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\begin{document}

\title{Predictors of VT recurrence in patients with VT inducibility at the end
of radiofrequency ablation: Should we use VT non-inducibility as a
routine endpoint?}



\author[1]{Kazutaka  Nakasone}%
\author[1]{Koji Fukuzawa}%
\author[1]{Kunihiko Kiuchi}%
\author[1]{Mitsuru Takami}%
\author[1]{jun sakai}%
\author[2]{Toshihiro Nakamura}%
\author[1]{atsusuke yatomi}%
\author[1]{Yusuke Sonoda}%
\author[1]{Hiroyuki Takahara}%
\author[1]{Kyoko Yamamoto}%
\author[3]{Yuya Suzuki}%
\author[4]{Kenichi Tani}%
\author[1]{Hidehiro Iwai}%
\author[1]{Yusuke Nakanishi}%
\author[1]{Ken-ichi Hirata}%
\affil[1]{Kobe University Graduate School of Medicine}%
\affil[2]{Kobe University}%
\affil[3]{Akashi Medical Center}%
\affil[4]{Kobe University Hospital}%


\vspace{-1em}



  
  \date{May 25, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
Introduction: It has been reported that ventricular tachycardia (VT)
non-inducibility at the end of ablation is associated with less likely
VT recurrence. However, it is not clear whether we should use VT
non-inducibility as routine end point in VT ablation. The aim of this
study was to evaluate VT recurrence in patients in whom VT
non-inducibility could not be achieved at the end of the RF ablation and
the factors attributing to the VT recurrence. METHODS and RESULTS: We
analyzed 84 consecutive patients that underwent RF ablation, and 64
patients in whom VT non-inducibility could not be achieved were studied.
The primary endpoint was recurrence of any sustained VT during the
follow-up. During a median follow-up period of 1.4 years (IQR:0.3-2.0),
22 (34\%) of the cases had VT recurrences. In the multivariate analysis
showed that an LVEF[?]35\% (HR:0.21; 95\% CI:0.07- 0.54; P\textless{}0.01)
and successful identification and ablation of all clinical VT isthmuses
(HR:0.21; 95\% CI:0.03- 0.72; P=0.01) were independent predictors of
fewer VT recurrences. RF ablation was associated with a 91.1\% reduction
in VT episodes. CONCLUSION: Even if VT non-inducibility could not be
achieved, the patients with LVEF[?]35\% or in whom all clinical VT
isthmuses could successfully be identify and ablated might be prevented
from having VT recurrences. The validity of VT non-inducibility of any
VT should be evaluated by each patient's background and the results of
the procedure.%
\end{abstract}%



\sloppy


\textbf{Predictors of VT recurrence in patients with VT inducibility at
the end of radiofrequency ablation: Should we use VT non-inducibility as
a routine endpoint?}

Kazutaka Nakasone\textsuperscript{1}, MD, Koji
Fukuzawa\textsuperscript{*1, 2}, MD, PhD, Kunihiko
Kiuchi\textsuperscript{1, 2}, MD, PhD, Mitsuru
Takami\textsuperscript{1}, MD, PhD, Jun Sakai\textsuperscript{1}, MD,
Toshihiro Nakamura\textsuperscript{1}, MD, Atsusuke
Yatomi\textsuperscript{1}, MD, Yusuke Sonoda\textsuperscript{1}, MD,
Hiroyuki Takahara\textsuperscript{1}, MD, Kyoko
Yamamoto\textsuperscript{1}, MD, Yuya Suzuki\textsuperscript{1}, MD,
Kenichi Tani\textsuperscript{1}, MD, Hidehiro Iwai\textsuperscript{1},
MD, Yusuke Nakanishi\textsuperscript{1}, MD, Ken-ichi
Hirata\textsuperscript{1}, MD, PhD

1 Division of Cardiovascular Medicine, Department of Internal Medicine,
Kobe University Graduate School of Medicine, Kobe, Japan

