Medtronic Revo Pacemaker (Designed to Permit MRI Scanning)

You see, up until the Revo, pacemakers were considered a very potent contraindication to MRI exams. Interference from the MRI acting on the pacemaker could turn the pacer off, turn it into a fairly benign ‘asynchronous mode’, start pacing your heart as if it were a hummingbird’s at 100′s of beats per minute, burn cardiac muscle, or drain the pacer’s battery precipitating an earlier-than-planned replacement.

Some pacemaker patients could still get MRI exams, but you had to be the right kind of pacemaker patient, with the right kind of pacing device, needing the right kind of MRI on the right kind of scanner. Even then, you ought to have had the cardiologist and a code team (to resuscitate you if the MRI and your pacer decided to not cooperate), plus someone to de-program and re-program your pacer. Even with those protections, some insurance companies simply forbid coverage of MRI exams for any pacemaker patient.

Along comes the Medtronic Revo pacemaker. This is the first FDA-approved biostimulation implant that has been specifically designed, from the ground up, to permit MR examinations (though it won’t be the last). It is not, however, carte blanche for MRI examinations. There are important limitations, or conditions, for its safe use.

There are three designations, each with very specific critera, that an object or medical device can obtain to describe its relative safety in the MR environment, ‘MR Safe’, ‘MR Conditional’, and ‘MR Unsafe’. Given the fact that I just described the Revo as having important limitations, or conditions for safe use, which of these three designations do you think the Revo has earned?

If an object receives the ‘MR Safe’ designation, it means that that object would be safe under any allowable MRI conditions. Field strength? Doesn’t matter. Magnetic spatial gradient? Who cares. Time-varying gradient? No worries, mate. RF deposition? Don’t worry your pretty little old head. In short, to receive the ‘MR Safe’ designation there can not be any restrictions on its use.

So here we are, with a pacemaker that isn’t ‘MR Safe’, but is being touted in nearly every medical media (or mass media with a health reporter) as the “MRI Safe pacemaker”.

[We'll ignore, for this entry, the fact that a company has already copyrighted the phrase "MRI Safe", as well as the fact that this company uses the copyrighted name to describe products that aren't classified as 'MR Safe'.]

For the lay person, my hair-splitting must seem awfully pedantic. The problem is that the technologist who will administer a patient’s MRI exam gets the bulk of the information about the patient’s medical history from the patient, himself. If the patient doesn’t remember the brand-name of the pacemaker (and so many of them seem to forget — or at least fail to disclose — that they even have the device, I think remembering the model and manufacturer is very unlikely), they’re probably likely to remember that this particular one was “MRI safe”. Now the technologist, charged with vetting the patient for MRI safety, is being given misleading information about the safety of scanning that patient.

So, my call to healthcare media and reporters is to please… PLEASE stop calling the Revo the “MRI Safe” pacemaker. Call it what it is, the first pacer designed to allow MRI scanning, or the first MR Conditional pacemaker, or even Medtronic’s towering achievement (which it is).

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Example of a Pacemaker Pulse-Generator Which Could Present Dangerous Contraindications For MRI Exams

The review has been requested by Robert Russo, MD, with Scripps Research Institute. A copy of Dr. Russo’s request can be viewed here.

The public comment period is open through July 28, 2010, and I strongly encourage anyone with questions or concerns about the safety of MR imaging for patients with implanted cardiac devices (Dr. Russo correctly points out that CMS’ restriction fails to speak directly to implanted cardio-defibrillators, or ICD’s) to offer their comments to CMS.

The full explanation of the current restrictions on MR imaging of pacemaker patients (also aneurysm clip patients, and pregnant patients), as well as the instructions for reviewing other public comments or submitting your own, can be found here.

