Government viewpoint: U.S. Food & Drug Administration: Pacemakers, ICDs and MRI

Access to MRI in Patients With Cardiac Implantable Electronic Devices is Variable and an Issue in Australia

AIMS

This study aimed to characterise the level of access to magnetic resonance imaging (MRI) in Australian hospitals for patients with MR-conditional and non-MR-conditional cardiac implantable electronic devices (CIED), and to identify any barriers impeding this access.

METHODS

All Australian Tertiary Referral Public Hospitals (n=38) were surveyed with a mixed qualitative and quantitative questionnaire. Provision of MRI to patients with MR-conditional and non-MR-conditional CIEDs; patient monitoring strategies during scan and personnel in attendance; barriers impeding MRI access.

RESULTS

Of the 35 (92%) hospitals that completed the survey, a majority (85.7%) scan MR-conditional CIEDs, while a minority (8.6%) scan non-MR-conditional CIEDs. MR-conditional device scanning is often limited to non-pacing dependent patients, excluding implantable cardioverter-defibrillators. In total, 21% of sites exclude thoracic MR scans for CIED patients. Although most centres scan on 1.5 Tesla (T) machines (59%), 10% scan at 3T and 31% scan at both strengths. Sites vary in patient monitoring strategies and personnel in attendance; 80% require staff with Advanced Cardiac Life Support to be present. Barriers to service expansion include an absence of national guidelines, formal training, and logistical device support.

CONCLUSIONS

Most surveyed Australian hospitals offer MRI for patients with MR-conditional CIEDs, however many still have exclusions for particular patient groups or scan requests. Only three surveyed sites offer MRI for patients with non-MR-conditional CIEDs in Australia. A national effort is needed to address the identified barriers including the development of national guidelines, formal training, and logistical support.

Performance and Physician Experience of INGEVITY+ Active Fixation Leads: Prospective INGEVITY+ Lead Clinical Study in Korea

Background

Boston Scientific INGEVITY+ pacing lead (Boston Scientific, Marlborough, MA, USA) has been upgraded to INGEVITY. The performance of the INGEVITY+ pacing lead has not yet been reported. This study aimed to evaluate the short- and long-term safety, effectiveness, and handling experience of INGEVITY+ leads.

Methods

Consecutive patients were included from 9 institutions in Korea, where 400 leads (200 right ventricular active fixation leads and 200 right atrial active fixation leads) were implanted or attempted in 200 subjects.

Results

During the implantation, only one patient required a lead change because of lead screw failure. The handling questionnaires of the lead received very positive feedback with 88% of operators agreeing that it is easy for leads to pass through small vessels or vessels with multiple leads. At the 3-month follow-up, 95.7% of RA leads and 99.5% of RV leads had pacing thresholds less than 1.5 V. A total of 92.4% of atrial leads had amplitudes greater than 1.5 mV, and 96.5% of ventricular leads had sensing amplitudes greater than 5 mV at 3 months. A total of 99.8% had impedances between 300 and 1,300 ohms. The lead-related complication-free rate for all leads during follow-up was 100%, and the overall rates of lead dislodgment, perforation, and pericardial effusion were all 0.0%.

Conclusions

The INGEVITY+ pacing lead exhibited exceptional clinical performance, with a high complication-free rate throughout the 3-month follow-up period. In addition, the lead displayed excellent electrical characteristics, and the lead-handling experience was reported to be very good.

Implantable Defibrillator System Shock Function, Mortality, and Cause of Death After Magnetic Resonance Imaging

BACKGROUND

Studies have shown that magnetic resonance imaging (MRI) does not have clinically important effects on the device parameters of non-MRI-conditional implantable cardioverter-defibrillators (ICDs). However, data on non-MRI-conditional ICD detection and treatment of arrhythmias after MRI are limited.

OBJECTIVE

To examine if non-MRI-conditional ICDs have preserved shock function of arrhythmias after MRI.

DESIGN

Prospective cohort study. (ClinicalTrials.gov: NCT01130896).

SETTING

1 center in the United States.

PATIENTS

629 patients with non-MRI-conditional ICDs enrolled consecutively between February 2003 and January 2015.

INTERVENTIONS

813 total MRI examinations at a magnetic field strength of 1.5 Tesla using a prespecified safety protocol.

MEASUREMENTS

Implantable cardioverter-defibrillator interrogations were collected after MRI. Clinical outcomes included arrhythmia detection and treatment, generator or lead exchanges, adverse events, and death.

RESULTS

During a median follow-up of 2.2 years from MRI to latest available ICD interrogation before generator or lead exchange in 536 patients, 4177 arrhythmia episodes were detected, and 97 patients received ICD shocks. Sixty-one patients (10% of total) had 130 spontaneous ventricular tachycardia or fibrillation events terminated by ICD shocks. A total of 210 patients (33% of total) are known to have died (median, 1.7 years from MRI to death); 3 had cardiac arrhythmia deaths where shocks were indicated without direct evidence of device dysfunction.

LIMITATIONS

Data were acquired at a single center and may not be generalizable to other clinical settings and MRI facilities. Implantable cardioverter-defibrillator interrogations were not available for a subset of patients; adjudication of cause of death relied solely on death certificate data in a subset.

