MRI with cardiac pacing devices – Safety in clinical practice

Accepted Manuscript

Title: MRI with cardiac pacing devices–Safety in clinicalpractice

Author: Touko Kaasalainen Sami Pakarinen Sari Kivisto MiiaHolmstrom Helena Hanninen Juha Peltonen Kirsi LauermaOuti Sipila

PII: S0720-048X(14)00222-8DOI: http://dx.doi.org/doi:10.1016/j.ejrad.2014.04.022Reference: EURR 6758

To appear in: European Journal of Radiology

Received date: 11-2-2014Revised date: 8-4-2014Accepted date: 13-4-2014

Please cite this article as: Kaasalainen T, Pakarinen S, Kivisto S, HolmstromM, Hanninen H, Peltonen J, Lauerma K, Sipila O, MRI with cardiac pacingdevicesndashSafety in clinical practice, European Journal of Radiology (2014),http://dx.doi.org/10.1016/j.ejrad.2014.04.022

This is a PDF file of an unedited manuscript that has been accepted for publication.As a service to our customers we are providing this early version of the manuscript.The manuscript will undergo copyediting, typesetting, and review of the resulting proofbefore it is published in its final form. Please note that during the production processerrors may be discovered which could affect the content, and all legal disclaimers thatapply to the journal pertain.

http://dx.doi.org/doi:10.1016/j.ejrad.2014.04.022

http://dx.doi.org/10.1016/j.ejrad.2014.04.022

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MRI with cardiac pacing devices – Safety in clinical practice Touko Kaasalainen1,2, Sami Pakarinen3, Sari Kivistö1, Miia Holmström1, Helena Hänninen3, Juha Peltonen1,4, Kirsi Lauerma1, Outi Sipilä1

1 HUS Medical Imaging Center, Helsinki University Central Hospital, Finland 2 Department of Physics, University of Helsinki, Finland 3 HUS Department of Cardiology, Helsinki University Central Hospital, Finland 4 Department of Biomedical Engineering and Computational Science, School of Science, Aalto University, Helsinki, Finland Corresponding author: Touko Kaasalainen HUS Medical Imaging Center, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 50 4272300 FAX: +358 9 47171339 Other Authors: Sami Pakarinen HUS Department of Cardiology, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 50 4271092 Sari Kivistö HUS Medical Imaging Center, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 50 4270877 Miia Holmström HUS Medical Imaging Center, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 504270553 Helena Hänninen HUS Department of Cardiology, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 4279865 Juha Peltonen HUS Medical Imaging Center, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 50 4272921 Kirsi Lauerma HUS Medical Imaging Center, Helsinki University Central Hospital POB 281 (Stenbäckinkatu 11), 00290 Helsinki, Finland [email protected] TEL: +358 50 4270621 Outi Sipilä HUS Medical Imaging Center, Helsinki University Central Hospital POB 340 (Haartmaninkatu 4), 00290 Helsinki, Finland [email protected] TEL: +358 50 4270807

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Abstract Objectives: The aim of this study was to introduce a single center “real life” experience of performing MRI

examinations in clinical practice on patients with cardiac pacemaker systems. Additionally, we aimed to evaluate the

safety of using a dedicated safety protocol for these patients.

Materials and methods: We used a 1.5 Tesla MRI scanner to conduct 68 MRI scans of different body regions in patients

with pacing systems. Of the cardiac devices, 32% were MR-conditional, whereas the remaining 68% were MR-unsafe.

We recorded the functional parameters of the devices prior, immediately after, and approximately one month after the

MRI scanning, and compared the device parameters to the baseline values.

Results: All MRI examinations were completed safely, and each device could be interrogated normally following the

MRI. We observed no changes in the programmed parameters of the devices. For most of the participants, the

distributions of the immediate and one-month changes in the device parameters were within 20% of the baseline values,

although some changes approached clinically important thresholds. Furthermore, we observed no differences in the

variable changes between MR-conditional and MR-unsafe pacing systems, or between scans of the thorax area and

other scanned areas.

Conclusion: MRI in patients with MR-conditional pacing systems and selected MR-unsafe systems could be performed

safely under strict conditions in this study.

Keywords: Magnetic Resonance Imaging, Cardiac pacemaker, Safety protocol

Introduction

The number of implanted cardiac pacemakers (PM) continues to grow in Western countries as pacing indications

broaden and life expectancy increases. Enormous advancements in new technologies and comprehensive research

ensure improved and more versatile device-based therapies for growing patient populations. Currently, more than two

million patients worldwide have implanted PM devices [1]. At the same time, the utilisation of magnetic resonance

imaging (MRI) as a non-invasive diagnostic tool is growing, especially in the diagnostics of central nervous system,

abdominal and musculoskeletal disorders, tumours, and some cardiovascular diseases [2,3]. Estimates indicate that each

patient with a PM or implantable cardioverter and defibrillator (ICD) has a 50-75% likelihood of showing a clinical

indication for MRI over the lifetime of their cardiac device [4].

