"The most important event that was found to be attributable to MRI was the occurrence of power-on reset in approximately one in 200 examinations," wrote lead author Dr. Saman Nazarian, PhD, an associate professor of medicine at the University of Pennsylvania, and colleagues. "Changes in device parameters were infrequent, and none resulted in long-term clinically significant adverse events."
The devices come with concerns about safety and proper function when exposed to the magnetic fields of MRI scanners. Patients are often denied scans unless their devices meet certain criteria specified by the U.S. Food and Drug Administration (FDA) that support their conditional use in the MRI environment.
The researchers targeted a number of potential adverse events that could occur immediately after an MRI scan. Possible malfunctions included the following:
- Generator failure
- Power-on reset, in which device settings are reset automatically to a backup mode as if the device had lost power and 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
The prospective, nonrandomized study included 1,509 subjects; 880 (58%) had a pacemaker and 629 (42%) had an implantable cardioverter-defibrillator (ICD) that was not considered to be MRI-conditional. The patients underwent a total of 2,103 thoracic and nonthoracic MRI scans most often with a magnet strength of 1.5 tesla (Magnetom Avanto and Magnetom Aera, Siemens Healthineers) (NEJM, December 28, 2017, Vol. 377:26, pp. 2555-2564).
Among the subjects, 196 (13%) had two MRI scans, 64 (4%) had three exams, 27 (2%) had four scans, and 33 (2%) had five or more MRI scans. The patients were evaluated for pain, warmth, palpitations, and other cardiac-related conditions. Clinicians monitored blood pressure every three minutes in conjunction with continuous electrocardiographic monitoring.
The researchers were able to collect long-term follow-up results for 1,327 MRI scans performed on 958 patients (63%). The median follow-up time was one year (range, 0.5-1.7 years).
Nazarian and colleagues found no long-term clinically significant adverse events among the subjects. Nine MRI scans (0.4%) prompted a patient's device to reset to backup mode. In one other case, a pacemaker with less than one month of battery life remaining reset to ventricular-inhibited pacing and could not be reprogrammed. That device was subsequently replaced.
The most common notable changes from baseline included increases in atrial capture threshold (4%), right ventricular capture threshold (4%), and left ventricular capture threshold (3%).
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