TECHNICAL ISSUES
Europace (2012) 14, 1054–1059
doi:10.1093/eupace/eur417
In vitro tests of electromagnetic interference of
electromagnetic navigational bronchoscopy to
implantable cardioverter defibrillators
Andrea Magnani 1, Roberta Matheoud 2, Marco Brambilla 2*, Serena Valzano 2,
Eraldo Occhetta 1, Paolo Marino 1, and Piero Balbo 3
1
Department of Cardiology, University Hospital ‘Maggiore della Carità’, Novara, Italy; 2Department of Medical Physics, University Hospital ‘Maggiore della Carità’, C.so Mazzini,
18, 28100 Novara, Italy; and 3Department of Pneumology, University Hospital ‘Maggiore della Carità’, Novara, Italy
Received 12 September 2011; accepted after revision 16 December 2011; online publish-ahead-of-print 25 January 2012
Aims
To characterize the electromagnetic field emitted by the electromagnetic navigational bronchoscopy (ENB) superDimensionw Bronchus system (SDBS) and to determine whether current implantable cardioverter defibrillator
(ICD) systems are suitable for use in conjunction with SDBS.
.....................................................................................................................................................................................
Methods
The electromagnetic emission of the SDBS location board were measured using a field strength meter connected to
and results
a low-frequency (5 Hz –100 kHz) electric and magnetic field analyser; the static magnetic field was measured using a
three-axis Tesla meter. A human torso simulator was used in the in vitro experiment: a polyethylene plastic box
(61 cm length × 43 cm depth × 16.5 cm height) was filled with a semisolid gel and a 0.45% saline solution to
provide electric conductance similar to tissue. The ICDs were immersed 1 cm into the gel and connected with a
dual-coil integrated bipolar pacing/sensing/shock lead. Tip and right ventricular coil of the lead were connected to
an arrhythmia simulator using low-impedance cables. The system transmits electromagnetic waves of 2.5, 3.0, and
3.5 kHz frequency. The maximum magnetic fields measured were B ¼ 53 and 12 mT at location board plane and
at ICD plane, respectively. Corresponding figures for the electric field were E ¼ 16.6 and 4.4 V/m. None of the
tested ICDs recorded any noise signal during the period in which the location board was switched-on. Stored electrogram analysis confirmed the correct detection of simulated tachyarrhythmia and therapy delivery by every tested
ICD.
.....................................................................................................................................................................................
Conclusion
The results of this study demonstrated that tested ICDs are compatible with ENB performed with SDBS. They
also suggest that these results may be extended to all ICDs manufactured in compliance with current EN
regulations.
----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords
Electromagnetic navigation bronchoscopy † Implanted cardioverter-defibrillator † Electromagnetic interference
Introduction
Electromagnetic navigational bronchoscopy (ENB) is an emerging
technology used to improve the clinical utility of fibre optic bronchoscopy in the management of lung cancer.1 Electromagnetic
navigational bronchoscopy is a real-time navigation system that
combines three-dimensional computed tomography (CT) imaging
with real-time fibre optic bronchoscopy using a low-frequency
electromagnetic field locator to guide the bronchoscope and
bronchial tools to a target in or adjacent the bronchial tree. This
technology was incorporated in the superDimensionw Bronchus
system (SDBS) (superDimension; Hertzliya, Israel) and has been
shown to be capable of reaching peripheral lung masses beyond
the reach of the standard bronchoscope in an animal model.2
The data are still insufficient to determine whether use of ENB
will avoid surgical biopsy procedures in surgical candidates
because of its low negative predictive value.3 – 6 However, if done
by a skilled brochoscopist, ENB appears to offer promise for
* Corresponding author. Tel: +39 0321 3733369; fax: +39 0321 3733327, Email: [email protected]
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2012. For permissions please email: [email protected].
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ENB electromagnetic interference to ICDs
Methods
patients in whom a diagnostic bronchoscopy has failed and in
whom more invasive procedures pose a significant risk, or patients
who are medically inoperable or those with non-resectable
disease.
Due to the use of an electromagnetic field, ENB has been considered contra-indicated by the manufacturers in patients with implantable cardioverter defibrillator (ICD) system who, nonetheless,
belong to the category of patients in whom invasive procedures
pose a significant risk. Concern about possible electromagnetic
interactions has lead until now to exclusions of patients with
implanted ICDs from clinical studies of SDBS.3 – 5,7,8
The technology of implantable pulse generators has evolved to
devices with titanium shielding, noise rejection circuits, improved
sensing algorithms, and feed through filters. These implantable
pulse generators are highly sensitive low-frequency receivers
that monitor physiological signals at levels as low as 0.15 mV.
