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\begin{document}

\title{Catheter-Tissue Contact Optimizes Pulsed Electric Field Ablation with a
Large Area Focal Catheter}



\author[1]{Mary Clare Flaherty}%
\author[2]{Shephal Doshi}%
\author[1]{Jacob Laughner}%
\author[1]{Melinda Quan}%
\author[3]{Ante Anic}%
\affil[1]{Galvanize Therapeutics Inc}%
\affil[2]{Pacific Heart Institute}%
\affil[3]{Klinicki bolnicki centar Split}%


\vspace{-1em}



  
  \date{June 13, 2024}


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





\selectlanguage{english}
\begin{abstract}
\textbf{Introduction:} Pulsed electric field (PEF) ablation relies on
the intersection of a critical voltage gradient with tissue to cause
cell death. Field-based lesion formation with PEF technologies may still
depend on catheter-tissue contact (CTC). The purpose of this study was
to assess the impact of CTC on PEF lesion formation with an
investigational large area focal (LAF) catheter in a preclinical model.
\textbf{Methods:} PEF ablation via a 10-spline LAF catheter was used to
create discrete RV lesions and atrial lesion sets in 10 swine (8 acute,
2 chronic). Local impedance (LI) was used to assess CTC. Lesions were
assigned to 3 cohorts using LI above baseline: No Tissue Contact (NTC:
[?][?]10\selectlanguage{greek}Ω, \selectlanguage{english}close proximity to tissue), Low Tissue Contact (LTC: [?]11-29\selectlanguage{greek}Ω\selectlanguage{english}),
and High Tissue Contact (HTC: [?][?]30\selectlanguage{greek}Ω\selectlanguage{english}). Acute animals were infused with
triphenyl tetrazolium chloride (TTC) and sacrificed [?]2hrs
post-treatment. Chronic animals were remapped 30 days post-index
procedure and stained with infused TTC. \textbf{Results:} Mean (\selectlanguage{ngerman}±SD) RV
treatment sizes between LTC (n=14) and HTC (n=17) lesions were not
significantly different (depth: 5.65±1.96mm vs 5.68±2.05mm, p=0.999;
width: 15.68±5.22mm vs 16.98±4.45mm, p=0.737) while mean treatment size
for NTC lesions (n=6) was significantly smaller (1.67±1.16mm depth,
5.97±4.48mm width, p\textless{}0.05). For atrial lesion sets, acute and
chronic conduction block were achieved with both LTC (N=7) and HTC
(N=6), and NTC resulted in gaps. \textbf{Conclusions:} PEF ablation with
a specialized LAF catheter in a swine model is dependent on CTC. LI as
an indicator of CTC may aid in the creation of consistent transmural
lesions in PEF ablation.%
\end{abstract}\selectlanguage{ngerman}%



\sloppy


\textbf{Catheter-Tissue Contact Optimizes Pulsed Electric Field Ablation
with a Large Area Focal Catheter}

\textbf{Short Title:} Optimizing PEF Ablation with Contact Detection

Shephal K Doshi, MD\textsuperscript{1}; Mary Clare Flaherty,
BS\textsuperscript{2}; Jacob Laughner, PhD\textsuperscript{2}; Melinda
Quan, BS\textsuperscript{2}; Ante Anic, MD\textsuperscript{3}

\textsuperscript{1}Pacific Heart Institute, Santa Monica, California,
USA

\textsuperscript{2}Galvanize Therapeutics, Redwood City, CA

\textsuperscript{3} Klini\selectlanguage{polish}č\selectlanguage{english}ki Bolni\selectlanguage{polish}č\selectlanguage{english}ki Centar (KBC) Split, Split, Croatia

\emph{Conflict of Interest Statement:} Flaherty, Laughner, and Quan are
paid employees of Galvanize Therapeutics. No other conflicts of
interests exist.

\emph{\textbf{Corresponding Author:}}

Name: Mary Clare Flaherty,

Address: 1325 Indiana St, Unit 102

San Francisco, CA 94107

Email Address: Mary.clare.flaherty@gmail.com

\emph{}

\emph{Abstract:}

\textbf{Introduction:} Pulsed electric field (PEF) ablation relies on
the intersection of a critical voltage gradient with tissue to cause
cell death. Field-based lesion formation with PEF technologies may still
depend on catheter-tissue contact (CTC). The purpose of this study was
to assess the impact of CTC on PEF lesion formation with an
investigational large area focal (LAF) catheter in a preclinical model.

