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 AT s 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 AT s 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 accordingly). Dense scar (<0.05 mV) and atrial volume were similar between groups. Acute success and freedom from arrhythmia recurrence were worse in group B (100% versus 77% P=0.009 and 11.3, CI 9.8-12.7 versus 4.9, CI 2.2-7.6 months, log rank P=0.004). Indexed low voltage area ≥0.24 cm2 /mL could predict recurrence with 100% sensitivity and 77% specificity (area under the curve 0.923, P=0.007). Conclusions Larger low voltage area but not dense scar is associated with the induction of multiple focal or re-entry AT s, which are subsequently associated with longer procedure duration and worse acute and midterm clinical outcomes.