Author + information
- Published online September 18, 2017.
- Theofanie Mela, MD∗ ()
- Pacemaker and ICD Clinic, Cardia Arrhythmia Service, Massachusetts General Hospital, Boston, Massachusetts
- ↵∗Address for correspondence:
Dr. Theofanie Mela, Pacemaker and ICD Clinic, Cardiac Arrhythmia Service, Massachusetts General Hospital, 75 Fruit Street, Boston, Massachusetts 02114.
Imaging has become the cornerstone of everyday diagnostics. Magnetic resonance imaging (MRI) and its many applications are the preferred test modalities because of their diagnostic capabilities and their lack of radiation exposure.
For years, the ability to have an MRI scan was at the top of the wish list of patients with cardiac rhythm management (CRM) devices and their physicians. Patients with long-standing back pain who were unable to have an MRI scan because of their CRM devices had to undergo painful myelograms to obtain a diagnosis and appropriate therapy. The American Heart Association and the American College of Cardiology suggested as recently as 2007 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 risk” (1).
Since the late 1990s, there had been a simultaneous research effort by both industry and academia to advance knowledge about the effect of the magnetic field on implantable devices and to design devices and leads that would withstand the impact of the magnetic field and mitigate the potential harmful effect on the patient. During that time, the majority of radiologists considered the presence of CRM devices to be an absolute contraindication to MRI scanning. Finally, the unmet technological need was reached in 2008 in Europe and in 2011 in the United States when the Conformité Européenne in Europe and the Food and Drug Administration in the United States, respectively, approved the first MRI-conditional pacemaker system. Since then a plethora of bradycardia and tachycardia devices have been released under the label of MRI-conditional devices. As a result of this revolution, whole-body MRI scans can now be performed in recipients of these newer CRM systems without any significant safety concerns for these patients. As a matter of fact, 20% of patients who received a Medtronic SureScan system (Medtronic, Minneapolis, Minnesota) had undergone an MRI scan within the first 2 years of having the system (2), and it is estimated that up to 75% of CRM device recipients will require a clinically indicated MRI scan during their lifetime (3).
Even before the evolution to MRI-conditional devices, there was a whole other effort to define the safety limits within which non–MRI-conditional devices could be scanned. Some centers in Europe and the United States had started scanning these patients years before the first MRI-conditional system was released. The Johns Hopkins database (4) and the more recently reported MagnaSafe registry (5) confirmed that on exposure to 1.5-T scanners, CRM devices made by all the different manufacturers can be safely scanned. Absolute prerequisites, however, are appropriate evaluation of the device before the scan and careful consideration of the programmed mode for the scan. The exclusion criteria for these studies included the presence of abandoned leads and epicardial leads. Newer data, however, from a small but significant registry including 57 patients with 63 abandoned leads from the Mayo Clinic in Rochester, Minnesota (6), were presented at the Heart Rhythm Society Scientific Sessions in 2017 and suggested that even in the presence of abandoned leads, an MRI scan can be performed safely, with no evidence of device malfunction, arrhythmias, or myocardial injury.
An integral part of the safety of the procedure is that, both for MRI-conditional and non–MRI-conditional devices, significant preparation involving both the radiology team and the cardiology team is required before the scan. The radiology team needs to confirm the eligibility of the device-bearing patient for an MRI scan by searching the device data and obtaining a chest radiograph to confirm the lack of abandoned or epicardial leads. Subsequently, the device needs to be interrogated, the implantable cardioverter-defibrillator needs to have the therapies turned off, and the pacing must be programmed according to the patient’s underlying conduction disease. Therefore, a technician needs to be readily available for the device to be programmed and reprogrammed before and after the MRI scan. For non–MRI-conditional devices, a cardiologist or a cardiology nurse must be present to supervise the patient during the scan. After the scan, the device needs to be interrogated again and programmed back to its original mode.
All this effort raises a number of questions: Is it really necessary for the patient to have an MRI scan? Are we exaggerating in our quest for MRI-safe device technology or safe MRI protocols so that we can scan patients with non–MRI-conditional devices? Is the extra effort rewarded? Are these studies even covered by the patient’s insurance? Should these patients have alternative tests, as in previous decades?
The paper by Samar et al. (7) in this issue of JACC: Clinical Electrophysiology answers some of these questions as it examines the clinical significance of MRI for patients with non–MRI-conditional CRM devices when there is either no alternative test or there is clinical uncertainty after other diagnostic tests have been performed.
