Long-term outcome of catheter ablation and other form of therapy for electrical storm in patients with implantable cardioverter-defibrillators
Long-term outcome of catheter ablation and other form of therapy for electrical storm in patients with implantable cardioverter-def ibrillators
Stanislaw Morawski 0 1
Patrycja Pruszkowska 0 1
Beata Sredniawa 0 1
Radoslaw Lenarczyk 0 1
Zbigniew Kalarus 0 1
0 Silesian Center for Heart Diseases , M.C Sklodowskiej Street 9, 40-055 Zabrze , Poland
1 Department of Cardiology, Congenital Heart Diseases and Electrotherapy, School of Medicine with Division of Dentistry in Zabrze, Medical University of Silesia , M.C Sklodowskiej Street 9, 40-055 Zabrze , Poland
2 Stanislaw Morawski
Purpose Radiofrequency catheter ablation (RFCA) for electrical storm (ES) has become a widely used therapeutic method. Its effectiveness in comparison to other forms of ES treatment is however uncertain. Methods This single-centre retrospective study investigated the long-term clinical outcome after RFCA for ES and compared long-time effects of ablation to other forms of treatment. The study population consisted of 70 consecutive patients hospitalised between January 2010 and June 2015 due to ES. Patients were recruited for the study if the following criteria were fulfilled: first ES caused by ventricular tachycardia (VT) or ventricular fibrillation (VF), implanted cardioverter defibrillator or cardiac resynchronisation therapy device and left ventricular ejection fraction < 50%. The follow-up data on VT/ES recurrence was obtained from pacemaker/implanted cardioverter defibrillator memory. Data on all-cause mortality was collected during outpatient visits or by telephone contact. Results Of the 70 patients enrolled, 28 (40%) were treated with RFCA (group A) and 42 (60%) received other forms of treatment for ES (group B). During a mean (±SD) 864 (629) days of follow-up, death occurred in 4 (14.3%) patients in the ablation group and in 16 (38.1%) patients treated with other methods [p = 0.03]. There was no significant between-group difference in VT/VF and ES recurrence. Statistical analysis revealed that the presence of cardiac resynchronisation therapy device during ES, stroke and/or transient ischaemic attack and lower baseline hematocrit level were the multivariate predictors of all-cause mortality. Conclusions In patients treated with RFCA for ES, all-cause mortality was significantly lower compared to the group treated with other methods.
Electrical storm; Catheter ablation; Ventricular tachycardia; Ventricular fibrillation; Implantable cardioverter-defibrillator
Heart failure (HF) is a growing medical problem in developed
countries, with incidences among adult population reaching
up to 2% [
]. It is well known that HF patients are
simultaneously at a significantly higher risk of sudden cardiac death.
The recommended and most efficient form of primary and
secondary prevention against sudden cardiac death in heart
failure patients is the implantation of automatic implantable
cardioverter defibrillators (ICD) [
]. 3.5% of patients with
an ICD for primary prevention, and even 10–40% of those
implanted for secondary prevention of SCD, will suffer from
the most malignant form of ventricular arrhythmia, known as
an electrical storm (ES) [
]. An electrical storm is defined as
the occurrence of three or more distinct episodes of ventricular
tachycardia (VT) and/or ventricular fibrillation (VF) within
24 h [
]. In patients with ICD, its usual presentation involves
multiple antitachycardia pacing therapies (ATP) and/or
highenergy therapies within a short-time period. Management in
this challenging group is generally focused on the elimination
of potentially reversible causes of electrical instability,
haemodynamic stabilisation and (once reversible causes have been
excluded or dampened) modification of the arrhythmogenic
substrate with catheter ablation of ventricular tachycardia
]. Most of the published data on radiofrequency catheter
ablation (RFCA) for ES is based on small series or case
reports, mainly describing single treatment method. No large
studies have compared RFCA with conservative treatment
and their effects on survival. The purpose of this study
was to assess the long-term clinical outcomes after
RFCA for ES and to compare this method with other
forms of treatment for ES.
2.1 Patients and eligibility criteria
The study population consisted of 70 consecutive patients,
who were hospitalised between January 2010 and June 2015
due to the occurrence of an electrical storm. In 68 patients, the
arrhythmia responsible for the occurrence of ES was VT; in 2,
the ES was due to VF.
