Discussion
Our study first quantitively illustrated the TEE feature of acute LAR
lesion CB ablation combined procedure, and explored its influence on
clinical outcomes. Our primary findings are: 1. Prominent acute LAR
lesion after CB ablation combined procedure could be frequently
observed, with a larger increment in width than thickness, 2. Higher
LSPV nadir temperature poses a higher incidence of 2-fold wider LAR
lesion, 3. Acute LAR lesion has no influence on overall combined
procedure outcome, but it affects measurement of pacifier device.
LAR—also known as coumadin ridge—had long been mistaken as a
thrombus attached to LAA revealed by transthoracic echocardiography
(TTE). Until 2008, a 3-dimensional TTE study demonstrated that the
high-echo attachment was a normal variant (16). LAR is an invagination
between the left PVs and LAA. A recent cadaveric study by Piątek-Koziej
et. al. (1) presented that the appearance of LAR varies, and the width
of 7.9±3.2 mm and the whole wall thickness of 4.3±1.8 mm at the level of
LSPV ostium. While in our study, we measured a smaller preprocedural
width of 5.2±1.6 mm/5.7±2.2 mm and a larger thickness of 11.0±3.8
mm/13.1±4.1 mm at 45°/90° planes. We believe that the minor
inconsistence is reasonable due to the difference between
paraformaldehyde processed specimens and TEE measured intravital LAR.
Acute edematous change of LAR following ablation has been reported by
several researches on combined procedure (8,9). Similarly, it was
observed in almost every patient in our study, with a greater increment
in width (Δwidth=3.6±2.3 mm) than thickness (Δthickness=2.6±3.5 mm).
From a basic aspect, we believe that “edema” is rather imprecise
albeit it subsides during follow-up. Study confirmed that lesion caused
by thermal ablation is primarily composed of not only interstitial
edema, but coagulative necrosis and hemorrhage (17). Besides, compared
with radiofrequency (RF), cryo-energy ablates local tissue through a
different mechanism that direct damage cellular structure and cause
vascular failure (18). Yamashita et al. (19) compared ventricular lesion
after cryo and RF ablation by MRI, and they found although the edematous
change were compareble, the time-course of the cryo lesion differed from
that of RF. We believe the feature of acute LAR lesion caused by
cryo-ablation is different from RF, and it requires further imaging or
histological confirmation.
Interestingly, we only found a higher balloon temperature correlates
with a higher incidence of 2-fold wider LAR lesion at 45°. Previously, a
study done by Miyazaki et al. (20) has demonstrated the acute PV edema
in 10 patients via intracardiac echocardiography, while they found a
lower right superior PV (RSPV) nadir balloon temperature in the group
with thicker edema (−49.3 ± 0.6 vs −58.8 ± 2.0℃). However, their sample
size is relatively small and they only find such relationship at RSPV. A
study has shown that a high balloon temperature indicates incomplete
sealing of PV (21) that could result from mismatch of small CB and large
PV antrum as commonly seen in persistent AF. In this situation, further
advancement of CB into PVs is required to achieve sealing, which moves
CB distally to LAR. Subsequently, less cryo-energy will be delivered to
LAR, and reversible vascular impairment predominates and lead to bulked
lesion. We believe a more suitably matched CB with LSPV antrum could
minimize the lesion size, while more well-designed studies focusing on
LAR lesion size and freezing parameters are warranted to support the
idea.
Although we found the LAR lesion had no influence on either early or
late recurrence and clinical outcomes, the impact on LAAC with different
types of LAAC device is noteworthy. In our study, there was little
change of the inner ostium diameter in the presence of LAR lesion.
Therefore, it had hardly no influence on measurement and closure for
plug device (Watchman) that land to the inner ostium of LAA. Follow-up
TEE further confirmed that only minimal residual flow occurred in 4
patients implanted with Watchman, and all residual flow presented on the
inferior border rather than LAR side.
However, the outer ostium diameter reduced significantly after the
procedure (Δouter ostium diameter=-3.4±4.0 mm), and it expanded to its
original size in the 3rd month follow-up. In this
situation, the selection of pacifier device (that requires gauge of the
outer ostium) could be masked by the acute bulked lesion. During
follow-up, 2 out of 9 patients implanted with LAmbre device (size 24×30
mm) developed residual flow on the LAR side. TEE reveals that both
patients had distinct bulked lesion and reduced outer ostium diameter
(30 mm) when performing combined procedure. Although the sample size of
LAmbre combined procedure is too small to detect a statistical
difference, masked outer LAA ostium interferes the selection of pacifier
device size. We recommend that the size of the outer disc should refer
to the measurement before ablation or a larger size outer disc should be
chosen if measured after ablation. More randomized controlled studies
are warranted to provide stronger evidences on choosing pacifier LAAC
device during combined procedure.
Our study should be interpreted with caution. First, we uniformly
applied CB ablation to achieve PVI, the conclusion cannot be
extrapolated to RF and other ablation techniques. Sencondly, only 96 out
of 117 TEE image series were available for measurement, the LAR lesion
remained unknown in the others, and the incidence of device related
event could be underestimated. Thirdly, all the TEE images were centered
at LAA rather than LAR. Although the LAAC complications were precisely
evaluated, the measurement of LAR and LAR lesion could be biased.
Fourthly, our postprocedural images were obtained after LAAC procedure
rather than instantly after CB ablation and before LAAC. Thus, the LAR
could be stretched and deformed due to the expansion of LAAC device,
which poses a potential bias. In addition, although we used both
Watchman and LAmbre devices to explore the relationship between LAR
lesion and different types of device, only 9 patients were implanted
with LAmbre, which is insufficient to detect a statistical difference.
Larger scaled randomized controlled studies are required to further
address the issue.