Atypical Re-Entrant Circuit of Cavo-Tricuspid Isthmus-Dependent Atrial Flutter Due to an Atrial-Septal Conduction Disturbance in a Patient With Cardiac Sarcoidosis

A 51-year-old woman with cardiac sarcoidosis presented with 2:1 atrial flutter (AFL) ([Figure 1Ai][1]) and was referred for catheter ablation. During sinus rhythm, a 12-lead electrocardiogram revealed trifascicular block ([Figure 1Aii][1]). Echocardiography revealed basal thinning of the