There is no typical change in serum myocardial zymogram in 40-50% of patients
Although the WHO (World Health Organization), national cardiology associations, and cardiovascular disease textbooks clearly point out that chest pain is the most typical symptom of AMI (acute myocardial infarction), it can not be ignored: 33% of patients do not show symptoms of chest pain. This fact. Similarly, 40% of patients did not show a lot of sweating symptoms; 40% of patients did not show diagnostic features in ECG (electrocardiogram); 40-50% of patients had no typical changes in serum myocardial zymogram.
There is no spectrum
Then, as a "gold standard" for myocardial injury diagnosis, is there a spectrum or a spectrum? Let's take a closer look.
Myocardial zymogram refers to a general term for all enzymes present in cardiomyocytes. When myocardial cells are damaged, these enzymes enter the blood circulation and are detected abnormally. Clinically, it is mainly used to detect five myocardial enzymes (mainly essential for cell energy metabolism or anabolism), including lactate dehydrogenase (LDH), creatine kinase (CK), and creatine kinase isoenzyme ( CK-MB), aspartate aminotransferase (AST), and α-hydroxybutyrate dehydrogenase (α-HBD).
Among these enzymes, LDH and AST are widely present in various tissues and organs of the body (the content of cardiomyocytes is not high), so the specificity is poor, and the test results are susceptible to damage by other tissues and organs. The other three enzymes, although relatively high in the myocardium, are also present in small amounts in other tissues and organs. Among the five components of myocardial zymogram, creatine kinase isoenzyme (CK-MB) has the highest specificity for the heart. In the age of no other means of detection or markers, myocardial zymograms, especially CK-MB, have long been regarded as the "gold standard" for the diagnosis of myocardial injury.
Creatine kinase (CK) is a dimer composed of two subunits. The M subunit is muscle type and the B subunit is brain type. Three isozymes are formed. CK-BB mainly exists in brain tissue, gastrointestinal tract and uterine smooth muscle. The brain tissue is almost entirely CK-BB, CK-MB is mainly present in myocardial tissue, and CK-MM is mainly present in skeletal muscle tissue.
CK-MB in biochemical tests often uses immunosuppression: that is, the M subunit is completely inhibited by an antibody against CK-M monomer, so CK-MM loses its activity, and CK-MB activity loses half, so it is measured. The activity is actually half that of CK-MB, so the activity of CK-MB should be twice the measured value.
Obviously, for patients with brain diseases and gastrointestinal diseases, the serum CK-BB will make the measurement falsely increase; for patients with muscle injury or inflammation, the serum CK-MB The content will also increase and affect the measurement results; for some tumor patients, the formation of giant CK caused by metabolic disorders will also affect the measured value. The phenomenon of CK-MB's enzymatic activity > CK activity is often caused by these factors, but these factors that cause the false increase of CK-MB enzyme activity have nothing to do with myocardial damage. Therefore, the current scientific research, clinical testing and clinical application areas recommend the use of more accurate CK-MB mass method to replace the CK-MB enzyme activity in myocardial enzymes to obtain more accurate test values.
The CK-MB mass method is mostly carried out by enzyme immunoassay with double-antibody sandwich, which completely excludes the effects of CK-BB and CK-MM. Due to the different influencing factors, the detection values ​​of the two methods do not have a good conversion relationship.
In summary, in view of the non-specificity of each enzyme in the myocardial enzyme spectrum, the increase in its value does not necessarily mean that the myocardial damage must be; likewise, its normal value does not prove that the patient is not at risk of myocardial damage, please remember: 40- There was no typical change in serum myocardial zymogram in 50% of patients with AMI.
The myocardial zymogram and the most specific CK-MB enzyme activity assay were analyzed. Do you also think that the myocardial zymogram is somewhat unrecognizable? At present, more clinical changes in reference troponin (cTn) levels, combined with myoglobin (Myo), CK-MB mass determination and other indicators (such as ECG, signs, imaging, etc.) for myocardial injury diseases The diagnosis and elimination, and the reference value of myocardial enzymes is becoming weaker and weaker.
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