Initial Clinical Experience with a Remote Magnetic
Catheter Navigation System for Ablation of
Cavotricuspid Isthmus-Dependent Right Atrial Flutter
ARASH ARYA, M.D., HANS KOTTKAMP, M.D., PH.D., CHRISTOPHER PIORKOWSKI, M.D.,
ANDREAS BOLLMANN, M.D., JIN-HONG GERDES-LI, M.D., SAM RIAHI, M.D., PH.D.,
MASAHIRO ESATO, M.D., and GERHARD HINDRICKS, M.D., PH.D.
From the Department of Electrophysiology, University of Leipzig, Heart Center, Leipzig, Germany
Background: A remote magnetic navigation system (MNS) is available and has been used with a
4-mm-tip magnetic catheter for radiofrequency (RF) ablation of some supraventricular and ventricular
arrhythmias; however, it has not been evaluated for the ablation of cavotricuspid isthmus-dependent right
atrial flutter (AFL). The present study evaluates the feasibility and efficiency of this system and the newly
available 8-mm-tip magnetic catheter to perform RF ablation in patients with AFL.
Methods: Twenty-six consecutive patients (23 men, mean age 64.6 ± 9.6 years) underwent RF ablation
using a remote MNS. RF ablation was performed with an 8-mm-tip magnetic catheter (70◦ C, maximum
power 70 W, 90 seconds). The endpoint of ablation was complete bidirectional isthmus block. To assess
a possible learning curve, procedural data were compared between the first 14 (group 1) and the rest
(group 2) of the patients.
Results: The initial rhythm during ablation was AFL in 20 (19 counterclockwise and 1 clockwise) and
sinus rhythm in six patients. Due to technical issues, the ablation in the 18th patient could not be done
with the MNS, and so we switched to conventional ablation. The remote magnetic navigation and ablation
procedure was successful in 24 of the 25 (96%) remaining patients with AFL. In one patient (patient 2),
conventional catheter was used to complete the isthmus block after termination of AFL. The procedure,
preparation, ablation, and fluoroscopy times (median [range]) were 53 (30–130) minutes, 28 (10–65) minutes, 25 (12–78) minutes, and 7.5 (3.2–20.8) minutes, respectively. Patients in group 2 had shorter procedure (45 [30–70] min vs 80 [57–130] min, P = 0.0001), preparation (25 [10–30] min vs 42 [30–65] min,
P = 0.0001), ablation (20 [12–40] min vs 31 [20–78] min, P = 0.002), and fluoroscopy (7.2 [3.2–12.2] min
vs 11.0 [5.4–20.8] min, P = 0.014) times. No complication occurred during the procedure.
Conclusion: Using a remote MNS and an 8-mm-tip magnetic catheter, ablation of AFL is feasible, safe,
and effective. Our data suggest that there is a short learning curve for this procedure. (PACE 2008; 31:597–
603)
ablation, remote magnetic navigation, atrial flutter, mapping, magnetic catheter
Introduction
Conventional ablation of cavotricuspid isthmus (CTI)-dependent right atrial flutter (AFL)
is a clinically efficacious, well-established, and
widely performed procedure in electrophysiology
(EP) laboratories.1–3 Recently, a magnetic catheter
navigation system capable of remote cardiac mapping has been introduced.4–13 The feasibility study
in animals and humans showed the continuous
stability of ablation catheters using the magnetic
catheter navigation system and its applicability
for ablation of various supraventricular and ventricular arrhythmias excluding AFL.7–14 Here, we
There are no conflicts of interest.
Address for reprints: Arash Arya, M.D., Department of
Electrophysiology, University of Leipzig, Heart Center,
Strümpellstrasse 39, 04289 Leipzig, Germany. Fax: 0049-341865-1460; e-mail: dr.arasharya@gmail.com
Received October 7, 2007; revised January 7, 2008; accepted
February 11, 2008.
report the first human experience on remote magnetic navigation system (MNS) in 26 consecutive
patients undergoing ablation of AFL.
Methods
Patient Population
Between May 2007 and August 2007, a total of 26 consecutive patients (23 men, mean age
64.3 ± 9.0 years) underwent catheter ablation for
AFL at our EP laboratories using remote magnetic
navigation NIOBE II system (Stereotaxis, Inc., St.