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The presence of a cardiac pacing device has previously been considered an absolute contraindication for MRI, and thus

served as grounds for excluding patients from MRI examinations. Concerns have been related to possible pacemaker-

MRI interactions which may, in the worst cases, lead to life-threatening situations [4-6]. The potential hazards of

performing MRI on PM patients include interactions of pacing devices and their components with a strong magnetic

field as well as gradient and radiofrequency fields. These interactions may increase the pacing rate, inhibit pacing, cause

asynchronous pacing or induce random pacing rates [5, 7-11]. MRI may also reset PM devices when the generator

voltage drops below a critical preset level determined by the manufacturer [10-12]. In addition to changes in pacing

rates and power-on-resets, current may be induced to the pacing leads and discharge heat into the myocardium. This

heat may then produce scar tissue in the myocardium around the lead tips, altering the capture thresholds and thus

impairing the function of the pacing device [7, 8]. However, because of the increasing prevalence of cardiac pacing

systems and the high frequency of clinical indications and needs for MRI, cardiac pacing device manufacturers have

recently introduced MR-conditional (devices are always classified according to the MR task group of the American

Society for Testing and Materials (ASTM) International to either to be as MR-safe, MR-conditional, or MR-unsafe) PM

and ICD systems which permit safe MRI scans under certain imaging conditions [13-16]. In addition, valuable clinical

information from MRI examinations is needed for treating patients with MR-unsafe pacing devices. Thus, despite the

potential for some adverse outcomes, patients with MR-unsafe PMs and ICDs have been scanned in some hospitals

using particular precautions [7-12, 17-26]. According to these studies and the recently published guidelines of the

European Society of Cardiology (ESC) [27], patients with a selected modern cardiac device can be scanned in MRI with

an acceptable risk/benefit ratio even though the cardiac device bears no MR-conditional labels. Nevertheless, some of

these studies have also reported changes, though mainly clinically irrelevant, in pacing capture threshold, lead

impedance and battery voltage after MRI [7-9, 11, 17-22, 28]. Additionally, some studies have also reported the

transient and reversible “power-on” resetting of the devices, magnet-mode pacing and frequent premature ventricular

contractions with no adverse consequences for the patient or for device function [8, 10-12, 17].

The literature offers several different proposed MRI safety protocols for MRI examinations of patients with cardiac

pacing devices [8, 9, 18, 23, 24, 27]. These protocols show considerable differences, as some centres have excluded

pacemaker-dependent patients and patients with ICDs, whereas others have imposed limitations on scanning body

regions or have restricted specific absorption rate (SAR) values. The aim of this study was to introduce and evaluate our

broader safety protocol for performing MRI examinations of patients with different cardiac pacing devices, including

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bradycardia PMs, ICDs and CRTs (cardiac resynchronisation therapy device), and to summarise our “real life”

experiences of scanning these patients.

Materials and Methods

Developing a Safety Protocol

The safety protocol was developed in close co-operation between the Departments of Cardiology and Radiology in the

autumn of 2011 after an increase in the demand for MRI in patients with different pacing devices. The multiprofessional

safety group comprised cardiologists, radiologists, physicists and radiographers. The protocol incorporated common

elements from the protocols in the published literature [8, 9, 18, 23, 24, 27] and was accepted by the Departments of

Radiology and Cardiology. The accepted protocol involved procedures for both MR-conditional and MR-unsafe cardiac

pacing devices and imposed no limitations on patients’ dependency on pacemakers or the body regions to scan. The

safety protocol was introduced to personnel (including radiologists of all sub spesialists) in several meetings in order to

implement it into the clinical practice.

The safety protocol and step-by-step procedures appear in Figs. 1 and 2 and are described below. Each patient was

evaluated separately and processed according to the protocol. We performed no emergency MRI examinations.

Patient Selection

We performed 68 consecutive MRI examinations for 64 patients with pacing devices at the Helsinki University Central

Hospital, Finland, between November 2011 and May 2013. The local institutional review board approved the study, and

the patients provided their written informed consent prior to MRI.

After receiving a referral from a requesting physician, a radiologist evaluated the need for an MRI study. If alternative

imaging techniques (e.g. ultrasound or CT) could provide similar information at less risk to the patient, MRI was

avoided. However, when MRI was considered necessary and the preferred imaging modality for the patient, the referral

was sent to the Department of Cardiology, where a cardiologist evaluated the feasibility of performing MRI for the

patient. If the patient was known to have abandoned or non-fixated leads, MRI was never performed. Additionally,

when the pacing device was manufactured before 2000, MRI was only seldom performed. A cardiologist added to the

patient’s electric medical records (EMR) the imaging decision, the type of pacing device and leads, as well as the

patient’s dependency on the pacemaker. After the cardiologist’s evaluation, the referral was sent back to the Department

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of Radiology, where a department secretary assigned an examination time for the patient for at least six weeks after the

PM installation and informed the referral unit, the pacemaker policlinic, and the radiologists and physicists of it.

Device Interrogation and Programming Prior to MRI

On the day of the MRI examination, the patient entered into the pacemaker policlinic, where a cardiologist recorded

device parameters, especially lead impedances and capture thresholds, sensing signal amplitudes, and battery voltage.

No MRI would have been performed if the patient showed any evidence of inadequate pacemaker function. When

needed, we assessed the patient’s dependency on the PM with transient inhibition of pacing. The pacing mode was

programmed to monitor-only (OAO / OVO / ODO) for non-PM-dependent patients in order to avoid MRI-induced

competitive pacing and possible proarrhythmias. Furthermore, the pacing mode was programmed to asynchronous

(AOO / VOO / DOO) for patients with no stable intrinsic rhythm. Additionally, since asynchronous pacing mode yields

a constant pacing rate, patients participating in cardiac MRI (CMR) were normally programmed to that mode.