2 Section of Arrhythmia, Division of Cardiovascular Medicine, Department
of Internal Medicine, Kobe University Graduate School of Medicine, Kobe,
Japan

*Corresponding Author

\textbf{Author contributions:}

Kazutaka Nakasone: ,,,,,,,clinical practice/data sampling/drafting
article

Koji Fukuzawa: ,,,,,,,,concept/design/data
analysis/interpretation/drafting article

Kunihiko Kiuchi: ,,,,,,data collection/statics

Mitsuru Takami: ,,,,,,data collection/statics

Jun Sakai: ,,,,,,data collection/statics

Toshihiro Nakamura: ,,,,,,data collection/statics

Atsusuke Yatomi: ,,,,,,data collection/statics

Yusuke Sonoda: ,,,,,,data collection/statics

Hiroyuki Takahara: ,,,,,,data collection/statics

Kyoko Yamamoto: ,,,,,,data collection/statics

Yuya Suzuki: ,,,,,,data collection/statics

Kenichi Tani: ,,,,,,data collection/statics

Hidehiro Iwai: ,,,,,,data collection/statics

Yusuke Nakanishi: ,,,,,,data collection/statics

Ken-ichi Hirata: approval of article

\textbf{Conflict of Interest} : The Section of Arrhythmia is supported
by an endowment from Abbott JAPAN and Medtronic JAPAN and has received a
scholarship fund from Biotronik JAPAN. Ken-ichi Hirata chairs the
Section, and Koji Fukuzawa and Kunihiko Kiuchi belong to the Section.
However, all authors report no conflict of interest for this
manuscript's contents.

\textbf{Sources of Funding: There are no sources of funding related to
this study}

\textbf{Total word count:} 4062 words

\textbf{Corresponding Author:} Koji Fukuzawa, MD, PhD

\textbf{Affiliation:} Section of Arrhythmia, Division of Cardiovascular
Medicine, Department of Internal Medicine, Kobe University Graduate
School of Medicine

\textbf{Address:} 7-5-2 Kusunoki-Cho, Chuoh-Ku, Kobe 650-0017, Japan

\textbf{Telephone:} +81-78-382-5846, Fax: +81-78-382-5859

\textbf{E-mail:} kfuku@med.kobe-u.ac.jp

Data availability statement: The data that support the findings of this
study are available from the corresponding author upon reasonable
request.

\textbf{Introduction}

Radiofrequency (RF) ablation is a well-established treatment for
recurrent ventricular tachycardia (VT) and many studies have shown that
a successful RF ablation can prevent VT recurrence and reduce mortality
in patients with structural heart disease (SHD).\textsuperscript{1-3}

In the early 1990s, the success of RF ablation was based on the
confirmation of clinical VT non-inducibility.\textsuperscript{4} After
that, in the era of 3D mapping system, various indicators such as the
disappearance of abnormal potentials was proposed,\textsuperscript{5}but
VT non-inducibility is still one of the most important
endpoints.\textsuperscript{6-9} Previous studies have demonstrated that
VT non-inducibility at the end of RF procedures is less likely to be
associated with a VT recurrence in patients with ischemic cardiomyopathy
(ICM)\textsuperscript{6} or non-ICM (NICM).\textsuperscript{7} However,
it is not clear whether we should use VT non-inducibility as a routine
endpoint of VT ablation. In sicker patients, the risk of repeated
induction tests, a prolonged operative time, and overtreatment should be
considered. In clinical practice, it may not be realistic to achieve
non-inducibility in some patients.

The primary purpose of this study was to evaluate VT recurrence in
patients in whom VT non-inducibility could not be achieved at the end of
the RF ablation and the factors attributed to VT recurrences in ICM and
NICM patients. Further, the impact of the clinical VT ablation on the
outcomes was also assessed as the secondary purpose.

\textbf{Methods}

\textbf{2.1. Study Population}

From January 2009 to April 2020, 84 consecutive patients with SHD
underwent RF ablation (116 procedures) for drug-resistant VT in our
hospital. Patients who underwent multiple procedures were evaluated
during the last procedure.

