New data show safety and efficacy of specifically designed implantable cardioverter defibrillators for MRI scans


Two studies presented at the late-breaking trial sessions of the Heart Rhythm Society 36th Annual Scientific Sessions demonstrated the safety and efficacy of two MRI-safe ICDs, which have been submitted for FDA approval.

Evera MRI ICD Clinical Study

The Evera MRI ICD Clinical study is the first-in-human, randomised, multinational study of an ICD system (Evera MRI SureScan ICD, Medtronic) specifically designed for full body MRI at 1.5T. The results of the study, presented by Michael Gold (Medical University of South Carolina, Charleston, USA), found that patients in the study did safely undergo full body MRI scans with the Evera MRI ICD with no adverse effect on the electrical performance of the ICD or on the treatment of ventricular arrhythmias.

Gold told delegates at the session: “There were no complications associated with MRI in this cohort. The Evera MRI ICD system showed no difference in pacing and sensing performance between the MRI and control group and there was no impact on ventricular fibrillation (VF) detection observed post-MRI exposure.”

Gold said that one of the strongest indications for an MRI is following a stroke or a transient ischaemic attack, he commented: “There is about a 50-fold less use of MRI in those patients who have an ICD compared to those patients who do not have an ICD. For those patients with back pain, another very common use of MRI for evaluation, there is about a 30-fold lower use of MRI in this population, while X-ray and CT and other imaging modalities are used as alternatives.”

The study design consisted of 275 patients enrolled at 42 centres in 13 countries within North and South America, Europe, Asia and the Middle East.

Patients received an Evera MRI single or dual chamber ICD, with more than 50% having a single chamber device.

“One important aspect of the study is that we had no restriction on pacing dependency, no restriction on hardware of amplitude, and no restriction on where the MRI can be performed on the body. So it broadly applies to virtually all patients with new ICDs being implanted,” said Gold.

He explained: “All patients were implanted with an MRI-ICD. They were randomised to either undergo the MRI scan, which is performed at one month, or in a control group. One week following the post-MRI/waiting period they were assessed and then one-month post-MRI is when the data were collected for sensing and capture.”

After fall out or rejection from the study, 156 patients remained in the MRI group. Of these, 147 were included in the endpoint. Nine were not included because they missed a post-MRI follow-up visit. There were 84 patients in the control group.

The study met the safety and efficacy endpoints. Gold said: “Looking at the primary safety endpoint, 100% of patients [147] who received an MRI achieved that, so there were no complications associated in this group with the MRI scan. The Evera MRI ICD system showed no difference in pacing and sensing performance between the MRI and the control group.”

One patient met the threshold of having a greater than 0.5V increase in ventricular pacing capture threshold (VPCT) in the control group. “No patient in the MRI group had a significant increase in ventricular pacing capture threshold. Obviously by non-inferiority this was highly statistically significant.”

Both efficacy endpoints were also met with minimal differences in the proportion of MRI and control patients who demonstrated a less than or equal to 0.5V decrease in VPCT, or a less than or equal to 50% decrease in R-wave amplitude. A total of 34 VT/VF episodes occurred in 24 patients (20 induced, 14 spontaneous) post-MRI, with no impact to sensing, detection or treatment observed. In addition, no impact on VF detection was observed post-MRI exposure.

Gold told delegates: “Most importantly we wanted to evaluate VT/VF detection post-MRI since ICDs are implanted primarily to detect and terminate ventricular tachyarrhythmias. There were 34 episodes in 24 patients. All episodes were appropriately detected and treated by the device.”

He summarised: “The Evera MRI trial is the first randomised study of an ICD system designed for full body MRI at 1.5T with no restrictions on R-wave amplitude or heart rhythm. All three co-primary endpoints were met. These data support the system’s safety and efficacy. We are very pleased and reassured to show in this first randomised study of a specific device developed and designed for MRI use that it performed very well and met the safety and efficacy endpoints.”

