MRI of Patients With Cardiac Pacemakers: A Review of the Medical ...

H e a l t h C a r e Po l i c y a n d Q u a l i t y • R ev i ew Zikria et al. MRI of Patients With Cardiac Pacemakers Health Care Policy and Quality Review

MRI of Patients With Cardiac Pacemakers: A Review of the Medical Literature Joseph F. Zikria1 Stephen Machnicki Eugene Rhim Tandeep Bhatti Robert E. Graham

OBJECTIVE. Numerous studies testing the use of pacemakers with MRI have been published. Our aim was to analyze these trials to determine the safety of MRI for patients with cardiac pacemakers. We performed a systematic search of peer-reviewed databases. A total of 31 articles were reviewed. CONCLUSION. The data are heterogeneous with regard to MRI being considered for patients with pacemakers, and the benefits of the imaging should outweigh the risks.

Zikria JF, Machnicki S, Rhim E, Bhatti T, Graham RE

R

Keywords: MRI, pacemaker, safety DOI:10.2214/AJR.10.4239 Received January 4, 2010; accepted after revision June 27, 2010. 1

All authors: Lenox Hill Hospital, 100 E 77th St., 6 Black Hall, New York, NY 10075. Address correspondence to J. F. Zikria ([email protected]).

AJR 2011; 196:390–401 0361–803X/11/1962–390 © American Roentgen Ray Society

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ecently, there has been debate about whether patients with cardiac pacemakers can undergo MRI. Risks associated with MRI arise from three distinct mechanisms that could affect the pacemaker: the static magnetic field causing attractive forces, radiofrequency energy causing heat damage, and gradient magnetic fields that could induce electrical currents in the device [1]. Since 2007, there have been at least 17 supposed MRI-associated deaths worldwide among patients with pacemakers, but none of the deaths occurred during appropriate physician-supervised monitoring [2]. Although there have been numerous published studies showing the ability of patients with pacemakers to undergo MRI without adverse events, past incidents continue to generate interest in this topic. A Cleveland Clinic survey asked academic radiologists and cardiologists whether they would image a patient with a pacemaker. Responses from radiologists suggested that 97% would not do so, whereas 34% of the cardiologists surveyed stated that they would under the right circumstances [3]. Currently, the U.S. Food and Drug Administration has labeled packages of all cardiac pacemakers as “MRI unsafe,” and these examinations are being performed only in specialized centers [4]. The Food and Drug Administration remains concerned that the extent to which arrhythmogenic risk is dependent on scan parameters, MR system, patient and device position, and device design has not been adequately characterized [5]. In 2007, the American Heart Association determined in concordance with the American

College of Cardiology Foundation that “MR examination of non-pacemaker-dependent patients is discouraged and should only be considered in cases where there is a strong clinical indication and in which the benefits clearly outweigh the risks” [1]. With regard to pacemaker-dependent patients, they recommended that MRI examinations “should not be performed unless there are highly compelling circumstances and when the benefits clearly outweigh the risks” [1]. The 2007 American College of Radiology guidelines further reiterate that the presence of implanted cardiac pacemakers should be considered a “relative contraindication” for MRI and should be considered only in a “case-bycase and site-by-site basis” [6]. However, it has been estimated that a patient with a pacemaker will have a 50–75% probability of being indicated for an MRI study over the lifetime of the device [7]. The aim of this review is to evaluate the literature on patients with pacemakers who underwent MRI examinations to determine its safety and help define a consensus statement. Materials and Methods In April 2009, a comprehensive search was conducted involving the electronic peer-reviewed literature databases PubMed and Cochrane Library. These searches were developed in close consultation with an internist, a cardiologist, a radiologist, and a generalist librarian. Reference lists from identified studies and reviews were manually scanned to identify any other relevant studies. A search of ClinicalTrials.gov was also done to identify any studies that were registered as completed but not

AJR:196, February 2011

MRI of Patients With Cardiac Pacemakers yet published. Requests for original data were made by contacting authors or principal investigators. Only articles that had abstracts available in English were included, for a total of 514 titles and abstracts. All studies that involved pacemaker interactions with humans or animals or had in vitro models were included. From the 514 articles identified, those that discussed implantable cardioverter defibrillators and other devices were excluded; duplicate articles were eliminated as well. Case reports or studies with only one test subject and editorials were not included in the analysis from the 107 publications selected, resulting in a total of 31 publications being selected for review (Fig. 1).

Results In Vitro Studies Of the 31 publications identified for the review, 17 were in vitro studies (Table 1). One study used a magnetic strength of 0.2 T, four studies used a magnetic strength of 0.5 T, nine studies used a magnetic strength of 1.5 T, and three studies used a magnetic strength of 3 T. Specific absorption rate (SAR) levels (the rate at which energy is absorbed by the body when exposed to a radiofrequency energy field) were not determined for 11 studies but ranged from 0.6 W/kg to 3.54 W/kg for the other six studies. Fourteen MRI studies focused on the pacemaker, one focused on the brain region, one was “extrathoracic,” and one study included three MRI scans of the head, two of the lumbar spine, and four of the thorax of a phantom. Twelve pacemaker companies were studied. Pacemaker function—Pacemaker functioning was evaluated in nine of the studies [8–16]. Four studies revealed no change in pacemaker function [8, 10, 13, 15]. One study observed inhibition at the most sensitive device settings when the pacemaker was programmed to dual-mode dual-pacing dual-sensing (DDD) mode [14]. Another study observed that there was inhibition in the ventricular pace ventricular sense ventricular inhibited (VVI) mode and complete inhibition of atrial and ventricular lead, as well as rapid ventricular pacing at 150 beats per minute (bpm) in DDD mode [16]. The remaining three studies showed pacemakers switching to demand mode, ventricular backup pacing activation, and electrical reset [4, 9, 11]. Reed switch activity—Reed switches in a pacemaker are composed of two ferromagnetic strips activated by a magnetic field for the purpose of testing the pacing capacity. One study found that all pacemakers had reed switch operation by static magnetic fields, re-


Fig. 1—Outline of review process.