\textbf{Methods:} PEF ablation via a 10-spline LAF catheter was used to
create discrete RV lesions and atrial lesion sets in 10 swine (8 acute,
2 chronic). Local impedance (LI) was used to assess CTC. Lesions were
assigned to 3 cohorts using LI above baseline: No Tissue Contact (NTC:
[?][?]10\selectlanguage{greek}Ω, \selectlanguage{english}close proximity to tissue), Low Tissue Contact (LTC: [?]11-29\selectlanguage{greek}Ω\selectlanguage{english}),
and High Tissue Contact (HTC: [?][?]30\selectlanguage{greek}Ω\selectlanguage{english}). Acute animals were infused with
triphenyl tetrazolium chloride (TTC) and sacrificed [?]2hrs
post-treatment. Chronic animals were remapped 30 days post-index
procedure and stained with infused TTC.

\textbf{Results:} Mean (\selectlanguage{ngerman}±SD) RV treatment sizes between LTC (n=14) and
HTC (n=17) lesions were not significantly different (depth: 5.65±1.96mm
vs 5.68±2.05mm, p=0.999; width: 15.68±5.22mm vs 16.98±4.45mm, p=0.737)
while mean treatment size for NTC lesions (n=6) was significantly
smaller (1.67±1.16mm depth, 5.97±4.48mm width, p\textless{}0.05). For
atrial lesion sets, acute and chronic conduction block were achieved
with both LTC (N=7) and HTC (N=6), and NTC resulted in gaps.

\textbf{Conclusions:} PEF ablation with a specialized LAF catheter in a
swine model is dependent on CTC. LI as an indicator of CTC may aid in
the creation of consistent transmural lesions in PEF ablation.

\emph{Keywords:} Arrhythmias, Pulsed Field Catheter Ablation, Local
Impedance, Atrial Fibrillation, Local Impedance

\emph{Abbreviations:}

\begin{itemize}
\tightlist
\item
  Catheter-Tissue Contact (CTC)
\item
  Cryoablation (Cryo)
\item
  Electroanatomic Mapping (EAM)
\item
  Inferior Vena Cava (IVC)
\item
  Interquartile range (IQR)
\item
  Intracardiac Echocardiography (ICE)
\item
  Local Impedance (LI)
\item
  Hematoxylin \& Eosin (H\&E)
\item
  Pulmonary Vein Isolation (PVI)
\item
  Pulsed Electric Field (PEF)
\item
  Radiofrequency (RF)
\item
  Superior Vena Cava (SVC)
\item
  Triphenyl Tetrazolium Chloride (TTC)
\end{itemize}

\emph{Funding:} Galvanize Therapeutics sponsored and funded this
study.\emph{}

\emph{Introduction:}

Pulmonary vein isolation (PVI) remains one of the most effective
treatment strategies for atrial fibrillation\textsuperscript{1}. Thermal
ablation technologies like radiofrequency (RF) and cryoablation (Cryo)
rely on direct contact to effectively transfer energy to produce
irreversible thermal damage to cardiac tissue and durable
PVI\textsuperscript{2--4}. After being introduced in oncology over 30
years ago\textsuperscript{5,6}, pulsed electric field (PEF) ablation has
been developed as a primarily non-thermal modality for cardiac tissue
ablation, achieved by applying short duration bursts of high voltage
electric fields. Cardiac myocytes within a critical voltage gradient
area undergo cell death due to destabilization of the cell
equilibrium\textsuperscript{7}.

PEF ablation treatment size is dependent on several factors, including
waveform characteristics, electrode configuration, and field interaction
with target tissues\textsuperscript{7}. Although it has been proposed
that, unlike thermal modalities, PEF ablation may not be dependent on
catheter-tissue contact (CTC) because of its field-based
nature\textsuperscript{8}, computational modeling data and \emph{ex
vivo} bench studies using a bipolar PEF system have demonstrated a
profound treatment size dependence on catheter-tissue
proximity\textsuperscript{9}. Proximity and contact dependence for PEF
ablation, however, has not been thoroughly examined \emph{in vivo} .

We investigated the relationship between CTC and monopolar PEF ablation
in a preclinical porcine model. This study sought to determine, 1) if
CTC is necessary for effective PEF treatment, and 2) how CTC can be used
to optimize PEF ablation workflows and efficacy.