Whenever possible, we disabled all other pacing functions, including the magnet rate, premature ventricular complex,

noise, ventricular sense, and conducted atrial fibrillation responses. The ICDs were programmed to therapy-off mode to

avoid delivering therapy as a result interpreting noise as tachyarrhytmia. Furthermore, we programmed the MR-

conditional systems according to the instructions of the pacing device manufacturers. We added the device settings and

parameters to the patient EMR.

MRI Scanning and Patient Monitoring During MRI

Before scanning, radiographers checked the EMR system to ensure that the patient had visited the pacemaker policlinic

and that the pacemaker was programmed for the MRI. Whenever the patient had an MR-unsafe PM or ICD system, a

cardiologist participated in the MRI examination. Otherwise, the patient arrived alone to the radiology department and

returned after the examination to the pacemaker policlinic for reprogramming. We updated the safety protocol after 61

patients, at which point the cardiologist typically stopped following the MRI scanning in the radiology department, but

remained available by phone in case of an emergency, whereas the radiologist continued monitoring the patient’s heart

rhythm.

All MRI examinations were performed with a Siemens Magnetom Avanto 1.5 Tesla MRI scanner (Siemens Healthcare,

Erlangen, Germany) with a maximum gradient field of 45 mT/m and a slew rate of 200 T/m/s. We scanned patients

with MR-conditional pacing systems according to the instructions of the device manufacturers, but scanned patients

with MR-unsafe devices in the International Electrotechnical Commission (IEC) normal operating mode (both SAR and

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dB/dt) [29], when possible, without sacrificing image quality. Thus, in patients with MR-unsafe pacing devices and

those MR-conditional PMs with restrictions required by the manufacturer, we limited the whole-body-averaged Specific

Absorption Rate (SAR) value to below 2 W/kg before scanning in sequences with high SAR. Furthermore, as RF-

induced thermal damage depends on RF-power and exposure time, we minimised the number of required pulse

sequences in order to minimise the scanning time.

We performed electrocardiographic (ECG) and pulse oximetry monitoring during MRI to detect any changes in heart

rate or rhythm related to MRI-induced pacemaker inhibition, loss of pacemaker capture, or ventricular arrhythmias. The

cardiologist or radiologist would have stopped the MRI acquisition immediately whenever he or she deemed it

necessary. Additionally, we monitored the patients with a camera and asked them to immediately inform the

investigators via an intercom audio system of any torque or heating sensation, pain, palpitations or any other unusual

symptoms during imaging. Resuscitation equipment was available outside the MRI room during all examinations in

case of an emergency.

Post-MRI Pacemaker Evaluation

Because MRI can alter the function of a pacing device, we recorded lead impedances and capture thresholds, sensing

signal amplitudes, and battery voltage after each examination. In the case of PMs from Boston Scientific, the battery

voltages were only informed to be good or not good, and thus these were excluded from battery status comparisons. We

also carried out PM interrogations and programmed the original PM settings immediately after the examination by a

cardiologist in either the Radiology Department or the pacemaker policlinic. We also added the device parameters to the

EMR and performed PM checks after one month of MRI during a routine follow-up in the pacemaker policlinic or

remotely with device specific home-monitoring systems. A few patients came to MRI examination from other hospitals,

and therefore, one month follow-up results were not available for the analysis.

Analysis of data

In this retrospective study, we evaluated our safety protocol by comparing the measured device parameters prior to and

after MRI examinations. For each patient, we measured atrial and ventricular pacing capture thresholds, lead

impedances, P/R wave sensing amplitudes, and battery voltage before, immediately after, and one month after MRI

scanning. Variations exceeding 30%, 40% and 50% for the lead impedances, sensing and capture thresholds,

respectively, were considered significant changes in the lead performance [11]. Additionally, we calculated the number

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of examinations that caused an atrial or ventricular capture threshold increase of ≥ 1.0 V at 0.4 ms pulse duration. The

changes of less than 1.0 V were considered to be clinically insignificant as these changes may be related to normal

variations in the underlying electrophysiological conditions [30]. We calculated and summarised absolute changes and

percentages of change from the baseline parameters using medians and interquartile ranges (IQRs). Discrete variables

are summarised as absolute numbers and percentages. We also used the paired data to compare the pre- and post-scan

samples, and the related-samples Wilcoxon signed-rank test with MRI as the unit of analysis to compare the PM

variables. Additionally, to compare non-normally distributed unpaired data, we used the independent-samples Mann-

Whitney U test. We performed all statistical tests at a 5% level of significance using SPSS, version 19 (SPSS Inc,

Chicago, IL, USA).

Results

Patients and examinations

Our study cohort consisted of 64 patients having altogether 68 MRI scans. From the 64 patients (100%), 60 patients

(94%) had a PM (including 22 (37%) MR-conditional and 38 (63%) MR-unsafe PMs), while two patients (3%) had an

MR-unsafe CRT device and two (3%) had an MR-unsafe ICD system. The devices studied in the current investigation

appear in Table 1. Four (6%) patients were scanned twice (two patients with an MR-unsafe PM and two patients with an

MR-conditional PM), and six patients had two body regions scanned in the same MRI examination.

