Mapping protocol and rotor identification
Mapping was performed using conventional high-density electroanatomical mapping catheters (IntellaMap ORION, Boston Scientific Inc.; PentaRay NAV, Biosense Webster Inc.; or Advisor HD Grid, Abbott Medical, Inc.) and their respective mapping system (Rhythmia, Carto3 or Ensite Precision). Bipolar voltage maps were created, with the threshold for dense scar set bellow 0.03 mV in all navigation systems, in order to allow annotation of low-voltage signals.
For patients with AT as initial rhythm, or AT induced from sinus rhythm, and posterior destabilization, mapping was initiated within the right atrium (RA) or LA, depending on the suspected origin of the AT according to initial entrainment. If destabilization occurred before or during entrainment, mapping was started within the atrium in which initial disorganization of electrical signals during AT presumably led to AF. For patients with AF as initial rhythm, mapping was initiated in the atrium with faster cycle length according to the Orbiter catheter signals. If rotors were identified in the initially mapped atrium, rotor ablation was performed; if rotors were not present, or rotor ablation was not successful to convert AF into AT or sinus rhythm, the other atrium was then mapped for rotor identification.
Rotors were subjectively identified as fractionated continuous (or quasi-continuous) bipolar EGMs on 1-2 adjacent bipoles of the mapping catheter, using a digital recorder (Bard LabSystem Pro) at 200 mm/s speed (Figure 1, panel A). Filters for bipolar signals were set at 30 and 250 Hz, with notch filter. When such EGMs were identified, the mapping catheter was kept still for 10 seconds to confirm temporal stability of the rotor, which was then annotated with a manual marker deployed on an electroanatomical bipolar voltage map. After mapping was complete, the mapping catheter was repositioned in sites with rotors to confirm temporal permanence before ablation. Temporally unstable rotors were neither annotated nor targeted for ablation.
If rotors were absent in both atria, or rotor ablation was unsuccessful to stabilize or terminate AF, sites with STD (i.e. all the AF cycle length comprised within the different bipoles of the mapping catheters) plus non-continuous fragmentation on single bipoles, arbitrarily defined as continuous bipolar EGMs with >4 deflections and total duration >70 ms, were manually annotated and targeted for ablation (Figure 1, panel B). At least 10 seconds of temporal stability was also required for these sites.