VT non-inducibility was achieved in 20 patients but it was not achieved
in 64. To evaluate the validity of ``VT non-inducibility'' as an
endpoint of RF ablation, 64 patients in whom VT non-inducibility was not
achieved were studied. The study was approved by the ethics committee of
Kobe University Hospital, and all patients gave their written informed
consent.

\textbf{2.2. Ablation Procedure}

The procedures were mostly performed under conscious sedation, but it
was done under general anesthesia in 7 cases. Transvenous multipolar
catheters were placed into the cardiac chambers appropriate for the
arrhythmia being studied (right and/or left ventricular {[}RV and/or
LV{]}). LV mapping was performed via the retrograde aortic or
transseptal approach. When necessary, an epicardial approach using a
percutaneous subxiphoid puncture was attempted at the beginning of the
procedure as previously described.\textsuperscript{10} Electroanatomic
mapping systems such as CARTO3 (Biosense Webster, Diamond Bar, CA, USA)
or Ensite (Abbott, ST. Paul, MN, USA) were used. Intracardiac
echocardiography assisted in defining the anatomical structures,
monitoring for potential complications, and performing transseptal
punctures. Systemic anticoagulation was achieved with intravenous
heparin targeted to a minimum activation clotting time of 350 seconds
during LV and 250 seconds during RV mapping. The radiofrequency current
was delivered with a 3.5-mm open irrigated tip catheter, with power
settings of 30 to 50 W and a temperature limit of 43. Contact force
sensing catheters were used by the operators while aiming for a 5-30g
contact force.

\textbf{2.3. Mapping, Ablation strategy, and the induction protocol}

Firstly, substrate mapping was performed during sinus rhythm (SR) or
ventricular pacing. The areas of abnormal electrograms, such as
fractionated or late potentials, were tagged to denote the type of
electrogram, and pace mapping was performed in those areas. Pace mapping
was also performed at the presumed isthmus and exit regions of the
clinical VT. The QRS morphology and stimulus to QRS (St-QRS) interval
were evaluated. At the area of interest, a pace map was performed at
maximum output (1.0ms, 20V), and the output was decreased until pacing
could no longer capture the myocardium to evaluate the functional pace
map response.

Secondly, programmed ventricular stimulation was delivered with up to
double extra-stimuli at two different basic cycle lengths (CLs) (600 and
400 milliseconds) from at least two sites (the right ventricular apex,
outflow tract, or left ventricle). If the induced VT was hemodynamically
tolerated, activation mapping was acquired, and entrainment pacing was
delivered if possible. In cases of hemodynamically unstable VT, the
tachycardias were interrupted by overdrive pacing or direct current (DC)
defibrillator. When VT was not induced, the induced VT was
hemodynamically unstable, or the VT was not sustained, pace mapping was
performed and compared to the clinical VT morphology to confirm the VT
exit.

The VT isthmus was defined as sites where mid-diastolic potentials
(MDPs) during the VT were present, and the RF ablation terminated the VT
or pace mapping showed multiple exit sites (MESs).\textsuperscript{11}RF
ablation was applied at the critical isthmus of the target VT during VT,
based on the findings from activation, entrainment, and pace mapping.
For hemodynamically unstable VTs, RF ablation was applied at sites with
abnormal electrograms, a longer St-QRS, and the presence of a functional
pace map response. Fundamentally, all the clinical VTs were targeted in
all cases. The non-clinical VTs were also targeted in cases with
electrical storms.

Finally, programmed ventricular stimulation was delivered with up to
double extra-stimuli at two different basic CLs from at least two sites,
down to 200ms or until the refractory period.

