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\begin{document}

\title{Can We Trust the Force?}



\author[1]{Frank Pelosi}%
\affil[1]{University of Michigan Health Systems}%


\vspace{-1em}



  
  \date{May 24, 2024}


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Can We Trust the Force?

Frank Pelosi, Jr., MD, FHRS, FACC

Associate Professor of Medicine

Department of Internal Medicine

Cardiac Electrophysiology Section

University of Michigan Medical School

Ann Arbor, Michigan

Corresponding Author:

Frank Pelosi, Jr, MD, FACC, FHRS

1500 East Medical Center Drive

Ann Arbor MI. 48109

734-232-0112

fpelosi@med.umich.edu

Key words: contact force, radiofrequency ablation

Word count: 1165 excluding references

Invited manuscript for JCE-22-0822.R2

\emph{``For my ally is the Force, and a powerful ally it is.'' -- Yoda}

For over 40 years, delivering quality radiofrequency (RF) ablation
lesions has been the unending quest for electrophysiology. The call from
attending to fellow for ``better contact'' begins during training and
forever echoes in an electrophysiologist's minds throughout their
career. For straightforward pursuits such as AV node, slow pathway, or
accessory pathway ablation, the reward for good contact is obvious and
almost immediate. Electrophysiologists who trained with only
electrograms and fluoroscopy regularly walked the precipice between
contact and perforation guided only by electrograms, catheter movement
and ``feel''.\textsuperscript{1} As we embarked into the no-man's land
of atrial fibrillation, we welcomed three-dimensional mapping systems
that allowed us to use a focal ablation catheter to create complex
lesion sets for both atrial and ventricular arrhythmias. But this
blessing comes with the burden of ensuring both continuous and
consistent ablation lesion quality to provide durable results. With only
rudimentary geometry to guide us, we all knew that to overly trust this
technology was at the peril of both patient and physician. The accuracy
of three-dimensional mapping systems was vulnerable to patient movement
or impedance changes, resulting in impressive images for our next
conference, but inconsistent clinical outcomes. For many of us, the
personal pride of creating beautiful left atrial lesion sets was
eclipsed by the bewilderment of early atrial fibrillation recurrence or
a more burdensome iatrogenic atrial tachycardia.

Seminal work on this subject showed that catheter contact was an
important factor to RF lesion quality.\textsuperscript{2} This led to
technologies that could assist the operator to assess contact as means
of improving RF lesion quality. The goal was simple: create a way to
know how much we can advance a RF catheter against living myocardium
without perforation. This required a system that could provide reliable
feedback across a range of applied force, catheter angles, ablation
energies, and tissue types. Introduced in 2008, contact force (CF)
technologies have been widely adopted to create more consistent RF
lesions and reduce fluoroscopy.\textsuperscript{3} In this issue of
the\emph{Journal of Cardiovascular Electrophysiology} , K\selectlanguage{ngerman}üffer and
colleagues offer insight on the accuracy and the limits of contact force
(CF) technology.\textsuperscript{4}

The investigators used a novel experimental model to assess the accuracy
and reliability of the four commercially available RF ablation
catheters. They used a counterweight-based system with two low-friction
pullies and a polymeric foam platform immersed in a
temperature-controlled saline tank. The platform is suspended with wires
guided through the pullies to a counterweight placed on a precision
scale outside of the tank. As the RF catheter presses downward on the
testing platform, upward force is applied to the counterweight causing a
change in weight on the scale and then compared with the contact force
measurement from the respective catheter's mapping system. The error was
calculated from the difference between the two measurements. The
investigators tested four available ablation catheters with
contact-force technologies. Two catheters-- Smarttouch SF (Biosense-
Webster, Inc) and Stablepoint (Biosense Webster, Inc)-- use machine
precision springs to determine CF. Tacticath (Abbot, Inc) uses a beam of
light and interferometers and AcQBlate Force (Biotronik, Inc) uses a
single optical fiber and deformable parallelogram to determine CF. Each
catheter was assessed at 4 different contact angles: perpendicular to
the platform (0°), 30°, 45°, 60°, and parallel to the platform (90°). A
minimum of 100 measurements were obtained at each angle with total of
6685 total measurements using three catheters for each of the four
models.

The investigators found that the force derived from the catheter's
mapping system was very accurate at lower contact force with a
perpendicular catheter angle. When the angle was adjusted to 30°, 45°,
and 60° degrees, there was more error, especially when higher force was
applied. When more than 40g of force was applied, variance between the
catheters were more marked, with some catheters (Smarttouch SF and
AcQBlate Force) underestimating CF as compared with the precision scale
and overestimated true CF when the catheter was applied parallel to the
testing platform. Tacticath appeared to have better performance, but the
study was not designed to compare the 4 models directly. The conclusions
of the study were that at CF of 10-40g, measurements errors were low,
but at CF of greater than 40g, combinations of catheter type and angle
could either underestimate or overestimate CF by as much as 15g.

