Cardiac markers in the assessment of acute coronary syndromes.

Biochemical markers provide clinicians with an important tool for the assessment of acute coronary syndromes. Biochemical markers, including total creatine kinase (total CK), creatine kinase-MB (CK-MB), the MB isoforms, and myoglobin, as well as the troponins--cardiac troponin T (cTnT) and cardiac troponin I (cTnI)--are all used for assessment of the suspected acute myocardial infarction (AMI) patient. In the context of myocardial infarction (MI) diagnosis, total CK is a relatively sensitive marker, but it lacks myocardial specificity because skeletal muscle contains high concentrations of CK. CK-MB is the benchmark for biochemical markers and has both high sensitivity and specificity; however, CK-MB is also present in skeletal muscle and is not diagnostic until eight to twelve hours after onset of symptoms. The MB isoforms are diagnostic earlier but have the same cardiac specificity issues as CK-MB. Myoglobin becomes abnormal about one hour after onset of symptoms and is a sensitive marker for MI; however, myoglobin is cleared quickly and is not cardiac specific. Both cTnT and cTnI are cardiac specific and show high sensitivity and specificity for MI. Risk stratification of acute coronary syndrome patients is another role for biochemical markers; CK-MB, cTnT and cTnI have all been proposed for this function. Compared with CK-MB, both cTnT and cTnI are better able to predict short-term mortality following the index event. Analysis using a logistic regression model that included the electrocardiogram, cTnT, and cTnI showed that cTnT was the most useful marker for risk stratification. Finally, cTnT was reported to be able to predict which patients will benefit from treatment with regimens of low molecular weight heparin.