WORLD HEALTH ORGANIZATION (WHO) DEFINITION

Historically, there has been tacit agreement as to the meaning of the term “myocardial infarction”. The World Health Organization definition, which has been widely used, requires the presence of two of the following three features: symptoms of myocardial ischaemia, elevation of cardiac marker (enzyme) concentrations in the blood, and a typical electrocardiographic pattern involving the development of Q waves or persistent T wave changes.^w1

Using specific and highly sensitive immunoassays for myocardial proteins, such as cardiac troponins T and/or I, it is now possible to identify patients with small areas of myocardial necrosis. The emphasis on cardiac protein markers in the new American College of Cardiology/European Society of Cardiology (ACC/ESC) definition of MI, published in September 2000, has simplified the classification of MI.¹ The new diagnostic criteria include a characteristic rise and fall in blood concentrations of cardiac troponins and/or creatine kinase (CK)-MB in the context of spontaneous ischaemic symptoms or coronary intervention (table 1).¹

If it is accepted that any myocardial necrosis caused by ischaemia constitutes MI, many patients who were formerly diagnosed as having unstable angina pectoris will be now diagnosed as having had a small MI. For example, in a review of data from the Hennepin County Medical Centre (Minnesota, USA), the incidence of MI increased by 37% when the new definition of MI was applied.^w2 However, the specificity of the new tests will reduce the number of false positive diagnoses of MI.

Under the WHO classification, which was expanded for the monitoring trends and determinants …