Results of this study have been published in the Journal of the American College of Cardiology and have been submitted to the FDA for device approval.

The Evera MRI ICD received the CE Mark in March 2014.

ProMRI ICD Clinical Study

Early performance results of the the ProMRI Clinical Study – Phase C were also presented at HRS 2015. Data showed that patients who were implanted, in the study, with the Iforia DX ICD and the Iforia DR-T ICD (Biotronik) were safe to undergo cardiac or thoracic spine MRI in 1.5T scanners with no exclusion zone, without affecting the efficacy of their device.

Lead investigator and presenter of the study, Khaled Awad (University of Alabama at Birmingham, Birmingham, USA) reported: “There have been no adverse outcomes. We did not detect any significant changes to pacing or sensing parameters. And most importantly, there was no impact on the ICDs’ main function of detecting and treating ventricular arrhythmias. This trial demonstrates the clinical safety and efficacy of the Iforia for MRI ICD system as configured in this trial.”

Studies have demonstrated that MRI-conditional pacemakers can be safe and effective, but the presence of an ICD usually contraindicates MRI, Awad explained. “[Concerns] mainly stem from the possibility of interactions between the ICD system and electromagnetic fields generated by the MRI machine. The chances of those interactions and adverse outcomes actually increases with ICDs compared to pacemakers.”

However, results of the MagnaSafe registry, presented at the American Heart Association Scientific Sessions in November 2014 and reported in Cardiac Rhythm News, indicated that patients with standard ICDs can undergo non-thoracic MRI scans at 1.5T, with no significant clinical risks, when the device is appropriately programmed.

In the ProMRI ICD Clinical Study, 170 patients were enrolled at 40 US centres, 61.7% were implanted with the Iforia DX ICD and the remainder with the Iforia DR-T ICD. Patients were eligible for enrolment five weeks after ICD implant, providing their lead parameters remained stable.

The device was tested before and after the MRI. The scan was a study-defined non-diagnostic cardiac or thoracic spine MRI performed at least one week after enrolment. ICDs were placed into MRI mode to disable the detection and therapy of ventricular tachyarrhythmias before the scan, and restored to original parameters afterwards. Cardiac rhythm was monitored during the MRI, and interrogation was performed before, immediately after, and one month following the scan.

Primary endpoints were freedom from serious adverse device effects, freedom from ventricular pacing threshold increase, and freedom from decrease in ventricular sensing at one-month post-MRI compared to pre-MRI.

Of the 170 patients enrolled in the study, 154 were analysed, 74.3% had a thoracic spine MRI and 25.7% a cardiac MRI. In all, 150 patients completed the one-month follow-up and 92 the three-month follow-up.

Most of the 43 adverse events reported by the investigators were not serious and all were judged to be non-device or procedure related by a data monitoring committee. No serious adverse device effects occurred. Freedom from the primary endpoints was met in all subjects except one, in whom reduced R-wave amplitude was detected one-month post-MRI. Awad said: “Interestingly, that patient did not undergo the MRI scan because of claustrophobia, so that change in the R-wave amplitude cannot be attributed to the MRI.

“Most patients had almost no change in the capture threshold value and no patients experienced an increase by more than 0.5V at one-month post MRI, resulting in 100% freedom from the occurrence of that endpoint. The observed change in the capture threshold was actually very miniscule.”

Post-MRI, 403 episodes of ventricular arrhythmias were identified in 39 patients, all of which were appropriately detected and treated.

Comparing with findings from the Evera MRI ICD system trial, Awad said: “There are similarities and certain differences but the overall results are similar. I think the community is privileged to have two reports with similar results. I think they just confirm each other.”

Biotronik announced that the completed study has been submitted to the FDA to support approval of the Iforia ProMRI ICD system.

The Iforia ProMRI ICD system was recently given CE Mark approval for MR conditional full body and 3T scans.

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