The mean age of the patients was 67 ± 14 years, and 42% (27/64) were women. Altogether 21 (31%) of the

examinations were scans of the thorax area, and 20 (29%), 17 (25%) and 16 (24%) of the examinations were MRI scans

of spine, head and cardiac, respectively. The remainder were scans of the pelvis, liver, vagina, rectum, wrist, lung,

carotid artery, soft tissue of the neck, pancreas and knee. All MRI examinations were performed with an adequate

image quality for diagnosis, although in a few CMR studies we found notable artifacts due to pacemaker generator and

pacing leads.

Clinical events during the MRI examinations

All MRI examinations (68/68, 100%) were completed safely, although two (3%) patients with an MR-unsafe pacemaker

(Guidant Insignia I Entra SR and Medtronic Kappa KSR 401) experienced a change in pacing rate when entering the

MRI environment. In the patient with a Guidant Insignia PM, the pacing mode was set to asynchronous prior to MRI

with a pacing rate of 70 bpm, but when exposed to the magnetic field, the pacing rate rose to 100 bpm, because the

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magnet-mode was unintentionally left active. Scanning was performed normally, and the patient felt no discomfort. In

the patient with Medtronic Kappa KSR401, the pacing rate decreased from 80 to 65 bpm due to low battery voltage.

Additionally, we observed no unexpected changes in the heart rate or rhythm, indicating inhibition of pacing. Nor did

we see any shock deliveries, sustained atrial or ventricular arrhythmias during the MRI examinations. Furthermore,

none of the patients reported any torque or heating sensations, palpitations, pain, dizziness or other unusual symptoms

during MRI.

Device function after MRI

We were able to interrogate all devices normally after MRI, and found no changes in the programmed parameters or

any damage to the pacemaker circuits or movement of the pulse generator. Detailed comparisons of the PM variables

obtained at baseline, immediately after the MRI examination and at the one-month follow-up revealed small variations

in several variables (Table 2). The variations observed in the scans of the thorax and other areas appear in the electronic

supplementary material (Tables i and ii). As Tables 3 and 4 show, we found no significant differences in the variable

changes between the MR-conditional and MR-unsafe pacing systems, or between scans of the thorax and other scan

areas.

The immediate and one-month changes in the device parameters fell within 20% of the baseline for most of the

participants (Table 5), although we did note significant variability in some parameters. The changes in generator voltage

were not clinically significant. Although we observed 50% of the increase in pacing capture thresholds, whether atrial

or ventricular, in 5 (7%) patients immediately after MRI and in 6 (9%) patients at the one-month follow-up, none of the

changes reached the level of ≥ 1.0 V, so they were therefore considered clinically insignificant. In the patients who were

scanned twice, the changes in device parameters between scans were negligible.

Two (3%) pacemakers switched to back-up mode after the one-month follow-up: one because of low generator voltage

in an older PM with a nearly depleted battery, and the other most likely because of radiation therapy treatment for

papillary thyroid carcinoma producing a high radiation dose to the PM generator. Furthermore, for clinical reasons and

guided by the MRI results, the PM for one patient was replaced with an ICD immediately after MRI scanning.

Discussion

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This study introduced our safety protocol for performing MRI in patients with both MR-conditional and MR-unsafe

implanted cardiac pacing devices. Development of the protocol was a collaborative effort between the Departments of

Radiology and Cardiology, and thus took advantage of the multiprofessional knowledge of cardiologists, radiologists,

radiographers and medical physicists. The results of the present study support the previous observations from other

studies [7-12, 17-26] that, when certain precautions are adhered to, MRI examinations in this particular patient group

could be performed safely. The image quality was sufficient to establish the diagnosis in all examinations. However,

PM generators and pacing leads containing ferromagnetic material caused perceivable artefacts, though not preventing

the diagnosis, in the CMR images.

Pacemaker-MRI interactions in this study cohort were rare, and no patients experienced power-on-resets. However, in

two examinations for patients with an MR-unsafe PM, magnet-rate pacing occurred due to the activation of a reed

switch in a strong magnetic field. Despite the pacing rate changes, the scans were performed normally, and the patients

experienced no discomfort. The interactions observed were transient and resulted in no adverse consequences for the

patient or cardiac device function. Though not observed in our study, in patients with higher heart rates and pacing

modes set to sense-only, the change in setting to asynchronous pacing mode could prove clinically significant due to a

competing rhythm; magnet-mode should therefore be switched off whenever possible [5]. Unfortunately, this is not

always possible with older MR-unsafe systems, so such devices are more vulnerable to changes in pacing mode or

pacing rate when exposed to an MRI environment.

We saw no evidence of device malfunction either immediately after MRI scans or during repeat testing one month after

examination. We were able to interrogate each pacing device normally after MRI, and found no changes in the

programmed parameters. Although the distributions of immediate and one-month changes in the device parameters fell

within 20% of the baseline for most of the participants, we also noted significant variability in some parameters, and

some changes approached clinically important thresholds. The observed changes immediately after the MRI and one

month later were not always observed in the same patients. These functional parameter changes may have occurred due

to the different investigators or extra systoles in the measurements. The variable changes were independent of the

scanned body region, and we found no differences in functional parameters between MR-conditional or MR-unsafe

devices. However, the patients with an MR-unsafe system were carefully selected, and a few of them with an older

pacing system or abandoned leads underwent no MRI examination. The decreases in generator voltage were scarce at

the one-month follow-up and were comparable to the normal depletion of battery voltage. Because pacing capture

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threshold values did not increase ≥1.0 V in any patient of our study cohort, local tissue heating was presumably

insufficient to lead to myocardial necrosis.

