The magnetic navigation system allows safety and high efficacy for ablation of arrhythmias
The magnetic navigation system allows safety and high efficacy for ablation of arrhythmias
Tamas Bauernfeind 0
Ferdi Akca 0
Bruno Schwagten 0
Natasja de Groot 0
Yves Van Belle 0
Suzanne Valk 0
Barbara Ujvari 0
Luc Jordaens 0
Tamas Szili-Torok 0
0 Department of Cardiology, Thoraxcenter, Clinical Electrophysiology, Erasmus MC , Postbus 2040, S Gravendijkwal 230, Kamer BD416, 3000 CA Rotterdam , The Netherlands
Aims We aimed to evaluate the safety and long-term efficacy of the magnetic navigation system (MNS) in a large number of patients. The MNS has the potential for improving safety and efficacy based on atraumatic catheter design and superior navigation capabilities. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods In this study, 610 consecutive patients underwent ablation. Patients were divided into two age- and sex-matched and results groups. Ablations were performed either using MNS (group MNS, 292) or conventional manual ablation [group manual navigation (MAN), 318]. The following parameters were analysed: acute success rate, fluoroscopy time, procedure time, complications [major: pericardial tamponade, permanent atrioventricular (AV) block, major bleeding, and death; minor: minor bleeding and temporary AV block]. Recurrence rate was assessed during follow-up (15 + 9.5 months). Subgroup analysis was performed for the following groups: atrial fibrillation, isthmus dependent and atypical atrial flutter, atrial tachycardia, AV nodal re-entrant tachycardia, circus movement tachycardia, and ventricular tachycardia (VT). Magnetic navigation system was associated with less major complications (0.34 vs. 3.2%, P ¼ 0.01). The total numbers of complications were lower in group MNS (4.5 vs. 10%, P ¼ 0.005). Magnetic navigation system was equally effective as MAN in acute success rate for overall groups (92 vs. 94%, P ¼ ns). Magnetic navigation system was more successful for VTs (93 vs. 72%, P , 0.05). Less fluoroscopy was used in group MNS (30 + 20 vs. 35 + 25 min, P , 0.01). There were no differences in procedure times and recurrence rates for the overall groups (168 + 67 vs. 159 + 75 min, P ¼ ns; 14 vs. 11%, P ¼ ns; respectively). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusions Our data suggest that the use of MNS improves safety without compromising efficiency of ablations. Magnetic navigation system is more effective than manual ablation for VTs. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Catheter ablation was introduced in clinical electrophysiology (EP)
in the 1980s.1,2 In past decades, it became well established as
firstline therapy for many types of arrhythmias, including
atrioventricular (AV) nodal re-entrant tachycardia (AVNRT), circus movement
tachycardia (CMT), and cavotricuspid isthmus (CTI)-dependent
atrial flutter (AFl), and as therapeutic option for the treatment
of atrial fibrillation (AFib), atrial tachycardia (AT), and ventricular
tachycardia (VT).3 Further developments were implemented such
as electroanatomical mapping, integration of cardiac imaging, and
improved catheter design.4,5 Until recently, all of the
abovementioned techniques were based on manual catheter navigation
in the heart. The innovation of the remote magnetic navigation
system (MNS) offered important theoretical advantages in safety
due to the atraumatic catheter design and less physical stress
and radiation exposure for the physician.6 – 11 Higher efficacy is
also expected due to the unrestricted and reproducible catheter
movement, and improved catheter stability.8,11 – 13 Numerous
centres reported their initial experiences with MNS confirming
its feasibility for ablation of most arrhythmias.14 – 23 However,
these early reports included only small numbers of patients, the
follow-up periods were short, and they failed to demonstrate
superiority of MNS in safety and efficacy.
The objective of the present study was to evaluate the safety
and long-term efficacy of MNS as compared with conventional
manual ablation techniques in a large number of patients with
consistent technique and workflow.
This study is an ongoing registry of the procedures performed in our
clinic. Six hundred and ten consecutive patients underwent ablation
from January 2008 to March 2010. All patients scheduled for EP
study and ablation were distributed from the waiting list based on
availability to the MNS-equipped or the conventional EP laboratory.
Accordingly, ablation was performed either using MNS (group MNS,
292 patients, age 48 + 19 years, 166 males) or using conventional
manual ablation (group MAN, 318 patients, age 52 + 16 year, 197
males). The procedures were performed over the entire study
duration by the same senior electrophysiologist group with the assistance
of four fellows, trained for manual catheter navigation and for MNS as
well. The attending physicians performed MNS and MAN procedures
in equal distribution.
