April 8th, 2014

Assessing the MRI Safety of New Pacemakers and ICDs

An estimated 50% to 75% of patients with a pacemaker or implantable cardioverter-defibrillator (ICD) have a clinical indication for MRI during the device’s lifetime. Device safety during MRI scanning is therefore an important issue to explore.

The Evidence Thus Far

Early concerns about device dislodgement and overheating during MRI have abated, thanks to evidence that the maximal force and torque acting on modern pacemakers/ICDs at 1.5T are unlikely to dislodge leads anchored in the myocardium and that small measured rises in temperature pose minimal risk for thermal injury. Several reported adverse electrical events — including diminished battery voltage, increased capture threshold, decreased pacing-capture threshold on repetitive MRI, decreased sensing amplitude and pace impedances, power-on-reset, and oversensing of electromagnetic interference — do represent real potential risks. However, many of the electrical changes detected on device interrogation immediately after MRI scanning have proven to be transient and clinically inconsequential. In general, ICDs’ tachycardia-detection capabilities and therapy can be temporarily suspended by placing a magnet over the device to change the built-in reed-switch function; therefore, unpredictable reed-switch behavior in an MRI environment could cause inappropriate shocks. However, a large clinical trial has failed to reveal any adverse events from the inappropriate shock during 1.5T MRI.

Ongoing Efforts to Ensure Safety

Although no device-related major adverse clinical events have been documented during MRI scanning, device makers have been working on features to further improve safety. We now have MRI conditional devices, which are those shown to pose no known hazards in a specified MRI environment under specified conditions of use. In 2011, Medtronic released an MRI conditional pacing system, Revo MRI SureScan, the first FDA-approved pacemaker system available in the U.S.; approval of the second-generation Advisa MRI SureScan followed in 2013.

Clinical trials have tested the safety and efficacy of the Revo and Advisa MRI pacemaker generators with CapSureFix MRI conditional leads, in a dual-chamber pacemaker design. The evidence shows no reports of MRI-related complications; no disturbances of pacemaker function during or after MRI; no ventricular arrhythmia inductions; and minimal differences in pre- and post-MRI pacing threshold, impedance, and sensing (similar to results in a control [no-MRI] group). CapSureFix MRI conditional leads have an encouraging safety and efficacy profile, with no lead displacement and no cases of high pacing thresholds or inadequate sensing. Compared with conventional leads, the CapSureFix MRI leads show no clinically relevant difference in pacing threshold, sensing, or impedance.

MRI conditional pacemaker design addresses the theoretical concerns of MRI and device interaction. The limited amount of ferromagnetic material minimizes the magnetic-field interaction and, therefore, reduces the risk for device dislocation. The reed switch is replaced by a Hall sensor and, consequently, mitigates program switching from unpredictable reed-switch behavior in an MRI environment. Internal circuits have also been improved to prevent internal power-supply interruption and to reduce the potential for cardiac stimulation, thereby diminishing the risk for electrical reset and tachyarrhythmia. To address concerns about thermal injury, leads are being modified to reduce RF lead tip heating from transmitted RF power.

Making MRI Conditional Systems Practical

Implanting an MRI conditional pacing system has been made more practical by giving the pulse generator a size of 12.7 cm3 and a weight of 21.5 g (Revo MRI) or 22 g (Advisa MRI), similar to the average size and weight of a conventional pulse generator. CapSureFix MRI conditional leads have greater diameter and stiffness, but there is no difference in procedural and fluoroscopy time, and the implant success rate for an MRI conditional pacing system is 100%. Ideally, MRI conditional devices should be implanted in patients with an anticipated future indication for MRI. However, a patient-selection strategy needs to be developed, in part because an MRI conditional device is $1000 to $3000 more expensive than a standard device.

What About Image Quality?