The 136 patients in this study had already undergone other diagnostic studies (computed tomography imaging or myelography for neurological or orthopedic cases, transthoracic echocardiography, transesophageal echocardiography, nuclear examination, or computed tomography angiography for cardiac cases), and either the diagnosis had remained unresolved or the patients could not tolerate studies such as myelography. The scans took place between 2005 and 2015, but mostly after 2009. The MRI protocol was similar to that followed by the MagnaSafe registry and involved only 1.5-T scans.
MRI of the brain or the spinal cord was performed in 73% of patients, and a cardiovascular examination was performed in 22% of these patients, thus suggesting that a serious indication for the MRI study was present in each case. In 75% of the neurological patients and in 90% of the cardiovascular patients, the MRI scan added substantial value to the management of the patient. The patient population was representative of a “real-life” practice and included patients with complete heart block, which had been excluded by other registries, and patients with abandoned leads or recently implanted leads (<6 weeks from implant) when the indication for the study was very strong. There were no negative sequelae of these MRI scans; however, Samar et al. (7) emphasize the significance of having these studies performed by expert personnel and under the supervision of an expert member of the cardiology team.
The finding that these studies occurred at a time when scant data on the safety of performing MRI scans in patients with non–MRI-conditional devices existed suggests that these patients had very strong indications for MRI and a high pre-test probability of benefiting from the scan. Therefore, the majority of the tests had a high diagnostic yield. As the use of MRI in such patients is constantly expanding, this strategy should continue to be applicable because the risk for a serious complication from an MRI scan of a non–MRI-conditional device is not negligible (8). This is especially true given that groups of patients who have not been studied extensively before (pacemaker-dependent patients were mostly excluded from previous registries, and patients with abandoned or epicardial leads have been studied in only very small numbers) are involved.
Although the ability to perform MRI has benefited patients with challenging neurological and cardiovascular conditions who have non–MRI-conditional devices, limitations still exist. Published studies have used only 1.5-T MRI. The risk of 3-T MRI, which offers much a better quality of imaging, for these devices is likely higher, and this technique is therefore avoided. Image quality may also be a limitation. The study by Samar et al. (7) reported that in 2 patients whose implantable cardioverter-defibrillator was inside the thoracic field of view, the device caused severe image distortion and field degradation. In addition, the quality of the image may be distorted by the presence of the leads in the heart and the proximity of the device. In 1 patient only partial data were obtained, and in another patient the data were uninterpretable for viability. There is increasing expertise, however, in improving image quality, and this limitation is becoming much less relevant (9). Finally, at this time, the Centers for Medicare and Medicaid Services are not reimbursing providers for MRI studies performed in patients with non–MRI-conditional devices, except under a research protocol (10).
Today, all the manufacturers produce MRI-conditional CRM devices. The use of these devices is gradually expanding, despite certain financial considerations. It is evident that the financial burden of performing multiple diagnostic tests that are inferior to MRI and the effort and expertise necessary to perform MRI examinations in non–MRI-conditional devices exceed the financial concerns about the use of MRI-conditional technology.
The future therefore appears to trend toward the increased use of MRI-conditional technology. The next step will include automatization of these devices so that when they are exposed to a magnetic field, they will be reprogrammed automatically to an MRI mode. A newly released feature by Biotronik (Lake Oswego, Oregon) enables the device to be programmed to an MRI mode 2 weeks before a scheduled MRI scan so that the device will automatically convert to the pre-selected mode once it enters the magnetic field.
The CRM device wish list has become shorter over the past 10 years, but the future seems to be even more exciting. The newly released leadless pacemaker is already MRI conditional, as is the subcutaneous implantable cardioverter-defibrillator. Future expectations include that MRI-conditional technology should have no price difference and that complete automatization of the MRI process will exist so that the intervention by the cardiologist is not required. The cardiologist will continue to supervise non–MRI-conditional devices closely to offer patients the safest way to undergo valuable MRI scans.
↵∗ Editorials published in JACC: Clinical Electrophysiology reflect the views of the author and do not necessarily represent the views of JACC: Clinical Electrophysiology or the American College of Cardiology.
Dr. Mela has reported receiving speaker’s honoraria from Biotronik, Medtronic, and St. Jude Medical.
The author attests that she is in compliance with human studies committees and animal welfare regulations of the authors’ institutions and Food and Drug Administration guidelines, including patient consent where appropriate. For more information, visit the JACC: Clinical Electrophysiology author instructions page.
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