CONCLUSION

Non-MRI-conditional ICDs appropriately treated detected tachyarrhythmias after MRI. No serious adverse effects on device function were reported after MRI.

PRIMARY FUNDING SOURCE

Johns Hopkins University and National Institutes of Health.

Outcome of MRI in Patients with Nonconditional Devices with Mismatch between Manufacturer of Leads and Generator

In a series of 35 MRI examinations with non-MRI-conditional devices with a mismatch between the manufacturer of the device generators and leads, there were no adverse events.

Feasibility of MRI in patients with non-Pacemaker/Defibrillator metallic devices and abandoned leads

Objective

To evaluate feasibility of MRI in patients with non-pacemaker (PM)/ Implantable cardioverter defibrillator (ICD) metallic devices and abandoned leads.

Background

Relative safety of MRI performed using specified protocol has been established in MR non-conditional PM/ICDs. With limited safety data, many non-PM/ICD metallic devices and abandoned leads continue to be a contraindication for MRI.

Methods

We retrospectively analyzed consecutive patients with extra-cardiac devices, non-programmable cardiac devices, and abandoned leads, who underwent MRI (GE 1.5 Tesla, WI) at a single tertiary care center over a span of 13 years. Scan protocol was designed to maintain specific absorption rate (SAR) < 4.0 W/kg and scan time < 60 minutes.

Results

The cohort comprised 127 MRI exams representing 94 patients, with 13 patients having two or more scans. The devices consisted of: 23 vagal nerve stimulators (VNS), 22 implantable loop recorders, 16 spinal stimulators, 5 peripheral nerve stimulators, 3 bladder stimulators, 2 deep brain stimulators, 1 gastric stimulator, 1 bone stimulator, 1 WATCHMAN device, 22 abandoned PM/lCD leads and 1 VNS lead. There was no immediate (peri-MRI exam) morbidity or mortality. Patients did not report any discomfort, palpitations, heating, or sensation of device migration during the exam. Local follow-up data was available in 65% (100% for thoracic imaging) with a mean of 190±475 days (median 13 days). No device malfunction reported during follow-up.

Conclusions

With appropriate precautions, MRI is feasible in patients with extracardiac devices, nonprogrammable cardiac devices, and abandoned leads.

Safety and Clinical Impact of MRI in Patients with Non-MRI-conditional Cardiac Devices

Purpose

To explore the safety and clinical utility of MRI in participants with non-MRI-conditional cardiac implantable electronic devices, by establishing the Patient Registry of Magnetic Resonance Imaging in Non-Approved DEvices (PROMeNADe).

Materials and Methods

From September 2015 to June 2019, 532 participants (211 women) with a mean age of 69 years ± 14 (standard deviation) were enrolled prospectively in the PROMeNADe registry (ClinicalTrials.gov identifier: NCT03081364) and underwent a total of 608 MRI examinations (61 cardiac MRI examinations). All participants had device interrogations performed before and after each MRI. Pacemaker-dependent patients received asynchronous pacing. Patients with an implantable cardioverter defibrillator (ICD) had tachycardia therapies disabled during the MRI. An electrophysiology nurse monitored participants for any hemodynamic or rhythm abnormalities. Referring physicians were surveyed regarding the clinical utility of the MRI. Standard descriptive analyses included summary statistics with percentages and means.

Results

Cardiac devices included pacemakers (46%), ICDs (30%), cardiac resynchronization therapy (CRT) pacemakers (4%), and CRT defibrillators (17%), as well as abandoned leads (2%). Pacemaker-dependent patients comprised 27% of all MRI examinations. There were no patient- or device-related complications. Clinical utility surveys of MRI examinations were completed by 150 physicians. According to the survey responses, these MRI examinations changed the suspected diagnosis 25% of the time and changed suspected prognosis in 26% of participants, with planned medical or surgical treatment being changed 42% of the time.

Conclusion

This registry demonstrates that MRI examinations, including thoracic MRI examinations, can be performed safely in patients who have non-MRI-conditional devices, in pacemaker-dependent patients with ICDs, and in patients with abandoned leads. These MRI examinations can have a substantial impact on patient care, justifying the extensive resources used to perform them.Supplemental material is available for this article.© RSNA, 2020See also the commentary by Peshock in this issue.

An eight-year prospective controlled study about the safety and diagnostic value of cardiac and non-cardiac 1.5-T MRI in patients with a conventional pacemaker or a conventional implantable cardioverter defibrillator

OBJECTIVES

To investigate safety and diagnostic value of 1.5-T MRI in carriers of conventional pacemaker (cPM) or conventional implantable defibrillator (cICD).

METHODS

We prospectively compared cPM/cICD-carriers undergoing MRI (study group, SG), excluding those device-dependent or implanted <6 weeks before enrolment or prior to 01/01/2000, with cPM/cICD-carriers undergoing chest x-ray, CT or follow-up (reference group, RG).