Their susceptibility to emitters depends primarily on the emitter’s
carrier frequency, modulation scheme, duty cycle, field strength,
proximity, and duration of the exposure. The implantable
cardiac device pass band is 3 dB points between 30 and 70 Hz
and corresponds to the frequency content of the physiological
signal of interest. Sustained electromagnetic interference (EMI),
including modulation content occurring in this physiological pass
band, may be interpreted by the device as a signal of interest
from the heart, potentially altering therapy. Implantable
pulse-generators are in many cases life-sustaining devices and
implications for patient safety are taken seriously by both
device manufacturers and clinicians.
The aim of this study was to characterize the electromagnetic
field emitted by SDBS and to determine whether current ICD
systems are suitable for use in conjunction with SDBS. To evaluate
the safety and feasibility of devices and leads subjected to SDBS
fields, we conducted in vitro experiments and measured EMI.
Electromagnetic navigational bronchoscope
system
The SDBS is an image-guided localization device that assists the endobronchial accessories in reaching the desired areas of the lung. A
detailed description of the system was previously reported.2 Briefly,
it is composed of an electromagnetic location board, a sensor
probe, and a computer software. The system transmits sinusoidal
and continuous electromagnetic waves of 2.5, 3.0, and 3.5 kHz, that
are emitted from an electromagnetic board (56 cm length × 47 cm
depth × 1 cm height) that is placed under the cephalic end of the mattress of the bronchoscopy table. A sensor probe (diameter 1 mm;
length 8 mm) mounted on the top of a flexible metal cable constitutes
the main assembly of the device. Once placed within the electromagnetic field, its position in the X, Y, and Z planes as well as orientation
(roll, pitch, and yaw movement) is captured by the SDBS. This information is then displayed on a monitor in real time, superimposed on previous acquired CT images. The brochoscopist is able to view the
reconstructed three-dimensional CT images in coronal, sagittal, and
axial views together with superimposed graphic information depicting
the position of the sensor probe as well as the pre-identified anatomic
landmarks and the position of the target lesion.
SuperDimensionw Bronchus system
electromagnetic field measurements
The static magnetic field emitted by the SDBS location board was measured using a three-axis Tesla meter ETM-1 (Metrolab Instruments,
Geneva, Switzerland). The instruments can measure static magnetic
fields in the range 0.01 mT– 2 T with an accuracy of +2% of reading.
The electromagnetic emission of the SDBS location board were
measured using a portable field strength meter PMM 8053 (Narda
Safety Test Solutions, Segrate, Italy) connected to a low frequency
(5 Hz– 100 kHz) electric and magnetic field analyser PMM EHP-50B.
Field strenght meter
EM field analyer
ICD + lead
Y
Torso
hpantom
Z
Arrhytmhia
simulator
X
Location
board
X
Top view
Front view
Figure 1 Drawing of torso simulator together with location board, measuring probe, and implantable cardioverter defibrillator plus lead
system in top and front view (arrhythmia simulator connection not drawn in front view).
1056
The EHP-50B probe can measure the intensity of electric fields in the
range of 10 mV/m– 100 kV/m with 1 mV/m resolution and magnetic
flux density in the range 1 nT – 10 mT with a 1 nT resolution, with
an accuracy of +0.5 dB. The spectral analysis of the signal is obtained
by mean of a powerful digital signal processor, it is performed on six
different span values and displayed on the PMM 8053 field meter
display; in selective mode the test frequency can be selected with a
marker. The EHP-50B external dimensions are 96 × 96 × 115 mm
and is connected to the PMM 8053 through a fibre optic cable. A
grid of 4 × 5 elements each of 10 × 10 cm was superimposed to
the SDBS location board and measurements were collected by
placing the EHP-50B probe directly in contact with the location
board in a fixed point of the underlying grid. The probe was next
moved in each point of the measurement grid. For each point three
measurements were collected and the results were averaged. This
reduced sampling region with respect to the physical dimensions of
the SDBS location board was adopted in order to avoid border
effects due to the physical dimensions of the EHP-50B probe.
