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\begin{document}

\title{Lesion Size Index (LSI)--guided catheter ablation for atrial
fibrillation: can tissue impedance drop help to identify desirable
ablation settings and target indices?}



\author[1]{Milena Leo}%
\author[2]{Abhirup Banerjee}%
\author[3]{Andre Briosa e Gala}%
\author[3]{Michael Pope}%
\author[3]{Michala Pedersen}%
\author[3]{Kim Rajappan}%
\author[3]{Matthew Ginks}%
\author[3]{Yaver Bashir}%
\author[4]{Ross Hunter J}%
\author[3]{Tim Betts}%
\affil[1]{Portsmouth Hospitals University NHS Trust}%
\affil[2]{University of Oxford Radcliffe Department of Medicine}%
\affil[3]{Oxford University Hospitals NHS Foundation Trust}%
\affil[4]{Barts and The London School of Medicine and Dentistry Postgraduate Studies}%


\vspace{-1em}



  
  \date{May 24, 2024}


\begingroup
\let\center\flushleft
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\endgroup





\selectlanguage{english}
\begin{abstract}
\textbf{Introduction.} When using Lesion Size index (LSI) to guide
catheter ablation, it is unclear what combination of power, contact
force and time would be preferable to use and what LSI target value to
aim for. This study aimed at identifying desirable ablation settings and
LSI targets by using tissue impedance drop as indicator of lesion
formation. \textbf{Methods.} Consecutive patients, undergoing their
first left atrial (LA) catheter ablation for atrial fibrillation, with
RF powers of 20, 30 and 40 W were enrolled. Tissue impedance, contact
force (CF), Force Time Integral (FTI) and LSI values were continuously
recorded during ablation and sampled at 100 Hz. Mean CF and Contact
Force Variability (CFV) were calculated for every lesion. The effect of
RF power, ablation time, CF and CFV on impedance drop and LSI were
assessed. \textbf{Results.} A total of 3258 lesions were included in the
analysis. For any target LSI value, use of higher RF powers translated
into progressively higher impedance drops. The impact of lower CF and
higher CFV on impedance drop was more relevant when using lower powers.
Target LSI values corresponding to maximum impedance drop were
identified depending on RF power, mean CF and CFV used.
\textbf{Conclusions.} Even in the context of an LSI-guided ablation
strategy, use of lower or higher powers might lead to different lesion
sizes. Different LSI targets might be needed depending on the
combination of RF power, CF and CFV used for ablation. Incorporating
indicators of catheter stability, like CFV, in the LSI formula could
improve the predictive value of LSI for lesion size. Studies with
clinical outcomes are required to confirm the clinical relevance of
these findings.%
\end{abstract}%



\sloppy


\textbf{Lesion Size Index (LSI)--guided catheter ablation for atrial
fibrillation: can tissue impedance drop help to identify desirable
ablation settings and target indices?}

\emph{Milena Leo\textsuperscript{a}, MD, Abhirup
Banerjee\textsuperscript{b}, PhD, Andre Briosa e
Gala\textsuperscript{c}, MD, Michael Pope\textsuperscript{c}, MD,
Michala Pedersen\textsuperscript{c}, MD, PhD, Kim
Rajappan\textsuperscript{c}, MD, Matthew Ginks\textsuperscript{c}, MD,
Yaver Bashir\textsuperscript{c}, MD, Ross J Hunter\textsuperscript{d},
MD, PhD, Tim Betts\textsuperscript{c}, MD.}

\textbf{Authors affiliations and email addresses}

\emph{a: Queen Alexandra Hospital, Portsmouth Hospitals University NHS
Trust, Portsmouth (UK)}

\emph{b:} \emph{Radcliffe Department of Medicine, Division of
Cardiovascular Medicine, University of Oxford, Oxford (UK)}

\emph{c: John Radcliffe Hospital, Oxford University Hospitals NHS
Foundation Trust, Oxford (UK)}

\emph{d: Barts Heart Centre, London (UK)}

Milena Leo: milena.leo@porthosp.nhs.uk

Abhirup Banerjee: abhirup.banerjee@cardiov.ox.ac.uk

Andre Briosa e Gala: andre.gala@ouh.nhs.uk

Michael Pope: mtbpope@doctors.org.uk

Michala Pedersen: michala.pedersen@ouh.nhs.uk

Kim Rajappan: kim.rajappan@ouh.nhs.uk

Matthew Ginks: matthew.ginks@ouh.nhs.uk

Yaver Bashir: yaver.bashir@ouh.nhs.uk

Ross J Hunter: rossjhunter@gmail.com

Tim Betts : tim.betts@ouh.nhs.uk

\textbf{Corresponding author:}

Dr Milena Leo

Consultant Cardiologist and Electrophysiologist

Queen Alexandra Hospital, Portsmouth Hospitals University Trust, Oxford
(UK)

email address: milena.leo@porthosp.nhs.uk

\textbf{STATEMENTS}

\textbf{Data availability}

The data that support the findings of this study are available from the
corresponding author upon reasonable request.

\textbf{Funding}

Prof. Betts is supported by the Oxford NIHR Biomedical Research Centre.
Dr Leo's salary was supported by an unrestricted research grant from
Abbott Medical. The study was partially supported by an Oxfordshire
Health Services Research Committee (OHSRC) research grant (reference
1182).

\textbf{Conflict of interests}

Dr Ginks has received speaker's fees from Abbott and Biosense Webster.
Dr Rajappan has received speaker's fees from Abbott. Prof. Hunter has
received research grants, educational grants and speaker's fees from
Biosense Webster and Medtronic; he is an inventor of the STAR Mapping
system and shareholder in Rhythm AI Ltd. Prof. Betts has received
research funding, speaker's fees and advisory board fees from Abbott.
The other authors have no conflict of interests to declare.

