Characterization of the Mechanism and Substrate of Atrial Tachycardia Using Ultra‐High‐Density Mapping in Adults With Congenital Heart Disease: Impact on Clinical Outcomes

Background Atrial tachycardia (AT) is common in patients with adult congenital heart disease and is challenging to map and ablate. We used ultra‐high‐density mapping to characterize the AT mechanism and investigate whether substrate characteristics are related to ablation outcomes. Methods and Results A total of 50 ATs were mapped with ultra‐high‐density mapping in 23 procedures. Patients were followed up for up to 12 months. Procedures were classified to group A if there was 1 single AT induced (n=12) and group B if there were ≥2 ATs induced (n=11 procedures). AT mechanism per procedure was macro re‐entry (n=10) and localized re‐entry (n=2) in group A and multiple focal (n=6) or multiple macro re‐entry (n=5) in group B. Procedure duration, low voltage area (0.05–0.5 mV), and low voltage area indexed for volume were higher in group B (159 [147–180] versus 412 [352–420] minutes, P<0.001, 22.6 [12.2–29.8] versus 54.2 [51.1–61.6] cm2, P=0.014 and 0.17 [0.12–0.21] versus 0.26 [0.23–0.27] cm2/mL, P=0.024 accor...