Initial Experience with MR-Conditional ICD Technology

Christian Allan, MD and the EP staff at Parkridge Medical Center implanted the area’s first MR-conditional implantable cardioverter-defibrillator (ICD) on October 1, 2015. The Medtronic Evera MRI XT DR device, which was announced as FDA approved on September 14, 2015, is the first ICD system safe enough for use during magnetic resonance imaging (MRI) scans on any part of the body without positioning restrictions. 

Until now, patients with ICD systems have been contraindicated by the FDA from receiving MRI scans because of risks such as the device being moved or damaged by electromagnetic interference, lead damage caused by heating of the coils, and depletion of battery life. MRI scans are considered the gold standard in soft tissue imaging and are used regularly for the diagnosis of conditions such as stroke, cancer, and various bone and joint problems. MRI restrictions for those with ICDs have resulted in a critical unmet need as data have shown that within four years, more than one-third (36%) of patients with ICDs are likely to need an MRI.¹ Other sources estimate that there is a 50-75% probability that cardiac device patients will require an MRI during their lifetime.²

In the Evera MRI Clinical Trial, results showed that the Evera MRI ICD’s ability to detect and deliver therapy for irregular and other potentially lethal heart rhythms is not impaired by full-body 1.5 Tesla MRI scans.³ Specifically, MRI scans did not affect the functioning of ICDs in patients who experienced ventricular tachycardia/ventricular fibrillation post MRI.³ The MR-conditional ICD also offers a significant, 25% increase in battery longevity (11 years), compared to the average battery longevity of previous ICDs.^4-6 The advantages of freedom from MRI-related complications and battery longevity convinced Dr. Allan that this was the device his patient needed to resume her normal life.

When Dr. Allan first consulted with the patient, a 32-year-old woman, he quickly assessed that her risk of experiencing sudden cardiac death was high. The patient had been diagnosed with non-ischemic dilated cardiomyopathy four months earlier. Her ejection fraction was 15%, and she was diagnosed with NYHA Class III heart failure. The patient’s home medication regimen included carvedilol, lisinopril, and furosemide. Therapy with the LifeVest Wearable Defibrillator (ZOLL Medical Corporation) had also been ordered and fitted, but the patient’s compliance was questionable.

Since the patient was young and likely to need an MRI at some point during her life, she was an ideal candidate for an MR-conditional ICD. Further education of the patient about her high risk of sudden cardiac death was given by Dr. Allan. Though she was initially reluctant to undergo surgery, after consideration of her concerns as a single mother of two children, the patient consented to the procedure. For patients with a condition serious enough to require defibrillation therapy for protection against a sudden cardiac death event, it is often difficult to comprehend what living with a defibrillator entails. Additional information emphasizing the function and advantages of MR-conditional ICDs for the individual’s condition will need to be offered to hesitant patients. 

Since the procedure to implant MR-conditional ICDs is no different than for standard ICDs, additional physician and staff training was not required in this case. Pre-scan programming requirements necessitate that the device company representative or another health professional trained in SureScan technology be present during the MRI test procedure after the ICD is implanted. Pacing support is available during the MRI test procedure with available modes of DOO, AOO, or VOO. For patients who do not require pacing support, the defibrillator should be set to ODO. The representative will confirm atrial and ventricular thresholds do not exceed 2.00 V @ 0.4 ms. He or she will then confirm that SureScan is programmed to “on.” It is important to note that when SureScan is programmed to “on,” all device diagnostic measurements and collection are suspended and the ICD does not detect tachyarrythmias or deliver shock therapy. For this reason, an external defibrillator must be available during the MRI scan and proper patient monitoring must be provided.

Once the MRI test procedure is complete, the representative will reprogram the ICD to its original settings. There is a safety timeout feature that will revert the device to its original settings if for some reason the patient were to leave the MRI suite without a post-scan check/reprogramming.⁴ 

Patients who receive MR-conditional ICDs must still follow certain safety guidelines before they receive an MRI. There must be verification that the patient has a complete SureScan system, both the device and the leads. There must be confirmation that the patient does not have any lead extenders, broken leads, lead adaptors, or abandoned leads. The cardiologist/device representative must ensure that the pulse generator was implanted in the pectoral region and that it has been implanted for more than six weeks. Leads must be checked to ensure that they are electrically intact (pacing lead impedance between 200-3000 ohms, defibrillator lead between 20-200 ohms). If the patient requires asynchronous pacing during the scan, the representative must ensure the absence of diaphragmatic stimulation. 

MR-conditional pacemakers are now standard after recognition in the medical community of an unmet need, and Dr. Allan is confident that the same will become true of MR-conditional ICDs. It is important that those who already have health conditions serious enough to require an ICD are able to access more comprehensive technology such as MRI scans. Dr. Allan and the EP staff at Parkridge Medical Center are excited to have had the opportunity to participate in setting the industry standard using this new innovative medical technology. Numerous advances in the field of electrophysiology are coming at an astounding rate. It is indeed a great time to be working in the EP lab.

Disclosure: The author has no conflicts of interest to report regarding the content herein.   

References

1. Nazarian S, Reynolds M, Ryan M, et al. Estimating the likelihood of MRI in patients after ICD implantation: a 10-year prediction model. J Am Coll Cardiol. 2015;65(10_S).
2. EOCD (2010), Health at a Glance: Europe 2010, OECD Publishing.
3. Gold MR, Tosten S, Schwitter J, et al. Full-Body MRI Scanning in Patients with an Implantable Cardioverter-Defibrillator: Primary Results of a Randomized Study. J Am Coll Cardiol. 2015;65(24):2581-2588. 
4. Evera XT DR/VR Manual.
5. Thijssen J, Borleffs CJ, van Rees JB, et al. Implantable cardioverter-defibrillator longevity under clinical circumstances: an analysis according to device type, generation, and manufacturer. Heart Rhythm. 2012;9(4):513-519.
6. Shafat T, Baumfeld Y, Novack V, Konstantino Y, Amit G. Significant differences in the expected versus observed longevity of implantable cardioverter defibrillators (ICDs). Clin Res Cardiol. 2013;102(1):43-49.