BASIC SCIENCE
Europace (2017) 19, 319–328
doi:10.1093/europace/euv458
Effect of lead position and orientation on
electromagnetic interference in patients with
bipolar cardiovascular implantable electronic
devices
Tobias Seckler1†, Dominik Stunder 1†, Christian Schikowsky 1, Stephan Joosten1,2,
Matthias Daniel Zink 3, Thomas Kraus 1, Nikolaus Marx 3, and Andreas Napp 3*
1
Research Center for Bioelectromagnetic Interaction, Institute of Occupational Medicine, University Hospital, RWTH Aachen University, Aachen, Germany; 2German Social Accident
Insurance Institution for Energy, Textile, Electrical and Media Products Sector (BG ETEM), Köln, Germany; and 3Department of Internal Medicine I (Cardiology, Angiology, Pneumology
and Internal Intensive Care Medicine), University Hospital, RWTH Aachen University, Pauwelsstr. 30, 52074 Aachen, Germany
Received 5 November 2015; accepted after revision 28 December 2015; online publish-ahead-of-print 2 February 2016
Aims
Electromagnetic interferences (EMIs) with cardiovascular implantable electronic devices (CIEDs) are associated with
potential risk for patients. Studies imply that CIED sensitivity setting and lead’s tip-to-ring spacing determine the susceptibility of CIEDs with bipolar leads to electric and magnetic fields (EMFs); however, little is known about additional
decisive parameters affecting EMI of CIEDs. We therefore investigated the influence of different patient-, device-, and
lead-depending variables on EMIs in 160 patients.
.....................................................................................................................................................................................
Methods
We ran numerical simulations with human models to determine lead-depending variables on the risk of EMI by calcuand results
lating the voltage induced in bipolar leads from 50/60 Hz EMF. We then used the simulation results and analysed 26
different patient-, device-, and lead-depending variables with respect to the EMI threshold of 160 CIED patients.
Our analyses revealed that a horizontal orientation and a medial position of the bipolar lead’s distal end (lead-tip)
are most beneficial for CIED patients to reduce the risk of EMI. In addition, the effect of CIED sensitivity setting and
lead’s tip-to-ring spacing was confirmed.
.....................................................................................................................................................................................
Conclusion
Our data suggest that in addition to the established influencing factors, a medial position of the lead-tip for the right
ventricular lead as achievable at the interventricular septum and a horizontal orientation of the lead-tip can reduce the
risk of EMI. In the right atrium, a horizontal orientation of the lead-tip should generally be striven independent of the
chosen position. Still important to consider remains a good intrinsic sensing amplitude during implant procedure.
----------------------------------------------------------------------------------------------------------------------------------------------------------Keywords
Electromagnetic interference † Implantable cardioverter-defibrillator † Pacemaker † Lead placement † Electric
and magnetic fields
Introduction
Cardiovascular implantable electronic devices (CIEDs) such as pacemakers (PMs) and implantable cardioverter-defibrillators
(ICDs) are increasingly implanted in patients with cardiovascular
diseases with over 1 million CIEDs implanted every year. 1,2
Seventy-six percentage of the implantations were performed in
†
Europe plus the USA and in these countries, 99% of the implanted
pacing leads in the right ventricle (RV) and the right atrium (RA)
have bipolar sensing capabilities. 1 In Germany, 50% of new
ICDs and 15% of new PM implantations are annually conducted
on patients who are younger than 70 years.3 Thus, there are a
high percentage of CIED patients in the working age when first
receiving a CIED.
The first two authors contributed equally to the work.
* Corresponding author. Tel: +49 241 80 89300; fax: +49 241 80 82545. E-mail address: [email protected]
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2016. For permissions please email: [email protected].
320
What’s new?
† Placement of the bipolar lead’s distal end (lead-tip) during the
implant procedure does significantly influence the susceptibility of cardiovascular implantable electronic devices
(CIEDs) to electric and magnetic 50 Hz fields.
† Lead-tip’s position and orientation together with CIED sensitivity setting and lead’s tip-to-ring spacing are the four major
parameters affecting the risk of electromagnetic interference
(EMI) in bipolar leads.
† A medial position of the lead-tip is beneficial to avoid EMI in
the ventricular lead.
† A horizontal orientation of the lead-tip makes CIEDs less
susceptible to EMI in the atrial and ventricular channel.
T. Seckler et al.
be changed during the implant procedure, thus potentially providing
new options for perioperative management to reduce the risk
of EMI.
Methods
We initially conducted an in vivo provocation study with 160 CIED patients to evaluate the threshold of EMI of the devices (the ICD thresholds were already published17). Subsequently, we ran numerical
simulations with human models to determine the influence of patientand lead-depending parameters on the induced voltage at bipolar leads.
We then used the results from the in vivo study and the simulations for
regression analyses to identify parameters influencing the susceptibility
of CIEDs to EMF.