514 Titles and abstracts were identified through database searches: • 216 (Pacemaker MRI) + 71 (Cardiac Pacemaker MRI Safety) + 209 (MRI Pacemaker) Medline/PubMed • 18 (MRI) Cochrane Library

Reference lists from identified publications were manually scanned.

107 Publications selected after review of titles and abstracts and elimination of duplicates.

31 Publications included in review that involved human, animal, or in vitro studies.

sulting in asynchronous pacing [16]. However, another study showed that four of 16 pacemakers had reed switch deactivation when the pacemakers were positioned in the bore of the magnet [10]. Another study observed that reed switches were closed in low magnetic fields (< 50 mT) and opened in 50% of the tested orientations in high magnetic fields (> 200 mT) [17]. Temperature changes—Temperature changes were recorded in six of the studies. One study found a maximum temperature change of 45.9°C at the lead tip with a 1.5-T scan, but the SAR level was not stated [18]. Another study showed a maximum temperature change of 23.5°C at the lead tip at 0.5 T [10]. One study reported that scans of the head and lumbar regions at 1.5 T had temperature changes less than or equal to 0.5°C, whereas chest area temperatures ranged from 0.4°C to 3.6°C at the lead tips [14]. Another study also revealed a temperature change of 11.9°C at 1.5 T when the lead lengths were longer and the pacemaker was placed in the right hemithorax compared with the left hemithorax (6.3°C), whereas one study found temperature changes of less than 4.0°C with the highest temperatures at the tip of the ventricular electrode [8, 19]. One study showed that a brain MRI scan at 3 T with a transmit-receive head coil may have caused a maximum temperature increase at the pacemaker lead tip of 2.98°C [15]. Battery changes—Two studies showed no changes in battery status at 1.5 T [12, 14]. Torque—One study determined that, after testing 31 pacemakers, there was no safety risk in modern pacemakers with respect to magnetic force and torque induced by the static magnetic field of a 1.5-T MRI scanner [20]. Torque was significantly reduced

in new-generation pacemakers. One study found that the force and torque generated was also negligible [12]. Another study (3 T) showed a mean translation force on the pacemaker of 374.38 ± 392.75 mN and a mean torque of 2.29 ± 4.08 × 10 −3 N × m with normal pacemaker function [15]. One study observed that three pacemakers exhibited angles greater than 45° on both long-bore and short-bore 1.5-T MRI scanning, and four pacemakers exhibited angles greater than 45° on 3-T MRI scanning [21]. In Vivo Animal Studies Four publications involved studies using in vivo animal trials (Table 2). A total of seven dogs and nine pigs were examined at a field strength of 1.5 T [22–24]. Two dogs were studied at a field strength of 0.15 T [25]. No deaths were reported. Pacemaker function—One study found that MRI-induced currents were less than or equal to 0.5 mA, which would make them unlikely to cause myocardial capture [22]. Another study showed significant impedance and minor stimulation threshold changes with no pacemaker resets or changes in programmed parameters [23]. However, one study also observed that seven of eight pulse generators paced rapidly when exposed to radiofrequency signal and caused a dramatic decrease in arterial blood pressure [24]. Reed switch activity—One study found that all pacemakers functioned in an asynchronous mode when placed within a certain distance of the magnet with transient reed switch observation [24]. Another study showed that VVI, atrial synchronous ventricular inhibited, and DDD modes were switched to asynchronous modes as a result of reed switch closure inside the nuclear magnetic resonance field [25].

391

392

Magnetom Avanto, Siemens Healthcare

Magnetom Sonata Maestro, Siemens Healthcare

Magnetom, Sonata, Maestro Class, Siemens Healthcare

Technicare Teslacon, Johnson & Johnson

Gyroscan T5II, Philips Healthcare

Gyroscan, Philips Healthcare

Nordbeck et al. (2009) [18]

Calcagnini et al. (2008) [19]

Shellock et al. (2006) [8]

Erlebacher et al. (1986) [9]

Sommer et al. (2000) [10]

Lauck et al. (1995) [11]

In vitro; seven dual chamber, two single chamber

In vitro, porcine heart

In vitro

In vitro

In vitro

In vitro

Type of Scan

At pacemaker

At pacemaker

At pacemaker

At pacemaker

At pacemaker

At pacemaker

MRI Location

0.5

0.5

0.5

1.5

1.5

1.5

Medtronic, Intermedics, Telectronics, Pacesetter, Biotronik

Medtronic, Vitatron, Intermedics, Telectronics, Pacesetter, Biotronik

Intermedic, Medtronic, Pacesetter

Guidant

Sorin Biomedica

Biotronik

Pacemaker Manufacturers

VVI, VVIR, VOO, DDD, DDDR, DOO

AOO, VOO, DOO

DDD

Not stated

Not stated

Not stated

Pacemaker Mode

Not stated

0.6, 1.3 W/kg

Not stated

1–3 W/kg

1–2 W/kg

Not stated

Specific Absorption Rate

Pacemakers in asynchronous mode were not affected with regard to stimulation rate; single-chamber pacemakers were inhibited and dual-chamber pacemakers were triggered in the demand mode during the scan preparation and the subsequent MRI sequence; Minix 8341, switch to VOO from VVI mode; Synergist II 7071, from DDD mode change to DOO mode and from VVI mode to VOO; Elite 7077, from DDD and VVI mode change to DOO and VOO, respectively; Cosmos II 283–01 and 284–05, switch to DOO and VOO, respectively; Meta II 1204, switch to VOO; Meta 1250, switch to DOO and VOO, respectively; Synchrony 2020, switch to DOO and VOO; Ergos 03, switch to DOO and VOO