\textbf{Ethical approval}

The study was approved by the South Central - Oxford C Research Ethics
Committee and conducted in accordance with the Declaration of Helsinki.

\textbf{Patient consent to partecipate}

All patients provided informed consent for participation in the study.

\textbf{Permission to reproduce material from other sources}

It was not required.

\textbf{Clinical trial registration}

Data for the study were collected from the PiLOT-AF trial (\emph{P}
ower,\emph{L} esion Size Index and \emph{O} esophageal \emph{T}
emperature Alerts during \emph{A} trial \emph{F} ibrillation ablation),
which was registered (NCT02619396).



\textbf{ABSTRACT}

\textbf{Introduction.} When using Lesion Size index (LSI) to guide
catheter ablation, it is unclear what combination of power, contact
force and time would be preferable to use and what LSI target value to
aim for. This study aimed at identifying desirable ablation settings and
LSI targets by using tissue impedance drop as indicator of lesion
formation.

\textbf{Methods.} Consecutive patients, undergoing their first left
atrial (LA) catheter ablation for atrial fibrillation, with RF powers of
20, 30 and 40 W were enrolled. Tissue impedance, contact force (CF),
Force Time Integral (FTI) and LSI values were continuously recorded
during ablation and sampled at 100 Hz. Mean CF and Contact Force
Variability (CFV) were calculated for every lesion. The effect of RF
power, ablation time, CF and CFV on impedance drop and LSI were
assessed.

\textbf{Results.} A total of 3258 lesions were included in the analysis.
For any target LSI value, use of higher RF powers translated into
progressively higher impedance drops. The impact of lower CF and higher
CFV on impedance drop was more relevant when using lower powers. Target
LSI values corresponding to maximum impedance drop were identified
depending on RF power, mean CF and CFV used.

\textbf{Conclusions.} Even in the context of an LSI-guided ablation
strategy, use of lower or higher powers might lead to different lesion
sizes. Different LSI targets might be needed depending on the
combination of RF power, CF and CFV used for ablation. Incorporating
indicators of catheter stability, like CFV, in the LSI formula could
improve the predictive value of LSI for lesion size. Studies with
clinical outcomes are required to confirm the clinical relevance of
these findings.

\textbf{Keywords:} left atrial ablation, tissue impedance drop, Lesion
Size Index, high RF power, contact force, contact force variability.

\textbf{Abbreviations:} AF= atrial fibrillation; AI= Ablation Index; CF=
Contact Force; CFV= Contact Force Variability; FTI= Force Time Integral;
LA= Left atrium; LSI= Lesion Size Index; Max-Imp-[?]= Maximum Absolute
Impedance Drop; Max-Imp-\%= Maximum Percentage Impedance Drop; PVI=
Pulmonary Vein Isolation; PVs= Pulmonary Veins; RF= Radiofrequency
energy; SD= Standard Deviation; STL= Seasonal-Trend decomposition of
time series by Loess.

\textbf{Main study findings}

\begin{itemize}
\tightlist
\item
  Use of LSI targets does not fully compensate for use of lower powers:
  lower RF powers produce smaller impedance drops regardless of the
  target LSI value. For any target LSI, lower powers might produce
  smaller lesions than higher powers.
\item
  Contact force values and catheter stability are more important
  determinants of impedance drop when using lower powers. Switching to
  higher power could be beneficial in case of low contact force or
  catheter instability.
\item
  For any combination of power and contact force, LSI targets can be
  identified, corresponding to achievement of maximum impedance drop. In
  its current formula, LSI might be more an indicator of lesion
  completeness than of lesion size.
\item
  The correlation of LSI with maximum impedance drop depends on contact
  force variability used during ablation. The addition of an indicator
  of catheter stability in the LSI formula could improve its predictive
  value for lesion size.
\end{itemize}

\textbf{INTRODUCTION}

Reliable creation of durable transmural lesions is the key for
successful catheter ablation procedures. To this aim, acute markers of
lesion formation are needed for real-time estimation of lesion width and
depth.

When using radiofrequency energy (RF) for catheter ablation, tissue
impedance is traditionally assessed as a real-time surrogate marker of
lesion formation. Local tissue heating during ablation produces
increased ion mobility and reduced myocardial resistivity that translate
into a drop in tissue impedance \textsuperscript{1,2}\emph{.} The
impedance reduction is typically rapid in the first seconds of RF
delivery, as result of faster resistive heating of the superficial
tissue layers from the catheter tip; it then progressively slows down
thereafter, due to slower conductive heating of deeper tissue layers,
until a plateau is reached. The magnitude of impedance drop at the
plateau point (maximum impedance drop) strongly correlates with lesion
size in in-vitro studies\textsuperscript{3}. Whether maximum impedance
drop also correlates with lesion transmurality is largely unknown to
date, but it certainly seems a reliable indicator of RF lesion
``completeness'', as no further lesion enlargement is expected with more
prolonged RF delivery once plateau has been reached \textsuperscript{4}.

Ablation indexes such as Force Time Integral (FTI), Ablation Index (AI)
and Lesion Size Index (LSI) are now available in clinical settings as
markers of lesion formation \textsuperscript{5,6} . When using Abbott
Medical contact force (CF)-sensing catheters, both FTI and LSI are
continuously displayed and can be monitored during ablation. Compared to
FTI, which includes CF and time, LSI combines in a non-linear formula
all three main determinants of RF lesion formation: power, CF and
ablation duration. In in-vitro studies, LSI is highly predictive of
lesion width and depth, exhibiting a stronger correlation with lesion
dimensions compared to FTI. Moreover, the correlation between LSI and
lesion size is linear and independent from the power used, meaning that
it is theoretically possible to achieve the same LSI --and therefore
possibly the same lesion size-- with lower powers by using a higher
contact force or by ablating for longer \textsuperscript{6}. However,
in-vitro data also suggest that ablation lesions reach maturity after
20-30 sec of energy delivery without any further increase thereafter
despite more prolonged ablation \textsuperscript{7}.