RESULTS

142 MRI (55 cardiac) were performed in 120 patients with cPM (n=71) or cICD (n=71). In the RG 98 measurements were performed in 95 patients with cPM (n=40) or cICD (n=58). No adverse events were observed. No MRI prolonged/interrupted. All cPM/cICD were correctly reprogrammed after MRI without malfunctions. One temporary communication failure was observed in one cPM-carrier. Immediately after MRI, 12/14 device interrogation parameters did not change significantly (clinically negligible changes of battery voltage and cICD charging time), without significant variations for SG versus RG. Three-12 months after MRI, 9/11 device interrogation parameters did not change significantly (clinically negligible changes of battery impedance/voltage). Non-significant changes of three markers of myocardial necrosis. Non-cardiac MRI: 82/87 diagnostic without artefacts; 4/87 diagnostic with artefacts; 1/87 partially diagnostic. Cardiac MRI: in cPM-carriers, 14/15 diagnostic with artefacts, 1/15 partially diagnostic; in cICD-carriers, 9/40 diagnostic with artefacts, 22 partially diagnostic, nine non-diagnostic.

CONCLUSIONS

A favourable risk-benefit ratio of 1.5-T MRI in cPM/cICD carriers was reported.

KEY POINTS

• Cooperation between radiologists and cardiac electrophysiologists allowed safe 1.5-T MRI in cPM/cICD-carriers. • No adverse events for 142 MRI in 71 cPM-carriers and 71 cICD-carriers. • Ninety-nine per cent (86/87) of non-cardiac MRI in cPM/cICD-carriers were diagnostic. • All cPM-carrier cardiac MRIs had artefacts, 14 examinations diagnostic, 1 partially diagnostic. • Twenty-three per cent (9/40) of cardiac MRI in cICD-carriers were non-diagnostic.

Safety of Magnetic Resonance Imaging in Patients with Cardiac Devices

BACKGROUND

Patients who have pacemakers or defibrillators are often denied the opportunity to undergo magnetic resonance imaging (MRI) because of safety concerns, unless the devices meet certain criteria specified by the Food and Drug Administration (termed "MRI-conditional" devices).

METHODS

We performed a prospective, nonrandomized study to assess the safety of MRI at a magnetic field strength of 1.5 Tesla in 1509 patients who had a pacemaker (58%) or an implantable cardioverter-defibrillator (42%) that was not considered to be MRI-conditional (termed a "legacy" device). Overall, the patients underwent 2103 thoracic and nonthoracic MRI examinations that were deemed to be clinically necessary. The pacing mode was changed to asynchronous mode for pacing-dependent patients and to demand mode for other patients. Tachyarrhythmia functions were disabled. Outcome assessments included adverse events and changes in the variables that indicate lead and generator function and interaction with surrounding tissue (device parameters).

RESULTS

No long-term clinically significant adverse events were reported. In nine MRI examinations (0.4%; 95% confidence interval, 0.2 to 0.7), the patient's device reset to a backup mode. The reset was transient in eight of the nine examinations. In one case, a pacemaker with less than 1 month left of battery life reset to ventricular inhibited pacing and could not be reprogrammed; the device was subsequently replaced. The most common notable change in device parameters (>50% change from baseline) immediately after MRI was a decrease in P-wave amplitude, which occurred in 1% of the patients. At long-term follow-up (results of which were available for 63% of the patients), the most common notable changes from baseline were decreases in P-wave amplitude (in 4% of the patients), increases in atrial capture threshold (4%), increases in right ventricular capture threshold (4%), and increases in left ventricular capture threshold (3%). The observed changes in lead parameters were not clinically significant and did not require device revision or reprogramming.

CONCLUSIONS

We evaluated the safety of MRI, performed with the use of a prespecified safety protocol, in 1509 patients who had a legacy pacemaker or a legacy implantable cardioverter-defibrillator system. No long-term clinically significant adverse events were reported. (Funded by Johns Hopkins University and the National Institutes of Health; ClinicalTrials.gov number, NCT01130896 .).

The Safety of Cardiac and Thoracic Magnetic Resonance Imaging in Patients with Cardiac Implantable Electronic Devices

RATIONALE AND OBJECTIVES

Studies reporting the safety of magnetic resonance imaging (MRI) in patients with a cardiac implantable electronic device (CIED) have mostly excluded examinations with the device in the magnet isocenter. The purpose of this study was to describe the safety of cardiac and thoracic spine MRI in patients with a CIED.

MATERIALS AND METHODS

The medical records of patients with a CIED who underwent a cardiac or thoracic spine MRI between January 2011 and December 2014 were reviewed. Devices were interrogated before and after imaging with reprogramming to asynchronous pacing in pacemaker-dependent patients. The clinical interpretability of the MRI and peak and average specific absorption rates (SARs, W/kg) achieved were determined.

RESULTS

Fifty-eight patients underwent 51 cardiac and 11 thoracic spine MRI exams. Twenty-nine patients had a pacemaker and 29 had an implantable cardioverter defibrillator. Seventeen percent (n = 10) were pacemaker dependent. Fifty-one patients (89%) had non-MRI-conditional devices. There were no clinically significant changes in atrial and ventricular sensing, impedance, and threshold measurements. There were no episodes of device mode changes, arrhythmias, therapies delivered, electrical reset, or battery depletion. One study was prematurely discontinued due to a patient complaint of chest pain of which the etiology was not determined. Across all examinations, the average peak SAR was 2.0 ± 0.85 W/kg with an average SAR of 0.35 ± 0.37 W/kg. Artifact significantly limiting the clinical interpretation of the study was present in 33% of cardiac MRI studies.

