CURRICULUM IN CARDIOLOGY - JOURNAL CLUB

Year : 2018  |  Volume : 4  |  Issue : 1  |  Page : 37-40

Safety of magnetic resonance imaging in patients with cardiac devices

Nitin Kumar Parashar¹, Mumun Sinha², Neeraj Parakh^3
1 Department of Cardiology, All India Institute of Medical Sciences, New Delhi, India
² Department of Cardiac Radiology, All India Institute of Medical Sciences, New Delhi, India
³ Department of Cardiology, Cardiothoracic Sciences Centre, All India Institute of Medical Sciences, New Delhi, India

Correspondence Address:
Dr. Neeraj Parakh
Department of Cardiology, Cardiothoracic Sciences Centre, All India Institute of Medical Sciences, New Delhi - 110 029
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/jpcs.jpcs_10_18

Introduction

• Many patients with cardiac pacemakers or implantable cardioverter-defibrillator (ICD) subsequently have an indication of magnetic resonance imaging (MRI)^[1]
• MRI in these patients is generally denied due to potentially dangerous interactions between these intracardiac devices and magnetic fields and radiofrequency energy used in MRI studies
• The interaction between the intracardiac device and MRI occurs due to three essential components of an MRI which are a static magnetic field, gradient magnetic field, and radiofrequency energy [Table 1]^[2]
• Due to these potential hazards, some modifications were done in cardiac devices so that MRI can be performed safely on these devices.^[3],[4] These devices were called MRI conditional devices, and others were termed legacy or conventional or nonMRI conditional devices
• The main modifications in MRI conditional devices include a reduction in ferromagnetic components, replacement of reed switch by hall sensor, change in lead coil design and insulation, and change in filter circuitry to prevent damage to the internal power supply and dedicated pacemaker programming to prevent inappropriate pacemaker inhibition. These MRI conditional devices were introduced in 2008 for the first time
• However, the vast majority of pacemaker and ICD systems in current use are not MRI conditional devices. Presence of the conventional intracardiac device is a standard contraindication for against the use of MRI
• Smaller studies have reported safety of MRI in patients with a legacy pacemaker or ICD. A recent larger study evaluated only nonthoracic examinations and revealed the safety of MRI in these patients.^[5]

Table 1: Potential effects of magnetic resonance imaging and interactions with cardiac devices Click here to view

Methods

• This was large, prospective study to evaluate the safety of MRI protocol in patients with a legacy pacemaker or ICD systems
• The study was funded by Johns Hopkins University and the National Institutes of Health
• Patient selection: Candidates who had an ICD or a pacemaker and a clinical indication for MRI
• Enrolled during the period from February 2003 to January 2015.

• Patients who had undergone lead implantation within the previous 4 weeks
• If the patient had permanent surgical epicardial leads or permanent nonfunctional leads
• If they were pacing-dependent and had an ICD without asynchronous pacing capability.

Device Interrogation and Programming

• An asynchronous pacing mode was programmed for pacing-dependent patients to avoid inappropriate inhibition of pacing resulting from the detection of electromagnetic interference
• In contrast, an inhibited pacing mode was used for patients without pacing dependence to avoid inappropriate pacing resulting from the tracking of electromagnetic interference
• Tachyarrhythmia monitoring and therapies were deactivated in ICD devices to avoid the delivery of unwarranted therapies
• After completion of the MRI, the devices were reprogrammed to the original settings. Long-term follow-up interrogation at 6 months was recommended
• Imaging was performed with the use of MRI scanners with the commonly used magnetic field strength of 1.5 tesla (Magnetom Avanto and Magnetom Aera, Siemens)
• Symptoms, such as pain, warmth, and palpitations, were monitored with the use of an in-room speaker system
• Blood pressure (BP), measured noninvasively, was assessed every 3 min
• Continuous electrocardiographic monitoring was performed.

Outcome Assessment

• Study outcome assessments included adverse events and changes in device parameters.

• Generator failure
• Power-on reset (PoR) – In which device settings are reset automatically to a backup mode as if the power to the device had been shutoff and then turned-on again
• Changes in pacing threshold or sensing that require system revision or programming changes
• Battery depletion
• Cardiac arrhythmia
• Inhibition of pacing
• Inappropriate delivery of antitachycardia pacing or shock
• Patient-reported events such as discomfort, pain, a warm sensation in the location of the device, and palpitations.

• P-wave amplitude
• Right ventricular and left ventricular R-wave amplitude
• Atrial, left ventricular, and right ventricular lead impedance
• Atrial, right ventricular, and left ventricular capture threshold
• Battery voltage.

• Given the expected variation in lead parameters on repeat measurement, percentage changes from baseline were categorized as follows:
  • No change (≤20% change)
  • Expected change (>20%–50% change)
  • Notable change (>50% change).

• Continuous variables are summarized as medians and interquartile ranges, and discrete variables as absolute numbers and percentages
• The associations between changes in device parameters that occurred either immediately after the MRI or at long-term follow-up were assessed with the use of the nonparametric k-sample test on the median (unordered groups) or a nonparametric test for trend (ordered groups).

