Читать книгу Practical Cardiovascular Medicine - Elias B. Hanna - Страница 15

A rise in troponin, per se, is diagnostic of myocardial necrosis or injury but is not sufficient to define myocardial infarction (MI), which is myocardial necrosis secondary to myocardial ischemia. Additional clinical, ECG, or echocardiographic evidence of ischemia is needed to define MI (Figure 1.1).

In fact, MI is defined as a troponin elevation above the 99th percentile of the reference limit (~0.03 ng/ml, depending on the assay) with a rise and/or fall pattern, along with any one of the following four features: (i) angina; (ii) new or dynamic ST-T abnormalities not explained by LVH or LBBB, or new Q waves; (iii) new wall motion abnormality on imaging; (iv) intracoronary thrombus on angiography.^1,2

Isolated myocardial necrosis is common in critically ill patients and manifests as a troponin rise, sometimes with a rise and fall pattern, but no clinical or ECG features of MI. This troponin rise is not called MI but is called “non-MI troponin elevation” or “non-ischemic myocardial injury”.

A rise or fall in troponin is necessary to define MI. A mild, chronically elevated but stable troponin may be seen in chronic heart failure, severe left ventricular hypertrophy, or advanced kidney disease. While having a prognostic value, this stable troponin rise is not diagnostic of MI. A fluctuating troponin pattern may be seen in myocarditis. Different cutoffs have been used to define a relevant troponin change, but, in general, a troponin that rises above the 99th percentile with a rise or fall of > 20% is characteristic of MI (50-80% cutoff is more applicable to low troponin levels <0.1 ng/ml).³