INTRODUCTION
Reentrant atrial tachycardias (ATs), excluding cavotricuspid isthmus
(CTI)-dependent atrial flutter, can be challenging to map, especially inunstable circuits (i.e. those with frequent circuit modification
or conversion to atrial fibrillation (AF)). These cases, which count for
up to 15-20%,1,2 are considered non-mappable and
ablation is frequently not attempted. Electrical cardioversion and
re-induction of the clinical AT can be tried, but arrhythmia induction
and stabilization is often difficult to achieve. Class Ic antiarrhythmic
agents can be used for this purpose,3 but modification
of atrial conduction properties can lead to non-clinical ATs. Other
strategy is to perform substrate mapping and ablation in sinus
rhythm.4
Patients with unstable circuits have been excluded from most reentrant
AT ablation series, which have focused on mappable
circuits.1,2,5-9 These patients are frequently
considered untreatable with ablation, and this may lead to stopping
rhythm control and accepting the atrial arrhythmia is permanent. During
the last years, ablation strategies that try to terminate AF, the ‘most
unstable’ atrial arrhythmia, via identification and ablation of AF
drivers (rotational or focal), have emerged.10 Another
approach is ablate areas with electrical spatiotemporal dispersion
(STD), as a surrogate of local rotational
activation.11 Given the known relationship between
atrial fibrillation and reentrant ATs,12 we
hypothesized that these strategies, specifically ablation of sites with
rotational activation (i.e. rotors), might as well be used to stabilize
or terminate unstable reentrant ATs.
The Conversion of Hardly mappable Atrial tachycardias via rOtor ablation
into Sinus rhythm (CHAOS) study was a prospective single-center study,
designed to test an ablation strategy in patients with unstable
reentrant ATs based on the ablation of rotors, which were subjectively
identified with conventional high-density mapping catheters as sites
with fractionated quasi-continuous electrograms (EGMs) on 1-2 adjacent
bipoles.