Detection of LVA
The mapping protocol is described in detail elsewhere [2]. Briefly, following pulmonary vein isolation (PVI) and cardioversion, all patients underwent high density-high resolution LA bipolar voltage mapping [2959 (2212-3143) points per map] during coronary sinus pacing using the CARTO®3 system (Biosense-Webster, BW) with a Pentaray catheter (BW) acquired with a CONFIDENSE™ module (BW). To ensure detailed mapping, the distance filling threshold was set at 5mm, the tissue proximity filter was always enabled and only mapping sites that were within a distance of 5mm from the acquired shell contributed to a voltage map. Further discrete mapping using a SmartTouch catheter (BW), which always covered less than 10% of the total LA surface area (TSA), at sites presenting inadequate Pentaray-tissue contact was performed if necessary. Electrograms were only accepted if a contact force was ≥6g. EGM amplitude ≥0.5mV was defined as normal and <0.5mV as diseased tissue. All points presenting low voltage were visually inspected and those incorrectly annotated were deleted from the map. An extension of all the areas showing low voltage potentials at least 5mm away from the ablation lesion set was measured with custom CARTO®3 system software. The global LVA burden was calculated as a sum of the LVA and then expressed as a percentage of the TSA. The section of the PV inside ablation encirclement, LAA and an area adjacent to the fossa ovalis were excluded from the TSA calculations. The extent of global LVA burden >20% of the TSA was arbitrarily considered as severe on the basis of an observation that all detected LVA can be easily ablated if it occupies less than 20% of the TSA[2]. The body of LA was segmented into 5 areas: septum, anterior, posterior, inferior and lateral wall. If LVA were identified within 3 out of 5 LA segments it was considered a disseminated pattern of voltage-defined remodelling (Figure 1).