Cardiology's Biggest Lie: No MRI for Your Device
Patient
Melissa Walton-ShirleyJuly 29, 2014
Drug & Reference Information
She's been a good friend for 23
years and an integral part of a team of healthcare providers. But now, she
stands disheveled in a hospital room with one sock on and one sock off. She
greets the nurse twice within five minutes of entering the room, tells the same
joke over and over, and at sundown, morphs from Dr Jekyll to Mr Hyde. After a
predictably nonspecific head CT, she desperately needs an MRI, but by the end
of the day, two tertiary centers, one regional center, and her local hospital
radiology department refused to place her in the MRI scanner because she has a
pacemaker. It's not their fault, really.
If this patient's home address
were Baltimore, for instance, her cardiologist would have dialed the radiology
department at Johns Hopkins Hospital and heard a friendly but mechanical female
voice invite her to "press 3 to order an MRI for a patient with a
device." Instead, in a country where the latticework of web-based
information rivals the neuronal complexity of the human brain, most hospitals
still can't move forward on the MRI-device issue. Johns Hopkins Hospital has.
It is part of a registry that opened a floodgate of diagnostic opportunity for
cardiologists, orthopedists, and neurologists. With well over 1000 MRIs
performed on device-laden individuals and no clinically adverse outcomes, it
should be lauded as one of the country's leaders in MR imaging; but you can't
be a leader in the US unless you have followers who can get past governmental
constraints.
Dr
Carsten Zobel (now
at Marien Hospital Euskirchen, Germany) and colleagues from the University
Hospital of Cologne, Germany, are also leaders. They published an excellent review
on the history of MRI scanning in device patients in the April 2012 issue of Deutsches
Ärzteblatt International [1].
It references another overview of MRI from Europace that revisited 10
deaths in the 1980s that were "poorly characterized with no ECG records
for review"[2,3].
From 1992 to 2001, there were six deaths during or following MRI scanning in
Germany, but no ECG records were available, and autopsy reports were
unrevealing. The authors "guessed" the cause was "[ventricular
fibrillation] due to inadequate asynchronous pacing on activation of magnetic
function."
Things are different now. In
Germany, there have been no deaths reported with MRI scanning in the past
decade. Johns Hopkins Hospital, following the lead of physicians like Dr Robert Russo at the Scripps
Institute, who championed the MagnaSafe registry, joined a handful of other facilities in
the US that now scan frequently. It too has deciphered the formula for safety:
sometimes resetting the device and performing an exit device interrogation and
then a few follow-up interrogations over the coming weeks and months. There is
beauty in the simplicity of those protocols, but to ignore the historic and
complex mechanical, thermal, and electromagnetic concerns of scanning would do
the topic a great injustice.
Modern
Devices, Modern Scanners
Modern MRI scanners, for
instance, create an electromagnetic field of only 1 to 3 T, far less than older
scanners. The more recent legacy pacer components are far less magnetic, including
both generators and lead tips.
Dog studies found no greater
increase in lead tip temperature than a piddling 0.2°C. Pigs,
however, demonstrate a 20° increase in temperature at the lead tip,
"approaching ablation-range" thermal energy, but histological studies
demonstrate no necrosis at the endocardium and little clinical implication for
adverse outcomes[4].
