The importance of identifying conduction breakthrough sites across the mitral isthmus by elaborate mapping for mitral isthmus linear ablation

A novel stepwise catheter ablation method of the mitral isthmus for persistent atrial fibrillation: efficacy and reproducibility

BACKGROUND

Ethanol infusion of the vein of Marshall (EI-VOM) has been widely used to facilitate mitral isthmus (MI) ablation. According to the literature, the success rate of achieving a bidirectional conduction block across the MI ranges from 51 to 96%, with no standardized strategy or method available for cardiac electrophysiologists.

OBJECTIVES

This study aimed to introduce and evaluate a novel ablation method of MI.

METHODS

Consecutive patients with persistent atrial fibrillation (PeAF) that underwent catheter ablation were included. The MI ablation procedure followed a stepwise approach. In step 1, ethanol infusion of the vein of Marshall (EI-VOM) was performed. In step 2, a "V-shape" endocardial linear ablation connecting the left inferior pulmonary vein (LIPV) to mitral annulus (MA) was performed. In step 3, earliest activation sites(EASs) near the ablation line were identified using activation mapping followed by reinforced ablation. In step 4, precise epicardial ablation was performed, with the catheter introduced into the coronary sinus(CS) to target key ablation targets (KATs).

RESULTS

135 patients with PeAF underwent catheter ablation with the stepwise ablation method adopted in 119 cases. Bidirectional conduction blocks were achieved in 117 patients (98.3%). The block rates of every step were 0%, 58.0%, 44.0%, and 92.9%, and the cumulative block rates for the four steps were 0%, 58.0%, 76.5%, and 98.3%, respectively. No patient experienced fatal complications.

CONCLUSIONS

Our novel stepwise catheter ablation method for MI yielded a high bidirectional block rate with high reproducibility.

Epicardial connections and bi-atrial tachycardias: From anatomy to clinical practice

Bi-atrial tachycardia (BiAT) is not rare after extensive atrial ablation or cardiac surgery. The complexity of bi-atrial reentrant circuits poses a great challenge for clinical practice. With recent advances in mapping technologies, we are now able to characterize atrial activation in detail. However, given the involvement of both atria and multiple epicardial conductions, endocardial mapping for BiATs is not easy to understand. Knowledge of the atrial myocardial architecture is the foundation for the clinical management of BiATs; as it is required to understand the possible mechanism of the tachycardia and identify the optimal target of ablation. In this review we summarize current knowledge about the anatomy of interatrial connections as well as other epicardial fibers and discuss the interpretation of electrophysiological findings and ablation strategies for BiATs.

Arrhythmogenesis of surgical atrial incisions and lesions in Maze procedure: insights from high-resolution mapping of atrial tachycardias

BACKGROUND

Atrial tachycardias (ATs) frequently develop after a surgical Maze procedure. We aimed to elucidate the electrophysiologic mechanisms and their arrhythmogenic substrates of these ATs.

METHODS AND RESULTS

We retrospectively reviewed 20 patients (14 females, mean age of 55.5 ± 8.6 years) with post-Maze ATs who underwent high-resolution mapping at three institutions. The slow conduction areas, reentry circuits, voltage signals, complex electrograms, and their correlation with the surgical incisions and lesions placed in the surgical Maze procedures were analyzed. Thirty-six ATs with a mean cycle length of 260.0 ± 67.6 ms were mapped in these patients. Among them, 22 (61.1%) were anatomical macro-reentrant ATs (AMAT), 12 (33.3%) non-AMATs (localized ATs), and 2 (5.6%) focal ATs, respectively. Epicardial conduction bridges were observed in 6/20 (30.0%) patients and 7/36 (19.4%) ATs. Different arrhythmogenic substrates were identified in these ATs, including slow conduction regions within the previous lesion areas or between the incisions and anatomical structures, the prolonged activation pathways caused by the short lesions connecting the tricuspid annulus, and the circuits around the long incisions and/or lesions.

CONCLUSIONS

Reentry is the main mechanism of the post-Maze ATs. The pro-arrhythmic substrates are most likely caused by surgical incisions and lesions. The slow conduction regions and the protected channels yielded from these areas are the major arrhythmogenic factors.

Revisiting the characteristics and ablation strategy of biatrial tachycardias: a case series and systematic review

AIMS

To describe the role of left atrial (LA) epicardial conduction and targets of ablation in biatrial tachycardias (BiATs).