In vivo provocation study
Parallel to this development, the number of electric and magnetic
fields (EMFs) in our environment increases due to technological advances producing electrical devices that all emit EMFs. Especially in
occupational environment, patients may be exposed to strong
EMFs.4,5 For CIED patients, this poses the risk of CIED malfunction
due to the fact that exogenous EMFs induce voltages in the human
body and in the implanted lead(s), which may subsequently result in
misinterpretation by the CIED signal processing.6 This effect is
known as electromagnetic interference (EMI) and can be hazardous
for CIED patients as reported in several case studies.7 – 9
According to a French survey, physicians are challenged by EMI;
23% of 410 questioned cardiologists indicated that they are managing CIED malfunctions due to EMI at least once a year.10 FDA’s
MAUDE database revealed 165 cases of CIED malfunctions attributable to EMF in the last 4 years.11 These data do not take into account those CIEDs which do not record episodes and EMI incidents
that remain unreported by patients or physicians. Thus, EMI with
CIEDs creates a rare but severe problem.
In clinical practice, the problem of CIEDs’ susceptibility to EMF
has been approached by increasingly using bipolar leads instead of
unipolar leads in the last 15 years. However, CIEDs with bipolar
leads remain vulnerable to strong EMFs.12,13 To date, only two parameters are known to affect EMI of bipolar CIEDs—the CIED sensitivity setting and leads’ tip-to-ring spacing.4,5,14,15 The current
literature, therefore, suggests noise detection algorithms, higher
sensitivity values, and shorter tip-to-ring spacing for patients with
foreseeable exposure to strong EMF.4,6,14,16 However, an in vivo
provocation study from our group in a cohort of 110 ICD patients
showed that the threshold of EMI widely differs even for patients
having the same device, sensitivity setting, and tip-to-ring spacing.17
Further influencing factors have not yet been identified for bipolar
leads, although the position and orientation of lead’s distal end
(lead-tip) are discussed as parameters which could help in prevention of EMI.18,19 However, there is a lack of experimental data, especially on in vivo investigations for confirmation.
Thus, the present study investigated, for the first time, the effect
of various patient-, device-, and lead-depending parameters on the
risk of EMI by using in vivo and in silico methods. While patient’s physiques are usually given, device- and lead-depending parameters can
The clinical in vivo provocation study was conducted to determine the
so-called interference threshold of CIEDs under worst-case conditions,
i.e. the lowest field strength at which EMI occurs. Therefore, patients
with ICDs or PMs were exposed to homogeneous EMFs with strengths
up to 30 kV m21 and 2550 mT at a frequency of 50 Hz.
The electric field is reproduced by a direct current injection and the
electric field strength is recalculated from the measured current
through the patient. The magnetic field is generated by Helmholtz coils.
The patients were exposed under worst-case conditions, i.e. worst-case
field direction, maximal inspiration, maximum sensitivity, and sustained
pacing. The details about the test set-up and procedure are described
elsewhere.17
The study design was approved by the Ethics Committee at the
RWTH Aachen Faculty of Medicine and complies with the Declaration
of Helsinki. The study was registered at ClinicalTrials.gov (Identifier
NCT01626261).
Patient population
In the period from September 2009 to December 2014, we screened
all patients presenting in the outpatient PM/ICD clinic of our department for the study. Patients who met the inclusion/exclusion criteria
were invited to participate. Inclusion criteria were: age between
18 and 80 years and device implantation .4 weeks ago. Exclusion
criteria were: PM dependency, hyperthyroidism, comorbidity which
impedes emergency assistance (e.g. morbus bechterew and glaucoma), serum electrolyte disorders on the trial day, clinically manifest
infection, acute myocardial infarction (,30 days), pregnancy, and
breastfeeding.
One hundred and sixty patients (81 ICD and 79 PM) were included in
the present study. All patients had bipolar leads implanted and analysable chest radiographs (i.e. the radiograph was straight recorded and
all leads were visible). All patients gave written informed consent.
For detailed patients’ characteristics, see Supplementary material online,
Table S1.
Numerical simulations
The objective of the simulations was to ascertain the influence on the
risk of EMI of different lead placements, heart positions in the thorax,
and tissue conductivities of the organs by numerically calculating the
voltage induced in bipolar leads. We therefore used two kinds of human
models: A XCAT-male model and a simplified body model (cf. Supplementary material online, Figure S1).
321
Effect of lead position and orientation on EMI
The XCAT-male model was developed by Simpleware Ltd using the
XCAT phantom data set from Duke University.20,21 It represented an
anatomically detailed normal male body taken from transverse CT,
MR, and cryosection images. The simplified body model we developed
consisted of 26 basic three-dimensional solids such as cubes, spheres,
and cylinders. Its advantage was that model size, organ positions, and tissue properties can be freely modified.
The influence of the heart position in the thorax was scrutinized at
four different positions in the simplified body model that represents individual heart positions and size.
The tissue conductivities are individual due to physiological causes
and vary over time.22 We therefore assigned four different conductivity
sets to the body, the blood in the heart, and the lung in the simplified
body model.
The influence of the position of the bipolar lead’s distal end was evaluated in the apex of the XCAT-male’s RV and in seven different positions within the heart of the simplified body model. The influence of
lead-tip’s orientation was evaluated at each position by rotating the
ring electrode around the tip electrode between 0 and 1808 in 108 steps
in all three anatomical planes.