Louis, MO, USA). In patients with sinus rhythm at
the time of ablation, typical electrocardiographic
(ECG) findings were used to confirm the diagnosis. In patients with AFL at the time of ablation,
besides ECG morphology, activation sequence and
entrainment mapping was used to confirm the
diagnosis. The study protocol was approved by
our local ethics committee. None of the patients
received antiarrhythmic medications at the time
C 2008, The Authors. Journal compilation
C 2008, Blackwell Publishing, Inc.
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Table I.
Baseline Patients’ Characteristics
Variable
Age (years)
Sex (male/female)
Structural heart disease§
Initial rhythm
Sinus rhythm
CWAFL*
CCWAFL†
Total
Group 1
Group 2
P-Value‡
64.3 ± 9.0
22/3
17 (63%)
66.0 ± 11.5
9/1
6 (60%)
63.0 ± 7.3
13/2
11 (64.7%)
0.59
0.90
0.80
6
18
1
2
8
0
4
10
1
0.35
*Clockwise cavotricuspid isthmus-dependent right atrial flutter.
† Counterclockwise cavotricuspid isthmus-dependent right atrial flutter.
‡ Comparison between groups 1 and 2.
§ Including coronary heart disease, hypertension and hypertensive heart disease, and left ventricular dysfunction. No patient had
structural lung disease.
of ablation procedure, and in cases who received
them, it was discontinued at least five half-lives
before the ablation procedure. Table I shows the
baseline characteristics of the patients. To assess
the possible effect of a learning curve on the procedure outcome, we divided the patients into two
groups. Due to technical issues (failure to move
the magnets from parking position), the ablation
procedure in the 18th patient could not be done
with remote MNS, and so, we switched to conventional ablation. This patient was excluded from the
study.
Remote MNS
The remote MNS consists of two permanent magnets which generate a uniform magnetic field (0.08 T) and are computer-controlled
and located on either side of the patient’s
body.13 The MNS consists of two components: the
Niobe Stereotaxis MNS (Stereotaxis, Inc.) and an
electroanatomical mapping system (CARTO-RMT;
Biosense Webster, Inc., Diamond Bar, CA, USA).
The CARTO-RMT system is similar to the standard CARTO system, but is able to localize the
ablation catheter without interference from the
magnetic field. The CARTO-RMT system sends
catheter-tip location and orientation data to Stereotaxis system. It also sends target locations, points,
and anatomical geometrical information from the
reconstructed map to the MNS. The real-time
catheter-tip location is displayed on the x-ray images, enabling continuous real-time monitoring of
the catheter-tip position even without acquiring a
fresh x-ray image.4,11 The operator is in a separate
control room, at a distance from the x-ray beam.
The details of the remote magnetic-guided navigation are described elsewhere.11–13
598
Catheter Ablation Procedure
All patients gave written informed consent.
The EP study and ablation procedure were performed with the patients in a fasting, nonsedated
state. All the ablation procedures were performed
by two authors (AA: 22 and JH-GL: 3). Before starting the ablation, the patients received fentanyl.
A quadripolar steerable catheter (Inquiry; Irvine
Biomedical, Inc., St. Jude Medical, Irvine, CA,
USA) and a decapolar steerable catheter (Inquiry;
Irvine Biomedical, Inc.) were placed in the right
ventricular apex and the coronary sinus, respectively. A long 8-F sheath (SR0; St. Jude Medical,
Minnetonka, MN, USA) was then placed at the
juncture of the inferior vena cava and the right
atrium through which an 8-mm-tip flexible magnetic catheter (NaviStar-RMT DS; Biosense Webster, Inc.) was advanced to the mid-right atrium.
There are small permanent magnets in the tip and
the distal portion of the catheter that enable it
to be deflected in the desired direction and be
guided by the MNS. The forward and backward
movement of the catheter was controlled by a mechanical device (Cardiodrive , Stereotaxis, Inc.).
In addition to Cardiodrive, the navigation of the
catheter was controlled by magnetic field vectors.
The Stereotaxis workstation (Navigant , Stereotaxis, Inc.) permits accurate positional changes of
the catheter by 1◦ increments and advancement or
retraction by 1-mm steps.
Using Cardiodrive and the magnetic field presaved vectors, the catheter was initially positioned
at the tricuspidal annulus in 12 o’clock position.
