NIH Study Shows MRI Provides Faster, More Accurate Way
To Diagnose Heart Attacks
Advanced magnetic resonance imaging (MRI) technology can detect heart attack
in emergency room patients with chest pain more accurately and faster than
traditional methods, according to a new study supported by the National Heart,
Lung, and Blood Institute (NHLBI). Published in the February 4 issue of Circulation:
Journal of the American Heart Association, the findings suggest that more
patients who are suffering a heart attack or who otherwise have severe blockages
in their coronary arteries could receive treatment to reduce or prevent permanent
damage to the heart if they are assessed with MRI. The article is available
online at http://circ.ahajournals.org/cgi/content/abstract/01.CIR.0000047527.11221.29.
Researchers evaluated the ability of high-resolution MRI to detect acute coronary
syndrome (heart attack or unstable angina) in emergency department patients
with chest pain. MRI results were compared with three standard diagnostic
tests: an electrocardiogram (ECG or EKG), blood enzyme test, and the TIMI
risk score, which assesses the risk of complications or death in patients
with chest pain based on a combination of several clinical characteristics.
MRI detected all of the patients’ heart attacks, including three in patients
who had normal EKGs. In addition, MRI detected more patients with unstable
angina than the other tests.
Of the more than 5 million patients who visit emergency departments with chest pain each year, only about 40 percent can
be immediately diagnosed with heart attack using standard tests. The majority
of patients must undergo a number of tests and further hospitalization for
a conclusive diagnosis to be reached.
“This study lays the groundwork for what could mean a dramatic change in how heart attacks are diagnosed and
how rapidly patients receive treatment once they arrive at the hospital,”
said NHLBI Director Dr. Claude Lenfant. “Using MRI to detect heart problems
in the emergency department will ultimately save lives. Because patients will
be diagnosed and treated more quickly, cardiac MRIs might save costs, as well.”
The study is part of a collaborative program among the NHLBI, the Warren Grant
Magnuson Clinical Center both components of the National Institutes of Health
(NIH), the Federal Government's primary agency for biomedical and behavioral
research and Suburban Hospital in Bethesda, Maryland. Another area of the
program, supported by NIH’s National Institute of Neurological Disorders and
Stroke, is studying the use of MRI to diagnose and treat stroke. NIH is part
of the U.S. Department of Health and Human Services.
In the chest pain study, 161 patients whose initial EKG did not indicate a heart attack were evaluated
with traditional diagnostic tests and a cardiac MRI after their condition
was stabilized. The MRI lasted around 38 minutes. All patients were followed
up 6 to 8 weeks after the initial visit to the emergency department.
Researchers studied the ability of each test to detect acute coronary syndrome (sensitivity)
as well as how often an abnormal test result correctly identified a patient
with acute coronary syndrome (specificity). MRI accurately diagnosed 21 of
the 25 patients (84 percent) determined to have acute coronary syndrome
a significantly higher level of sensitivity than EKG criteria for ischemia
(restricted blood flow), blood enzyme levels, and TIMI risk score. MRI was
also more specific than abnormal EKG.
“MRI was the strongest predictor of acute coronary syndrome for both heart attacks and unstable angina,” said
Dr. Andrew Arai, principal investigator of the study, who leads the cardiovascular
imaging section of the NHLBI Laboratory of Cardiac Energetics. “MRI allows
us to look at how well the heart is pumping, how good the supply of blood
to the heart is in specific areas, and whether there is evidence of permanent
damage to the heart.”
MRI is a type of body scan that uses magnets and computers
to provide high-quality images based on varying characteristics of the body’s
tissues. The technology allows physicians to study the heart’s overall structure
and functioning continuously in three dimensions.
MRI addresses another critical issue in assessing patients with acute coronary syndrome: time. Patients can
be scanned in under 40 minutes; if severe blockages are found, they could
receive vital treatment to restore blood flow, such as clot-busting drugs,
angioplasty, or coronary artery bypass surgery. Current recommendations are
for such therapies to begin within one hour from the start of a heart attack
for optimal effectiveness.
