Under normal conditions, the aforementioned enzymes are detectable in the blood only in minimal concentrations; however, when the myocytes of the heart undergo significant damage or stress, these enzymes are released into the circulation in significantly higher quantities.
The measurement of cardiac enzymes is therefore useful as an aid in diagnosing myocardial infarction and acute coronary syndrome, two diseases associated with an insufficient blood supply to the heart. Their evaluation can also be used to determine the risk of developing one of these. diseases or to monitor patients suspected of such conditions.
What are enzymes?
Enzymes are biological catalysts that regulate and speed up metabolic reactions, thus maintaining cellular homeostasis.
Cardiac enzymes are of clinical interest as markers of myocardial injury, as they reflect the presence of necrosis (without indicating, however, the responsible mechanism).
;In particular, altered values of these markers confirm the diagnosis in case of acute myocardial infarction in progress: when the muscle fibers suffer damage due to the reduction of blood supply to the coronary arteries, cardiac enzymes are released into the blood in high quantities.
In addition to being an indicator of acute myocardial infarction, an increase in cardiac enzymes can also be found in cases of intense exertion, trauma and muscular dystrophies.
The most commonly tested myocardial enzymes in testing laboratories include:
- Creatine phosphokinase (CK or CPK), in particular the isoform released by the heart muscle (CK-MB);
- Lactate dehydrogenase (LDH);
- Myoglobin;
- Troponin I;
- Aspartate aminotransferase (AST or GOT).
Myocardial infarction
Acute myocardial infarction reflects a loss of cardiac myocytes (necrosis) caused by prolonged ischemia.
Necrosis of large areas of myocardium results in a significant rise in serum levels of cardiac enzymes. In addition to these parameters, ischemia can be identified early through history and electrocardiogram (ECG).
The enzymes of diagnostic utility for myocardial infarction are divided into:
- EARLY INDICATORS (<6 hours)
- Creatine kinase (CK): enzyme found mainly in skeletal muscle tissue and heart fibers.
The measurement of the amount of creatine kinase (CK) present in the blood makes it possible to detect and monitor inflammation (myositis) or severe muscle damage, including heart damage.
In the presence of muscle distress, increased amounts of CK are released into the blood within hours. If further damage occurs, CK concentrations can remain elevated. This makes the CK test useful for monitoring progressive heart damage.
Creatine kinase-MB (CK-MB) is a particular form of the enzyme, found mainly in the heart muscle. Levels of this marker increase when damage (such as acute myocardial infarction), trauma or heart surgery.
The CK-MB concentration can be measured in the follow-up, after an increase in total CK is detected, and / or when the troponin test is not available. - Troponins: are proteins found in skeletal and heart muscle. These regulate muscle contraction by controlling the calcium-mediated interaction of actin and myosin.
The specific isoforms of the heart (TnI and TnT) are considered highly specific markers for the myocardium and represent one of the most important diagnostic references for assessing the state of health of the heart; in clinical practice, the dosages of these enzymes are used to understand if the patient has had a heart attack or other inflammatory or ischemic problems.
However, small increases in troponins can also occur in patients with heart failure, myocarditis or pulmonary embolism. - Myoglobin: together with troponin, this protein is one of the most used markers to confirm or exclude any damage to the heart.
Myoglobin levels begin to increase within 2-4 hours of the heart attack, reaching high levels in the following 8-12 hours; generally, the values return to normal the day after the disease event. Consequently, the test is used to help rule out a heart attack in the emergency room.
High levels of myoglobin must be compared with the results of other tests, such as creatine kinase (CK-MB) or troponin; this allows us to establish whether the damage is actually to the heart or involves another skeletal muscle. - LATE INDICATORS (> 6 hours)
- Lactate dehydrogenase (LDH): enzyme found in most of the body's cells. Its main task is to metabolize glucose to make it usable energy.
Lactate dehydrogenase is found in many tissues, but is mainly concentrated in the heart, skeletal muscles, liver, kidneys, pancreas and lungs. When cells are damaged or destroyed, the LDH enzyme is released in the liquid fraction of the blood (serum or plasma), as well as increasing its concentration in other biological liquids (eg liquor) in the presence of some pathologies.
Therefore, LDH represents a general indicator of tissue and cellular damage. - Aspartate aminotransferase (AST, GOT or SGOT): enzyme that is found in the cells of the body, but is prevalent in the myocardium and liver, and to a lesser extent, in the kidneys and muscles.
In healthy subjects, blood AST values are low. When the heart, liver or muscles are damaged, this transaminase is released into the blood.
The AST enzyme does not provide additional diagnostic information to that already obtained with the determination of CK and LDH.
Note
It should be remembered that these parameters could also increase in other diseases such as muscle, stroke and liver disease.
and myocarditis (heart inflammation).
Creatine kinase
The presence of a high creatine kinase value can be traced to heterogeneous causes, including fatigue (eg physical exertion, intense sports training, etc.), muscle diseases (such as dystrophy) or myocardial infarction.
The causes that determine the increase of these enzymes also include trauma, thyroid dysfunction, alcohol abuse and infectious diseases.
CK-MB
In cases of myocardial infarction, the increase of the CK-MB isoenzyme is early; it begins to increase in the first 4-6 hours, peaks rapidly (12-18 hours) and returns to normal limits more rapidly than the total CK.
The return to normal values generally occurs within 48 hours and therefore precedes that of the total CPK by 24 hours.
Myoglobin
When myoglobin rises, it means there has been recent damage to the heart or other muscle tissue. The increase in this marker indicates ongoing heart distress and may be related to myocardial infarction.
High levels of myoglobin must be compared with the results of other tests, such as creatine kinase (CK-MB) or troponin; this allows us to establish whether the damage is actually to the heart or involves another skeletal muscle.
An increase in myoglobin values can also be found in cases of trauma, surgery or myopathies, such as muscular dystrophy.
Lactate dehydrogenase
The increase in LDH can occur in all pathological conditions characterized by the development of irreversible cell damage (necrosis), with loss of cytoplasmic content.
During an acute myocardial infarction, the increase in serum LDH concentration increases 8-24 hours after the onset of the event, peaking after 3-6 days and returning to normal within 8-14 days.
Lactate dehydrogenase therefore represents an indicator of previous heart attack.
Aspartate aminotransferase
In myocardial infarction, serum levels of aspartate aminotransferase increase 8-12 hours after the onset of painful symptoms, peak after 24-48 hours and return to normal after 3-4 days.
Elevated AST values in the blood can also be observed following trauma and muscle diseases.
Sometimes, to determine the value of these indicators, a sample of fluid is collected from a particular area of the body (for example, around the heart) with a specific procedure. of 8-10 hours.
Some medications interfere with the result, so it is always advisable to tell your doctor if you are undergoing any treatments.
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