The induced voltage was determined with respect to the lead-tip’s
orientation for all lead-tip’s positions, heart positions, and tissue conductivities—in total 113 separate model configurations. Detailed information about the numerical simulations can be found in Supplementary
material online, Methods.
Statistics
Regression analyses were performed to identify parameters which affect
the susceptibility of CIEDs to EMF using potentially influencing patient-,
device-, and lead-depending variables as independent variables and the
interference threshold of CIEDs determined in the in vivo provocation
study as a dependent variable.
the in vivo provocation study, current literature, and the numerical simulations, and can be categorized in patient-, device-, and lead-depending
variables. The variables and their references are summarized in Table 1.
Three variables represented conditions of each interference
threshold in the in vivo study: sensitivity setting and operating mode
(pacing/sensing) as well as the status of inspiration (maximal inspiration
yes/no) of the patient.
Patient-depending variables were gender, body weight, and height,
which were measured in light clothing with shoes. The circumferences
of the thorax, the abdomen, the hip, and the upper arm as well as the
distance between the shoulders were taken.
Devices’ manufacturer and type (PM or ICD), the insertion site, and
the lead manufacturer were taken from the CIED identity card. The
lead’s tip-to-ring spacing and active/passive fixation type were noted
from the technical manual. The date of market release was recorded
as time period related to December 2014.
The diameter of the heart and the thorax as well as the lead-tip’s position and orientation were measured from patients’ postero-anterior
(PA) chest radiograph using Philips DICOM Viewer (Version R2.2).
The horizontal distance from the outer edges of the heart and the maximum distance between left lateral and right lateral aspect of the ribcage
were measured and noted as the diameter of heart and thorax. Also the
straight distance from the lead-tip to the upper surface of vertebra Th1
(longitudinal direction) and to the lateral rib cage (transverse direction)
were measured to record the lead-tip’s position in relation to the thorax. For orientation measurements, the distance between lead’s tip and
ring along the transverse (medio-lateral) and longitudinal (craniocaudal) axes was taken. The distance in sagittal (antero-posterior) direction was calculated using the tip-to-ring spacing and the distance measurements along the transverse and longitudinal axes. Also, the
so-called polar angle (u) between the tip-ring line and the transverse
plane was calculated by trigonometric functions. Figure 1 shows an example of the measurement technique.
Variables potentially influencing risk of electromagnetic
interference
Regression analysis
We defined 26 variables that potentially influence the susceptibility of
CIEDs to 50/60 Hz EMF. They were derived using the results from
For regression analyses, the Cox and Tobit models24 – 26 were applied
because patients’ devices with interference thresholds above the tested
Table 1 The 26 patient-, device-, and lead-depending variables that were considered potentially influencing the
interference thresholds of CIEDs
Category
Variables
References
Patient
Sex, weight, height, circumference of the thorax, abdomen, hip,
and upper arm, distance between the shoulders, diameter
of heart, and thorax
Maximal inspiration (yes/no)
Joosten et al. 23 found the influence of body measurements for
unipolar PMs. Therefore, we decided to scrutinize these also
for bipolar PMs and ICDs.
Napp et al. 17 and Joosten et al. 23
Device
Manufacturer, time period since market release
Sensitivity setting
Insertion site
Type, operating mode (pacing or sensing)
Napp et al. 17
Toivonen et al. 16 and Scholten and Silny14
Irnich6 found the influence of insertion sites for unipolar CIEDs.
Device manuals explain that some types change their sensitivity
threshold in the event of pacing.
Lead
Manufacturer, fixation type
Hille et al. 18 published the suspicion of the influence of the lead
design on EMI.
Irnich6
Those variables were the results of the numerical simulations.
...............................................................................................................................................................................
Tip-to-ring spacing
Distance from lead-tip to vertebra Th1 and lateral rib cage, distance
between tip and ring along the transverse (medio-lateral) axis,
longitudinal (cranio-caudal) axis, and the sagittal (antero-posterior)
axis, polar angle (u)
322
A
T. Seckler et al.
B Atrial lead
Reference line
L
pa
Longitudinal
tip-to-ring
distance
Distance from
lead-tip to
vertebra Th1
Transverse
tip-to-ring distance
Distance from lead-tip
to lateral rib cage
C
Ventricular lead
Distance from lead-tip
to lateral rib cage
Heart I
Diameter of
heart (I+II)
Longitudinal
tip-to-ring
distance
Heart II
Transverse
tip-to-ring distance
Diameter of thorax
Figure 1 Input variables for the regression analyses obtained from PA chest radiography of the patients. The measurement technique is depicted
for the following variables: diameter of the heart and thorax, distance from the lead-tip to the vertebra Th1 and to the lateral rib cage (A), as well as
distance between the tip and the ring along the transverse and longitudinal axis (B for the atrial lead and C for the ventricular lead).
limits could thus be included in the analysis and were considered as censored observations.
Cox regression was used for electric field interference thresholds as
they are censored individually, i.e. the exposed maximum of the electric
field differed between patients due to calculation from the injected current. Tobit regression was used for magnetic field interference thresholds as they are fixed censored, i.e. all participants were exposed up to a
maximum magnetic field of 2550 mT.17
For a more precise regression analysis, the device type was used as a
stratification factor in order to consider the system differences in sensing algorithm between PMs and ICDs.
