Activation patterns and electrophysiological characteristics of Marshall Bundle related left atrial tachycardias post atrial fibrillation ablation

BACKGROUND

Epicardial Marshall bundle (MB) are frequently utilized in left atrial tachycardias (LATs) post atrial fibrillation (AF) ablation with pulmonary vein isolation and substrate modification.

OBJECTIVE

This study sought to classify different activation patterns of MB mediated LATs and the corresponding electrophysiological characteristics.

METHODS

From 2019 to 2021, 28 cases of atrial tachycardias（ATs）post-AF-ablation were diagnosed as MB-mediated LATs by ultra-high density mapping and entrainment. Cannulation and mapping in the vein of Marshall (VOM) and epicardial mapping in the MB region were also performed in selected cases to further prove the mechanism.

RESULTS

Three activation patterns were identified with a critical isthmus via MB: 1）peri-mitral macro-reentry (PM LAT) (n=20, 71.4%); 2) Left atrial appendage (LAA)-related reentry (n=5, 17.9%); and 3) Left pulmonary vein (LPV)-related reentry (n=3,10.7%). In 18 patients, a characteristic triple potential observed along the previously endocardial LA ridge block line was composed of near-field double potentials and far-field MB potential. These findings were further delineated in 24 patients with either cannulation in the VOM (19 patients) or epicardial mapping(5 patients). Ethanol infusion of the VOM resulted in AT termination in 20/28 patients.

CONCLUSION

Different types of MB-Mediated LATs post AF-ablation could be identified by ultra- high density mapping. Ethanol infusion within the VOM was effective in eliminating these tachycardias.

Morphometry of left atrial appendage isthmus and mitral isthmus: implications for atrial fibrillation catheter ablation

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.

Comparison of anterior mitral line and mitral isthmus line for ablation of mitral annular flutter

BACKGROUND

Mitral annular flutter (MAF) is the most common left atrial macro-reentrant arrhythmia following catheter ablation of atrial fibrillation (AF). The best ablation approach for this arrhythmia remains unclear.

METHODS

This single-center, retrospective study sought to compare the acute and long-term outcomes of patients with MAF treated with an anterior mitral line (AML) versus a mitral isthmus line (MIL). Acute ablation success, complication rates, and long-term arrhythmia recurrence were compared between the two groups.

RESULTS

Between 2015 and 2021, a total of 81 patients underwent ablation of MAF (58 with an AML and 23 with a MIL). Acute procedural success defined as bidirectional block was achieved in 88% of the AML and 91% of the MIL patients respectively (p = 1.0). One year freedom from atrial arrhythmias was 49.5% versus 77.5% and at 4 years was 24% versus 59.6% for AML versus MIL, respectively (hazard ratio [HR]: 0.38, confidence interval [CI]: 0.17-0.82, p = .009). Fewer patients in the MIL group had recurrent atrial flutter when compared to the AML group (HR: 0.32, CI: 0.12-0.83, p = .009). The incidence of recurrent AF, on the other side, was not different between both groups (21.7% vs. 18.9%; p = .76). There were no serious adverse events in either group.

CONCLUSION

In this retrospective study of patients with MAF, a MIL compared to AML was associated with a long-term reduction in recurrent atrial arrhythmias driven by a reduction in macroreentrant atrial flutters.

Vein of Marshall Ethanol Infusion for AF Ablation; A Review

The outcomes of persistent atrial fibrillation (AF) ablation are modest with various adjunctive strategies beyond pulmonary vein isolation (PVI) yielding largely disappointing results in randomised controlled trials. Linear ablation is a commonly employed adjunct strategy but is limited by difficulty in achieving durable bidirectional block, particularly at the mitral isthmus. Epicardial connections play a role in AF initiation and perpetuation. The ligament of Marshall has been implicated as a source of AF triggers and is known to harbour sympathetic and parasympathetic nerve fibres that contribute to AF perpetuation. Ethanol infusion into the Vein of Marshall, a remnant of the superior vena cava and key component of the ligament of Marshall, may eliminate these AF triggers and can facilitate the ease of obtaining durable mitral isthmus block. While early trials have demonstrated the potential of Vein of Marshall 'ethanolisation' to reduce arrhythmia recurrence after persistent AF ablation, further randomised trials are needed to fully determine the potential long-term outcome benefits afforded by this technique.

