus (MI), and ethanol infusion into the VOM (EI-VOM) is useful to ablate it. However, its detailed effect on the MI, which contains the LAM, CSM, and those connections, is unknown.Objective: The purpose of this study was to investigate the impact of EI-VOM on the MI by assessing the AECS.Methods: Eighty-four consecutive patients with atrial fibrillation undergoing MI ablation with successful EI-VOM were included. After EI-VOM, radiofrequency (RF) catheter touchup ablation was performed at MI gap sites or inside the CS (RFCS), as needed, to achieve bidirectional conduction block. Ablation effects on AECSs were evaluated during the MI ablation procedure.Results: AECSs demonstrated double potentials consisting of low-amplitude LAM components and high-amplitude CSM components in 31 patients (37%). Of those patients, 21 had a distal-to-proximal activation sequence of the LAM along with a proximal-to-distal activation sequence of the CSM during left atrial appendage pacing, suggesting CSM isolation from the LAM due to electrical LAM-CSM disconnection. Only 2 of the 21 patients required RFCS. The remaining 10 patients with distal-to-proximal activation in both CSM and LAM, suggesting incomplete CSM isolation and persistent LAM-CSM conduction, required RFCS. Overall, combined EI-VOM with RF created bidirectional conduction block at the MI in 78 patients (93%).Conclusion: EI-VOM can ablate the LAM and myocardial connections between the LAM and CSM. Careful assessment of AECSs can predict a requirement for RFCS. [ABSTRACT FROM AUTHOR]

Background: Epicardiac conduction via the vein of Marshall (VOM) can bypass the mitral isthmus (MI) line, making MI ablation difficult. This study aimed to assess the contribution of the VOM in achieving MI conduction block. Methods: This study included 143 consecutive patients with nonparoxysmal atrial fibrillation who underwent initial MI ablation. They were retrospectively classified into two groups, a VOM‐guided group (n = 28) and a conventional group (n = 115), according to the use of a 2‐Fr electrode catheter inserted in the VOM. The acute success rate of achieving MI block and the ablation data were assessed. When the bidirectional block was verified exclusively in the VOM or coronary sinus (CS) electrodes, we defined it as a pseudo MI block. In the VOM‐guided group, we ascertained the complete MI block, verified both in the VOM and CS electrodes. Results: In the VOM‐guided group, the pseudoblock was observed in 33.3% of the patients during MI ablation. With significantly less radiofrequency energy (19 322.6 ± 11 352.8 vs 25 389.3 ± 19 951.9, P = 0.04), we achieved a similar level of success rate in MI ablation in the VOM‐guided group (96.4% vs 91.3%, P = 0.36). Notably, after achieving complete MI block, atrial burst pacing induced two perimitral flutters in the VOM‐guided group, which were successfully terminated by the additional radiofrequency application. Conclusions: Assessment of electrical conduction through the VOM could clarify the existence of a pseudo MI conduction block. However, the existence of a slow conduction through the MI could be detected only after induction of perimitral atrial tachycardia with atrial programmed stimulation. [ABSTRACT FROM AUTHOR]