New diagnostic criteria of acute myocardial infarction.

735 For the last four decades the diagnosis of MI has been based on the WHO criteria. The definition of MI required the presence of at least two of the following three factors: clinical history of ischemic chest pain; serial changes in ECG; a rise and fall in serum cardiac enzymes. These criteria have been extensively modified by the clinicians in their application: chest pain is often non-specific; the ECG criteria were based on evolving Q-waves. Today we know that about one-half of all infarcts are non-Q wave. However, ST-T changes without Q waves do not differentiate between myocardial ischemia and MI. We have come to rely heavily on biochemical markers which have been, for the last two decades, total CK and CKMB. Refinement of this definition has expanded it to include the use of more sensitive and specific cardiac markers, including troponins. They are structural proteins of the sarcomere and would be released only with ischemia. So, biomarkers of myocardial necrosis have, in recent years, become the cornerstone of myocardial necrosis in the clinical context of ischemia. A new definition of MI was needed. The basic concept behind this definition is that any amount of myocardial necrosis caused by ischemia should be labelled as an infarct. Consequently any patient who was formerly considered as having angina pectoris, stable or unstable, could be diagnosed today as having a small MI. The modern concept of the pathophysiology of acute coronary syndromes (ACS) has been previously explained in this session by Prof. Paulo Ribeiro. The clinical picture of ACS may present with two different ECG patterns, ST elevation and non-ST elevation, that may progress to MI (Fig. 1). In the first situation the changes include new ST segment elevation at the J point in two or more contiguous leads with the cut-off points of 0.2mV in leads V1V3 and 0.1 mV in the other leads. In patients without ST segment elevation, we may find ST segment depression or T wave abnormalities. These ECG criteria reflect myocardial ischemia and are not sufficient by themselves to define MI. The final diagnosis of MI depends on the detection of elevated levels of cardiac biomarkers in the blood. The time release of various biomarkers following myocardial necrosis is different and so we may choose the most appropriate to clarify the clinical picture according to its characteristics. The most recently described biomarkers of myocardial damage are cardiac troponin (I and T) which are highly sensitive and specific, thereby reflecting even microscopic zones of myocardial necrosis. The value for troponin must present elevated on at least one occasion during the first 24 hours after the index clinical event. In the absence of technology for detection of troponin, CK-MB is the best alternative. It is less tissue specific than troponins but has the advantage of earlier peak value and more robust data documenting its clinical specificity. The other enzyme tests in current use in the sixties and seventies, namely total CK and lactate dehydrogenase and its isoenzymes, are no longer used due their low specificity. Rev Port Cardiol 2003;22 (Supl. III) :735-740