EKG records the electrical activity of the heart to detect abnormal heart rhythms, some areas of damage, inadequate blood flow,
and heart enlargement. Like MRI, EKG is noninvasive. Because of its low degree
of sensitivity, however, EKG immediately diagnoses only about 10 percent of
patients with acute coronary syndrome. It is not uncommon for an EKG to appear
normal during a heart attack or an episode of unstable angina.
Patients suspected of having a heart attack that is not confirmed by an EKG typically have their
blood tested for enzymes or other substances (“markers”) that indicate permanent
damage to the heart tissue. Because the markers are not evident in the blood
until several hours after a heart attack, patients whose EKG appears normal
may need to stay in the hospital for 12 to 24 hours to ensure the blood test
is accurate. Furthermore, because the blood test detects only permanently
damaged tissue, it does not detect unstable angina.
Unstable angina can be considered an “impending heart attack.” Heart attacks are caused by a blood
clot from a tear or break in fatty deposits (plaque) that have built up inside
a coronary artery; when the blood clot suddenly cuts off most or all blood
supply to the heart, heart tissue is permanently damaged. In unstable angina,
the coronary artery has many or all of the same characteristics as a heart
attack, except that the problems are not quite severe enough to cause permanent
heart damage. Because no heart cells die in unstable angina, the condition
is harder to detect with standard tests.
Approximately two percent of patients with a heart attack are discharged home from the emergency department without
the heart attack being detected and treated. In addition, many patients with
unstable angina are sent home without diagnosis; they may progress to a heart
attack after discharge or require urgent medical therapy soon thereafter.
Patients with undetected acute coronary syndrome are twice as likely to die
as those whose condition is detected and treated. In the study, three of the
patients were not characterized as having acute coronary syndrome until their
“MRI provides us with additional and more precise information than is currently accessible from other imaging methods, such as echocardiography,
coronary angiography, and positron emission tomography,” added Dr. Robert
S. Balaban, scientific director of the NHLBI Laboratory Research Program,
and a co-author of the paper. “MRI technology could help us get another 20
percent of patients with acute coronary syndrome to life-saving treatment
more quickly, and reduce the number of patients spending hours in the hospital
for long-term EKG and enzyme monitoring.”
Balaban estimates that MRI to detect acute coronary syndrome in the emergency department could be used in hospitals
nationwide within a few years. Many U.S. hospitals currently have equipment
that could be upgraded for this use.
“This study represents a shift of moving technology directly from the basic science laboratory to the clinical setting,”
added Balaban. “Working with physicists and engineers, we hope to further
develop MRI to provide even more precise imaging and quantifiable ways to
measure coronary blockages.
“MRI is a noninvasive imaging tool that we can
now interact with in ‘real time’ allowing us to see soft tissues, such as
the wall of a diseased artery or the heart muscle itself while measuring physiological
functions such as contraction, blood flow, and viability,” Balaban noted.
“The future of MRI is to go from diagnostic uses, as described in this study,
to therapeutic applications. MRI can be used to guide minimally invasive procedures,
including cardiac catheterization to open blocked arteries, direct the injection
of therapeutic agents such as gene vectors or stem cells into damaged areas
of the heart, replace heart valves, or remove cells that are causing arrhythmias.”
To arrange an interview with Dr. Andrew Arai or Dr. Robert Balaban, contact
the NHLBI Communications Office at (301) 496-4236. Dr. Arai will summarize
the results of the chest pain study in a plenary lecture at the Society of
Cardiac Magnetic Resonance in Buena Vista, Florida, February 8, 2003. For
an interview with Dr. Wayne Olan, director of MRI services at Suburban Hospital
or Dr. Eugene Passamani, director of cardiology at Suburban, contact Ronna
Borenstein-Levy at (301) 896-2598.
NHLBI press releases and other materials, including information about
heart disease and heart attack (http://www.nhlbi.nih.gov/actintime/index.htm)
are available online at www.nhlbi.nih.gov.