4 Discussion
This meta-analysis provides a more comprehensive assessment of HPSD RFA
and conventional RFA in patients with AF. Our results suggest that HPSD
RFA may be more effective with higher first-pass isolation and freedom
from atrial arrhythmia and lower acute PVR when compared with
conventional RFA. However, there was no difference in safety outcomes
between two groups. Unlike previous studies8,9,32, our
study had more findings. In our study, there was no difference in PVR
between the two groups that described redo procedures. In subgroup
analysis, there was no difference between the two groups using AI/LSI
guided ablation for freedom from atrial arrhythmia. And HPSD group with
a power setting of 40-50W had better efficacy when compared with
conventional group.
PVI is the cornerstone of AF ablation 33, however, PVR
is frequent and is mostly the result of catheter instability, tissue
edema, and a reversible non-transmural injury 34. One
of the main reasons for AF recurrence is the recovery of the conduction
between the pulmonary veins and left atrium 35, so
continuous and transmural lines are key to the success of ablation. In
animal studies, the lesions were wider and HPSD ablation resulted in
100% contiguous lines with transmural lesions which improved
lesion-to-lesion uniformity 36. In 6 swine, HPSD
ablation was performed using the QDOT MICROTMCatheter at a setting of
90W for 4s and conventional ablation was delivered using a Thermocool
Smarttouch SF Catheter at a setting of 30W for 30s, Barkagan et al found
that all lines remained intact after 30 days in HPSD ablation, while
none of the lines were continuous in conventional ablation37. Although there was variation in the definition of
freedom from arrhythmia in each study and the use of AADs, our analysis
favors the HPSD RFA strategy over LPLD RFA strategy for lower acute PVR,
higher first-pass isolation and higher freedom from atrial arrhythmia.
Nevertheless, in our analysis, there was no difference between two
groups in PVR during the redo procedure. Some patients might have had
recurrence during the follow-up period, but they did not undergo redo
procedures. Furthermore, the follow-up was determined to one year,
therefore all the reasons above may underestimate the rate of chronic
PVR.
However, the appropriate power for the RF ablation is not clear. One
study 31 used higher power of 70W for 5-7s and
demonstrated significantly less arrhythmia recurrence during one-year
follow-up (26.9% vs 34.9%, P < 0.013) with no major
complications. The QDOT-FAST trial 38 used 90W for 4s
per site in 52 patients with paroxysmal atrial fibrillation and 94.2%
patients were in sinus rhythm at 3 months with one pseudoaneurysm and
one asymptomatic thromboembolism. In our meta-analysis, mostly half of
studies of HPSD RFA used 50W and the others using 45-50W. For freedom
from atrial arrhythmia at one year, the HPSD RFA group demonstrated
higher efficacy with the power setting of 45-50W, whereas the two groups
were similar with the power setting of 50W. To reduce complications when
ablating with 50W on the posterior atrial wall, ablation duration was
shorter than that of 40/45W. Less total energy and shallower lesions
which possibly not reaching transmural, resulting in no difference in
the recurrence rate between the two groups39. Winkle
et al 40 reported that 6 independent predictors
affected the outcomes for HPSD ablation including age, gender, type of
AF, left atrial size, type of catheter and posterior wall isolation.
Therefore, further studies will be required to explore the most optimal
power and duration for HPSD RFA to bring the highest clinical value.
Previous studies indicate force time integral (FTI) as a target value to
achieve permanent PVI, while not considering power settings.
Consequently, only 72% of PVs remained isolated in 3 months41. AI is a novel ablation quality marker that
incorporates contact force (CF), time and power in a weighted formula
and LSI is a multi-parametric index incorporating CF and radiofrequency
current data across time. Many reports demonstrated that AI or LSI can
be used as the correlation index of pulmonary vein persistent isolation42,43. HPSD-AI or LSI groups had lower recurrence of
atrial arrhythmia at 12 months, higher first-pass isolation, lower acute
PVR and similar complication rates in the AI-guided group compared with
non-AI-guided group 32,44. Okamatsu et
al45 studied a group of persistent AF patients
undergoing AI-guided PVI with target values of 550 for anterior and 400
for posterior left atrial regions, with 22% patients demonstrating late
PVR during repeat procedures after 2 months and 95% patients were in
sinus rhythm at 12 months. However, freedom from atrial arrhythmia and
acute PVR failed to demonstrate a significant advantage with AI or LSI
in our analysis. It is regrettable that only 5 studies were included in
our subgroup analysis with AI or LSI guided procedure, of which only 4
studies and 2 studies respectively illustrated freedom from atrial
arrhythmia at one year and acute PVR rates. We did not analyze
first-pass isolation because only one study reported this data.
Therefore, more well-designed and large-scale RCTs are required to
confirm these findings.
Safety during elective PVI procedures is of worthwhile concern.
Radiofrequency catheter ablation is a technique where conductive and
resistive heating are delivered through electrode catheters to
myocardial tissue creating a thermal lesion. Irreversible myocardial
tissue injury with cellular death occurs once the temperature of
approximately 50℃ has been reached, whereas conductive heating transfers
thermal energy directly to deeper tissue 46. Unlike
conventional ablation, the HPSD ablation strategy results in a higher
resistive heating and lower conductive heating, which may reduce
collateral injury to surrounding structures such as the esophagus36,47. Late gadolinium enhancement MRI of the
oesophagus in 574 patients following AF ablation using HPSD settings of
50 W for 5 seconds reported a 14.3% incidence of moderate to severe
thermal oesophageal late gadolinium enhancement with no fistulas22. Takemoto et al 48 reported that
high power settings based on the AI or LSI might reduce the collateral
thermal damage comparing use of 20W and 40W with the same AI or LSI for
RF applications. HPSD RFA strategies performed at 45-50W have very low
complication rates 49. Likewise, in our analysis,
there was no difference between the two groups across each subgroup
analysis.
In terms of procedure duration, RF duration and fluoroscopy time, the
HPSD RFA strategy represents distinct advantages compared with the
conventional RFA strategy whether in the subgroup analysis or not.
Additionally, the reduction in procedure times can decrease the
intravenous fluid volumes administered to patients which may benefit
patients with cardiac insufficiency. Finally, less radiation exposure
will also benefit both patients and physicians 9.
To conclude, our results of the pooled analysis favour the use of HPSD
settings over conventional settings. However, more RCT studies are
needed to further assess the above results.