Strategy to achieve mitral isthmus flutter ablation by radiofrequency: the SHERIFF plan

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.

Clinical effect of vein of Marshall ethanol infusion on mitral isthmus ablation

Purpose

This study aimed to investigate the effect of Marshall ethanol infusion (VOM-Et) in the vein on mitral isthmus (MI) ablation.

Methods

Patients with persistent atrial fibrillation (AF) were grouped into vein of VOM-Et combined with radiofrequency (RF) ablation (VOM-Et-RF) and RF groups. The primary outcome was MI block immediate block rate after surgery. Stratified analysis was also performed for factors affecting the outcome measures.

Results

A total of 118 consecutive patients underwent AF ablation at Taizhou Hospital of Zhejiang Province from January 2018 to December 2021. Successful bidirectional perimitral block was achieved in 96% of patients in VOM-Et-RF (69 of 72) and in 76% of patients in the RF group (35 of 46) (P < 0.01). In the subgroup analysis, male sex, elder than 60 years, Left atrial diameter <55 mm, and AF duration <3 years were associated with the benefits of VOM-Et in AF Patients.

Conclusion

The vein of Marshall ethanol infusion for catheter ablation can improve the MI block rate. Male sex, elder age, smaller Left atrial diameter and shorter AF duration may have significant benefits for VOM-Et.

Managing peri-mitral flutter

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.

Identification of the dominant loop of a dual-loop macro-reentry left atrial flutter without prior intervention using high-density mapping technology: A case report

BACKGROUND

Left atrial flutter without prior cardiac interventions is uncommon, especially dual-loop macro-reentry atrial flutter. The critical step to ablate dual-loop macro-reentry atrial flutter is to identify the dominant loop and key isthmus. Although entrainment mapping could help identify the dominant loop and key isthmus, it may alter or terminate tachycardia. High-density mapping allows the generation of electroanatomic maps without altering or terminating tachycardia.

CASE SUMMARY

Here, we report a case of symptomatic left atrial flutter without prior intervention. In this case, high-density mapping revealed a dual-loop macro-reentry around the mitral annulus and central scar of the anterior wall. The propagation result showed that the dominant loop was around the mitral annulus, and the key isthmus was between the central scar and mitral annulus. The atrial flutter terminated successfully after ablation was performed.

CONCLUSION

In this case, we demonstrate that high-density mapping technology may help identify the dominant loop of dual-loop atrial flutter without entrainment, which makes ablation easier.

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.

Temperature-controlled ablation of the mitral isthmus line using the novel DiamondTemp ablation system

Background

The novel DiamondTemp™ (DT)-catheter (Medtronic®) was designed for high-power, short-duration ablation in a temperature-controlled mode.

Aim

To evaluate the performance of the DT-catheter for ablation of the mitral isthmus line (MIL) using two different energy dosing strategies.

Materials and methods

Twenty patients with recurrence of atrial fibrillation (AF) and/or atrial tachycardia (AT) following pulmonary vein (PV) isolation were included. All patients underwent reisolation of PVs in case of electrical reconnection and ablation of a MIL using the DT-catheter. Application durations of 10 (group A, n = 10) or 20 s (group B, n = 10) were applied. If bidirectional block was not reached with endocardial ablation, additional ablation from within the coronary sinus (CS) was conducted.

Results

In 19/20 (95%) patients, DT ablation of the MIL resulted in bidirectional block. Mean procedure and fluoroscopy time, and dose area product did not differ significantly between the two groups. In group B, fewer radiofrequency applications were needed to achieve bidirectional block of the MIL when compared to group A (26 ± 12 vs. 42 ± 17, p = 0.04). Ablation from within the CS was performed in 8/10 patients (80%) of group A and in 5/10 (50%) patients of group B (p = 0.34). No major complication occurred.

Conclusion

Mitral isthmus line ablation with use of the DT-catheter is highly effective and safe. Longer radiofrequency-applications appear to be favorable without compromising safety.

