Discussion
The present study investigated the details after catheter ablation in
patients with non-paroxysmal AF, particularly those who underwent LAPW
cryoballoon ablation including the LA roof. The main results showed that
cryoballoon ablation of the LAPW was not associated with AT recurrence
after the ablation procedure, but LA roof-dependent AT was observed in
several patients (1.5%). Moreover, clinical outcomes were improved
after the ablation procedure compared with the strategy without LAPW
ablation, especially regarding the recurrence of the persistent type of
AF. The details of recurrence patterns, including the type of AT, and
the durability of lesions created in the index ablation procedure, were
also investigated in this single-center large cohort study.
PVI has been established as the gold standard for treating AF, and
cryoballoon ablation has emerged as a novel ablation method instead of
the conventional method utilizing RF energy7; however,
its efficacy may be limited, especially in patients with non-paroxysmal
AF. Various therapeutic approaches have been investigated for AF
catheter ablation; linear ablation, such as LA roof line and MI line, is
one such approach. In particular, linear ablation that targets the LAPW,
including isolation of the LA roof line and LAPW bottom line, has been a
prominent focus.2 Recently, it has been demonstrated
that a cryoballoon could be utilized for linear ablation at the LAPW,
and this additional ablation could generate a broader isolated area
after PVI with a cryoballoon.4,8,9 Complete conduction
block at the LA roof line was reportedly achieved in 81.0%–95.0% of
ablations with RF energy10,11 and in 88.0%–99.8%
with a cryoballoon.4,8 Regarding the chronic status of
the lesions, the reported durability of the LA roof line was
37.5%–72.0% with RF energy12,13 and 74.5% with a
cryoballoon.6 Indeed, several reports have shown
additional LAPW ablation results in better clinical
outcomes,8,14 but the adjunctive value of LAPW
ablation in addition to PVI is controversial.15 In our
study, the LA roof line was successfully ablated with a cryoballoon in
97.0% of patients, of whom 72.0% had confirmed durable lesions, which
is consistent with previous reports. Moreover, further analysis
regarding the recurrence type in this study revealed that LAPW ablation
in addition to PVI could reduce the persistent type of AF recurrence,
which seemed to be clinically important. A prior examination
investigated the atrial substrate size by utilizing the parameter of
conduction velocity, refractory period, and LA body
area.16 Considering the mechanism of reduced
persistence of AF after ablation based on the reported theory,
cryoballoon ablation of the LA roof might be effective in reducing the
atrial substrate size because it could produce a broader scar area, as
previously reported.4,6,9 In this regard, cryoballoon
ablation might be preferable to a conventional RF method for creating LA
roof line. AF persistence seems to depend on the site of AF drivers, and
it might be an important factor where AF drivers exist; however,
findings regarding AF drivers were not examined in the present study.
Moreover, A wave was significantly lower in the patients who underwent
cryoballoon ablation of the LAPW in this study, although that of those
who underwent cryoballoon ablation of the LAPW seems compatible
according to the previous study17. Further studies
might be required for assessing atrial function after the ablation more
precisely, and selecting candidates who should undergo cryoballoon
ablation of the LAPW.
One of the reasons for hesitation in performing linear ablation was the
possibility of iatrogenic AT occurrence after the ablation procedure.
After PVI, including both RF energy and cryoballoon ablation, AT
recurrence was observed in approximately 10% of patients according to
previous reports.18-20 In several studies that
compared the prevalence of AT recurrence between patients who underwent
PVI with RF energy and those who underwent PVI with a cryoballoon, the
AT recurrence rate tended to be lower in those who underwent PVI with a
cryoballoon.18 Among recurrent ATs, perimitral AT was
reportedly the most frequently observed, accounting for approximately
30% of AT recurrences in previous
investigations.19,20 Regarding linear ablation with RF
energy, the recurrence of AT originating from the LA was reported to be
4% in patients.21 Data regarding the prevalence of AT
recurrence after linear ablation with a cryoballoon are limited. Aryana
et al. investigated cryoballoon ablation of the LAPW and demonstrated
that approximately 20% of patients experienced AT recurrence regardless
of whether cryoballoon ablation of the LAPW was performed in addition to
PVI; however, detailed descriptions regarding the type of recurrent ATs
are lacking.8 In our study, 7.4% (10/135) of the
patients who underwent cryoballoon ablation of the LAPW had AT
recurrence, which is comparable with previous reports, including RF
ablation. We demonstrated that perimitral AT was the most frequent type
of recurrent AT, accounting for half of the identified recurrent ATs in
our study cohort. LA roof-dependent AT was confirmed in only two
patients, who both underwent cryoballoon ablation for LAPW in the index
ablation. However, considering previous reports in which the prevalence
of LA roof-dependent AT recurrence was 1%–2% after PVI with a
cryoballoon,19,20 the recurrence rate of the LA
roof-dependent AT in the present study might not be high. The high
durability of the lesions created at the LAPW might contribute to the
low prevalence of LA roof-dependent AT recurrence.
Our study had a few limitations. First, this was a single-center,
non-randomized retrospective study. Therefore, the results regarding
additional cryoballoon ablation of the LAPW should be carefully
interpreted, although there were no significant differences in patient
characteristics such as left atrial diameter (LAD) or the existence of
left common pulmonary vein (LCPV) or right middle pulmonary vein (RMPV)
between the patients who underwent cryoballoon ablation of the LAPW and
those who did not. Finally, the use of AADs after the index ablation was
also different among study patients; thus, clinical follow-up data
requires prudent interpretations. A randomized multicenter study with a
fixed protocol is necessary to confirm the efficacy and impact of LAPW
ablation with a cryoballoon. Nonetheless, we presented detailed data in
terms of acute and long-term success rates and clinical outcomes after
ablation, including the type of recurrence. We consider that these
findings will contribute to further examinations regarding cryoballoon
ablation of the LAPW in the future.