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\begin{document}

\title{Bipolar Ablation for Outflow Tract Ventricular Arrhythmias: When the
Going gets Tough, Two Catheters may be Better than One}



\author[1]{Anurut Huntrakul}%
\author[1]{Jackson Liang}%
\affil[1]{University of Michigan}%


\vspace{-1em}



  
  \date{June 18, 2024}


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\textbf{Bipolar Ablation for Outflow Tract Ventricular Arrhythmias: When
the Going gets Tough, Two Catheters may be Better than One}

Anurut Huntrakul, MD\textsuperscript{1,2} and Jackson J. Liang,
DO\textsuperscript{1}

1 Electrophysiology Section, Division of Cardiology, Cardiovascular
Center, University of Michigan Medical Center, Ann Arbor, MI 48109, USA.

2 Division of Cardiovascular Medicine, Department of Medicine, Faculty
of Medicine, Chulalongkorn University, King Chulalongkorn Memorial
Hospital, Bangkok 10330, Thailand

Funding: None

Disclosures: None

\textbf{Correspondence:}

Jackson J. Liang, DO

Assistant Professor of Medicine

Electrophysiology Section, Division of Cardiology

University of Michigan

Ann Arbor, MI 48109, USA

Email: liangjac@med.umich.edu

Twitter: @Jackson\_J\_Liang

Radiofrequency catheter ablation (RFCA) is an effective treatment
strategy for patients with symptomatic ventricular arrhythmias (VAs).
Conventional RFCA involves unipolar ablation in which the radiofrequency
energy current is delivered between the catheter tip and a dispersive
skin electrode. Ablation lesion size with unipolar ablation depends on
multiple factors such as power, temperature, impedance, duration of
energy delivery and catheter-tissue contact force but is generally
limited to 5-6 mm in depth. However, the substrate for VAs may
occasionally be intramural, residing deep within the myocardium, and in
some cases unipolar ablation- even sequential unipolar ablation from
both sides of the intramural substrate- may be inadequate to eliminate
the VA substrate. Several adjunctive methods of creating deeper lesions
have been used in clinical practice such as use of half-normal saline as
a catheter irrigant, simultaneous unipolar RFCA, bipolar RFCA, coronary
venous ethanol ablation, radiofrequency needle ablation, electroporation
and noninvasive radiotherapy. With bipolar ablation, a second ablation
catheter functioning as a return electrode in the circuit can be
positioned opposite to the other active ablation catheter and
simultaneous heating and concentrated thermal injury with RF delivery
between the catheter tips can then lead to deeper, more transmural
lesions.

In this issue of \emph{Journal of Cardiovascular Electrophysiology} ,
Zhou, et al. report results from a retrospective 2-center study,
describing outcomes in 12 patients with outflow tract ventricular
arrhythmias (OT-VAs) (7 left ventricular (LV) summit, 3 intramural
septal OT, and 2 with right ventricular (RV) diverticuli at the
anterolateral free wall) who were treated with bipolar RFCA after
sequential unipolar RFCA had failed (transient suppression or no
effect).\textsuperscript{1} In their experience, bipolar RFCA was rarely
required (only done in 1\% of patients treated with ablation over the
study period). Bipolar RFCA was successful in 10 patients (mean
inter-catheter distance 9.7 mm) and unsuccessful in 2 patients
(inter-catheter distances 23.9 and 13.5 mm). Bipolar configuration was
from within to the along the outer edge of a diverticulum in 2 patients
with VAs originating from RV diverticuli; from the RVOT to aortic cusp
in 3 patients with intramural septal OT VAs; and from the LV to cusps,
cusps to great cardiac vein (GCV), and LV to GCV in patients with VAs
originating from LV summit. Interestingly 2 patients with unsuccessful
outcome acutely had eventual late resolution of VAs over time. There was
1 steam pop and no other complications related to bipolar RFCA.

The efficacy of bipolar RFCA to treat VAs has been well described.
Intramural VAs originating from various areas such as the LV summit,
intramural OT, interventricular septum, LV free wall and papillary
muscles which were unable to be eliminated with unipolar RFCA have been
reported to be successfully eliminated with bipolar RFCA. One unique
aspect of this study is that the authors are the first to describe
bipolar ablation targeting outflow tract VAs originating from RV
diverticuli.

