Targeting an epicardial‐endocardial breakthrough in a case with an intractable common atrial flutter using ultra–high‐resolution three‐dimensional mapping

The recent development of high‐density high‐spatial resolution three‐dimensional mapping has provided detailed information for understanding complicated atrial activation patterns at a level not previously possible. Using this technology, we report a case with recurrent common atrial flutter, demonstrating the presence of a bridging epicardial fiber that traveled across the previous cavotricuspid isthmus ablation lesion with apparent epicardial‐endocardial breakthrough (EEB) sites located on both sides of the ablation line. The entrainment study indicated that the EEB site, located adjacent to the coronary sinus ostium, was part of the recurrent circuit and a focal ablation targeting that site terminated the tachycardia.