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Definition of Cardiac Enzymes
Blood tests that measure the levels of these enzymes help doctors determine whether, and how long ago, a heart attack has taken place.
All muscle tissue releases certain enzymes when injured, so the combination of enzymes present in the blood provides the most useful clues as to the source of the injury.
The cardiac-specific enzymes that indicate heart attack are cardiac troponin-T and cardiac troponin-I.
The levels of these enzymes in the blood rise 3 to 6 hours after damage to the heart and remain elevated for 7 to 10 days.
Nonspecific enzymes that may suggest heart attack include creatine kinase (CK), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH). Elevations of these enzymes occur whenever there is significant damage to muscle tissue of any kind.
To cardiologists determining whether a person has had a heart attack, it is the rise and fall of the enzyme levels that are more useful than the levels themselves at any one point in time.
Creatine kinase MB (CK-MB), one of the protein components of creatine kinase, rises more rapidly and dramatically when the damage is to heart muscle, providing a strongly suggestive marker. CK-MB rises within a few hours of heart damage though returns to normal in about 24 hours.
Cardiologists evaluate cardiac enzyme levels in combination with other clinical evidence such as electrocardiogram (ecg) and echocardiogram to confirm the diagnosis of myocardial infarction (death of heart muscle cells due to lack of oxygen).
See also CARDIAC CATHETERIZATION.