The success rate of bipolar ablation in Zhou, et al.'s study was 83\%
acutely and increased to 100\% after subsequent follow-up. Delayed
suppression of intramural septal outflow tract VAs after RFCA despite
acute failure has been previously described in the
literature,\textsuperscript{2} and the late suppression with bipolar
ablation which was seen in 2 patients in the current series despite
acutely unsuccessful ablation is especially interesting and hypothesis
provoking. The authors have appropriately acknowledged some important
limitations to their study including small sample size, lack of
pre-procedural cardiac magnetic resonance imaging (MRI), the fact that
several mapping tools such as intracardiac echocardiography and
multielectrode microcatheters were not used. Furthermore, the use of
half normal saline as a catheter irrigant was not attempted prior to
bipolar ablation. Several issues regarding the application of bipolar
RFCA in this study remain to be elucidated. First, as this is a
retrospective study, the population included may subject to a selection
bias. The question of which patients would theoretically benefit most
from bipolar ablation remains unanswered. Second, the configuration and
orientation of both ablation catheters plays a vital role in determining
the trajectory of the bipolar ablation current, and the current study
does not clearly explain the catheter configurations in detail. While
the authors describe that several bipolar ablation configurations were
attempted in some patients, further analysis comparing the ineffective
and effective configurations would have been helpful. Detailed mapping
of coronary venous system branches with multielectrode microcatheters to
identify the true site of origin can facilitate more accurate targeting
of OT VAs via anatomic approach,\textsuperscript{3, 4} and
identification of true site of origin can help pinpoint the optimal
ablation trajectory to guide catheter placement during bipolar ablation.
Lastly, pre-ablation cardiac MRI can be helpful to identify areas of
scar which may represent VA substrate which can be targeted with
ablation.\textsuperscript{5}

While bipolar RFCA can be an effective bailout strategy for some
patients with intramural OT VAs refractory to standard sequential
unipolar ablation, its general use still remains limited by potentially
increased risk of complications as well as technical challenges
including the requirement for specific cables and setup to visualize
both catheters simultaneously on 3D mapping system and to deliver RF
energy. With the current bipolar ablation systems, temperature at the
catheter tip cannot be accurately monitored simultaneously for both
catheters. Impedance is affected by catheter tip-tissue orientation of
both catheters, which needs to be monitored closely to avoid steam pops.
Potential collateral damage to nearby structures such as the coronary
arteries or the conduction system may be possible and coronary
angiography should be performed in some cases to ensure that the
ablation catheter is distant from major epicardial coronary arteries.

We applaud the authors for sharing their experience describing the
efficacy and safety of bipolar RFCA in a series of patients with
challenging OT-VAs refractory to unipolar ablation. Pre-procedural
cardiac MRI to delineate VA substrate and detailed mapping with
multielectrode microcatheters or wires to identify the true site of
origin would be helpful to guide selection of appropriate tools and
alternative strategies in these challenging cases. Further clinical
studies in a larger study population with various structural heart
diseases are required to confirm the generalizability of bipolar
ablation for OT VAs.

\textbf{REFERENCES:}

1. Zhou B., Yu J., Ju W., Li X ., Zhang F. , Chen H., Li M., Gu K., Xie
X. , Cheng D., Wang X. , Wu Y. , Zhou J., Zhang B. , Kojodjojo P., Cao
K. , Yang B. , and Chen M. , \emph{Bipolar Catheter Ablation Strategies
for Outflow Tract Ventricular Arrhythmias Refractory to Unipolar
Ablation.} J Interv Cardiovasc Electrophysiol, 2022.

2. Ding L, Hou B, Wu L, Qiao Y, Sun W, Guo J, Zheng L, Chen G, Zhang L,
Zhang S, Yao Y. Delayed efficacy of radiofrequency catheter ablation on
ventricular arrhythmias originating from the left ventricular
anterobasal wall. \emph{Heart Rhythm.} 2017; 14(3):341-349.

3. Liang JJ, Bogun F. Coronary Venous Mapping and Catheter Ablation for
Ventricular Arrhythmias. \emph{Methodist Debakey Cardiovasc J.} 2021.

4. Ghannam M., Liang J., Sharaf-Dabbagh G., Latchamsetty R.,
Jongnarangsin K., Morady F., and Bogun F., \emph{Mapping and Ablation of
Intramural Ventricular Arrhythmias: A Stepwise Approach Focused on the
Site of Origin.} JACC Clin Electrophysiol, 2020; 6(11): p. 1339-1348.

5. Ghannam M., Liang J. J., Dabbagh G. S., Siontis K. C., Attili A.,
Cochet H., Jais P., Juhoor M., Latchamsetty R., Jongnarangsin K., Morady
F., and Bogun F., \emph{Impact of Intramural Scar on Mapping and
Ablation of Premature Ventricular Complexes.} JACC Clin Electrophysiol,
2021; 7(6): p. 733-741.

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