Studies have revealed a slightly higher proportion of battery voltage, pacing lead threshold and impedance, as well as

high-voltage impedance parameter change events, though mainly clinically irrelevant, in a small percentage of patients

who underwent MRI [7-9, 18, 22]. Nevertheless, despite the changes observed in functional parameters in MRI patients,

similar changes have also occurred in patients who have not undergone MRI [22]. In our study cohort, we also found a

small but statistically significant increase in P wave detection [0.2 mV (0.00 mV to 0.60 mV)] immediately after MRI,

as well as a small but statistically significant decrease in right ventricular lead impedance [-10 Ω (-40 Ω to 16 Ω)] at the

one-month follow-up.

Because the implantations and use of MR-conditional PMs and ICDs have grown in recent years, the vital diagnostic

capabilities provided by MRI are nowadays also available to patients with cardiac pacing devices. However, because a

long time passes before MR-unsafe devices are entirely replaced with MR-conditional systems, protocols should also be

available which permit low-risk MRI scans of patients with MR-unsafe devices. It is reasonable for all MRI providers to

adjust their policies and procedures either to appropriately scan or to refuse to scan patients with pacing systems. MRI

examinations for such patients should be performed only in experienced centres with close co-operation between the

departments of radiology and cardiology, as the use of multiprofessional co-operation is essential to providing safe MRI

examinations and procedures for patients with cardiac pacing devices. In practice, patient evaluation and safety

decisions should be done with a consultation with a radiologist and cardiologist. Because deciding on the appropriate

pacing mode during MRI examination requires arrhythmia expertise, as well as an understanding of the patient’s initial

indication for the device, arrhythmia history, and underlying rhythm/pacemaker dependency, a cardiologist is needed to

perform pacemaker interrogations and programming before and after MRI. Additionally, a cardiologist or radiologist

should be present to monitor the patient during MRI. Because RF and gradient pulses during MRI scans sometimes

strongly affect ECG, pulse oximetry is also necessary to provide a reliable monitoring signal. Radiologists should plan

scanning protocols, and a physicist should assist in adjusting scanning parameters in order to ensure sufficient image

quality for diagnosis. Additionally, MRI radiographers should be familiar with the safety procedures for scanning these

patients and also be prepared to immediately remove the patient from the MRI scanner upon discovery of a significant

problem. Furthermore, proper resuscitation equipment should be at hand and ready for immediate use in case of an

emergency.

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Our retrospective “real life” study had certain limitations. First, there was a relatively small sample size, and thus, the

results of this study may have insufficient power to detect uncommon complications related to MRI scanning.

Specifically, only two patients had a CRT system, and only two others had an ICD device. However, previous studies

have shown that MRI scanning of patients with these systems can be performed safely under certain conditions even

though ICDs and CRTs are larger, contain more ferromagnetic material, and have larger capacitors and longer leads

than PMs [9-11, 18, 20-22, 24, 25, 27]. Second, while the population of the current study was quite inhomogeneous, this

study still had a limited number of different cardiac pacing device models to study, so the results cannot be generalised

to all cardiac pacing devices and pacing leads. Third, because of the nature of this study, several cardiologists

programmed and measured the devices prior to and after MRI, which may have caused variations in the measurements,

but continues to reflect the clinical procedure. Fourth, it may be questioned if one month follow-up was sufficient to

assess the consequences of lead tip heating, as scarring might not be in its final state at one month. Therefore, we might

be unable to detect possible long-term complications. Last, the present findings are limited to 1.5 Tesla scanners and

should not be extrapolated to scanners with other field strengths.

Conclusions

The current study introduced and evaluated the safety of a dedicated protocol for performing MRI scans in patients with

cardiac pacing devices in a single institution. In our study, the MRI examinations of these patients could be performed

safely when proper pacing device programming and patient monitoring was adhered and there were no alternative

imaging modalities available for a diagnosis. We observed no differences between the results of the MR-conditional and

MR-unsafe devices selected in this particular study, and none between scans of the thorax area and of other scanning

regions.

Conflict of interest

SP has been a consultant for St. Jude Medical, Medtronic, Boston Scientific and Biotronik. These vendors have also

paid him congress fees. All other authors declare that they have no competing interests.

Funding

This study was supported by the State Subsidy for University Hospitals in Finland.

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[20] Mollerus M, Albin G, Lipinski M, Lucca J. Magnetic resonance imaging of pacemakers and implantable

cardioverter-defibrillators without specific absorption rate restriction. Europace 2010;12:947-951.

[21] Naehle CP, Kreuz J, Strach K et al. Safety, feasibility, and diagnostic value of cardiac magnetic resonance imaging

in patients with cardiac pacemakers and implantable cardioverters/defibrillators at 1.5 T. Am Heart J 2011;161:1096-

1105.

[22] Cohen JD, Costa HS, Russo RJ. Determining the risks of magnetic resonance imaging at 1.5 tesla for patients with

pacemakers and implantable cardioverter defibrillators. Am J Cardiol 2012;110:1631–1636.

[23] Pulver AF, Puchalski MD, Bradley DJ et al. Safety and imaging quality of MRI in pediatric and adult congenital

heart disease patients with pacemakers. PACE 2009;32:450–456.

