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\begin{document}

\title{Validation of the accuracy of contact force measurement by contemporary
force-sensing ablation catheters}



\author[1]{Thomas Küffer}%
\author[1]{Andreas Haeberlin}%
\author[2]{Sven Knecht}%
\author[1]{Samuel Baldinger}%
\author[1]{Antonio Madaffari}%
\author[1]{Jens Seiler}%
\author[1]{Aline Mühl}%
\author[1]{Hildegard Tanner}%
\author[1]{Laurent Roten}%
\author[1]{Tobias Reichlin}%
\affil[1]{Inselspital Universitatsspital Bern Universitatsklinik fur Kardiologie}%
\affil[2]{Department of Cardiology University Hospital Basel Basel Switzerland}%


\vspace{-1em}



  
  \date{May 18, 2024}


\begingroup
\let\center\flushleft
\let\endcenter\endflushleft
\maketitle
\endgroup





\selectlanguage{english}
\begin{abstract}
\textbf{Introduction:} Contact force-sensing catheters are widely used
for ablation of cardiac arrhythmias. They allow quantification of
catheter-to-tissue contact, which is an important determinant for lesion
formation and may reduce the risk of complications. The accuracy of
these sensors may vary across the measurement range, catheter-to-tissue
angle, and amongst manufacturers and we aim to compare the accuracy and
reproducibility of four different force sensing ablation catheters.
\textbf{Methods:} A measurement setup containing a heated saline water
bath with an integrated force measurement unit was constructed and
validated. Subsequently, we investigated four different catheter models,
each equipped with a unique measurement technology: Tacticath Quartz
(Abbott), AcQBlate Force (Biotronik/Acutus), Stablepoint (Boston
Scientific), and Smarttouch SF (Biosense Webster). For each model, the
accuracy of three different catheters was measured within the range of
0-60 grams and at contact angles of 0\selectlanguage{ngerman}°, 30°, 45°, 60°, and 90°.
\textbf{Results:} In total, 6685 measurements were performed using 4x3
catheters (median of 568, IQR 511-606 measurements per catheter). Over
the entire measurement-range, the force measured by the catheters
deviated from the real force by the following absolute mean values:
Tacticath 1.29g ±0.99g, AcQBlate Force 2.87g ±2.37g, Stablepoint 1.38g
±1.29g, and Smarttouch 2.26g ±2.70g. For some models, significant under-
and overestimation of \textgreater{}10g were observed at higher forces.
Mean absolute errors of all models across the range of 10-40g were
\textless{}3g. \textbf{Conclusion:} Contact measured by force-sensing
catheters is accurate with 1-3g deviation within the range of 10g to
40g. Significant errors can occur at higher forces with potential
clinical consequences.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Validation of the accuracy of contact force measurement by
contemporary force-sensing ablation catheters}

Thomas Kueffer MSc\textsuperscript{a}, Andreas Haeberlin MD,
PhD\textsuperscript{a,b}, Sven Knecht DSc\textsuperscript{c}, Samuel H
Baldinger MD\textsuperscript{a}, Antonio Madaffari
MD\textsuperscript{a}, Jens Seiler MD\textsuperscript{a}, Aline M\selectlanguage{ngerman}ühl
MSc\textsuperscript{a}, Hildegard Tanner MD\textsuperscript{a}, Laurent
Roten MD\textsuperscript{a}, Tobias Reichlin MD\textsuperscript{a}

\textsuperscript{a} Department of Cardiology, Inselspital, Bern
University Hospital, University of Bern, Bern, Switzerland

\textsuperscript{b} ARTORG Center for Biomedical Engineering, University
of Bern, Switzerland

\textsuperscript{c} Department of Cardiology, University Hospital Basel,
Basel, Switzerland

Running title: Accuracy of force sensing ablation catheters

Word count: 2368

\subsection*{Corresponding author}

{\label{corresponding-author}}

Prof. Dr. med. Tobias Reichlin, MD

Department of Cardiology, Inselspital -- University Hospital Bern

Freiburgstrasse, CH-3010 Bern, Switzerland Email:
tobias.reichlin@insel.ch Phone: +41 (0)31 634 00 50

\subsection*{Conflict of interest}

{\label{conflict-of-interest}}

A. Haeberlin: Research grants from the Swiss National Science
Foundation, the Swiss Heart Foundation, the University of Bern, the
University Hospital Bern, the Velux Foundation, the Hasler Foundation,
the Swiss Heart Rhythm Foundation, and the Novartis Research Foundation.
He is Co-founder and CEO of Act-Inno, a cardiovascular device testing
company. He has received travel fees/educational grants from Medtronic,
Philips/Spectranetics and Cairdac without impact on his personal
remuneration.