\emph{Methods:}

In ten animals, pre-ablation CTC between a novel large area focal (LAF)
ablation catheter and cardiac targets was evaluated using a custom local
impedance (LI) system, with guidelines established in previous pilot
studies using intracardiac echocardiography (ICE), electrogram
amplitude, and electroanatomic mapping (EAM) . Isolated ventricular
lesions and atrial lesion sets were created with varying amounts of CTC.
Treatment size and isolation of targeted structures were examined at
acute and chronic timepoints using EAM and histology.

\textbf{Ablation System}

An 8.5Fr, bi-directional, irrigated catheter (6mL/min) with a 10mm
diameter spheroid tip comprised of 10 nitinol composite
splines\textbf{(Figure 1A)} was connected to an investigational PEF
system consisting of a generator and connection box \textbf{(Figure
1B)}(Galvanize Therapeutics; Redwood City, CA). The system is designed
to create large focal lesions \textbf{(Figure 1C)} that reduce the
number of applications required to create a typical lesion set.
Monopolar PEF energy is delivered asynchronously using a proprietary
biphasic waveform (25A,1.6ms) that minimizes microbubble formation and
muscle contraction. The system measures LI between each spline and a
central ring electrode. LI information is displayed using a graphical
representation of the catheter tip where a color and bar length changes
represent increasing impedance on each spline (\textbf{Figure 1D} ). The
system is compatible with multiple EAM systems and is capable of
creating electroanatomic maps of the heart and monitoring local
electrograms (\textbf{Figure 1E} ).

\textbf{Preclinical Procedure}

The study protocol was approved by the Institutional Animal Care and Use
Committee of GMD Laboratories (Pomona, CA). Discrete ventricular lesions
and atrial lesion sets were studied using a Yorkshire hybrid swine model
(N=10, 50-70 kg, male and female) in acute (N=8) and chronic procedures
(N=2). Chronic procedures included recovery post-index procedure and
invasive remapping at 30 days to analyze lesion durability and
pathology. All catheters were introduced via femoral access under
inhaled anesthesia (isoflurane, 1-5\%) and without paralytics.
Intravenous heparin was administered to maintain an activated clotting
time \selectlanguage{english}[?]350 seconds prior to catheter introduction.

Operators guided the LAF catheter into bloodpool to determine a
no-contact location and establish a LI baseline. After navigating the
catheter to the myocardium, electrograms and ICE were used to determine
CTC. No catheter-tissue contact (NTC) with close proximity to tissue
(approximately \textless{}2mm) induced \selectlanguage{english}[?]\selectlanguage{english}[?]10\selectlanguage{greek}Ω \selectlanguage{english}from baseline, Low
catheter-tissue contact (LTC) induced [?]11-29\selectlanguage{greek}Ω, \selectlanguage{english}and High catheter-tissue
contact (HTC) induced [?][?]30\selectlanguage{greek}Ω \selectlanguage{english}(\textbf{Figure 2} ).



\textbf{Experimental Workflow}

\emph{Ventricular Lesions}

Ventricular lesions were created in the RV (4-6 applications/chamber)
with lesions assigned to one of the 3 CTC cohorts prior to ablation. ICE
and EAM were used to position lesions [?]20mm apart to prevent lesion
overlap. Acute lesions were allowed to dwell for [?]2hrs prior to
euthanasia to enable sufficient maturation\textsuperscript{10}.

\emph{Atrial Lesion Sets}

Lesion sets were created in the RA and LA in all animals. A posterior
line was created from the superior vena cava (SVC) to the inferior vena
cava (IVC) using 10mm center-to-center interlesion spacing. Similarly,
PVI was performed around the inferior common pulmonary vein. Lesion sets
were assigned to one of the 3 CTC cohorts prior to treatment. For LTC
and HTC cohorts, all lesions were assigned LTC or HTC, respectively. For
the NTC cohort (acute intercaval only), the beginning of an intercaval
line was started with HTC, followed by 1-2 applications with NTC (using
ICE to confirm close proximity to tissue and targeting LI response
\textless{}10\selectlanguage{greek}Ω\selectlanguage{english}), and the remainder completed with HTC. EAM and pacing
maneuvers were used to assess acute block across intercaval lines and
isolation of pulmonary veins. In chronic animals, remapping was
performed at 30 days to confirm durability of all lesion sets.