This study was conducted to investigate the relationship between
ablation parameters and impedance drop in the context of an LSI-guided
left atrial (LA) catheter ablation strategy. We hypothesised that
impedance drop, as a surrogate marker of lesion size, could help to
establish ideal ablation settings and optimal target LSI indices for
ablation.

\textbf{METHODS}

The trial was approved by the local ethics committees and it complied
with the Declaration of Helsinki.

\textbf{Atrial fibrillation ablation protocol}

Data were collected from the PiLOT-AF trial (\emph{P} ower, \emph{L}
esion Size Index and \emph{O} esophageal \emph{T} emperature Alerts
during\emph{A} trial \emph{F} ibrillation ablation)\textsuperscript{8},
which was a randomised study enrolling patients undergoing their first
LA ablation for symptomatic paroxysmal or persistent atrial fibrillation
(AF) (see supplementary materials section for more details).

Tissue contact force, FTI, and LSI were sampled at 100 Hz, displayed in
real time during ablation and automatically recorded for further
analysis. Tissue impedance was measured between the tip of the ablation
catheter and the ground patch (on the patient's left thigh) by using a
50kHz current at the same sampling rate of 100 Hz.

Any steam pops occurring during the procedures were noted.

\textbf{Data analysis}

The tissue impedance data recorded during RF delivery were processed
offline using the R statistical software (version 4.0.3) to remove noise
(see supplementary materials section).

Ablation lesions were excluded if any of the following occurred: short
duration of less than 5 sec (as no LSI value is generated before 5 sec
of RF delivery); sudden and progressive impedance rise, suggestive of
catheter tip or tissue overheating with charring
formation\textsuperscript{9}.

After processing of the raw data, the maximum absolute impedance drop
(Max-Imp-[?]), the maximum percentage impedance drop (Max-Imp-\%), the
mean CF, and the contact force variability (CFV) were calculated for
each study ablation lesion. The maximum absolute impedance drop
(Max-Imp-[?]) was calculated as the difference between maximum impedance
value per lesion, which corresponded to the impedance at the beginning
of the ablation, and minimum impedance reached during ablation. The
maximum percentage impedance drop (Max-Imp-\%) was calculated by
converting the Max-Imp-[?] into a percentage of the starting impedance to
minimise any influence from the initial impedance value. The contact
force variability (CFV) was calculated as difference between mean of the
peaks and mean of the troughs of CF during ablation, as previously
described \textsuperscript{10} (Figure 1).

The ablation lesions were grouped by RF power used (20, 30 and 40W), by
mean CF used (\textless{} 5, 5-10, 10-15 or \textgreater{}15 g) and by
CFV ([?] 5g or \textgreater{} 5 g) and the Max-Imp-\% values in each group
were compared.

The variation of impedance drop over ablation time was investigated by
dividing each ablation delivery into consecutive, cumulative 0.5 sec
time intervals and calculating the mean and the standard deviation (SD)
of all lesions Max-Imp-\% at each interval compared to the initial
impedance at the start of ablation. The relative plateaus of Max-Imp-\%
and the corresponding times at plateau for each group of study ablations
were identified by finding the point after which the SD of the
Max-Imp-\% at each time interval became negligible (less than 0.1) and
the difference between Max-Imp-\% at that point and Max-Imp-\% at the
end of ablation was very low (less than 0.25).

The relation between impedance drop and FTI was assessed as described in
the supplementary section.

The relationship between impedance drop and LSI was assessed by dividing
the ablation lesions into consecutive, cumulative 0.1 LSI intervals and
calculating the Max-Imp-\% of each interval compared to the initial
impedance at the start of ablation. The mean and SD of Max-Imp-\% were
calculated for each interval. The relative plateaus of impedance drop
and the corresponding LSI values at plateau were identified by finding
the point after which the SD of the Max-Imp-\% at each LSI interval
became negligible (less than 0.1) and the difference between Max-Imp-\%
at that point and Max-Imp-\% at the end of ablation was very low (less
than 0.25). To confirm the accuracy of the technique used to identify
the plateau values of the FTI/LSI over time curves, both per-patient
analyses and combined analyses of all-patients lesions were performed
and their results were compared.

\textbf{Statistical analysis}

Categorical variables were expressed as absolute number and percentage
(\%). Continuous variables were expressed as mean \selectlanguage{ngerman}± SD or median and
interquartile range (IQR), as appropriate after checking for normality
by using the Shapiro-Wilk test. Categorical variables were compared with
the use of the Pearson's Chi-square test or Fisher's exact test, as
appropriate. Continuous variables were compared with the use of one-way
ANOVA test or Kruskal-Wallis test, as appropriate based on data
distribution. Correlation between variables was assessed using Pearson's
product-moment correlation coefficient (\(r)\) or Spearman's
rank correlation coefficient (\selectlanguage{greek}ρ\selectlanguage{english}), as appropriate.

A two-sided p value of less than 0.05 was considered to indicate
statistical significance. Data were analysed with the use of R
statistical software version 4.0.3 and SPSS software version 24 (IBM
Statistics, Chicago, Illinois).

