Enzymatic Diagnosis of Acute Myocardial Infarction

Abstract

The diagnosis of acute myocardial infarction for some time has been based on the World Health Organization's “two out of three” criteria, namely: angina, electrocardiographic changes, and elevated plasma enzymes. This was devised in 1959 before clinical application of plasma isoenzymes. It was soon realized that Q-waves on the ECG, while very specific, are not very sensitive. The combination of chest pain and nonspecific ECG changes, namely: alterations in the ST-T segment, does not differentiate angina from infarction. Similarly, elevated plasma activity of LDH, SGOT, or CK with nonspecific ECG changes or chest pain could incorrectly include many patients with chest pain without cardiac necrosis, or even cardiac disease, particularly if associated with minor trauma such as from intramuscular injections. The diagnostic application of isoenzymes, the widespread availability of the coronary care unit (CCU), and the implementation of interventions early during the course of acute myocardial infarction (AMI) stimulated the need for an earlier and more precise diagnosis. At the present time, it is estimated that only about 25–30 percent of patients admitted to the CCU are subsequently proved to have AMI. The need to be cost-effective and to appropriately allocate critical care beds requires an early diagnosis to determine who can be appropriately transferred and when. The recent widespread use of early thrombolytic therapy provided further impetus since, when successful, the rapid washout enhances release of cardiac enzymes and accelerates the evolution of ECG manifestations.