Local activation mapping at sites of termination of persistent atrial fibrillations (AF) shows repetitive patterns including rotational or focal activity reports a study in Circulation: Arrhythmia and Electrophysiology1.
Therapy for persistent atrial fibrillation is limited by uncertainty about sustaining mechanisms. The authors hypothesised that mapping AF sites of clinical relevance may provide insights, ultimately improving therapy.
The authors hypothesised that sites where localised ablation terminates persistent atrial fibrillation, prior to pulmonary vein isolation, have identifiable characteristics when using traditional activation mapping during AF. Mapping data was examined by systematically reviewing the unprocessed pre-ablation electrograms and activation patterns at and around sites of unequivocal termination by ablation for consecutive patients who met this criterion in a multicentre registry. Computer modelling was also used to gain further insight and to identify possible unifying characteristics of these unique sites that are necessary for driving persistent atrial fibrillation.
Conducted in five centres in the USA and Europe, this study represents one of the largest series of acute terminations of persistent atrial fibrillation before pulmonary vein isolation. 57 patients with persistent atrial fibrillation (defined as AF for >7 days without self-termination) and longstanding persistent AF (continuous for >12 months) undergoing ablation were recruited, only if localised ablation terminated AF to sinus rhythm or organised tachycardia. For each patient, electrograms were collected during AF from multipolar basket catheters. After the case, the maximum –dV/dt was applied to unprocessed unipolar signals to identify the onset time of each electrogram, assigned automatically by custom software, and used to construct isochronal activation maps for multiple cycles. Additional computational modelling and phase analysis were used to study mechanisms of map variability. At all sites of AF termination, localised repetitive activation patterns were observed. Partial rotational circuits were observed in 26 of 57 (46%) cases, focal patterns in 19 of 57 (33%), and for the first time using traditional activation mapping, complete rotational activity in 12 of 57 (21%) cases.
The authors wrote that the presence of rotational or focal patterns may explain termination of persistent AF by localised ablation at these sites. How partial rotations, commonly reported in AF mapping studies, could explain AF termination was less clear and thus explored in computational models.
These showed that the observed activation sequence was sensitive to the assignment of activation timing, particularly difficult in segments of slow conduction where electrograms may be complex. In simulations, subtle changes in the assignment of activation timing may convert observed partial rotations to complete rotational circuits.
One limitation of the study is that by specifically examining sites at which focal ablation terminated AF, the selected population consisting only of patients with acute termination and hence is not representative of all patients with persistent AF.
This study adds to the growing body of evidence for organised activation pattern during persistent AF. In every patient with a targeted site leading to AF termination, a repetitive activation pattern was identified and mapped, suggesting that this phenomenon is more than a pattern of passive activation. These findings may help reconcile debate on AF mechanisms and lead to better mapping and ablation strategies for patients.
1Zaman, J.A.B, et al. Identification and Characterization of Sites Where Persistent Atrial Fibrillation Is Terminated by Localized Ablation. Circulation: Arrhythmia and Electrophysiology. 2018. DOI: 10.1161/CIRCEP.117.005258