CONCLUSIONS

When a comprehensive CIED magnetic resonance safety protocol is followed, the risk of performing 1.5-T magnetic resonance studies with the device in the magnet isocenter, including in patients who are pacemaker dependent, is low.

Immediate and 12 months follow up of function and lead integrity after cranial MRI in 356 patients with conventional cardiac pacemakers

BACKGROUND

Conventional cardiac pacemakers are still often regarded as a contraindication to magnetic resonance imaging (MRI). We conducted this study to support the hypothesis that it is safe to scan patients with cardiac pacemakers in a 1.5 Tesla MRI, if close supervision and monitoring as well as adequate pre- and postscan programming is provided.

METHODS

We followed up 356 patients (age 61.3 ± 9.1 yrs., 229 men) with single (n = 132) or dual chamber (n = 224) cardiac pacemakers and urgent indication for a cranial MRI for 12 months. The scans were performed at 1.5T. During the scan patients were monitored with a 3-lead ECG and pulse oximetry. Prior to the scan pacemakers were programmed according to our own protocol.

RESULTS

All 356 scans were completed without complications. No arrhythmias were induced, programmed parameters remained unchanged. No pacemaker dysfunction was identified. Follow-up examinations were performed immediately, 2 weeks, 2, 6, and 12 months after the scan. There was no significant change of pacing capture threshold (ventricular 0.9 ± 0.4 V@0.4 ms, atrial 0.9 ± 0.3 V@0.4 ms) immediately (ventricular 1.0 ± 0.3 V@0.4 ms, atrial 0.9 ± 0.4 V@0.4 ms) or at 12 months follow-up examinations (ventricular 0.9 ± 0.2 V@0.4 ms, atrial 0.9 ± 0.3 V@0.4 ms). There was no significant change in sensing threshold (8.0 ± 4.0 mV vs. 8.1 ± 4.2 mV ventricular lead, 2.0 ± 0.9 mV vs. 2.1 ± 1.0 mV atrial lead) or lead impedance (ventricular 584 ± 179 Ω vs. 578 ± 188 Ω, atrial 534 ± 176 Ω vs. 532 ± 169 Ω) after 12 months.

CONCLUSIONS

This supports the evidence that patients with conventional pacemakers can safely undergo cranial MRI in a 1.5T system with suitable preparation, supervision and precautions. Long term follow-up did not reveal significant changes in pacing capture nor sensing threshold.

MRI-conditional pacemakers: current perspectives

Use of both magnetic resonance imaging (MRI) and pacing devices has undergone remarkable growth in recent years, and it is estimated that the majority of patients with pacemakers will need an MRI during their lifetime. These investigations will generally be denied due to the potentially dangerous interactions between cardiac devices and the magnetic fields and radio frequency energy used in MRI. Despite the increasing reports of uneventful scanning in selected patients with conventional pacemakers under close surveillance, MRI is still contraindicated in those circumstances and cannot be considered a routine procedure. These limitations prompted a series of modifications in generator and lead engineering, designed to minimize interactions that could compromise device function and patient safety. The resulting MRI-conditional pacemakers were first introduced in 2008 and the clinical experience gathered so far supports their safety in the MRI environment if certain conditions are fulfilled. With this technology, new questions and controversies arise regarding patient selection, clinical impact, and cost-effectiveness. In this review, we discuss the potential risks of MRI in patients with electronic cardiac devices and present updated information regarding the features of MRI-conditional pacemakers and the clinical experience with currently available models. Finally, we provide some guidance on how to scan patients who have these devices and discuss future directions in the field.

Different brain activation under left and right ventricular stimulation: an fMRI study in anesthetized rats

BACKGROUND

Myocardial ischemia in the anterior wall of the left ventricule (LV) and in the inferior wall and/or right ventricle (RV) shows different manifestations that can be explained by the different innervations of cardiac afferent nerves. However, it remains unclear whether information from different areas of the heart, such as the LV and RV, are differently processed in the brain. In this study, we investigated the brain regions that process information from the LV or RV using cardiac electrical stimulation and functional magnetic resonance imaging (fMRI) in anesthetized rats because the combination of these two approaches cannot be used in humans.

METHODOLOGY/PRINCIPAL FINDINGS

An electrical stimulation catheter was inserted into the LV or RV (n = 12 each). Brain fMRI scans were recorded during LV or RV stimulation (9 Hz and 0.3 ms width) over 10 blocks consisting of alternating periods of 2 mA for 30 sec followed by 0.2 mA for 60 sec. The validity of fMRI signals was confirmed by first and second-level analyses and temporal profiles. Increases in fMRI signals were observed in the anterior cingulate cortex and the right somatosensory cortex under LV stimulation. In contrast, RV stimulation activated the right somatosensory cortex, which was identified more anteriorly compared with LV stimulation but did not activate the anterior cingulate cortex.

CONCLUSION/SIGNIFICANCE

This study provides the first evidence for differences in brain activation under LV and RV stimulation. These different brain processes may be associated with different clinical manifestations between anterior wall and inferoposterior wall and/or RV myocardial ischemia.

