Discussion:
The major findings of this study are: 1) LA PWI lesion set dimensions determined based on LA geometry, with or without voltage mapping, may attenuate the adverse ablation outcomes related to LA dilation and LA fibrosis, and 2) The extent of ablation within the LA PWI lesion set, in the presence of rigorous assessed LA PWI, does not appear to impact ablation outcomes. These conclusions are consistent with findings of prior meta-analysis of PWI ablation outcomes suggestive of benefit regardless of PWI ablation technique utilized 11.
Greater LA fibrosis as assessed by MRI or voltage mapping12,13 has consistently been associated with worse outcomes after AF ablation. Additionally, ablation targeting LA low voltage areas has been previously associated with ablation outcomes similar to those of patients without abnormal LA voltage14. Outcomes of voltage map guided LA posterior wall isolation have not been previously reported. Our data suggests that the benefits of “Box Isolation of Fibrotic Areas,” as described by Kottkamp, et al14. may be present with inclusion of low voltage areas in LA PWI, but with the added benefits of PWI, and decreased theoretical risk of creating substrate for reentrant atrial tachycardia by ablating patches of fibrosis.
Despite this outcome, the observed decrease in arrhythmia-free survival in the largest quartile of LA size implies that this cohort is grossly similar to those cited in prior studies. Similar to Kece et. al. univariate regression analysis noted several predictors of increased arrhythmia recurrence (WACA area, LA area, and ejection fraction), however none of them were significant in the follow-up multivariate analysis (Figure 11). The association of increased arrhythmia recurrence with smaller LA sizes and larger WACA areas in the univariate analyses as opposed to smaller box surface ratios in Kece et. al. may be a consequence of performing multivariate analysis with collinear variables (given that LA surface area is accounted for in both the box surface area ratio and LA volume index). It is also possible that our cohort had a larger burden of LA scar, which was not accounted for in the Kece et. al. analysis. The variables in Table 2 were also not found to be predictive of the density of posterior wall ablation in a separate multivariate regression analysis.
Study Limitations :
This retrospective, single-center study may have been underpowered to detect small, but clinically meaningful differences in ablation outcomes between groups. Operators were not restricted in selection of their lesion sets, thus lesion set dimensions and ablation density may have been influenced by unmeasured confounders. Additionally, LA PWI lesion sets encompassing proportions of electrically-isolated LA surface area outside the range represented in this cohort (35-75%) were not analyzed, thus outcomes associated with these lesion sets remain unknown. The same could be said of outcomes for LA scar burden proportions outside upper bound of the ranges observed in this cohort.