L. Roten: speaker honoraria from Abbott/SJM and consulting honoraria
from Medtronic.

T. Reichlin: Research grants from the Swiss National Science Foundation,
the Swiss Heart Foundation, and the sitem insel support funds, all for
work outside the submitted study. Speaker/consulting honoraria or travel
support from Abbott/SJM, Astra Zeneca, Brahms, Bayer, Biosense-Webster,
Biotronik, Boston-Scientific, Daiichi Sankyo, Farapulse, Medtronic,
Pfizer-BMS and Roche, all for work outside the submitted study. Support
for his institution's fellowship program from Abbott/SJM,
Biosense-Webster, Biotronik, Boston-Scientific and Medtronic for work
outside the submitted study.

J. Seiler: The spouse of Dr Seiler is an employee and stock owner of
Boston Scientific.

F. Noti: Medtronic, Abbott: Travel fees, speaker fees, educational
grant; Boston Scientific, Philips Spectranetics: Travel fees,
educational grant; Biotronik: Institutional grant all for work outside
the submitted study.

All other authors report no conflicts of interest related to this paper.

\textbf{Data availability statement:}

The authors had full access to and take full responsibility for the
integrity of the data.

\textbf{Funding statement:}

This study was not funded by external sources.

\section*{Abstract}

{\label{abstract}}

\textbf{Introduction:} Contact force-sensing catheters are widely used
for ablation of cardiac arrhythmias. They allow quantification of
catheter-to-tissue contact, which is an important determinant for lesion
formation and may reduce the risk of complications. The accuracy of
these sensors may vary across the measurement range, catheter-to-tissue
angle, and amongst manufacturers and we aim to compare the accuracy and
reproducibility of four different force sensing ablation catheters.

\textbf{Methods:} A measurement setup containing a heated saline water
bath with an integrated force measurement unit was constructed and
validated. Subsequently, we investigated four different catheter models,
each equipped with a unique measurement technology: Tacticath Quartz
(Abbott), AcQBlate Force (Biotronik/Acutus), Stablepoint (Boston
Scientific), and Smarttouch SF (Biosense Webster). For each model, the
accuracy of three different catheters was measured within the range of
0-60 grams and at contact angles of 0°, 30°, 45°, 60°, and 90°.

\textbf{Results:} In total, 6685 measurements were performed using 4x3
catheters (median of 568, IQR 511-606 measurements per catheter). Over
the entire measurement-range, the force measured by the catheters
deviated from the real force by the following absolute mean values:
Tacticath 1.29g ±0.99g, AcQBlate Force 2.87g ±2.37g, Stablepoint 1.38g
±1.29g, and Smarttouch 2.26g ±2.70g. For some models, significant under-
and overestimation of \textgreater{}10g were observed at higher forces.
Mean absolute errors of all models across the range of 10-40g were
\textless{}3g.

\textbf{Conclusion:} Contact measured by force-sensing catheters is
accurate with 1-3g deviation within the range of 10g to 40g. Significant
errors can occur at higher forces with potential clinical consequences.

\textbf{Keywords:} Radiofrequency Ablation; Contact Force; Catheter
Ablation; Force Sensing

\textbf{Graphical abstract (Central Illustration):}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\section*{Introduction}