Implantable cardioverter defibrillators
and covered with a plastic sheet to support the EHP-50B probe. Electric and magnetic fields were reported not only as root-mean-squares
(RMS) but also as X, Y, and Z components. Indeed, magnetic fields in
the Z-axis (perpendicular to the lead) and electric fields in the X– Y
plane (iso-planar with the lead) are expected to be the most
influencing.
Implantable cardioverter defibrillators
testing procedure
The testing procedure included:
† Connection of ICD to implanted lead and location of the device in a
‘left subclavear’ position. When necessary, ports for atrial and left
ventricular lead were closed with plugs.
A
70
60
B (µT)
Implantable cardioverter defibrillators explanted for various reasons
(e.g. elective replacement, system upgrading, infection) were used for
in vitro testing of potential EMI of SDBS. Devices were excluded
from the study if the elective replacement indication had already
been reached or if suspected device malfunction had been the
reason for explantation. Seven ICDs models were tested: Alto 2
(ELA Medical Sorin, Milan, Italy); Epic II HF V-357 and Atlas II HF
V-367 (St Jude Medical, St Paul, MN, USA); Insync Sentry 7298;
Maximo VR 7232; EnTrust D154VRC (Medtronic, Minneapolis, MN,
USA); Vitality T175 (Guidant Boston Scientific, Natick, MA, USA).
A. Magnani et al.
40
30
50
Y- 40
ax
is 30
(c
20
m
)
10
Implantable cardioverter defibrillators
testing setup
40
30
)
(cm
xis
20
a
10
X-
60
50
40
30
B
E (Vlm)
The testing setup is a modified version of the AAMI PC69 Standard, a
standard recognized for developing in vitro electromagnetic compatibility test protocols for implantable pacemakers and ICDs.9 A human
torso simulator was used. A polyethylene plastic box (61 × 43 ×
16.5 cm) was filled with a semisolid gel prepared to simulate the dielectric properties of human tissues. This was accomplished using a
gelling agent and a 0.45% saline solution, which provides electric conductance similar to tissue.10 The simulated torso did not contain discontinuity barriers since the measure of real pacing and shock
impedances were not within the aim of the study. The device under
testing was immersed 1 cm into the semisolid gel and connected
with a dual-coil pacing/sensing/shock lead Endotak Reliance 0148
(Boston Scientific, Natick, MA, USA). This lead operates in an integrated bipolar configuration, which has been reported as more
prone to over sensing of far-field signals,11,12 with right ventricular
(RV) coil acting as pacing/sensing anode. Lead configuration was positioned in an anatomical pattern, mimicking lead bends in the vascular
system. Tip and RV coil of the lead were connected to an arrhythmia
simulator ARSI-4 (ARSI, HKP, Bannewitz, Germany) using lowimpedance cables. Lead heating was measured with a digital thermometer with a range of 220 – 858C and resolution of 0.18C. The probe
was connected to the electrode tip.
A drawing of torso simulator together with location board,
measuring probe, and ICD system in top and front view is reported
in Figure 1.
To better approximate the real coupling fields into the lead systems,
the electromagnetic field measurements were repeated using a polyethylene plastic box (61 × 43 × 15.5 cm) filled with a saline solution
50
20
18
16
14
12
10
8
6
50
0
Y- 4
ax
0
is 3
0
(c
m 2
)
10
20
40
30
)
(cm
xis
10
a
X-
18
16
14
12
10
8
6
Figure 2 Three-dimensional surface graphs of B (mT) (A) and E
(V/m) (B) emitted by superDimensionw Bronchus system and
measured at the surface of the location board with respect to
the coordinate system of the location board. Surfaces were
fitted to experimental data using a distance-weighted least
square smoothing algorithm. Also displayed in this graph are
the experimental points measured.
1057
ENB electromagnetic interference to ICDs
Figure 3 Example of tracings derived during initial electromagnetic navigational bronchoscopy operation. Medtronic Maximo VR7232, VVI
40 b.p.m., ventricular sensitivity 0.15 mV, ventricular fibrillation detection 182 b.p.m., 18 of 24 cycles. Paper speed 25 mm/s. Integrated
bipolar sensing. During operation of electromagnetic navigational bronchoscopy, telemetric monitoring of implantable cardioverter-defibrillator
right ventricular pacing/sensing channel documents the absence of any electromagnetic noise and correct sensing of simulated ventricular
rhythm. Episodic artefacts (second and eighth marker) are due to loose contact with arrhythmia simulator cable. Upper tracing: right ventricular
electrogram; lower tracing: markers channel.