Maximum temperature increase in pacemaker electrodes was 23.5°C with mean of 4.68°C at 1.3 W/kg; maximum temperature increase in pacemaker electrodes was 8.9°C with mean of 1.79°C at 0.6 W/kg; reed switch deactivated in four of 16 pacemakers when pacemakers were positioned in bore of magnet; none displayed pacing dysfunction; no change in programmed parameters was seen

All four pacemakers malfunctioned with total inhibition of atrial and ventricular output in three; the fourth had ventricular backup pacing activated at high radiofrequency pulse repetition rates

Temperature changes were at levels that are not expected to pose a risk for specific MRI conditions (< 4.0°C); highest temperatures were at tip of ventricular electrode (pacing lead) and lowest temperatures were at head or lumbar spine; function was unaffected

No temperature difference with unipolar and bipolar pacemaker; longer lead lengths and pacemakers in right side of chest showed highest temperature changes (11.9°C); pacemakers in left side of chest showed 6.3°C change

45.9°C temperature change with implanted pulse generator close to right thoracic wall; 10.4°C temperature elevation at implanted pulse generator in right pectoral region

Outcomes

Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. DDD = dual-mode dual-spacing dual-sensing, VVI = ventricular pace ventricular sense ventricular inhibited, NS = not specified. (Table 1 continues on next page)

MRI Scanner

Study

Field Strength (T)

TABLE 1: In Vitro Studies Analyzing the Safety of Pacemakers With MRI

Zikria et al.



Artoscan, Esaote

Magnetom Sonata, Siemens Healthcare

Achieva, Philips Healthcare

MAGNETOM Vision, Siemens Healthcare

MAGNETOM Allegra, Siemens Healthcare

Sigma SP, GE Healthcare



Naehle et al. (2008) [15]



Luechinger et al. (2002) [17]

Type of Scan

In vitro

In vitro, 14 pacemakers


In vitro

In vitro

In vitro, seven pacemakers

In vitro

In vitro, 15 dual chamber, 16 single chamber

MRI Location

At pacemaker

At pacemaker

At pacemaker

Brain phantom

Head (3), lumbar spine (2), thorax (4)

Extrathoracic locations, away from pacemaker

At pacemaker

At pacemaker

0.5

3

1.5

3

1.5

0.2

1.5

1.5

Medtronic

Intermedics, Cardiac Pacemakers, Medtronic

Intermedics, Medtronic, Cardiac Pacemakers

Medtronic, Vitatron, Biotronik, Pacesetter, Intermedics, Siemens

St. Jude Medical

Medtronic

Medtronic

Medtronic, CPI, Intermedics, Pacesetter, Siemens, Biotronik, Vitatron


Not stated

Not stated

Not stated

Not stated

DDD, DOO

Not stated

Not stated

VVI (11), DDD (4), DDDR (11), VVIR (5)

Pacemaker Mode

Not stated

Not stated

Not stated

≤ 3.2 W/kg

2–3 W/kg

Not stated

3.54 W/kg

Not stated

Specific Absorption Rate Outcomes

If the reed switches were oriented parallel to magnetic fields, they closed at 1.0 ± 0.2 mT and opened at 0.7 ± 0.2 mT; in low magnetic fields ( 200 mT), reed switches opened in 50% of all tested orientations

Four pacemakers had deflection angles ≥ 45° on long bore; nine pacemakers had deflection angles ≥ 45° on short bore

Three pacemakers exhibited deflection angles ≥ 45° on both long and short bore

Mean translational force on the pacemaker at 3 T was 374.38 ± 392.75 mN (range, 0.15–1.65 N/ kg); mean torque was 2.29 ± 4.08 x 10 −3 N x m, maximal temperature increase measured at pacemaker lead tip was 2.98°C (range, 0–2.98°C); no changes were observed in the programmed parameters of any of the devices

All scans of head and lumbar regions had temperature changes ≤ 0.5°C at specific absorption rates ranging from 2 to 3 W/kg; chest area temperature increase ranged from 0.4°C to 3.6°C at specific absorption rate of 2.0 W/kg; no memory corruption, hardware changes, changes in battery voltage, change to reset mode, or alterations in device parameters occurred

Each pacemaker paced normally before, during, and after MRI, with no alteration of programmed parameters, inhibition of pacing outputs, or distortions of MR images

One pacemaker had “electric reset”; no change in battery status; force and torque generated were negligible; no significant heating was induced in the lead tips

All of pacemakers except for five, with four being released before 1985, had an acceleration value lower than that of the gravity of the earth (< 9.81 N/kg); pacemakers released after 1985 had a maximal torque level of 3/6, whereas those released after 1995 had a maximal torque of 2/6

Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. DDD = dual-mode dual-spacing dual-sensing, VVI = ventricular pace ventricular sense ventricular inhibited, NS = not specified. (Table 1 continues on next page)

NS, GE Healthcare

Roguin et al. (2004) [12]

MRI Scanner

Gyroscan ACS NT, Philips Healthcare

Study


Field Strength (T)

TABLE 1: In Vitro Studies Analyzing the Safety of Pacemakers With MRI (continued)

MRI of Patients With Cardiac Pacemakers

393

Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. DDD = dual-mode dual-spacing dual-sensing, VVI = ventricular pace ventricular sense ventricular inhibited, NS = not specified.