Susceptibility artifacts from MRI conditional devices continue to affect image quality on cardiac magnetic resonance (CMR). Most image distortions and artifacts are within 10 cm to 15 cm around the device generator — and are pronounced in CMR, especially on steady-state and inversion-recovery sequences. The artifacts are substantially greater for ICD than for pacemaker generators and for left-sided than for right-sided systems. Using gradient-echo and wide-band sequences helps to improve quality on cine and viability images, respectively. With these imaging-sequence modifications, sufficient image quality can be obtained in most cases.

Translating What We Know Into Practice

MRI conditional devices are considered safe in specified MRI environments and conditions of use when standard safety protocols are followed. However, experience with conditional devices is still limited in CMR and in 3T MRI, and we have no postmarketing data on long-term adverse events. Given the current evidence, what would you do if a patient with a conventional device is scheduled for CMR? Should patients with conventional devices switch to an MRI conditional device? Would it be cost-effective to implant an MRI conditional device in all patients with appropriate clinical indications?

Please share your answers to these questions here.

5 Responses to “Assessing the MRI Safety of New Pacemakers and ICDs”

  1. Shaumik Adhya, MBBS BSc MRCP CCDS says:

    We’ve had MRI conditional devices for some years in the UK. The hospital gets a fixed tariff for each procedure, and the tariff only just covers the cost of an MRI device. I have yet to formulate a formal strategy for who gets an MRI safe device or not. I tend to use them in younger patients – though perhaps they are less likely to need an MRI than the older patients.

    I find the handling of the CapSureFix leads different, with it taking longer for torque to transmit to the helix. Some of my patients initially experienced pericarditic pain after the atrial lead, so I became more careful with deployment of the atrial helix.
    Medtronic have belatedly discovered that their existing 5076 leads are MRI conditional and are now marketing them as such in the UK, so I’ve gone back to using these.
    I routinely use these leads for patients, no matter which system they receive as that means that at generator change they can have an MRI conditional system (I’m assuming they will be cheaper by then).

  2. Vincenzo Pazzano, MD says:

    I have absolutely no conflict of interests, but I wonder why you mention only MRI compatibile systems manufactured by Medtronic, when Boston Scientific, St Jude Medical and Biotronik have developed such products as well, the latter being by now the only productor of MRI-conditional ICDs.
    I think that a very large number of patients could benefit from a MRI compatibile device, both older patients with conorbidities and consequent indication for MRI scans and young patients with long life expectancy and subsequent high probability to develop a clinical condition wich will determine an indication for a MRI scan

  3. Shaumik Adhya, MBBS BSc MRCP CCDS says:

    Simply that I have been using Medtronic MRI systems for 4 years and have more experience with them than the other manufacturers. Sorin also have an MRI conditional system but again I have little experience with it yet.

  4. Vincenzo Pazzano, MD says:

    Thank you for your reply, my comment was mainly directed to the original post.
    I have to correct a statement of my previous post, as Medtronic as well has recently obtained a certification of MRI safety for ICDs (Evera MRI, announced April 9th, http://newsroom.medtronic.com/phoenix.zhtml?c=251324&p=irol-newsArticle&ID=1917142&highlight=) in Europe (not yet in the US). This is the first ICD to be certified safe for a full body scan (in the case of the ICDs produced by Biotronik, by now, the thoracic area is excluded), and yesterday we have been the first in our country to implant one of these devices.

  5. Promporn Suksaranjit, M.D. says:

    Thank you for your insightful comments and updates. I have no conflict of interest. My primary focus in the original post was only the FDA approved devices that are available in US market. MRI conditional pacemakers from Biotronik (ProMRI)/St.Jude(Accent MRI)and MRI conditional ICDs from Biotronik (Lumax 740 seires)/Medtronic (Evera MRI) got CE approval, however, those are not FDA approved and available in US market yet. The European experience is more on these devices. Thank you for sharing an invaluable expertise and perspective. In the future, it would also be interesting to see if new device design could help address the image quality issue for cardiac MRI.