\textbf{Gross Necropsy and Histology}

Deeply sedated swine were perfused intravenously with 1\% TTC, then
euthanized with an intravenous bolus of 130-150mg/mL saturated potassium
chloride. Hearts were explanted, examined, and photographed. Ventricular
lesions were cross-sectioned and individually assessed and measured by a
blinded operator using a digital microscope (Dino-Lite Edge, AnMo
Electronics). Ventricular lesions and atrial lesion sets were formalin
fixed and processed for histological evaluation with hematoxylin and
eosin (H\&E) and Masson's Trichrome stains.

\textbf{Statistical Analysis}

Eight samples (2s) of LI data from the spline with the highest delta
from baseline were averaged to determine CTC before and after each
ablation. Continuous variables are expressed as mean \selectlanguage{ngerman}± standard
deviation or median with interquartile range (IQR). Categorical
variables are presented as counts or percentages. ANOVA was performed to
determine significant between variable groups where appropriate, with
p-values \textless{}0.05 considered significant. Statistical analyses
were performed with Minitab (v21.1.1)

\emph{}

\emph{Results:}

\textbf{Ventricular Lesion Analysis}

In 8 acute animals, 41 lesions were attempted using LI and ICE to guide
the catheter to NTC (n=6), LTC (n=14), or HTC (n=17) with 37 of 41
lesions identified and cross-sectioned for analysis during necropsy.
Four lesions were excluded because they could not be identified (n=1) or
cross-sectioned (n=3). Starting impedance relative to bloodpool was \selectlanguage{english}[?]8\selectlanguage{greek}Ω
\selectlanguage{english}(IQR, 7-9\selectlanguage{greek}Ω\selectlanguage{english}) for NTC, [?]19\selectlanguage{greek}Ω \selectlanguage{english}(IQR, 15-25\selectlanguage{greek}Ω\selectlanguage{english}) for LTC, and [?]42\selectlanguage{greek}Ω \selectlanguage{english}(IQR, 33-50\selectlanguage{greek}Ω\selectlanguage{english})
for HTC (\textbf{Figure 3A} ). Comparison of pre-ablation impedance
deltas confirmed all 3 groups were statistically distinct (HTC-LTC:
p\textless{}0.005, HTC-NTC: p\textless{}0.005, LTC-NTC: p=0.006). No
microbubbles, muscle contractions, induced arrhythmias, or ST-elevation
were observed during index procedures. No endocardial trauma, thrombus,
or char were observed acutely or chronically.

In 2 chronic animals, N=8 lesions were attempted (NTC: n=2, LTC: n=3,
HTC: n=3). All LTC and HTC lesions were identified and cross-sectioned
and no NTC lesions were identifiable after 30 days. Of the 6 identified
lesions, 4 were transmural and therefore not
measurable\textbf{(Supplemental Figure 1).} No adverse events were
observed during the 30-day waiting period.

Representative acute lesions following TTC staining are provided for
each cohort (\textbf{Figure 3B)} . LTC and HTC lesions were similar in
appearance and size (consistently \textgreater{}3mm depth), while NTC
yielded superficial lesions, moderate endocardial blanching, or no
visible effect. H\&E and Masson's Trichrome (\textbf{Figure 1C} ),
revealed necrotic myocardium, mild edema, and early-stage fibrosis on
ventricular lesions with no visible impact to surrounding vessels.

\textbf{Figure 3C} further represents the relationship between lesion
size and CTC. Average RV lesion size was not significantly different
between LTC and HTC cohorts (depth: 5.7\selectlanguage{ngerman}±2.0mm vs 5.7±2.1mm,
p\textgreater{}0.99; width: 15.7±5.2mm vs 17.0±4.5mm, p=0.74). Mean NTC
lesion size was significantly smaller than mean LTC and HTC sizes
(1.7±1.2mm depth, 6.0±4.5mm width, p\textless{}0.001). Above a minimum
threshold of \selectlanguage{english}[?]10\selectlanguage{greek}Ω, \selectlanguage{english}increasing CTC did not increase lesion depth. Lesion
depth and width were not impacted by catheter orientation or spline
placement once [?]2 splines reached LI \textgreater{}[?]10\selectlanguage{greek}Ω
\selectlanguage{english}(\textbf{Supplemental Figure 2} ).

