MRI didn't hurt me

I needed an MRI for my lower back -- a lumbar scan -- and got it. You need to be persistent, you need to know your facts, and you may need to be prepared to feel some pulse changes without freaking out. But it can be done.

I managed to do all three. The pacemaker was undamaged, according to pre- and post-MRI pacemaker diagnostics. I am not recommending this procedure, just saying I had one and suffered no ill effects. I'll get to that in a couple of paragraphs, but some background first. If you just want the data, scroll down to RESULTS.

BACKGROUND. I am not a doctor, an employee or contractor for anyone, and I do not own stock in Guidant, Medtronic or St. Jude. I made a personal medical decision based on things I've learned over a lifetime as well as the months since I received my pacemaker. I do not say you should have an MRI. But I asked my cardiologist if he would support me in getting the test, and he said, "I do it all the time." All I had to do was overcome the inertia of my spine center and medical center, and coordinate them with my cardiologist.

I'd had MRIs before getting my pacemaker about six months ago. In the last four months, though, I've had an unrelated medical problem and an intensification of chronic lower back pain. Those required X-rays, CT scans, ultrasounds and video cameras down my throat. Maybe if the first digestive system doctor had pushed for that MRI I could have avoided all that radiation, discomfort, time and expense.

Most doctors don't want to do MRIs on people with pacemakers. I consider that unfair. Why? Because while rumors persist that pacemakers cannot deal with magnetic fields, experts whom I've spoken with, and published documents I've researched indicate nothing of the sort. Conduct a search of medical literature of the past 15 years, and you'll find no factual, documented interactions between pacemakers and MRIs that resulted in adverse medical results -- that is, anything that harmed or killed a pacemaker wearer. I'm not talking about rumor or urban myth or medical professionals sharing a story they heard somewhere else.

Still, some experts say there is a risk or don't believe there's incontrivertible proof that they're safe. And the manufacturers are non-commital: They give instructions on how to safely get an MRI, but not say it's safe when you follow their instructions.

Pacemakers are engineered, programmed and tested to perform in extraordinarily challenging environments. They have to be, in order for them to pass FDA muster. These standards are tougher than those for the Space Shuttle, for a space suit, for a nuclear weapon's circuitry. They have built-in redundancy, they're hermetically sealed against leaks and pressure both in and out, and the circuitry is designed to withstand various kinds of radiation: X-rays, radio, cell phone, some level of electric shock, and -- brace yourselves, critics -- magnetic fields. Even huge ones. Rotating, shifting, pulsing ones. As in MRIs. All pacemakers still implanted in living people are about the same as mine, as far as that goes. And mine went inside.

Our leads also help protect us. As do the connections through which the leads pass to the pacemaker circuits. The connections contain shielding and electronic/electrical filters.

It all adds up. Nearby lightning, arc welding, radios, cell phones, motors, lights, car alternators and spark systems, and airport scanners can't get at our pacemakers. But supercooled, superconducting magnets? They don't seem to do anything until the scan starts.

As you probably know, doctors are quite comfortable giving you CTs and X-rays. I've had "electric scalpel" surgery in my bile ducts performed through my throat. No problem.

RESULTS

Device: The St. Jude Model 5816 dual-lead pacemaker and leads underwent diagnostics two days before and one day after the MRI. Important: The magnet response was set to off. The device was not affected by the MRI, but during the actual scanning periods it switched as programmed when it detected waveform changes through the leads. It reverted to normal programming as soon as the brief preliminary setup scans and the main, two- to four-minute scans ended. No settings were changed, heart conduction was unaffected, and lead impedance was unchanged. I could not feel any motion or heat in the device during the scans or when being moved into or out of the magnet.

My medical support team and I have reviewed the pacemaker tests: Atrial and ventricular capture tests, sense tests, and lead impedance were unchanged from before. Pulse current and amplitude are unchanged. Pulse amplitude, width and sensitivity were unchanged. No resets or programming faults were recorded. It all means that the MRI made no changes to my heart or my pacemaker and its leads. While undergoing the scans, the pacemaker underwent preprogrammed change, and I could feel it.

Patient, settings: The patient (yours truly) received a normal MRI for his lower back pain. Only the MRI tech attended. No cardiac monitoring was connected. The MRI tech was at first unwilling to conduct the study without the doctor's presence, but proceeded after checking reference publications.