{\label{introduction}}

Radiofrequency ablation (RFA) is commonly used for the treatment of
cardiac arrhythmias. In recent years, advancements in catheter
manufacturing technologies allowed for more complex catheter designs,
including the assessment of contact by force measurement at the
catheter's tip. These catheters are widely used and have been
demonstrated to be effective in complex ablation procedures including
ablation of atrial fibrillation as well as ventricular
arrhythmias.\textsuperscript{1--5} The biophysics of RFA are well
understood and lesion size is mainly a function of power, energy
delivery time, catheter-to-tissue contact force per area, and
stability\textsuperscript{6}. This knowledge and the rise of force
sensing catheters allowed the field to develop algorithms to predict
lesion formation and --quality\textsuperscript{7--12}. These novel
algorithms are nowadays used in conjunction with conventional markers
like tactile feedback, impedance drop, loss of pace capture, or
electrogram amplitude attenuation\textsuperscript{1,13}. For the
algorithms to perform well, reliance on accurate cather-to-tissue
contact force measurement is key. For some force sensing catheters, the
accuracy of their sensors was externally validated
previously\textsuperscript{14}. Several latest generation models however
have not been tested yet, including two catheter designs that newly
gained CE mark approval in 2020 (Stablepoint\textsuperscript{}, Boston
Scientific; and AcQBlate\selectlanguage{ngerman}\textsuperscript{®} Force, Biotronik/Acutus).

This study aimed to compare the four currently commercially available
contact force-sensing ablation catheters regarding the accuracy of their
contact force sensor measurements.

\section*{Materials \& Methods}

{\label{materials-methods}}

\subsection*{Measurement setup}

{\label{measurement-setup}}

We constructed and validated a bench setup that can assess the accuracy
of the force sensors integrated in force sensing ablation catheters. The
measurement system consists of an acrylic glass tank containing 0.9\%
saline solution heated to 37°C to emulate the electrical and thermal
properties of the human body (Figure 1). It further offers a catheter
fixation mechanism and a suspended platform on which a force can be
applied. The force is redirected to the outside of the water bath onto a
precision scale (resolution = 0.5g, FXN 3K-4N, Kern, Balingen, Germany),
using low friction pulleys. The force pulls on a counterweight lying on
the scale, consequently lifting the weight (Figure 1). After initial
zeroing, the force applied to the platform can be read off directly from
the scale. The surface of the platform consists of a slightly
compressible polymeric foam, mimicking the flexibility of myocardial
tissue. A custom-made catheter fixation mechanism allows holding the
catheter at different angles from 0° to 90° against the platform. 0° is
defined as perpendicular to the platform, such that the force is applied
axially to the catheter (Z-axis), while 90° is defined as parallel to
the platform, resulting in a force applied radially to the tip of the
catheter (X- and Y-axis). The position of the catheter can be adjusted
vertically to adjust the force exerted onto the platform. For simplicity
reason, the terms ``weight'' and ``force'' are used interchangeably.

\textbf{Validation of the measurement setup}

The accuracy of the setup for measuring the force applied to the
platform was validated in the air by measuring standard weights, which
were put on the platform. The validation procedure is detailed further
in the online supplement.

\subsection*{Ablation catheter models}

{\label{ablation-catheter-models}}

Four ablation catheter models were investigated. Each model was used in
conjunction with the corresponding equipment needed to read out the
force sensor. Tacticath\selectlanguage{english} Quartz, Smarttouch\textsuperscript{(r)}, and
Stablepoint\selectlanguage{english} must all be paired with a specific 3D mapping system while
the AcQBlate\textsuperscript{(r)} Force can be used as a standalone
solution. An overview of additional technical details can be found in
table 1.

All four catheter models provide a force sensing tip, temperature
measurement, irrigation, and catheter deflection. However, the force
sensing technology is different for each model and described in the
following section as well in Figure 2:

\selectlanguage{english}\subsection*{\texorpdfstring{Tacticath\textsuperscript{} Quartz (Abbott,
Abbott Park, IL,
USA):}{Tacticath Quartz (Abbott, Abbott Park, IL, USA):}}

{\label{tacticath-quartz-abbott-abbott-park-il-usa}}

A beam of light is emitted by the TactySys\selectlanguage{english}\textsuperscript{} system and
travels through three optical fibers towards the catheter's tip into a
complex, deformable 3-D structure incorporating three Fabry-Perot
interferometers made of two semi-reflective parallel surfaces. When a
force is applied to the catheter tip, the flexible titanium-alloy
structure deforms, changing its length and, therefore, the reflected
interference pattern. By knowing the deformation characteristics, both
the magnitude and orientation of the acting contact force can be
computed.