\textbf{RESULTS}

\textbf{Ablation settings (RF power, time, CF and CFV) and relative
tissue impedance drop changes}

A total of 4406 ablation lesions were screened for the analysis. Among
them, 274 lesions were removed due to short duration and
non-availability of LSI values and 874 lesions due to sudden and
progressive impedance rise during RF delivery {[}20W: 95 lesions (11\%);
30W: 69 lesions (20\%); 40W: 710 (24\%){]}. The final analysis
considered 3258 study ablations lesions. The baseline characteristics of
the study patients are showed in Table 1. Of note, no steam pops were
recorded during the study ablation procedures.

As presented in Table 2, use of higher RF powers translated into
progressively higher Max-Imp-[?] and Max-Imp-\% despite shorter ablation
durations.

The incremental time analysis showed a logarithmic relation between
impedance drop and time in each RF power group, consisting in a first
steep increase in impedance drop followed by a progressively slower
impedance drop until plateau. The per-patient analysis showed
progressively higher percentage impedance drop values at time of plateau
with the use of higher power (20W = 8.6 \selectlanguage{ngerman}± 2.2\%; 30W = 10.4 ± 3.8\%; 40W
= 11 ± 2.5\%; p = 0.0057) which also corresponded to shorter times to
plateau (20W RF time at plateau = 30.9 ± 9.5 sec; 30W RF time at plateau
= 25.1 ± 12.7 sec; 40W RF time at plateau = 21 ± 7 sec; p \textless{}
0.0005). As shown in Figure 2, the combined analysis of all-patients
lesions showed the same trends. The plateau values of the curves
corresponded to percentage impedance drop values of 8.59\% at 34.5 sec,
10.32\% at 30 sec, and 10.94\% at 21.5 sec for RF powers of 20W, 30W,
and 40W respectively. In all cases, the average maximum impedance drops
and times to plateau for all patients fell very near to the mean values
computed from individual patients and well within their standard
deviations.

In all RF power groups, weak correlations were observed between mean CF
and impedance drop (20W RF power: \selectlanguage{greek}ρ \selectlanguage{english}= 0.061, p = 0.094; 30W RF power: \selectlanguage{greek}ρ
\selectlanguage{english}= 0.148, p = 0.015; 40W RF power: \selectlanguage{greek}ρ \selectlanguage{english}= 0.205, p \textless{} 0.0001) and
between CFV and impedance drop (20W RF power: \selectlanguage{greek}ρ \selectlanguage{english}= -0.202, p \textless{}
0.0005; 30W RF power: \selectlanguage{greek}ρ \selectlanguage{english}= 0.225, p = 0.0002; 40W RF power: \selectlanguage{greek}ρ \selectlanguage{english}= 0.021, p
= 0.316). However, if grouping the ablation lesions according to range
of mean CF used and to range of CFV, progressively higher Max-Imp-\%
values were seen with higher mean CF and lower CFV in the 20W and the
40W group, as showed in Table 3. In the 30W group, increase of mean CF
from 10-15 g to \textgreater{} 15 g and reduction of CFV from
\textgreater{}5 to [?] 5 g in the 5-10 g and \textgreater{} 15 g CF
sub-groups translated in reduction rather than in increase of
Max-Imp-\%, however the number of observations in these subgroups was
quite small with a larger variance of the data. In each power group the
largest Max-Imp-\% increase was observed when increasing the mean CF
from \textless{} 5g to 5-10g.

The independent effect of mean CF and CFV on impedance drop within each
RF power group was also confirmed by a mixed-effect model analysis (see
supplementary section).

\textbf{Relationships between impedance drop and FTI/LSI}

Correlation analyses showed a stronger correlation of LSI with impedance
drop (\selectlanguage{greek}ρ \selectlanguage{english}= 0.319; p \textless{} 0.0001) compared to FTI with impedance
drop (\selectlanguage{greek}ρ \selectlanguage{english}= 0.263; p \textless{} 0.0001).

The incremental FTI analysis showed progressively lower FTI values
corresponding to higher percentage impedance drop values at plateau with
increasing RF power (see supplementary section).

The incremental LSI analysis showed a first linear phase of impedance
drop increase over LSI followed by a plateau phase. Due to
unavailability of LSI data in the first few seconds of RF delivery, the
LSI curves started with a minimum LSI of 2. At any LSI stage, impedance
drop was progressively higher with increasing RF power. The per-patient
analysis showed progressively higher LSI values required to reach
plateau of impedance drop with increasing RF power used (20W: LSI = 4.2
\selectlanguage{ngerman}± 0.5; 30W: LSI = 4.6 ± 1.5; 40W: LSI = 5.4 ± 0.5; overall p \textless{}
0.0015), with higher impedance drop reached at plateau (20W = 8.6 ±
2.2\%; 30W = 10.4 ± 3.8\%; 40W = 11 ± 2.6\%; overall p = 0.0062). As
shown in Figure 3, the combined analysis of all patients' lesions showed
the same trends of the per-patient analysis. The 20W, 30W and 40W curves
reached plateaus corresponding to percentage impedance drop values of
8.71\% at LSI 4.7, 10.43\% at LSI 5.5, and 11.07\% at LSI 5.9
respectively. In all cases, the average maximum impedance drops and LSI
values to plateau for all patients fell very near to the mean values
computed from individual patients and well within their standard
deviations.

Figure 4 represents graphically the impact of different combinations of
RF power, CF and CFV on Max-Imp-\% and the corresponding LSI. Each line
represents a combination of RF power and range of CFV, while the various
points of the lines are the mean CF. Mean CF showed a larger effect on
impedance drop in the 40W group than in the 20W group. Vice versa, CFV
showed a more pronounced effect on impedance drop in the 20W group than
in the 40W one. Provided a mean CF of at least 5 g, use of 40W produced
a bigger impedance drop irrespective of target LSI or CFV. In each RF
power group, approximate LSI values indicative of achievement of
Max-Imp-\% could be identified for the different ranges of CF. However,
depending on the range of CFV, each LSI value corresponded to two
different actual values of Max-Imp-\% achieved.

