Marshall bundle reentrant atrial tachycardia after the Cox-Maze IV procedure: The last barrier of the conduction pathway between the coronary sinus and left atrium

A 74-year-old woman who developed atrial tachycardia following the Cox-Maze IV procedure underwent catheter ablation. The reentrant circuit included the coronary sinus (CS), Marshall bundle (MB), distal MB-left atrial (LA) connection, and anterolateral mitral annulus. The distal MB-LA connection was the last barrier in the conduction pathway between the CS and the left atrium.