Background: The electrophysiological mechanisms for successful catheter ablation of atrial flutter (AFI) targeting the inferior vena cava-tricuspid annulus (IVC-TA) isthmus have not been determined.
Methods and results: Twenty patients with common AFI were studied. All had inducible common AFI, and 8 of them had both common and reverse AFI. Right atrial (RA) activation sequences were investigated during pacing from sites proximal (low lateral RA) and distal (proximal coronary sinus) to the IVC-TA isthmus both during entrainment of common or reverse AFI and during pacing in sinus rhythm. This was repeated after ablation. During pacing in sinus rhythm from the low lateral RA, the septum was activated by caudocranial and craniocaudal wave fronts. Similarly, during pacing from the proximal coronary sinus, the lateral RA was activated by two wave fronts. Catheter ablation of the IVC-TA isthmus induced dramatic changes in mapping due to the loss of caudocranial wave front in all but 1 patient. The septum and the lateral RA were activated by a single craniocaudal front as during entrainment of reverse or common AFI, respectively. After a follow-up of 8 +/- 2 months, common or reverse AFI occurred in 4 patients. Two had no or only unidirectional changes in the isthmus conduction induced by ablation. The other 2 had a late recovery of conduction.
Conclusions: The present study provides evidence that the mechanism of successful AFI ablation targeting the IVC-TA isthmus is local bidirectional conduction block. This change can be used as a new and complementary electrophysiological end point for the procedure. AFI recurrences are associated with failure to achieve a permanent block.