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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