Cardiac Markers Of Infarction

Cardiac markers for myocardial infarction

The detection of markers of myocardial injury have improved from less specific (e.g. myoglobin) to more specific markers such as the cardiac isoform of Creatine Kinase (CK-MB) and the cardiac isoforms of troponin (Troponin I & T). Currently, troponin is the favoured marker as it is both more selective and more sensitive than CK-MB. Where troponin detection is not available, CK-MB is currently considered an acceptable alternative. Potential alternative markers are still being investigated.

Levels of both troponin and CK-MB do not increase until at least 3 hours after onset of chest pain, so it is entirely possible for a recent emergency admission to have normal levels. Repeated measurements need to be made; changes (or lack of them) can assist in differentiating MI from non-MI acute coronary syndromes (ACS).

Troponin

• Two isoforms (T and I) seem to have equal clinical value
• Increases 3-12 hours after onset of chest pain
• Can stay elevated for weeks after an MI
• Should be measured at presentation and ca. 10 hours later to assess changes
• Troponin will not be elevated in unstable angina
• Increased troponin in non-ST-elevation ACS is MI
• The higher the troponin level the higher the risk of death
• Any other cause of myocyte death can raise troponins
• e.g. Myocarditis, heart failure, ventricular overload (e.g. massive pulmonary embolism)

CK-MB

• Increases over similar time as Troponin but returns to baseline with 3 days
• Less specific to MI and less sensitive (smaller fold increase above cut-off level)