Two pacemakers moved when placed on the MRI bed; all pacemakers showed no effect on the programmed pacemaker settings; in all pacemakers, reed switch was operated by static magnetic field resulting in asynchronous pacing; no pacemakers displayed pacing dysfunction when programmed to VOO or DOO mode; in VVI mode, inhibition was observed on exposing the pacemakers to MRI with the magnet function inactivated; in DDD, complete inhibition of atrial and ventricular lead and isolated sensing/inhibition of one lead was observed, and it also had atrial triggering with consequent rapid ventricular pacing at the upper frequency limit (150 beats/min) Not stated VVI and VOO (single-chamber pacemaker); VOO, VVI, DOO, DDD (dual chamber) Telectronics, Biotronik, Cardiac Pacemakers, Pacesetter 1.5 At pacemaker Magnetom 1.5 T, Siemens Healthcare Achenbach et al. (1997) [16]


If the reed switches were oriented parallel to magnetic fields, they closed at 1.0 ± 0.2 mT and opened at 0.7 ± 0.2 mT; in low magnetic fields ( 200 mT), reed switches opened in 50% of all tested orientations Not stated Not stated Medtronic 3 At pacemaker Intera 3 T, Philips Healthcare Luechinger et al. (2002) [17]

In vitro

If the reed switches were oriented parallel to magnetic fields, they closed at 1.0 ± 0.2 mT and opened at 0.7 ± 0.2 mT; in low magnetic fields ( 200 mT), reed switches opened in 50% of all tested orientations Not stated Not stated Medtronic 1.5 At pacemaker In vitro Gyroscan ACS NT, Philips Healthcare

MRI Location Type of Scan MRI Scanner Study


Outcomes Specific Absorption Rate Pacemaker Mode Pacemaker Manufacturers Field Strength (T)

TABLE 1: In Vitro Studies Analyzing the Safety of Pacemakers With MRI (continued)

394

Zikria et al.

Temperature changes—One study found temperature increases of up to 20°C, but no heat-induced damage could be seen in histologic analysis, and results of troponin tests were negative at 1.5 T [23]. In Vivo Human Studies Fifteen publications involved human subjects (Table 3, Fig. 2). A total of 1,419 MRI examinations were performed, with no deaths reported. One study did not state the field strength of the MRI examination, one study was conducted at 0.35 T, four studies were conducted at 0.5 T, eight studies were conducted at 1.5 T, one study was conducted at 2 T, and two studies were conducted at 3 T (Fig. 3). One study with 40 examinations did not state the location of the MRI scan conducted. For the remaining 14 studies, MRI scans were performed in the following anatomic locations: brain (n = 677); lumbar spine (n = 504); neck, cervical spine, brachial plexus, and jaw (n = 53); heart (n = 49); abdomen and pelvis (n = 40); lower extremities and knee (n = 35); chest and thorax (n = 11); and upper extremities, including shoulder and arm (n = 10). Of the 677 brain MRI examinations, 464 (68%) were examinations with the Medtronic EnRhythm pacemaker. Of the 504 MRIs of the lumbar spine, 464 (92%) were examinations with the Medtronic EnRhythm pacemaker [26]. There were 12 studies that involved pacemakers in off or asynchronous modes [10, 15, 26–35]. Four studies had pacemaker-dependent patients enrolled in their trials and set pacemakers to asynchronous mode [26, 30, 33, 35]. Of the 12 studies that involved brain MRI examinations of patients with pacemakers, three studies used a transmitreceive head coil [15, 26, 30]. Of the 15 trials, six [10, 15, 29–31, 33] followed patients for 3 months, two studies [26, 35] followed patients for 1 month, and one study [32] followed patients for 1 week. Pacemaker function—Of the 15 human studies, 11 studies encompassing 1,170 (82%) of 1,419 MRI examinations found no significant change in pacemaker function after MRI examination [10, 26, 27, 29, 30, 32– 37]. Of 1,170 examinations, 928 were conducted at 1.5 T with the use of the Medtronic EnRhythm, the first pacemaker approved in Europe for MRI, at less than or equal to 2.0 W/kg [26]. Without accounting for the Medtronic study, in 242 (49%) of 491 cases, there were no significant changes in pacemaker function after MRI examinations. MRI magnetic strength ranged from 0.35 to


Temperature increases of up to 20°C were measured of the heart; significant impedance and minor stimulation threshold changes could be seen; however, pathologic and histologic examination could not clearly show heat-induced damage; all troponin tests were negative; no pacemaker resets or changes in programmed parameters during any MRI scan; there was no observable mechanical or electrical damage to the pacemaker components


Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. NMR = nuclear magnetic resonance, VVI = ventricular triggered, NS = not specified.

VVI, VDD, and DDD switched to VOO, VOO and DOO, respectively, inside NMR field Not stated VVI, DDD, VDD Medtronic 0.15 Not stated NS, Picker Fetter et al. (1984) [25]

Two dogs

All pacemakers functioned in asynchronous mode when placed within a certain distance of magnet; transient reed switch was inhibition observed; seven of eight pulse generators paced rapidly when exposed to radiofrequency signal, and there was a dramatic decrease in arterial blood pressure Not stated AAI, VVI (4), DDD (4), VVI U, VVI B, VVT, VOO Cordis, Telectronics 1.5 Not stated NMR, GE Healthcare Hayes et al. (1987) [24]

One dog, 13 MRI examinations

3.8 W/kg ODO Medtronic 1.5 Thorax Nine pigs Gyroscan NT, Philips Healthcare Luechinger et al. (2005) [23]

Outcomes

Low frequency–induced current was ≤ 0.5 mA with conventional implant; unlikely myocardial capture Not stated VOO Insignia Ultra, Guidant, Boston Scientific 1.5 Not stated Six dogs

Pacemaker Mode MRI Scanner

NS, GE Healthcare

Study

Tandri et al. (2008) [22]

Specific Absorption Rate Pacemaker Manufacturers Field Strength (T) MRI Location No. and Type of Scans