METHODS AND RESULTS

Consecutive patients with BiAT diagnosed by high-density mapping and appropriate entrainment were enrolled. A systematic review of case reports or series was then performed. Biatrial tachycardia was identified in 20 patients aged 63.5 ± 11.1 years. Among them, eight had LA epicardial conduction, including four via the ligament of Marshall, two via myocardial fibres between the great cardiac vein (GCV) and LA, one via septopulmonary bundle, and one via myocardial fibres between the posterior wall and coronary sinus. Ablation was targeted at the anatomical isthmus in 14, including 5 undergoing vein of Marshall ethanol infusion and 2 undergoing ablation in the GCV. Another six underwent ablation at interatrial connections, including one with septopulmonary bundle at the fossa ovalis and five at the atrial insertions of Bachmann's bundle. After a mean follow-up of 8.7 ± 3.8 months, five patients had recurrence of atrial fibrillation/flutter. Systematic review enrolled 87 patients in previous and the present reports, showing a higher risk of impairment in atrial physiology in those targeting interatrial connections (30.4 vs. 5.0%, P < 0.001) but no significant difference in short- and long-term effectiveness.

CONCLUSION

Left atrial epicardial conduction is common in BiATs and affects the ablation strategy. Atrial physiology is a major concern in selecting the target of intervention.

Simplified stepwise anatomical ablation strategy for mitral isthmus: efficacy, efficiency, safety, and outcome

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.

Endocardial ablation at the mitral valve vestibule and its surroundings for the treatment of arrhythmias linked to the greater cardiac vasculature

BACKGROUND

The role of the epicardial vasculature in supraventricular and ventricular arrhythmias was described in clinical studies as well as its treatment by intravascular point ablation or alcohol injection. We report on a case series of patients with different arrhythmias linked to an epicardial site of origin with evidence supporting transmural extensions that were targeted for ablation with successful outcomes.

METHODS

The records of patients who has catheter ablation for Supraventricular or Ventricular arrhythmias between 2015-2020 was searched for patients with (1) arrhythmias linked to the epicardial vasculature and (2) findings to support an endocardial connection to the epicardial vasculature by activation mapping, pace mapping, or differential pacing, and (3) were successfully ablated via an endocardial approach only.

RESULTS

From the data searched, we identified 5 patients with the following arrhythmias left ventricular summit ectopy, peri-mitral atrial flutter, preexcitation with inducible atrioventricular reentry tachycardia (AVRT) and a concealed left side accessory pathway with inducible AVRT that were linked to the following vessels: Great Cardiac vein, persistent left superior vena cava, left coronary cusp and left ventricular outflow tract. Endocardial connections were supported by a combination of electro anatomical activation mapping, pace-mapping, and differential pacing. Endocardial ablations performed in all patients were successful without complications CONCLUSION: : This report highlights a subset of patients with arrhythmias linked to the greater cardiac vascular system that can be safely and effectively ablated endocardially, given the limitations and possible complications of epicardial ablation within or in the proximity of the epicardial vasculature. This article is protected by copyright. All rights reserved.

Perimitral atrial tachycardias dependent on residual nonligament of Marshall conduction

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.

Incidence, electrophysiological characteristics, and long-term follow-up of perimitral atrial flutter in patients with previously confirmed mitral isthmus block

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.

Systematic Evaluation of High-Resolution Activation Mapping to Identify Residual Endocardial and Epicardial Conduction Across the Mitral Isthmus

OBJECTIVES

This study sought to systematically evaluate the ability of a high-resolution mapping system (Rhythmia, Boston Scientific, Marlborough, Massachusetts) to rapidly and accurately localize residual endocardial and epicardial conduction after mitral isthmus (MI) ablation, facilitating MI block.

BACKGROUND

Achieving conduction block across the mitral isthmus (MI) is challenging.

METHODS

Fifty consecutive patients undergoing MI ablation after pulmonary vein isolation were enrolled. After initial endocardial radiofrequency (RF) ablation across the lateral MI, high-resolution activation mapping of the MI with simultaneous coronary sinus (CS) mapping was performed to verify block or localize residual conduction across the MI during left atrial (LA) appendage and CS pacing. Propagation maps were used to identify residual conduction across the MI as endocardial, via the CS or Marshall tract.

