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.
Online
Resources
(Our Organization is not
responsible for the content of Internet sites.)
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
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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
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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