\textbf{DISCUSSION}

This study assessed the relationship between ablation settings and
tissue impedance drop in the context of an LSI-guided catheter ablation
strategy. The main findings of the study were:

\begin{itemize}
\tightlist
\item
  for any target LSI value, higher RF powers produced progressively
  greater impedance drops and prolonging ablation time when using lower
  powers did not compensate;
\item
  increasing the mean CF to at least 5 g produced the largest increase
  in impedance drop in all RF power groups;
\item
  lower CF values and higher CFV translated in a lower impedance drop
  especially when using lower powers;
\item
  although LSI was found to be a better predictor of Max-Imp-\% compared
  to FTI, its correlation with Max-Imp-\% was found to depend on
  combination of RF power, mean CF and also CFV used.
\end{itemize}

As shown in Figures 2 and 3, in our study higher powers translated into
larger impedance drops regardless of ablation duration and of LSI value
achieved. These data suggest that the use of LSI targets does not fully
compensate for higher powers, which might be due to the plateau of
lesion growth over time and to the less relevant effect of CF at lower
powers. If considering impedance drop as a surrogate marker of lesion
size, they are in keeping with the growing body of evidence on high RF
power. Increases in RF power produce larger lesions as result of a shift
to more effective resistive heating, whereas an increase in ablation
duration simply gives more time for convective heating, which reaches
its limit after a 30-40 second period\textsuperscript{11}. High-power
short-duration ablation produces broad and slightly shallower lesions
which in the LA are still transmural, translating into better clinical
outcomes and reduced risk of collateral
damage\textsuperscript{8,12,13.}Although sudden impedance rise during RF
delivery was observed more frequently with use of increasing power (11\%
of 20W power lesions versus 24\% of 40W power lesions), no steam pops
were recorded in our study ablation procedures, possibly due to prompt
termination of RF delivery in the case of an impedance rise.

In keeping with previous data \textsuperscript{14-16}, we generally
observed a progressive increase of Max-Imp-\% with use of higher mean CF
in the different RF power groups. In all groups the largest increase in
percentage impedance drop was observed by increasing the mean CF from
less than 5 g to more than 5 g, which may suggest the importance of a
minimum mean CF of at least 5 g for effective ablation. The effect of
increasing CF on Max-Imp-\% was progressively larger with use of
increasing power, as expected as both factors play a role in maintaining
a constant catheter electrode-tissue interface temperature required for
RF lesion formation \textsuperscript{17}, and in keeping with previous
data\textsuperscript{18}. As result, higher CF values were required to
achieve the same impedance drop when using lower powers. As previously
demonstrated by Ullah et al \textsuperscript{10}, CFV was found to play
a role on Max-Imp-\%: this is not surprising considering that CFV is an
indicator of catheter stability. Of note, the effect of increasing CFV
on Max-Imp-\% was progressively smaller with use of higher powers. Taken
all together, these data might suggest that CF and CFV are more
important when using lower powers. Switching to higher power could be
considered in case of catheter instability or in case of difficulty to
increase CF, like during sedation cases or if performing left atrial
ablation without steerable sheaths.

The relation between impedance drop and LSI was found to be similar to
the relation observed between impedance drop and AI by Ullah et
al\textsuperscript{19}, apart from the lack of an initial lag phase of
impedance drop which might just not have been visible due to
unavailability of LSI data in the first few seconds of RF delivery. As
expected given the crucial role of RF power on Max-Imp-\%, LSI showed a
stronger correlation than FTI with impedance drop. However, as shown in
Figure 4, each LSI value was found to correspond to different impedance
drop values depending on combination of RF power, mean CF ad also CFV.
Progressively higher LSI values were found to be required to achieve
plateau of impedance drop with higher powers, higher mean CF and lower
CFV. Target LSI values corresponding to achievement of Max-Imp-\% were
identified for each combination of RF power and mean CF, but they were
found to correspond to different Max-Imp-\% values depending on CFV. In
its current formula not including CFV, LSI could represent more an
indicator of lesion completeness (corresponding to plateau of impedance
drop) rather than of lesion size (correlating with the value of
impedance drop at plateau).

\textbf{Limitations}

No histological assessment of the ablation lesions was possible to
confirm that impedance drop is a reliable marker of lesion size.

Tissue impedance at the catheter-tissue interface was classically
measured as transthoracic impedance of the energy delivery pathway from
the ablation catheter tip electrode to an indifferent electrode on the
skin. This approach is known to be influenced by variation of thoracic
impedance and in fact local tissue impedance measurements, now provided
by innovative catheters with miniature electrodes, seem to correlate
better with lesion size \textsuperscript{20}. However, impedance changes
during RF ablation are almost entirely due to variations in local tissue
impedance, and thus the variations of impedance and especially the
percentage variations of impedance should remain a useful measure.

The use of different catheter irrigation rates for different RF powers,
as per Tacticath manufacture instructions, could have had an impact on
the percentage impedance drop values recorded with the different powers.
Irrigation may impact on impedance drop by preventing heating of the
endocardial surface and therefore making impedance drop less predictive
of lesion depth progression. However, the greater impedance fall in the
higher power lesions despite higher irrigation rate suggest that this is
a genuine effect of high power compared to low power.

\textbf{Conclusions}

Even in the context of an LSI guided ablation strategy, use of lower or
higher powers might lead to different lesion sizes. Use of higher powers
might be preferrable in case of catheter instability or in case of
difficulty to increase CF. Different LSI targets might be needed,
depending on power and mean CFV used, to prevent unnecessary ablation
and reduce the risk of collateral damage. Incorporating indicators of
catheter stability, like CFV, in the LSI formula could improve the
predictive value of LSI for lesion size. Larger studies with clinical
outcomes are required to confirm the clinical relevance of these
findings.