\subsection*{\texorpdfstring{AcQBlate\textsuperscript{(r)} Force
(Biotronik, Berlin,
Germany):}{AcQBlate(r) Force (Biotronik, Berlin, Germany):}}

{\label{acqblate-force-biotronik-berlin-germany}}

The tip is suspended by a Z-Axis (In-axis to the catheter) sensor that
is realized by a deformable parallelogram, sensitive to axial forces on
the catheter. Additionally, separate X- and Y-Axis sensors are located
more proximally along the shaft. They are sensitive to lateral forces
only. One single optical fiber, incorporating a fiber Bragg grating
(FBG) runs through the deformable sensors. At each sensor, a different
wavelength is reflected. As soon as the catheter tip is exposed to a
force, the fiber changes its length at the respective section, therefore
shifting the reflected wavelength along the spectrum. Knowing the forces
along all axes, the acting force vector can be calculated.

\selectlanguage{english}\textbf{Stablepoint\textsuperscript{} (Boston Scientific, Marlborough,
MA, USA):}

The tip is suspended by a machined precision spring, which can be
compressed and bent. Three inductive sensors, comprising a ferromagnetic
core and a coil are located in the proximal part of the catheter tip.
The ferromagnetic cores are attached to the tip and move within the
coils as the tip is deflected by an applied force. This results in a
change of inductance of individual sensors. Knowing the rigidity of the
spring, the axial and lateral forces acting on the tip can be calculated
by Hooke's law.

\textbf{Smarttouch\textsuperscript{(r)} SF (Johnson\&Johnson, New
Brunswick, NJ, USA):}

The tip of the catheter is suspended by a machined precision spring. A
magnetic transducer generates a small magnetic field in the distal part
of the catheter. Three magnetic field sensors are located in the more
proximal part of the catheter, distributed around the circumference. As
forces are acting on the catheter tip, it moves slightly towards the
sensors, changing the signal received by the sensor coils. By Hooke's
law, the acting force and direction can be calculated from the three
sensors and the known characteristics of the spring.

\subsection*{Measurement protocol}

{\label{measurement-protocol}}

All catheters were fixed 18-20mm proximal to the tip to get an
adequately low bending of the distal part while not compromising the
force sensor tip by the clamping mechanism. Prior to the measurements,
the catheters were submerged in the heated saline bath for five minutes,
allowing for warm-up. The catheter was zeroed after each change of the
contact angle. Measurements were taken repeatedly adjusting the exerted
force in-between measurements until a minimum of 100 measurements at one
specific angle was reached. During acquisition, equal distribution of
the measurements across the full measurement range of 0g to 60g was
ensured. Subsequently, the catheter was fixed at a different angle and
the same protocol was repeated for all angles of 0deg, 30deg, 45deg, 60deg, and
90deg. The error made by the catheter was calculated by subtracting the
weight displayed on the scale (real force) from the contact force
displayed on the catheter readout (measured force). A resulting negative
value means that the catheter underestimates the real force; a positive
value means the catheter overestimates the real force. We evaluated
three catheters for each model to verify reproducibility and to quantify
inter-catheter variability. For the
Stablepoint\selectlanguage{english}\textsuperscript{}catheter, measured-force values above 50g
are not displayed at angles \textgreater{}45deg.

\subsection*{Statistical analysis}

{\label{statistical-analysis}}

Continuous variables are presented as mean +- standard deviation or as
median and interquartile range as appropriate. Linear regression
analysis was used to determine the measurement error due to friction.
Spearman correlation coefficients were used to assess the correlation
between measured force and real force. A local smoothing function
(locally estimated scatterplot smoothing (LOESS)) was used for the
interpretation of the measurement data (loess function, span = 0.3).
Statistical analyses were made by using R 4.0.2 (R Core Team, Vienna,
Austria).