TABLE 2: In Vivo Animal Studies Analyzing the Safety of Pacemakers With MRI

MRI of Patients With Cardiac Pacemakers 3 T, with six studies accounting for 978 MRI examinations conducted at 1.5 T [26, 30, 32– 34, 37]. Three studies [10, 29, 34] with a total of 84 MRI examinations were conducted at 0.5 T. In 11 studies, SAR levels ranged from 0.6 to 3.7 W/kg. Seven studies [10, 26, 27, 29, 30, 32, 35] accounting for 1,081 patients had all pacemakers set on asynchronous mode. Of the total of 1,419 examinations, four studies encompassing 249 MRI examinations found that the examination affected the functioning of the pacemaker [15, 28, 31, 38]. MRI magnet strength ranged from 0.5 to 3 T, with 193 examinations conducted at 1.5 T. SAR levels ranged from 0.08 to less than or equal to 3.2 W/kg. In one cardiac MRI study (at 0.5 T), a patient was removed after the pacemaker programmed to VVI mode during MRI paced at maximum voltage at fixed 100 bpm [28]. One study (at 1.5 T) determined that 37% of leads underwent changes, with 9.4% having significant changes (more than one voltage) and 1.9% of leads requiring change in programmed output [38]. Another study (at 1.5 T) found a significant increase in pacing capture threshold and electrical reset after MRI in seven of 115 examinations, but all were able to be reprogrammed to previous parameters after imaging [31]. A study involving brain MRI (at 3 T) with pacemakers set to asynchronous mode found that eight pacemakers were reset [15]. Reed switch activity—Two studies reported changes in reed switch activity during MRI examination [29, 33]. One study found that all patients had reed switch activation in the MRI scanner and deactivation when patients left the scanning room, but 12 (37.5%) of 32 patients had reed switch deactivation when the patients were positioned in the center of the scanner [29]. The reed switch behavior did not depend on pacemaker model or anatomic region investigated. Another study found that 10 devices had reed switch activation by static magnetic field of the MRI that led to transient asynchronous pacing at the device-specific magnet rate of 85 bpm, which ceased on patient positioning in the magnet bore [33]. The Medtronic EnRhythm pacemaker, which accounted for 928 of 1,149 MRI examinations, does not have a reed switch (Cronin C, personal communication). Symptoms—Of the 15 human studies, two reported symptoms felt by the patient during the MRI [35, 38]. One study observed one patient transiently feeling the pacemaker vibrate during coronary artery imaging [38]. Another study observed one patient reporting 10 seconds of chest burning sensation during a brain scan, but the symptoms resolved before the

395

396

Vista, Picker

Signa CV/I, GE Healthcare



Heatlie et al. (2007) [28]

Martin et al. (2004) [38]


Vahlhaus et al. (2001) [29]

32

51

78

5

40

Lumbar spine (1) and neck (2), knee (6), brain (15), shoulder (2), heart (2), pancreas, arm, liver, and abdomen (4)

Knee (10), brain (21), shoulder, cervical spine, and lumbar spine (3), neck (2), humerus and cardiac (8), and brachial plexus, pancreas, liver, and abdomen (11)

Abdomen (12), neck (13), brain (15), heart (4), lumbar spine (10), lower extremities (5), cervical spine (12), chest (3), shoulder (2), brachial plexus (1), and pelvis (1)

Heart (5)

Not stated

MRI Location

0.5

0.5

1.5

0.5

Not stated

Field Strength (T)

Intermedics, CPI, Telectronics, Siemens Healthcare, Vitatron, Medtronic, ELA Medical, Sorin, Biotronik

Medtronic, Telectronics, Intermedics, ELA Medical, Sorin Biomedica, CPI, Pacesetter, Vitatron, Biotronik, Siemens Healthcare

Medtronic, Pacesetter, Intermedics

Medtronic, Pacesetter, Biotronik

Not stated


Nondependent

Nondependent

Nondependent; one dependent

Nondependent

Two dependent

Dependence

AOO (1), VOO (16), and DOO (15)

AOO (2), VOO (21), DOO (26), and VVI (2)

Not programmed asynchronous

OOO, DDD, VVI, VVIR

OOO or asynchronous mode

Pacemaker Mode

Not stated

0.6 W/kg

0.08–2.0 W/kg

Not stated

Not stated


No reported symptoms; no arrhythmic events; MRI did not affect pacemaker programmed data, or the ability to interrogate, program, or use telemetry; in all patients, reed switch was activated in MRI scanner and deactivated when patients left scanning room; no significant difference in sensing thresholds immediately after MRI and at 3-month follow-up; lead impedance was not altered significantly; battery voltage decreased from 2.763 ± 0.043 V before to 2.758 ± 0.044 V immediately after MRI but 3 months later battery voltage recovered to 2.760 ± 0.045 V

No patient reported symptoms during MRI; 69% of reed switches remained closed, and 31% of reed switches deactivated; ECG detected no significant changes; MRI did not affect programmed data of pacemaker; at 3-month follow-up, there were no significant pacing thresholds, sensing thresholds, and lead impedance changes

37% of leads underwent changes; 9.4% of leads underwent significant (> 1 voltage) changes; 1.9% of leads required a change in programmed output; ECG was not significant; one patient transiently felt pacemaker vibrate during coronary artery image

One pacemaker paced at maximum voltage at fixed 100/min in VVI mode

“Without complications or significant changes to device settings” [27]

Outcomes

Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. bpm = beats per minute, NMR = nuclear magnetic resonance, NS = not specified. (Table 3 continues on next page)

Not stated

MRI Scanner

Sierra et al. (2008) [27]

Study

No. of MRI Examinations

TABLE 3: In Vivo Human Studies Analyzing the Safety of Pacemakers With MRI

Zikria et al.



