AHA: MRI has little disruption for pacemakers, ICDs
It appears to be safe for patients with pacemakers and implantable cardioverter defibrillators to undergo MR imaging. Additionally, the diagnostic benefits of MRI far outweigh the perceived risks in patients with implantable devices, according to two studies presented at the 2008 American Heart Association (AHA) Scientific Sessions.
Jennifer D. Cohen, MD, and colleagues at the Scripps Clinic in La Jolla, Calif., studied 51 patients who underwent 61 MRI scans from January 2006 to April 2008.
Patients were from the MagnaSafe Registry, a prospective study to determine the safety of MRI for patients with pacemakers (PMs) and implantable cardioverter defibrillators (ICDs).
The MagnaSafe Registry protocol includes informed consent by a cardiologist who is present during the exam; noninvasive monitoring during the study; available ACLS equipment; and device interrogation before and after MRI.
Prior to imaging, researchers programmed all ICD tachycardia therapies to “monitor only.” Patients with symptomatic bradycardias or PM dependence were programmed to an asynchronous pacing mode and patients with sinus rhythm greater than 50/minute were programmed to “no pacing.”
Researchers restored initial device parameters immediately after imaging. They recorded pacing thresholds, lead impedance, P and R wave amplitude and battery voltage pre- and post-MRI. Of the 51 patients in the study, 17 had coronary artery disease and one was pacer-dependent.
Researchers found that a change in battery voltage occurred in six of 19 patients with complete data sets. Four patients experienced a decrease in battery voltage and two experienced an increase.
Complete lead impedance data were available for 47 leads. The mean change in impedance was -5.3. Complete threshold data were available for 34 leads—15 atrial, 16 RV and 3 LV—with eight threshold increases and two decreases. No patient had more than one lead affected, Cohen reported.
One device with a 0.75V-threshold rise required reprogramming. None of the four patients undergoing cardiac MRI had threshold changes and there was no association between the scan performed and the occurrence of a threshold change.
Of eight patients with a threshold increase, two also had a change in battery voltage. One patient had a magnet response and was removed from the scanner.
“Preliminary results of the MagnaSafe Registry demonstrate an acceptable safety profile and a low incidence of battery voltage, lead impedance and pacing threshold change after MRI in patients with pacemakers and ICDs,” Cohen concluded.
In the second study, Henry R. Halperin, MD, from the department of medicine, radiology, and biomedical engineering at Johns Hopkins University, and colleagues sought to determine the clinical utility of MRI in patients with ICDs.
“While MRI is currently unavailable for millions of patients because of the presence of ICDs, we and others have previously reported the safety of noncardiac and cardiac MRI at 1.5T using a protocol that incorporates device selection and programming and limits the estimated specific absorption rate of MRI sequences,” Halperin said.
Researchers performed 228 scans on 186 patients with devices shown to be MRI safe by phantom and preclinical testing. They changed the pacing mode to “asynchronous” for pacemaker-dependent patients and to “demand” for others. They also disabled magnet response and tachyarrhythmia functions.
Blood pressure, ECG, oximetry and symptoms were monitored. Researchers took efforts to limit the system-estimated whole-body average specific absorption rate to 2.0 W/kg (successful in more than 99 percent of sequences, Halperin noted), while maintaining diagnostic quality MRI scans.
Researchers found no episodes of inappropriate inhibition or activation of pacing. They found no differences between baseline and immediate or long-term sensing amplitudes, lead impedances or pacing threshold.
The diagnostic yield of alternative testing was 19 percent in 47 patients who underwent ultrasound, nuclear imaging or CT prior to MRI. In contrast, diagnostic questions were answered in 95 percent of MRI studies, Halperin said.
He concluded that the diagnostic benefits of MRI significantly outweigh the theoretical risks in patients with ICDs when appropriate safety measures are taken.
Jennifer D. Cohen, MD, and colleagues at the Scripps Clinic in La Jolla, Calif., studied 51 patients who underwent 61 MRI scans from January 2006 to April 2008.
Patients were from the MagnaSafe Registry, a prospective study to determine the safety of MRI for patients with pacemakers (PMs) and implantable cardioverter defibrillators (ICDs).
The MagnaSafe Registry protocol includes informed consent by a cardiologist who is present during the exam; noninvasive monitoring during the study; available ACLS equipment; and device interrogation before and after MRI.
Prior to imaging, researchers programmed all ICD tachycardia therapies to “monitor only.” Patients with symptomatic bradycardias or PM dependence were programmed to an asynchronous pacing mode and patients with sinus rhythm greater than 50/minute were programmed to “no pacing.”
Researchers restored initial device parameters immediately after imaging. They recorded pacing thresholds, lead impedance, P and R wave amplitude and battery voltage pre- and post-MRI. Of the 51 patients in the study, 17 had coronary artery disease and one was pacer-dependent.
Researchers found that a change in battery voltage occurred in six of 19 patients with complete data sets. Four patients experienced a decrease in battery voltage and two experienced an increase.
Complete lead impedance data were available for 47 leads. The mean change in impedance was -5.3. Complete threshold data were available for 34 leads—15 atrial, 16 RV and 3 LV—with eight threshold increases and two decreases. No patient had more than one lead affected, Cohen reported.
One device with a 0.75V-threshold rise required reprogramming. None of the four patients undergoing cardiac MRI had threshold changes and there was no association between the scan performed and the occurrence of a threshold change.
Of eight patients with a threshold increase, two also had a change in battery voltage. One patient had a magnet response and was removed from the scanner.
“Preliminary results of the MagnaSafe Registry demonstrate an acceptable safety profile and a low incidence of battery voltage, lead impedance and pacing threshold change after MRI in patients with pacemakers and ICDs,” Cohen concluded.
In the second study, Henry R. Halperin, MD, from the department of medicine, radiology, and biomedical engineering at Johns Hopkins University, and colleagues sought to determine the clinical utility of MRI in patients with ICDs.
“While MRI is currently unavailable for millions of patients because of the presence of ICDs, we and others have previously reported the safety of noncardiac and cardiac MRI at 1.5T using a protocol that incorporates device selection and programming and limits the estimated specific absorption rate of MRI sequences,” Halperin said.
Researchers performed 228 scans on 186 patients with devices shown to be MRI safe by phantom and preclinical testing. They changed the pacing mode to “asynchronous” for pacemaker-dependent patients and to “demand” for others. They also disabled magnet response and tachyarrhythmia functions.
Blood pressure, ECG, oximetry and symptoms were monitored. Researchers took efforts to limit the system-estimated whole-body average specific absorption rate to 2.0 W/kg (successful in more than 99 percent of sequences, Halperin noted), while maintaining diagnostic quality MRI scans.
Researchers found no episodes of inappropriate inhibition or activation of pacing. They found no differences between baseline and immediate or long-term sensing amplitudes, lead impedances or pacing threshold.
The diagnostic yield of alternative testing was 19 percent in 47 patients who underwent ultrasound, nuclear imaging or CT prior to MRI. In contrast, diagnostic questions were answered in 95 percent of MRI studies, Halperin said.
He concluded that the diagnostic benefits of MRI significantly outweigh the theoretical risks in patients with ICDs when appropriate safety measures are taken.