Functional Substrate Mapping of the Right Atrium: A Novel Method to Identify Critical Isthmus of Re-entry in Atrial Tachycardia.

Right atrial tachycardia (AT) is a frequent rhythm disorder in patients with atrial scar mainly due to surgical incisions or congenital heart diseases. Despite the mounting evidence about AT mechanisms and types, data are scarce regarding the conduction properties as well as the functional characteristics of the atrial substrate during sinus rhythm, which plays a role in the maintenance of tachycardia. We sought to evaluate the relationship between the functional substrate mapping (FSM) characteristics of the right atrium (RA) and the critical isthmus (CI) of re-entrant ATs in patients with underlying atrial scar. Patients with a history of right AT who underwent catheter ablation with three-dimensional mapping were retrospectively enrolled. A voltage map and isochronal late activation map were created during the sinus/paced rhythm using multielectrode catheters to detect deceleration zones (DZs). Subsequently, AT was induced with programmed stimulation, and activation mapping was performed to detect the CI of the tachycardia. Atrial tachyarrhythmia (ATa) recurrence was defined as the detection of atrial fibrillation or AT (≥30 s) during follow-up. A total of 24 patients (mean age, 46 ± 15 years; 13 [54%] women) with right AT were included. A total of 36 ATs were mapped (16 [44.4%] localized re-entry, 20 [55.6%] macro-re-entry). Atrial low-voltage zones composed 23.3% ± 13.0% of the total RA. The mean values of bipolar voltage, electrogram duration, and conduction velocity during sinus rhythm corresponding to the CI of ATs were 0.18 ± 0.10 mV, 121.7 ± 29.4 ms, and 0.06 ± 0.04 m/s, respectively. The total number of DZs per chamber was 1.1 ± 0.3, with all being located in the low-voltage zone (<0.5 mV) detected by high-density mapping. All CIs of non-cavotricuspid isthmus (CTI)-dependent re-entry were co-localized with DZs detected during FSM. The positive predictive value of DZs to detect the CI of inducible ATs was 80.8%. During a mean follow-up of 11.7 ± 8.1 months, freedom from atrial tachyarrhythmias was 87.5%. Although CTI-dependent macro-re-entry is the most common mechanism in patients with RA scar, our findings demonstrated the relevance of FSM to predict non-CTI-dependent ATs. Conduction slowing manifested as DZs with continuous-fragmented signal morphology may guide ablation strategy tailoring in the case of underlying RA scar.