Signa, GE

Signa CV/I, GE

Goldsher et al. (2006) [32]

Nazarian et al. (2006) [33]

31

3

115

11

MRI Location

Thorax (2) and heart (29)

Brain (3)

Brain (64), neck (4), lumbar spine (17), abdomen (12), pelvis (8), and lower extremities (10)

Brain (10) and cervical neck (1)

1.5

1.5

1.5

1.5

Field Strength (T)

St Jude Medical, Guidant, Medtronic

Medtronic, St Jude Medical

Medtronic

Pacesetter, Medtronic

Pacemaker Manufacturers Dependence

Twelve dependent

Nondependent

Nondependent

Dependent

For dependent, VOO or DOO; for nondependent, VVI/DDI

Pacing off, OVO or ODO

With intrinsic heart rate 60 bpm, OAO, OVO, and ODO

VOO or DOO

Pacemaker Mode

< 2.0 W/kg

3.7 W/kg

1.5 W/kg

1–2 W/kg

Specific Absorption Rate Outcomes

Ten devices had reed switch activation by static magnetic field of MRI that led to transient asynchronous pacing; no unexpected or rapid activation of pacing observed; no symptoms; no episodes of inappropriate inhibition or activation of pacing; no significant differences between baseline and immediate or long-term sensing amplitudes, lead impedances, or pacing thresholds; no mean changes in battery voltage or sensing signal amplitudes

No symptoms consistent with device movement, torque, or heating; all devices were functioning appropriately after MRI and no changes in programming were observed; no significant changes in acute or chronic battery voltage, lead thresholds, lead impedances, or sensing signal amplitudes

All MRI examinations were completed safely. Inhibition of pacemaker output or induction of arrhythmias was not observed; pacing capture threshold increased significantly from before to after MRI (p = 0.017); in four of 114 cases, troponin increased from normal baseline value to above normal after MRI; in seven of 115 cases after MRI, electrical pacemaker reset was revealed; significant (p = 0.0012) decrease in battery voltage immediately after MRI with maximum decrease of 0.03 V

No pauses or rapid pacing or change in rate from the prescan setting; no patients reported any symptoms; programmed settings remained unchanged; no device experienced a “Power-on-Reset”; no relevant long-term deleterious effects to the patients or pacemakers were observed at 3-month follow-up


Intera, Philips Healthcare


MRI Scanner

Vision, Siemens Healthcare

Study

Gimbel et al. (2005) [30]


TABLE 3: In Vivo Human Studies Analyzing the Safety of Pacemakers With MRI (continued)


397

398

NS, GE Healthcare; NS, Siemens Healthcare; NS, Philips Healthcare

Prestige, Elscint

Not stated

Excite, GE Healthcare

Sutton et al. (2008) [26]

Del Ojo et al. (2005) [36]



16

5

13

928

51

Brain (13), left thigh, jaw, and lumbar spine (3)

Heart (1), brain (3), cervical disk (1)

Cervical spine (2), head (3), thoracic spine (5), lumbar spine (1), and neck (2)

464 Patients with brain and lumbar spine for each patient

Brain (51)

MRI Location

3

0.35, 0.5, 1.5 (3)

2

1.5

3

Field Strength (T)

Guidant, Intermedics, Medtronic, ELA Medical, St. Jude Medical

Pacesetter

St. Jude

Medtronic

Medtronic, CPI, Biotronik, Vitatron, ELA Medical, St. Jude Medical


Two dependent, 14 nondependent

One dependent, four nondependent

Nondependent

Included pacemaker dependent

Not stated

Dependence

For nondependent, OOO, ODO, and OVO; for dependent, VOO and DOO

OOO (2), DOO (2), DDD

DDD

Sure Scan pacing mode, analogous to asynchronous

If < 60 bpm, asynchronous mode; if > 60 bpm, sense-only mode; DOO, VOO, ODO, AOO

Pacemaker Mode

≤ 2.0 W/kg

Not stated

Not stated

≤ 2.0 W/kg

≤ 3.2 W/kg


All patients were successfully scanned; no arrhythmias; programmed settings remained unchanged; ECGs after MRI were uncompromised, and no change in battery status was noted; no device experienced a “Power-on-Reset”; no clinically relevant change in pacing thresholds, sensing, or impedance were noted; one patient reported brief (10 seconds) chest burning during brain scan; no pauses or rapid pacing observed

All pacemakers continued to function normally after MRI except for a transient pause of 2 seconds toward the end of the scan in a pacemaker-dependent patient with a unipolar dual-chamber device programmed DOO; no patient experienced any torque or heat sensation

No patient reported symptoms; no arrhythmia, inappropriately rapid pacing, pacemaker inhibition, or switch to asynchronous mode was observed; no change in pulse generator programming occurred, and all parameters before and after MRI scans were similar

No complications including adverse results, symptoms, device resetting, battery status, capture threshold changes, sensing changes, or impedance changes (Sutton R, personal communication; Wilkoff BL, et al., 2009 Heart Rhythm Society)

Examinations were completed safely; no significant (p < 0.05) changes in lead impedance, pacing capture threshold level, or serum troponin I level; no patients reported any symptoms; significant decrease (before MRI, 2.756 ± 0.063; after MRI, 2.751 ± 0.650) in battery voltage with transient decrease in 31% (16/51), which returned to baseline values at follow-up; no unexpected changes in heart rate or rhythm; eight (16%) pacemakers were reset

Outcomes


Achieva, Philips Healthcare

MRI Scanner

Naehle et al. (2008) [15]

Study



Zikria et al.