Written, informed consent for the ablation procedure was obtained
from all patients. Resting 12-lead electrocardiogram (ECG), and
laboratory tests, an X-ray thorax image, and a two-dimensional
echocardiography were acquired from all patients within 1 month before and
within 48 h following the procedure.
Local peri-procedural medication protocols were followed in all
patients. In short, AVNRT, CMT, AT, and elective VT patients were
instructed to stop taking antiarrhythmic drugs for a period of at least
four half-lives prior undergoing the procedure. In cases of AFib, AV
junction (AVJ) and emergency VT ablation medication remained
unchanged. The procedures were performed during a fasting state,
using local or general anaesthesia. Market-approved diagnostic and
ablation catheters were used as clinically required at the discretion
of the operator. The left heart could be accessed via the retrograde
aortic route or transseptal puncture (TSP) based on the operator’s
preference. Generally, left-sided ventricular arrhythmias were
performed via the retrograde approach (MNS 93%, MAN 89%; P ¼ ns),
left-sided atrial arrhythmias always via TSP, and left-sided accessory
pathways distributed between the two methods (MNS 22% TSP,
group MAN 20% TSP; P ¼ ns). The use of three-dimensional
mapping system was allowed in both groups if necessary. Intracardiac
echocardiography (ICE) was used to guide TSPs in both groups.
Crossover from the magnetic navigation catheter to manual
navigation catheter was allowed at the discretion of the investigator, although
the crossover counted as an acute failure for the MNS group.
Crossover from the MAN to the MNS group was not possible due to
logistical reasons (see below).
The endpoints of procedural success were defined as the
elimination of accessory pathway conduction for CMT, the elimination of
inducibility and no more than single echo beats for AVNRT, complete
AV block for AVJ ablation, bi-directional isthmus block for
CTIdependent AFl, and complete electrical pulmonary vein isolation for
AFib. For VT patients; if the VT was inducible, non-inducibility was
the endpoint, if only ventricular extrasystoles (VES) were present,
then the complete abolishment of VES assessed by 24 h telemetry
counted as acute success. The presence of a pacemaker (PM) or an
implantable cardioverter defibrillator (ICD) was not considered as
contraindication for MNS-guided ablations.
According to an institutional protocol for the treatment of patients
with AFib, all paroxysmal AFib patients were ablated using the
cryoballoon technique, the persistent AFib patients were ablated using
cryoballoon or MNS, and all long-standing persistent (.12 months) AFib
patients were ablated using MNS. Persistent and long-standing
persistent AFib procedures included additional linear ablation in the left and/
or right atrium. Whenever linear ablation was performed, conduction
block was mandatory to be proven. Regardless of the type of AFib
patients pulmonary vein isolation was mandatory in all patients. This
was always controlled by a ‘lasso-type’ catheter. Also, atypical AFl
and AT patients were ablated generally using MNS (50 of 56, 89%).
Magnetic navigation system-guided ablations
The procedures were performed in group MNS using the Stereotaxis
Niobe II (Stereotaxis, Inc., St Louis, MO, USA) implemented in an EP
lab equipped with a Siemens Axiom Artis (Siemens, Erlangen,
Germany) fluoroscopy system. The following ablation catheters were
used: for AVNRT, CMT and AVJ Celsius RMT (4 mm) (Biosense
Webster, Diamond Bar, CA, USA), and for AFib NaviStar RMT
ThermoCool (Biosense Webster), AFl/AT and VT Navistar RMT DS
(8 mm), NaviStar RMT ThermoCool (Biosense Webster), or
Trignum Flux Gold-tip (Biotronik GMBH, Berlin, Germany). The use
of an 8 mm tip RMT catheter was associated with a char formation
in some patients. Therefore, after the thermocool RMT catheter
became available the 8 mm tip catheter was no longer used.
When needed, electroanatomical mapping was performed using the
CARTO RMT (Biosense Webster) system.
The procedures in the MAN group took place in an EP lab equipped
with a Siemens Megalix (Siemens) fluoroscopy system.