Magnetic resonance imaging conditional pacemakers: rationale, development and future directions

Pacemakers and other cardiac implantable electronic devices (CIEDs) have long been considered an absolute contraindication to magnetic resonance imaging (MRI), a crucial and growing imaging modality. In the last 20 years, protocols have been developed to allow MR scanning of CIED patients with a low complication rate. However, this practice has remained limited to a relatively small number of centers, and many pacemaker patients continue to be denied access to clinically indicated imaging. The introduction of MRI conditional pacemakers has provided a widely applicable and satisfactory solution to this problem. Here, the interactions of pacemakers with the MR environment, the results of MR scanning in patients with conventional CIEDs, the development and clinical experience with MRI conditional devices, and future directions are reviewed.

[Magnetic resonance imaging and implantable cardiac devices. Current status and future perspectives of MR-compatible systems]

Conventional pacemakers and implantable cardioverter-defibrillators (ICD) have always been regarded as a contraindication to magnetic resonance imaging (MRI). MR-compatible systems represent a recent and particularly important innovation, since they will provide device patients with significantly improved access to MR examinations. However, the safe application of MR-compatible technology requires a detailed understanding of the strictly defined cardiologic and radiologic requirements and conditions that are to be adhered to before and during an MR examination. The present article gives an overview of problematic MR interactions with implanted devices, illustrates the most important aspects of MR-compatible pacemaker and ICD systems, analyzes their current clinical status, and offers a critical perspective.

Magnetic resonance imaging in patients with cardiac pacemakers: era of "MR Conditional" designs

Advances in cardiac device technology have led to the first generation of magnetic resonance imaging (MRI) conditional devices, providing more diagnostic imaging options for patients with these devices, but also new controversies. Prior studies of pacemakers in patients undergoing MRI procedures have provided groundwork for design improvements. Factors related to magnetic field interactions and transfer of electromagnetic energy led to specific design changes. Ferromagnetic content was minimized. Reed switches were modified. Leads were redesigned to reduce induced currents/heating. Circuitry filters and shielding were implemented to impede or limit the transfer of certain unwanted electromagnetic effects. Prospective multicenter clinical trials to assess the safety and efficacy of the first generation of MR conditional cardiac pacemakers demonstrated no significant alterations in pacing parameters compared to controls. There were no reported complications through the one month visit including no arrhythmias, electrical reset, inhibition of generator output, or adverse sensations. The safe implementation of these new technologies requires an understanding of the well-defined patient and MR system conditions. Although scanning a patient with an MR conditional device following the strictly defined patient and MR system conditions appears straightforward, issues related to patients with pre-existing devices remain complex. Until MR conditional devices are the routine platform for all of these devices, there will still be challenging decisions regarding imaging patients with pre-existing devices where MRI is required to diagnose and manage a potentially life threatening or serious scenario. A range of other devices including ICDs, biventricular devices, and implantable physiologic monitors as well as guidance of medical procedures using MRI technology will require further biomedical device design changes and testing. The development and implementation of cardiac MR conditional devices will continue to require the expertise and collaboration of multiple disciplines and will need to prove safety, effectiveness, and cost effectiveness in patient care.

Initial experience with magnetic resonance imaging-safe pacemakers : a review

Due of its superior soft tissue imaging capabilities, magnetic resonance imaging (MRI) has become the imaging modality of choice in many clinical situations, as illustrated by the tremendous growth in the number of MRIs performed over the past 2 decades. In parallel, the number of patients who require pacemakers or implantable cardiac defibrillators is increasing as indications for these devices broaden and the population ages. Taken together, these phenomena present an important clinical issue, as MR scans are generally contraindicated—except in urgent situations—in patients who have implanted cardiovascular devices. Potentially deleterious interactions between the magnetic fields and radio frequency (RF) energy produced by MR equipment and implantable devices have been identified, including inhibition of pacing, asynchronous/high-rate pacing, lead tip heating, and loss of capture. New devices that incorporate technologies to improve MR safety in patients with pacemakers have recently received approval in Europe and are under evaluation in the United States. Initial data from these devices suggest that these devices are safe in the MRI environment.

A prospective evaluation of a protocol for magnetic resonance imaging of patients with implanted cardiac devices

BACKGROUND

Magnetic resonance imaging (MRI) is avoided in most patients with implanted cardiac devices because of safety concerns.

OBJECTIVE

To define the safety of a protocol for MRI at the commonly used magnetic strength of 1.5 T in patients with implanted cardiac devices.

DESIGN

Prospective nonrandomized trial. (ClinicalTrials.gov registration number: NCT01130896) SETTING: One center in the United States (94% of examinations) and one in Israel.

PATIENTS

438 patients with devices (54% with pacemakers and 46% with defibrillators) who underwent 555 MRI studies.

INTERVENTION

Pacing mode was changed to asynchronous for pacemaker-dependent patients and to demand for others. Tachyarrhythmia functions were disabled. Blood pressure, electrocardiography, oximetry, and symptoms were monitored by a nurse with experience in cardiac life support and device programming who had immediate backup from an electrophysiologist.

MEASUREMENTS

Activation or inhibition of pacing, symptoms, and device variables.

