Cardiac enzymes are molecules released into the circulation as a consequence of cardiac injury. They are used in the diagnosis of myocardial infarction, but elevations are not synonymous with an ischaemic mechanism of injury and results should be interpreted in the context of clinical and ECG findings.

It is important to note that cardiac enzymes such as creatine kinase (CK), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) are of variable specificity to cardiac muscle.

Cardiac Troponins T and I are the preferred markers for the diagnosis of myocardial injury. These markers are more sensitive and more specific than measuring CK, AST or LDH. Some authorities believe that these latter assays should no longer be used to evaluate cardiovascular disease. It is accepted however that total CK may have a role in trials to allow comparison with previous data and also that CK-MB measurement may help clarify whether a cardiac event has occurred within the preceding 48 hours.

Cardiac enzymes include:

• cardiac Troponin T and I, CK - earliest to rise
• AST - second to rise
• LDH - latest to rise

Peaks tend to occur earlier and are often higher, following successful thrombolytic therapy. This is attributed to the "washout" of enzymes from the infarcted area immediately after reperfusion occurs.