At the second step, using the presaved magnetic
field vectors, the catheter was positioned at tricuspidal annulus (6 o’clock position). To maximize
the catheter contact and pressure, the magnetic
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REMOTE MAGNETIC ABLATION OF AFL
Figure 1. The figure shows our approach to catheter positioning on isthmus. The upper panels
show the fluoroscopy image and the lower ones show the corresponding magnet vectors in Stereotaxis. TA = tricuspidal annulus; CS = coronary sinus; RAO = right anterior oblique; LAO = left
anterior oblique.
field vector was then oriented inferiorly and posteriorly (Fig. 1). At this point, the navigation success was judged by a combination of electrogram
and fluoroscopic images analysis.1–3 Stable contact was judged based on fluoroscopic image, electrogram stability, and the position of the catheter
on the CARTO-RMT system. The x-ray imaging
angles were limited to approximately 38–42◦ left
anterior oblique and 10–12◦ right anterior oblique.
Ablation of the CTI was performed using 90second radiofrequency (RF) application with a target temperature of 70◦ C and a power limit of 70 W.
Ablation lines were performed by sequentially
navigating to contiguous points after termination
of each RF application. The RF endpoint was complete bidirectional isthmus block. After completing the first line of lesions, we carefully remapped
all the ablation lines during coronary sinus (CS)
and lateral pacing to control for double potentials and conduction times. The double potentials
along the ablation line should have been at least
100 ms apart. And, the activation mapping with
ablation catheter should have confirmed the complete block. In cases of incomplete lesion lines,
gaps were identified based on the activation times
and double potentials along the ablation line, and
RF energy was then, specifically, applied to the
identified gaps, as previously described.1–3 The detailed method for the ablation of AFL at our laboratory is described elsewhere.3
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Statistical Analysis
Continuous variables are expressed as median
with range values and compared using the MannWhitney U-test. For categorical variables, the χ 2
test (or the exact Fisher test when applicable)
was performed. Statistical tests were performed
with SPSS for Windows (version 13.0, SPSS, Inc.,
Chicago, IL, USA).
Results
Remote Catheter Mapping and Ablation
Twenty-five patients had counterclockwise
and one patient had clockwise AFL (Table II). In
the 18th patient, the ablation procedure could not
be performed for technical issues (the magnets
could not be moved from the parking position),
and so, we switched to the conventional ablation
technique. The total procedure time was 53 (30–
130) minutes. The preparation time, including
puncture, catheter placement, setting up the
remote navigation system, and CARTO-RMT, was
28 (10–65) minutes. The ablation phase duration
was 25 (10–30) minutes. We were able to obtain an
optimum contact (assessed by Navigant Contact
Bar) and stable catheter position on CTI using the
remote magnetic navigation and Cardiodrive in
all of our twenty-five patients (Fig. 2). The AFL
was terminated during the ablation in all patients.
After termination of the AFL, the line of block was
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ARYA, ET AL.
Table II.
Results of the Remote-Guided Catheter Ablation
Variable
Tachycardia CL (ms)*
Procedure time (minutes)
Preparation time (minutes)†
Ablation time (minutes)
RF time (seconds)§
Fluoroscopy time (minutes)¶
Termination of AFL (%)‡
Successful isthmus block (%)
Total
Group 1
Group 2
P-Value**
230 (200–260)
53 (30–130)
28 (10–65)
25 (12–78)
614 (262–1,728)
7.5 (3.2–20.8)
100
96
230 (205–260)
80 (57–130)
42 (30–65)
31 (20–78)
628 (405–1,547)
11 (5.4–20.8)
100
90
228 (200–245)
45 (30–70)
25 (10–30)
20 (12–40)
613 (262–1,728)
7.2 (3.2–12.2)
100
100
0.84
0.0001
0.0001
0.002
0.313
0.014
–
0.92
*Cycle length.
†Preparation time consist of the total time that was required for puncture, catheter placements, and preparation of magnetic navigation
system and CARTO-RMT.
‡Isthmus-dependent right atrial flutter.
§Radiofrequency.
¶MGycm2 /s.
