Tunnel-Like Myocardial Structure Formed by Sequential Left Atrial Appendage Closure and Resection as a Substrate for Macroreentrant Atrial Tachycardia

Left atrial appendage closure (LAAC) is frequently performed during cardiac surgery to reduce thromboembolic risk; however, incomplete closure with residual appendage flow is not uncommon. In selected cases, additional left atrial appendage resection (LAAR) may be undertaken, although the electrophysiological consequences of this sequential surgical strategy remain poorly characterized. We report a 59-year-old man with a history of mitral valve repair, tricuspid annuloplasty, Cox-Maze procedure, and surgical LAAC who presented with sustained atrial tachycardia (AT). Persistent residual appendage flow following LAAC necessitated subsequent stapler-based LAAR. Postoperative contrast-enhanced computed tomography revealed a contrast-filled, tunnel-like myocardial structure bridging the LAAC site and the LAAR plane, remaining endocardially continuous with the left atrium and adjacent to the mitral annulus. High-density electroanatomic mapping demonstrated macroreentrant AT anatomically and functionally associated with this surgically created myocardial structure, supported by entrainment pacing findings. Radiofrequency ablation at sites anatomically adjacent to the tunnel-like structure resulted in reproducible prolongation of the tachycardia cycle length, with definitive termination achieved only after additional perimitral and pericoronary sinus ablation. This case highlights a previously unrecognized postoperative arrhythmogenic substrate created by sequential LAAC and LAAR. It underscores the importance of integrating preprocedural imaging with detailed electrophysiological mapping to identify noncanonical conduction pathways in patients with complex surgically altered atrial anatomy.