† Programming of brady pacing to low rate (30 – 40 b.p.m.) VVI mode
with maximum sensitivity (to operate in the worst case scenario as
for noise detection) and standard pacing voltage/pulse duration.
† Programming of tachy section with rate detection .160 – 180 b.p.m.
and shock delivery after tachycardia confirmation.
† Measure of sensing amplitude, pacing impedance, and shock
impedance.
† Telemetric monitoring of ICD RV pacing/sensing channel to assess
the lack of EMI.
† With the SDBS system switched on a few minutes navigation session
was simulated during ‘sinus’ rhythm of 65 b.p.m. generated by the
arrhythmia simulator. During this phase, measures of sensing amplitude, pacing impedance, and shock impedance were repeated and,
again, telemetric monitoring of ICD electrogram was performed.
† Arrhythmia simulator activation to generate a 30 s ventricular
fibrillation.
† SDBS switched-off.
† ICD interrogation to verify programmed parameters and to assess
noise detection during ‘sinus’ rhythm, recognition of simulated
arrhythmia, and therapy delivery.
According to our institutional policies Institutional Review Board approval was not requested since this is an in vitro study, not involving
human patients.
Results
The static magnetic field emitted by the location board of the
SDBS was below the instrument sensitivity of 0.01 mT. The
system transmits electromagnetic waves of 2.5, 3.0, and 3.5 kHz.
The maximum magnetic field measured is B ¼ 53 mT, while the
maximum electric field amounts to E ¼ 16.6 V/m. In Figure 2A
and B are displayed the three-dimensional surface graphs of the
measured B (mT) and E(V/m) with respect to the coordinate
system of the location board. A surface was fitted to experimental
points using a distance-weighted least square smoothing algorithm.
The U-shape of the magnetic field across the coordinate system of
the location board and the decrease of the electric field with increasing X values allow the localization of the probe during the
endoscopic navigation.
The maximum electric field measured at 15.5 cm above the location board with the torso phantom interposed was E ¼ 4.4 V/m
(EX ¼ 1.4 V/m, EY ¼ 2.1 V/m, EZ ¼ 3.6 V/m). The corresponding
figures for the magnetic field were B ¼ 12 mT (BX ¼ 3.9 mT, BY ¼
1.9 mT, EZ ¼ 11.5 mT).
None of the tested ICDs recorded any noise signal during the
period in which the location board was switched-on, even though
a high sensitivity level was programmed (Figure 3). Stored electrogram analysis confirmed the correct detection of simulated tachyarrhythmia and therapy delivery by every tested ICD (Figure 4). Lead
temperature in vitro did not show any measurable increase.
Discussion
In recent years, implantation of rhythm devices and cardioverter
defibrillators has been proven to supersede the effectiveness of
other therapeutic approaches and their application is increasing.13,14 In turn, this increasing number of patients implanted
with ICD raises the probability that some of them may warrant a
diagnostic or therapeutic EMB.
Magnetic and time-varying electromagnetic fields such as those
emitted by the SDBS might interfere with the correct functioning
of the implanted devices. Electromagnetic interference may
change the functioning of the implanted devices because of spurious
signals induced by electromagnetic coupling. These signals may be
recognized by the logic of the ICD as physiological signals. A
major difference between the electromagnetic and the magnetic
tests concerns the mechanism of coupling with the device: the
major influence of electromagnetic fields is through induced voltages and currents in the leads; magnetic fields could cause malfunctions due to direct effects on the internal circuitry of the device.
All marketed ICDs are approved according to either the international standard ANSI/AAMI PC69:200710 or to the medical device
European Norms EN 45502-2-115 and EN 45502-2-216 which establish procedures for EMI check on implantable devices on different
ranges of frequency. However, it is impossible for the producer to
test the devices in all different EMI environments that can occur.
As long as the EMI levels are below the reference levels for
general public exposure to time-varying electric and magnetic
fields set by the International Commission on Non-ionizing Radiation Protection (ICNIRP),17 there should be no problem for the
1058
A. Magnani et al.
Figure 4 Example of stored electrogram during electromagnetic navigational bronchoscopy operation and ventricular tachyarrhythmia simulation. Medtronic Maximo VR7232, VVI 40 b.p.m., ventricular sensitivity 0.15 mV, ventricular fibrillation detection 182 b.p.m., 18 of 24 cycles.
