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Cardiac enzymes. How to use serial determinations to confirm acute myocardial infarction
1Mayo Clinic Scottsdale, Scottsdale, AZ 85259.
Insights
Diagnosing acute myocardial infarction relies on cardiac enzyme tests. Elevated creatine kinase-MB (CK-MB) with a flipped lactate dehydrogenase (LDH) pattern confirms heart attack, while normal CK-MB rules it out.
Area of Science:
- Cardiology
- Biochemistry
Background:
- Acute myocardial infarction diagnosis traditionally involves clinical history, ECG, and cardiac enzyme levels.
- Creatine kinase (CK) and lactate dehydrogenase (LDH) are key cardiac biomarkers.
Purpose of the Study:
- To evaluate the reliability of cardiac enzyme measurements, specifically CK-MB and LDH isoenzymes, in diagnosing acute myocardial infarction.
- To determine the diagnostic utility of CK-MB and LDH isoenzyme patterns in confirming or excluding myocardial infarction.
Main Methods:
- Measurement of creatine kinase (CK) and its MB isoenzyme (CK-MB) levels.
- Analysis of lactate dehydrogenase (LDH) isoenzyme patterns, focusing on the LDH2:LDH1 ratio.
- Correlation of enzyme levels and patterns with clinical diagnosis over a 48-hour period post-event.
Main Results:
- Normal CK-MB levels within 48 hours reliably exclude acute myocardial infarction.
- Elevated CK-MB with a "flipped" LDH isoenzyme pattern (LDH2:LDH1 ratio) reliably confirms myocardial infarction.
- Elevated CK-MB with a normal LDH isoenzyme pattern indicates a less certain diagnosis, potentially requiring further investigation.
Conclusions:
- Cardiac enzyme analysis, particularly CK-MB and LDH isoenzymes, is crucial for accurate myocardial infarction diagnosis.
- Specific patterns of CK-MB and LDH isoenzymes offer high reliability in confirming or excluding acute myocardial infarction.
- Uncertain enzyme results may necessitate complementary diagnostic tools like ECG and myocardial imaging.
Abstract:
Although acute myocardial infarction can be diagnosed on the basis of clinical history, electrocardiographic (ECG) findings, and abnormalities of creatine kinase (CK) and lactate dehydrogenase (LDH) enzyme levels, measurement of cardiac enzyme levels is the most reliable way to confirm or exclude the diagnosis. If the MB isoenzyme of creatine kinase (CK-MB) remains normal during the 48 hours after the suspected clinical event, acute myocardial infarction can be reliably ruled out; if CK-MB values become elevated and the LDH isoenzyme pattern (LDH2:LDH1 ratio) becomes "flipped," the diagnosis can reliably be made. However, if CK-MB values become elevated but the LDH isoenzyme pattern remains normal, the diagnosis is less firm and ECG and myocardial imaging techniques may be needed to confirm or exclude myocardial infarction.