Clinical utility and safety of a protocol for noncardiac and cardiac magnetic resonance imaging of patients with permanent pacemakers and implantable-cardioverter defibrillators at 1.5 tesla

Abstract

Background: Magnetic resonance imaging (MRI) is an important diagnostic modality currently unavailable for millions of patients because of the presence of implantable cardiac devices. We sought to evaluate the diagnostic utility and 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.

Methods and results: Patients with no imaging alternative and with devices shown to be MRI safe by in vitro phantom and in vivo animal testing were enrolled. Of 55 patients who underwent 68 MRI studies, 31 had a pacemaker, and 24 had an implantable defibrillator. Pacing mode was changed to "asynchronous" for pacemaker-dependent patients and to "demand" for others. Magnet response and tachyarrhythmia functions were disabled. Blood pressure, ECG, oximetry, and symptoms were monitored. Efforts were made to limit the system-estimated whole-body average specific absorption rate to 2.0 W/kg (successful in >99% of sequences) while maintaining the diagnostic capability of MRI. No episodes of inappropriate inhibition or activation of pacing were observed. There were no significant differences between baseline and immediate or long-term (median 99 days after MRI) sensing amplitudes, lead impedances, or pacing thresholds. Diagnostic questions were answered in 100% of nonthoracic and 93% of thoracic studies. Clinical findings included diagnosis of vascular abnormalities (9 patients), diagnosis or staging of malignancy (9 patients), and assessment of cardiac viability (13 patients).

Conclusions: Given appropriate precautions, noncardiac and cardiac MRI can potentially be safely performed in patients with selected implantable pacemaker and defibrillator systems.

Figure 1

Safety protocol for imaging of patients with permanent pacemaker and ICD systems. Devices listed have previously undergone satisfactory in vitro phantom and in vivo animal testing.

Figure 2

Typical susceptibility artifacts with (A) inversion recovery prepared gradient echo and (B) steady-state free-precession sequences. In A, the region of anterolateral hyperenhancement is due to artifact compared with subendocardial hyperenhancement in the septum, which likely represents prior infarction.

Figure 3

Cardiac MRI with minimal artifact using (A) time-of-flight sequence to demonstrate the anatomy of congenitally corrected transposition of great vessels in a patient with a permanent pacemaker and (B) steady-state free-precession sequence to assess coronary sinus patency in a patient with an implantable defibrillator.

Figure 4

Comparison of computed tomography versus diffusion-weighted MRI images of the brain in a pacemaker-dependent patient who presented with new-onset loss of balance. Although the imaging planes are different due to computed tomography versus MRI technique, both sets of images span similar areas of the cerebellum and occipital cortex. No abnormalities were noted on computed tomography, whereas MRI readily identified infarcts involving the cerebellum and occipital cortex (arrows).