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The National Council on Aging just released a study which details these alarming numbers. The matter-of-fact language of their release did nothing to diminish my welling fear as the study went on to detail chronic failures in our healthcare system to educate, alert, and prevent the dangers inherent in MR imaging of medical implant patients. Here are a few of the particulars:

• Medical implant patients over age 65 have between a 50% and 75% chance of requiring imaging during the useful life of their implant.
• While 90% of physicians knew of MRI risks for some pacemakers, over half of doctors say that they aren’t informed about imaging limitations when a patient is implanted.
• Nearly a third of patients who receive medical implants are not informed of MRI restrictions.
• After exposed to the MRI risks to their implant, nearly 20% of these device patients experience some sort of problem or malfunction with their implant.

Example of a Pacemaker Pulse-Generator Which Could Present Dangerous Contraindications For MRI Exams

The near universal opinion (98%) of healthcare providers is that they require additional information and training on these MRI safety risks.

Let’s hope that regulatory (FDA and States) and accreditation (JCAHO, ACR, and IC) bodies for MR imaging look at ways that they can take a more active role in promoting education and protecting these patients.

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As far as the MRI machine is concerned, there are two different types of metal, ferromagnetic and non-ferromagnetic. You may remember back to high school chemistry and the periodic table of elements where many of us learned (and then promptly forgot) that Fe is the symbol for iron.

Fe - Iron from the Periodic Table

“Fe”, the symbol, is derived from ferrum, the Latin word for iron. Ferromagnetic does not mean that a metal contains iron, but rather that the material has magnetic properties as iron can.

Ferromagnetic metals are iron, cobalt and nickel. These raw ingredients are common in many, many things made from metal, including (likely) the steel grommets in your shoes, to the zipper in your pants, to components in your wristwatch. Another common area to find these metals is in batteries, such as those found in your hearing aid, cell phone and iPod. There are a few non-metal ferromagnetic materials, but these are not very common.

Alright, alright, already… enough chemistry. What does this mean?

When exposed to magnetic fields, ferromagnetic materials become magnets themselves. You can prove this yourself with a fridge-door magnet and a few paper clips. You’ll probably find that paper clips right out of the box aren’t capable of magnetically ‘sticking’ to one another. If you stick one to a chunky fridge-door magnet, however, that paper clip is now magnetized and will likely be able to magnetically ‘stick’ to another paper clip. The length of the magnetic chain of paper clips you can create is a function of how strong the fridge-door magnet is and the magnetic properties of the paper clip steel.

Now, the exact same thing happens with ferromagnetic metals approaching the MRI, but a crucial difference is the distance at which the materials get attracted. With your fridge-door magnet test, the paper clip needs to be touching (or very nearly so) the magnet before the attractive effects are felt. MRI’s, by virtue of the fact that they’re both 1,000′s of time stronger and larger than your fridge-door magnet, can exert profound attractive force at a good distance away from the magnet.

The size and strength of MRI magnets is so great that people have been trapped, injured, and even killed by the force of ferromagnetic objects attracted to the MRI. From concealed roller-skate tennis shoes, to steel-reinforced furniture, to conventional hospital wheelchairs and gurneys, to steel oxygen cylinders, all of these normally harmless (outside the MRI suite) items become life-threatening when subjected to the enormous pull of the MRI’s magnet.

Not all metals are ferromagnetic. In fact, in an MRI suite a concerted effort is usually made to rid the area of ferromagnetic materials and use non-ferromagnetic replacements whenever possible. Non-ferromagnetic metals include aluminum, titanium, brass, copper, and many others. These (and other) non-ferromagnetic metals can present other problems and hazards during MRI imaging, but that’s a topic for another day.

It is almost impossible to determine whether a material is ferromagnetic just by looking at it. In fact, even sometimes when you know what an object is made of, it still isn’t enough to know whether it’s ferromagnetic or not. Stainless steel, is one of these examples.

Stainless steel is not a metal, but rather a family of recipes for metal. Some stainless steel ‘recipes’ (alloys) call for ingredients with ferromagnetic properties. Others which include ferromagnetic ingredients are specially formulated to change the structure of magnetic materials into non-magnetic versions of the material. These special ‘de-magnetized’ stainless steels can become ferromagnetic if the steel is manipulated (shaped, bent, heated, or stressed), so even magnetically ‘safe’ stainless steels can become ‘unsafe’ under certain circumstances (a change that isn’t observable to the eye).

