Unstable angina / non ST elevation myocardial infarction biomarkers

 Associate Editor-In-Chief: ; Varun Kumar, M.B.B.S.; Lakshmi Gopalakrishnan, M.B.B.S.

Cardiac biomarkers
If there is an elevation of a marker of myocardial necrosis (CK-MB or troponin), then the patient does not have unstable angina, but instead has a syndrome of either ST elevation MI or Non ST elevation MI depending upon the electrocardiogram changes.

According to consensus document in 2007 from the joint task force of the ESC, ACC, AHA and World Heart Federation (WHF), the term myocardial infarction is defined as myocardial necrosis in clinical setting consistent with myocardial ischemia with an elevation of troponin above the 99th percentile of normal together with any one of the following signs of ischemia:
 * symptoms of ischemia
 * ECG changes indicative of new ischemia (new ST T wave changes or new left bundle branch block)
 * development of pathological Q wave in ECG
 * Imaging evidence of new wall motion abnormalities.

Biomarkers currently used to detect ischemia are Creatine Kinase-MB and Troponins. Other biomarkers like aspartate transaminase and lactate dehydrogenase which were earlier used should be avoided.

Creatine kinase-MB
It is a cytosolic carrier protein for highenergy phosphates, has long been the standard marker for the diagnosis of MI. However, it is less sensitive and less specific for MI than cardiac troponins. However, it is useful in special clinical situations one of which is the diagnosis of early infarct extension (reinfarction), because the short half-life of CK-MB compared with troponin permits the detection of a diagnostic new increase after initial peak. Another situation is the diagnosis of a periprocedural MI, because the diagnostic and prognostic value of CK-MB in these situations has been extensively validated.

Cardiac Troponins
Cardiac troponin provides highly sensitive and specific result in detecting cell necrosis. There are 3 types of tropnins- Troponin T(cTnT), troponin I(cTnI) and troponin C(cTnC). Cardiac troponins refers specifically to either TnT or TnI. Because cTnT and cTnI generally are not detected in the blood of healthy persons, the cutoff value for elevated cTnT and cTnI levels may be set to slightly above the upper limit of the performance characteristics of the assay for a normal healthy population. Therefore, physicians need to know the sensitivity and the cut off of the test used in their hospital.