RESULTS

In 3 patients (0.7% [95% CI, 0% to 1.5%]), the device reverted to a transient back-up programming mode without long-term effects. Right ventricular (RV) sensing (median change, 0 mV [interquartile range {IQR}, -0.7 to 0 V]) and atrial and right and left ventricular lead impedances (median change, -2 Ω [IQR, -13 to 0 Ω], -4 Ω [IQR, -16 to 0 Ω], and -11 Ω [IQR, -40 to 0 Ω], respectively) were reduced immediately after MRI. At long-term follow-up (61% of patients), decreased RV sensing (median, 0 mV, [IQR, -1.1 to 0.3 mV]), decreased RV lead impedance (median, -3 Ω, [IQR, -29 to 15 Ω]), increased RV capture threshold (median, 0 V, IQR, [0 to 0.2 Ω]), and decreased battery voltage (median, -0.01 V, IQR, -0.04 to 0 V) were noted. The observed changes did not require device revision or reprogramming.

LIMITATIONS

Not all available cardiac devices have been tested. Long-term in-person or telephone follow-up was unavailable in 43 patients (10%), and some data were missing. Those with missing long-term capture threshold data had higher baseline right atrial and right ventricular capture thresholds and were more likely to have undergone thoracic imaging. Defibrillation threshold testing and random assignment to a control group were not performed.

CONCLUSION

With appropriate precautions, MRI can be done safely in patients with selected cardiac devices. Because changes in device variables and programming may occur, electrophysiologic monitoring during MRI is essential.

Safety of serial MRI in patients with implantable cardioverter defibrillators

OBJECTIVE

While patients with cardiac implantable electronic devices could benefit from magnetic resonance (MR) imaging, the presence of such devices has been designated as an absolute contraindication to MR. Although scanning algorithms are proposed for cardiac implantable electronic devices, their safety remains uncertain. To address this issue, the safety of serial cardiac MR scans was evaluated in patients with implantable cardioverter defibrillators (ICDs).

METHODS

Three serial cardiac MR scans were prospectively performed at 1.5 T on 10 patients (9 men) of median age 56 years (range 51-68) with ICDs. ICD interrogation was performed before and after the MR scan and at a follow-up of median 370 days (range 274-723). Image quality was also assessed.

RESULTS

In all patients MR scanning occurred without complications. There were no differences between pre- and post-MR pacing capture threshold, pacing lead or high voltage lead impedance, or battery voltage values. During follow-up there were no occurrences of ICD dysfunction. Although most patients had image artifacts, the studies were generally diagnostic regarding left ventricular function and wall motion. Delayed enhancement imaging was of good quality for inferior wall and inferolateral infarcts, but ICD artifacts often affected the imaging of anterior wall infarcts.

CONCLUSION

Serial MR scans at 1.5 T in patients with ICDs, when carefully performed in a monitored setting, have no adverse effects on either patient or device. When required, single or multiple MR scans at 1.5 T may therefore be considered for clinical diagnostic purposes in these patients.

Pacemaker lead tip heating in abandoned and pacemaker-attached leads at 1.5 Tesla MRI

PURPOSE

To assess the risk of RF-induced heating in pacemaker-attached and abandoned leads using in vitro temperature measurements at 1.5 Tesla as a function of lead length.

MATERIALS AND METHODS

Five custom lead lengths, 20-60 cm, were exposed to a uniform magnitude and phase radiofrequency electric field to examine the effect of lead length on pacemaker lead tip heating for pacemaker-attached and abandoned pacemaker leads.

RESULTS

Abandoned and pacemaker-attached leads show resonant heating behavior and maximum heating occurs at different lead lengths due to the differences in termination conditions. For clinical lead lengths (40-60 cm) abandoned leads exhibited greater lead tip heating compared with pacemaker-attached leads.

CONCLUSION

Current recommendations for MRI pacemaker safety should highlight the possible increased risk for patients with abandoned leads as compared to pacemaker-attached leads.

Designing passive MRI-safe implantable conducting leads with electrodes

PURPOSE

The presence of implanted electronic devices with conducting leads and electrodes are contraindicated for magnetic resonance imaging (MRI), denying many patients its potential benefits. The prime concern is MRI's radio frequency (RF) fields, which can cause elevated local specific absorption rates (SARs) and potential heat injury. The purpose of this article is to develop and compare a range of passive implantable "MRI-safe" lead designs.

METHODS

Conducting leads incorporating different lengths (3-75 cm), insulation thicknesses (0-105 microm), resistances (100-3000 omega), coiled conductors (inner diameter < or = 1.2 mm), high-impedance (135-2700 omega) RF traps, and single-coiled and triple-coiled coaxial-wound "billabong" leads with reversed coil sections that oppose and reduce the induced current, are investigated both experimentally using local temperature measurements, and by numerical full-wave electromagnetic field analysis of the local SAR, in three different-sized bioanalogous model saline-gel phantoms at 1.5 T MRI and 4 W/kg exposure.

RESULTS

In all designs, the maximum computed 1 g average SAR and experimental temperature rise occur at the bare electrodes. Electrode heating increases with lead insulation thickness and peaks for uncoiled leads 25-50 cm long. A reasonable match between computed SAR and the point SAR estimated from thermal sensors obtained by approximating the computation volume to that of the thermal probes. Factors that maximize the impedance of leads with resistive, coiled, RF trap and billabong elements can effectively limit heating below 1-2 degrees, but folded lead configurations can be a concern. The RF trap and billabong designs can both support multiple conductors and electrodes, with billabong prototype leads also heating <1 degrees C when tested for 3 T MRI.

CONCLUSIONS

Lead insulation and length strongly affect implanted lead safety to RF exposure during MRI. Lead designs employing impedance and reversed winding sections offer hope for the development of passive, MRI-safe, implantable conducting leads for future human use.