\emph{}

\textbf{Atrial Lesion Set Analysis}

\textbf{Table 1} summarizes all atrial lesion sets by CTC cohort. LTC
and HTC pre-ablation LIs were within the intended ranges for the
attempted lesion sets. All LTC and HTC intercaval lines (Acute: LTC n=3,
HTC n=2; Chronic: LTC n=1, HTC n=1) and PVIs (Acute: n=4 LTC, n=4 HTC;
Chronic: n=1 LTC, n=1 HTC) resulted in acute and chronic conduction
block. NTC intercaval lines (HTC lesions interposed by 1-2 NTC lesions,
Acute: n=3) resulted in visible gaps where NTC lesions were placed, and
0\% conduction block.

\textbf{Figure 4} displays representative acute and chronic maps and
chronic histology for LTC and HTC intercaval lines. In both cohorts, the
low-voltage area (\textless{}0.1mV) produced acutely corresponded to
persistent low voltage and expansion of the low-voltage area after 30
days, reflected in gross pathological width measurements (LTC acute:
21.8\selectlanguage{ngerman}±4.5mm vs chronic: 37.8mm; HTC acute: 23.8±3.4mm vs chronic:
43.2mm). No statistical difference was identified between acute LTC and
HTC intercaval widths (p=0.62). Histologically, sections showed similar
morphological changes and tissue composition for LTC and HTC chronic
atrial lesion sets. Acute atrial tissue showed necrotic cardiomyocytes,
early-stage fibrosis, and sparing of blood vessels (\textbf{Figure 4, 1B
\& 2B} ). Chronic histological sections revealed complete transmural
lesions and clear distinction between healthy and ablated myocardium at
the border zone (\textbf{Figure 4, 1D and 2D} ) with complete fibrotic
and fatty tissue replacement of the cardiomyocytes within the ablated
region (\textbf{Figure 4, 1E and 2E} ).

\textbf{Figure 5} shows an example of the NTC intercaval line.
Pre-ablation LI was significantly different between NTC and HTC regions
(\selectlanguage{english}[?]10+-4\selectlanguage{english} vs \selectlanguage{english}[?]35+-8\selectlanguage{english}, p=0.03). The site of the NTC lesion shows a distinct
unaffected high-voltage area (\selectlanguage{english}[?]1mV) in comparison to the surrounding
low-voltage ablated regions (\textless{}0.1mV) (\textbf{Figure 5A} ).
Gross pathology of all NTC intercaval lines revealed unaffected
myocardium in the areas of NTC lesions (\textbf{Figure 5C} ).
Histological analysis revealed necrotic myocardium noted by contraction
band necrosis, cell shrinkage, and irregular morphology on the
transmural ablated HTC region (\textbf{Figure 5B} ) versus healthy
myocardium on the NTC region (\textbf{Figure 5D} ).

\textbf{Additional LI Analysis}

There was no meaningful LI drop observed after PEF ablation for any
cohort (NTC: 3\selectlanguage{greek}Ω, \selectlanguage{english}LTC: 1\selectlanguage{greek}Ω, \selectlanguage{english}HTC: 2\selectlanguage{greek}Ω; \selectlanguage{english}p\textgreater{}0.7 for all cohort
combinations). After 30 days, under guidance of EAM and ICE, the LAF
catheter was placed in three areas of varying bipolar electrogram
voltage: High-Voltage Zone ([?]1mV), Border Zone (0.1-0.9mV), and Scar
Zone (\textless{}0.1mV). LI response was reduced in the border zone
([?]12\selectlanguage{greek}Ω, \selectlanguage{english}IQR: 10-14\selectlanguage{greek}Ω\selectlanguage{english}) and scar zone ([?]8\selectlanguage{greek}Ω, \selectlanguage{english}IQR: 6-9\selectlanguage{greek}Ω\selectlanguage{english}) compared to the
high-voltage zone ([?]29\selectlanguage{greek}Ω, \selectlanguage{english}IQR: 28-33\selectlanguage{greek}Ω\selectlanguage{english}) using similar levels of contact
(\textbf{Figure 6} ). Analysis of lesion depth by the number of splines
with CTC\textgreater{}10\selectlanguage{greek}Ω \selectlanguage{english}revealed PEF treatment size was largely not
impacted by catheter orientation or the number of splines in contact as
long as stable CTC was achieved \textbf{(Figure 7).}

\emph{}

\emph{Discussion:}

As new ablation modalities are introduced, it is important to develop
tools that enable safe and effective treatment. For RF and Cryo, there
have been decades of development to optimize the safety and efficacy of
catheters, algorithms, and workflows. Innovations such as contact force
sensing and real-time ablation indices have helped move thermal ablation
workflows from empirical to reproducible\textsuperscript{11}. PEF
ablation for arrythmia treatment is still early in its development, as
are the tools that will optimize its safe and effective delivery. Most
current PEF platforms rely on fluoro or ICE to guide ablation as EAM
integration is limited. Overtreatment is commonplace, and tools
confirming tissue contact are lacking.

