Introduction: Human atria comprise distinct epicardial layers, which can bypass endocardial layers and lead to downstream centrifugal propagation at the “epi-endo” connection. We sought to characterize anatomical substrates, electrophysiological properties, and ablation outcomes of “pseudo-focal” atrial tachycardias (ATs), defined as macroreentrant ATs mimicking focal ATs. Methods and Results: We retrospectively analyzed ATs showing centrifugal propagation with post-pacing intervals (PPIs) after entrainment pacing suggestive of a macroreentry. A total of 26 patients had pseudo-focal ATs consisting of 15 perimitral, 7 roof-dependent, and 5 cavotricuspid isthmus (CTI)-dependent flutters. A low-voltage area was consistently found at the collision site and co-localized with epicardial layers like the: (1) coronary sinus-great cardiac vein bundle (22%); (2) vein of Marshall bundle (15%); (3) Bachmann bundle (22%); (4) septopulmonary bundle (15%); (5) fossa ovalis (7%); and (6) low right atrium (19%). The mean missing tachycardia cycle length (TCL) was 67 ± 29 ms (22%) on the endocardial activation map. PPI was 9 [0-15] ms and 10 [0-20] ms longer than TCL at the breakthrough site and the opposite site, respectively. While feasible in 25 pseudo-focal ATs (93%), termination was better achieved by blocking the anatomical isthmus than ablating the breakthrough site [24/26 (92%) vs. 1/6 (17%); p < 0.001]. Conclusion: Perimitral, roof-dependent, and CTI-dependent flutters with centrifugal propagation are favored by a low-voltage area located at well-identified epicardial bundles. Comprehensive entrainment pacing maneuvers are crucial to distinguish pseudo-focal ATs from true focal ATs. Blocking the anatomical isthmus is a better therapeutic option than ablating the breakthrough site.

We demonstrated a 47 year-old woman with ischemic-VT with repetitive ICD-shocks, requiring ablation. Pre-procedural CT demonstrated a single anatomical channel on the inferior-basal infarcted area between <3mm wall thinning area and the mitral annulus, which suggested the circuit of two VTs observed. Additionally, distribution of <2mm and <3mm scars can explain the mechanism of the variation of QRS morphology and S-QRS interval during entrainment. Ablation on this region resulted in no VT- inducibility and absence of any VTs for 2yrs. CT wall thinning data may allow us to understand the mechanism and circuit of VT and aid VT ablation procedures.

Background: Ventricular arrhythmia inducibility is one of the ideal endpoints of ventricular tachycardia(VT) ablation. However, it may be challenging to implement programmed electrical stimulation (PES) at the end of the procedure under several circumstances. The long-term outcome of patients who did not undergo PES after VT ablation remains largely unknown. Purpose: To investigate the details and long-term outcome of VT ablation in patients who did not undergo PES at the end of the ablation procedure. Methods: Among 184 VT ablation procedures in patients with structural heart disease who underwent VT ablation using an irrigated catheter, we enrolled those who did not undergo PES after VT ablation. VT ablation strategy involved targeting induced VT plus pacemap-guided substrate ablation if inducible. If VT was not inducible, substrate-based ablation was performed. The primary endpoint was VT recurrence. Results: In 58 procedures, post-ablation VT inducibility was not assessed. The causes were non-inducibility of sustained VT before ablation(27/58, 46.6%), long procedure time(27.6%, mean 392 min), complications(10.3%), intolerant hemodynamic state(10.3%), and inaccessible or unsafe target(6.9%). With regard to the primary endpoint, 23 recurrences(39.7%) were observed during a mean follow-up period of 2.5 years. Patients with non-inducibility before ablation showed less VT recurrences(4/27, 14.8%) during follow-up than patients with other causes of untested PES after ablation(19/31, 61.2%)(Log-rank<0.001). Conclusions: VT recurrence was not observed in approximately 60% of the patients who did not undergo PES at the end of the ablation procedure. PES after VT ablation may be not needed among patients with pre-ablation non-inducibility.