What is troponin? Norm, basic indicators and their interpretation

In 2000, the European Cardiology Community and the American College of Cardiology agreed on the diagnosis of myocardial infarction. To verify the diagnosis, we decided to use the analysis for the level of cardiac troponins, since it is considered more specific in the diagnosis of damage to the heart muscle than creatine phosphokinase, even in cases of minor myocardial necrosis.

Troponins

Troponin is a protein molecule consisting of three subunits (T, C, 1). It is located on the actin threads in the musculature of the myocardium and participates in its contractions. Each subunit performs its specific role in regulating the activity of the heart muscle. In the body, in most cases, bound troponin predominates. The norm in the blood (ng / ml) is 2.0, because only six percent of these proteins are freely located in the cytosol.

It was found that the destruction of cardiomyocytes in peripheral blood increases the level of different fractions of troponins. Sometimes this figure is higher than the norm in hundreds or even thousands of times.

Function

As already mentioned above, troponin joins the protein tropomyosin. In the inactive state, when the muscle is relaxed, this protein interferes with the attachment of myosin to actin. When the action potential reaches the muscle cell, positively charged ions enter the cytoplasm of the cell through the calcium channels. A part of the calcium joins the troponin and binds it. This allows the myosin to reach the actin filaments and cause a contraction.

Not only in the myocardium is the troponin. The rate of its binding is ninety-five percent. The remainder is in a free state or distributed in other types of muscle tissue. The key difference is that in skeletal muscles in troponin there are four subunits, and in the heart muscle - three.

Physiology

Reductions of all types of muscles are coordinated by changing the intracellular concentration of calcium ions. When their number rises, the muscle contracts, and vice versa. The protein, to which calcium is attached in the cell, is troponin. The norm of its location on tropomyosin corresponds to the length of the latter, namely 40 nanometers.

Troponin has three subunits, each of which has its own functions. When calcium is added to the C-fragment, tropomyosin moves along the actin filament so that myosin can join it. If calcium is not enough, tropomyosin blocks active centers and does not allow myosin to attach to myofilaments.

Microbiologists and histologists also found that troponin 1 suppresses the formation of new vessels. Troponin C binds calcium ions and this causes changes in troponin 1. Troponin T is needed to bind to tropomyosin, and troponin 1 binds to actin, and also helps actin interact with myosin when calcium ions in the cytoplasm are inadequate.

Preparation and indications for the purpose of the analysis

The level of troponin and its norm in peripheral blood is better judged by quantitative analysis. For his surrender, no specific training is required, but, like in all cases of blood donation, it is best to do this four hours after eating.

If a patient enters the hospital in the acute period of myocardial infarction, he immediately takes blood for analysis. According to the protocol, it should be repeated after 4 hours, and then after 8. After a day, the determination of troponin is carried out once a day for two weeks. In modern medicine methods for determining the amount of this protein directly at the patient's bed with the help of test systems have been developed. A negative result allows excluding such a patient from individuals who may develop an acute coronary syndrome in the near future.

In addition to the definition of acute myocardial infarction (MI), an analysis of the amount of troponin is done to identify a subacute form of myocardial infarction, a microinfarction, a "mute" heart attack, and also monitor the quality of thrombolytic therapy and the effect of direct anticoagulants, for example heparin.

Increased concentration of troponin 1

Troponin 1 ( serum levels of up to 0.1 ng / ml) may increase after surgery on the heart. So, when transplanting this organ, the concentration of troponin increases to 5 nanograms per milliliter. This value can be stored for up to three months.

Inflammatory diseases and traumas of the heart cause a slight increase in the level of troponin T, but the dynamics of its changes in the blood differs from that in infarction. The norm of troponin in the blood of men and women is the same. This indicator is not related to the sex or age of the patient. Sometimes there may be false-positive test results if the patient is in a state of acute alcohol intoxication.