[Magnetic resonance imaging in patients with pacemakers and implantable cardioverter-defibrillators: a systematic review]

The presence of a pacemaker or an implantable cardioverter-defibrillator was historically considered a contraindication to magnetic resonance imaging (MRI), due to the risks for both patient and device: reed-switch closure responsible for asynchronous pacing, inhibition of pacing, rapid ventricular pacing, heating on the lead tip or even device displacement... However, many recent studies demonstrate that if MRI is crucial for the management of the patient, it can be performed under specific monitoring and scanning conditions and after device reprogramming. The growing implication of device constructors in constructing a MRI safety device will perhaps extend in the future the indications of this imaging modality in implanted patients.

MRI assessment of pacing induced ventricular dyssynchrony in an isolated human heart

This study demonstrates the capabilities of MRI in the assessment of cardiac pacing induced ventricular dyssynchrony, and the findings support the need for employing more physiological pacing. A human donor heart deemed non-viable for transplantation, was reanimated using an MR compatible, four-chamber working perfusion system. The heart was imaged using a 1.5T MR scanner while being paced from the right ventricular apex (RVA) via an epicardial placed lead. Four-chamber, short-axis, and tagged short-axis cines were acquired in order to track wall motion and intramyocardial strain during pacing. The results of this study revealed that the activation patterns of the left ventricle (LV) during RVA pacing demonstrated intraventricular dyssynchrony; as the left ventricular mechanical activation proceeded from the septum and anterior wall to the lateral wall, with the posterior wall being activated last. As such, the time difference to peak contraction between the septum and lateral wall was approximately 125 msec. Likewise, interventricular dyssynchrony was demonstrated from the four-chamber cine as the time difference between the peak LV and RV free wall motion was 180 msec. With the ongoing development of MR safe and MR compatible pacing systems, we can expect MRI to be added to the list of imaging modalities used to optimize cardiac resynchronization therapy (CRT) and/or alternate site pacing.

Numerical model for estimating RF-induced heating on a pacemaker implant during MRI: experimental validation

MRI may cause tissue heating in patients implanted with pacemakers (PMs) or cardioverters/defibrillators. As a consequence, these patients are often preventatively excluded from MRI investigations. The issue has been studied for several years now, in order to identify the mechanisms involved in heat generation, and define safety conditions by which MRI may be extended to patients with active implants. In this sense, numerical studies not only widen the range of experimental measurements, but also model a realistic patient's anatomy on which it is possible to study individually the impact of the many parameters involved. In order to obtain reliable results, however, each and every numerical analysis needs to be validated by experimental evidence. Aim of this paper was to design and validate through experimental measurements, an accurate numerical model, which was able to reproduce the thermal effects induced by a birdcage coil on human tissues containing a metal implant, specifically, a PM. The model was then used to compare the right versus left pectoral implantation of a PM, in terms of power deposited at the lead tip. This numerical model may also be used as reference for validating simpler models in terms of computational effort.

Role of MRI in patient selection for CRT

Magnetic resonance imaging has great potential for aiding in the selection of patients who will respond to CRT. MRI is the only imaging tool that can simultaneously assess mechanical dyssynchrony, determine the amount and location of myocardial scar tissue, and map the location of cardiac venous anatomy-three important factors in predicting a patient's response to CRT. The goal of this manuscript is to review the MRI methods that can be used in the selection of patients for CRT.

Application of a clinical magnet over implantable cardioverter defibrillators: is it safe and useful?

The growing number of implantable cardioverter defibrillator (ICD) implants mean that a high number of patients carrying these devices are attended by physicians. In an attempt to simplify their management, articles have been published on the safety of applying magnets to the ICD in order to avoid the administration of shocks during surgery. However, performance of these procedures without the supervision of expert personnel can be accompanied by serious and potentially fatal complications. We report a case where the use of a clinic magnet over an ICD caused it to switch to "end of life" in the battery indicator and lose some antitachycardia therapies.

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

Advances in magnetic resonance (MR) imaging over the past 2 decades have led to MR becoming an increasingly attractive imaging modality. With the growing number of patients treated with permanent implanted or temporary cardiovascular devices, it is becoming ever more important to clarify safety issues in regard to the performance of MR examinations in patients with these devices. Extensive, although not complete, ex vivo, animal, and clinical data are available from which to generate recommendations regarding the safe performance of MR examination in patients with cardiovascular devices, as well as to ascertain caveats and contraindications regarding MR examination for such patients. Safe MR imaging involves a careful initial patient screening, accurate determination of the permanent implanted or temporary cardiovascular device and its properties, a thoughtful analysis of the risks and benefits of performing the examination at that time, and, when indicated, appropriate physician management and supervision. This scientific statement is intended to summarize and clarify issues regarding the safety of MR imaging in patients with cardiovascular devices.

Clinical utility and safety of a protocol for noncardiac and cardiac magnetic resonance imaging of patients with permanent pacemakers and implantable-cardioverter defibrillators at 1.5 tesla

BACKGROUND

Magnetic resonance imaging (MRI) is an important diagnostic modality currently unavailable for millions of patients because of the presence of implantable cardiac devices. We sought to evaluate the diagnostic utility and safety of noncardiac and cardiac MRI at 1.5T using a protocol that incorporates device selection and programming and limits the estimated specific absorption rate of MRI sequences.