Vein of Marshall Ethanol Infusion as First Step for Mitral Isthmus Linear Ablation

OBJECTIVES

In this study, the authors sought to investigate the added value of vein of Marshall ethanol infusion (VOMEt) as first step in facilitating radiofrequency (RF)-guided mitral isthmus (MI) block.

BACKGROUND

Achieving MI block with the use of RF ablation is challenging.

METHODS

Seventy patients planned for MI ablation were randomized 1:1 to VOMEt as a first step preceding RF (endocardial and epicardial, VOM_FIRST group) vs RF ablation as a first step preceding VOMEt (RF_FIRST group). The study end point was incidence of MI block after RF ablation and after the 2 steps.

RESULTS

In VOM_FIRST, VOMEt was successful in 30/35 patients (86%) resulting in a low-voltage area of 12 ± 7.4 cm² and MI block in 2/35 patients (6%). VOM_FIRST, compared with RF_FIRST, was associated with higher incidence of MI block after endocardial (46% vs 11%; P < 0.001) and epicardial ablation (94% vs 43%; P < 0.001), with fewer endocardial applications (4 vs 11 vs 4; P < 0.001) and similar epicardial applications (7 vs 8; P = 0.68). Incidence of MI block after the 2 steps was 94% vs 63% (P = 0.001) in VOM_FIRST vs RF_FIRST, respectively. Additional touch-up RF ablation in both groups resulted in final MI block in all but 1 patient (99%).

CONCLUSIONS

VOMEt as a first step in RF-guided MI line ablation significantly reduced the number of RF applications needed to achieve MI block, even if the sequence of the ablation steps did not affect the final incidence of block. (Evaluation of Vein of Marshall Ethanol Infusion During Left Atrial Linear Ablation in Patients With Persistent Atrial Fibrillation [MARSHALINE]; NCT04124328).

Left atrial wall thickness and its relationship with reconnection after pulmonary vein isolation in patients with atrial fibrillation evaluated using a three-dimensional wall thickness map

Background

The major cause of recurrence after pulmonary vein (PV) isolation for atrial fibrillation (AF) is PV reconnection, and thicker wall could be associated with reconnection.

Objectives

This study aimed to evaluate the wall thickness of the PV antrum in reconnection sites using a three-dimensional (3D) wall thickness map.

Methods

A total of 91 patients who underwent a second ablation procedure due to AF recurrence were evaluated. The locations of the PV reconnection sites were confirmed in electroanatomical maps. A 3D atrial wall thickness (AWT) map was created using computed tomography scan data. The AWT values of the ablation lines of the index procedure were graded in each segment of the PV antrum: grade 1, 0.5 < AWT ≤ 1.0 mm; grade 2, 1.0 < AWT ≤ 1.5 mm; grade 3, 1.5 < AWT ≤ 2.0 mm; grade 4, 2.0 < AWT ≤ 2.5 mm; grade 5, AWT > 2.5 mm.

Results

A total of 281 PV reconnection sites among 1256 segments of the PV antrum in 79 patients were detected. The average AWT grades were 2.7 ± 1.0 and 2.2 ± 1.0 in the reconnected and non-reconnected segments, respectively (P < 0.01). Higher AWT grades were observed in the reconnected superior segments of the left superior PV, carina and inferior segments of the left inferior PV, superior and posterior segments of the right superior PV, and posterior and inferior segments of the right inferior PV.

Conclusion

The reconnected segments of the PV antrum showed thicker myocardium than the non-reconnected ones in patients with recurrent AF after catheter ablation. A wall thickness map for PV isolation could be considered for customized ablation in order to reduce PV reconnection.

Primer on Pulsed Electrical Field Ablation: Understanding the Benefits and Limitations

Pulsed electrical field (PEF) energy is a promising technique for catheter ablation of cardiac arrhythmias. In this article, the key aspects that need to be considered for safe and effective PEF delivery are reviewed, and their impact on clinical feasibility is discussed. The most important benefit of PEF appears to be the ability to kill cells through mechanisms that do not alter stromal proteins, sparing sensitive structures to improve safety, without sacrificing cardiomyocyte ablation efficacy. Many parameters affect PEF treatment outcomes, including pulse intensity, waveform shape, and number of pulses, as well as electrode configuration and geometry. These physical and electrical characteristics must be titrated carefully to balance target tissue effects with collateral implications (muscle contraction, temperature rise, risk of electrical arcing events). It is important to note that any combination of parameters affecting PEF needs to be tested for clinical efficacy and safety. Applying PEF clinically requires knowledge of the fundamentals of this technology to exploit its opportunities and generate viable, durable health improvements for patients.

