MRI
Predicts Heart Attack Risk
Imaging
test creating 'revolution' in heart care
Is
that chest pain a harbinger of a future heart attack? Magnetic resonance
imaging can tell.
 The
scan, called MRI, can predict the odds of a heart attack or heart-related
death in people with chest symptoms, even after accounting for conventional
risk factors such as high blood pressure, smoking, and diabetes. Intriguingly,
researchers on a new study said, the device is able to detect reduced
blood flow to the crown of the heart that dramatically magnifies the
risk of these bad outcomes.
"With
the MRI, the pictures are clearer and the spatial resolution is higher"
than conventional heart imaging, said Dr. W. Gregory Hundley, a radiologist
at Wake Forest University School of Medicine in Winston-Salem, N.C.,
and leader of the research team. "And one thing we found is the location
within the heart of [the blocked blood] appeared to portend a poor prognosis,"
Hundley said.
The
results of the study appear in Circulation: Journal of the American
Heart Association.
Unlike
other scanners, an MRI takes three-dimensional images. While MRI is
now a standard tool for peering at other organs, it has only lately
been turned on the heart as a way to assess pumping power, blood flow
and other important features. However, experts said the non-invasive
test is the future of cardiac screening, thanks to the precision images
it provides without radiation or invasive procedures.
The
Limitations of Echocardiography
The
leading method for looking at the heart is echocardiography, which uses
sound waves to generate its image of the organ. The test is a good one,
both inexpensive and portable, but it does not work particularly well
in people who are obese or those who smoke, and in 15 percent to 20
percent of patients the resulting pictures are difficult to read.
In
the latest study, Hundley's group gave MRI "stress tests" to 279 men
and women with cardiovascular disease and poor showings on echocardiography.
To simulate the effects of exercise on the heart the patients received
injections of the drugs dobutamine and, if necessary, atropine, which
cause the organ to beat faster.
As
expected, people with severely constricted blood flow, or ischemia,
in the heart after the injections had more than three times the risk
of a heart attack or sudden heart-related death over the next two years
as those with normal results on the stress test. For those whose pumping
outflow—a measure called left ventricular ejection fraction—was
reduced by 40 percent or more vs. normal, the risk of suffering these
problems jumped more than fourfold.
In
other words, Hundley said, the results demonstrate that MRI can effectively
tell physicians which patients are at high risk of serious or fatal
heart problems in the future.
Damage
to Heart Apex Increases Risk
Two
previous studies had linked problems with the heart's apex—which
normally resembles the point of a football—to impaired exercise
ability and poor prognosis after a heart attack.
Hundley's
group was able for the first time to take pictures of damage to the
apex, and they found that people with such damage—the result of
a previous heart attack, perhaps—were six times more likely than
those without injury to suffer additional heart attacks or to die of
cardiovascular illness.
"When
you lose that football shape you get into trouble," said Hundley. Treatment
to restore blood flow to the heart may want to focus on the apex, Hundley
said, though that needs to be studied further.
The
Limitations of MRI
MRI
is not for everyone, at least for the moment. The machines do not like
metal plates, pacemakers, or defibrillators, so a small percentage of
people with heart rhythm anomalies cannot undergo the test.
But
"it really is turning into something of a revolution in cardiology,"
said Dr. Dudley Pennell, a heart expert at London's Royal Brompton Hospital
and past president of the Society for Cardiovascular Magnetic
Resonance. "It's opening up new vistas for us. We can see things
we haven't seen before."
Over
the last five years, Pennell said, researchers have used MRI to watch
blood flow problems in patients with insulin resistance and to gauge
the true extent of damage from heart attacks, neither of which was possible
without the technology.
Dr.
Gerald Pohost, chief of cardiovascular medicine at the University of
Southern California's Keck School of Medicine in Los Angeles and an
MRI advocate, acknowledged that the scans are more expensive than other
heart imaging tools. "But it has great potential to do a lot of things,"
Pohost said, from generating three-dimensional pictures of the pump
to observing how it processes energy.
Always
consult your physician for more information.
MRI
Services at St. John's Mercy
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Online
Resources
American
Heart Association
Centers
for Disease Control and Prevention (CDC)
Circulation:
Journal of the American Heart Association
The
Lancet
National
Heart, Lung, and Blood Institute (NHLBI)
Society
for Cardiovascular Magnetic Resonance
Stroke,
Journal of the American Heart Association
|
November
2002
Imaging
Test Creating 'Revolution' in Heart Care
The
Limitations of Echocardiography
Damage
to Heart Apex Increases Risk
The
Limitations of MRI
Magnesium
No Way to Treat a Heart Attack
Online
Resources
MRI
Services at St. John's Mercy
Find
a St. John's Mercy Physician
In
Other News About Your Heart:
Magnesium
No Way to Treat a Heart Attack
Physicians
hoped it would be an easy and inexpensive way of improving the odds
of surviving a heart attack.
But
a new study shows that magnesium given intravenously to people hospitalized
for heart attacks does nothing.
The
study appears in The Lancet.
"In
viewing the totality of available evidence in current coronary care
practice, there is no indication for the routine administration
of intravenous magnesium to patients," says Dr. Elliott Antman,
the lead author of the study and the director of the coronary care
unit at Brigham and Women's Hospital in Boston.
Researchers
gave 3,113 heart attack patients magnesium sulfate intravenously
for the first 24 hours after they were hospitalized. Another 3,100
patients received a placebo.
Researchers
found no difference in the death rate over the next 30 days.
The
finding shows just how far treating heart attacks patients has come,
physicians believe.
Magnesium
was commonly given to heart attack victims in the 1970s and 1980s.
The reason: A primary cause of death from heart attacks is the dangerous
arrhythmias that force the heart to beat wildly before finally giving
out. Magnesium is known to calm the heart muscle, Antman says.
Studies
back then showed that magnesium reduced short-term mortality by
as much as 50 percent.
But
studies in the 1990s showed magnesium had little effect.
"Since
magnesium is such a cheap treatment, we felt it was important to
evaluate this highly cost-effective and potentially life-saving
treatment," Antman says.
In
the 1990s, more effective heart attack medications became available,
he adds.
When
treating a heart attack, physicians can attempt to minimize the
damage in two ways, explains Dr. Chris White, chairman of the department
of cardiology at Ochsner Clinic Foundation in New Orleans.
The
first is by calming the heart, making it work less so it requires
less oxygen. That is how physicians treated heart attacks prior
to the 1990s, with treatments such as magnesium, White says.
The
second method—one that has been the focus of much research
for the last 15 years—is increasing the amount of oxygen to
heart tissue.
One
way is the use of "thrombolytic"—or "clot-busting"—drugs
that limit damage to the heart muscle by dissolving clots that block
arteries.
Then
there is angioplasty, in which a catheter is threaded through an
artery to improve blood flow in a narrowed vessel. At the tip of
the catheter is a tiny balloon that is inflated to stretch the vessel.
It
is also now know that aspirin, which interferes with blood clotting,
can help keep arteries open in people who have had a heart attack.
And ACE inhibitors block an enzyme in the body that is necessary
to produce a substance that causes blood vessels to tighten.
These
treatments were not widely available until the 1990s, Antman says.
"It's
possible the beneficial effect of magnesium is superceded by the
effects of current medical regimen," Antman says.
Magnesium
is no longer routinely given to patients, White says. "The real
hope was that . . . it would work synergistically with the clot-busters.
Unfortunately, that didn't happen."
Always
consult your physician for more information.
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