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\begin{document}

\title{Dielectric concept: ``A Magnification Lens in EP Lab?''}



\author[1]{Claudio Tondo}%
\affil[1]{Cardiac Arrhythmia Research Centre, Centro Cardiologico Monzino, IRCCS}%


\vspace{-1em}



  
  \date{May 21, 2024}


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\begin{abstract}
Myocardial wall thickness is one of the crucial parameters affecting the
lesion formation produced by radiofrequency current (RF) delivering.
Knowing the tissue characterization is critical for improving the
durability of the RF lesion. A novel dielectric based method (KODEX-EPD)
has been developed for measuring the tissue thickness at the
catheter-tissue interface. The authors of this study report for the
first time the tissue characterization (i.e. atrial wall thickness) of
the cavo-tricuspid isthmus in a series of patients undergoing common
atrial flutter ablation, showing a higher thickness close to the
tricuspid valve as compared to the inferior vena cava. This can affect
the outcome of ablation%
\end{abstract}%



\sloppy


\emph{Dielectric concept: ``A Magnification Lens in EP Lab?''}

Claudio Tondo, MD, PhD, FESC, FHRS

Heart Rhythm Center at Monzino Cardiac Center, IRCCS,

Department of Biomedical, Surgical and Dentistry Sciences, University of
Milan, Milan, Italy.

Correspondence to:

Claudio Tondo, M.D., Ph.D., FESC, FHRS

Director, Heart Rhythm Center at

Monzino Cardiac Center, IRCCS

Department of Biomedical, Surgical and Dentist Sciences

University of Milan, Milan, Italy

Via Carlo Parea, 4 - 20138 Milan, Italy

Mail: claudio.tondo@ccfm.it; claudio.tondo@unimi.it

``Funding None''

``Conflict of Interest: None''

It is well recognized that radiofrequency (RF) energy effect, is
dependent upon several variables that impact lesion size and
transmurality including catheter stability, contact force, power output,
temperature, duration of RF output, and tissue characteristics and
thickness. The notion that tissue thickness can impair the effectiveness
of RF ablation is well known from experimental studies (1) and this
again might have a role in the durability of lesions. Many advances in
catheter technology have recently shown the potential to transform the
approach to arrhythmia ablation and to improve its completeness in terms
of transmurality and durability of the sets of lesions created. However,
the chance to tailor RF delivery according to myocardial thickness is
still lacking. A new dielectric-based method (KODEX-EPD mapping system,
EPD Solutions, a Philips company) for measuring tissue thickness at the
catheter- tissue interface has recently been developed. This should
provide significant information on tissue thickness in different cardiac
areas and, theoretically provide clue for titrating power aiming at the
most effective lesion formation. In this issue of the Journal, Schillaci
et al. (2) reported preliminary data on real-time catheter-based
measuring myocardial wall thickness in vivo, during typical atrial
flutter (AFL) RF ablation in a small group of patients. Importantly,
they used a KODEX version (1.5.0.30.) not commercially available yet but
only for case replay and research purpose. Therefore, this study
represents a preliminary attempt to describe in real time how the
myocardial wall tissue can affect the RF energy delivering.

\emph{Why ``Dielectric''?}

Dielectric concept is based on gradients in the electrical field
promoted by the different cardiac structures, such as the endocardial
surface, cardiac veins and heart valves. The KODEX-EPD imaging system
(3) properly creates high-resolution images of cardiac anatomy by
exploiting the distinct dielectric properties of biological tissue. The
system receives and analyzes the~electrical field transmission and
reflection from all catheter used in the procedure. (4). This
``gradients of the ~electrical field'' is sensed by the system and used
to calculate the geometric characteristics of ~the three-dimensional
(3D) image. With this technique, it is possible to collect anatomic
information without immediate physical surface contact a few
~millimeters ahead of the catheter electrodes, resulting in a certain
degree of ``far-field~imaging''. Moreover, tissue thickness was measured
by means of the Wall Viewer (WV) function,~assessing a series of
dielectric signals derived directly from real-time local interrogation
of the catheter-tissue interface. The electric-field characteristics
(e.g., the field shape) and dielectric tissue signature are acquired
when the ablation catheter is stable and engaged with the endocardial
wall momentarily (\textless{}1.5 sec). The Wall Viewer is displayed in
millimeters and as a color code scale. The~characteristic electrical
field distribution can differentiate correctly between 7, 4 and 1.35 mm
currently corresponds with the regional average wall thickness, although
it can be calibrated ~to match the ECG gated diastolic phase as utilized
in computed tomography-based atrial wall thickness measurement (5,6)

