Researchers at Johns Hopkins have painstakingly
figured out how to safely perform magnetic resonance
imaging scans on men and women who have any one of 24
modern types of implanted defibrillators and pacemakers.
Henry Halperin and his team have developed a
combination of methods that reduces the risk of
life-threatening meltdowns and other complications posed by
MRI's ability to charge and manipulate the electrical
properties of cells to produce real-time images from inside
the body.
"We have turned a once exceptional procedure into one
that is now a routine at Hopkins," Halperin said.
Among other things, the Johns Hopkins group reprograms
the devices, fixing them to a specific sequence. This makes
the implanted devices "blind" to their external
environment, reducing the potential for their electronics
to confuse the radiofrequency generated by the MRI with an
irregular heartbeat and preventing misfires. The team also
turns off the defibrillators' shocking function for the
brief duration of the MRI scan, about 30 to 60 minutes.
Also changed is the amount of electrical energy used
at peak scanning in MRI. The Johns Hopkins team reduced the
strength of the electromagnetic field by half, from as much
as 4 watts per kilogram to 2 watts per kilogram per
patient.
"This lower-energy scan still provided images of
sufficient quality to make an accurate diagnosis in more
than 90 percent of cases tested," Halperin said in an
article published in the Sept. 18 issue of the journal
Circulation, reporting on 55 of more than 100
patients scanned at Johns Hopkins so far.
The report comes just two years after the same journal
published the team's initial, positive findings in animals,
stirring fierce debate at several international conferences
as to whether or not MRI could truly be made safe.
The Johns Hopkins team says that since 2004 its
expanded use of MRI has made more than a dozen potentially
life-saving diagnoses, despite the fact that the tiny
battery-driven heart devices, which help the body's main
pump maintain a beat, have long been considered unsafe and
off-limits for testing.
"The risk to patients of burning heart tissue or
misfiring is still there," Halperin cautioned. "But our
results show that with appropriate precautions, MRI is a
safe and effective diagnostic tool to use for those with
modern implanted heart devices." An electro-physiologist
and professor of medicine, radiology and biomedical
engineering at the School of Medicine and its
Heart Institute, Halperin has long led efforts to
expand access to MRI.
Except for research purposes, the U.S. Food and Drug
Administration has not authorized any implanted cardiac
device for MRI testing. But Halperin says that opening up
this diagnostic option is important for the estimated 2
million Americans, many of them elderly, who have these
implanted devices but who are also denied the benefits of
the quick and accurate images that MRI provides.
Lead author Saman Nazarian, a cardiac
electrophysiology, clinical and research fellow, said,
"Once these precautions are better understood and further
refined, we hope policy-makers will see fit to review
current restrictions on scanning anyone with a device.
These images are critical to early diagnosis of certain
cancers of the brain, head and neck, and to guide invasive
procedures."
Of those scanned in the study, 31 had a pacemaker and
24, an implantable defibrillator. Only modern devices
— pacemakers made after 1996 and defibrillators
manufactured after 2000 — were tested, Nazarian said,
because the latest models were deemed to be safer than
older versions. Newer models are made of titanium, a
nonmagnetic metal; are smaller and more lightweight; and
have better protection from the radiofrequency energy of
the MRI scanner, he said.
Using a single scanner, a 1.5 Tesla by General
Electric, the Johns Hopkins group was able to help plan
artery-opening procedures for more than a half-dozen in the
test group; improve measurements of tumor growth in nine
others; and detect two strokes, a benign brain mass and a
blood clot in the spine that had been missed by alternative
imaging from CT scanning.
Nazarian cautions that only physicians specially
trained in MRI safety, or with access to specialists
familiar with the specific precautions taken in his study,
should undertake this approach. "It is also important at
this time to restrict MRI use to those with implanted
devices specifically tested, and scanners of the same type
and magnetic strength as that used in our study," he
added.
All study participants were closely monitored during
the scans with electrocardiography and pulse oximetry, and
staff members were on hand to resuscitate patients in the
event of an emergency.
All subjects were over age 19 and were followed from
three months to six months to look for any post-test heart
damage or changes in the devices' programming.
Patients were disqualified from testing if they had
any leads placed on the surface of the heart or that were
capped with metal and therefore not connected to the
battery and at greater risk of overheating. When the leads
— the electrical components connecting the device to
the heart muscle — are attached to the battery or
embedded in the blood vessels, they are less likely to be
overheated by the MRI field.
An analysis of records showed that scans provided
definitive answers to physicians' diagnostic questions 100
percent of the time for conditions affecting areas outside
the chest and 93 percent of the time for conditions that
affected the heart and the upper body; in the latter
category, the remaining 7 percent of the scans were too
distorted by imaging artifacts from the implanted devices
to make a clear diagnosis.
Device monitoring showed that lead sensing did not
fluctuate or change during the scan. Battery measurements
showed that scans did not deplete or strengthen the
battery's charge. Indeed, pacemakers and defibrillators
performed successfully after the scans without any
premature firing or false alarms.
Pacemakers and defibrillators are implantable devices
used to treat people with an abnormal heartbeat, a
condition known as arrhythmia. More than 2.2 million
Americans are living with arrhythmia. It can occur in a
healthy heart and be of minimal consequence or it can lead
to more serious heart disease, stroke or sudden cardiac
death.
Funding for this study was provided by the National
Institutes of Health and the Donald W. Reynolds Foundation.
Halperin is a paid consultant to defibrillator manufacturer
Medtronic, and co-investigators Ronald Berger and Albert
Lardo are paid consultants to Guidant Corp., another device
manufacturer. Co-author David Bluemke has received
honoraria from General Electric Health Care for
presentations. None of these companies provided funding for
the study, and the terms of the physicians' arrangements
are managed by The Johns Hopkins University in accordance
with its conflict-of-interest policies.
Other investigators in this research, conducted solely
at Johns Hopkins, were Ariel Roguin, Menekhem Zviman, Timm
Dickfeld, Robert G. Weiss and Hugh Calkins.
GO TO