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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