Electroanatomical mapping was performed using CARTO (Biosense Webster) or
EnSite (St Jude Medical Inc., St Paul, MN, USA) system. The following
ablation catheters were used: for AVNRT, CMT, and AVJ Biosense
Webster B – D curve 4 or 8 mm tip (Biosense Webster), for AFib,
AFl/AT, and VT Biosense Webster Navistar ThermoCool (Biosense
Webster). The Artic Front cryoballoon catheters (Medtronic Inc.,
Minneapolis, MN, USA) were used for cryo-isolation of the pulmonary
veins; Freezor Max (Medtronic Inc.) catheters were used in cases
when complete electrical isolation could not be achieved with the
Data collection and analysis
The following parameters were analysed both in group MNS and group
MAN: acute success rate, fluoroscopy time, procedure time, and
complications. Acute success rate was assessed according to the terms
mentioned above. Fluoroscopy time and procedure time (latter
began with subcutaneous injection application of lidocaine by the
physician to the groin and ended when catheters were removed from the
patient’s body) were recorded in the clinical procedure log and
included a 30 min waiting time. Any adverse event recognized by the
operator during the procedure, by the attending cardiologist prior to
hospital discharge, or by the general physician during follow-up was
investigated by a trained electrophysiologist, and was considered as a
complication if the event could be related to the procedure.
Complications were categorized as major and minor [major: pericardial
effusion or/and tamponade, permanent AV block, stroke, major bleeding
(requiring blood transfusion or haemoglobin serum level drop of
.20 g/L) or death; minor: minor bleeding, transient ischaemic attack,
and temporary AV block].
Subgroup analysis of the above-mentioned parameters was
performed for the following groups: AFib, AFl, atypical AFL (aAFl)/AT,
AVNRT, CMT, AVJ, and VT. The AFib group was further divided into
the following subgroups: paroxysmal, persistent, and long-standing
persistent. Because different techniques were used for the treatment of
paroxysmal and long-standing persistent AFib patients, paroxysmal
and long-standing persistent AFib subgroups were not compared in
efficacy; however, data from these groups were included into the
safety comparison (Tables 1 and 2). Patients included into the
persistent AFib group were comparable (Tables 1 and 2). The VT group was
further analysed in subgroups of patients with and without structural
heart disease (SHD and NSHD).
Follow-up visits were scheduled for all patients at the outpatient clinic
of the Department of Cardiology, Erasmus MC 3 months following the
procedure, and every 3 months thereafter, except for CMT, AFl, and
AVNRT patients, when other than the first follow-up visit was
scheduled only if the symptoms recurred. Atrial fibrillation patients were
more rigorously followed at the AFib clinic of the department,
including daily transtelephonic rhythm strips.
Parameters obtained from the registry were analysed using SPSS 15.0
(SPSS Inc., Chicago, IL, USA). Patient demographic and baseline
characteristics were presented as mean + SD. The two-tailed Student’s t-test
was used for comparing continuous unpaired samples, assuming
unequal variances (age, fluoroscopy time, procedure time, and
follow-up period). For categorical variables the x 2 test was performed
(number of patients with different arrhythmias, gender, success rate,
recurrence rate, and number of complications). Two-sided P values
,0.05 were considered significant.
There were no differences in the gender and age between group
MNS and MAN (Table 1). There were no differences in the
number of patients enrolled into the subgroups based on the
diagnosed arrhythmias, except for the subgroups mentioned in the
Methods section—paroxysmal and long-standing persistent AFib
and AFL/AT (Table 1). There was no difference in the presence
of PMs or ICDs between the study groups (PM: 4 MNS vs. 6
MAN, P ¼ NS; ICD 20 MNS vs. 21 MAN, P ¼ NS). In, two patients
(both in the VT group, both had abdominal implant) the ICD
switched to magnet mode (asynchronous pacing). None of these
patients were PM dependent; therefore, temporary programming
allowed electro-anatomical mapping without further problems.
No long-term effect on ICD or PM function was observed.
Magnetic navigation system was equally effective as MAN in acute
success rate for the overall groups (Table 2). In the subgroups only
VT results were different, where MNS was more successful
(Table 2). The success rate in the NSHD-VT subgroup was
higher in MNS group, whereas the difference in VT subgroup
with SHD did not reach statistical significance (Table 2). For the
other subgroups no differences were observed in success rates
Crossovers occurred only before the availability of irrigated tip
MNS catheters, whereas one CMT patient and two AFl patients
underwent crossover from MNS catheters (4 mm for CMT,
8 mm for AFl) to manual guided irrigation tip catheters. Following
the crossover all the three patients were ablated successfully.
However, the MNS still proved to be non-inferior for the ablation
of AFl and CMT. Overall, less fluoroscopy was used in group MNS
(Table 3). In the AVNRT and VT subgroups, less fluoroscopy was
used in group MNS, otherwise there were no differences
between the two groups (Table 3). There were no differences in
procedure times between group MNS and MAN. Concerning
subgroups, procedure times were higher using MNS in AFl, but were
shorter in the VT subgroup.