It is remarkably difficult to distinguish magnetically ‘safe’ metals from magnetically ‘unsafe’ metals, either by simply looking at them or, sometimes, even if you know what the metal is. As a result, MRI facilities must assume all metals to be magnetically unsafe unless and until they’ve been verified to be non-magnetic.

So, how do MRI facilities distinguish magnet-unsafe metals? They can use magnets, which shouldn’t be used on patients or sensitive equipment, limiting their applicability. The safer option (and arguably more effective, to boot) is to use a ferromagnetic detector, at least on patients and sensitive equipment.

Ferromagnetic detection instruments, such as the Mednovus products, should be used to help identify magnetically-unsafe materials. This is the standard established by the American College of Radiology, the VA’s MRI Design Guide, and even recommended by the Joint Commission in Sentinel Event Alert #38.

As a patient, it is vital to take seriously the admonitions against wearing or carrying metal into the MRI suite. If you have shrapnel, penetrating metal injuries (particularly in the eye), or any surgeries, implants or prosthetics, it’s critical to have the full information on each to share with your MRI provider. Metal inside the body may not fly across the MRI room like a loose oxygen cylinder (don’t believe what you see on House), but the twisting an pulling that the magnet will exert on an internal ferromagnetic object can be just as dangerous. Active implanted devices, such as pacemakers or nerve stimulators, present particular problems because of both the magnetic attraction and potential interference with the normal function of the device.

Patients should also actively seek out MRI providers that conform with the contemporary safety recommendations, including the use of ferromagnetic detection. You can even contact Mednovus when you want to find providers near you who have this technology available.

Providers of MRI services should make sure that the pre-screening and safety services they provide are in accord with the contemporary best practices, including the use of ferromagnetic detection. With available ferromagnetic detection products equal in cost to only a few hours worth of technical revenue, there’s no financial rationale for not providing this valuable safety benefit to patients and staff. Plus, when weighed against the costs of ferromagnetic object accidents, these instruments of safety are clearly effective risk-management investments.

In all cases, metal brought to the MRI suite (either inside or outside the body of the visitor) should be scrutinized by a trained MRI staff person. This investigation should be aided through the use of ferromagnetic detectors, both to help characterize the hazards of any particular object and to help find ferromagnetic materials that weren’t caught in the prior screening process.

First, before we jump into the issue of where in the sequence ferromagnetic detection is best deployed, it’s important to break pre-MRI screening into its two constituent parts: clinical screening and physical screening.

Clinical Screening:

Before being brought to the MRI magnet, everyone (and this means patients, visitors and staff) needs to be screened for contraindications. Most often we think of pacemakers, but other contraindications include nerve stimulators, insulin pumps, prosthetics, halo vests, and a number of other objects. The screening is typically accomplished through the use of forms to help the subject identify any clinical risks for the MRI provider. The screening form is then to be reviewed between the patient and the MRI Technologist.

Once clinically cleared of contraindications for the MRI exam, then the subject should proceed to the next step…

Physical Screening:

Contrasted with the widespread uniformity of the clinical screening, the physical screening takes very different forms at different provider. However, all have the same objective, namely, to remove ferromagnetic materials from the subject and keep them away from the MRI scanner. Even small quantities of ferromagnetic material can cause artifacts in the MRI scan when near the imaging volume. Small ferromagnetic items, such as bobby pins and nail clippers, have caused serious harm when propelled by the magnetic force of an MRI magnet. And obviously, large items such as oxygen cylinders and floor polishers can have catastrophic consequences if brought to the MRI room.

Some MRI providers have outpatients simply empty their pockets, others provide gowns or scrubs for MR patients to change into, and all should use ferromagnetic screening to help verify patients’ compliance with screening instructions.

When performed in the above order, providers avoid gowning patients only to find out that the patient can’t receive the MR exam. Additionally, when clinical screening is accurately completed first, the Technologist has done everything within his or her human capabilities to mitigate the contraindication risks associated with exposure to magnetic fields. Although it is impossible to completely eliminate the chances of accidents, by following the recommended industry-standard procedures of  conscientious clinical and physical screenings followed by properly-performed ferromagnetic detection, the safety of your MRI center has been significantly enhanced.