Patients were initially recruited for the study if they
fulfilled the following criteria: diagnosed with the first electrical
storm caused by VT or VF, previous or present implantation of
an ICD or cardiac resynchronisation therapy device (CRT-D)
during the first ES hospitalisation, and heart failure with left
ventricular ejection fraction (LVEF) < 50% (assessed by
transthoracic echocardiography). Patients were excluded if they
were suffering from inherited arrhythmogenic diseases (long
QT syndrome, Brugada syndrome, catecholaminergic
polymorphic ventricular tachycardia, short QT syndrome
arrhythmogenic right ventricular cardiomyopathy), had suffered from
a previous electrical storm, had been previously treated with
VT ablation or were aged < 18 years old. The clinical
characteristics of the total study population of patients with a
particular emphasis on age, sex, comorbidity, basic
electrocardiographic, echocardiographic parameters, the type of
cardiomyopathy and the type of prevention causing ICD/CRT-D
implantation are shown in Table 1. To evaluate the effect of
catheter ablation for the long-term prognosis of patients
treated because of an electrical storm, the research group was
divided depending on ablation procedure (group A) or no
ablation procedure (group B) during primary hospitalisation. The
clinical characteristics of group A (28 patients) were
compared with those of the remaining study population (42
patients; group B) as show in Table 1.
During hospitalisation, if presenting VT episodes were
recorded based on 12-lead ECG and/or 12-lead Holter ECG, the
corresponding ECG morphologies were defined as clinical
VT. Coronary angiography was performed in 44 patients in
whom myocardial ischaemia was suspected. In the remaining
population, coronary arteriography was performed in referral
hospitals (5 patients) and in the previous 12 months (9
In 7 patients, this was not conducted because of no clinical
suspicion of myocardial ischaemia or because of
nonischaemic cardiomyopathy (5 patients). Percutaneous
coronary intervention was performed in 18 patients.
No additional non-pharmacological beta blockade
procedures were performed (such as left stellate ganglion blockade).
No overdrive atrial pacing was used to tide over the storm in
any of the patients. Patients underwent standard treatment in
terms for reversible reasons of ES. In retrospective analysis
during primary hospitalisation, 28 patients were treated using
the catheter ablation. A RFCA was performed in all patients
who underwent the invasive electrophysiological study.
2.2 Electrophysiological study and ablation strategy
Written informed consent was obtained from all patients
before RFCA. All procedures were performed under local
anaesthesia. In all cases, retrograde femoral access was used.
Mapping was performed using the three-dimensional
electro-anatomical mapping system Carto 3 (Biosense
Webster, Diamond Bar, CA, USA) and a saline irrigated tip
catheter NaviStar ThermoCool (Biosense Webster). In all
cases, endocardial mapping was routinely undertaken. An
initial bolus of heparin, in dose 80 IU/kg of patient body weight,
was administered after the electrode was positioned in the left
ventricle. Every 15 min, the activating clothing time (ACT)
was measured and an additional heparin bolus was
administered to maintain ACT above 250 s. In all patients in sinus
rhythm (SR), three-dimensional left ventricular bipolar
voltage maps were constructed. A dense scar was defined as an
area of local bipolar peak-to-peak voltage of < 0.5 mV and a
border zone < 1.5 mV. In patients with haemodynamically
stable VT, arrhythmia was induced by programmed
stimulation and a three-dimensional activating map was obtained as
in patients with an incessant VT or if arrhythmia occurred
Targets for ablation were determined as mid-diastolic
potentials, areas of slow conductions, or identifying isthmus and
exit zones with prolonging time stimulus to QRS in sinus
rhythm (SR) patients using pacemapping. During VT, the
target for application was determined in areas central to the exit
zone and identified by entrainment. Radiofrequency current
was delivered with an open irrigated tip catheter with a 30 ml/
min saline flow at a power setting of 30 up to 50 W and a
temperature limit of 45 °C. After ablation, programmed
stimulation with up to three extra stimuli was performed. The
success was defined as non-inducibility of clinical VT. In
cases of inducibility, another form of sustained VT, additional
BMI body mass index, CRT-D cardiac resynchronization therapy defibrillator, EDV end-diastolic volume, ESV end-systolic volume, ICD implantable
cardioverter-defibrillator, LA left atrium, LVEDD left ventricular end-diastolic diameter, LVEF left ventricular ejection fraction, LVESD left ventricular
end-systolic diameter, MI myocardial infarction, MVR mitral valve regurgitation, NYHA class New York Heart Association Class, SCA sudden cardiac
arrest, VF ventricular fibrillation
a Native QRS duration—duration of QRS complex in patients without ventricular stimulation
b Paced QRS duration—duration of QRS complex in patients with ventricular stimulation
mapping and ablation was performed according to the
protoc o l d e s c r i b e d a b o v e . A p a r t f r o m i n t r a - p r o c e d u r a l
anticoagulation with unfractionated heparin, in every patient,
a standard prophylactic dose of low-molecular-weight heparin
was administered in the early post-procedural period. Further
anticoagulation was carried out with the use of vitamin K
antagonists, which were instituted on the first post-operative
day, and continued for 1 month, with the target INR between 2
and 3. This therapy was subsequently withdrawn, if long-term
anticoagulation was not required due to other reasons.