\textbf{2.4. The definition of non-inducibility and the impact of the
clinical VT}

At the end of the RF ablation, in those that no sustained VT could be
induced, they were designated with VT non-inducibility. The patients in
whom only non-sustained VT (termination within 30 seconds) or
ventricular fibrillation (VF) was induced, were also classified as
having VT non-inducibility. In contrast, if sustained VT was induced,
regardless of whether it was clinical or non-clinical, the patient was
judged as having residual VT inducibility. Among the patients in whom
VTs were sustained or induced at baseline, the patients that did not
undergo a VT induction test or only received an inadequate VT induction
test at the end of the procedure due to the patient's condition, were
also classified as having residual VT inducibility. The induced VTs were
defined as being clinical if they matched the arrhythmia captured
clinically on the 12 lead ECG or, in cases where no ECG was available,
they matched the tachycardia cycle length of the implantable
cardioverter defibrillator log (difference \textless{}30ms).

In order to analyze the impact of the clinical VT inducibility at the
end of the procedure, the patients were classified into 2 groups
according to the presence or absence of inducibility of the clinical VT
at the end of the procedure: Group A -- all clinical VT isthmuses were
identified and ablated, and those VTs could no longer be induced
thereafter (Figure 2), and Group B -- none or some of the clinical VT
isthmuses could not be identified or were identified and ablated but
remained inducible.

\textbf{2.5. Follow-up}

Clinical follow-up visits and implantable cardioverter defibrillator
(ICD) interrogations were scheduled at 1, 3, 6, and 12 months after the
procedure, with remote device monitoring when possible.

\textbf{2.6. VT burden}

The pre-procedure VT burden was defined as the number of VT episodes and
shock therapies up to 2 years from the time of the ablation procedure.
The post-procedure VT burden was determined after 2 years from the day
of ablation procedure. In redo procedures, the pre-procedure VT burden
was defined as the number of VT episodes occurring between the previous
ablation procedure and the when the redo ablation procedure was
performed. VT episodes were defined as continuous VT for 30 seconds
and/or a syncopal events, or as VT that required an appropriate
intervention for termination. We also defined incessant VT that
persisted or immediately reoccurred despite appropriate intervention to
terminate the VT.

\textbf{2.7. Statistical Analysis}

Continuous variables are presented as either means (\selectlanguage{ngerman}± SD) or medians
(with interquartile ranges {[}IQR{]}) and categorical variables as
numbers and percentages (\%). Differences in the continuous variables
between the 2 groups were assessed by an unpaired t test or Mann-Whitney
test. Categorical variables were compared through a Fisher exact test.
The estimated event free survival probabilities were calculated using a
Kaplan-Meier analysis; log-rank statistics were used for group
comparisons. The follow-up period from the last procedure was calculated
with the median value and interquartile range. At first, to assess the
clinical predictors of VT-free survival and survival from cardiac death,
a univariable Cox proportional analysis was performed. Sequentially,
variables with a P\textless{}0.10 in the univariable analysis were
included in the multivariable analysis, and the hazard ratios (HR) and
95\% CI were calculated. A P\textless{}0.05 was considered statistically
significant. All statistical analyses were performed using SAS 9.4
software (SAS Institute, Cary, NC).

\textbf{Result}

\textbf{3.1. Patient Characteristics}

During the study period, 84 patients underwent VT ablation, and 64 in
whom VT non-inducibility was not achieved at the end of the procedure
were studied (Figure 1). The baseline patient characteristics are
summarized in Table 1. The mean age was 66 ± 14 years, and 54 patients
(84\%) were male. The average LV ejection fraction (LVEF) was 38 ± 13\%.

The most frequent underling heart disease of the VT was ischemic
cardiomyopathy (ICM; 38\%); sarcoidosis (23\%) and dilated
cardiomyopathy (19\%) were also common. Thirty-one patients (48\%) had
electrical storms before the RF ablation, and 19 (30\%) had persistent
incessant VT at the beginning of the RF procedure.