\emph{Can ``tissue tickness'' guide our ablation strategy?}

Schillaci et al. have tested the KODEX-EPD system in patients with
cavo-tricuspid isthmus-dependent atrial flutter, showing that the
tickest atrial wall was pretty close to tricuspid valve (3.6\selectlanguage{ngerman}±0.5 mm vs
2.4±0.3 mm, p\textless{}0.001) and a trend towards a progressive
decrease of atrial wall thickness was observed moving the mapping
catheter from the tricuspid valve to the inferior vena cava. This should
suggest that more RF power needs to be transferred deeply in the atrial
portion close to the valve as compared to the area towards the inferior
vena cava. They claim to have used power between 30 and 40 Watts all
along the line with a ``point-by-point'' RF delivering approach,
reaching an acute bidirectional block in each patient. It would have
been conceivable that RF delivering would be at higher power close to
the tricuspid valve as to achieve a deeper lesion (and hopefully a
durable one). Unfortunately, they do not describe any significant change
in RF delivering while they are ablating. In fact, it is well known that
missing the atrial portion close to the tricuspid valve is one of the
reasons of resumption of conduction through the cavo-tricuspid isthmus.
Moreover, the possibility to measure~the substrate thickness before RF
delivery could change the way to perform RF~ablation, allowing a
tailored energy delivering thus increasing the efficiency of the
ablation procedures ~and potentially reducing the risk of complications.

\emph{The dream of ``an eye through''}By measuring the myocardial tissue
thickness in any part of each cardiac chamber, we might envision to
titrate the transfer of energy in relation to specific tissue
characterization. This could be particularly crucial in the atria, where
the wall thickness is reduced compared to the ventricles or close to the
valves. Tailoring the power can increase the safety profile and reduce
the likelihood of complications. None of the currently available 3D
non-fluoroscopic mapping systems provides detailed information about the
tissue thickness; the incorporation of a function (i.e. Wall Viewer)
capable to yield thickness measurement could greatly improve our ability
to effectively produce ``durable'' lesions and, thus improve the
long-term clinical outcome of ablation procedures. Furthermore, one of
potential advantages of the application of ``tissue thickness
measurement'' over the cardiac MRI, is the real time information
provided that can guide the strategy of ablation based on the ``
ablating by measuring'' concept\emph{Future applications}Theoretically,
the analysis of tissue characterization in terms of wall thickness can
be of value in the ventricles as well; just imaging to investigate not
only the scar extension in ischemic or non-ischemic ventricular
arrhythmias but also viewing ``in depth'' the pathological area could
guide the ablation strategy, accordingly. Needless to say that the
lesion created through different energy sources (RF, Cryo, Laser, PFA,
etc) and the ablative techniques employed (impedance-driven,
irrigated-tip electrode, high power-short duration) can have different
and variable impact on effectiveness and durability of the lesion itself
also in relation to the tissue thickness. Schillaci et al. have had the
privilege to test the novel KODEX-EPD function showing the potential
capability of the system to analyze the myocardial wall thickness and
provide crucial information during RF energy delivering. They need to be
congratulated for having paved a new avenue in the field and now we hope
other EP ``runners'' could join the ``ultramarathon'' of ablation and
produce brilliant results. References

\begin{enumerate}
\tightlist
\item
  Kotadia I, Williams ISM, Roney CH, et al (2021) Dielectric imaging
  accurately measures regional cardiac chamber wall thickness -- An in
  vivo study. doi:https://doi.org/10.1016/j.hrthm.2021.06.570
\item
  Schillaci V, Stabile G, Arestia A, Shopova G, Agresta A, Salito A,
  Gianniti CM, Natalizia A, De Simone A, Solimene F. Dielectric-based
  Tissue Thickness Measured during Radiofrequency Catheter Ablation.
  Journal of Cardiovascular Electroph, 2022\ldots{}.
\item
  Romanov A, Dichterman E, Schwartz Y, et al (2019) High-resolution,
  real-time, and nonfluoroscopic 3-dimensional cardiac imaging and
  catheter navigation in humans using a novel dielectric-based system.
  Heart Rhythm 16(12):1883-1889.
\item
  Maurer T, Mathew S, Schlu\selectlanguage{english}ter M, et al (2019) High-Resolution Imaging
  of LA Anatomy Using a Novel Wide-Band Dielectric Mapping System: First
  Clinical Experience. JACC Clin Electrophysiol 5(11):1344-1354.
\item
  Maurer T, Mathew S, Schlu\selectlanguage{english}ter M, et al (2019) High-Resolution Imaging
  of LA Anatomy Using a Novel Wide-Band Dielectric Mapping System: First
  Clinical Experience. JACC Clin Electrophysiol 5(11):1344-1354.
\item
  Chinitz LA, Barbhaiya C, Fabbricatore D, et al (2021) Dielectric-based
  tissue thickness measured with a radiofrequency ablation catheter:
  initial clinical results.
  doi:https://doi.org/10.1016/j.hrthm.2021.06.218
\end{enumerate}

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