IDF and AF substrate
The factors for the persistence of AF are regarded as trigger factors
and arrhythmogenic substrate factors, which play a role as an AF
perpetuator.17, 18 The triggers generally initiate AF
and the substrate plays a critical role in AF persistence. Therefore, as
the AF duration prolongs, LA remodeling proceeds, and the AF substrates
increase. Thus, the success rate of AF cardioversion is inversely
correlated to the LA size, because the fibrosis accompanying atrial
dilatation increases the AF substrate.19 There are
many reports about predictors associated with recurrence of AF after
electrical cardioversion, such as the LA size, age, and
BNP.20-22 However, there are few reports on
cardioversion after AF ablation.
In the present study, RFCA significantly decreased the IDF threshold for
restoring SR (Figure 1). The conditions for IDF were the same before and
after the RFCA; we induced AF artificially with high rate burst pacing
and ISP. After the AF sustained for more than two minutes, IDF was
performed to detect any AF triggers. Although the main strategy for RFCA
in our institute is an AF trigger ablation, an extensive encircling PVI
or posterior wall isolation might decrease the AF substrate. That
suggests that RFCA could eliminate or decrease both AF triggers and the
substrate, and further, it could decrease the cardioversion threshold.
Thus, the difference in the cardioversion threshold before and after
RFCA may reflect the elimination of the AF substrate and triggers. There
were some cases with LA enlargement but without a low voltage area in
our study. In those cases, the IDF threshold could reflect the AF
substrate, which could not be assessed by electrophysiology.
Additionally, our study revealed that the lower output IDF (≤ 5 J) group
after the RFCA was associated with a lower recurrence of AF. In fact, in
patients with an output > 5 J, the LAD was larger, and
there was a greater presence of an LVZ in the LA. Thus, the LA
remodeling proceeded in those patients. An IDF threshold of
> 5 J was a strong predictor of AF recurrence in a
multivariate analysis after adjusting for the patient background, LAD,
LVZ, duration of AF, and administration of AADs after the RFCA.
Furthermore, the presence of an LVZ disappeared in the multivariate
analysis model 1. Additionally, the ablation strategies (such as an SVC
isolation, posterior wall isolation, and focal ablation) did not have
any significant value for detecting AF recurrence or the IDF threshold
(Tables 1 and 2 ). The IDF method was useful for assessing whether
RFCA could decrease the AF substrate during the RFCA procedure.