[24] Burke PT, Ghanbari H, Alexander PB, Shaw MK, Daccarett M, Machado C. A protocol for patients with

cardiovascular implantable devices undergoing magnetic resonance imaging (MRI): should defibrillation threshold

testing be performed post-(MRI). J Interv Card Electrophysiol 2010;28:59-66.

[25] Mollerus M, Albin G, Lipinski M, Lucca J. Cardiac biomarkers in patients with permanent pacemakers and

implantable cardioverter-defibrillators undergoing an MRI scan. PACE 2008;31:1241-1245.

[26] Sasaki T, Hansford R, Zviman MM et al. Quatitative assessment of artifacts on cardiac magnetic resonance

imaging of patients with pacemakers and implantable cardioverter-defibrillators. Circ. Cardiovasc Imaging 2011;4:662-

670.

[27] European Society of Cardiology (ESC): European Heart Rhythm Association (EHRA), Brignole M, Auricchio A,

Baron-Esquivias G et al. 2013 ESC guidelines on cardiac pacing and cardiac resynchronization therapy: the task force

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on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in

collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J 2013;34:2281-2329.

[28] Roguin A, Zviman MM, Meininger GR et al. Modern pacemaker and implantable cardioverter/defibrillator system

can be magnetic resonance imaging safe – in vitro and in vivo assessment of safety and function at 1.5 T. Circulation

2004;110:475-482.

[29] International Electrotechnical Commission (IEC). IEC 60601-2-33, Ed. 2.0 Medical electrical equipment – Part 2-

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[30] Preston TA, Fletcher RD, Lucchesi BR, Judge RD. Changes in myocardial threshold: physiologic and

pharmacologic factors in patients with implanted pacemakers. Am Heart J 1967;74:235-242.

Figure legends:

Fig. 1 Evaluation before MRI examination. EMR = Electric Medical Record

Fig. 2 Procedures immediately before and after the MRI examination. * The safety protocol was updated after 61

patients; at that point, the cardiologist no longer needed to be present during the MRI examination. EMR = Electric

Medical Record; AOO / VOO / DOO = asynchronous pacing modes for atrial / ventricular / dual chamber systems;

OAO / OVO / ODO = pacing inhibited modes for atrial / ventricular / dual chamber systems; ECG =

Electrocardiography; IEC = International Electrotechnical Commisson

Table legends:

Table 1 The pacing device models studied. The grey colour indicates the MR-conditional pacing devices studied

Table 2 Device variables before MRI and median difference after MRI (all MRI examinations)

Table 3 Comparison of device variable changes between MR-conditional and MR-unsafe cardiac pacing devices before

and after MRI

Table 4 Comparison of changes in device variables between examinations of the thorax area and other areas before and

after MRI

Table 5 Distribution of changes in device variables (all MRI examinations)

Electronic supplementary material

Table i Device variables before MRI and median differences after MRI (all examinations of the thorax area)

Table ii Device variables before MRI and median differences after MRI (all examinations except scans of the thorax

area)

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Table 1. The pacing device models studied. The grey colour indicates the MR-conditional pacing devices studied

Boston Scientific Guidant Medtronic St. Jude Medical

Device type Model

Patients,

n Model

Patients,

n Model

Patients,

n Model

Patients,

n

Pacemaker S502 2 1290 1 REDR01 4 PM2224 19

J176 1 1198 2 SEDR01 1 5156 3

EN1DR01 2 5386 5

KDR901 2 PM2212 3

KSR401 1 5826 5

5816 9

5610 1

PM2136 2

2404 1

ICD CD1211-36 1

CD1277-36 1

CRT-D CD3251-40 1

CRT-P PM3212 1

ICD = implantable cardioverter-defibrillator, CRT = cardiac resynchronisation therapy device

n = number of patients

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Table 2. Device variables before MRI and median difference after MRI (all MRI examinations)

Variable Patients,

n

Median value at baseline

(IQR)

Median difference

(IQR)

Median percentage

change from

baseline (IQR)

P value

§

Immediately after MRI

Atrial capture threshold, V 50 0.75 (0.50 to 0.75) 0.00 (0.00 to 0.08) 0.0 (0.0 to 8.3) 0.406

Right ventricular capture threshold, V 58 0.75 (0.60 to 0.90) 0.00 (-0.08 to 0.00) 0.0 (-6.8 to 0.0) 0.888

Left ventricular capture threshold, V 2 2.18 (1.89 to 2.46) -0.48 (-0.59 to -0.36) 26.4 (-35.1 to -17.8) 0.180

P-wave amplitude, mV 45 2.60 (1.58 to 4.08) 0.2 (0.00 to 0.60) 7.1 (0.0 to 25.9) <0.001*

Right ventricular R-wave amplitude, mV 51 11.4 (7.50 to 12.00) 0.00 (0.00 to 0.00) 0.0 (0.0 to 0.0) 0.709

Atrial lead impedance, Ω 50 440 (395 to 490) -2 (-26 to 17) -0.5 (-4.6 to 3.5) 0.231

Right ventricular lead impedance, Ω 58 510 (399 to 567) 0 (-18 to 16) 0.0 (-3.8 to 3.2) 0.697

Left ventricular lead impedance, Ω 2 915 (878 to 953) -80 (-90 to -70) -8.6 (-9.4 to -7.9 0.180