Some of the most sensitive ferromagnetic detectors currently available use passive magnetic fields to improve sensitivity. These GS (Greater Sensitivity) detectors use a localized DC field (i.e. stronger versions of a similar type of the permanent magnet that holds your notes on your refrigerator door). While the magnetic field strength very close to the GS detector can exceed the 5-gauss threshold, that limit is for persons who haven’t been successfully cleared for MRI contraindications (a step which was just completed if the pre-MRI screening was conducted in the proper order).

While patients and caregivers should be concerned about exposing unscreened persons to the extraordinarily powerful magnetic fields around the MRI, momentary exposure of post-screened persons to the passive “fridge-door” magnetic fields of a GS ferromagnetic detector is very, very small on the relative risk-o-meter. And this minute risk comes with an enormous potential safety upside…

No ferromagnetic detection system on the market from any manufacturer is intended (or approved) for finding objects internal to the body of the patient. However as an incidental finding, ferromagnetic detectors have alarmed on the ferromagnetic content of implants (including pacemakers) that were disavowed by the patient in the clinical screening process. While ferromagnetic detection should never be used in lieu of conscientious clinical screening, they have helped to identify critical contraindications that may have otherwise jeopardized the safety of the MR patient — had they not been found by the ferromagnetic detector.

And the relative risk of being exposed to 5, 10 or even 100 gauss as a part of a physical pre-screen (particularly when already cleared of clinical contraindications) is microscopic, when compared to either the risk of the planned exposure to 15,000 / 30,000 gauss, or the potential benefit of identifying a contraindication that the patient themselves didn’t communicate.

The take-home messages from this are these:

• MRI providers should provide as thorough and comprehensive clinical screening as humanly possible for everyone approaching the MRI.
• Once the clinical screening is complete, the provider’s standard physical screening (emptying pockets, changing into scrubs, etc…) should be conducted as appropriate to the MR patient / visitor.
• And following the clinical and physical screenings, patient / visitor compliance should be verified with a ferromagnetic detector.
• If these industry-standard procedures are correctly followed, there should remain only minute (accepted) risks associated with exposure to any magnetic field, either the enormous field of the MR or the comparatively tiny field present in GS detectors.

Clearly, providers should feel free to use whatever ferromagnetic detection they wish – from their choice of manufacturer – in order to conform with ACR, VA and Joint Commission guidance, whether it be an instrument which relies on only the trace-magnetism of the Earth’s own magnetic field, or one in which the detection sensitivity has been enhanced through the use of a locally-provided, passive DC magnetic field as found in GS ferromagnetic detectors.

My recommendation is always to use a detector with the greatest possible sensitivity. Because, while they are wonderful instruments that can make a substantial improvement in a provider’s MR safety protocols, ferromagnetic detectors are dumb. They can’t differentiate ‘good’ ferromagnetic material from ‘bad’. These sorts of value judgments should be made by a trained MR technologist and not by a machine.

In my opinion, ferromagnetic detectors should be used to help find every piece of ferromagnetic material that they can, so that the Technologist knows what is about to enter their magnet room (and can make re-screening decisions as appropriate). The greater the sensitivity of the detector, the more informed those Technologist decisions will be.

Pass-through ferromagnetic detection systems, such as the newly released Mednovus Sentinel® GS 2.0 portals, also have user-adjustable sensitivity settings, so that the system can be ‘dialed back’ as needed for special circumstances, further supporting the concept of having the instrument with the greatest sensitivity, and tuning it to meet your specific needs.

As evidenced by repeated, and increasing MRI projectile accidents, there is enormous room for improvement from the prior standards. Effective pre-screening of MRI patients, including the use of ferromagnetic detection at the appropriate point, can make an significant difference in the safety of the MR exam. Providers should turn to the current best practice guidance and compare their pre-MRI screening processes, making any indicated changes to help assure the safety of their patients, visitors, and staff.