Results

• A total of 2103 MRI examinations was performed in 1509 patients, 880 (58%) of whom had a pacemaker, and 629 (42%) of whom had an ICD
• Of the 1509 patients, 137 (9%) were pacing dependent (22 of whom had an ICD with asynchronous programming mode capability)
• This study included patients underwent thoracic MRI examination also (n = 257, 12%)
• A total of 1189 of the 1509 patients (79%) underwent a single MRI examination
• The repeat MRI examination was performed in 320 patients (21%); about 18 patients underwent six or more examinations
• PoR occurred during a total of nine MRI examinations (0.4% of the examinations) in eight patients (0.5% of patients). Six out of these eight patients completed MRI study successfully, and MRI examination in two patients was terminated prematurely
• None of the patients who had a transient event of PoR had device dysfunction at long-term follow-up
• 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 the right ventricular capture threshold (4%), and increases in the left ventricular capture threshold (3%)
• Premature atrial and ventricular beats and occasional nonsustained episodes of ventricular tachycardia, as well as an episode of paroxysmal atrial fibrillation, were observed. However, no arrhythmias were temporally associated with MRI sequence initiation, rhythmicity, or termination.

Discussion

• As the study protocol, asynchronous pacing mode was used for pacing-dependent patients and inhibited pacing mode was used for pacing independent patients and tachyarrhythmia monitoring and shock therapy were terminated in ICD patients
• The most important event that was found to be attributable to MRI was the occurrence of PoR in approximately 1 in 200 examinations [Table 2]
• During the events of PoR, the device is susceptible to inhibition of pacing output and activation of antitachycardia therapies ^[6]
• Of the nine MRI examinations in which events of PoR occurred, one examination was associated with mild physical symptoms, one (which occurred near the end of the battery life of the device) resulted in an inability to reprogram the device and in the consequent replacement of the device, and one was associated with transient inhibition of pacing
• The observed changes in device parameters (lead sensing, impedances, and capture thresholds) were not clinically significant and did not require device revision or reprogramming
• Previous reports had suggested that MRI of the thorax may present a greater risk of safety issues than MRI of nonthoracic regions owing to the greater power deposition over the region containing the device
• However, the current larger study, in which the follow-up period was longer, does not suggest any association between the region of imaging and detrimental changes in device parameters
• A recently published study by Padmanabhan et al. showed that brain MRI in patients with pacemaker or ICD does not carry increased mortality risk as compared with brain computed tomography.^[7]

Table 2: Power-on reset events Click here to view

• This study showed that MRI studies are safe in cardiac devices patients
• Legacy intracardiac devices are generally considered unsafe for the MRI studies. However, no definite evidence has been provided for the same. The present study refuted this hypothesis by revealing safety of MRI in legacy intracardiac devices
• This study included the patients having both pacemakers and ICDs
• A significant number of patients underwent thoracic MRI studies also. These patients were excluded in the previous studies
• Pacing-dependent patients require extra care and monitoring during MRI studies; however, MRI can be done in these patients also.

• This study is a single-center study
• The authors were unable to obtain long-term follow-up of a large number of patients (n = 302, 20%)
• Device technology is constantly in evolution. Hence, results should not be generalized to older or newer generation devices
• All the MRIs were performed at 1.5 tesla strength in this study. Further studies will be required to reveal safety of MRI at three-tesla strength in the patients having intracardiac devices.

Conclusion

• Both thoracic and extrathoracic 1.5 T MRI studies can be carried out safely in patients with legacy pacemakers/ICD (non-MRI conditional devices) with the following conditions:
• The presence of trained nurse/doctor
• Immediate availability of an electrophysiologist
• Under the proper supervision and monitoring (Electrocardiogram, BP, Pulse rate, and O₂ saturation) with the availability of external pacing backup.

References

1.	Nazarian S, Reynolds MR, Ryan MP, Wolff SD, Mollenkopf SA, Turakhia MP, et al. Utilization and likelihood of radiologic diagnostic imaging in patients with implantable cardiac defibrillators. J Magn Reson Imaging 2016;43:115-27.
2.	Roguin A, Schwitter J, Vahlhaus C, Lombardi M, Brugada J, Vardas P,et al. Magnetic resonance imaging in individuals with cardiovascular implantable electronic devices. Europace 2008;10:336-46.    [PUBMED]
3.	Forleo GB, Santini L, Della Rocca DG, Romano V, Papavasileiou LP, Magliano G, et al. Safety and efficacy of a new magnetic resonance imaging-compatible pacing system: Early results of a prospective comparison with conventional dual-chamber implant outcomes. Heart Rhythm 2010;7:750-4.   [PUBMED]
4.	Wollmann CG, Thudt K, Kaiser B, Salomonowitz E, Mayr H, Globits S, et al. Safe performance of magnetic resonance of the heart in patients with magnetic resonance conditional pacemaker systems: The safety issue of the ESTIMATE study. J Cardiovasc Magn Reson 2014;16:30.
5.	Russo RJ, Costa HS, Silva PD, Anderson JL, Arshad A, Biederman RW, et al. Assessing the risks associated with MRI in patients with a pacemaker or defibrillator. N Engl J Med 2017;376:755-64.   [PUBMED]
6.	Higgins JV, Sheldon SH, Watson RE Jr., Dalzell C, Acker N, Cha YM, et al. “Power-on resets” in cardiac implantable electronic devices during magnetic resonance imaging. Heart Rhythm 2015;12:540-4.
7.	Padmanabhan D, Jondal ML, Hodge DO, Mehta RA, Acker NG, Dalzell CM, et al. Mortality after magnetic resonance imaging of the brain in patients with cardiovascular implantable devices. Circ Arrhythm Electrophysiol 2018;11:e005480.   [PUBMED]

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