Paper speed 25 mm/s. Integrated bipolar sensing. Interrogation of stored electrogram after simulated ventricular tachyarrhythmia shows prompt
detection and shock therapy release; persistence of ventricular tachyarrhythmia after shock release is due to manual activation of arrhythmia
simulator. Upper tracing: right ventricular electrogram; lower tracing: markers channel.
patient. In Table 1 such reference levels are reported in the frequency range emitted by the SDBS. According to EN 45502-2-1
and EN 45502-2-2 protection from exposure to weak and
strong static magnetic fields and to varying magnetic fields which
patients may encounter in the general public environment is
addressed according to the tests reported in Table 2.
Interference of the SDBS location board with ICDs due to static
magnetic fields can be definitely ruled out on the basis of our measurements since magnetic fields ≤10 mT cannot cause any interference for devices that are planned to work properly in static
magnetic fields as high as 1 mT.
Time-varying magnetic fields emitted by the SDBS location
board are above the 6.25 mT reference levels for general public exposure of ICNRIP 1998. The ICNIRP standard of 1998 with its
6.25 mT reference level is now in revision with a reference level
of 20 mT for 0.8 –150 kHz according to ICNIRP draft 2009. Moreover, there is one paper with measured interference for continuous sinusoidal voltages:18 between 1.2 and 4 kHz the calculated
peak value of the magnetic induction is 37.8 or 31.5 mT (26.7 or
22.3 mT RMS), respectively, demonstrating that our 12 mT measured field is sufficiently below.
Indeed, all tested ICD did not show any spurious noise signal in
the integrated bipolar sensing configuration while inserted in the
torso phantom during the period in which the location board
was switched-on. Correct recognition of ventricular tachyarrhythmia and therapy delivery should allow carrying out ENB without
preliminary reprogramming of the ICD and should grant implanted
patients with greater safety during ENB procedure, as patients who
should suffer a ventricular tachyarrhythmia episode while undergoing ENB will receive a correct electrical therapy.
Table 1 Reference levels for general public exposure to
time-varying electric and magnetic fields (unperturbed
root-mean-squares values) in the frequency range of
interest adopted by the ICNIRP
E-field
strength
(V/m)
H-field
strength
(A/m)
B-field
(mT)
0.8– 3
250/f a
5
6.25
3– 150
87
5
6.25
Frequency range
(kHz)
................................................................................
a
f as indicated in the frequency range column.
Study limitations
The sampling of the time-varying electric and magnetic fields
emitted by the location board of the SDBD was only coarse due
to the physical dimensions of the EHP-50B probe. However, the
accurate determination of the spatial variation of electromagnetic
fields was beyond the aims of the study. For the purpose of characterizing maximal amplitude of varying magnetic fields emitted by
the location board, we believe that our measurements are sufficiently accurate.
One set of ICD leads was chosen for test reproducibility;
however, varying the lead length, make, or type of lead could
affect implantable ICD electromagnetic compatibility.
In vitro testing may not be predictive of the clinical experience.
Past experience with electromagnetic compatibility testing
ENB electromagnetic interference to ICDs
Table 2 Implanted active cardiac devices: EMC tests
with static and time-variable magnetic fields, in
accordance with EN 45502-2-1 and prEN 45502-2-2
Frequency Type of
signal
Amplitude
Compliance if
DC
DC
Constant
Constant
1 mT
10 mT
1 –140 kHz
Sinusoidal 150 A/m for
The device is normally
1 kHz ≤ f ≤
affected mostly
100 kHz
working in its
interference mode
during test but should
be unaffected after the
test
................................................................................
Unaffected
Recovery within 5 s
f, frequency.
between cell phones and pacemakers indicates that if the bench
test detects interference, interference will also be seen clinically.19
In vitro testing of a torso simulator represents a static environment in which the patient is still.
Conclusions
The results of the present in vitro study demonstrated that
tested ICDs are compatible with ENB performed with SDBS in
the integrated bipolar sensing configuration. True bipolar sensing
configuration was not tested in the present work and may lead
to other results. They also suggest that these results may be
extended to all ICDs manufactured in compliance with current
EN regulations. Further in vitro studies and carefully monitored
patient studies are needed before firm recommendations can be
made.
Conflict of interest: none declared.
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