Discussion
This proof of concept study suggest that a standardized approach for AF
ablation using circumferential high power 50W setting guided by the
ablation index, which was proofed in the CLOSE-protocol, was highly
effective by reducing the total procedure time and RF application time,
with low procedural complication rates, compared to the standard power
settings. Especially in light of oesophageal lesions (EDEL), this study
could not reveal increased rates of oesophageal lesions under ablation
with 50W at the posterior left atrial wall, compared to the standard
power settings, even without oesophageal temperature monitoring. Of
note, the oesophageal lesions occurring with the 50W ablation were
smaller, more superficial and had a faster healing tendency in
comparison to the standard power settings. Further, fixed 50W AI-guided
ablation did not result in any steam pops, increased incidence of
pericardial tamponade or early AF recurrence rate compared to the
standard power settings. The absence of steam-pops is remarkable, since
Chen et al reported up to 8% steam-pop rates in comparable ablation
settings. Close monitoring of impedance drop and stability during lesion
formation, as well as avoiding excessive contact force and operator
experience in a single-centre setting might have contributed.
Sustainable RF lesions are the most important requirement for a durable
PVI. Lesion formation is influenced by RF power, RF application time,
catheter contact force and catheter stability 6.
Duytschaever and colleagues evaluated the ablation index in the CLOSE
and close-to-cure study 3,4. The AI combines the
different above mentioned factors in a nonlinear weighted formula, in
which the RF power has the greatest contribution. The resulting index
seems to be very predictive for the lesion quality and quantity.
Nonetheless, there is an ongoing discussion about the most important
contributor of this index - the ideal RF power. Whereas most ablation
centres use conventional power settings of 25-35W, some previous trials
like the power-AF study showed that a 45W RF-power CLOSE-protocol in
paroxysmal AF patients significantly increases the global procedural
efficiency with similar mid-term efficacy 12. Other
studies compared ablation protocols with very high power settings and
short RF application time not relying on the ablation index: Deisenhofer
et al. could show that a high power short-duration ablation using 70W
for 5–7 s leads to significantly less arrhythmia recurrences after 1
year and to significantly shortened RF- and procedural time13. In addition, the QDot-fast trial was able to show
that an irrigated very high power short duration ablation (vHPSD:
90W/4s) is feasible and safe to achieve durable PVI in the most cases in
a very short procedural- and fluoroscopy time 14. Of
note, only in 78.8% of cases, PVI was achieved using the vHPSD mode
only. Early PV reconnection occurred predominantly in the area of the
posterior wall, requiring re-ablation with standard settings in some
cases 14. The biophysical background of the different
RF power settings is the way in which the energy is delivered into the
tissue. Using higher RF power (HPSD), the tissue heating is caused
resistive as direct catheter-myocardium interaction and within the
myocardium itself. This direct heating begins immediately and stops with
the end of RF energy application 6. Histological data
shows that the resulting HPSD lesions differ compared to the standard RF
power. In contrast, ablation with standard RF settings and a longer RF
application time causes a conductive, i.e. indirect heating which
transfers the energy as passive process to more distant tissue. This
conductive heating continues, even after the RF power application has
stopped and results in deeper lesions compared to HPSD6. Therefore, from a biophysical point of view, it is
quite conceivable that HPSD ablation may cause less damage on
neighbouring structures such as the oesophagus.
Here, procedural safety was high both in the standard and HPSD group,
underlining the advances in atrial fibrillation procedures15. Chest pain was reported by almost ever second
patient treated in the HPSD group, however, most patients reported
merely minor discomfort and did not require pain medication or prolonged
hospitalisation. The pain was mostly described as being breath
dependant, i.e. pleuritic. Typically, the development of Dressler’s
syndrome is a rare complication after catheter ablation of AF16 - while the occurrence of Dressler’s syndrome in
one patient receiving HPSD PVI with extensive left atrial substrate
modification might be coincidence, it will require further alert
attention, since the mechanism of tissue damage differ between normal
and HPSD ablation.
Recently, Sommer and colleagues could show in the OPERA trial that the
peak oesophageal temperature during AF ablation was not predictive for
the development of thermal oesophageal lesions 17. In
the present study no more EDEL could be detected compared to previously
reported ablation studies, even without oesophageal temperature
monitoring and HPSD ablation at the posterior wall 17.
While the overall incidence of EDEL was identical in the standard and
HPSD ablation approach, lesion characteristics differed significantly,
with most of the HPSD lesions consisting of small ulcerations or only
superficial mucosal detachments that are poorly characterized in the
currently used classification of EDEL 11. These
findings support the above mentioned biophysical considerations and are
in line with previous publications of HPSD lesions 18.
In the present trial, all patients received post-procedural
esophagoscopy and were followed up until the lesions resolved, or showed
healing tendency. In further clinical practice, one might consider
performing index esophagoscopy to characterise lesions. Smaller
ulcerations or mucosal detachments are likely to resolve within 1-2
weeks, without the need for extensive follow-up, whereas patients with
larger lesions might be monitored more intensively. However, there is
little to no experience and evidence in the development of
atrial-oesophageal fistula after HPSD ablation, and time-line
characteristics might differ from fistula formation previously described
for normal power ablation 19,20. To avoid the
development of EDEL while using HPSD at the posterior wall, the
recommendations published in the power-AF study should be followed:
avoiding high contact force and adapted stability criteria to avoid
delayed appearance of the Visitag above the target AI value12. In our study, post-hoc analysis revealed that the
largest EDEL occurred in a patient where some posterior points where
achieved with a mean contact force of 24 and above grams, with maximum
lesion AI of 430 on the posterior wall.
There are some limitations of the current study. First, the study was
not designed as a mid-term or long-term outcome trial including
re-ablation of patients suffering from AF recurrence. Thus, the long
term durability of the ablation lesions, created with the AI guided 50W
setting, as well as the resulting clinical outcome remains speculative
in lack of robust follow-up data. Further, like in the previous trials
the number of the studied subjects was too small to make a valid
statement about the real incidence of atrial-oesophageal fistulas using
the fixed 50W power setting.
However, while most previous studies have used higher-power ablation
with less than 50W, or with reduced power on the posterior wall to
<35W, or without relying on ablation index guidance, our study
is the one of the first to perform circumferential 50W HPSD PVI with AI
guidance and the CLOSE protocol, confirming the data of the FAFA AI High
Power Study by Chen et al 21 - but in contrast,
without performing esophageal temperature monitoring, and including more
complex left atrial procedures with an additional substrate based
approach, even including 50W HPSD inferior wall isolation.