Note—Position 1 of the three-letter placing code defines the chambers paced: A = atrium, V = ventricle, D = dual chamber. Position 2 refers to the chambers sensed: A = atrium, V = ventricle, D = dual chamber, 0 = absence of sensing. Position 3 refers to how the pacemaker responds to sensed events: I = sensed event inhibits the output pulse, D = dual modes of response, 0 = no response to sensed input. bpm = beats per minute, NMR = nuclear magnetic resonance, NS = not specified.

battery voltage immediately after MRI with a maximum decrease of 0.03 V, but there was full recovery at 3-month follow-up, and the decrease did not interfere with pacemaker function [31]. One study (at 3 T) determined that there was also a significant decrease in battery voltage with a transient decrease in 31% (16/51) of cases that returned to baseline values at 3 months of follow-up [15].

end of the scan [35]. Pacemaker settings were not changed as a result of magnetic interference during these events. Troponin levels—Of the 15 trials, three studies determined troponin levels for the patients undergoing imaging with the pacemaker [15, 31, 37]. One study (at 1.5 T) reported that there was no statistically significant increase in troponin levels when compared with levels before and after the MRI examination [31]. However, in four of 115 patient examinations, the troponin level increased from a normal baseline value to above-normal values afterward (threshold, 0.1 ng/mL) with one patient also showing an increase in pacing capture threshold [31]. One study of brain MRI scans performed at 3 T reported no significant changes in serum troponinI level after the MRI scans [15]. One study (at 1.5 T) reported no changes in cardiac troponin-I and myoglobin levels [37]. Battery changes—Three studies found changes in battery function after MRI examinations, but all of these studies determined that battery function recovered fully at 3 months [15, 29, 31]. Four studies examining battery changes did not find any significant change in battery voltage [26, 32, 33, 35]. One study (at 0.5 T) reported that battery voltage decreased from 2.763 ± 0.043 V before MRI to 2.758 ± 0.044 V immediately after MRI, but 3 months later, battery voltage recovered [29]. One study (at 1.5 T) found a significant (p = 0.0012) decrease in

600 No. of Studies

Discussion There have been case reports of deaths among patients with pacemakers undergoing MRI in both Europe and America [39, 40]. In vitro studies have found oversensing, inhibition of atrial and ventricular output, electric reset, reed switch activity, drastic temperature changes based on the location of the pacemaker and lengths of the leads, and increased torque in older-generation pacemakers. Temperature changes in phantom studies, however, may not indicate true temperature differences in in vivo studies because of the dissipation of heat through circulating blood flow. In vivo animal studies have found that generators paced rapidly when exposed to radiofrequency signal and caused a dramatic decrease in arterial blood pressure. Furthermore, temperature increases of up to 20°C have been observed, despite the fact that no heat-induced damage could be seen in histologic analysis and results of troponin tests were negative in animals [23]. Finally, there are in vivo human trials that have conclud-

677

700

504

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40

100

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Outcomes

No programming changes, no device resetting, no changes in battery status, cardiac troponin-I and myoglobin levels were unchanged before and after scan; capture thresholds remained unchanged (Mollerus M, personal communication) 2.4 W/kg DDI and VVI with lower rate of 40 bpm Nondependent Guidant, Medtronic, St. Jude Medical 1.5

Dependence MRI Location

Brain and head (16), jaw (2), lumbar spine and sacrum (7), cervical spine (7), shoulder and humerus (3), thorax (1), pelvis (1), hip (1), and knee and foot (2)

MRI Scanner

Symphony,Siemens Healthcare

Study

Mollerus et al. (2008) [37]

40

Specific Absorption Rate Pacemaker Mode Pacemaker Manufacturers Field Strength (T) No. of MRI Examinations




Location

Fig. 2—Anatomic location of MRI scans in studies of human patients with pacemakers.

399

Zikria et al.


1,400

1,209

1,200 1,000 800 600 400 200 0

1

0.35

89

0.5

13

1.5

2.0

67

3.0

40

Not Stated

Magnet Strength (T)

Fig. 3—Magnet strength in MRI examinations performed in studies of human patients with pacemakers.

ed that MRI examinations affect pacemaker function, ECG readings, reed switch activity, symptoms, and battery changes. However, the clinical significance of the trials examined in this review was minor. Although the American Heart Association considers the presence of a pacemaker a strong relative contraindication to MRI, they state that it can be considered in cases where the potential benefit to the patient clearly outweighs the risks. Furthermore, they recommend obtaining only written informed consent, a person with expertise in MRI physics and safety to optimally plan the scan, the presence of a physician during the scan, and availability of a “crash cart” including a defibrillator during the scan. The pacemaker should be interrogated before and after the procedure. Throughout the scan, visual and voice contact with the patient should be maintained, as well as monitoring of the heart rhythm and vital signs [1]. The 2007 American College of Radiology guidelines reiterate these measures [6]. The area of controversy that arises between the American Heart Association and American College of Radiology guidelines and other reviews involves the decision to reprogram the pacemaker before the MRI examination. Although the American Heart Association and American College of Radiology do not consider it necessary to reprogram the pacemaker, many studies regarding MRI protocol among patients with pacemakers require pacemakers to be placed in an asynchronous mode before imaging. This review was limited in its conclusions because of the heterogeneous nature of the medical literature. Great variability existed regarding the pacemaker model, patient de-

400

pendence, anatomic location of the MRI scan, lead polarity, MRI field strength, and SAR to be able to correlate the outcomes. Furthermore, one human study accounts for 928 (65%) of the 1,419 MRI human studies that used the Medtronic EnRhythm pacemaker [26]. SAR also “may not be a valid measure” because “different MR manufacturers incorporate evolving proprietary methodologies to calculate the SAR” and the calculation may vary “considerably even when the same body part, coil, pulse sequence, and the individual patient are held constant on different MR machines—even from the same manufacturer” [30]. For this reason, we have also added the manufacturer of the MRI scanner in our data assessment along with the SAR calculation. Errors in estimations of implant heating with comparison with SAR measurements have also been shown in studies [41, 42]. A factor that has not been analyzed in our article is the variability of leads. Theoretically, connecting a lead to a different pacemaker could slightly change the maximum heating measured. However, there are many combinations of pacemaker devices and leads available today. Currently, there is testing of MRI with cardiac pacing leads, and one study has determined the safety of fiberoptic leads at 1.5 T and 1.5 W/kg SAR levels [43]. Another limitation to our review is that we reviewed only English-language articles. When conducting a PubMed search using the query “pacemaker MRI,” 262 studies were selected, but this number was reduced to 216 when limited to only English-language articles. Another important consideration is publication bias and “in view of the threats of lawsuits, it clearly would be unusual for all such incidents to be reported in the literature” [3].