This study sought to evaluate the utility of CTC for PEF ablation using
a unique investigational LAF catheter, LI system, and PEF system.
Ventricular lesions and atrial lesion sets were successfully created in
ten swine with CTC assessed using LI. Treatment size, conduction block,
and electrical isolation of target structures were examined acutely
(N=8) and chronically (N=2) using EAM, pacing maneuvers, and tissue
histology. No adverse events or collateral damage were observed.
Analysis of LI, tissue characteristics, and EAM demonstrated that with a
unique LAF catheter 1) CTC is critical for consistent and effective PEF
treatment, 2) above a minimum contact threshold, increasing CTC does not
increase treatment size, and 3) LI can be an effective tool for
assessing CTC during PEF ablation, but its application will differ from
that of focal RF.

\textbf{Is Contact Needed for PEF Ablation?}

Proximity of the field origin to targets and tissue homogeneity both
directly influence the impact of a critical PEF voltage
gradient\textsuperscript{7}. Howard \emph{et al}
\textsuperscript{9}demonstrated \emph{ex vivo} that maximum treatment
size is achieved when a catheter is in apposition to target tissue while
displacement of the electric field source from the tissue surface
reduced lesion depth. Contact force and LI are both well-established
indicators of CTC\textsuperscript{12,13}. In this study, with ICE
guidance, LI consistently \textgreater{}\selectlanguage{greek}Δ\selectlanguage{english}10\selectlanguage{greek}Ω \selectlanguage{english}from baseline was found to
be correlated to stable CTC. PEF treatments delivered with
\textgreater{}\selectlanguage{greek}Δ\selectlanguage{english}10\selectlanguage{greek}Ω \selectlanguage{english}LI resulted in maximum treatment size and
transmurality while treatments delivered with [?]\selectlanguage{greek}Δ\selectlanguage{english}10\selectlanguage{greek}Ω \selectlanguage{english}LI (even with close
proximity to tissue) resulted in reduced lesion size or no discernable
lesion acutely and chronically. Intercaval lines containing 1-2 lesions
with [?]\selectlanguage{greek}Δ\selectlanguage{english}10\selectlanguage{greek}Ω \selectlanguage{english}LI resulted in gaps. Therefore, the data indicate CTC can
optimize PEF treatment similar to how thermal ablation feedback tools
have improved workflows and patient outcomes\textsuperscript{14--16}.

\textbf{Does amount of contact matter for PEF ablation?}

While research indicates a relationship between contact force and PEF
treatment depth with focal catheters\textsuperscript{17}, the LAF
catheter investigated in this study did not demonstrate increased
treatment depth with increased contact. LTC and HTC yielded similar
lesion dimensions (approximately 6mm depth, 16mm width across all CTC
ranges \textgreater{}[?]10\selectlanguage{greek}Ω\selectlanguage{english}). Unique catheter and electric field geometry
contribute to this difference. Although LI is a measurement of electrode
surface area in contact with resistive myocardium and not a direct
measurement of contact force, LI has been shown to correlate with
contact force over relevant operational ranges for focal
catheters\textsuperscript{18}. Similarly in this study, increased LI
correlated with increased CTC; however, in contrast to a traditional
solid-tip catheter, the LAF spheroid tip compresses in response to
increased contact rather than indenting into the myocardium
(\textbf{Supplemental Figure 1} ). Additionally, solid-tip catheters
produce small electric fields that are more susceptible to differences
in contact than bigger LAF catheter electric fields \textsuperscript{7}.
These mechanical behaviors and field-size discrepancies may explain the
differing impacts of increased contact force on PEF treatment sizes for
compressible LAF catheters versus solid-tip catheters. This study also
indicates that the number of splines in contact and the amount of each
spline in contact with myocardium do not influence lesion size if the
spline(s) have stable CTC (\textbf{Figure 7)} .