Because of heart block and an intrinsic base heart rate below 50, Mode is set to DDDR at 70 bpm, and the Automatic Mode Switch is set to DDIR and 85 bpm. As designed, this setting was invoked whenever the MRI affected the atrial sensing circuitry. This was at the rate of about 85 bpm. The result was that during scan operation, I sometimes had ventricular but not atrial pacing -- basically my non-paced life before installation. I could feel when the atrial pulses were absent. No settings were affected, and no changes were made afterwards. Seven "high atrial rate episodes" in my heart were logged and four were charted by the pacemaker, but Automatic Mode Switch occurred each time the MRI turned on. (The pacemaker is programmed to save the four most recent "episodes," so three were lost.)

INSIDE THE MRI TUBE

I underwent a routine lumbar MRI study one day before this writing. I was inside the magnet tube about 20 minutes. The study consisted of several short pulses to set up, followed by three scans varying between two and four minutes. Some processing and prep time was involved between and after the scans, accounting for the total time between being rolled into and out of the MRI machine. Apparently, the three major scans and the four brief setup scans all affected the pacemaker's atrial sensing circuitry, causing it to switch as programmed from DDDR to DDIR mode.

Because I'd had MRIs before my pacing days, I knew what to expect in normal circumstances. The tube is tight for a tall, 225-lb. guy; many people can't stand the claustrophobia, which was a bit unnerving for me every time I've had an MRI.

During the scans, which are noisy and can be felt vibrating the machine, I was able to sense my heart beating beneath my sternum, much as I had before receiving a pacemaker, but quite a bit more often. The sensations went away when the scans ended. They resulted from temporary mode shift, which is programmed into the pacemaker. Before receiving the pacemaker, my cardiologist showed me that when I was feeling a certain thumping beat, the atrium was not pumping blood into the ventricle. That was my heart block not driving the atrium. That also is sort of what DDIR mode allows. I was told after that the mode switch and rate increase are set because, often when a patient's atrial sensing is erratic, the change is theraputic.

I did not feel any motion of my pacemaker or leads, nor did I expect to, not only because they've been stitched and screwed into my body: They are not ferrous, and are unmoved by magnets. I sensed no heating or burning, which if present could be caused by induction. If the lead tips were to have been so heated (as theorized in a St. Jude white paper I have), blood circulating over and through the heart wall tissues likely would have absorbed and thus prevented overheating. The Magnet Response setting, which allows the patient to send data over the phone or to record events, was turned off. I don't know what strange effects I would have felt if it had been set to Battery Test, for example, which changes your pulse rate to tell the tech/doctor your battery's life when the diagnostic computer and "wand" aren't available.

CT scans aren't as good as MRIs for doing bone and other studies. I've had three or four CTs for abdominal pain since Christmas, and an MRI might have provided better diagnostic value; I don't know. I did a lot of research on MRIs and pacemakers, and could only find rumors and "friend of a friend's cousin" reports of problems. One case of an MRI causing an actual problem was documented by Medtronic 17 years ago, but that's Model Ts compared to Mercedeses now. I also got some documentation from St. Jude's in Sylmar, Calif., that is aimed at surgeons and pacemaker techs. I also include a life of newspaper and magazine reporting and research; learning enough to be credentialed to teach high school health and science; a fascination with doodads and science magazines. I consider myself skeptical

These little titanium-encased puppies are designed to keep us alive under adverse circumstances, and that includes any normal job (welding too), any normal hobby (running an outboard motor or a radar?), anti-theft devices at store exits, and body scanners at airports and courts. They even tolerate external defibrillators. The people who design, build, sell and implant pacemakers take pride in helping us have safe, productive lives.

They made my pacemaker so that (even though they won't advertise it) would withstand an MRI, and it did for me.

Bob


1 Comments

No Pain

by SMITTY - 2007-04-13 02:04:20

Bob,

Glad your MRI came off with no problems. Based on what the EP that implanted my PM and my primary care physician told me about a MRI and my pacemaker it sounds like you got away with tickling the dragons tail.

It wasn’t the PM they were concerned about for as you said, the shielding provided by the titanium case would probably protect the electronics in the PM. However, it was the possibility of heating up the leads that go from the PM to the heart they were concerned about. As a result I settled for a cat-scan.

Bob (aka Smitty)

You know you're wired when...

Your ICD has a better memory than you.

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My pacemaker is intact and working great.