\section*{Results}

{\label{results}}

We acquired a total of 6685 measurements using 12 catheters, three for
each of the 4 models. For each catheter, a median of 107 (IQR 100-128)
measurements was taken at each of the five specific angles. The overall
correlation between measured force and real force was high with
\selectlanguage{english}?\selectlanguage{english}\textsubscript{????????} \selectlanguage{english}[?] 0.98 for all models. The results of all
measurements are displayed in Figure 3. The mean absolute error for each
model, across the full range, was 1.29g +-0.99g for
Tacticath\selectlanguage{english}\textsuperscript{}, 2.87g +-2.37g for
AcQBlate\textsuperscript{(r)} Force, 1.38g +-1.29g for
Stablepoint\selectlanguage{english}\textsuperscript{}, and 2.26g +-2.70g for
Smarttouch\textsuperscript{(r)}. However, for some combinations of a
catheter, angle, and applied force, overestimation and underestimation
of the real force were higher with a maximum of 6.5g / -5.6g for
Tacticath\selectlanguage{english}\textsuperscript{}, 11g / -11.6 for
AcQblate\textsuperscript{(r)} Force, 7.4g / -5.6g for
Stablepoint\selectlanguage{english}\textsuperscript{}, and 8.5 / -22.6g for
Smarttouch\textsuperscript{(r)}.

In the clinical range of 10-40g, all catheters had a lower absolute mean
error with 1.19g +-0.88g for Tacticath\selectlanguage{english}\textsuperscript{}, 2.86g +-2.08g
for AcQBlate\textsuperscript{(r)} Force, 1.02g +-0.77g for
Stablepoint\selectlanguage{english}\textsuperscript{}, and 1.52g +-1.17g for
Smarttouch\textsuperscript{(r)} (figure 4).

In the high force range, overestimation of more than 10g was observed
for the AcQblate\textsuperscript{(r)} Force catheter at 90deg, while both
Smarttouch\textsuperscript{(r)} and AcQblate\textsuperscript{(r)} Force
underestimated forces by more than 10g at angles of 30deg and 45deg. The
Stablepoint\selectlanguage{english}\textsuperscript{} catheter overestimated higher contact
forces at 0deg and 30deg. Finally, the Tacticath did not over- nor
underestimate forces by more than 5g at all angles.

AcQBlate\textsuperscript{(r)} Force and
Smarttouch\textsuperscript{(r)}showed a higher variance between individual
catheters (figure 3, second and fourth row). In addition, when fitting
the data using a local estimate function (figure 3), the measurement
errors of two models seem to scatter a bit more: The residual standard
errors are numerically higher for AcQBlate\textsuperscript{(r)} Force
(14.5g) and Smarttouch\textsuperscript{(r)} (14.0g), compared to
Tacticath\selectlanguage{english}\textsuperscript{} (12.3g) and
Stablepoint\selectlanguage{english}\textsuperscript{}(10.1g).

\section*{Discussion}

{\label{discussion}}

In this study, we provide an industry-independent validation of the
accuracy of contemporary contact force ablation catheters. The main
findings of this study are:

First, the overall correlation between measured force and real force was
excellent with \selectlanguage{english}?\selectlanguage{english}\textsubscript{????????} \selectlanguage{english}[?]0.98 for all models. Second,
within the clinical range of 10g-40g the absolute measurement errors
were low with mean errors of \textless{}3g. Third, at higher forces,
some combinations of catheter and angle can result in significant
underestimation or overestimation of the real force by more than 15g.

\textbf{Clinical implications}

\emph{Efficacy}

Contact force is an important predictor of lesion formation and accurate
estimation therefore is important to predict lesion size and ablation
efficacy\textsuperscript{6,13,15}. Regarding an effective and safe
contact force during ablation procedures, there is a U-shaped
relationship with too low contact forces being less effective and too
high forces increasing the risk for complictions\textsuperscript{1}. In
clinical trials, different minimal contact forces have been proposed for
effective ablation by multiple investigators of clinical trials and
range from \textgreater{}6.5g (SMART-AF) to \textgreater{}10g
(TOCCASTAR), and \textgreater{}20g (EFFICAS II)\textsuperscript{2,3,16}.

\emph{Safety}

Contact force enacted on tissue is linked to the potential for
complications like cardiac perforations. In an ex-vivo porcine study,
minimal contact forces needed for perforation were ranging from 131g for
the right atrium to 227g for the left ventricle\textsuperscript{17}. In
another study on human heart specimens, previously ablated tissue had a
2-fold reduced minimal force when compared to healthy tissue and the
minimal force needed for perforation was as low as
38g\textsuperscript{18}. An underestimation of high contact forces could
therefore lead to an increased risk for perforations. Here,
Smarttouch\textsuperscript{(r)} and AcQblate\textsuperscript{(r)} Force
showed significant underestimation at 30deg and 45deg.