The majority of the patients (65; 92.9%) already had
implanted ICD (41; 58.6%) or CRTD (24; 34.3%) before
primary admission. In the rest, ICD (5; 7.1%)/CRDT (0; 0%)
devices were implanted before the discharge.
The follow-up date for VT/ES recurrence/mortality
(average 864 days; mean 706 days, SD 629) was obtained in our
pacemaker/ICD outpatients’ clinic through interrogation of
t h e d ev i c es , r em o t e m on i t o r i n g ( R M ) , s u bs eq ue nt
hospitalisations and telephone contact.
2.4 Statistical analysis
Continuous variables are described as mean ± standard
deviation (SD), or median and range for skewed distributions.
Categorical variables are described as numbers and
percentages. Between-group comparisons were performed with
Student’s t test or the χ2 test as appropriate. Univariate and
multivariate analyses were performed using a Cox
proportional hazards model, with hazard ratio (HR) and 95% confidence
intervals (CI) reported. Two multivariate Cox regression
models were constructed to predict long-term mortality. The
first tested parameters which had significance in the univariate
model < 0.05 (model 1), and the second included variables
with p < 0.1 (model 2). Some variables (e.g. creatinine level)
were not included into multivariate models due to redundancy
with other parameters already included (chronic kidney
disease in this case).
Long-term success (i.e. time to VT recurrence, time to ES
recurrence and time to death) was also examined in a survival
analysis framework. Time-to-event survival curves were
graphed for different patient subgroups using the Kaplan–
Meier estimation technique. Differences between strata were
assessed by a log-rank test.
The study was carried out in accordance with the
Declaration of Helsinki and International Committee on
Harmonization guideline for good clinical practice.
S e v e n t y c o n s e c u t i v e p a t i e n t s ( 9 1 . 4 % m a l e , a g e
[64.71 ± 10.71] years; LVEF 26.2% ± 7.31%), the majority
with ischaemic cardiomyopathy (81.43%) and ES, constituted
our study population. As described in the BMethods^ section,
patients were divided into two groups according to execution
of catheter ablation during the primary episode of ES. Among
the groups, no significant difference in baseline clinical and
electrocardiography characteristics were observed except
BMI (group A: 28.66 ± 3.65 vs. group B: 26.76 ± 3.61;
p = 0.04), myocardial infarction treated non-invasively (20
[71.4%] vs. 19 [45.2%]; p = 0.03) and duration of native
QRS respectively (group A: 140.61 ± 30.42 ms vs. group B:
122.0 ± 23.88 ms; p = 0.04) (Table 1).
In group A, the majority of cases showed no clear cause of
ES during primary hospitalisation (n = 24 [85.71%]), in
contrast to group B, where nearly half of the patients had clear
causes of ES (n = 22 [53.4%]). In group B, RFCA was
abandoned in 20 patients during hospitalisation despite undetected
and potentially reversible cause of electrical instability, due to
the disappearance of arrhythmia as a result of the
intensification of antiarrhythmic therapy (increased doses of β-blockers
(20 patients) and to the inclusion of treatment with
antiarrhythmic class III drugs (14 patients; 13 with amiodarone, 1
with sotalol) (Table 2). After the first ES, 28 patients
underwent a catheter ablation procedure. Nine (32.1%)
patients from group A and 13 (31%) from B group underwent
subsequent ablation during the follow-up because of VT and
ES recurrence (p = 0.92). Importantly, no statistical
differences were observed in terms of VT (group A: 16 [57.1%];
group B: 31 [73.8%]; p = 0.15) and ES (group A: 9 [32.1%];
group B: 19 [45.2%]; p = 0.28) recurrence in both groups.
