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\begin{document}

\title{The Mini Electrode-equipped Catheter: Utility for Paroxysmal
Supraventricular Tachycardia Ablation}



\author[1]{Jin Iwasawa}%
\author[2]{Jacob Koruth}%
\affil[1]{Mount Sinai Hospital and School of Medicine}%
\affil[2]{Massachusetts General Hospital}%


\vspace{-1em}



  
  \date{June 13, 2024}


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\textbf{The Mini Electrode-equipped Catheter: Utility for Paroxysmal
Supraventricular Tachycardia Ablation}

\emph{Short title}\textbf{: Mini Electrode Recordings for Paroxysmal
Supraventricular Tachycardia}

\emph{Jin Iwasawa MD\textsuperscript{1}, Jacob S. Koruth
MD\textsuperscript{2}}

\textsuperscript{1}Cardiovascular Center, International University of
Health and Welfare Mita Hospital, Tokyo,
Japan;\textsuperscript{2}Helmsley Electrophysiology Center, Department
of Cardiology, Icahn School of Medicine at Mount Sinai, New York, New
York, USA

\textbf{Word count:} 1095

\textbf{Keywords:} Mini electrodes, catheter ablation, cardiac mapping,
atrioventricular node, tachyarrhythmia, Wolff-Parkinson-White syndrome

\textbf{Funding:} . None

\textbf{Disclosures:} Dr Koruth owns stock in Affera; and has served as
a consultant for Abbott, Farapulse and CardioFocus

\emph{Address for correspondence} :

Jin Iwasawa, MD

Cardiovascular Center, International University of Health and Welfare
Mita Hospital, 1-4-3, Mita, Minato, Tokyo, Japan 108-8329.

Fax: +81-3-3454-0067

E-mail: \emph{jin\_iwasawa@nifty.com}



\textbf{Abbreviation list}

AP = accessory pathway

AVNRT = atrioventricular nodal reentrant tachycardia

AVRT = atrioventricular reentrant tachycardia

CTI = cavo-tricuspid ishmus

ME = mini electrodes

PSVT = paroxysmal supraventricular arrhythmias

RF = radiofrequency

WPW = Wolff-Parkinson-White

The role of catheter ablation for paroxysmal supraventricular
arrhythmias (PSVT) is well established given that it is often a simple,
safe, and successful procedure.\textsuperscript{1} However, in some
instances, identifying a suitable ablation target can be challenging,
and can lead to multiple energy applications, prolonged fluoroscopy and
procedural times. The IntellaTip MiFi OI (Boston Scientific) catheter
offers increased mapping resolution due to the 3 mini electrodes (ME)
located at the distal tip of the catheter that allows for
high-resolution electrograms. It has been shown that the use of this
catheter may help to avoid unnecessary radiofrequency (RF) ablation at
the cavotricuspid ishmus\textsuperscript{2} (CTI) \textsuperscript{3}.
While this may be the case, ME facilitated high resolution electrogram
capability may not provide sufficient advantages in the setting of CTI
ablation when compared to current irrigated force sensing catheters.
This is likely related to CTI ablation being an anatomical approach that
is not dependent on the identification of minute potentials. Therefore,
it may be most meaningful to evaluate this particular catheters
advantages, as it relates to identifying small potentials such as slow
pathway and accessory pathway (AP) potentials during PSVT ablation. The
manuscript by Choi et al in the current issue of the journal aims to
address this.

In this prospective, randomized, controlled trial, the authors
investigated clinical records of 136 patients with AVNRT or
atrioventricular reentrant tachycardia (AVRT) or Wolff-Parkinson-White
(WPW) syndrome in two medical centers between 2020 to 2021. They found a
two-fold higher incidence of the slow pathway or accessory pathway
potential detection in the ME group. This group also had a lower mean
number of ablation attempts (2 vs. 3) and a reduced ablation time to
achieve the primary ablation endpoint: the emergence of junctional
rhythm in AVNRT and conduction block of AP potential (23.5 vs. 64.5
sec). In fact, 15/27 patients (55\%) had a discrete pathway potential
identified by the ME catheter. There was no significant difference
between the two groups in terms of total ablation time and procedure
time. Applied RF power and temperature during ablation in the ME group
were significantly higher and lower, respectively because of saline
irrigation (although ablation was performed with minimal irrigation
rates). The acute reinduction rate was similar in both groups and there
were 4 patients with recurrence during follow-up, but the relationship
between recurrence and the presence of pathway potential on the ME
catheter is not clear.

When considering cases of AVNRT and AVRT/WPW syndrome separately, only
the mean ablation time to the emergence of junctional rhythm in the
patients with AVNRT was significantly shorter in the ME group. Other
measures were not significantly different. From these observations, the
authors concluded that the ME catheter was advantageous for identifying
pathway potentials and reducing initial ablation attempts and ablation
time to reach the acute endpoint.