Durability of Left Atrial Lesions After Ethanol Infusion in the Vein of Marshall

OBJECTIVES

The aim of this study was to assess the persistence of left atrial (LA) lesions created by ethanol infusion in the vein of Marshall (EIVM) by electroanatomical mapping on repeat catheter ablation for recurrent atrial tachyarrhythmia.

BACKGROUND

Little is known about the durability of LA lesions created by EIVM.

METHODS

The study included consecutive patients who underwent EIVM for persistent atrial fibrillation or perimitral LA flutter (index procedure) and repeat catheter ablation for recurrent atrial tachyarrhythmia or atrial fibrillation at a single center between January 2019 and April 2020. The acute effect of EIVM was assessed at the index procedure by comparing the area of bipolar voltage <0.05 mV in the vein of Marshall (VOM) region before and immediately after EIVM. The long-term effect of EIVM was assessed by comparing this area in the VOM region between the redo procedure and the index procedure.

RESULTS

Twenty-four consecutive patients (mean age 68.6 ± 6.1 years, 58% men) underwent redo procedures after previous EIVM for persistent atrial fibrillation (n = 21 [88%]) or perimitral LA flutter (n = 5 [21%]). In each patient, the EIVM-related lesion persisted, with a chronic scar in the VOM region (median 13.1 cm² [interquartile range: 8.1-15.9 cm²] vs 12.4 cm² [interquartile range: 7.6-15.7 cm²] acutely, respectively). One quarter of patients (9 of 20) had late mitral isthmus reconnection, which was located at the mitral annular edge or in the coronary sinus.

CONCLUSIONS

Atrial lesions created by EIVM are durable, which reinforces the efficacy profile of EIVM. Reconduction sites in the mitral isthmus are located at the edge of the scar and in the coronary sinus.

An improved window of interest for electroanatomical mapping of atrial tachycardia

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 (WOI_{p 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 (WOI_conv.) or WOI_{p 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%). WOI_{p 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 WOI_conv.. 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.

Impact of Vein of Marshall Ethanol Infusion on Mitral Isthmus Block: Efficacy and Durability

BACKGROUND

Achieving bidirectional mitral isthmus (MI) block using radiofrequency catheter ablation (RFCA) alone is challenging, and MI reconnection is common. Adjunctive vein of Marshall (VOM) ethanol infusion (VOM-Et) can facilitate acute MI block. However, little is known about its long-term success. This study sought to evaluate the impact of adjunctive VOM-Et on MI block achievement and durability compared with RFCA alone.

METHODS

Patients undergoing the first attempt of posterior MI ablation were grouped according to their MI block index strategy: adjunctive VOM-Et and RFCA alone. Rates of acute MI block and MI reconnection observed during repeat procedures were compared between the 2 groups.

RESULTS

The VOM-Et group consisted of 152 patients (63.8±9.4 years) undergoing adjunctive VOM-Et for MI block. The RFCA group consisted of 110 patients (60.9±9.2 years) undergoing MI ablation using RFCA alone. Acute MI block was more frequently achieved in the VOM-Et group (98.7% [150/152] versus 63.6% [70/110]; P<0.001) with shorter RFCA duration (5.00 [3.00-7.00] versus 19.0 [13.6-22.0] minutes; P<0.001). Of the 220 patients with MI block achieved during the index procedure, 81 underwent a repeat procedure during follow-up (VOM-Et group: 23.3% [35/150] versus RFCA group: 65.7% [46/70], respectively; P<0.001). A significantly greater number of patients exhibited durable MI block in the VOM-Et group (62.9% [22/35] versus 32.6% [15/46], respectively; P=0.008).

CONCLUSIONS

Beyond facilitating acute MI block, VOM-Et is associated with greater lesion durability as evidenced by higher rates of MI block during repeat procedures.

