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

Evaluation of posterior mitral isthmus ablation in the absence of a vein of Marshall

AIMS

Achieving acute and durable mitral isthmus (MI) block remains challenging using radiofrequency (RF) catheter ablation alone. Vein of Marshall (VoM) ethanolization results in chemical damage along the MI resulting in the creation of a durable transmural lesion with a very high rate of procedural block. However, no studies have systematically assessed the efficacy of MI ablation alone when no anatomical VoM is present.

METHODS AND RESULTS

Thirty seven patients without VoM evidenced after careful angiographic examination were included. Ablation parameters and result were compared with a matched control group in whom the posterior MI line was performed without assessing the presence of the VoM. Mitral isthmus block was achieved in 36 out of 37 patients without VoM (97%), with endocardial ablation only in 5/37 (14%) and combined endocardial and coronary sinus ablation in 32/37 patients (86%). There was a significant difference in the occurrence of block between patients without a VoM and the control group (97.3% vs. 65% respectively, P < 0.01), with a trend towards less needed RF {26 [interquartile range (IQR) 20-38] vs. 29 [IQR 19-40] tags [P = 0.8], 611 [IQR 443-805] vs. 746 [IQR 484-1193] seconds [P = 0.08]}.

CONCLUSION

The absence of a VoM is associated with a very high rate of procedural block during posterior MI ablation. The higher rate of MI block in this specific population would also suggest the crucial role of the VoM (when present) in resistant MI block.

Anatomical Treatment Strategies for Persistent Atrial Fibrillation with Ethanol Infusion within the Vein of Marshall-Current Challenges and Future Directions

Currently, pulmonary vein isolation (PVI) is the gold standard in catheter ablation for atrial fibrillation (AF). However, PVI alone may be insufficient in the management of persistent AF, and complementary methods are being explored. One such method takes an anatomical approach-improving both its success rate and lesion durability may lead to improved treatment outcomes. An additional approach complementary to the anatomical one is also attracting attention, one that focuses on epicardial conduction. This involves ethanol ablation of the vein of Marshall (VOM) and can be very effective in blocking epicardial conduction related to Marshall structure; it is becoming incorporated into standard treatment. However, the pitfall of this "Marshall-PLAN", a method that combines an anatomical approach with ethanol infusion within the VOM (Et-VOM), is that Et-VOM and other line creations are not always successfully completed. This has led to cases of AF and/or atrial tachycardia (AT) recurrence even after completing this lesion set. Investigating effective adjunctive methods will enable us to complete the lesion set with the aim to lower the rates of recurrence of AF and/or AT in the future.

Trans-aortic mitral isthmus ablation after surgical patch closure for an atrial septal defect

INTRODUCTION

In patients with prior atrial septal defect (ASD) closure and atrial tachyarrhythmias, transseptal puncture can be challenging.

METHODS AND RESULTS

This case report discusses a 65-year-old man who had previously undergone pulmonary vein isolation (PVI) and cavo-tricuspid isthmus ablation for atrial fibrillation before ASD closure, respectively. He developed atrial tachycardia (AT) and underwent catheter ablation. AT was diagnosed as peri-mitral flutter and the mitral isthmus (MI) linear ablation via a trans-aortic approach successfully terminated it.

CONCLUSION

This case demonstrates the feasibility and safety of transaortic MI linear ablation in patients with ASD closure devices or anatomical challenges when transseptal puncture is difficult.

Comparison of the Anterior Septal Line and Mitral Isthmus Line for Perimitral Atrial Flutter Ablation Using Robotic Magnetic Navigation

Background

Perimitral atrial flutter (PMAFL) is one of the most common macro-reentrant left atrial tachycardias. Mitral isthmus (MI) linear ablation is a common strategy for the treatment of PMAFLs, and anterior septum (AS) linear ablation has emerged as a novel ablation approach. We aimed at assessing the effectiveness of AS linear ablation using robotic magnetic navigation for PMAFL ablation.