\textbf{ACKOWLEDGEMENTS}

We thank the John Radcliffe Hospital Cardiac Angiography Suite Team and
the Oxford Cardiac Research Team for their invaluable help and support
for the conduction of the study.

\textbf{REFERENCES}

1. Hartung WM, Burton ME, Deam AG, Walter PF, McTeague K, Langberg JJ.
Estimation of temperature during radiofrequency catheter ablation using
impedance measurements. Pacing and clinical electrophysiology : PACE
1995;18:2017-21.

2. Nsah E, Berger R, Rosenthal L, et al. Relation between impedance and
electrode temperature during radiofrequency catheter ablation of
accessory pathways and atrioventricular nodal reentrant tachycardia.
American heart journal 1998;136:844-51.

3. Avitall B, Mughal K, Hare J, Helms R, Krum D. The effects of
electrode-tissue contact on radiofrequency lesion generation. Pacing and
clinical electrophysiology : PACE 1997;20:2899-910.

4. Eick OJ, Gerritse B, Schumacher B. Popping phenomena in
temperature-controlled radiofrequency ablation: when and why do they
occur? Pacing and clinical electrophysiology : PACE 2000;23:253-8.

5. Das M, Loveday JJ, Wynn GJ, et al. Ablation index, a novel marker of
ablation lesion quality: prediction of pulmonary vein reconnection at
repeat electrophysiology study and regional differences in target
values. Europace : European pacing, arrhythmias, and cardiac
electrophysiology : journal of the working groups on cardiac pacing,
arrhythmias, and cardiac cellular electrophysiology of the European
Society of Cardiology 2017;19:775-83.

6. Calzolari V, De Mattia L, Indiani S, et al. In~Vitro Validation of
the Lesion Size Index to Predict Lesion Width and Depth After Irrigated
Radiofrequency Ablation in~a~Porcine Model. JACC Clinical
electrophysiology 2017;3:1126-35.

7. Wittkampf FH, Hauer RN, Robles de Medina EO. Control of
radiofrequency lesion size by power regulation. Circulation
1989;80:962-8.

8. Leo M, Pedersen M, Rajappan K, et al. Power, Lesion Size Index and
Oesophageal Temperature Alerts During Atrial Fibrillation Ablation: A
Randomized Study. Circulation Arrhythmia and electrophysiology
2020;13:e008316.

9. Haines DE, Verow AF. Observations on electrode-tissue interface
temperature and effect on electrical impedance during radiofrequency
ablation of ventricular myocardium. Circulation 1990;82:1034-8.

10. Ullah W, Hunter RJ, Baker V, et al. Factors affecting catheter
contact in the human left atrium and their impact on ablation efficacy.
Journal of cardiovascular electrophysiology 2015;26:129-36.

11. Borne RT, Sauer WH, Zipse MM, Zheng L, Tzou W, Nguyen DT. Longer
Duration Versus Increasing Power During Radiofrequency Ablation Yields
Different Ablation Lesion Characteristics. JACC Clinical
electrophysiology 2018;4:902-8.

12. Leshem E, Zilberman I, Tschabrunn CM, et al. High-Power and
Short-Duration Ablation for Pulmonary Vein Isolation:
Biophysical~Characterization. JACC Clinical electrophysiology
2018;4:467-79.

13. Winkle RA. HPSD ablation for AF high-power short-duration RF
ablation for atrial fibrillation: A review. Journal of cardiovascular
electrophysiology 2020.

14. Kumar S, Haqqani HM, Chan M, et al. Predictive value of impedance
changes for real-time contact force measurements during catheter
ablation of atrial arrhythmias in humans. Heart rhythm 2013;10:962-9.

15. Ullah W, Hunter RJ, Baker V, et al. Target indices for clinical
ablation in atrial fibrillation: insights from contact force,
electrogram, and biophysical parameter analysis. Circulation Arrhythmia
and electrophysiology 2014;7:63-8.

16. De Bortoli A, Sun LZ, Solheim E, et al. Ablation effect indicated by
impedance fall is correlated with contact force level during ablation
for atrial fibrillation. Journal of cardiovascular electrophysiology
2013;24:1210-5.

17. Haines DE. Determinants of Lesion Size During Radiofrequency
Catheter Ablation: The Role of Electrode-Tissue Contact Pressure and
Duration of Energy Delivery. Journal of cardiovascular electrophysiology
1991;2:509-15.

18. Ikeda A, Nakagawa H, Lambert H, et al. Relationship between catheter
contact force and radiofrequency lesion size and incidence of steam pop
in the beating canine heart: electrogram amplitude, impedance, and
electrode temperature are poor predictors of electrode-tissue contact
force and lesion size. Circulation Arrhythmia and electrophysiology
2014;7:1174-80.

19. Ullah W, Hunter RJ, Finlay MC, et al. Ablation Index and Surround
Flow Catheter Irrigation: Impedance-Based Appraisal in
Clinical~Ablation. JACC Clinical electrophysiology 2017;3:1080-8.

20. Gunawardene M, Münkler P, Eickholt C, et al. A novel assessment of
local impedance during catheter ablation: initial experience in humans
comparing local and generator measurements. Europace : European pacing,
arrhythmias, and cardiac electrophysiology : journal of the working
groups on cardiac pacing, arrhythmias, and cardiac cellular
electrophysiology of the European Society of Cardiology 2019;21:i34-i42.