However, there was significantly lower all-cause mortality in
group A (4 [14.3%] vs. 16 [38.1%]; p = 0.03) (Table 3).
Significant differences in survival between ablated and
nonablated groups are shown in Fig. 1. At the end of the ablation
procedures, 23 patients underwent programmed electrical
(n = 28)
stimulation. In 2 of those patients, non-clinical VTs were
inducible. There was no inducible clinical VT at the end of the
procedure. Five patients (17.9%) were not tested due to
haemodynamic instability after CA.
Analysis of the early post-operative period (< 30 days)
revealed a non-significantly (p = 0.16) higher rate of VA
recurrence rates in the group which underwent RFCA (7 [25%]) vs.
the conservative group (5 [12%]), respectively. However,
subanalysis of the late (> 30 days postoperatively) period only, a
significantly (p = 0.02) lower rate of recurrences was found in
the ablated group (46.4%) vs. in the non-ablated group (75%;
2 patients from the non-ablated group died during the
blanking period, and consequently, they were not included
in the analysis).
Variables evaluated in the univariate analysis were as
follows: age, gender, BMI, NYHA class, LVEF, severe MVR,
implantation of ICD/CRTD in secondary prevention of SCA,
presence of an implanted CRT-D (during the storm), ischemic
cardiomyopathy, previous myocardial infarction treated
conservatively, complete revascularisation after angiography,
diabetes type 2, chronic kidney disease, stroke and/or transient
ischaemic attack, chronic obstructive pulmonary disease,
atrial fibrillation, haematocrit level, C-reactive protein level,
creatinine level, GFR, NT-pro-BNP level, potentially
reversible causes of ES, primary RFCA procedure, VT recurrence
and ES recurrence.
The univariate analysis revealed that severe mitral valve
regurgitation (MVR), presence of CRT-D during ES, diabetes
type 2, stroke and/or a transient ischaemic attack, a lower
baseline haematocrit level, a higher NT-pro-BNP level, a
higher C-reactive protein (CRP) level and infective
endocarditis as a potentially reversible cause of ES were significant
prognostic predictors for all-cause mortality. Further details
are provided in Table S1 in the Supplementary Appendix.
The multivariate Cox regression model, incorporating
parameters which had significance in the univariate model
< 0.05 as covariates (model 1), demonstrated that both the
presence of CRT-D during ES and stroke and/or a transient
ischaemic attack were independently associated with the
increased risk of total mortality (HR 7.99, 95%CI 2.35–27.16;
p = 0.001; and HR 4.78, 95%CI 1.43–15.93; p = 0.01,
respectively). In the second model (including all variables with
p < 0.1), the presence of CRT-D during ES (HR 6.83,
95%CI 1.93–24.24; p = 0.003), stroke and/or a transient
Death from any cause
Electrical Storm recurrence
Ventricular Tachycardia recurrence
Log Rank test, p = 0.35 group A, n = 28
2000 2500 group B, n = 42
group A, n = 28
2500 group B, n = 42
Log-R2a0nk00test, p=0.320500 ggrroouupp BA,, nn == 4228
NGGo.rrooauutppRiABsk 4228 2260 1173 87 10 NGGo.rrooauutppRiABsk 2482 1154
Fig. 1 Kaplan–Meier event-free survival estimates in the patient
population during follow-up (group A vs. group B). The Kaplan–Meier
curve shows a difference between group A (RFCA treatment in primary
hospitalisation) and group B (no-RFCA in primary hospitalisation) in
No. at Risk
180 63 01 4228 1133 87 23 10
terms of total mortality, electrical storm recurrence and ventricular
tachycardia recurrence at 864 ± 629 days of follow-up. A statistically
significant difference in terms of total mortality is observed (log-rank
test, p = 0.04)
ischaemic attack (HR 9.86, 95%CI 1.71–56.65; p = 0.01) and
a lower baseline haematocrit level (HR 0.84, 95%CI 0.72–
0.99; p = 0.04) were all independently associated with the
higher risk of all-cause mortality. A thorough analysis of these
multivariates analyses (both models 1 and 2) is also provided
in Table S1 in the Supplementary Appendix.