Methods

In this retrospective study, a total of 36 consecutive patients presented with AFL as the unique arrhythmia or accompanied with atrial fibrillation (AF) who underwent catheter ablation were enrolled. Patients were classified into two groups according to the different ablation strategies, the MI line group (10 patients) and the AS line group (26 patients).

Results

The clinical baseline characteristics of patients in the two groups were nearly identical. There were no significant differences in procedure time (148.7 ± 46.1 vs. 123.2 ± 30.1 min, P=0.058) or radiofrequency ablation time (25.9 ± 11.4 vs. 23.5 ± 12.6 min) between the two groups. Fluoroscopy time was longer in the MI line group (8.0 ± 4.4 vs. 5.1 ± 2.7 min, P=0.024), and the acute success rate was higher in the AS line group versus the MI line group (96.2% vs. 70%, P=0.025). The long-term freedom from arrhythmia survival rate was higher in the AS line group (73%) than in the MI line group (40%) after a mean follow-up time of 37.4 months with a 3-month blanking period (P=0.049).

Conclusions

AS linear ablation is an effective and safe strategy for PMAFL ablation using robotic magnetic navigation.

Endocardial and epicardial activation maps for three-dimensional perimitral flutter using a three-dimensional mapping system: a case report

Background

Perimitral flutter (PMF) is a macro-reentrant tachycardia, and mitral isthmus (MI) linear ablation is considered to be the preferable mode of treatment. Additionally, PMF can sometimes develop via epicardial connections, including coronary sinus and vein of Marshall. However, there are no reports of three-dimensional (3D) atrial tachycardia (AT) via the intramural tissue.

Case summary

A 78-year-old man underwent catheter ablation for paroxysmal atrial fibrillation and AT, including pulmonary vein isolation, left atrial posterior wall isolation, superior vena cava isolation, and MI linear ablation in a total of four procedures. However, AT reoccurred, and he underwent a 5th procedure for AT. Although the MI block line was complete in both the endocardial and epicardial voltage maps, AT indicated PMF. The total activation time did not cover all phases of tachycardia cycle length due to the conduction pathway through the intramural muscle/bundles that could not be mapped with the addition of epicardial mapping. The tachycardia was terminated by ablation at the mitral valve annulus in the 2 o’clock position, where the bundles might have been attached.

Discussion

Both endocardial and epicardial activation maps indicated 3D-PMF, whose circuit included the intramural muscle and bundles in a tachycardia circuit. It is necessary to recognize AT, which is involved via intramural tissues.

Extended early meets late for assessment of conduction block along an ablation line

PURPOSE

The purpose of the study was to investigate the usefulness of the extended early meets late (EEML) feature of the HD Coloring software for confirmation of bidirectional block along an ablation line.

METHODS

A single-center prospective observational study of consecutive patients with atypical atrial flutter or persistent atrial fibrillation submitted to catheter ablation including linear lesions from January 2019 to June 2020, with confirmation of bidirectional block across ablation lines assessed with the feature EEML and a multipolar catheter was conducted. Patients were divided into two groups - those with versus those without bidirectional block - and different EEML thresholds were analyzed to assess which one had the better sensitivity and specificity to predict block.

RESULTS

During the 24-month enrollment period, a total of 94 patients were included (50% males, mean age of 64 ± 10 years, 60% with structural heart disease) - 55 patients with versus 39 patients without confirmed a bidirectional block. Activation maps were performed during atrial pacing, with a median number of 1340 (interquartile range 1135-2060) points acquired in 11 ± 3 min, and a mean mapped cycle length of 287 ± 51 ms. The EEML feature was highly useful in detecting bidirectional block along ablation lines, with a 25% threshold value showing the highest discriminative performance (area under the curve of 0.93), 95% sensitivity and 92% specificity in predicting block.

CONCLUSIONS

The EEML feature of the HD Coloring software is a useful addition to the CARTO mapping system for assessment of block across an ablation line. The threshold value of 25% is the most accurate.