All data were analysed using the R statistical software (Version 3.1.0,
www.r-project.org). The analysis was separately done for the atrial and
ventricular lead, each with its interference thresholds for EMF. The
models were fit through a stepwise selection algorithm, which combines
aspects of forward and backward selection. The criterion used for model selection was the Bayesian information criterion (BIC) and the selection process stops when BIC does not further decrease, meaning that
the remaining (unselected) variables do not contribute statistically significant information to the model. The values for P and pseudo-R 2
were taken from the likelihood ratio test and maximum-likelihood
estimation, respectively.
Results
Influence of the lead-tip’s orientation on
the risk of electromagnetic interference
(numerical simulations)
The influence of the lead-tip’s orientation on the risk of EMI is presented in Table 2 for both body models. The results for the simplified body model were averaged over all lead-tip positions, heart
positions, and tissue conductivity sets. Table 2 lists the mean
values + standard deviation of the so-called polar angle where the
induced voltage reached its maximum (uVMax) and minimum (uVMin)
for EMFs each with sagittal and frontal plane results. The polar
angle u is defined as angle between the transverse plane and a
straight line connecting the tip and the ring electrode (Figure 2).
The results of simulations for the induced voltage can be mapped
on a quarter-sphere where the centre represents the tip electrode
and the orientation of the lead-tip determines the ring position on
the shell of the sphere (see Figure 2 for the results of the XCAT-male
model). The maximum occurred mainly when the lead-tip is
oriented vertically (uVMax 908) independent of electric or
323
Effect of lead position and orientation on EMI
Table 2 The angles where the induced voltage became maximum (uVMax) and minimum (uVMin) for the simplified body
model and the XCAT-male model
Field type
Plane
Simplified body model
XCAT-male
.....................................................
..........................................
uVMax (88 )
uVMin (88 )
uVMax (88 )
uVMin (88 )
90.36 + 1.86
91.61 + 3.67
90.71 + 11.29
105.18 + 19.41
0.09 + 0.94
1.61 + 3.93
0.71 + 2.91
18.13 + 15.74
92
99
92
100
0
9
0
10
...............................................................................................................................................................................
Electric
Sagittal
Frontal
Sagittal
Frontal
Magnetic
The values for the simplified body model are averaged over all lead-tips’ positions, heart positions, and tissue conductivity sets.
Max, maximum; Min, minimum; V, volt.
100%
A
1
B
Ring position 2
10%* VEMax
0
q2 = 5°
1
Rig
ht
Tip position
ve
ntr
icle
/ap
ex 0 −1
80%
60%
q1 = 75°
40%
1
r
o
i
r
0
e
post
rior/
Ante
20%
VBMax
Inferior/superior
Inferior/superior
1
Ring position 1
95%* VEMax
0
1
Rig
ht
ve
ntr
icle
/ap
ex
VBMin
0 −1
1
r
o
i
r
0
oste
ior/p
r
e
t
An
Figure 2 The induced voltage for all orientations of the lead-tip can be mapped on a quarter-sphere. Shown here are the results from XCATmale model. The colour at a certain point on the sphere indicates the portion of the maximum-induced voltage for the corresponding polar angle
(u) from 100% (red) to 0% (blue). (A) The voltage induced by an electric field (VE). As examples two different orientations (polar angles u1 ¼ 58
and u2 ¼ 758) are indicated. Ring position 1 (u1) leads to 95% of the maximum-induced voltage (VEMax), whereas ring position 2 (u2) leads to a
portion of only 10% of the maximum-induced voltage. (B) The equivalent quarter-sphere of the induced voltages (VB) due to the magnetic field
for any orientation of the lead-tip. The arrows indicate the positions of the maximum- (VBMax) and minimum- (VBMin) induced voltage.
magnetic field exposure. The minimum occurred both for the electric and for the magnetic field for a small polar angle u (uVMin 08),
meaning that a horizontal orientation of the lead-tip minimizes the
risk of EMI. The low standard deviation proves the independency of
the results for the polar angle from the conductivity, from the leadtip’s position, and from the heart position. The results for the transverse plane are not provided as they can be considered insignificant,
because the induced voltage was low near the transverse plane
(uVMin 08).
Influence of the lead-tip’s position on the
risk of electromagnetic interference
(numerical simulations)
The most medial of the seven scrutinized lead-tip positions within
the simplified body model’s heart revealed the lowest induced voltage. From this position to the most lateral lead-tip position, which
was 6 cm apart along the transversal axis, the induced voltage
from magnetic fields increased by 185% (cf. P2 and P3 in Supplementary material online, Table S6). Furthermore, between the most anterior and the most posterior lead-tip position, which was 6 cm
apart along the sagittal axis, the induced voltage differed only by
2.7% (cf. P6 and P7 in Supplementary material online, Table S6).
Therefore, in magnetic fields, the lead-tip’s position along the transversal axis is a decisive parameter concerning the risk of EMI, whereas the position along the sagittal axis is negligible. Thus, a medial
position of the lead-tip minimizes the risk of EMI in magnetic fields.