Initial multicenter experience with a new high-density coloring module: impact for complex atrial arrhythmias interpretation

BACKGROUND

High-density automated mapping of complex atrial tachycardias (ATs) requires accurate assessment of activation maps. A new local activation display module (HD coloring, Biosense Webster®) provides higher map resolution, a better delineation of potential block reducing color interpolation, and a new propagation display. We evaluated the accuracy of a dedicated local activation display compared with standard algorithm.

METHODS

High-density maps from 10 AT were collected with a multipolar catheter and were displayed with standard activation or HD coloring. Six expert operators retrospectively analyzed activation maps and were asked to define (1) the tachycardia mechanism, (2) ablation target, and (3) level of difficulty to interpret those maps.

RESULTS

Using HD coloring, operators were able to reach a correct diagnosis in 93% vs. 63%, p < 0.05 compared to standard activation maps. Time to diagnosis was shorter 1.9 ± 1.0 min vs. 3.9 ± 2.1 min, p < 0.05. Confidence level would have allowed ablation without necessity for entrainment maneuvers in 87% vs. 53%, p < 0.05. Operators would have needed to remap or proceed with multiple entrainments in 3% vs. 13% of cases, p < 0.05. Finally, ablation strategy was more accurately identified in 97% vs. 67%, p < 0.05.

CONCLUSION

Activation mapping with the new HD coloring module allowed a more accurate, reliable, and faster interpretation of complex ATs mechanisms compared to standard activation maps.

Mechanism of Recurrence of Atrial Tachycardia

Background:

Atrial fibrillation ablation–related atrial tachycardia (AT) is complex and may demonstrate several forms: anatomic macroreentrant AT (AMAT), non-AMAT, and focal AT. We aimed to elucidate the recurrence rate and mechanisms of atrial fibrillation ablation–related AT recurrence.

Methods:

Among 147 patients with ATs treated with the Rhythmia system, 68 (46.3%) had recurrence at mean 4.2 (2.9–11.6) months, and 44 patients received a redo procedure. AT circuits in the first procedure were compared with those in the redo procedure.

Results:

Although mappable ATs were not observed in 7 patients, 68 ATs were observed in 37 patients during the first procedure: perimitral flutter (PMF) in 26 patients, roof-dependent macroreentrant AT (RMAT) in 18, peritricuspid flutter in 10, non-AMAT in 14, and focal AT in 3. During the redo AT ablation procedure, 54 ATs were observed in 41/44 patients: PMF in 24, RMAT in 14, peritricuspid flutter in 1, non-AMAT in 14, and focal AT in 1. Recurrence of PMF and RMAT was observed in 15 of 26 (57.7%) and 8 of 18 (44.4%) patients, respectively, while peritricuspid flutter did not recur. Neither the same focal AT nor the same non-AMAT were observed except in 1 case with septal scar–related biatrial AT. Epicardial structure–related ATs were involved in 18 of 24 (75.0%) patients in PMF, 4 of 14 (28.6%) in RMAT, and 4 of 14 (28.6%) in non-AMAT. Of 21 patients with a circuit including epicardial structures, 6 patients treated with ethanol infusion in the vein of Marshall did not show any AT recurrence, although 8 of 15 (53.3%) treated with radiofrequency showed AT recurrence ( P =0.04).

Conclusions:

Although high-resolution mapping may lead to correct diagnosis and appropriate ablation in the first procedure, the recurrence rate is still high. The main mechanism of atrial fibrillation ablation–related AT is the recurrence of PMF and RMAT or non-AMAT different from the first procedure. Epicardial structures (eg, coronary sinus/vein of Marshall system) are often involved, and ethanol infusion in the vein of Marshall may be an additional treatment.

Topographic characteristics of the left atrial medial isthmus

BACKGROUND

The purpose of this study was to provide detailed topography of the left atrial medial isthmus (situated between the right inferior pulmonary vein ostium and the medial part of the mitral annulus).

METHODS

Two hundred human hearts (Caucasian, 22.5% females, 48.7 ± 4.9 years old) were investigated.

