Biomarkers in acute coronary syndrome – Myoglobin, CK, LDH

Previous

Biomarkers in acute coronary syndrome

Biomarkers in acute coronary syndrome – Myoglobin, CK, LDH:

Myoglobin

Myoglobin is a heme protein which is rapidly released from damaged muscle. Elevations of myoglobin levels can be seen as early as one hour post-infarct. Hence it is a marker which appears earlier than the other ones, but it is much less cardiac specific and hence of very little diagnostic use. It can be considered a marker protein for early diagnosis in conjunction with more specific ones like troponins. Myoglobin has a high negative predictive value at 2-6 hours post infarct, meaning that a low myoglobin level can be used to rule out myocardial infarction as it is released quite early after infarction.

Myoglobin levels can also be elevated in strenuous exercise, trauma, uremia, with some toxic drugs, intramuscular injections, after cardiopulmonary resuscitation, cardiac transplant, seizures and inflammatory myopathies.

LDH isoenzymes

In the bygone era, LDH (lactate dehydrogenase) isoenzymes were used as a biomarker for myocardial infarction. Five isoenzymes – LDH 1 to LDH 5 were described. LDH 5 is elevated in liver disease and LDH 1 is elevated in acute myocardial infarction and was more than LDH 2. The isoenzymes were separated by electrophoresis.

CK-MB isoforms

Though CK-MB isoforms made a debut in 1994, it was not widely used due to technical issues. High voltage electrophoresis was used to estimate them. The cardiac specific isoform MB2 is relatively increased (MB2 > 2 U/L and MB2/MB1 > 1.7) in acute myocardial infarction. Positive results could be obtained within 3 hours [1].

Role of Biomarkers

Thus biomarkers are useful in rapid and early identification of acute myocardial infarction. They are also useful to rule in or rule out acute myocardial infarction, especially in situations where ECG and clinical history atypical or non-diagnostic, provided the time window and kinetics of the marker are taken into consideration. They are also useful in risk stratification of continuum of the acute coronary syndrome, which may very from unstable angina to ST elevation myocardial infarction, that too of different severities. They are useful in assessment of successful reperfusion, which is usually associated with early peaking due to alteration in the release kinetics, especially of CK-MB, with lower peaks and area under the curve, indicating lower mass of myocardial necrosis with early reperfusion. Some of the biomarkers like CK-MB can detect re-infarction with a second peak after the first one. Determination of infarct size from biomarker kinetics is useful in prognostication.

Reference

1. Bock JL, Brogan GX Jr, McCuskey CF, Thode HC Jr, Hollander JE, Gunther T.. Evaluation of CK-MB isoform analysis for early diagnosis of myocardial infarction. J Emerg Med. 1999 Jan-Feb;17(1):75-9

Next