In 82% of MRI examinations, there were no significant changes in pacemaker function after imaging. However, without accounting for the Medtronic study, in 49% of cases, there were no significant changes in pacemaker function after MRI examination. According to our findings, the data on MRI are heterogeneous, and a definitive statement cannot be made about imaging patients with pacemakers. We think that MRI of patients with pacemakers may be considered but with caution and with the benefits outweighing the risks of the examination. Although various case reports have reported deaths among patients with pacemakers who underwent MRI, no deaths were reported in the studies analyzed in this review. Only one trial was randomized and controlled, with the final results of the study pending publication [26]. Although the data are promising, future studies such as those by Sutton et al. [26], which are randomized controlled trials, will ultimately change the views of conducting MRI on patients with pacemakers. Acknowledgments We thank Michael Mollerus, Richard Sutton, and Christopher Cronin for their help in clarifying their published trials. References 1. Levine GN, Gomes AS, Arai AE, et al. Safety of magnetic resonance imaging in patients with cardiovascular devices: an American Heart Association scientific statement from the Committee on Diagnostic and Interventional Cardiac Catheterization, Council on Clinical Cardiology, and the Council on Cardiovascular Radiology and Intervention: endorsed by the American College of Cardiology Foundation, the North American Society for Cardiac Imaging, and the Society for Cardiovascular Magnetic Resonance. Circulation 2007; 116:2878–2891 2. Martin ET, Sandler DA. MRI in patients with cardiac devices. Curr Cardiol Rep 2007; 9:63–71 3. Loewy J, Loewy A, Kendall EJ. Reconsideration of pacemakers and MR imaging. RadioGraphics 2004; 24:1257–1267 4. Mitka M. Researchers seek MRI-safe pacemakers. JAMA 2009; 301:476 5. Faris OP, Shein M. Food and Drug Administration perspective: magnetic resonance imaging of pacemaker and implantable cardioverter-defibrillator patients. Circulation 2006; 114:1232–1233 6. Kanal E, Barkovich AJ, Bell C, et al. ACR guidance document for safe MR practices: 2007. AJR 2007; 188:1447–1474 7. Kalin R, Stanton MS. Current clinical issues of MRI


MRI of Patients With Cardiac Pacemakers scanning of pacemaker and defibrillator patients. Pacing Clin Electrophysiol 2005; 28:326–328 8. Shellock FG, Fieno DS, Thomson LJ, Talavage TM, Berman DS. Cardiac pacemaker: in vitro assessment at 1.5 T. Am Heart J 2006; 151:436–443 9. Erlebacher JA, Cahill PT, Pannizzo F, Knowles RJ. Effect of magnetic resonance imaging on DDD pacemakers. Am J Cardiol 1986; 57:437–440 10. Sommer T, Vahlhaus C, Lauck G, et al. MR imaging and cardiac pacemakers: in-vitro evaluation and in-vivo studies in 51 patients at 0.5 T. Radiology 2000; 215:869–879 11. Lauck G, von Smekal A, Wolke S, et al. Effects of nuclear magnetic resonance imaging on cardiac pacemakers. Pacing Clin Electrophysiol 1995; 18:1549–1555 12. Roguin A, Zviman MM, Meininger GR, et al. Modern pacemaker and implantable cardioverter/ defibrillator systems 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 13. Shellock FG, O’Neil M, Ivans V, et al. Cardiac pacemakers and implantable cardioverter defibrillators are unaffected by operation of an extremity MR imaging system. AJR 1999; 172:165–170 14. Shellock FG, Fischer L, Fieno DS. Cardiac pacemakers and implantable cardioverter defibrillators: in vitro magnetic resonance imaging evaluation at 1.5-tesla. J Cardiovasc Magn Reson 2007; 9:21–31 15. Naehle CP, Meyer C, Thomas D, et al. Safety of brain 3-T MR imaging with transmit-receive head coil in patients with cardiac pacemakers: pilot prospective study with 51 examinations. Radiology 2008; 249:991–1001 16. Achenbach S, Moshage W, Diem B, Bieberle T, Schibgilla V, Bachmann K. Effects of magnetic resonance imaging on cardiac pacemakers and electrodes. Am Heart J 1997; 134:467–473 17. Luechinger R, Duru F, Zeijlemaker VA, Scheidegger MB, Boesiger P, Candinas R. Pacemaker reed switch behavior in 0.5, 1.5, and 3.0 Tesla magnetic resonance imaging units: are reed switches always closed in strong magnetic fields? Pacing Clin Electrophysiol 2002; 25:1419–1423 18. Nordbeck P, Weiss I, Ehses P, et al. Measuring RFinduced currents inside implants: impact of device configuration on MRI safety of cardiac pacemaker leads. Magn Reson Med 2009; 61:570–578 19. Calcagnini G, Triventi M, Censi F, et al. In vitro investigation of pacemaker lead heating induced by magnetic resonance imaging: role of implant geom-


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