Background: Ablation of persistent AF remains a significant challenge. Charge density mapping is a novel tool for use in atrial fibrillation (AF) ablation. The AcQMap system (Acutus Medical) maps the chamber via a non-contact static hybrid charge density/ultrasound catheter. Its algorithm identifies regions of interest (ROIs) according to three subtypes: local irregular activity (LIA), local rotational activity (LRA) and focal activation (FA).
Methods: Consecutive patients attending for ablation for persistent AF had both bipolar voltage maps (Ensite Precision, Abbott) and charge density maps recorded at baseline in AF. Voltage maps were recorded using multipolar catheters with thresholds of <0.1 mV for dense scar and >0.5 mV for healthy tissue. AcQMaps were parameterised according to operator experience. Images were co-registered and visual comparison of the AcQMap ROIs and voltage maps performed by two independent observers (TN/JL). Discrepancies were discussed and agreed by consensus.
Results: Paired maps for 8 male patients (mean age 63, range
58–70 years) were analysed. Four had previously undergone pulmonary vein (PV) isolation, one had undergone three prior procedures with PV, LA roof and mitral isthmus ablation and the remainder were de novo procedures. In all cases PVersus were (re)isolated and then AcQMap guided ablation performed.
The mean atrial voltage across all subjects was 0.59 mV (SD 0.89) with an average of 66% of points below 0.5 mV (range 38– 86%) indicating a significant scar burden in our cohort. Areas of low voltage were observed in 70 of 96 atrial segments, with the PV exhibiting the lowest voltage (19 of 32 veins had areas with voltage <0.1 mV).
6 ± 1 AcQMap ROIs were identified for each individual for a total of 46 ROIs (20 LIA, 14 LRA and 12 FA). Seventeen ROIs were posterior, 15 anterior and 14 were within PVs. We did not identify a predilection for ROIs in any anatomic location. When compared with voltage maps, most ROIs (n=29, 63%) occurred in either low- or
intermediate-voltage regions, with a further 6 (13%) adjacent to low voltage areas. 11 (24%) were in preserved voltage areas. FA tended to occur in low voltage areas, whereas LIA / LRA occur most commonly where voltage >0.1 mV.
Currently mean follow up duration is 155 days and 5 of 8 patients are free from AF. Two have had cardioversion for AF within a 1 month blanking period post ablation, while one had a cardioversion for right atrial flutter.
Discussion: Most ROIs were situated in or adjacent to low (<0.5 mV) or very low (<0.1 mV) voltage areas, and this may reflect the diseased substrate of our PeAF population. Given this extensive scarring, an effective ablation strategy was challenging to determine based on voltage data alone. Approximately one third of ROIs were seen within PVersus and a further one third in the posterior LA. These ROIs would have been treated by our usual strategy of PVI and posterior box, but in one third of patients the ROIs were anterior and would have been missed with standard approaches. Further analysis of the relationship between AF activation (LIA, LRA, focal) and LA substrate is planned.
