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.