Electrophysiological characteristics of epicardial to endocardial breakthrough in intractable cavotricuspid isthmus-dependent atrial flutter

Cryoablation as an alternative strategy for bidirectional cavotricuspid isthmus block following multiple failed sessions of radiofrequency ablation due to epicardial-endocardial breakthrough: A case report

Cavotricuspid isthmus (CTI)-dependent atrial flutter (AFL) is difficult to manage with antiarrhythmic drugs, with radiofrequency (RF) ablation being the standard treatment. However, achieving a bidirectional CTI block can be challenging due to complex anatomy and epicardial-endocardial breakthrough (EEB). This case report illustrates that cryoablation can serve as an effective bail-out strategy to achieve a permanent CTI block when RF ablation fails, particularly in cases complicated by EEB. We present the case of a 66-year-old woman who underwent multiple catheter ablations for persistent atrial fibrillation (AF) and CTI-dependent AFL. Despite two prior sessions of RF-based CTI ablation, a durable bidirectional block was not achieved. During her fourth ablation, recurrent AFL persisted despite extensive RF applications. Cryothermal ablation, utilizing a Freezor MAX catheter with point-by-point freezing along the CTI line, successfully terminated the AFL and created a durable bidirectional CTI block. While RF ablation remains the primary treatment for CTI-dependent AFL, the formation of a durable bidirectional CTI block can be challenging due to complex CTI anatomy, EEB, and tissue edema. Cryothermal ablation offers a viable alternative in these difficult cases. The enhanced tissue adhesion and improved catheter stability provided by cryoablation, along with the reduced risk of steam pops, allow for more consistent lesion formation. This case underscores the utility of cryoablation as a bail-out strategy when RF ablation alone is insufficient.

Electrophysiological evidence of right atrial epicardial connections in a case with recurrent common atrial flutter

The majority of the cavotricuspid isthmus (CTI) region consists of discretely arranged muscle bundles separated by connective tissue. Heterogeneity in the anatomic arrangement of the muscle bundles results in differences in the endocardial and epicardial activation patterns. We present a case of recurrent atrial flutter (AFL) despite the presence of a complete endocardial CTI block. We found epicardial-endocardial breakthrough (EEB) sites on the right atrial high septum. In addition, the epicardial excitation confirmed by endocardial activation mapping was detected as far-field potentials. Radiofrequency ablation was performed at the EEB site. No AFL has recurred for 12 months after the present procedure.

Case Report: Epi-endocardial bridges in refractory cavotricuspid isthmus-dependent atrial flutter: technical analysis of epi-endocardial breakthrough

Background

Typical isthmus-dependent atrial flutter (AFL) is traditionally treated through radiofrequency (RF) ablation to create a bidirectional conduction block across the cavo-tricuspid isthmus (CTI) in the right atrium. While this approach is successful in many cases, certain anatomical variations can present challenges, making CTI ablation difficult.

Methods

We enrolled four patients with typical counter-clockwise AFL who displayed an epicardial bridge at the CTI. Patients underwent high-resolution mapping of the right atrium and CTI ablation.

Results

Post-mapping identified areas of early focal activation outside the lesion line which suggested the presence of an epi-endocardial bridge with an endocardial breakthrough, confirmed by recording a unipolar rS pattern on electrograms at that site. A stable CTI block was achieved in all patients only after ablation at the site of the epi-endocardial breakthrough.

Conclusions

The presence of an epicardial bridge at the CTI, allowing conduction to persist despite endocardial ablation, should be considered in challenging cases of CTI-dependent AFL. Understanding this phenomenon and utilizing appropriate mapping and ablation techniques are essential for achieving successful and lasting CTI block.

Does Unidirectional Block Exist after a Radiofrequency Line Creation? Insights from Ultra-High-Density Mapping (The UNIBLOCK Study)

BACKGROUND

Whether unidirectional conduction block (UB) can be observed after creation of a radiofrequency (RF) line is still debated. Previous studies reported a prevalence of 9 to 33% of UB, but the assessment was performed using a point-by-point recording across the line. Ultra-high-density (UHD) system may bring some new insights on the exact prevalence of UB.

PURPOSE

A prospective study was conducted to assess the prevalence of UB and bidirectional block (BB) using UHD system after RF line creation.

METHODS

Patients referred for atrial RF ablation procedure were included in this multicenter prospective study. UHD maps were performed by pacing both sides of the created line.

RESULTS

A total of 80 maps were created in 40 patients (67 ± 12 years, 70% male) by pacing (mean cycle length 600 ± 57 ms) from both sides of the cavotricuspid isthmus line. After a 47 ± 17 min waiting time after the last RF application, UHD maps (mean number of 4842 ± 5010 electrograms, acquired during 6 ± 5 min) showed that BB was unambiguously confirmed on all of them. UB was not observed in any map. After a mean follow-up of 12 ± 4 months, 6 (14%) patients experienced an arrhythmia recurrence.

CONCLUSION

After creation of an RF line, no case of UB was observed using UHD mapping, suggesting that the presence of a conduction block along a RF line is always associated with a block in the opposite direction.