\textbf{3.2. Procedural Details}

Table 2 reports the procedural data of the VT ablation performed in this
study. An epicardial access was required in 13 (20\%) patients.
Forty-one patients (64\%) underwent a first procedure, 18 (28\%) a
second, and 2 (3\%) a third. The mean procedural and RF times were 246 ±
66 and 31 ± 20 minutes, respectively. The electroanatomical maps were
created with CARTO in 86\% of the cases and Ensite in 13\%. The 3D
mapping system was not used in 1 case (2\%) because of the influence
from a ventricular assist device.

\textbf{3.3. Procedural Outcomes}

The number of VT morphologies documented prior to ablation, which were
considered clinical VTs, was 1 (IQR, 1 -- 1; range, 1 -- 5; total 83)
(Table 1), and the number of VT morphologies documented during the
procedure was 2 (IQR, 1 -- 2; range, 0 -- 10; total 126) (clinical VT
was 1 {[}IQR, 1 -- 1; range, 0 -- 5; total 66{]}, and non-clinical VT
was 1 {[}IQR, 0 -- 1; range, 0 -- 9; total 60{]}.) (Table 2).

Among the 83 clinical VTs, 19 (23\%) persisted incessantly at the
beginning of the ablation, 47 (57\%) were induced during the procedure,
and 17 (20\%) were not induced during the procedure (Supplementary Table
1.). Among the 66 clinical VTs, which were documented during the
procedure, an adequate activation map could be acquired in 24 VTs
(36\%). The critical isthmus could be identified in 35 clinical VTs
(53\%); for 26 VTs non-inducibility after ablation could be achieved,
and 9 VTs could not be eliminated because the isthmus was deep (7 VTs)
or a coronary artery was nearby (2 VTs).

Table 3 shows the ablation data per patient. All clinical VT isthmuses
were identified and ablated, and those VTs could not be induced
thereafter in 18 patients (28\%, Group A); 12 patients (19\%) were found
by the presence of MDPs and VT termination during the RF ablation, and 6
patients (9\%) were found by MESs. On the other hand, all or some
clinical VT isthmuses could not be identified or were identified and
ablated but remained inducibility in 46 patients (72\%, Group B). Among
them, 8 patients (13\%) underwent ablation after identifying the
clinical VT isthmus, but the ablation failed because the isthmus was
deep (6 patients) or a coronary artery was nearby (2 patients). In 4
patients (6\%), some but not all clinical VT isthmuses were ablated, and
in 2 patients (3\%) only a nonclinical VT isthmus ablation was
performed. Further, thirty patients (47\%) underwent only a substrate
ablation because no VT isthmuses could be identified.

\textbf{3.4. Procedural complications}

Cardiac tamponade occurred in 1 case (2\%) and required drainage. One
groin hematoma (2\%) was conservatively managed (Table 2).

\textbf{3.5. Clinical Outcome}

\textbf{VT Recurrence}

During the median follow-up period of 1.4 years (IQR, 0.3-2.0), 22
(34\%) of the cases experienced VT recurrences (Table 4 and Figure 3).

\textbf{Predictive factors of VT recurrence}

Table 5 shows the univariable and multivariable Cox regression analyses
of VT recurrence. In the univariable analysis, an LVEF\selectlanguage{english}[?]35\% (HR 0.20;
95\% CI 0.06- 0.51; P=0.01) and successful identification and ablation
of all clinical VT isthmuses (Group A) (HR 0.22; 95\% CI 0.03- 0.74;
P=0.01) were associated with fewer VT recurrences (Figure 4). A Cox
proportional model was used for the multivariate analysis, and variables
with a P\textless{}0.10 in the univariable analysis were included in the
model. An LVEF\selectlanguage{english}[?]35\% (HR 0.21; 95\% CI 0.07- 0.54; P\textless{}0.01) and
the successful identification and ablation of all clinical VT isthmused
(Group A) (HR 0.21; 95\% CI 0.03- 0.72; P=0.01) were independent
predictors of fewer VT recurrences in the multivariate analysis.