A slight increase in troponin is possible with massive damage to skeletal muscles. For comparison: creatine phosphokinase (CK) in such patients is increasing significantly, which leads to erroneous registration of myocardial infarction.

Acute myocardial infarction

Troponin 1 (norm in the blood to 0.1 ng / ml) is a pathognomonic sign of acute myocardial infarction only if its value exceeds 100 ng / ml, or more than 99 percentile from normal values. But only in combination with clinical and instrumental symptoms of myocardial ischemia.

As a result of the introduction of this analysis into medical practice, the number of diagnosed infarcts has increased, since this test is more sensitive than CK. In addition, in the prognostic plan, an elevated level of troponin is a negative sign. Some researchers argue that the size of the thrombus is directly proportional to the level of troponin in the blood serum.

The increase in the level of this protein in patients with a heart attack is fixed as early as six hours after the onset of a pain attack. After fourteen days, the level of troponin progressively decreases and returns to normal.

Acute coronary syndrome

The norm of troponin in the blood in acute coronary syndrome (ACS) corresponds to that of myocardial infarction and ranges from 50 to 100 ng / ml. Increase of this protein allows to differentiate ACS from unstable angina. Sometimes in patients with characteristic clinical symptoms and elevated troponin levels, coronary angiography does not detect a serious hemodynamic disorder. The reason for this phenomenon is the spontaneous formation of the plaque, which dissolves during the treatment with thrombolytics. The second theory states that a thrombus simply descends lower in the vessels and is not visible on the screen.

Percutaneous coronary intervention

The level of troponin (normal to 2.0 ng / ml) slightly increases after angioplasty or stent placement. Scientists no longer had doubts that the proteins that are determined appeared from cardiomyocytes. The cause of their appearance is temporary, passing ischemia, which is caused by inflation of the balloon and compression of the coronary arteries.

Even in the case of micro-traumas of the myocardium, troponins were extremely sensitive, which, of course, was reflected in the peripheral blood test. But, among other things, this indicates that patients with similar changes in protein levels are at high risk of developing coronary syndrome and myocardial infarction. Unfortunately, there is no specific figure that doctors could rely on in their forecasts. Some pathophysiologists suggest talking about myocardial infarction in cases when the level of troponin is exceeded by more than three times.

Surgical interventions

Troponin (norm to 2.0 ng / ml) is increased after radical operations on the cardiac muscle. This is due to the shortcomings of cardioprotective measures. In theory, they must protect the patient's body from hypoxia, but in practice this is not always possible by one hundred percent. But not in all cases, the increase in troponin should be regarded as a perioperative myocardial infarction.

The volume and duration of the operation, as well as the baseline level of the protein, should be considered. To diagnose "myocardial infarction" is possible only by the presence of clinical, laboratory and instrumental signs simultaneously.

Other states

Numerous studies have confirmed the fact that troponin (norm 2.0 ng / ml) is a highly specific marker of myocardial infarction. But there are a number of pathological conditions that are also accompanied by an increase in the amount of this protein in the peripheral blood. These include sepsis, pulmonary embolism (PE), heart failure, cardiac inflammation, myocarditis, chronic renal failure, excessive physical exertion, heart transplantation, chemotherapy.

This phenomenon is caused by fever, tachycardia, hypoxia, a microcirculatory disorder, a decrease in pressure and anemia. All this leads to myocardial ischemia and destruction of cardiomyocytes, which causes an increase in troponin.

Troponin 1 or T

Norm troponin in the blood up to 2.0 ng / ml, but to date there are methods for determining the different fractions of troponin. This allows more accurate determination of myocardial damage. During several studies, it was found that troponin-T is more sensitive to renal failure, the troponin 1, but they are similar in other parameters, and therefore have the same diagnostic value.

The peculiarity of troponin T is also that only one firm lets out the diagnosticum for it, whereas for troponin 1 there are several test systems. Because of this, there may be some difficulties in comparing the results. But clinicians are trying to derive a single formula, with which it would be possible to level the difference in parameters among the results of different labolatories.