How best should we interpret the data the authors provide? Patients with
AVNRT and AVRT/WPW must be considered separately due to the differences
in ablation targets which reflect the different mechanisms and
anatomical locations/approaches of the targets. The authors show
improved appreciation of slow pathway potentials with the study catheter
which support the concept of the advantages of ME. However, this didn't
impact the median RF attempts needed for junctional rhythm in both
groups. On the other hand median ablation time to junctional rhythm was
16 seconds in the ME group and 48 seconds in the control group (p=0.043)
which may simply reflect improved efficiency of the ME catheter or
biases related to lack of blinding. Finally, there was no significant
difference in total ablation time, procedure time, or acute AVNRT
reinduction rates between the two groups. In one patient in the control
group, AVNRT recurred three days after discharge. Thus the impact of
realizing SP potentials using the ME catheter isn't immediately obvious
in this group- which questions the overall utility of SP potential
ablation in AVNRT or simply the lack of larger number of patients in
this study.

The immediate strength of the study is the prospective and randomized
fashion it was conducted but a significant limitation is the lack of
blinding (would have been difficult to do, but on the other hand
ablation could have been performed with the ME catheter but without the
ME electrode recordings to eliminate the uncontrollable difference
between catheter types). Most studies pertaining to AVNRT are
retrospective and observational and thus the authors are to be
congratulated for their efforts. ME catheters have been evaluated in
prior reports but are limited to CTI ablation: some studies show that
the ME catheter was helpful in terms of avoiding unnecessary
ablation,\textsuperscript{2.3} but others indicate that CTI ablation
efficacy was inferior compared to conventional 8 mm tip non-irrigation
and cryothermal catheters.\textsuperscript{4} Iwasawa et al, explained
this discordance as follows- ablation was conducted with temperature
control mode. with a maximum power output of 50W and temperature limit
of 58. The thermosensor being on the surface of the tip of the ME
catheter allowed for the temperature to rise to limit rapidly during
ablation limiting power thus potentially explaining the reduced
efficacy. In this study, the target temperature was set to 60 but also
saline irrigation during ablation was used. Reduction in ablation
attempts and time to achieve junctional rhythm are important endpoints
and of value to the clinician. More ablation attempts likely increase
the risk of atrioventricular block (especially in the setting of
underlying first-degree atrioventricular block.\textsuperscript{5}) The
ME catheter in this situation can provide improved identification of
slow pathway potentials allowing for a more directed approach to AVNRT
ablation rather than the usually anatomical approaches. Although the
endpoint was achieved with a shorter time and less RF attempts, the
outcome in both acute and chronic phases were not improved. This is
partly because this study was conducted in an unblinded fashion and with
limited number of patients. When looking at patients with AVRT/WPW,
there was no significant difference in terms of both the procedural
results and recurrence. Although the sample size is small, this result
shows that the use of the ME catheter for identifying the accessory
pathway potential was not obviously helpful. However, this doesn't
necessarily mean this catheter is not helpful- in the clinical setting,
there are occasionally difficult cases and such a catheter may make the
difference and it is understandable these sort of situations was not
have been captured in this report.

Finally, this report highlights the utility of using the study catheter
in the PSVT population and suggests that it can successfully be used to
rapidly map and ablate AVNRT and WPW/AVRT with meaningful reduction in
ablation attempts and time.



\textbf{References}

\begin{enumerate}
\tightlist
\item
  Nakagawa H, Jackman WM. Catheter ablation of paroxysmal
  supraventricular tachycardia. Circulation 2007;116:2465-2478
\item
  Binkowski BJ, Kucejko T, Lagodzinski A, Lubinski A. How to avoid
  unnecessary RF applications in cavo-tricuspid isthmus: common atrial
  flutter ablation using 8-mm-tip mini-electrode-equipped catheter. J
  Interv Card Electrophysiol 2021;60:109-114
\item
  Takagi T, Miyazaki S, Niida T, et al. Prospective evaluation of a
  novel catheter equipped with mini electrodes on a 10-mm tip for
  cavotricuspid isthmus ablation - The efficacy of a mini electrode
  guided ablation. Int J Cardiol 2017;240:203-207.
\item
  Iwasawa J, Miyazaki S, Takagi T, et al. Cavotricuspid isthmus ablation
  using a catheter equipped with mini electrodes on the 8 mm tip: a
  prospective comparison with an 8 mm dumbbell-shaped tip catheter and 8
  mm tip cryothermal catheter. Europace 2016;18:868-872.
\item
  Li YG, Gronefeld G, Bender B et al. Risk of development of delayed
  atrioventricular block after slow pathway modification in patients
  with atrioventricular nodal reentrant tachycardia and a pre-existing
  prolonged PR interval.~Eur Heart J\emph{.~} 2001;22:89--95.
  doi:~10.1053/euhj.2000.2182.
\end{enumerate}

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