Focal intra-cavotricuspid isthmus atrial tachycardias occurring after typical atrial flutter ablation: incidence and electrocardiographic and electrophysiological characteristics

Purpose: Focal atrial tachycardias (ATs) from the septal cavotricuspid isthmus (CTI) occurring after successful CTI ablation can mimic typical atrial flutter (tAFL). This study investigated the incidence, and electrocardiographic and electrophysiological characteristics of these ATs. Methods: Among 1082 consecutive patients undergoing successful CTI ablation without any congenital heart diseases, 7 were diagnosed with focal ATs originating from the septal CTI that occurred a median of 74 days after the CTI ablation. Results: The electrocardiographic characteristics of the ATs were similar to those of the tAFLs. The AT’s cycle length was never shorter than and often similar to that of tAFLs. The activation patterns along the tricuspid annulus during the ATs were the same as those of tAFLs in 4 patients with foci adjacent to the CTI line, and centrifugal from foci around the coronary sinus (CS) ostium in 3. Entrainment pacing from the lateral CTI during the ATs revealed a manifest fusion and long post-pacing interval. Entrainment pacing from the lateral CTI during the ATs revealed that the atrial electrograms recorded from the CS and high-lateral right atrium were orthodromically captured, while that from the proximal CS revealed that the atrial electrograms recorded from the CS and lateral right atrium were antidromically captured without manifest fusion. Conclusions: Focal intra-CTI ATs with a microreentrant mechanism very rarely occurred after successful CTI ablation. The electrocardiographic and electrophysiological characteristics of these ATs were similar to those of tAFLs. Overdrive pacing from the lateral CTI and proximal CS was helpful for distinguishing these ATs from recurrent tAFLs.