What Constitutes a Diagnosis of Myocardial Infarction in 2001?
Kristian A. Thuygesen
Aarhus University Hospital, Aarhus, Denmark

The definition of myocardial infarction has changed considerably over time as the defining medical technologies have advanced. Recently, European and American physicians have issued revised guidelines for the diagnosis of myocardial infarction, with revisions based largely on advances in the use of biochemical markers for myocardial cell death.

Dr. Thuygesen began by reviewing the factors that contribute to the evolving clinical concept of myocardial infarction, including historical perspective, pathophysiology, diagnostic timing, diagnostic procedures, treatment strategies, and changing classification schemes. In 2000, the Joint European Society of Cardiology/American College of Cardiology Committee on Guidelines for the Diagnosis of Myocardial Infarction published parallel articles in the European Heart Journal and the Journal of the American College of Cardiology. The articles were entitled "Myocardial Infarction Redefined -- a Consensus Document of the Joint European Society of Cardiology/American College of Cardiology Committee for Redefinition of Myocardial Infarction."

Although the definition of myocardial infarction includes pathological evidence, clinical presentation, biochemical markers, and electrocardiographic evidence of infarction, Dr. Thuygesen focused on the areas that have changed. The pathological definition is the same as it has always been: "myocardial cell death due to prolonged ischemia." The clinical presentation is the same, essentially involving chest pain or similar anginal symptoms, with exertion or at rest, lasting for 20 minutes or more. The electrocardiographic indications have not changed all, either. Thus, he said "Our main focus is on the biochemical markers -- on the troponin assay, with which you are all quite familiar."

Dr. Thuygesen said that the troponin assay is now the preferred biochemical marker for use in diagnosis of myocardial infarction, although the creatine kinase (CKMB) assay may still be used until the transition to troponin is complete. One important factor in the transition to use of troponin as the major biochemical marker of infarction is the need for better standardization of troponin assays. At present, there are many assays available and there is too much variability in standards among different laboratories. For now, he said, physicians should develop relationships with the clinical laboratories they use and obtain clear definitions of the reference standards and cutoffs used for normal and elevated troponin values. With a highly sensitive and specific assay such as the troponin assay, we generally like to use a level above 99% of the normal reference population, or 3 standard deviations above the mean, as the cutoff point for abnormal readings. Dr. Thuygesen concluded: "It is also essential for us to understand our decision limits better -- what assay values do we use as cutoff points to prompt which specific action steps?"

Reporter: Andre Weinberger, MD


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