In electric fields, different lead-tips’ positions within the heart had
negligible influence on the induced voltage (maximum difference
7%). Thus, the numerical simulation showed no influence of the
lead-tip’s position for electric fields.
A detailed compilation of the results for all scrutinized tissue conductivities, heart positions, and lead-tips’ positions is provided in
Supplementary material online, Results.
324
T. Seckler et al.
Parameters affecting electromagnetic
interference with the ventricular lead
(in vivo results)
the sensitivity setting, and the transverse tip-to-ring distance. If the
CIED acted in the pacing mode, the interference threshold dropped
by 1673 mT. The higher the distance was in transverse direction
from lead-tips to lateral rib cage, in other words, the more medial
the lead-tip was positioned, the lower the risk of interference
was—interference threshold increased by 20 mT for each mm. If
the sensitivity was set 0.1 mV higher, the interference threshold increased by 240 mT. The transverse tip-to-ring distance influenced
the susceptibility by an increase in the interference threshold by
159 mT with every additional mm, suggesting that a more horizontal
orientation of the lead-tip reduces the risk of EMI.
For the ventricular lead, 213 observations, respectively interference
thresholds, were evaluated. The results are presented in Table 3 for
the electric and magnetic field. The influencing variables of interference with the ventricular lead can be summarized to device sensitivity setting, lead-tip’s position, and orientation.
For the analysis of the electric field, the interference thresholds of
91% of the patients had to be considered as censored observations
because they could not be disturbed in the in vivo study. The model
fit by Cox regression reached therefore 0.1 for pseudo-R 2 and only
the sensitivity setting was determined as an influencing variable. The
sensitivity setting reduced the risk of interference by 32.7% for every
increase of 0.1 mV as the hazard ratio (HR) of 0.673 shows.
In the magnetic field, the Tobit regression model seemed to show
a good fit with a pseudo-R2 of 0.344 because pseudo-R2 cannot
reach one, even for a perfect model fit.27 The influencing variables
for the ventricular lead contributed in the following priority order:
the operation mode, the distance from lead-tip to lateral rib cage,
Parameters affecting electromagnetic
interference with the atrial lead
(in vivo results)
For the atrial lead, 238 observations, respectively interference
thresholds, were evaluated. The results are presented in Table 4
for the electric and magnetic field. The two most influencing variables for the susceptibility to 50 Hz fields were the device sensitivity
setting and the lead’s polar angle (u).
Table 3 Influencing variables of interference with the ventricular lead determined by Cox and Tobit regression analysis
Variable
Step
Estimate(s)
Electric field
1. Sensitivity setting
0.1 mV
0.673a
1. Operation mode
2. Distance lead-tip to lateral rib cage
Sensing to pacing
1 mm
21673b
+19.9b
3. Sensitivity setting
0.1 mV
4. Transverse tip-to-ring distance
1 mm
95% CI
P-value
Pseudo-R 2
...............................................................................................................................................................................
0.047
0.10 (n ¼ 108)
22310 to 21035
+2.14 to +37.6
,0.001
0.028
0.34 (n ¼ 105)
+240b
+101 to +380
,0.001
+159b
+53.1 to +265
0.003
0.456 to 0.995
Magnetic field
CI, confidence interval.
a
HR from Cox regression.
b
Regression coefficient in mT from Tobit regression.
Table 4 Influencing variables of interference with the atrial lead determined by Cox and Tobit regression analysis
Variable
95% CI
P-value
Pseudo-R 2
,0.001
0.008
0.49 (n ¼ 120)
Step
Estimate(s)
1. Sensitivity setting
2. Polar angle (u)
0.1 mV
18
0.527a
1.026a
0.412 to 0.675
1.007 to 1.046
3. Maximal inspiration
No to yes
2.449a
1.344 to 4.465
0.004
4. Tip-to-ring spacing
5. Time period since market release
1 mm
1 year
1.335a
0.883a
1.164 to 1.532
0.799 to 0.976
,0.001
0.015
1. Sensitivity setting
2. Polar angle (u)
0.1 mV
18
+274b
232.7b
+193 to +354
247.7 to 217.7
,0.001
,0.001
3. Longitudinal tip-to-ring distance
1 mm
270.2b
2123 to 216.6
0.01
...............................................................................................................................................................................
Electric field
Magnetic field
CI, confidence interval.
a
HR from Cox regression.
b
Regression coefficient in mT from Tobit regression.
0.35 (n ¼ 118)
325
Effect of lead position and orientation on EMI
When exposed to electric fields, increasing the sensitivity setting
by 0.1 mV reduced the risk of interference by 47.3% (HR 0.527).
With every additional degree of the lead’s polar angle (u) towards
a more vertical position, the risk of interference rose by 2.6% (HR
1.026). The third, fourth, and fifth variables affecting the interference
threshold in electric fields were the status of inspiration (at maximal
inspiration the susceptibility rose by 144.9%; HR 2.449), tip-to-ring
spacing (increase of 1 mm rose the susceptibility by 33.5%; HR
1.335), and time period since market release (per additional year,
the susceptibility was reduced by 11.7%; HR 0.883).
