DISCUSSION
To the best of our knowledge, this is the first reported study to
compare the clinical efficacy and safety of HBA and CBA performed for
PerAF. The study was conducted on a propensity score-match sample, and
the isolation areas were carefully evaluated by high-resolution mapping.
Our two main findings were as follows: (1) The isolation areas produced
by HBA and by CBA were generally wide, but those produced by HBA were
significantly larger than those produced by CBA, although additional
energy applications were needed when HBA was performed. (2) The
procedural safety and the clinical efficacy shown at 18 months were
comparable between the 2 balloon systems.
Isolation areas created by the 2
balloon
systems
Recently, a single “big balloon” technique has become a standard CBA
technique because the large freezing surface of the second-generation
cryoballoon allows for coverage of both small and large PVs as well as
creation of antral lesion
sets.8 Our study
findings are in line with those of a previously reported study showing
that the lesion created by the cryoballoon was relatively
large.9 Miyazaki et al.
reported that the isolation area ratio at the LSPV antrum was
significantly smaller in patients with a funnel-shaped or common left PV
than in others.10 This
may be attributable to the spherical nature of the cryoballoon and size
mismatch of the balloon to the PV orifice, suggesting that the area
covered by the cryoballoon depends highly on the patient’s LA anatomy.
Anatomical factors might have affected our patients only slightly, if at
all; our study included only patients with AF of relatively short
duration (average: 6 months) and minimal LA remodeling (average LAD: 41
mm).
Unique to HBA is the fact that the balloon remains compliant even during
energy delivery; the cryoballoon stiffens during energy delivery.
However, the hot balloon often yields a relatively small ablation area
because this type of balloon tends to inside the PV orifice1. Results of reported
studies have indicated that larger PV antral isolation and LA posterior
wall isolation areas improve clinical outcomes for patients with
PerAF.11,12Further, feasibility of cryoballoon-based linear ablation along the LA
roof and/or floor has been demonstrated
recently.13,14On the basis of these reported findings, we employed additional upper
posterior wall energy application to create a larger ablation area and
so reduce the risk of recurrence. As a result, our HBA protocol yielded
a wider antral isolation area than that of the standard CBA protocol.
Notably, the balloon can be adjusted to fit the antral region,
regardless of its size, including part of the posterior wall because it
is highly compliant. Further, since HBA is performed under temperature
control, it allows for stable lesion creation without complete occlusion
of the PV even when the balloon is positioned near the LA antrum. Thus,
the hot balloon appears be particularly suitable for creation of a wide
planar antral isolation area in patients with PerAF. Additional studies
are needed to further establish the validity of the approach.
Efficacy of the 2 balloon systems
for
PerAF
CBA-based antral PVI has been shown to be efficacious in patients with
paroxysmal AF, and the 84–93% 1-year success rates have been reported
after performance of PVI by HBA in such
patients.1,15,16Several groups of investigators have compared antral PVI performed by
CBA or by contact force-guided RF ablation in patients with paroxysmal
AF 17 and those with
PerAF,3 but there are no
comparative data regarding clinical outcomes of PVI performed by HBA in
patients with PerAF. Although recent reports have documented 1-year
procedural success rates as high as
76–79%,18,19ablation for PerAF remains challenging. Our study revealed good clinical
outcomes, whether by HBA or by CBA. One possible explanation for the
improved outcome is that our cohort consisted of patients with
relatively early-phase PerAF and a minimally remodeled LA. A wide and
sufficient ablation region might have been created easily in these
patients. Another possible explanation is that nearly a third of the
patients were on AAD therapy even during the follow-up period.
Nonetheless, the high success rates of both balloon modalities may be
due to durable PVI and partial modification of the LA substrate
resulting from the wide ablation areas. Randomized studies are warranted
to elucidate the clinical efficacy of each of the 2 balloon systems.
Procedural safety and
complications
The incidence of complications among our study patients did not differ
significantly from previously reported
incidences.6,14,15,20A multicenter randomized study has already revealed the safety of the
hot balloon system.4Basically, myocardial tissue is ablated by conductive heating from the
balloon surface via agitated fluid, which is warmed by Joule heating
derived from coil electrodes within the balloon. Thus, the tissue
temperature will be highest at the site were the balloon contacts the
endocardial tissue surface, and the temperature will gradually decrease
at deeper levels. Thus, the hot balloon poses a low risk for an abnormal
rise in temperature inside the tissue, and this may prevent both
thrombus formation and steam pops.
When LIPV-targeted HBA was performed, the esophageal temperature tended
to rise due to placement of the balloon in close proximity to the
esophagus. To avoid esophageal complications, we applied an active
esophageal cooling protocol by injecting cooled saline during the energy
delivery.5 This resulted
in aspiration pneumonia in 1 of our patients, Although rare, care should
be taken to avoid this complication during HBA. Phrenic nerve injury
(PNI) is of major concern during
CBA.6,21PNI occurred in 1 of our patients during CBA, and no PNI was observed
during HBA. The reported incidence of PNI during HBA for paroxysmal AF
is
0–3.7%,4,15and additional PV antrum application did not significantly affect the
occurrence of PNI. We found additional extra PV ostial application
during HBA for PerAF to be as safe as reported previously.
Study
limitations
Because our study was conducted as a dual-center study that involved a
relatively small number of patients with PerAF, our findings should be
confirmed by further studies. Also, asymptomatic episodes might have
been underestimated because the AF recurrence rate was evaluated only on
the basis of spot electrocardiograms obtained during patients’ follow-up
visits or by and Holter monitoring. Our study results should be
interpreted cautiously because the patients were not randomized to
treatment. The patients were matched on the basis of propensity scores,
but unknown clinical characteristics or anatomical considerations that
might have affected the outcomes could not be ruled out.