Battery voltage, V 56 2.79 (2.78 to 2.98) 0.00 (0.00 to 0.00) 0.0 (0.0 to 0.0) 0.279

One-month follow-up after MRI

Atrial capture threshold, V 41 0.75 (0.50 to 0.75) 0.00 (0.00 to 0.10) 0.0 (0.0 to 20.0) 0.985

Right ventricular capture threshold, V 49 0.75 (0.60 to 0.90) 0.00 (-0.15 to 0.10) 0.0 (-20.0 to 20.0) 0.945

Left ventricular capture threshold, V 2 2.18 (1.89 to 2.46) -0.63 (-0.69 to -0.56) -29.3 (-30.3 to -28.3) 0.180

P-wave amplitude, mV 38 2.60 (1.58 to 4.08) 0.00 (-0.08 to 0.38) 0.0 (-3.1 to 11.2) 0.535

Right ventricular R-wave amplitude, mV 42 11.4 (7.50 to 12.00) 0.00 (-0.15 to 0.10) 0.0 (-1.3 to 5.0) 0.904

Atrial lead impedance, Ω 40 440 (395 to 490) 0 (-16 to 15) 0.0 (-3.4 to 3.6) 0.577

Right ventricular lead impedance, Ω 49 510 (399 to 567) -10 (-40 to 16) -2.1 (-7.6 to 3.7) 0.032*

Left ventricular lead impedance, Ω 2 915 (878 to 953) -10 (-10 to -10) -1.1 (-1.2 to -1.1) 0.157

Battery voltage, V 47 2.79 (2.78 to 2.98) 0.00 (-0.01 to 0.00) 0.0 (-0.2 to 0.0) 0.179

IQR = interquartile range, MRI = magnetic resonance imaging

§ Obtained by using the related-samples Wilcoxon signed-rank test

* Statistically significant results


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Table 3. Comparison of device variable changes between MR-conditional and MR-unsafe cardiac pacing devices

before and after MRI

Variable Patients

(MR-

conditional)

, n

MR-conditional: Median

difference between values at

baseline and immediately

after MRI (IQR)

MR-unsafe: Median

difference between values at

baseline and immediately

after MRI (IQR)

Patients

(MR-

unsafe), n

P

value

§


Atrial capture threshold, V 19 0.00 (0.00 to 0.10) 0.00 (0.00 to 0.00) 31 0.139

Right ventricular capture threshold, V 19 0.00 (0.00 to 0.14) 0.00 (-0.10 to 0.00) 39 0.062

Left ventricular capture threshold, V 0 -0.48 (-0.59 to -0.36) 2 NA

P-wave amplitude, mV 18 0.20 (0.00 to 0.60) 0.20 (0.00 to 0.60) 27 1.000

Right ventricular R-wave amplitude, mV

17 0.00 (0.00 to 0.00) 0.00 (0.00 to 0.00) 34 0.974

Atrial lead impedance, Ω 19 0 (-30 to 20) -5 (-20 to 9) 31 0.833

Right ventricular lead impedance, Ω 19 0 (-35 to 0) 2 (-12 to 16) 39 0.139

Left ventricular lead impedance, Ω 0 -80 (-90 to -70) 2 NA

Battery voltage, V 19 0.00 (0.00 to 0.00) 0.00 (0.00 to 0.00) 37 0.540



Right ventricular capture threshold, V 18 0.00 (-0.19 to 0.25) 0.00 (-0.13 to 0.00) 31 0.449


P-wave amplitude, mV 17 0.00 (-0.20 to 0.20) 0.00 (-0.00 to 0.40) 21 0.728


17 0.00 (0.00 to 0.80) 0.00 (-0.20 to 0.50) 25 0.791


Right ventricular lead impedance, Ω 18 -30 (-55 to 0) -10 (-27 to 18) 31 0.168


Battery voltage, V 18 0.00 (0.00 to 0.00) 0.00 (-0.01 to 0.00) 29 0.399


§ Obtained by using the independent-samples Mann-Whitney U test


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Table 4. Comparison of changes in device variables between examinations of the thorax area and other areas

before and after MRI

Variable Patients

(thorax), n

Thorax: Median

difference between values

at baseline and

immediately after MRI

(IQR)

Other: Median difference

between values at baseline

and immediately after MRI

(IQR)

Patients

(other), n

P value §





P-wave amplitude, mV 16 0.20 (0.00 to 0.60) 0.20 (0.00 to 0.60) 29 0.838


15 0.00 (-0.25 to 0.00) 0.00 (0.00 to 0.00) 36 0.801


Right ventricular lead impedance, Ω 18 0 (-18 to 3) 0 (-17 to 16) 40 0.069


Battery voltage, V 20 0.00 (0.00 to 0.00) 0.00 (0.00 to 0.00) 36 0.014*




Left ventricular capture threshold, V 0 -0.63 (-0.69 to -0.56) 2

P-wave amplitude, mV 12 0.05 (-0.08 to 0.23) 0.00 (-0.08 to 0.40) 26 0.699


12 0.00 (-0.55 to 1.10) 0.00 (0.00 to 0.43) 30 0.773


Right ventricular lead impedance, Ω 15 0 (-40 to 18) -18 (-37 to 10) 34 0.529

Left ventricular lead impedance, Ω 0 -10 (-10 to -10) 2

Battery voltage, V 17 0.00 (0.00 to 0.00) 0.00 (-0.01 to 0.00) 30 0.007*


§ Obtained by using the independent-samples Mann-Whitney U test

* Statistically significant results


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Table 5. Distribution of changes in device variables (all MRI examinations)

