Subcutaneous implantable cardioverter-defibrillator patients may be safe to be exposed to magnetic resonance imaging (MRI) procedures at 1.5T with a pre-specified scanning and monitoring protocol.
Jiri Keller from Petr Neuzil and Vivek Reddy group (Heart Center Homolka Hospital, Prague, Czech Republic) reported-ahead-of-print in Europace-the results of a first-of-its-kind study exploring the potential for safely imaging patients with the subcutaneous implantable cardioverter system (S-ICD, Boston Scientific).
According to Keller et al, it is estimated that as many as 75% of active cardiac device recipients will become indicated for MRI. However, the majority of such devices are contraindicated for MRI due to potential hazards such as heating of the electrode that resides in the heart, damage to myocardium, elevation of pacing thresholds, unintended induction of ventricular tachycardia or ventricular fibrillation, pacing inhibition, permanent device malfunction, and distortion of the MRI scan.
The authors note that none of the components of the S-ICD system are on or in the heart, hence heating near or around the electrode cannot harm the myocardium. However, they say, heating near the S-ICD’s electrode and can may still cause serious patient discomfort.
In this single-centre prospective non-controlled study, 15 patients (12 males, mean age 53 years) were enrolled for MRI testing over a period of 18 months. They underwent a total of 22 randomised examinations, which included cardiac, brain, cervical, lumbar and knee scans. Keller et al comment that there was not a specific requirement for an MRI. The S-ICD is currently not certified for use with an MRI; therefore, the authors note, the Ethics committee of Homolka Hospital approved this clinical study.
For the scanning protocol, the S-ICD was programmed off to minimise the risk of inappropriate therapy and patients were monitored throughout the procedure with pulse oximetry and standard ECG to detect any arrhythmia. An external defibrillator was available. The S-ICD was evaluated prior and immediately after the scan to verify proper functioning.
Patients were also asked to report immediately any pain, torqueing movement, or heating sensation in the area of pocket or electrode. They were also questioned immediately following the MRI to assess any discomfort around the can or electrode.
Keller et al report that no anomalies were perceived via pulse oximetry or ECG during the scans for any of the patients. Most patients (11) did not experience sensation or pain from heating. Two patients reported intolerable heating.
Additionally, one patient who underwent a lumbar scan and reported heating had an ulcer on the surface of the skin over the can. The cause of this anomaly is not known; however, the authors note, it was healed after 10 days of the scan.
All the S-ICD systems were not affected after the scan. The researchers also report no changes in the battery voltage, ability to detect the QRS signal or stored diagnostic data. None of the patients reported any pulling or twisting of the can or pain from heating of the S-ICD electrode.
“While more data are required to support a claim of MRI-conditional, this study is the first to demonstrate the feasibility of exposing S-ICD patients to MRI using the scanning and monitor protocol described, with some precautionary measures,” the authors conclude.