Discussion
Catheter-based PVI has emerged as a cornerstone in AF therapy and
improves clinical outcomes compared to medical treatment in selected
patients (6). However, roughly 50% of all patients experience
recurrence of AF within 2 years (7). Thus, new techniques of AF ablation
have been investigated in the past, such as the minimal-invasive
epicardial HIFU electroablation treatment. First studies reported rather
high efficacy rates, with 83-85% freedom from atrial arrhythmias 6
months after treatment (8,9). In contrast, the recurrence rate of atrial
arrhythmias was found to be much higher in more recent studies (2,3,10).
Furthermore, rate of complete or near-complete box isolation resulting
in successful PVI 6 months after HIFU AF ablation was less than 40%
(2). Accordingly, in this case, multiple gaps have been found along the
EpicorTM ablation line, which resulted in the
occurrence of a focal AT and persistent electrical connection of the PV.
Activation mapping of these complex scar-related AT can be challenging
because of difficulties in the accurate annotation of multicomponent
electrograms, the correct differentiation between active and passive
diastolic activity, and the dependency on a window of interest with
arbitrarily defined early and late activation (11). Consequently, a new
activation mapping algorithm has been developed that identifies and
highlights zones of slow or no conduction, and calculates the most
coherent pattern of activation (4). In the present case, the application
of this new technical feature helped to interpret the mechanism of the
AT and to identify the critical site for ablation.