Variable Patients

, n

Decrease, n (%) Increase, n (%)

Immediately after MRI > 50% 41-50% 31-40% 21-30% ≤ 20% 21-30% 31-40% 41-50% > 50%

Atrial capture threshold, V 50 0 (0) 2 (4) 2 (4) 1 (2) 35 (70) 5 (10) 2 (4) 1 (2) 2 (4)

Right ventricular capture

threshold, V

58 0 (0) 2 (3) 2 (3) 2 (3) 42 (72) 1 (2) 4 (7) 2 (3) 3 (5)

Left ventricular capture

threshold, V

2 0 (0) 1 (50) 0 (0) 0 (0) 1 (50) 0 (0) 0 (0) 0 (0) 0 (0)

P-wave amplitude, mV 45 0 (0) 1 (2) 0 (0) 0 (0) 29 (64) 4 (9) 4 (9) 5 (11) 2 (4)

Right ventricular R-wave

amplitude, mV

51 1 (2) 2 (4) 0 (0) 1 (2) 43 (84) 0 (0) 2 (4) 1 (2) 1 (2)

Atrial lead impedance, Ω 50 0 (0) 0 (0) 0 (0) 2 (4) 48 (96) 0 (0) 0 (0) 0 (0) 0 (0)

Right ventricular lead

impedance, Ω

58 0 (0) 0 (0) 0 (0) 2 (3) 54 (93) 1 (2) 0 (0) 1 (2) 0 (0)

Left ventricular lead

impedance, Ω

2 0 (0) 0 (0) 0 (0) 0 (0) 2 (100) 0 (0) 0 (0) 0 (0) 0 (0)

Battery voltage, V 56 0 (0) 0 (0) 0 (0) 0 (0) 56 (100) 0 (0) 0 (0) 0 (0) 0 (0)

One month after MRI

Atrial capture threshold, V 41 2 (5) 0 (0) 4 (10) 0 (0) 26 (63) 5 (12) 1 (2) 0 (0) 3 (7)

Right ventricular capture

threshold, V

49 0 (0) 4 (8) 3 (6) 4 (8) 26 (53) 1 (2) 5 (10) 3 (6) 3 (6)

Left ventricular capture

threshold, V

2 0 (0) 0 (0) 1 (50) 1 (50) 0 (0) 0 (0) 0 (0) 0 (0) 0 (0)

P-wave amplitude, mV 38 0 (0) 0 (0) 0 (0) 3 (8) 28 (74) 3 (8) 3 (8) 1 (3) 0 (0)

Right ventricular R-wave

amplitude, mV

42 1 (2) 1 (2) 2 (5) 2 (5) 29 (69) 3 (7) 2 (5) 0 (0) 2 (5)

Atrial lead impedance, Ω 40 0 (0) 0 (0) 0 (0) 1 (3) 39 (98) 0 (0) 0 (0) 0 (0) 0 (0)

Right ventricular lead

impedance, Ω

49 0 (0) 0 (0) 0 (0) 3 (6) 44 (90) 1 (2) 1 (2) 0 (0) 0 (0)

Left ventricular lead

impedance, Ω

2 0 (0) 0 (0) 0 (0) 0 (0) 2 (100) 0 (0) 0 (0) 0 (0) 0 (0)

Battery voltage, V 47 0 (0) 0 (0) 0 (0) 0 (0) 47 (100) 0 (0) 0 (0) 0 (0) 0 (0)

Variations in lead performance exceeding 30%, 40% and 50% for lead impedance, sensing and capture threshold, respectively, were considered significant

[11]


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Evaluation of the referral (radiologist)

Alternative modality

Yes

Cardiologist’s evaluation of the

pacing system for MRI and entry of

decision to patient’s EMR (type and

manufacturer of the pacing system)

Requesting physician - referral

Is MRI the imaging

method of choice?

Referral send back to MRI department secretary

Allocate MRI examination

time for patient (at least 6

weeks from the implantation

of the device) and inform the

referral unit of the allocated

time

Inform the pacemaker

policlinic of the allocated time

Inform the patient of the

allocated time and fix visits to

the pacemaker policlinic before

and after the MRI examination

No

No

Yes

Inform a radiologist and a

physicist of the examination time

Figure 1

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Programming all other diagnostic

and therapeutic features off

Patient arrives to the

pacemaker policlinic

Check and entry of device parameters: lead

impedance and pacing capture thresholds,

P/R wave amplitudes, and battery voltage

Pacemaker dependent?

AOO / VOO / DOO OAO / OVO / ODO

Adding the applied system settings and

measured parameters to the patient’s EMR

MR-conditional

pacing system

Patient arrives to the MRI department

Scanning at 1.5 T according

to the instructions of the

pacing device manufacturer

Scanning at 1.5 T with IEC normal

mode if possible without sacrificing

image quality, minimizing the number

of pulse sequences

Cardiologist participates to

the MRI examination *

Monitoring of ECG,

pulse oximetry and

patient symptoms

Interrogation and reprogramming of the

original settings after MRI. Adding

device parameters to the patient’s EMR

No Yes

MR-unsafe

pacing system

Device check one month

after the MRI examination

Figure 2

Documents

MRI with cardiac pacing devices – Safety in clinical practice