Combining the evidence for efficacy and safety, a range of 10g to 40g is
generally considered appropriate for clinical ablation. The accuracy
within this range was good for all models with a mean absolute error of
\textless{}3g and should therefore not affect the estimation of lesion
formation by much as long as forces are kept within this range.

\textbf{Technical considerations}

\emph{Accuracy}

For clinical use, the error of force-sensing catheters ideally should be
as low as possible and the accuracy should be independent of other
parameters such as catheter-to-tissue angle. Bourier et al. found an
overall mean error of 1.2g for the Tacticath\selectlanguage{english}\textsuperscript{} catheter
when measuring at different contact angles, with individual catheters,
irrigation, and catheter deflection\textsuperscript{14}. Irrigation and
deflection did not have an influence on the accuracy of the sensor and
therefore were not repeated here.

Further, the contact angle may influence the accuracy, as the individual
sensors on each axis are strained differently. In that regard, we did
not find a decreased accuracy for contact parallel to tissue, however,
it seems that the Z-axis sensor of Stablepoint\selectlanguage{english}\textsuperscript{} is too
sensitive. For comparison, Bourier et al. found a decreased accuracy for
the SmartTouch\textsuperscript{(r)} catheter at 90deg of
contact\textsuperscript{19}.

\emph{Impact of catheter orientation}

Some important considerations regarding parallel-to-tissue contact
remain: While the force acting on the very distal end of the catheter
produces accurate results, even a slightly more proximal application of
the force naturally results in a reduced deflection of the tip (law of
leverage) and therefore in an underestimation of the true force. In
addition, forces acting on even more proximal parts of the catheter
cannot be measured at all. This limitation of the technology applies to
all models and should be considered when the catheter is oriented
parallel to the tissue as can be the case during ablation of the ridge
on the left pulmonary veins.

\emph{Impact of force sensing technology}

Regarding the force sensing technology implemented in each catheter
model, no differences in measurement accuracy were observed between
optical sensors (Tacticath\selectlanguage{english}\textsuperscript{} \&
AcQBlate\textsuperscript{(r)} Force) and electromagnetic sensors
(Stablepoint\selectlanguage{english}\textsuperscript{} and SmartTouch\textsuperscript{(r)}). In
addition, between the two models with increased scattering, one
implements an optical sensor and the other an electromagnetic one which
speaks against a class effect.

\textbf{Limitations}

Despite an extensive set of measurements, some limitations remain:
First, with n=3 catheters for each model, the variability within one
catheter model cannot be assessed reliably and it cannot be excluded
that another catheter performs better or worse than described here.
Second, we measured static contact force, while in-vivo contact force is
dynamic. Given that the sensor technology involved is the same and that
contact force sampling rates are significantly higher than the heart
rate, this should not have a major impact on the clinical implications
of our findings.

\subsection*{Conclusion}

{\label{conclusion}}

The catheter-to-tissue contact force measured by force-sensing ablation
catheters is accurate with an absolute mean error of \textless{}3g in a
clinical range of 10g to 40g for all four currently available
force-sensing ablation catheters. Some combinations of model and angle
may be prone to significant errors at higher forces with
\textgreater{}10g of overestimation and \textgreater{}15g of
underestimation of true contact force, which may be clinically relevant.

\section*{Literature}

{\label{literature}}

1. Ariyarathna N, Kumar S, Thomas SP, Stevenson WG, Michaud GF. Role of
Contact Force Sensing in Catheter Ablation of Cardiac Arrhythmias:
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EP}2018;\textbf{4} :707--23.

2. Reddy VY, Dukkipati SR, Neuzil P, Natale A, Albenque JP, Kautzner
J,\emph{et al.} Randomized, Controlled Trial of the Safety and
Effectiveness of a Contact Force-Sensing Irrigated Catheter for Ablation
of Paroxysmal Atrial Fibrillation: Results of the TactiCath Contact
Force Ablation Catheter Study for Atrial Fibrillation (TOCCASTAR)
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:907--15.

