4.1 Main findings
The main findings of our study were as follows: (1)
A gap following attempted LAPWI
was often located either at the center or right aspect of the line; (2)
HVZs ≥ 2.64 mV and an LA wall ≥ 2.04 mm in thickness at the ablation
line, and a long roof ablation line ≥ 43.4 mm were predictive of a gap
in the ablation line; and (3) the best cutoff modified AI value for
predicting acute durable LAPWI was ≥ 199 AU/mV.
Whether LAPWI provides additional benefits over PVI alone is
controversial.2–4,15 Achievement of complete LAPWI
without additional ablation within the lines is only modest
(45%–72%),15 which might hinder the efficacy of the
procedure. Incomplete LAPWI may result from failure to create transmural
lesions in the roof line or floor line. To overcome this problem,
several new technologies such as AI and high-power short duration
ablation have been developed. These modalities are aimed at improving
the “operator factors” by generalizing and standardizing the
physicians’ skills and experience as applied to the ablation procedure.
However, ablation lesions can also be influenced by “patient factors,”
such as the wall thickness and tissue characteristics, e.g., diseased
vs. healthy tissue. Results of our previous studies have shown that a
high bipolar voltage area ≥ 2.69 mV and a thick LA wall were obstacles
to achievement of complete PVI, and the modified AI, which takes into
account both operator and patient factors, of ≥ 189 AU/mV was found to
predict acute durable PVI.8 In the study reported
herein, we obtained similar results, with our data indicating that the
modified AI can also be applied to LAPWI.
Among our study patients, average LAPW thickness varied, ranging from
0.6 mm to 5.5 mm. The center of the roof line lies above the thickest
part, measuring up to 6.5 mm. This is because the septopulmonary bundle
runs behind Bachmann’s bundle and passes over the
roof.16,17 Other investigators have reported that gaps
were frequently located at the center and right of the roof line because
of lower stability and thicker tissue with interatrial muscular
bridges.16,18 Results of our study are consistent with
these reported findings. Furthermore, bipolar voltage is reported to be
a surrogate marker of LA wall thickness.9Although wall thickness is also a
good predictor of acute PV reconnections,11 it is not
informative with respect to tissue characteristics. Real-time assessment
and accurate measurement of the thickness of the wall just underneath
the ablation tags are also limited due to the technical difficulties of
incorporating such information into a 3D mapping system. Bipolar voltage
is a simple real-time variable obtained at sites accurately mapped in
3D.
In contrast, another major obstacle to creating a continuous floor line
lesion would be its proximity to the esophagus, frequently forcing a
limit on the ablation power or duration to avoid esophageal temperature
rises.15 However, we found no association between gaps
and sites where the esophageal temperature rose. A gap in the floor line
might be due simply to catheter instability.
One major concern is that patient factors cannot be adjusted by the
operators. Therefore, an AI that accounts for both the operator and
patient factors is needed for predicting durable LAPWI.
With the goal of producing durable
but non-excessive ablation, we developed a modified AI, which accounts
for both operator and patient factors. We intended to deliver the RF
energy with same output, duration, and contact force resulting in the
same AI to all the lesion for the calculation of the modified AI. We
found the modified AI to be of good prognostic performance for
predicting gaps in the ablation lines when attempting LAPWI, and
we found the best cutoff value to
be ≥ 199 AU/mV. For example, this cutoff value indicated that an AI of ≥
398 AU will be needed if bipolar voltage at the target ablation site is
2 mV and an AI of ≥ 597 AU for 3 mV. The modified AI-guided ablation
strategy considering bipolar voltage might be a potential ablation
method to increase the acute lesion durability and reduce the procedure
time and complications. Repeated ablation sessions for acute PV
reconnections are time-consuming and may produce tissue edema that can
cause failure of transmural lesions.19 Further
prospective studies are needed to clarify the effectiveness of modified
AI-guided LAPWI.