For magnetic fields, three variables were added: sensitivity setting,
polar angle (u), and longitudinal tip-to-ring distances. The interference threshold was increased by 274 mT if the sensitivity was set
0.1 mV higher. An increase in the leads polar angle (u) by 18 towards
a more vertical position reduced the interference threshold by
33 mT. The longitudinal tip-to-ring distance, as a third variable, decreased the interference threshold by 70 mT for each additional
mm, indicating that a more horizontal orientation of the lead-tip
minimizes the risk of EMI.
Overall, the determined variables seem to be good predictors for
EMI with the atrial lead reaching a pseudo-R 2 of 0.49 for the electric
field (Cox regression) and a pseudo-R 2 of 0.35 for the magnetic field
(Tobit regression).27
Discussion
The present study demonstrates that lead-tip’s position and orientation are decisive parameters regarding the susceptibility of bipolar
CIEDs to exogenous EMF. The main goals of standard CIED implant
procedures remain high local sensing amplitude, good pacing threshold, and low risk of dislodgement or perforation. For patients with
foreseeable exposure to strong EMF, however, the following two
lead placement objectives should be considered to prevent patients
from EMI:
(i) more medial position of the lead-tip (only RV lead, the RA leadtip already has an anatomically inherent medial position).
(ii) more horizontal orientation of the lead-tip (RA and RV lead).
The influence of the lead-tip’s orientation and position was revealed
by numerical simulations with two computational body models and
by regression analyses of in vivo data, even though computational
body models resemble an average of real human bodies and the applied radiograph measurements may contain angulation errors. It is,
however, a strong proof of methodology that the results were obtained by two independent methods. Furthermore, the large number of measured patients (n ¼ 160) should markedly reduce the
potential impact of individual errors of PA radioscopic projections.
By using the distance measurement presented in Figure 1B and C and
the leads tip-to-ring spacing, we calculated the lead’s coordinates in
three-dimensions as described in the methods. We are, therefore,
confident that PA chest radiograph is sufficient to determine leadtip’s position and orientation in the matter of assessing the risk of
EMI. For three-dimensional information on the lead-tip’s position
and orientation during implant procedures, it is applicable to use
PA, right and left anterior oblique radioscopic projections in order
to avoid measurements and calculations. The options for lead placement in RA and RV are discussed in the following sections.
Ventricular lead placement
Since the introduction of transvenous cardiac pacing, the right
ventricular apex (RVA) has been the preferred site for ventricular
lead implantation.28,29 Alternative lead positions are the interventricular septum (IVS) and the right ventricular outflow tract (RVOT).
For high RV septal positions (e.g. RVOT), an active lead fixation is
needed for stable anchoring. Due to the RV anatomy, every position
determines the lead-tip’s orientation. Our data extend the knowledge on lead placement in the RV by suggesting that a medial
position of the lead-tip may reduce the risk of EMI for RV leads.
Such a medial position can be achieved by choosing placement at
the RV septum instead of the RVA. In most of the cases, lead placement at RVOT allows an even more medial position. In addition, we
have shown that a more vertical orientation of the lead-tip increases
the risk of EMI, thus being potentially harmful for CIED patients.
Considering the impact of the EMI affecting variables for RV lead
placement (cf. Table 3), the orientation appears less important
(fourth variable) than the lead-tip’s position (second variable).
However, a horizontal orientation of the lead-tip should be
taken into account at every position of the lead-tip (RVA, IVS,
and RVOT) as far as possible. Especially at the RVOT position, a
horizontal orientation is difficult to achieve due to the RVOT
anatomy.
We therefore conclude that IVS positions (as medial as possible)
and an orientation of the lead-tip as horizontal as possible are most
beneficial for CIED patients to reduce the risk of EMI (cf. Figure 1 for
an example of IVS lead position). If IVS is not accessible, RVOT
should be chosen over RVA. If an apical position remains as the
only acceptable pacing site, special emphasis should be taken on a
high intrinsic EGM signal. Achieving a good sensing amplitude offers
the opportunity for programming higher sensitivity values, thus
leading to less susceptibility to EMF. In the case of ICDs, defibrillator
testing should be considered. Ensuring a proper sensing of fibrillation waves with a high sensitivity value provides options for reprogramming the sensitivity settings in the case of EMI.
Atrial lead placement
The most often used position is the right atrial appendage (RAA).
The J-type electrode shape as occurring in the RAA position
leads to a vertical orientation of the lead-tip, thus increasing the
risk of EMI for CIED patients. Alternative atrial lead positions are
the Bachmann’s bundle, the right atrial lateral free wall, or the interatrial septum near the coronary sinus ostium. These positions give
options of horizontal lead placement (an example is depicted in
Figure 3).
Independent of the chosen position achieving a horizontal orientation should be the general aim. However, a horizontal orientation
of the lead-tip should not be chosen in abandonment of a good intrinsic sensing amplitude or risk of lead dislodgement. Particularly,
the atrial sensing amplitude is of importance with regard to the
risk of EMI due to the corresponding signal-to-noise ratio. Small intrinsic atrial signals cause settings of low sensitivity values that make
the CIED more susceptible to EMI (cf. Tables 3 and 4). Due to smaller interference thresholds in the atrial lead, a stable anchoring, good
measuring values and a horizontal orientation of the lead-tip should
be the main goal for every patient.