\textbf{VT burden reduction}

Figure 5 shows the VT episodes before and after the RF ablation. A
significant VT burden reduction after the VT ablation was observed in
the entire population. RF ablation was associated with a 91.1\%
reduction in VT episodes. Before and after the RF ablation, the median
VT episodes were 3 (IQR, 2 - 9) and 0 (IQR, 0 - 1) (P\textless{}0.01),
and the number of shock therapies was 2 (IQR, 1 - 5) and 0 (IQR, 0 - 0)
(P\textless{}0.01).

\textbf{Mortality}

Fourteen patients died during the follow-up. The cause of death was
arrhythmogenic cardiac death (29\%), terminal heart failure (36\%), and
non-cardiovascular death (36\%) (Table 4).

\textbf{Discussion}

\textbf{Main Findings}

We evaluated the VT recurrence in patients in whom VT non-inducibility
could not be achieved at the end of the RF ablation and the factors
attributed to the VT recurrence in ICM and NICM patients.

The main findings of our study were:

1. During the median follow-up period of 1.4 years (IQR, 0.3-2.0), 66\%
of the patients in whom VT non-inducibility could not be achieved at the
end of RF ablation had no recurrence.

2. Patients whose LVEF was more than or equal to 35\%, or in whom all
clinical VT isthmuses could successfully be identify and ablated were
independent predictors of fewer VT recurrences in the multivariate
analysis.

3. Even in patients with VT recurrences, VT ablation could significantly
reduce the VT burden.

\textbf{Endpoint of the VT ablation}It is known that VT non-inducibility
at the end of the VT ablation is less likely to be associate with a VT
recurrence\textsuperscript{6,7}and achieving the combined endpoint of
the abolition of the abnormal electrograms and VT non-inducibility
further reduces the VT recurrence.\textsuperscript{8,9} In the present
study, 20 patients in whom VT non-inducibility was achieved had a small
VT recurrence rate of 15\%. However, we need to consider the risk of
overtreatment at the same time; the enlargement of a scar area by RF
ablation may lead to a more depressed cardiac function. There is not
enough detailed reporting on the subsequent events in patients with
residual VT inducibility at the end of the procedure. In our study,
patients with an LVEF\selectlanguage{english}[?]35\% or successful identification and ablation of
all clinical VT isthmuses were independent predictors of VT
non-recurrence in patients in whom VT non-inducibility was not achieved.
This may indicate that we should try to identify the isthmus of the
clinical VT as much as possible, and that in this group of patients,
inducible residual non-clinical VT is acceptable.

\textbf{LV dysfunction and VT recurrence}

In this study, the recurrence rate was lower in the patients with an
LVEF\selectlanguage{english}[?]35\%, even with residual VT inducibility. In a sub-analysis of the
AVID (Antiarrhythmics Versus Implantable Defibrillator) trial, the
efficacy of ICD therapy was reported to depend on the degree of LV
dysfunction in patients with secondary prevention of sudden cardiac
death, and in patients with an LVEF\textless{}35\%, ICD therapy had an
advantage. On the other hand, in patients with an LVEF\selectlanguage{english}[?]35\%, the
efficacy of the ICD therapy was equivalent to that of antiarrhythmic
drugs.\textsuperscript{12} Also in a recent trial, Groeneveld et al.
reported that in 42 patients with an LVEF\textgreater{}35\% and a
hemodynamically not tolerated VT, only 6 patients (14.3\%) had VT
recurrences, and all were hemodynamically
tolerated.\textsuperscript{13}That suggests that the classification by
the degree of LV dysfunction may make sense, and may help determine how
aggressively induced VT should be treated.

Patients with an EF\textless{}35\% are considered to have more
myocardial dysfunction and are more likely to have multiple arrhythmia
substrates. Although a more aggressive induction and ablation may be
necessary to reduce the VT recurrence rate in them, the dilemma is that
patients with such a reduced cardiac function may be more susceptible to
hemodynamic compromise and invasive procedures with a prolonged
operative time. In the present study, the VT burden was significantly
reduced even in the group with an EF\textless{}35\%, suggesting that a
balanced protocol that ensures safety is desirable.