3. Natale A, Reddy VY, Monir G, Wilber DJ, Lindsay BD, McElderry
HT,\emph{et al.} Paroxysmal AF Catheter Ablation With a Contact Force
Sensing Catheter: Results of the Prospective, Multicenter SMART-AF
Trial. \emph{J Am Coll Cardiol} Elsevier; 2014;\textbf{64} :647--56.

4. Reichlin T, Baldinger SH, Pruvot E, Bisch L, Ammann P, Altmann
D,\emph{et al.} Impact of contact force sensing technology on outcome of
catheter ablation of idiopathic pre-mature ventricular contractions
originating from the outflow tracts. \emph{Europace}2021;\textbf{23}
:603--9.

5. Elbatran AI, Li A, Gallagher MM, Kaba R, Norman M, Behr ER, \emph{et
al.} Contact force sensing in ablation of ventricular arrhythmias using
a 56-hole open-irrigation catheter: a propensity-matched
analysis.\emph{J Interv Card Electrophysiol} 2021;\textbf{60} :543--53.

6. HAINES DE. Determinants of Lesion Size During Radiofrequency Catheter
Ablation: The Role of Electrode-Tissue Contact Pressure and Duration of
Energy Delivery. \emph{J Cardiovasc Electrophysiol} John Wiley \& Sons,
Ltd; 1991;\textbf{2} :509--15.

7. Virk SA, Bennett RG, Trivic I, Campbell T, Kumar S. Contact Force and
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:1037--47.

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18. Quallich SG, Heel M Van, Iaizzo PA. Optimal contact forces to
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:347--50.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 1:} \textbf{Bench-top set-up to measure forces acting on
an ablation catheter.}

Panel A shows a schematic drawing of the setup. The platform is
suspended in a heated saline bath. The force applied by the catheter to
the platform is redirected by two low-friction pulleys and measured by
the scale, which is placed outside the water bath. Panel B shows the
implementation with a water tank and heating, the measurement platform
and the catheter fixation mechanism, the low friction pulleys, and the
scale. Panel C shows a close-up view of the platform and the catheter
fixation mechanism. The clamp can hold the catheter at different angles
and is displaceable in the vertical axis to adjust the force applied to
the platform.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 2: Force sensing technology overview}

Schematic drawing of commercially available contact force sensing
catheters and their implemented measurement technology. All catheters
incorporate a 3-axis force sensor allowing for precise quantification of
catheter-to-tissue contact during cardiac ablation interventions. Panel
A: Tacticath\textsuperscript{} Quartz (Abbott, Abbott Park, IL, USA),
Panel B: AcQBlate\selectlanguage{ngerman}\textsuperscript{®} Force (Biotronik, Berlin, Germany),
Panel C: Stablepoint\selectlanguage{english}\textsuperscript{} (Boston Scientific, Marlborough,
MA, USA), Panel D: Smarttouch\textsuperscript{(r)} SF (Johnson\&Johnson,
New Brunswick, NJ, USA). For additional details see methods section and
table 1.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 3: Measurement errors at different contact angles}

Measurement errors of four commercially available contact force sensing
catheters across their measurement range. Each row shows the results for
different catheter models. Different catheter-to-tissue angles are
displayed in columns (0\selectlanguage{ngerman}° equals perpendicular to tissue, 90° equals
parallel to tissue). The x-axis of each graph shows the real force
exerted on the tissue and the y-axis the measurement error made by the
catheter. Points above the black line in each graph mean the catheter
overestimates the force and points below the black line mean the
catheter underestimates the force. Different colors indicate different
catheters. A local smoothing function was used for easier interpretation
of the measurement data (loess function, span = 0.3). For the
Stablepoint\selectlanguage{english}\textsuperscript{} catheter, measured-force values above 50g
are not displayed at angles \textgreater{}45deg.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 4: Measurement errors in the clinical range}