326
Figure 3 Example of lead placement with low susceptibility to
EMFs. The lead-tip is positioned at the septal aspect of the RA.
The atrial lead-tip has now a near horizontal orientation, thus
reducing the risk of EMI.
Study consistency in the context
of literature
The regression analyses of our in vivo data identified the following
variables affecting the risk of EMI: lead-tip’s position and orientation,
the sensitivity settings, the operation mode, the tip-to-ring spacing,
the time period since market release, and the status of inspiration
(cf. Tables 3 and 4).
The quality of the regression analysis is specified by pseudo-R 2 values. Considering the achieved values (0.34 – 0.49) for the RA, the
quality of the regression analysis is good to very good according
to Menard.27 The regression analysis for the RV in electric fields
achieved a pseudo-R 2 of 0.1, which is why we consider this regression analysis as sufficient but incomplete. The lower value of the
pseudo-R 2 is due to the small number of patients (9%) in which
EMI could be provoked in the RV channel in electric fields. Whereas
in the RA channel in magnetic/electric fields in 53%/43% of the patients, EMI could be provoked, subsequently increasing the number
of significant variables of the regression model and the pseudo-R 2.
First assumptions about the influence of the lead-tip’s position
and orientation on EMI were published 2009 in a conference proceeding by Hille et al. 18 However, Hille et al. used a cuboid phantom
model, filled with saline solution, and numerical simulations of that
cuboid phantom to scrutinize five positions of the lead-tip under
magnetic field exposure. The orientation of the lead-tip was only
changed in the frontal plane and only one lead angle was recorded
for each position. Nevertheless, this first in vitro/in silico approximation also revealed that, in magnetic fields, a more medial position of
lead-tip reduces the risk of EMI. In our study, the influence of the
lead-tip’s position and orientation on EMI was found out by using
two computational body models. This was confirmed by the regression analyses of the in vivo data, which revealed the lead-tip’s position
as the second and the lead-tip’s orientation (transverse tip-to-ring
T. Seckler et al.
distance) as the fourth influencing variable for RV leads in magnetic
fields as Table 3 shows. The RA lead-tip already has an anatomically
inherent medial position, explaining the fact that no influence of the
RA lead-tip’s position was found. Therefore, in return, the lead-tip’s
orientation (polar angle) in the RA was found to be of critical importance (second variable in magnetic and electric fields, Table 4).
The major influence of device sensitivity settings on the risk of
EMI has been well described by Toivonen et al. 16 (in vivo) and Scholten and Silny14 (in vitro). In three of four regression analyses performed in our study, sensitivity setting turned out to be the first
significant variable. Only for the ventricular lead in magnetic fields,
sensitivity setting was revealed as a third variable. However, the first
variable in this case was operating mode of the device, which is
strongly connected to the device sensitivity setting considering
the lower starting values during pacing.5 Napp et al. 5 showed that
different sensitivity progressions after sensing and pacing occur.
Regarding the influence of lead’s tip-to-ring spacing, Irnich15 published, in 2002, an analytical approach suggesting a longer spacing to
increase the risk of EMI. Our in vivo data confirmed this finding by
revealing the tip-to-ring spacing as the fourth variable for atrial leads
in electric fields and indirectly in terms of the horizontal/vertical
component of the tip-to-ring spacing in magnetic fields (fourth variable in RV and third variable in RA).
In eight ICD patients, integrated bipolar leads from Boston Scientific were implanted in the RV. The integrated bipolar lead’s ring
electrode is also the defibrillation electrode. The missing dedicated
ring electrode results in a longer tip-to-ring spacing of integrated bipolar leads than the average tip-to-ring spacing of other ICD leads—
in our case, 12 mm at Boston Scientific ICD leads vs. 10 mm for the
remaining ICD leads. The regression analyses, however, revealed no
significant influence of any particular lead manufacturer. The lead
model was not included in statistics (Table 1) due to the high diversity of lead models, which is why a direct statement regarding the
integrated bipolar leads is not possible. However, the percentage
of integrated bipolar leads in which EMI could be provoked was
12.5%, compared with 11.9% in the remaining ICD patients with
true bipolar leads. This is most likely due to the revealed influence
of the tip-to-ring spacing. Therefore, we assume that using the defibrillation electrode as a ring electrode is not of importance for the
risk of EMI.
Given novel developments in device technology, the time period
since market release also seemed to have an influence on EMI
(Table 4). Further investigations indicated, however, that this result
is probably related to the lower programmable maximum sensitivity
of modern devices. Thus, direct comparison of device generations is
not feasible to estimate the quality of EMF noise suppression.