Küffer and colleagues should be commended for a novel, rigorous
methodology to assess contact force. However, there are limitations in
applying their observations to clinical practice. The model appears to
be reliable, but other factors could affect its accuracy. CF applied to
the intact, moving myocardium is dependent on the force applied and the
properties of the tissue such as thickness and pliability. Therefore, a
static polymeric foam platform may not be an appropriate surrogate for
dynamic myocardial tissue. The investigators did not attempt to simulate
other factors that could affect accuracy such as prolonged dwell time in
the blood pool, measuring CF during ablation, or the effect of repeated
ablations or catheter manipulation on the CF measurement components.

Other experimental models have shown similar
results.\textsuperscript{5,6} Therefore, we can have more confidence
in\emph{Küffer's, et al} methodology especially when the catheter is
positioned parallel to testing platform. Both investigators observed
that at higher CF measures, force is underestimated. Why is this
important? Operators could have a false sense of security when advancing
the catheter, but higher contact force pressure mitigates the effects of
saline irrigation, resulting in lower RF ablation quality, more steam
pops and catheter thrombus formation.\textsuperscript{7,8}

Almost a generation of electrophysiologists have trained virtually
exclusively with CF catheters and increasingly depend on it to reduce
fluoroscopy and optimize contact. Ask some trainees to use a catheter
without CF, and you may find that the once confident second-year fellow
regresses to the uneasy, tentative trainee of early July. As contact
force became widely adopted, several observational studies touted the
promise of CF as a means of improving outcomes with reduced
complications. This led many to trust CF as the standard of ensuring
quality ablation to the point that some found the lack of faith by
others disturbing. However, randomized studies in patients undergoing RF
ablation for atrial fibrillation demonstrated no such improvement in
clinical outcomes or perforations.\textsuperscript{9,10} This could be
due to the paucity of perforations for analysis or the variances in the
rigor of ensuring CF-based quality lesions.

If there is one lesson that we can all learn it is that, like the
previous advances before it, understanding CF's limitations allow us to
better appreciate its capabilities. We do not know if CF is accurate
when using an increasingly popular high-power short-duration strategy to
create durable lesions, so we should look forward to technologies that
give us a more direct tissue-level assessment of ablation quality as our
strategies evolve.

From, \emph{Küffer et al} ., we are reminded that the advice of
another\emph{Star Wars} character, Darth Vader, ``Do not underestimate
the force'' can also apply to certain CF ablation catheters.

References

1. Strickberger SA, Vorperian VR, Man KC, et al. Relation between
impedance and endocardial contact during radiofrequency catheter
ablation. \emph{American heart journal.} 1994;128(2):226-229.

2. Haines DE. Determinants of lesion size during radiofrequency catheter
ablation: The role of electrode\selectlanguage{english}-tissue contact pressure and duration of
energy delivery. \emph{Journal of cardiovascular
electrophysiology.}1991;2(6):509-515.

3. Yokoyama K, Nakagawa H, Shah DC, et al. Novel contact force sensor
incorporated in irrigated radiofrequency ablation catheter predicts
lesion size and incidence of steam pop and thrombus. \emph{Circulation:
Arrhythmia and Electrophysiology.} 2008;1(5):354-362.

4. Kuffer T HA, Knecht S, Baldinger S, Madaffari A, Seiler J, Muhl A,
Tanner H, Roten L, Reichlin T. Validation of the accuracy of contact
force measurement by contemporary force-sensing ablation catheters.

\emph{Journal of cardiovascular electrophysiology.}

5. Bourier F, Hessling G, AMMAR\selectlanguage{english}-BUSCH S, et al. Electromagnetic
contact\selectlanguage{english}-force sensing electrophysiological catheters: how accurate is
the technology? \emph{Journal of cardiovascular
electrophysiology.}2016;27(3):347-350.

6. Bourier F, Gianni C, Dare M, et al. Fiberoptic contact\selectlanguage{english}-force sensing
electrophysiological catheters: how precise is the
technology?\emph{Journal of cardiovascular electrophysiology.}
2017;28(1):109-114.

7. Eick OJ. Factors influencing lesion formation during radiofrequency
catheter ablation. \emph{Indian pacing and electrophysiology
journal.}2003;3(3):117.

8. 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. \emph{Circulation: Arrhythmia and
Electrophysiology.} 2014;7(6):1174-1180.

9. Conti S, Weerasooriya R, Novak P, et al. Contact force sensing for
ablation of persistent atrial fibrillation: a randomized, multicenter
trial. \emph{Heart Rhythm.} 2018;15(2):201-208.

10. Virk SA, Ariyaratnam J, Bennett RG, Kumar S. Updated systematic
review and meta-analysis of the impact of contact force sensing on the
safety and efficacy of atrial fibrillation ablation: discrepancy between
observational studies and randomized control trial data. \emph{EP
Europace.} 2019;21(2):239-249.

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