Fewer than 1% of patients with implanted cardiac devices encountered device-related problems during MRI, suggesting the imaging technique can be used safely in selected patients with implanted devices, investigators reported.
In three of 438 patients (0.3%), MRI triggered back-up programming mode in implanted devices. Right ventricular sensing and atrial and ventricular lead impedance values declined immediately after MRI. Long-term follow-up revealed decreased right ventricular sensing and lead impedance, increased right ventricular capture, and reduced battery voltage.
None of the changes required revision or replacement of an implanted device, as reported in the October issue of Annals of Internal Medicine.
"Using a protocol based on device selection and programming, MRI can be performed safely in patients with certain pacemaker and ICD [implantable cardioverter defibrillator] systems," Saman Nazarian, MD, of Johns Hopkins, and co-authors wrote in conclusion.
"Given the potential for changes in device variables and programming, monitoring by device experts is necessary. The decision to perform MRI in each patient with an implantable device should be made by balancing the potential benefit of MRI against the attendant risks."
An estimated 75% of patients with implanted cardiac devices develop an indication for MRI associated with comorbid conditions (Pacing Clin Electrophysiol 2005; 28: 326-328, Circulation 2007; 116: 2878-2891). Though MRI use has traditionally been avoided in patients with implanted cardiac devices, reported experience with standard devices has been limited, according to background information in the article.
Nazarian and colleagues sought to address the lack of information by conducting a prospective study to define the safety of an MRI protocol in patients with a pacemaker or ICD. They designed a protocol on the basis of data from in vitro, in vivo, and pilot clinical studies. From 2003 to 2010, investigators in Baltimore and Haifa, Israel, enrolled 438 consecutive patients who had an implanted cardiac device (237 with a pacemaker and 201 with an ICD) and a medical indication for MRI. Scans were performed according to the participating institutions' standards.
Monitoring during imaging consisted of serial noninvasive blood pressure measurements, continuous electrocardiography, and pulse oximetry. During imaging of the first 55 patients, the specific absorption rate (SAR) of MRI sequences was limited to <2.0 W/kg. Thereafter, investigators followed manufacturer recommendations related to SAR.
Assessment of device and lead functioning consisted of measures of sensing, lead impedance, and capture threshold. Implantable devices have an electronic switch that responds to magnetic fields and provides for emergent asynchronous pacing or deactivation of therapy. Exposure to electromagnetic interference also may cause devices to revert into a backup programming mode, which sets pacing to an inhibited mode and enables tachycardia therapies.
Investigators identified events that triggered back-up programming mode by monitoring changes in pacing rate and interrogating devices after MRI. The 438 patients underwent a total of 555 MRI examinations, consisting of 222 brain scans, 122 studies of the spine, 89 heart studies, 72 studies of the abdomen or pelvis, and 50 studies of an extremity.
Device interrogation was performed before and immediately after MRI for all 438 patients, of whom 266 (61%) were followed long term (median of 214 days). Telephone follow-up for the remaining patients showed that 103 (60%) were alive without device dysfunction, 26 (15%) had died, and 43 (25%) were lost to follow-up.
Post-MRI device interrogation showed reductions in: Right ventricular (RV) sensing (median 0 mV, interquartile range ([QR] -0.7 to 0 V) Atrial lead impedance (median -2 Ω, IQR -13 to 0 Ω) Right and left ventricular impedance (median -4 Ω and -11 Ω, IQR -16 to 0 Ω and -40 to 0 Ω) Of the patients with long-term follow-up data, the investigators found: 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) Decreased battery voltage (median -0.01 V, IQR -0.04 to 0 V)
The authors acknowledged several limitations of the study, including lack of representation among all available cardiac devices, missing data on the 43 patients lost to follow-up, lack of a control group, and no defibrillation threshold testing. The authors of an accompanying editorial wrote, "Nazarian and colleagues found that MRI, done according to their protocol in this widely representative population of devices, was remarkably safe."
The results of Nazarian and colleagues, as well as those of other studies, suggest the risks of MRI in patients with implanted cardiac devices probably have been overestimated, they asserted. "In our opinion, the presence of a cardiac rhythm management device [CRMD] should no longer be considered an absolute contraindication to MRI," wrote Matthew R. Reynolds, MD, and Peter Zimetbaum, MD, of Beth Israel Deaconess Medical Center and Harvard Medical School. "Rather, the risks and benefits of MRI in a patient with a CRMD should be assessed on an individual basis, as with any important medical decision.
The authors have not demonstrated that MRI in these patients is risk free -- only that the risks are quantitatively small." The study was supported by the National Institutes of Health.