With RF ablation, increased contact force leads to larger treatments,
but also increased safety risks\textsuperscript{19}. Increased CTC with
the LAF catheter did not yield any additional safety risk. No damage to
collateral structures, steam pops, perforations, or incidences of char
were noted acutely or chronically for any CTC cohort. The spheroid
catheter tip inherently lends itself to reduced risk of perforation and
the flexibility of the nitinol splines allows force to be absorbed by
the catheter rather than tissue, reducing tissue trauma. However,
because the structure of the LAF catheter creates sizeable lesions even
at LTC, splines that are in proximity to critical structures (e.g., AV
node, HIS) should be closely monitored to prevent inadvertent damage.
Tissue thinning and remodeling were noted after 30 days at ventricular
lesion sites; observations similar to previous work with a different LAF
catheter \textsuperscript{20} and require further investigation
(\textbf{Supplemental Figure 2} ).

This study determines that, in relation to PEF treatment size and
safety, the amount of CTC does not matter once CTC is established with a
LAF catheter. These results may extend to ``single-shot'' catheters
where apposition to myocardium, rather than embedding a catheter tip
into tissue, is the primary mode of operation\textsuperscript{21}. It is
critical to note that both catheter electrode configuration (e.g.,
electrode spacing, size) and system configuration (e.g., monopolar,
bipolar) play important roles in contact dependence. Monopolar
modalities have the ability to create deeper lesions for comparable
energy outputs relative to bipolar configurations, making them more
robust to intermittent contact\textsuperscript{7}. Contact detection
systems will need to be harmonized with PEF platforms to ensure
appropriate feedback for the catheter design and delivery mechanism.

\textbf{How should LI be used with PEF ablation?}

Impedance metrics have been useful clinical tools in monitoring
resistive heating and predicting lesion transmurality for RF
ablation\textsuperscript{22--24}. When used in a clinical RF workflow,
targeting a \textgreater{}20 LI drop effectively predicted lesion
efficacy and durability\textsuperscript{25,26}. For PEF ablation, LI is
a useful way to measure CTC and confirm optimal catheter placement for
lesion formation. However, LI may be limited in informing real-time PEF
lesion formation. PEF ablation does not rely on electrode-tissue
coupling to conduct current to tissue and cause resistive heating for
cell death\textsuperscript{7}. Therefore, starting impedance as an
indicator of resistive potential or electrode coverage is not critical
in PEF ablation. Once contact was established, no correlation was
observed between starting impedance and treatment size in this study.
Additionally, inconsequential impedance drops immediately post-PEF
delivery (1-3) indicate negligible resistive heating is occurring from
energy delivery (\textbf{Figure 6} ). These PEF-specific differences
limit the utility of impedance drop as an acute metric of therapy
success. The effects of the induced electric field cause a cascade of
cellular activity which impacts cell homeostasis and viability over the
course of hours to days. LI, a wholistic measurement of tissue
properties (e.g., temperature and relative health), changes with the
evolution of myocardial damage and fibrosis\textsuperscript{27}. In
previous RF studies, tissue impedance was reduced in more fibrotic
tissue compared to healthy myocardium\textsuperscript{28}. Similarly, in
this study, there was a substantial decrease in LI response on treated
myocardium that presented evidence of transmural fibrosis at 30 days.
When considering LI as an indicator of CTC, the decrease in feedback on
scar tissue poses a potential shortcoming. Determining contact with
previously treated myocardium or in fibrotic tissue will be challenging
with LI and warrants further investigation.

\emph{Limitations:}

This study was conducted in healthy swine and results may vary in humans
or in scarred or diseased tissue. Lesion assessment was done on fresh
TTC-stained tissue and all images were retrospectively analyzed for
lesion dimensions using methods that are well established preclinically
but impossible to validate clinically. Steps were taken to ensure
measurement systems were calibrated correctly and TTC procedures were
identical in all animals. All findings in this study use a proprietary
biphasic waveform and investigational catheter design that may not be
generally applicable for predicting treatment results of different PEF
waveforms, systems, and catheters.

