True type of intra-cavotricuspid isthmus re-entrant atrial tachycardia: a case report

Intra-isthmus re-entry, in which the tachycardia circuit is localized within the cavotricuspid isthmus region and the coronary sinus ostium, has been reported as an atypical form of atrial tachycardia. It has been delineated by three-dimensional mapping as either macro-re-entrant type around the cavotricuspid isthmus and coronary sinus area (but with the coexistence of typical atrial flutter), or focal type from the cavotricuspid isthmus area.

We present the first reported case of an apparently new form of macro-re-entrant intra-isthmus re-entry that occurred in a patient with history of prior cardiac surgery. By correcting incorrect annotation of double potentials at the cavotricuspid isthmus lesion, the local activation time map showed a re-entrant circuit rotating around a low-voltage area within the cavotricuspid isthmus region. Preoperative computed tomography revealed a pouch on the septal side of the cavotricuspid isthmus that was anatomically adjacent to the boundary of the tachycardia circuit. Termination of tachycardia was achieved by typical cavotricuspid isthmus linear ablation.

The formation of a low-voltage area, which might have been created by prior surgery, was presumed to contribute to the maintenance of intra-isthmus re-entry as a kind of boundary. By use of an ultra-high-resolution mapping system and the entrainment pacing manoeuvre, we could clearly delineate the tachycardia circuit and determine an ablation strategy.