Cavotricuspid isthmus conduction split by pouch-like recesses during typical atrial flutter.

A 58-year-old man had typical cavotricuspid-isthmus-dependent atrial flutter (AFL). Right atrial angiography and multidetector computed tomography revealed a deep pouch-like recess in the mid-isthmus region. Linear ablation from the pouch to the edge of the inferior vena cava resulted in widely split double potentials without any change in the AFL cycle length. This observation suggested that the pouch played an electrophysiological role by dividing the flutter wavefront into 2 parallel conduction wave fronts through both sides of the pouch along the isthmus during typical AFL. When a widely split potential is created on 1 side of the pouch, the other side of the pouch should be targeted.