\emph{Conclusion:}

This study confirmed the necessity and utility of CTC during monopolar
PEF ablation of cardiac tissues via an investigational LAF catheter in a
swine model. Using LI as an indicator, consistent CTC resulted in
effective PEF ablation across a range of cardiac targets suggesting that
contact, per se, is more important than the degree of contact. These
results diverge from previous research using focal catheters, where
increased contact resulted in increased lesion size and indicate LAF
catheter require unique research and workflows. Lesion characteristics
were optimized and reproducible across a wide range of LI changes and,
notably, acute lesion characteristics were preserved chronically. These
results suggest an important role for contact detection in the guided
delivery of PEF energy.

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\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Table 1. Atrial Lesion Set Data by Catheter-Tissue Contact
Cohort}



\textbf{Figure 1. LAF Catheter with Investigational PEF Ablation and LI
Measurement Systems}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{A.}LAF catheter featuring 10 splines for energy delivery and 4
additional electrodes for sensing and tracking. \textbf{B.}
Investigational PEF system: generator and connection box. \textbf{C.}
Representative lesion with a single application of 25A PEF energy
(\textbf{C Left} : TTC stained lesion, \textbf{C Right} : Fixed lesion
with Masson's trichrome staining). \textbf{D.} LI graphical user
interface (GUI) featuring an\emph{en face} representation of the LAF
catheter tip. \textbf{E.} EAM post ablation map using the LAF catheter.

\textbf{Figure 2. Pre-Defined Catheter-Tissue Contact Cohorts: A.} NTC
Example: ICE image of the LAF catheter (outlined in white) in close
proximity to the tissue surface (dotted yellow). No color change in LI
GUI as impedance change is [?][?]10 threshold. \textbf{B.} LTC Example: ICE
image of catheter touching the tissue surface and light green GUI tip
graphic corresponding to light contact. \textbf{C.} HTC Example: ICE
shows some deformation of the spheroid tip while pushing into tissue and
dark green GUI tip graphic corresponding to heavy contact. All lesions
were assigned to one of the three CTC cohorts prior to energy delivery.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3: Acute Ventricular Lesion Data} \textbf{A.}Pre-ablation
LI deltas from all lesions. \textbf{B.} Representative TTC-stained
lesions for each CTC cohort. \textbf{C.} NTC lesions are statistically
smaller than LTC and HTC lesions. Lesion dimensions do not continue to
increase once LI \textgreater{}[?]10 is achieved.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4. Representative electroanatomic maps and histology}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{1A and 2A.} Pre-Ablation, acute, and chronic voltage maps
(0.1-1mV) of RA intercaval lines treated with LTC and HTC. \textbf{1B
and 2B.} Gross pathology of representative intercaval lines (outlined in
dotted yellow) show areas of damage and samples of this tissue (white
boxes) with Masson's Trichrome stain demonstrate pink, healthy
myocardium on unablated border regions \textbf{(1C,D and 2C,D)} , and
transmural blue fibrosis for both LTC and HTC lesions \textbf{(1E and
2E)} .

\textbf{Figure 5: NTC Intercaval Line A.} EAM of an NTC intercaval line
shows low voltage where HTC lesions were placed and high voltage where
the NTC lesion was placed. Tissue treated with NTC also showed no signs
of significant damage in gross pathology (\textbf{C} ), or in histology
with Masson's Trichrome staining (\textbf{D} ) while areas treated with
HTC showed gross damage (\textbf{C,} yellow dotted line) and signs of
edema and myocytolysis in histology (\textbf{B).}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

\textbf{Figure 6: LI Drop \& LI on Treated Tissue A.} Comparison of
pre-ablation and post-ablation local impedance by CTC cohort.\textbf{B.}
LI response at 30 days by bipolar electrogram voltage.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}

\textbf{Figure 7. Number of Splines in Contact:} Catheter orientation
can be estimated by evaluating the number of splines showing
\textgreater{}[?]10 LI from baseline. Once a minimum of 2 splines have
consistent CTC \textgreater{}[?]10, lesion depth does not change
substantially.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

\textbf{Supplemental Figure 1:} Increased contact causes distortion of
both the tissue and the LAF catheter. The LI display can be calibrated
to show a proportional response to increased contact.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

\textbf{Supplemental Figure 2:} \textbf{A.} RV lesions are visible from
the epicardium after 30 days, showing transmurality and significant
remodeling. \textbf{B.} Fibrosis of treated RV wall tissue resulted in
roughly 33\% thinning of the ventricular wall.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image10/image10}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image11/image11}

\end{center}
\end{figure}

\textbf{Graphical Abstract}

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

