Background: Magnetic resonance imaging (MRI) offers excellent soft tissue resolution and is the preferred imaging modality for diagnosis of musculoskeletal, neurological and many thoracic and abdominal conditions. While MRI is currently unavailable for millions of patients because of the presence of implantable cardiac devices, 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. In this study we report the clinical utility of MRI in implantable cardiac device recipients.
Methods: One hundred and eighty six patients with devices shown to be MRI safe by in vitro phantom and in vivo animal testing underwent 228 MRI studies. 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.
Results: No episodes of inappropriate inhibition or activation of pacing were observed. There were no significant differences between baseline and immediate or long-term sensing amplitudes, lead impedances, or pacing thresholds. The diagnostic yield of alternative testing was 19% in 47 patients who underwent ultrasound, nuclear imaging or computed tomography prior to MRI. In contrast, diagnostic questions were answered in 95% of MRI studies.
Conclusions: The diagnostic benefits of MRI significantly outweigh the theoretical risks in patients with implanted cardiac devices when appropriate safety measures are implemented.
Ideal current patterns yielding optimal signal-to-noise ratio and specific absorption rate in magnetic resonance imaging: Computational methods and physical insights