Recurrent ventricular arrhythmias, which as they are the cause
of electrical storms, are the most common problem among
ICD/CRT-D recipients. In our study, catheter ablation in such
patients was more effective than any other form of therapy in
reducing death at any time. Despite the interdisciplinary
approach to the treatment, long-term mortality remains high. In
our study, more than a quarter of patients died during the
course of the study, with the majority of deaths taking place
during a few months after an episode of electrical storm. This
is concordant with several studies, which have shown that ES
occurrence in patients with ICD/CRT-D is an independent risk
factor for death, with an increase in risk of at least 2–3-fold in
long-term follow-up. The risk is highest in the first 3 months
post an electrical storm episode [
]. For many years,
consensus statements and guidelines have recommended the
use of catheter ablation (CA) when antiarrhythmic therapy
does not prevent recurrences of ventricular arrhythmias;
however, these recommendations have been largely based on
expert opinion and non-randomised case series [15–17]. These
recommendations were in force up until the publication of the
2015 ESC guidelines for the management of patients with
ventricular arrhythmias and the prevention of sudden cardiac
death where urgent catheter ablation is recommended
(classification of recommendation II B) in patients with scar-related
heart disease with incessant VT or electrical storm .
However, these guidelines were mainly created based on the
Carbucicchio et al. study, where catheter ablation for the
management of ES was evaluated in detail [
]. The authors
included 95 patients with structural heart disease and electrical storm
refractory to antiarrhythmic drug therapy. At a median
followup of 22 months, ES recurred in 8% and cardiac mortality was
significantly higher in patients in whom at least one clinical
VT could not be abolished, when compared with patients after
successful CA defined as non-inducible VT in programmed
electrical stimulation. Similar findings were reported by
Nayyar et al.  in their meta-analysis of 39 publications
including a total number of 471 patients with structural and
non-structural heart disease, who underwent invasive ablation
management of ventricular arrhythmia (VA) storm with total
follow-up 61 ± 37 weeks. The odds of death were found to be
four times higher after a failed procedure, compared to those
with a successful procedure (95%CI 2.04–8.01; p < 0.001).
The value of information from our study is that it focuses on
patients with structural heart disease and with a first episode of
ES, excluding those who had already undergone previous
RFCA. Our trial provides evidence that catheter ablation is
the most effective first-line life-saving therapy for ES and
should not be used only as a bailout therapy. Interestingly,
no significant benefit of RFCA with respect to composite of
all-cause death, electrical storm recurrence and ventricular
tachycardia/ventricular fibrillation recurrence was observed
in the group treated with RFCA, compared with those in the
remaining population. We hypothesise that the observed
reduction of all-cause mortality in the RFCA group (despite lack
of statistical significance in recurrence rates) was due to
trigger and substrate modification caused by ablation. This
modification in turn might have led to different arrhythmias (with
more benign characteristics: slower and with lower burden).
We can speculate that tissue oedema, which is created during
ablation, could render a new reentrant circuit in the
surrounding myocardium responsible for creation of new non-clinical
VT (e.g. with lower cycle and burden). Indeed, our study has
shown a high rate of early VA recurrence after RFCA
procedure only within the 30 days after procedure compared with
the conservative group (7 [25%] vs. 5 [12%], p = 0.16,
respectively). On the other hand, if blanking periods were used
(30 days), the recurrence rate was 46.4% in RFCA vs. 75%
in non-ablated group; p = 0.02.
Our strong feeling has been based on the assumption that
not every early recurrence will lead to late recurrence, and as
such, it does not necessarily represent treatment failure. Lack
of late recurrences in the ablated group, but their presence in
the conservative group, might be responsible for survival
benefit (what is also reflected by progressively more divergent
with time Kaplan–Meier curves). However, this is only a
hypothesis, which has to be confirmed in further studies.
Our concept is supported by an important recent study
by Muser et al. . The authors compared the long-term
outcomes after VT ablation for ES in patients with
nonischemic dilated cardiomyopathy and ischemic
cardiomyopathy. Compared to our results, the authors reported a
lower incidence of VT recurrence (33%) in median
follow-up 45 months. This difference may be related to
the fact that in contrast to our study, they also included
patients who underwent endo-epicardial RFCA (22%).
