Sequential low-resolution contact mapping to guide radiofrequency (RF) atrial fibrillation (AF) ablation is used but controversial. Whether ultra-high density (UHD) mapping can produce maps useful for ablation is unknown.

To sequentially map left atrial (LA) activation during ablation with Rhythmia (circumferential pulmonary vein isolation, CPVI, followed by defragmentation).

Using an LA appendage (LAA) electrogram (EGM) as reference, and the Orion catheter for signals acquisition, beats were automatically selected based on cycle length (CL) stability, electrode location stability and respiratory gating. In case of extremely low voltage or lack of statistical coherence between neighbouring points, grey is displayed. Regions with uniform colour (meaning predominantly simultaneous activation) were defined as organized.

Seventeen patients (patients; 68±5 years) underwent repeated AF mapping at baseline and after each ablation step. Initial LA maps (162±49ml, 30947±14061 EGM, 95±26 cm²) were acquired in 15.7±6.5min. All patients had CPVI followed by ablation of sites with fragmented bipolar EGM. After CPVI, LAA CL rose from 171±10 to 199±14ms (P=0.02). Surface of organized areas increased from 16±3% of total LA before to 29±5% after CPVI (P=0.01; Fig. 1), increasing the accuracy of appropriate fragmented site identification for ablation. AF termination with RF was obtained in 62%. Only 2 AF recurrences occurred within 6 months.

Sequential AF UHD contact activation mapping visualized increasing organization with ablation, unmasking optimal residual ablation targets.