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

## TL;DR

This case report describes a rare anatomical variation in the heart that complicates treatment for a type of arrhythmia, requiring a specific ablation technique for successful outcomes.

## Contribution

The paper introduces a novel technical approach to identify and treat epi-endocardial bridges during CTI ablation for atrial flutter.

## Key findings

- Epi-endocardial bridges at the CTI can cause persistent conduction despite endocardial ablation.
- High-resolution mapping and targeted ablation at the breakthrough site achieved stable CTI block in all four patients.
- Unipolar rS patterns on electrograms confirmed the presence of epi-endocardial breakthrough.

## Abstract

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.

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.

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.

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.