Word Count: 1141 excluding title page and references
Keywords: Atrial Fibrillation, Catheter Ablation, Esophagus,
Pulsed Field Ablation
Conflicts of Interest and Funding: Dr. Baykaner reports grant
support from National Institutes of Health (HL145017) and serves in the
advisory boards of Medtronic, BIOTRONIK and PaceMate. Dr. Nguyen has no
disclosures.
Ablation is a cornerstone of treatment for atrial fibrillation (AF),
with increasing data on its safety and efficacy. A rare but dreaded
complication related to AF ablation is esophageal injury, potentially
leading to esophageal ulceration, upper gastrointestinal bleeding, and
atrioesophageal fistula formation due to esophageal proximity to areas
of the left atrium (LA) that are targeted with
ablation1–3.
To mitigate the risk of esophageal injury, preoperative, intraoperative,
and post-operative measures have been utilized (Figure).Preoperative imaging to establish esophageal location and its
three-dimensional relationship to the LA may allow for a tailored
ablation approach; however, since the esophagus is a mobile structure,
it is unclear if such preoperative imaging and planning can accurately
assess esophageal location at the time of the ablation
procedure4,5.
Intraoperative measures to limit esophageal thermal injury include using
high power, short duration radiofrequency ablation to avoid thermal
injury to the deeper structures6. Use of
contact force sensing catheters, and limiting the contact force to
< 20 grams, may also lead to less thermal injury to the
esophagus7.
Other postulated intraoperative strategies include imaging with
intracardiac ultrasound for real-time assessment of esophageal
location8,
mechanical displacement or active cooling of the
esophagus7,
avoidance of general
anesthesia9,
and monitoring intraluminal temperatures with esophageal temperature
monitoring probes, although results are
mixed7.
Postoperative strategies to reduce esophageal thermal injury are limited
and include the use of proton pump
inhibitors7.
In this issue of the Journal of Cardiovascular Electrophysiology,Nakatani et al. retrospectively studied 97 patients with AF who
underwent ECG-gated, contrast-enhanced chest computed tomography (CT)
with adequate quality 405±258 days apart and 1-3 days prior to
consecutive AF ablation procedures. The authors determined esophageal
position and assessed for changes in esophagus location between
these two timepoints, assuming that the esophagus is a mobile
structure10.
They also evaluated if preoperative planning of ablation lesion sets to
avoid LA sites in close proximity to the esophagus was feasible and
reliable, taking into consideration the change in position of the
esophagus over time.
Left atrial segmentations from CTs were done automatically and
esophageal segmentation was added in a semiautomated method, with
eventual calculation of the distance between LA surface to the
esophagus. A distance of ≤ 3 mm between the LA and esophagus was
considered to be relevant and termed area at risk (AAR). The
average distance of the esophagus to the LA reported by the authors, as
well as their finding that the most common AAR was near the left
pulmonary veins, is in line with prior
studies11,12.
The authors measured the difference in AAR, as well as the absolute
difference in esophageal position, between two consecutive CT scans.
The authors demonstrated that, on the baseline CT, a mean LA surface
area of 9.4±3.6 cm2 was in close proximity to the
esophagus (AAR). This area was larger in women, people with lower body
mass index (BMI), and left atria with greater dimensions. Positional
change of the esophagus between the two CT scans was found to be
moderate, with a median of 3.6mm [2.7 to 5.5mm]. Patients with a
higher BMI had a larger positional change of the esophagus, and
therefore had a larger AAR mismatch of the LA surface between two CT
scans; however, patients with higher BMI generally had smaller AAR and
thus the greater AAR mismatch may not be as clinically significant. The
authors also showed that empiric wide area circumferential ablation
(WACA) and WACA with linear ablation (WACA+L) lesions would
significantly overlap at areas in close proximity to the esophagus (i.e.
AAR), which can be mitigated by using personalized lesion sets that
consider the esophageal location on the first CT. The authors concluded
that this personalized approach might reduce the ablation lesions
corresponding to AAR on the second CT by 75% and 53% for WACA and
WACA+L respectively.
The authors confirmed several important points. First, the esophagus,
although considered a mobile structure, remains in a relatively confined
position when assessed in repeat imaging studies. Second, this finding
can allow for preoperative planning of lesion sets that do not
incorporate left atrial sites in close proximity to the esophagus.
Importantly, the study also showed that women, patients with lower BMI,
and patients with larger LA volumes have greater LA surface areas in
close proximity to the esophagus, and thus these patients may
hypothetically benefit to a greater extent from this personalized
approach.
Limitations of this study are mainly due to the retrospective,
single-center, and virtual nature of the methodology, which are well
acknowledged by the authors. A clinical validation study would be the
next important step to demonstrate that a predefined, personalized
approach, based on preoperative imaging to avoid ablation at AAR, can
indeed reduce esophageal injury. Furthermore, whether preoperative
imaging is more accurate or more effective than intraoperative imaging
and registration of the esophagus with intracardiac echocardiography and
3D electroanatomic mapping still needs to be determined.
To this point, another limitation is that the study provides no data
with regards to intra-procedural imaging to localize the esophagus, or
monitoring of esophageal temperatures, as AF ablations in this study
were performed under conscious sedation without the use of esophageal
temperature probes. We are therefore unable to correlate the findings
that AAR defined by the authors are indeed areas in the LA that lead to
esophageal temperature rise during ablation. A counter argument is that
esophageal temperature monitoring may be suboptimal, does not cover the
entire width and length of the esophagus, and can only detect
intraluminal temperatures rather than intramural temperatures. In
addition, routine preoperative TEEs to exclude left atrial appendage
thrombus were not utilized in this study, which may affect esophageal
position on the day of the procedure.
The authors further acknowledge that the relative stability of the
esophageal course, despite a prolonged delay between two CT
acquisitions, may not have adequate temporal resolution to firmly
conclude that the esophageal position could be predicted during the
procedure from preoperative imaging studies, and thus may result in
erroneous ablation planning. In addition, mechanical esophageal
displacement, active cooling strategies, or increasing use of pulsed
field ablation with minimal collateral damage to nearby structures, may
render the findings of this study to design personalized lesion sets to
avoid esophageal damage less relevant7.
Finally, although esophageal injuries are relatively common, esophageal
injuries leading to significant morbidity and mortality are rare, and it
is unclear whether any strategy to mitigate esophageal heating can have
an impact on serious complication rates.
In summary, the authors should be commended on providing some of the
first evidence on long term temporal stability of esophageal position,
and in demonstrating feasibility of a personalized ablation strategy to
avoid ablation at left atrial sites that are in close proximity to the
esophagus. Further studies, however, are necessary to validate this
approach, and whether this approach will have meaningful clinical
implications is still to be determined.
Figure: Strategies for esophageal protection. CT: computed
tomography, MRI: magnetic resonance imaging, LA: left atrium.