RESULTS

The mean length of the medial isthmus was 42.4 ± 8.6 mm. Additionally, the medial isthmus line was divided by the oval fossa into three sections with equal mean lengths (upper: 14.2 ± 7.2 vs middle: 14.1 ± 6.1 vs lower: 14.9 ± 4.6 mm; P > .05). The left upper section of the atrial wall was thinner than the lower section (2.5 ± 1.1 vs 3.4 ± 1.6 mm; P < .0001). This study noted three separate spatial arrangements of the isthmus line. Type I (54.5%) had an oval fossa located outside the isthmus line; type II (32.5%) had an oval fossa crossed by the isthmus line, and type III (13.0%) had an oval fossa rim located tangentially to the isthmus line. In 68.5% of the examined specimens, the isthmus area had a smooth surface. Conversely, the remaining 31.5% had additional structures within its borders such as diverticula, recesses, and tissue bridges.

CONCLUSION

This study is the first to describe the morphometric and topographical features of the left atrial medial isthmus. Interventions within the medial isthmus line should be performed cautiously, especially when they are transected by the oval fossa (32.5%). Careful navigation of the area is also recommended due to the possibility of existent additional structures. The latter could lead to catheter entrapment during ablation procedures.

Evaluation of left atrial linear ablation using contiguous and optimized radiofrequency lesions: the ALINE study

Aims

Achieving block across linear lesions is challenging. We prospectively evaluated radiofrequency (RF) linear ablation at the roof and mitral isthmus (MI) using point-by-point contiguous and optimized RF lesions.

Methods and results

Forty-one consecutive patients with symptomatic persistent AF underwent stepwise contact force (CF)-guided catheter ablation during ongoing AF. A single linear set of RF lesions was delivered at the roof and posterior MI according to the 'Atrial LINEar' (ALINE) criteria, i.e. point-by-point RF delivery (up to 35 W) respecting strict criteria of contiguity (inter-lesion distance ≤ 6 mm) and indirect lesion depth assessment (ablation index ≥550). We assessed the incidence of bidirectional block across both lines only after restoration of sinus rhythm. After a median RF time of 7 min [interquartile range (IQR) 5-9], first-pass block across roof lines was observed in 38 of 41 (93%) patients. Final bidirectional roof block was achieved in 40 of 41 (98%) patients. First-pass block was observed in 8 of 35 (23%) MI lines, after a median RF time of 8 min (IQR 7-12). Additional endo- and epicardial (54% of patients) RF applications resulted in final bidirectional MI block in 28 of 35 (80%) patients. During a median follow-up of 396 (IQR 310-442) days, 12 patients underwent repeat procedures, with conduction recovery in 4 of 12 and 5 of 10 previously blocked roof lines and MI lines, respectively. No complications occurred.

Conclusion

Anatomical linear ablation using contiguous and optimized RF lesions results in a high rate of first-pass block at the roof but not at the MI. Due to its complex 3D architecture, the MI frequently requires additional endo- and epicardial RF lesions to be blocked.

Achieving durable mitral isthmus block: Challenges, pitfalls, and methods of assessment

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.

Importance of the vein of Marshall involvement in mitral isthmus ablation

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.

Mitral isthmus ablation using a circular mapping catheter positioned in the left atrial appendage as a reference for conduction block

Background

For perimitral atrial flutter (PMFL) developing after catheter ablation of atrial fibrillation (AF), to create a complete conduction block at the mitral isthmus (MI) is mandatory to terminate it, however, it is still challenging.

Methods

This study consisted of 80 patients (74 male, 61 ± 8.1 years) undergoing MI ablation. After a circular mapping catheter was positioned at the neck of the left atrial appendage (LAA), the MI ablation was performed on the MI line just below the LAA neck targeting the earliest activation recording site of the LAA catheter during pacing from the coronary sinus (CS). When ablation during CS pacing was not successful, an RF delivery during LAA pacing was applied targeting the earliest activation site just below the MI line. If the endocardial approach failed, an RF application inside the CS was attempted.