The use of MNS was associated with a lower complication rate (4.5
vs. 10%; P ¼ 0.005). Moreover, concerning major complications
the difference was also significant between the two groups (0.34
vs. 3.2%; P ¼ 0.01). One permanent AV block occurred in the
MNS, magnetic navigation system; MAN, manual navigation; AFib, atrial fibrillation; AFl, cavotricuspid isthmus-dependent atrial flutter; aAFl, atypical atrial flutter; AT, atrial
tachycardia; AVNRT, atrioventicular nodal re-entrant tachycardia; CMT, circus movement tachycardia; AVJ, atrioventricular junction; VT, ventricular tachycardia; SHD, structural
heart disease; NSHD, non-structural heart disease; na, not applicable.
P values listed were calculated based on a two-sample t-test assuming unequal variances between group MNS and group MAN.
There were no differences in follow-up periods between group
MNS and MAN (15 + 9.5 vs. 14 + 9.5 months, P ¼ ns). There
were no differences in recurrence rates between group MNS
and MAN in overall (14 vs. 11%, P ¼ ns) or in any of the subgroups
[(AFib persistent 14 vs. 19%) (AFib paroxysmal — vs. 16%) (AFib
long-standing persistent 33 vs. 0%) (aAFL/AT 14 vs. 25%) (AFl 13
vs. 11%) (AVNRT 6.9 vs. 7.4%) (CMT 7.7 vs. 5.2%) (AVJ 0 vs. 0%)
(VT 14vs. 14%), P ¼ ns].
This is the first study that assesses the efficacy and safety of
ablations using MNS vs. manual navigation involving statistically
equivalent, large-scaled patient groups. Our series includes all types of
arrhythmias, arising from all four heart chambers. There are
three major findings of this study. First, MNS proved to be equal
to manual ablation not only in acute success rate, but for a
reasonable follow-up period in a broader aspect of arrhythmias. Second,
MNS was superior in safety as compared with manual navigation
resulting in lower number of complications as well as less
fluoroscopy times. Third, MNS was found to be better for the ablation
Rationale of using MNS for ablations
The success of catheter ablation procedures depends on accurate
substrate location, followed by optimal delivery of energy provided
by good tissue contact.24 Manual navigation of catheters in the
human heart has limitations: some regions are difficult to reach,
and compromised catheter positioning may result in insufficient
lesion formation.13,24 Catheter movement in some positions is
accompanied by the risk of major complications, including
pericardial effusion or tamponade.7,24 Although several pre-defined
catheter curves were introduced to help appropriate lesion delivery,
there are no optimal curves available for the treatment of
paediatric patients with small hearts, patients with complex congenital
heart defects, or some type of VTs.25 The introduction and
utilization of MNS was aimed at surmounting these difficulties. It
provides improvement of safety by the flexible catheter design, and
no pericardial effusion or tamponade was reported related to
catheter navigation using MNS.20 Magnetic navigation system also
provides better navigation capability, which is not limited by
preformed or evolved catheter curves.19,25,26 Theoretically,
nonfluoroscopic imaging and recently built-in automated functions
(AutoMap, stored magnetic vectors) allow less fluoroscopy time
(to both operator and patient).18 Stored magnetic vectors also
make it possible to re-navigate to spots defined and stored
during the procedure.26 Promising initial results were published
concerning these above-mentioned issues.22,23,25,27 In our
experience, automated map function was used in all AFib, aAFl/AT and
VT patients undergoing MNS ablation. Manual correction was
performed after automated mapping, which could be completed
in 5 – 6 min on average.
Acute success rates and recurrences
Based on the theoretical advantages mentioned above, MNS could
be superior to manual navigation in the analysed parameters.
Reports until now focused more on feasibility rather than
assessment of efficacy of MNS.10,11,15,17,23,25 – 30 Contrary to this, we
aimed at comparing large groups of patients treated using MNS
or MAN, with a long follow-up period. We confirm that MNS is
feasible for ablation of different kinds of arrhythmias, and clearly
demonstrate that it provides better safety and uses less
fluoroscopy than manual navigation (see below). Furthermore,
superiority in acute success rate can be achieved in the VT subgroup (see
Certainly, some issues are still to be solved that may play a role
in limiting of MNS. The delivered contact force is unknown relative
to manual catheters in which it had been shown to affect adequate
lesion formation. However, based on the high acute success and
low recurrence rates found in all subgroups during the reasonably
long follow-up period, it does not seem to effect patient outcomes.
Preparation of the system consumes considerable time
(isocentering, registration, merging with CARTO, checking magnet
movement). However, it does not result in significant prolongation of
the procedures in overall. Although improvements were made
recently, we also lack of fully automated functions (no need or
automated isocentering; reliable, well-defined automapping) yet.
