Mark A. Meier, M.D., and colleagues studied the implications of the new definition published in September 2000 by a joint committee of the European Society of Cardiology and the American College of Cardiology. According to background information in the article, previous criteria set by the World Health Organization required two of three conditions for diagnosis: symptoms of ischemia such as chest pain, electrocardiographic changes consistent with ischemia, and elevated blood levels of certain enzymes (usually creatine kinase-MB).

The new definition includes measurement of troponins. According to the new criteria, elevated levels of enzymes (including creatine kinase-MB or troponin I or T) with either symptoms or electrocardiographic changes suggestive of ischemia constitute an acute myocardial infarction.

Dr. Meier and colleagues studied 493 consecutive patients admitted to a university hospital between May 1, 1999 and January 1, 2000. Patients who had elevated enzymes and symptoms of ischemia (n=275) were divided into two groups. Group A (n=224) was diagnosed according to the old definition; they had elevated levels of creatine kinase-MB and electrocardiographic readings indicative of infarction regardless of troponin levels. Group B (n=51) had normal creatine kinase-MB levels but elevated levels of troponin; these patients represent additional individuals diagnosed with myocardial infarction using the new guidelines to make the diagnosis.

The authors noted that none of the patients identified under the old criteria would have been missed with use of the new criteria --- the difference was in identification of additional patients, the 51 people in Group B.

Additionally, the authors found that six-month death rates were higher in Group B participants (16.3 percent versus 5.8 percent for Group A), but that this difference was not statistically significant after adjustment for different characteristics (age, sex, etc.) between the groups. The researchers also reported that "... additional patients diagnosed as having acute myocardial infarction by the new definition had more comorbid conditions and as a result were at greater risk of adverse events."

The authors conclude, "... unlike the World Health Organization definition, the use of the new European Society of Cardiology/ American College of Cardiology criteria enhances identification of a high-risk subset of patients with acute myocardial infarction. Identification of high-risk patients with acute myocardial infarction allows physicians to target more aggressive treatments in this cohort that have the potential of improving their outcomes."