Even Thoracic MRI Safe for 'Legacy' ICDs, Pacemaker Systems: Large Cohort Study

December 28, 2017

BOSTON, MA — Most magnetic resonance imaging (MRI) is safe to perform in patients with implantable cardioverter defibrillator (ICD) and pacemaker systems that aren't classified as MRI-conditional as long as appropriate safety protocols are followed, concludes a large cohort study with a long follow-up[1].

"The scans were safely performed even when performing thoracic or cardiac MRI and with patients that were dependent on cardiac pacing for every heartbeat," Dr Saman Nazarian (University of Pennsylvania, PA) told theheart.org | Medscape Cardiology. He is lead author of the study published December 27, 2017 in the New England Journal of Medicine.

The finding supports a growing body of evidence that MRI can be safe in such nonMRI-conditional "legacy" devices when appropriate patient-selection and device-programming cautions are followed, especially from the prospective MagnaSafe Registry study, which was limited to patients undergoing nonthoracic MRI.

Imaging in the current study of 1509 patients from a single center, as in the multicenter MagnaSafe with its 1500 patients, was performed using 1.5-Tesla scanners. Similar preliminary findings had been previously reported for its first 438 patients.

As a result of imaging, "Changes in device parameters were infrequent, and none resulted in long-term clinically significant adverse events," the current report states. "The most important event that was found to be attributable to MRI was the occurrence of power-on reset in approximately 1 in 200 examinations."

"Given the results of our study and those of MagnaSafe, it is hard to understand the position of the Centers for Medicare and Medicaid Services to restrict access to patients with MRI-conditional labeling of their leads and ICD systems," Nazarian said.

"The idea that access to the potentially lifesaving diagnostic data from MRI would be limited for patients with legacy pacemakers and ICD leads or generators is outdated," he said.

"Additionally, no patient should ever be exposed to the risks of lead extraction to enable an MRI that could safely be performed with the leads in place."

Of the 1509 patients who underwent 2103 clinically indicated thoracic and nonthoracic MRI examinations from 2003 to 2015, 58% had pacemaker-only systems and the remainder had ICDs that had been implanted >4 weeks previously. None had permanent epicardial lead systems or nonfunctional abandoned leads.

Pacemaker-dependent patients had their devices reprogrammed to asynchronous mode prior to imaging; devices in other patients were set to demand mode.

Eight of the nine cases of device power-on reset associated with imaging were transient with all functions "fully restored."

Five imaging sessions were stopped prematurely, including one in a patient getting MRI prior to planned ventricular ablation who developed ventricular tachycardia, and three because of artifacts that spoiled interpretation of the images, according to the report.

"No other examinations were stopped because of clinical symptoms or changes in heart rate, oxygenation, or other variables," the group writes.

At the median 1-year follow-up, available in 63% of 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 message for patients, according to Nazarian, is that "if you are one of the millions of patients with a pacemaker or ICD system and have been told you need an MRI, contact a center with the expertise to enable the imaging. Many centers across the US are capable of performing safe imaging despite your device."

Nazarian reports receiving consulting fees and serving as the principal investigator for St Jude Medical and Biosense Webster, serving as an unpaid consultant for CardioSolv, and receiving consulting fees from Siemens. Disclosures for the other authors are listed in the report.

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