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.