Magnetic resonance
imaging may result in a faster and more accurate diagnosis of acute
myocardial infarction Advanced
magnetic resonance imaging can diagnose an acute myocardial infarction
in emergency-room patients with angina more accurately and faster
than traditional methods, according to an article in the February
4th issue of Circulation. American
researchers evaluated the ability of high-resolution magnetic resonance
imaging to detect acute coronary syndrome in emergency-room patients
complaining of chest pain. The results were compared with three
standard diagnostic tests: an electrocardiogram, blood enzyme test,
and the TIMI risk score, the last of which assesses the risk of
complications or death in patients with chest pain based on a combination
of several clinical characteristics. Magnetic resonance imaging
detected all of the myocardial infarctions, including 3 in patients
who had normal electrocardiograms. In addition, high-resolution
imaging detected more patients with unstable angina.
Of the more than 5 million American patients
who annually visit emergency
rooms with chest pain, only about 40 percent can be immediately
diagnosed with acute myocardial infarction with use of standard
tests. The majority must undergo
several tests and further hospitalization before a conclusive diagnosis
can 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 Dr. Claude Lenfant of the National Institutes
of Health. "Using magnetic resonance imaging to detect heart
problems in the emergency department will ultimately save lives.
Because patients will be diagnosed and treated more quickly, cardiac
magnetic resonance imaging might save costs, as well."
In the current study, 161 patients whose initial electrocardiogram
did not indicate a myocardial infarction were evaluated with traditional
diagnostic tests and a cardiac imaging study after their condition
was stabilized. The procedure for magnetic resonance imaging lasted
roughly 38 minutes. All patients were followed up 6 to 8 weeks after
the initial visit to the emergency department.
Researchers studied the sensitivity and specificity
of each test in detection of acute coronary syndrome. The high-resolution
imaging technology accurately diagnosed 21 of 25 patients (84 percent)
found to have acute coronary syndrome -- a significantly higher
level of sensitivity than that that for electrocardiography, blood
enzyme levels, and TIMI risk score. Imaging was also more specific
than an abnormal electrocardiogram.
"Magnetic resonance imaging was the strongest
predictor of acute coronary syndrome -- for both heart attacks and
unstable angina," said Andrew Arai, M.D., principal investigator.
"[Imaging] 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."
Use of the imaging technology also addresses the critical issue
of time. Because patients can be scanned in under 40 minutes, it
is relatively likely that reperfusion can be started within 1 hour
of symptom onset in patients who arrive quickly at a medical facility.
"Magnetic resonance imaging 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
Robert S. Balaban, M.D., a coauthor. "[The imaging] 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 electrocardiographic
and enzyme monitoring."
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