RESULTS

In all 50 patients, after the initial endocardial ablation across the MI, repeat high-resolution mapping of the LA and CS was obtained (median: 3,329 mapped points; 4.0 min of mapping time). The initial endocardial MI ablation resulted in block in 9 of 50 patients (18%). In the remaining 41 patients, the propagation map identified residual conduction in 4 patterns: 1) only endocardial gap in 12 patients (29%); 2) only CS connection in 10 patients (24%); 3) both endocardial and CS connections in 14 patients (34%); and 4) Marshall tract connection in 5 patients (12%). In 8 patients, the propagation map revealed residual conduction, despite differential atrial pacing suggesting bidirectional block. Focal ablation at the identified residual conduction site (median: 0.7 min of RF) resulted in block in 49 of 50 (98%) patients.

CONCLUSIONS

High-resolution propagation maps of the LA/CS rapidly and accurately localize residual endocardial and epicardial conduction across the MI. Focal ablation with short RF time at the identified gap(s) achieved complete block across MI in 98% of cases.

Flutter Wave Morphology of Peri-Mitral Atrial Flutters Is Mainly Determined by Right Atrial Activation: Insights From High-Resolution Mapping

BACKGROUND

Peri-mitral atrial flutters frequently develop post-atrial fibrillation ablation or postcardiac surgery. The determinants of the flutter wave morphology on surface ECG have been less studied.

METHODS

We retrospectively reviewed 24 patients with peri-mitral atrial flutters who underwent biatrial high-resolution mapping at 3 institutions with LUMIPOINT software. We analyzed the overlap between the right atrial (RA) activation time and flutter wave duration and compared the proportion of the endocardial area that was activated in both atria during the flutter wave duration. Biatrial activation patterns and interatrial conductions were also identified.

RESULTS

The mean tachycardia cycle length was 264±60 ms, with RA activation time 155±45 ms (60.8±20.6% of the tachycardia cycle length), and the flutter wave duration 107±31 ms (41.6±11.7% of the tachycardia cycle length). The overlap between the RA activation time and the flutter wave duration was 102±29 ms, which takes 68.5±17.2% of the RA activation time and 95.7±9.1% of the flutter wave duration, respectively. Quantitative analysis also showed that during the flutter wave duration, more percentage of the endocardial area was activated in the RA than in the left atrium (73.0±12.7% versus 45.2±13.0%, P<0.001). We consistently observed that the RA anterior wall rightward activation corresponded to the positive component in V1 in both flutter patterns, and the RA downward activation corresponded to the positive component in the counterclockwise group or the upward activation corresponded to the negative component in the clockwise group in the inferior leads. The passive RA activation patterns were varied with spontaneous atrial scarring or previous linear ablation.

CONCLUSIONS

ECG flutter wave morphology of peri-mitral atrial flutters is mainly dependent on RA activation patterns.

Mitral isthmus block is associated with favorable outcomes after reablation for long-standing persistent atrial fibrillation

Background

Mitral isthmus (MI) ablation was limited due to technical challenges in the index ablation for long‐standing persistent atrial fibrillation (LPeAF). The role of adjunctive MI ablation was controversial.

Hypothesis

MI block could be achieved in most patients undergoing repeat LPeAF ablation and was associated with favorable clinical outcomes.

Methods

Of 87 consecutively patients undergoing reablation for recurrent atrial tachyarrhythmias (ATa), 41 patients with residual MI conduction but without pulmonary vein reconnection or left atrial roof conduction were enrolled to treat recurrent atrial flutter (AFL) (n = 20) and AF (n = 21). After AFL ablation and AF cardioversion, MI conduction gaps (CGs) were mapped and closed.

Results

MI line was successfully blocked in 37 (90.2%) of 41 patients after closing 1.4 ± 0.5 CGs (31 endocardial CGs and 16 epicardial ones) in the initial MI lines. CGs were more often located at the endocardial sites close to the lateral ridge between left atrial appendage and left‐sided PVs, midportion of MI and at the epicardial breakthroughs within coronary sinus. At the end of 16.0 ± 1.9 months' follow‐up, 31 (83.8%) of 37 patients with MI block and 1 of 4 patients without MI block were free of further recurrence of ATa off anti‐arrhythmic drugs. MI block was positively associated with ATa‐free survival by Cox's regression analysis (hazard ratio [HR]: 0.012, 95% confidence interval [CI]: 0.000‐0.456, P = .02).

Conclusions

MI block could be achieved in the majority of patients during repeat ablation for LPeAF. MI block was associated with favorable clinical outcomes after LPeAF reablation.