Overall, this outcome may favourably affect long-term
outcomes of RFCA. Although VT recurred in 33% patients
after the ablation, a substantial reduction in VT burden
was observed in most of these cases. Moreover, the
majority of patients (69%) with VT recurrence had only isolated
(≤ 3 VT) episodes during the 6 months after the RFCA
The open question remains, what is the rate of clinical to
non-clinical arrhythmias among patients with recurrences and
what is the impact of non-clinical VT or of early VA
recurrence on clinical outcome?
This issue is even more interesting because, in contrast to
our study, Sapp et al. recently reported a significantly lower
rate of composite of death as the primary outcome, three or
more episodes of ventricular tachycardia within 24 h
(ventricular tachycardia storm) or appropriate ICD shock (59.1%) in
groups of patients with ventricular tachycardia, who were
randomly assigned to receive CA with continuation of baseline
antiarrhythmic medication vs. 68.5% of those in the escalated
pharmacological therapy group, p = 0.04 . There was also
no significant difference in mortality between the groups .
Their results may be explained by several reasons. The
authors only conducted their analysis with a follow-up period of
27.9 ± 17.1 months in the group of patients with ischaemic
cardiomyopathy after myocardial infarction and implanted
with ICD, and who had experienced an episode of VT within
the 6 months before enrolment. During follow-up, they
analysed only the VT episodes and appropriate ICD shock
after the 30-day treatment period. There is also lack of data
on the percentage of previous RFCA and ES, which may
reflect on their outcomes. Notably and surprising is the fact
that our study, based on multivariable Cox regression analysis,
provides the evidence that the presence of CRT-D is an
independent predictor of all-cause mortality in patients with
electrical storm. We suppose that this may be attributed to the fact
that in contrast to ICD recipients, patients who initially
demand the implantation of CRT-D are characterised by
increased severity of heart failure, and may be much more
exposed to the worsening of heart failure, resulting from
multiple high-energy therapies within a short time period.
4.1 Study limitation
The first important limitation is the relatively small sample
size. However, because of the lack of data surrounding the
efficiency of RFCA treatment in ES, our study contributes
valuable information. Secondly, although the
electrophysiologists who performed RFCA in our study were experienced in
the procedure, we cannot rule out that specialised referral
centres for endo- and epicardial RFCA could achieve better
clinical outcomes. The third limitation is that we also cannot rule
out that there might also be some preferences and intrinsic bias
among practicing clinicians who perform CA procedures (e.g.
preferring patients who are more likely to have a successful
outcome for referring to the electrophysiology lab) which may
have an influence on differences in the long-term treatment
effect of ES in ablated and non-ablative group. The fourth and
the most important limitation of our study was the
retrospective analysis of short- and long-term outcomes in patients
treated because of the occurrence of ES, and its retrospective
comparison of RFCA treatment with non-RFCA therapy, not
a controlled randomised trial comparing RFCA with other
forms of treatment ES. Therefore, our study cannot
unambiguously prove that RFCA is more effective than other
therapies to enhance survival in patients with ES.
By comparing long-time effects of ablation to other forms of
electrical storm treatment among patients with heart failure
and implanted ICD/CRT-D, who had a first episode of
electrical storm, a statistically significant reduction in terms of total
morality in the group treated with RFCA compared with those
of the remaining population was observed.
Compliance with ethical standards
Conflict of interest Author Morawski Stanislaw has received financial
support for attending cardiology congresses from Biotronik.
Author Patrycja Pruszkowska has received consultant fees from
Biotronik, Medtronic and St Jude Medical.
Author Sredniawa Beata has received consultant fees from Medtronic
Bakken Research Center and has received financial support for attending
cardiology congresses from Medtronic, St. Jude Medical, Biotronik and
Author Lenarczyk Radoslaw has received consultant fees from
Biotronik, Medtronic, St. Jude Medical, Boston Scientific and
Author Kalarus Zbigniew is a member of advisory committee:
Boehringer Ingelheim, Amgen and Astra Zeneca. He is a speaker bureau
representing the following: Pfizer, Eli Lilly, Boehringer Ingelheim,
Abbott and Bayer. He has received a financial support for attending
cardiology congresses from Adamed and St. Jude Medical.
Ethical approval All procedures performed in studies involving
human participants were in accordance with the ethical standards of the
institutional and/or national research committee and with the 1964
Helsinki declaration and its later amendments or comparable ethical
standards. For this type of study, formal consent is not required.
Informed consent Informed consent was not required
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