Results

With the endocardial approach, acute success was achieved in 51/80 patients (64%). Additional epicardial ablation from the CS was performed in 26/29 (90%) endocardially unsuccessful patients and conduction block at the MI was achieved in 21/26 (81%). Overall, complete conduction block at the MI was achieved in 72/80 patients (90%). At a mean follow-up of 16 ± 6 months, 20 patients (25%) had recurrence of atrial arrhythmias (AT: 12, AF: 8), and 10 (AT: 7, AF : 3) underwent a second procedure in which an LMI block line was completed in 3 (33%). PMFL was diagnosed in 6 out of 7 AT patients. No complications were observed.

Conclusions

Creating linear lesions just beneath the neck of the LAA was highly successful under the guidance of a circular mapping catheter in the LAA using a steerable sheath. An RF application from the CS was needed in less than half of the cases.

Association Between Local Bipolar Voltage and Conduction Gap Along the Left Atrial Linear Ablation Lesion in Patients With Atrial Fibrillation

A bipolar voltage reflects a thick musculature where formation of a transmural lesion may be hard to achieve. The purpose of this study was to explore the association between local bipolar voltage and conduction gap in patients with persistent atrial fibrillation (AF) who underwent atrial roof or septal linear ablation. This prospective observational study included 42 and 36 consecutive patients with persistent AF who underwent roof or septal linear ablations, respectively. After pulmonary vein isolation, left atrial linear ablations were performed, and conduction gap sites were identified and ablated after first-touch radiofrequency application. Conduction gap(s) after the first-touch roof and septal linear ablation were observed in 13 (32%) and 19 patients (53%), respectively. Roof and septal area voltages were higher in patients with conduction gap(s) than in those without (roof, 1.23 ± 0.77 vs 0.73 ± 0.42 mV, p = 0.010; septal, 0.96 ± 0.43 vs 0.54 ± 0.18 mV, p = 0.001). Trisected regional analyses revealed that the voltage was higher at the region with a conduction gap than at the region without. Complete conduction block across the roof and septal lines was not achieved in 3 (7%) and 6 patients (17%), respectively. Patients in whom a linear conduction block could not be achieved demonstrated higher ablation area voltage than those with a successful conduction block (roof, 1.91 ± 0.74 vs 0.81 ± 0.51 mV, p = 0.001; septal, 1.15 ± 0.56 vs 0.69 ± 0.31 mV, p = 0.006). In conclusion, a high regional bipolar voltage predicts failure to achieve conduction block after left atrial roof or septal linear ablation. In addition, the conduction gap was located at the preserved voltage area.

Selection of Critical Isthmus in Scar-Related Atrial Tachycardia Using a New Automated Ultrahigh Resolution Mapping System

Background—

Accurate activation mapping of reentrant scar-related atrial tachycardias (AT) allows efficient radiofrequency ablation by targeting the critical isthmus (CI). We aimed to assess the electrophysiological properties of CI channels during mapping with the IntellaMap Orion basket and the Rhythmia system.

Methods and Results—

We prospectively studied 33 AT (post– atrial fibrillation ablation or surgical mitral valve repair). The noise of bipolar electrogram (EGM) was systematically measured at 10 prespecified sites, as well as on a standard catheter and on the surface ECG. Bipolar EGM of CI regions were analyzed for amplitude, duration, and conduction velocity. The isthmus region to be targeted was chosen based solely on propagation. For each AT, 25 684±14 276 EGMs were automatically annotated. Noise of the Orion EGM was 0.011±0.004 mV, lower than that of a standard catheter (0.016±0.019) and surface ECG (0.02±0.01; P <0.05). For reentrant AT, within the CI, bipolar EGM amplitude (0.08±0.11 mV) and conduction velocity (0.27±0.19 m/s) were lower than those orthodromically before (0.62±0.93 mV; 1±0.49 m/s) and after (0.80±1.59 mV; 1±0.73 m/s) the isthmus ( P <0.001 for all). In 97% of AT, ablation at the CI resulted in AT termination. No complications occurred.

Conclusions—

This new automated ultrahigh resolution mapping system produces low noise and allows accurate diagnosis of AT circuits. CI on reentrant scar-related AT showed much lower EGM amplitude with a significantly slower conduction velocity than the surrounding parts of the circuit. Ablation of the areas of slow conduction resulted in a high acute success.