\textbf{TABLES}

\textbf{Table 1. Patients' baseline characteristics.}\selectlanguage{english}
\begin{longtable}[]{@{}ll@{}}
\toprule
\begin{minipage}[b]{0.47\columnwidth}\raggedright\strut
\textbf{Total number of patients}\strut
\end{minipage} & \begin{minipage}[b]{0.47\columnwidth}\raggedright\strut
44\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{Age (years)} Mean (\selectlanguage{ngerman}±SD)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
58.17 \selectlanguage{ngerman}\textbf{±} 9.57\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{Sex (males)} Number of patients (\%)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
32 (73\%)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{Paroxysmal AF patients} Number of patients (\%)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
19 (43.2\%)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{AF duration (months)} Median (IQR)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
27.5 (18-48)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{EHRA class} Median (IQR)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
3 (3-3)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{BMI} Mean (\selectlanguage{ngerman}±SD)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
28.4 \selectlanguage{ngerman}\textbf{±} 6.6\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{CHA\textsubscript{2}DS\textsubscript{2}VASC score} Median
(IQR)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
1 (0-2)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{HAS-BLED score} Median (IQR)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
0 (0-2)\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{LA dimension (mm)} Mean (\selectlanguage{ngerman}±SD)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
42.5 \selectlanguage{ngerman}\textbf{±} 7.3\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
\textbf{LV systolic function (\%)} Mean (±SD)\strut
\end{minipage} & \begin{minipage}[t]{0.48\columnwidth}\raggedright\strut
56.8 \selectlanguage{ngerman}\textbf{±} 9.7\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{ngerman}

\textbf{Legend:} IQR = Interquartile range; SD = Standard Deviation.

\textbf{Table 2. Ablation parameters in the different RF power groups.}\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
\begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{20 W} \textbf{(763 lesions)}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{30 W} \textbf{(272 lesions)}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{40 W} \textbf{(2223 lesions)}\strut
\end{minipage} & \begin{minipage}[b]{0.19\columnwidth}\raggedright\strut
\textbf{p}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{Max-Imp-[?] ()} Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
10.16 \selectlanguage{ngerman}± 5.32\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
11.65 \selectlanguage{ngerman}± 6.63\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
12.53 \selectlanguage{ngerman}± 6.81\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{\textless{} 0.0001}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{Max-Imp-\% (\%)} Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
8.81 \selectlanguage{ngerman}± 4.27\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
10.08 \selectlanguage{ngerman}± 5.3\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
11 \selectlanguage{ngerman}± 5.23\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{\textless{} 0.0001}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{Ablation duration (sec)} Mean \selectlanguage{ngerman}± SD\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
27.44 \selectlanguage{ngerman}± 16.04\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
24.49 \selectlanguage{ngerman}± 16.3\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
16.95 \selectlanguage{ngerman}± 11.03\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{\textless{} 0.0001}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{CF (g)} \selectlanguage{ngerman}\textbf{Mean ± SD}\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
17.5 \selectlanguage{ngerman}± 9.4\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
19.4 \selectlanguage{ngerman}± 14\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
14.8 \selectlanguage{ngerman}± 8.6\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{\textless{} 0.0001}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
\textbf{CFV (g)} \selectlanguage{ngerman}\textbf{Mean ± SD}\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
5.1 \selectlanguage{ngerman}± 4.1\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
4.5 \selectlanguage{ngerman}± 3.6\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
4.8 \selectlanguage{ngerman}± 3.4\strut
\end{minipage} & \begin{minipage}[t]{0.19\columnwidth}\raggedright\strut
0.083\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\textbf{Legend:} CF = Contact Force; CFV= Contact Force Variability;
Max-Imp-[?] = Maximum absolute impedance drop; Max-Imp-\% (\%) = Maximum
percentage impedance drop; SD = Standard Deviation.

