La nuova definizione di infarto miocardico: Analisi del Documento di Consenso ESC/ACC e riflessioni sull'applicabilità alla realtà sanitaria italiana

The recent document of the ESC/ACC Committee for the redefinition of myocardial infarction (MI) has introduced the measurement of cardiac troponin as the biochemical standard for the diagnosis of MI. This change has been mainly driven by the demonstration that any amount of myocardial damage, as detected by cardiac troponins, implies a worse long-term outcome of the patient. The results of several studies consistently show that there is a continuous relationship between the degree of troponin elevation and the patient's prognosis. The new definition has important consequences on the diagnostic and therapeutic approaches to patients with acute coronary syndromes; in fact, patients with increased troponins, i.e. patients with MI, necessitate more aggressive treatment than those without troponin elevations, i.e. patients with unstable angina. The application of the new definition is expected to increase the number of cases of MI by about 30% and to decrease mortality. We believe that several aspects of the new definition need to be discussed before the new criteria for MI are used in clinical practice in Italy. The most relevant issues are the following: 1) the definition of troponin elevation should meet the analytical performance of the available assays, the diagnostic cut-off of which is frequently too imprecise. We propose that troponin elevations be defined as values exceeding the concentration corresponding to a total analytical imprecision of 10%. We disclose such a concentration for the currently available assays and suggest its use in clinical practice to mitigate the possibility of false-positive values; 2) the number of samples required for the diagnosis should be sufficient for the assessment of the changes in concentration over time. When only one sample is available, or when the temporal pattern of the changes in marker concentration is not consistent with the time elapsed from the onset of symptoms, we suggest that objective evidence that myocardial ischemia is the likely cause of myocardial damage should be obtained; 3) the diagnosis of MI after a percutaneous coronary intervention represents a unique situation. In contrast with myocardial damage occurring during spontaneous ischemia, available data do not support the concept that any troponin elevation is associated with an adverse prognosis. In the absence of conclusive studies, we suggest that the diagnosis of MI after a percutaneous coronary intervention be based on conventional criteria. Finally, we propose this summary with the aim of overcoming some of the more controversial aspects of the ESC/ACC redefinition of MI: Criteria for acute, evolving or recent MI. Either one of the following criteria satisfies the diagnosis for an acute, evolving or recent MI: 1) elevation* of biochemical markers of myocardial necrosis (preferably troponin) with at least one of the following: a) ischemic symptoms; b) development of pathologic Q waves on the ECG; c) ECG changes indicative of ischemia (ST segment elevation or depression); d) coronary artery intervention (e.g., coronary angioplasty)**. Marker elevations should be accompanied by objective evidence that myocardial ischemia is the likely cause of myocardial damage when: a) only one blood sample is available; b) marker changes over time are not consistent with the onset of symptoms; 2) pathologic findings of an acute MI. Criteria for established MI. Anyone of the following criteria satisfies the diagnosis for established MI: 1) development of new pathologic Q waves on serial ECGsGS. The patient may or may not remember previous symptoms. Biochemical markers of myocardial necrosis may have normalized, depending on the length of time that has passed since the infarct developed; 2) pathologic findings of a healed or healing MI. *if troponin is used, the marker concentration should be higher than the value associated with a 10% coefficient of variation, possibly detected in ≥ 1 of at least two occasions. Changes in concentrations should be consistent with the time elapsed from the onset of symptoms; ** since there is no definite evidence that the degree of troponin elevation is correlated with long-term mortality in this setting of "iatrogenic" myocardial damage, we suggest that the physician continues to rely on conventional criteria.