**Comparison between groups 1 and 2.
complete in nine patients (three in group 1 and six
in group 2), and further ablation was required to
complete the linear block along the CTI. In group
1, we switched to conventional ablation in order
to complete the isthmus block in one patient (second patient) as repeated RF energy applications
were not able to complete the isthmus block. In
this patient, further ablation using an irrigated-tip
catheter together with a steerable sheath (Agilis ;
St. Jude Medical, Inc.) resulted in complete isthmus block. No major complication occurred during the procedure. Significant charring on the
ablation catheter was observed in five (19.2%)
patients.
Effect of Learning Curve
Figure 2. Projection of the anatomical location of the
ablation line reconstructed in CARTO-RMT on fluoroscopy images. The red dots show the projection of
ablation lesions imported from CARTO-RMT on the fluoroscopy image in Stereotaxis workstation. The white
arrow shows the position of the tip of the ablation
catheter projected from CARTO-RMT on fluoroscopy image. The yellow and the green arrows show the system and the desired magnetic vectors, respectively.
RAO = right anterior oblique; LAO = left anterior
oblique; ABL = Ablation catheter; CS = coronary
sinus.
600
In order to compare the possible effect of
learning curve on the procedure outcome, we compared the procedure data between the first 10 and
the last 15 patients (Table II). Compared to the first
group, patients in group 2 had shorter procedure
(45 [30–70] min vs 80 [57–130] min, P = 0.0001),
preparation (25 [10–30] min vs 42 [30–65] min,
P = 0.0001), ablation (20 [12–40] min vs 31 [20–
78] min, P = 0.002), and fluoroscopy (7.2 [3.2–12.2]
min vs 11.0 [5.4–20.8] min, P = 0.014) times. With
respect to RF ablation time, there was no significant difference between the two groups (Table II).
Comparison with Historical Control Group
Although our study was not randomized, to
assess the possible effect of the remote magnetic
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REMOTE MAGNETIC ABLATION OF AFL
navigation on the procedure and the fluoroscopy
times, we compared these times between procedures performed by remote magnetic navigation
and 40 CTI-dependent AFL ablation performed directly before (n = 20) and after (n = 20) the study
period with comparable baseline characteristics to
our patients. With respect to the fluoroscopy time,
there was no difference in the first and second
parts of the control group (P = 0.45). The fluoroscopy times in the study and the historical control group were 7.5 (3.2–28.0) and 14.3 (4.0–45.3)
minutes, respectively (P < 0.0001). However, the
total procedure time was not different between the
two groups (45 [30–110] min vs 53 [30–130] min,
P = 0.12).
Discussion
Main Findings
To the best of our knowledge, this is the first
study of a remote magnetic catheter navigation system with the use of the new 8-mm-tip magnetic
catheter for ablation of AFL in humans. Our results
indicate that (1) the remote magnetic catheter navigation is able to obtain an optimum contact and
stable catheter position on CTI (Fig. 2); (2) using
the 8-mm-tip catheter remote magnetic catheter,
navigation and ablation of AFL is feasible, safe,
and effective; and (3) there is a short learning curve
for using this system for the ablation of AFL, and
therefore, operating the system would be easy to
learn.
Previous Studies
To the best of our knowledge, there are no
published data on the remote magnetic catheter
navigation for the ablation of AFL using the 8-mmtip magnetic catheter in humans. Previous studies assess the efficacy of this remote MNS for the
ablation of various arrhythmias using a 4-mm-tip
catheter.4–15
Ernst et al. performed RF catheter ablation using the remote MNS in 42 consecutive patients
with atrioventricular nodal reentrant tachycardia.13 Using a 4-mm-tip magnetic catheter (55◦ C,
maximum power 40 W, 60 seconds), the ablation
procedure was successful in all patients. Slow
pathway ablation and modification were achieved
in 15 and 27 patients, respectively. There were no
complications.
Pappone et al. assessed the feasibility of remote magnetic catheter navigation in patients with
atrial fibrillation undergoing circumferential pulmonary vein ablation.11 Ablation was done with
a 4-mm-tip magnetic catheter (65◦ C, maximum
power 50 W, 15 seconds) and the remote ablation
was successful in 38 of 40 patients without complications. Di Biase et al. have recently assessed
PACE, Vol. 31
the efficacy of remote magnetic navigation in 45
consecutive patients with atrial fibrillation.15 The
ablation endpoint was complete electrical isolation of all pulmonary veins. During the ablation,
using MNS, the pulmonary veins were isolated
in only 8% of the patients. After switching to
the conventional approach with thermocool ablation catheter, the authors were able to isolate
all the pulmonary veins in 22 (49%) patients. In
23 (51%) patients, only the right pulmonary veins
were isolated. They reported significant charring
on the catheter in 33% of the patients. After a mean
follow-up of 11 ± 2 months, 25 patients (56%) had
atrial fibrillation recurrence.