\textbf{Importance of a successful ablation of all clinical VT
isthmuses}

Previous randomized multicenter trials have shown that substate ablation
reduces any VT recurrences during the follow-up as compared to targeting
only a clinical and stable VT, making substate ablation a basic strategy
for VT ablation.\textsuperscript{14-16} In the present study, the
identification and RF ablation of the clinical VT isthmus in addition to
a substate ablation was shown to be associated with fewer VT
recurrences. Hadjis et al. reported that the identification of the VT
isthmus in addition to a substate ablation significantly reduced the
recurrence rate (HR 0.21, 95\% CI: 0.07-0.63, P \textless{}
0.01).\textsuperscript{17} Cano et al. also reported that a baseline
inducibility of greater than 1 VT morphology was an independent
predictor of VT recurrence (HR 12.05, 95\% CI: 1.60-90.79, P = 0.02) and
complete activation mapping was associated with a reduction in the VT
recurrence.\textsuperscript{18}

In this study, patients in whom VT non-inducibility could not be
achieved at the end of the RF ablation were included, so in many cases,
VT was induced with or without hemodynamic stability at the end of the
RF ablation. Nevertheless, a successful ablation of all clinical VT
isthmuses was correlated with non-recurrence, suggesting that the
identification of the VT isthmus is important in addition to the basic
strategy of substate ablation.

\textbf{VT burden reduction}

The term ''recurrence'' has been used to evaluate the outcome of the
ablation therapy, however, recently the concept of a VT burden reduction
has been proposed.\textsuperscript{19, 20} The VT burden can be more
valuable in terms of clinical benefit than recurrence as a dichotomous
event. In the present study, the VT burden was reduced by 91.1\% even in
patients in whom VT non-inducibility could not be achieved at the end of
RF ablation, and VT ablation significantly reduced the number of VT
episodes and shock therapies. Although the design of the current study
did not allow us to examine the prevention of mortality, a reduction in
the ICD shock therapies may improve the patient
survival.\textsuperscript{21}

\textbf{Clinical Implications}

It is known that the achievement of VT non-inducibility at the end of
the VT ablation in patients with SHD leads to a lower recurrence. So VT
non-inducibility has been used as an endpoint in many cases. However, in
some cases, the ablation may be excessive or the risk of an induction
test may be high. In this study, we included patients in whom VT
non-inducibility could not achieved at the end of the VT ablation. We
found that the recurrence rate was lower in patients with an EF\selectlanguage{english}[?]35\% or
in patients who could successfully identify and undergo ablation of all
clinical VT isthmuses. In these patients, even if non-clinical VT
inducibility remains, it may not affect the subsequent prognosis. In
addition, the VT burden was reduced after the VT ablation, and the shock
therapy was also significantly reduced before and after the ablation.
That suggested that it may be necessary to examine the validity of the
VT non-inducibility in each patient.

\textbf{Study Limitations}

This study was a single-center retrospective observational analysis.
Therefore, the number of study patients was relatively small. And this
study included the patients with ICM and NICM, and the NICM consisted of
a non-uniform etiology. The response to the RF ablation and clinical
course may differ for each cardiomyopathy. Further, the methods used for
antiarrhythmic drugs were dependent on each physician. However, because
of the limited number of operators, our strategy to treat patients with
VTs has been consistent and our results can be applied to clinical
practice.

\textbf{Conclusion}

Even if VT non-inducibility could not be achieved at the end of the RF
ablation, 66\% of the patients had no VT recurrences. Among them, in the
patients whose LVEF was more than or equal to 35\% or in whom all
clinical VT isthmuses could be identified and ablated, that successful
identification and ablation of those might prevent VT recurrences. In
addition, even if the VT recurred, the VT burden decreased after the VT
ablation. The validity of VT non-inducibility for any VT should be
evaluated by each patient's background and the results of the procedure.

\textbf{Acknowledgments}

The authors would like to thank Mr. John Martin for his linguistic
assistance.

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