In our series, we encountered only three patients, where
crossover to manual navigation became necessary (one CMT and two
AFl patients). Although the endpoint could be reached using
manual navigation in all three cases, no difference was found in
general between MNS and MAN concerning the acute success
rates in these subgroups. Also, it is important to notice that
these crossovers happened before the availability of irrigation tip
catheters for MNS.
Safety of ablations
The use of atraumatic, flexible designed ablation catheters
combined with magnetic field-guided navigation resulted in significantly
reduced number of complications. No pericardial effusion or
tamponade was observed in the MNS group, whereas in the MAN
group these proved to be the most frequent major complications.
All TSPs were guided by ICE, and none of these complications
were related to them. This finding is consistent with previous
reports, but these reports failed to substantiate it with significant
statistical difference. Two atrioventricular blocks (AVB) occurred
in the MSN group (one in a patient with parahisian AT; the risk
was discussed with the patient after the diagnosis of the
tachycardia was established. The other AVB occurred in a patient with
AVNRT during an application near the ostium of the coronary
sinus. In this case, our hypothesis is either an ectopic fast
pathway or the occlusion of the AVN artery).
Concerning minor complications—dominantly minor bleeding
related to the femoral punctures, we also found somewhat
higher number in the MAN group, which could be explained by
the greater diameter of sheaths used for manual ablation such as
cryoballoon sheaths and decreased movement of the sheath at
the puncture site during remote catheter manipulation.
The high manoeuvrability and atraumatic design of the
MNS-guided ablation catheter allows navigation without constant
fluoroscopy control, while re-imaging is typically required after
each repositioning of the manual-guided catheter.18 Furthermore,
stored MNS vectors also help to navigate the catheter without
repeated fluoroscopic pulses.
As we mentioned in the Methods section, our clinic is an
academic centre, and the fellows are taking part of the procedures,
including femoral vein and artery punctures, and diagnostic
catheter positioning. This significantly influences fluoroscopy or
procedure times, and minor complication rates in both groups.
Although our data may seem too high at first glance concerning
these parameters, they are not really deviated from recently
published available data.31
Transseptal puncture or retrograde aortic approach
In our centre, standard approach for left-sided VT is retrograde
aortic ablation. Also, in case of left-sided accessory pathway the
retrograde aortic approach is preferred. In our experience, this
method helps to avoid the chance for serious complications
(pericardial effusion/tamponade) and/or the need for expensive
diagnostic tools (ICE).
Ablation of ventricular tachycardia
This is the first large-scale study to prove the superiority of MNS
for ablation of VT compared with manual navigation. This is
demonstrated in most of the analysed parameters, such as acute
success rate, and procedure and fluoroscopy times. There are
multiple reasons to explain this finding. The MNS-guided catheter
retains its manoeuvrability even in difficult positions, e.g. in
cusp-related VTs, papillary muscle-originated VTs, where the
capabilities of manual navigation are seriously limited by the multiple
curves of the catheter.11 The MNS controls the tip of the catheter,
which means that the unavoidable curves of the catheter do not
hinder the positioning of the tip, and good contact can be achieved,
resulting in appropriate lesion formation.13 An MNS-guided
catheter has no pre-defined curve, which also contributes to the
high manoeuvrability. Moreover, catheter stability using MNS is
improved due to the constant magnetic force directing the tip
unchanged during application.13 The above-mentioned capabilities
are especially beneficial for patients in whom the arrhythmia
substrate is located in a difficult position (i.e. posteroseptal wall in the
right or left ventricular outflow tract) or where stability is the
major issue (i.e. papillary muscle VTs). Two patients had papillary
muscle-originated VT, and five patients had aortic cusp VT in the
MNS group, all the seven patients were ablated successfully.
This can explain the difference in success rates between the VT
subgroups, whereas statistical significance could be only proven for
the NSHD-VT subgroup.
Limitations of the study
Although this registry is not a randomized, prospective trial, there
was not any difference between the two groups and the
assignment of the patients to the groups was independent of the
operators. However, because of local protocols for the treatment of
AFib patients, there were no paroxysmal patients treated with
the MNS, and there were no long-standing persistent AFib patients
treated manually. This means that only persistent AFib subgroups
were comparable, and these groups were not different indeed.
In conclusion, the MNS is equal in terms of acute and long-term
success rates compared with MAN, whereas MNS-guided procedures
can be performed with a lower complication rate and using less
fluoroscopy. For the ablation of VT, MNS is superior to MAN.
Conflict of interest: Tamas Szili-Torok is a consultant of
Stereotaxis Inc., St Louis, MO, USA.
Funding to pay for the Open Access publication charges was provided
by Erasmus MC, Rotterdam, the Netherlands.
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