METHODS AND RESULTS

Patients with no imaging alternative and with devices shown to be MRI safe by in vitro phantom and in vivo animal testing were enrolled. Of 55 patients who underwent 68 MRI studies, 31 had a pacemaker, and 24 had an implantable defibrillator. Pacing mode was changed to "asynchronous" for pacemaker-dependent patients and to "demand" for others. Magnet response and tachyarrhythmia functions were disabled. Blood pressure, ECG, oximetry, and symptoms were monitored. Efforts were made to limit the system-estimated whole-body average specific absorption rate to 2.0 W/kg (successful in >99% of sequences) while maintaining the diagnostic capability of MRI. No episodes of inappropriate inhibition or activation of pacing were observed. There were no significant differences between baseline and immediate or long-term (median 99 days after MRI) sensing amplitudes, lead impedances, or pacing thresholds. Diagnostic questions were answered in 100% of nonthoracic and 93% of thoracic studies. Clinical findings included diagnosis of vascular abnormalities (9 patients), diagnosis or staging of malignancy (9 patients), and assessment of cardiac viability (13 patients).

CONCLUSIONS

Given appropriate precautions, noncardiac and cardiac MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems.

Strategy for safe performance of extrathoracic magnetic resonance imaging at 1.5 tesla in the presence of cardiac pacemakers in non-pacemaker-dependent patients: a prospective study with 115 examinations

BACKGROUND

The purpose of the present study was to evaluate a strategy for safe performance of extrathoracic magnetic resonance imaging (MRI) in non-pacemaker-dependent patients with cardiac pacemakers.

METHODS AND RESULTS

Inclusion criteria were presence of a cardiac pacemaker and urgent clinical need for an MRI examination. Pacemaker-dependent patients and those requiring examinations of the thoracic region were excluded. The study group consisted of 82 pacemaker patients who underwent a total of 115 MRI examinations at 1.5T. To minimize radiofrequency-related lead heating, the specific absorption rate was limited to 1.5 W/kg. All pacemakers were reprogrammed before MRI: If heart rate was <60 bpm, the asynchronous mode was programmed to avoid magnetic resonance (MR)-induced inhibition; if heart rate was >60 bpm, sense-only mode was used to avoid MR-induced competitive pacing and potential proarrhythmia. Patients were monitored with ECG and pulse oximetry. All pacemakers were interrogated immediately before and after the MRI examination and after 3 months, including measurement of pacing capture threshold (PCT) and serum troponin I levels. All MR examinations were completed safely. Inhibition of pacemaker output or induction of arrhythmias was not observed. PCT increased significantly from pre- to post-MRI (P=0.017). In 2 of 195 leads, an increase in PCT was only detected at follow-up. In 4 of 114 examinations, troponin increased from a normal baseline value to above normal after MRI, and in 1 case (troponin pre-MRI 0.02 ng/mL, post-MRI 0.16 ng/mL), this increase was associated with a significant increase in PCT.

CONCLUSIONS

Extrathoracic MRI of non-pacemaker-dependent patients can be performed with an acceptable risk-benefit ratio under controlled conditions and by taking both MR- and pacemaker-related precautions.

Safety of MRI-guided vascular interventions

Longer electrically conducting parts are needed for various instruments such as pacemakers, defibrillators, deep brain stimulators and interventional instruments. Magnetic resonance imaging in the presence of these instruments can be potentially harmful, due to resonance effects and heating of conducting wires. A review of the literature revealed that neither manufacturers of pacemakers and defibrillators nor the FDA consider these medical instruments to be MR-safe, despite the fact that there are some reports about MR scanning of pacemaker patients without critical incidents. MR-guided angiographic interventions require not only high quality real-time imaging, but also MR compatible and MR-safe instruments. Consequently, metallic guidewires as used for angiographic interventions were examined during in vitro experiments in the MR environment. Heating of guidewires to>70 degrees was reported during in vitro experiments. Our own in vivo experiments using commercially available metallic guidewires observed heating to up to 35 degrees at the guidewire tip, despite the cooling effect of blood flowing around the guidewire. Moreover, we saw the development of sparks at the end of the guidewire if it was bent inside of the MR scanner and touched to the animal. But it was not possible to reliably repeat these heating results. We conclude that longer metallic parts have to be avoided inside the MR scanner to guarantee patient safety. In order to exploit more sophisticated technologies such as active tip tracking, solutions without the need for conducting wires have to be further developed before interventional MR can safely move into the clinical setting.

Strategy for Safe Performance of Magnetic Resonance Imaging on a Patient with Implantable Cardioverter Defibrillator

Clinically indicated magnetic resonance imaging (MRI) of the brain was safely performed at 1.5 T on a patient with an implantable cardioverter defibrillator (ICD). The ICD was reprogrammed to detection only, and imaging hardware and protocols were modified to minimize radiofrequency power deposition to the ICD system. The integrity of the ICD system was verified immediately post-MRI and after 6 weeks, including an ICD test with induction of ventricular fibrillation. This case demonstrates that in exceptional circumstances, in carefully selected patients, and using special precautions, an MRI exam of the brain may be possible in patients with ICDs.