Joosten et al. 23 found in 2009 that status of inspiration, physique,
and insertion site are affecting the risk of EMI in electric fields for
unipolar PMs. The importance of inspiration status for EMI risk is
consistent with the regression analysis for electric fields presented
in our study, revealing the maximal inspiration as a third variable for
the RA channel. For the RV channel, no influence was found. Possibly due to a lag of observations, this variable did not reached statistical significance in the regression model. Further research on this
particular topic is needed. Regarding the influence of physique and
insertion site, our regression analysis did not reveal a significant influence to the risk of EMI with bipolar CIEDs. The insertion site,
327
Effect of lead position and orientation on EMI
which is one of the most influencing variables for unipolar CIEDs,
was also considered insignificant for bipolar CIEDs in Irnich’s prior
discussed analytical approach.15 The influence of the physique on
the risk of EMI for bipolar CIEDs has to be further investigated in
subsequent research.
Our study applied two different regression models (Cox and
Tobit) each with two in vivo data sets (RA and RV), which sum up
to four independent regression analyses (cf. Tables 3 and 4). In addition, two independent computational body models (XCAT-male
and simplified body model) were scrutinized in a total of 113 different configurations in magnetic and electric fields. The results of our
study not only provide systematical in vivo proof of prior published
influencing factors,14,15,18,23 but also extend our current knowledge
by elaborating the influence of the lead placement on the risk of
EMI and by providing novel information how patients could benefit
from this.
Limitations
The orientation of the lead is changing within one heart cycle.
However, the chest radiograph is just a snapshot which is not
synchronized to the heart beat. The angle information taken from
the radiograph data may have uncertainties, but given the cohort
size (n ¼ 160) we believe that this error is compensated.
The interference thresholds collected with the provocation study
are found for frontal magnetic field exposure and vertical electric
field exposure, which is the worst-case exposure. Other exposure
set-ups could lead to different influencing variables, but will also lead
to a reduction in the risk of EMI. Therefore, it is assumed that
the variables found for the worst-case exposure also cover other
exposure set-ups.
The EMFs generated during the provocation study are operating
at powerline frequency (50 Hz). The resulting interference thresholds can only be scaled to certain frequencies (16 – 1000 Hz).
Indeed, 50/60 Hz fields are very common, given the fact that those
frequencies are used for power lines.
Conclusions
Our data show that orientation and position of the lead-tip influences the susceptibility to EMF in CIED patients with a potential
beneficial effect of more horizontal orientation and a medial position of the atrial and ventricular lead-tip. In case of foreseeable
strong EMF exposition, this fact has to be taken into account and
during the implant procedure, special attention should be paid to
the orientation of the lead-tip. Still, as recommended, highest possible intrinsic signals should be obtained at the implant procedure
and under these conditions, a high value for the sensitivity should
be programmed as clinically reasonable.
Supplementary material
Supplementary material is available at Europace online.
Acknowledgements
The authors thank the volunteers who participated in this study.
Funding
This work was supported by the German Social Accident Insurance
Institution for the Energy, Textile, Electrical, and Media Products Sectors (BG ETEM); the research unit for electropathology (FFE); and a
research grant from the B. Braun Foundation, Melsungen, Germany.
Conflict of interest: A.N. and M.D.Z. received travel grants by
Biotronik, Boston Scientific, Medtronic, and St Jude Medical.
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EP CASE EXPRESS
doi:10.1093/europace/euw245
Online publish-ahead-of-print 12 October 2016
.............................................................................................................................................................................
Catheter ablation of incessant irregular ventricular tachycardia originating
from the right bundle branch
Xiaobo Pu†, Xingbin Liu†, and Kaijun Cui*
Department of Cardiology, West China Hospital, Sichuan University, 37 Guoxue Street, Chengdu 610041, PR China
* Corresponding author. Tel: +86 189 80602036; fax: +86 028 85422353. E-mail address: [email protected]
†
The first two authors contributed equally to the study.
A 32-year-old woman presented with a history of
palpitations over the prior 7 days. Twelve-lead
ECG indicated an irregular, wide QRS complex
tachycardia with a left bundle branch block
(LBBB) morphology and a late precordial R/S
transition. Two attempts of electrical cardioversion of 200 J failed to restore sinus rhythm, and
the administration of intravenous amiodarone
slowed but failed to terminate the arrhythmia.
Because the tachycardia was incessant, urgent
catheter ablation was planned. Using a threedimensional electroanatomic mapping system
(CARTO 3), the site of the earliest local ventricular activation was found in mid-anteroseptal region of the right ventricle. Here, the right
bundle branch (RBB) potentials were slightly earlier than the ventricular activation. Intra-cardiac
electrocardiograms demonstrated that the RBB
potentials precede the earliest ventricular activation, and the His potentials lag behind the right
ventricle apical activation during tachycardia.
This activation sequence of RBB – V – His ruled
out the possibility of BBR or junctional rhythm
with LBBB because these rhythms should have a
His – RBB – V activation pattern. Ablation at the
site of the earliest RBB potential activation terminated the tachycardia with subsequent sinus rhythm and complete RBB block morphology, supporting that this arrhythmia was of RBB origin.
The full-length version of this report can be viewed at: http://www.escardio.org/Guidelines-&-Education/E-learning/Clinical-cases/
Electrophysiology/EP-Case-Reports.
Published on behalf of the European Society of Cardiology. All rights reserved. & The Author 2016. For permissions please email: [email protected].