Mean absolute errors within a clinical range of 10-40g for all catheter
models, regardless of catheter-to-tissue contact angle. All catheters
have a mean error of \textless{}3g.\selectlanguage{english}
\begin{longtable}[]{@{}lllll@{}}
\toprule
& Tacticath\textsuperscript{} & AcQBlate\selectlanguage{ngerman}\textsuperscript{®} Force &
Stablepoint\textsuperscript{} & Smarttouch\selectlanguage{ngerman}\textsuperscript{®}
SF\tabularnewline
\midrule
\endhead
Measurement Principle & Optical & Optical & Inductive &
Magnetic\tabularnewline
Catheter Size & \(8\ F\) & \(8\ F\) &
\(7.5\ F\) & \(8\ F\)\tabularnewline
Recommended Sheath & \(8.5\ F\) & \(8.5\ F\) &
\(8.5\ F\) & \(8.5\ F\)\tabularnewline
Tip length & \(3.5\ mm\) & \(3.5\ mm\) &
\(4\ mm\) & \(3.5\ mm\)\tabularnewline
Recommended Irrigation & \({\leq 30W:\ 17\frac{\text{ml}}{\min}\backslash n}{>30W:\ 30\frac{\text{ml}}{\min}}\) & \({\leq 30W:\ 8\frac{\text{ml}}{\min}\backslash n}{>30W:15\frac{\text{ml}}{\min}}\) &
\({\leq 30W:\ 17\frac{\text{ml}}{\min}\backslash n}{>30W:\ 30\frac{\text{ml}}{\min}}\) & \({\leq 30W:\ 8\frac{\text{ml}}{\min}\backslash n}{>30W:15\frac{\text{ml}}{\min}}\)\tabularnewline
Measurement range & Not specified & 0g -- 60g & 0g -- 50g & Not
specified\tabularnewline
Compatibility & Ensite & Standalone & Rhythmia & Carto\tabularnewline
Force: vector display & Angle of 0 to 90\selectlanguage{ngerman}° & Angle of 0 to 90\selectlanguage{ngerman}° & Angle of
0 to 90\selectlanguage{ngerman}° & Full 3D vector\tabularnewline
Sampling rate & 50 Hz & Unknown & 20 Hz & 10 Hz\tabularnewline
Smoothed graph / number & Yes & Planned & Yes, customizable & Yes,
customizable\tabularnewline
Stability indication & Yes, highly customizable & No & Yes, customizable
& Yes, customizable\tabularnewline
Non-deflectable tip-length & 18 mm & 24 mm & 21 mm & 17
mm\tabularnewline
\bottomrule
\end{longtable}

Table 1: Overview of all four currently available force-sensing
catheters.

\textbf{Supplement 1 -- Validation of the measurement setup}

\emph{Methods}

The accuracy of the setup for measuring the force applied to the
platform was validated by measuring standard weights which were put on
the platform. A set of weights in the range from 1g to 100g were put on
a precision scale with precision = 0.01g (Kern 572-35, Kern,
Konolfingen, Switzerland) and the weight was noted. The weights were
then put on the platform and the resulting force on the scale was
recorded. The difference between those two measurements is due to the
friction incorporated in the measurement system and accounts for any
manufacturing tolerances of the weights. The weight displayed on the
scale correlates with the force acting on the platform with:

\begin{equation}
F_{\text{Scale}}={F_{0}-(\ F}_{w}-\mu_{0}*(F_{w}+F_{P}))\nonumber \\
 \end{equation}

Where:

\begin{equation}
{F_{0}=Force\ of\ the\ counterweight\ \backslash n}{Fw=Force\ exerted\ on\ the\ platform,\ \backslash n}{Fp=Force\ of\ the\ platfrom\ \backslash n}{\mu_{0}=friction\ coefficient\ of\ pulleys}\nonumber \\
 \end{equation}

The friction determined with this validation data can further increase
the accuracy of the catheter measurements, by adjusting the results by
the known error.

\emph{Validation Results}

The validation of the measurement setup showed that the force measured
by the system correlates very well with the true force exerted on the
platform (R\textsuperscript{2} = 0.999, n = 35). The absolute
measurement error was low with a mean of 0.34g \selectlanguage{ngerman}±0.39g, including the
error of the scale. A linear model with \(y=\ 0.992x-0.151\) best fits the
data and reflects the friction of the measurement system. All catheter
measurements were adjusted accordingly, by using this linear model.\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/Graphical-Abstract-2/Graphical-Abstract-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}