Aryana et al. reported the results of ablation
of ischemic ventricular tachycardia in 24 consecutive patients with 77 inducible ventricular tachycardias. Among 21 tachycardias that were targeted
with MNS (4-mm-tip catheter), 81% were successfully ablated, and in the remaining patients, conventional ablation with an irrigated-tip catheter
was required to complete the ablation procedure.
In the conventional ablation arm of the study, the
success rate of the ablation was 97% (irrigatedtip catheter). Although the success rate of the
ablation in this study was lower than the conventional group, it is worth mentioning that different catheter types have been used in these two
groups.4
The cumulative success rate in our patients
was 95% (Table II), which is comparable to other
published studies.3,16–19 Kottkamp et al. studied
50 patients with AFL and assessed the efficacy
of RF catheter ablation. Overall, complete bidirectional isthmus block was achieved in 47 of
50 patients (94%).3 Sacher et al. have recently
in a prospective, randomized study compared the
clinical efficacy of an 8-mm gold-tip, externally
irrigated-tip, and an 8-mm platinum-iridium-tip
catheters. The complete bidirectional isthmus
block was achieved equally with the three different
catheters (95% for both 8-mm-tip catheters, 100%
for irrigated-tip catheter, P = NS).16
Safety
No major complication occurred in our patients. One patient experienced a hematoma in
the left groin. Echocardiography after the ablation
was done in all patients and showed no pericardial effusion. Previous studies have also confirmed
the safety of the remote MNS, and to the best of
our knowledge, no perforation and tamponade has
been reported using this system so far.4–13
Learning Curve
Our data suggested that there is a learning
curve using the MNS (Fig. 3). Previous studies
have also showed the presence of such a learning
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ARYA, ET AL.
Figure 3. Panels A through D show the procedure, preparation, fluoroscopy, and ablation times
of our patients (see text for detailed discussion).
curve using this system for ablation of other arrhythmias.11 Our data showed that although the
ablation phase duration was shorter in group 2,
the RF ablation time was not statistically different
between the two groups. It shows that by doing
more procedures the operators needed less time to
achieve optimum contact and stable catheter position on CTI (Fig. 2).
Limitations
This study was conducted to assess the acute
results of RF catheter ablation using remote MNS
and an 8-mm-tip magnetic catheter. Therefore, no
comment on the long-term outcome of this system
for the ablation of AFL can be made. No randomized control group is included in our study; however, the aim of our study was just to assess the
feasibility and efficacy of the remote MNS for the
ablation of AFL using the newly available 8-mmtip magnetic catheter. However, comparison with
matched historical controls at our EP laboratory
suggested that the remote magnetic navigation and
ablation might reduce the fluoroscopy time; however, this finding should be verified in a randomized study. We did not define the anatomy of the
CTI before the ablation procedure; therefore, we
cannot comment on the potential applicability of
602
this system in such difficult cases. Finally, we did
not use Hallo catheter to confirm the bidirectional
isthmus block and this might have overestimated
our success rate.20 However, our long-term success in these patients ablated at our center is 93%,
which is comparable to the published series.
Conclusion
In conclusion, our study showed that when
using the remote MNS and the 8-mm-tip catheter,
the ablation procedure of AFL is safe, feasible,
and effective. The bidirectional isthmus block was
achieved in 96% of the patients, which is comparable with the recently published patient series using conventional approaches for the ablation of AFL.3,16–19 Considering the effect of learning curve on the fluoroscopy times and its comparison with the abovementioned published studies
and our historical control group, this system could
reduce the radiation exposure to the patients, and
especially, operators, while the efficacy of the ablation procedure is comparable to other conventional methods.
Acknowledgment: The authors want to thank the nursing
and technical staff at our department. Without their dedicated
work, this study would not have been possible in the presented
way.
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REMOTE MAGNETIC ABLATION OF AFL
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