[Medical Q&A] Does a test report showing abnormal myocardial enzyme spectrum mean myocardial infarction?

Planner: Chinese Medical Association

Reviewer: Ning Yongzhong, Chief Technician, Beijing Chuiyangliu Hospital

Abnormal myocardial enzyme spectrum does not necessarily mean myocardial infarction!

1.What is myocardial infarction?

The global unified definition of myocardial infarction is: elevated serum myocardial markers (mainly troponin) (at least exceeding the 99% upper limit of the reference value) accompanied by at least one of the following clinical indicators: ① ischemic symptoms; ② new ischemic electrocardiogram changes (new ST-T changes or left bundle branch block); ③ pathological Q wave formation on the electrocardiogram; ④ imaging evidence showing new myocardial cell necrosis or new local wall motion abnormalities; ⑤ coronary angiography or autopsy confirms the presence of thrombus in the coronary artery.

2.What markers are included in the myocardial enzyme spectrum?

(1) Creatine kinase (CK): It includes three isoenzymes. There is no CK-BB isoenzyme in normal human serum, and the content of CK-MB is very low. Only CK-MM exists in normal human serum. Among them, CK-MB has a high clinical specificity for judging myocardial injury and can be used to diagnose acute myocardial infarction at an early stage, but it is not sensitive to minor myocardial injury. In addition, the activity of serum CK-MB is proportional to the degree of myocardial infarction.

(2) Aspartate aminotransferase (AST): Although AST is most active in myocardial cells, it is also highly active in hepatocytes, skeletal muscle, and kidney tissue. Therefore, elevated AST does not specifically point to myocardial problems, but may be caused by a variety of factors.

(3) Lactate dehydrogenase (LDH) and its isoenzymes (especially LDH1): An increase in the concentration of LDH1 in the blood may indicate a problem in a certain part of the body, especially in myocardial injury, acute myocardial infarction, cardiomyopathy, hemolytic anemia, pernicious anemia, pulmonary embolism, etc. However, an increase in LDH levels cannot determine the specific disease alone, and a diagnosis must be made in combination with other test results and symptoms.

(4) Troponin (cTn): It is the most specific and sensitive marker of choice for diagnosing myocardial injury. When cTn exceeds the upper limit of the reference interval and is combined with evidence of myocardial ischemia, acute myocardial infarction can be diagnosed.

(5) Myoglobin (MYO): It is a sensitive indicator for early detection of myocardial damage and can also be used to diagnose recurrent myocardial infarction. However, in addition to myocardial damage, other conditions may also lead to elevated MYO levels, such as skeletal muscle damage, crush syndrome, hypothyroidism, etc.

Once the myocardial enzyme spectrum is detected abnormally, you should communicate with your doctor in time. The doctor will make a comprehensive judgment on whether myocardial damage has occurred based on the test results, combined with symptoms and other examinations (such as electrocardiogram).