\textbf{Table 3. Maximum percentage impedance drop achieved during
ablation in the different RF power groups depending on mean contact
force (CF) only and on combination of mean CF and contact force
variability (CFV).}\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
& \textbf{20W RF power} & \textbf{30W RF power} & \textbf{40W RF power}
& \textbf{p}\tabularnewline
\midrule
\endhead
\textbf{Mean CF [?] 5 g} & 7.54 \selectlanguage{ngerman}± 5.25 & 5.28 \selectlanguage{ngerman}± 3.30 & 7.88 \selectlanguage{ngerman}± 4.63 &
0.043\tabularnewline
\textbf{5 g \textless{} Mean CF [?] 10 g} & 8.38 \selectlanguage{ngerman}± 4.79 & 9.99 \selectlanguage{ngerman}± 5.01 &
10.2 \selectlanguage{ngerman}± 4.78 & 0.002\tabularnewline
\textbf{10 g \textless{} Mean CF [?] 15 g} & 8.88 \selectlanguage{ngerman}± 4.22 & 11.4 \selectlanguage{ngerman}± 5.36 &
10.9 \selectlanguage{ngerman}± 5.13 & \textless{} 0.0001\tabularnewline
\textbf{Mean CF \textgreater{} 15 g} & 8.95 \selectlanguage{ngerman}± 4.08 & 10.4 \selectlanguage{ngerman}± 5.27 & 12.1
\selectlanguage{ngerman}± 5.40 & \textless{} 0.0001\tabularnewline
\textbf{p} & 0.309 & \textless{} 0.0001 & \textless{} 0.0001
&\tabularnewline
\textbf{Mean CF [?] 5 g and:} & & & &\tabularnewline
\textbf{- CFV [?] 5 g} & 7.54 \selectlanguage{ngerman}± 5.25 & 5.28 \selectlanguage{ngerman}± 3.30 & 7.88 \selectlanguage{ngerman}± 4.63 &
0.043\tabularnewline
\textbf{- CFV \textgreater{} 5 g} & - & - & - & -\tabularnewline
\textbf{p} & - & - & - &\tabularnewline
\textbf{5 g \textless{} Mean CF [?] 10 g and:} & & & &\tabularnewline
\textbf{- CFV [?] 5 g} & 8.97 \selectlanguage{ngerman}± 4.93 & 9.74 \selectlanguage{ngerman}± 5.12 & 10.3 \selectlanguage{ngerman}± 4.73 &
0.055\tabularnewline
\textbf{- CFV \textgreater{} 5 g} & 5.55 \selectlanguage{ngerman}± 2.70 & 10.6 \selectlanguage{ngerman}± 4.81 & 9.84 \selectlanguage{ngerman}±
5.08 & 0.002\tabularnewline
\textbf{p} & 0.005 & 0.554 & 0.398 &\tabularnewline
\textbf{10 g \textless{} Mean CF [?] 15 g and:} & & & &\tabularnewline
\textbf{- CFV [?] 5 g} & 9.74 \selectlanguage{ngerman}± 4.56 & 12.2 \selectlanguage{ngerman}± 5.41 & 11.0 \selectlanguage{ngerman}± 5.21 &
0.007\tabularnewline
\textbf{- CFV \textgreater{} 5 g} & 7.23 \selectlanguage{ngerman}± 2.84 & 9.60 \selectlanguage{ngerman}± 4.95 & 10.7 \selectlanguage{ngerman}±
4.97 & \textless{} 0.0001\tabularnewline
\textbf{p} & \textless{} 0.0001 & 0.101 & 0.445 &\tabularnewline
\textbf{Mean CF \textgreater{} 15 g and:} & & & &\tabularnewline
\textbf{- CFV [?] 5 g} & 9.71 \selectlanguage{ngerman}± 4.53 & 9.74 \selectlanguage{ngerman}± 5.60 & 13.0 \selectlanguage{ngerman}± 5.17 &
\textless{} 0.0001\tabularnewline
\textbf{- CFV \textgreater{} 5 g} & 8.13 \selectlanguage{ngerman}± 3.37 & 11.3 \selectlanguage{ngerman}± 4.71 & 11.4 \selectlanguage{ngerman}±
5.48 & \textless{} 0.0001\tabularnewline
\textbf{p} & \textless{} 0.0001 & 0.087 & \textless{} 0.0001
&\tabularnewline
\bottomrule
\end{longtable}

\textbf{Legend:} CF = Contact Force; CFV= Contact Force Variability; RF
= radiofrequency energy.



\textbf{FIGURE LEGENDS}

\textbf{Figure 1. Contact Force Variability (CFV): example of automated
measurement from contact force (CF) waveform over ablation time.} The
continuous horizontal line corresponds to the mean CF, the superior
dotted line to the mean of the peaks and the inferior dotted line to the
mean of the troughs.

\textbf{Figure 2. Variation of percentage impedance drop over time in
the different RF power groups.} Each data point represents the average
percentage of impedance drop. The dots on each curve correspond to the
plateau of percentage impedance drop.

\textbf{Figure 3. Relationship between LSI and percentage impedance drop
in the different RF power groups.} Each data point represents the
average percentage of impedance drop. The dots on each curve represent
the plateau of percentage impedance drop.

\textbf{Figure 4. Relationship between maximum percentage impedance drop
and corresponding LSI depending on RF power, mean CF and CFV.}

\textbf{Figure 1. Contact Force Variability (CFV): example of automated
measurement from contact force (CF) waveform over ablation time.} The
continuous horizontal line corresponds to the mean CF, the superior
dotted line to the mean of the peaks and the inferior dotted line to the
mean of the troughs.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 2. Variation of percentage impedance drop over time in
the different RF power groups.} Each data point represents the average
percentage of impedance drop. The dots on each curve correspond to the
plateau of percentage impedance drop.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 3. Relationship between LSI and percentage impedance drop
in the different RF power groups.} Each data point represents the
average percentage of impedance drop. The dots on each curve represent
the plateau of percentage impedance drop.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}



\textbf{Figure 4. Relationship between maximum percentage impedance drop
and corresponding LSI depending on RF power, mean CF and CFV}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\subsection*{LSI values corresponding to maximum Percentage Impedance
Drop}

{\label{lsi-values-corresponding-to-maximum-percentage-impedance-drop}}\selectlanguage{english}
\begin{longtable}[]{@{}llll@{}}
\toprule
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{}

{\label{section}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{20 W}

{\label{w}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{30W}

{\label{w-1}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{40W}

{\label{w-2}}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{Mean CF [?] 5 g}

{\label{mean-cf-5-g}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{2.5}

{\label{section-1}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{3}

{\label{section-2}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{3.5}

{\label{section-3}}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{5 g \textless{} Mean CF [?] 10 g}

{\label{g-mean-cf-10-g}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{3.5}

{\label{section-4}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{4.5}

{\label{section-5}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{4.5}

{\label{section-6}}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{10 g \textless{} Mean CF [?] 15 g}

{\label{g-mean-cf-15-g}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{4}

{\label{section-7}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{5}

{\label{section-8}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{5}

{\label{section-9}}\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{Mean CF \textgreater{} 15 g}

{\label{mean-cf-15-g}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{4.5}

{\label{section-10}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{5.5}

{\label{section-11}}\strut
\end{minipage} & \begin{minipage}[t]{0.24\columnwidth}\raggedright\strut
\subsection*{5.5}

{\label{section-12}}\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-1/Figure-1}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-2/Figure-2}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-3/Figure-3}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/Figure-4/Figure-4}

\end{center}
\end{figure}

\selectlanguage{english}
\FloatBarrier
\end{document}

