Diagnosis of myocardial infarction, a dangerous cardiac disease, in which necrosis of the heart muscle area develops against the background of impaired blood flow in the coronary arteries, is based on the recommendations of the World Health Organization.

The diagnosis is made if at least two of the three diagnostic criteria are present:.

characteristic clinical picture;

typical changes on the electrocardiogram;

hyperenzymemia.

A preliminary diagnosis is made on the basis of characteristic symptoms, primarily anginal pain, however, the diagnosis of a heart attack may be difficult with the development of atypical forms of pathology, low-symptom or asymptomatic (typical for patients with diabetes mellitus) course. Atypical forms of heart attack are more common in women.

In case of acute sudden pain in the heart, suspect myocardial infarction and call an ambulance Since it is impossible to reliably establish a diagnosis without examination, if you suspect a myocardial infarction, you should immediately call an ambulance and hospitalize the patient to the clinic. Only after a series of laboratory and instrumental studies can the diagnosis be finally confirmed..

In some cases, differential diagnosis of heart attack is carried out with infectious-toxic and allergic shock, which are also characterized by a decrease in blood pressure and shortness of breath, and chest pain may occur..

The name of this or that test, and when it is most informative in time, is described below..

Laboratory diagnostics.

The destruction of the muscle cells of the heart (cardiomyocytes) and the release of the released cellular enzymes into the blood leads to hyperenzymemia in patients with myocardial infarction.

Of greatest importance for the diagnosis of heart attack is the determination of the concentration of creatine phosphokinase (MB fraction), aspartate aminotransferase, lactate dehydrogenase (and its isoenzyme 1), as well as the level of troponin and myoglobin.

Creatine phosphokinase An increase in the activity of creatine phosphokinase (MB-fraction), which is found mainly in the heart muscle, is specific for a heart attack. This fraction does not respond to damage to skeletal muscles, brain, thyroid gland.

3-4 hours after a heart attack, the activity of the CF-fraction of creatine phosphokinase begins to increase, after 10-12 hours the indicator reaches its maximum figures, after 2 days it returns to its original values. By the end of the first day, the concentration of creatine phosphokinase exceeds the norm by 3-20 times. The degree of increase in this fraction of the enzyme correlates with the size of the lesion of the heart muscle - the larger the volume of myocardial damage, the higher the activity of this indicator. It should be borne in mind that a short-term increase in the level of the CF fraction of creatine phosphokinase can be observed after any surgical interventions performed in cardiology (including electrical pulse therapy, coronary angiography, catheterization of cardiac cavities, etc.).

Since it is impossible to reliably establish a diagnosis without examination, if you suspect a myocardial infarction, you should immediately call an ambulance and hospitalize the patient to the clinic..

Sometimes, with extensive myocardial damage, the release of enzymes into the blood is slowed down; in such cases, the absolute value of the activity of the MB fraction of creatine phosphokinase and the rate of its achievement may be less than with the usual washout of the enzyme.

A study for creatine phosphokinase is indicated for all patients who were hospitalized on the first day after the onset of an attack. Normal values \u200b\u200bof creatine phosphokinase (and its MB-fraction), which were obtained in a single study at the time of admission of the patient to the hospital, are not sufficient grounds for excluding the diagnosis of myocardial infarction.. In this case, the analysis is recommended to be repeated after 12 and 24 hours..

When a patient is admitted to the hospital 1-14 days after the onset of the disease, biochemical studies are carried out to determine the concentration of lactate dehydrogenase, alanine and aspartate aminotransferase with the calculation of the de Ritis coefficient.

Lactate dehydrogenase The activity of lactate dehydrogenase in myocardial infarction increases more slowly than creatine phosphokinase, and remains elevated longer. The peak of the activity of this enzyme falls on 2-3 days from the onset of the disease.. Return to initial values \u200b\u200bis noted after 8-14 days. It should be borne in mind that the level of lactate dehydrogenase also increases with congestive heart failure, pulmonary thromboembolism, myocarditis, liver pathologies, shock, megaloblastic anemia, hemolysis, as well as after excessive physical exertion.

ALT, AST and de Ritis coefficient The concentration of aspartate aminotransferase (AST) increases after 1-1.5 days from the moment of manifestation of the disease and returns to the initial values \u200b\u200bafter 4-7 days. The change in AST activity for myocardial infarction is nonspecific, it also occurs in liver diseases and some other pathologies.

An increase in the activity of creatine phosphokinase (MB-fraction), which is found mainly in the heart muscle, is specific for a heart attack. This fraction does not respond to damage to skeletal muscles, brain, thyroid gland.

In the case of liver disorders, the activity of alanine aminotransferase (ALT) increases to a greater extent, and in heart disease - AST. In myocardial infarction, the de Ritis coefficient (ratio of AST to ALT) is higher than 1.33, and in case of liver disorders, it is lower.

Troponin The troponin complex consists of three components - troponin C, I and T. Troponin I and T exist in cardiac muscle-specific isoforms that differ from those in skeletal muscle, which is the reason for the absolute cardiospecificity of the indicator.. 4-5 hours after the death of cardiomyocytes in myocardial infarction, troponin enters the peripheral blood. The peak concentration is reached 0.5-1 days after the onset of myocardial infarction. Troponin I is detected in the blood within 5-7 days, troponin T - within 2 weeks. Determination of troponin in the blood, as a rule, is carried out using the method of immunoassay diagnostics using specific antibodies.

Markers of myocardial infarction, detected during biochemical blood tests, allow to confirm the diagnosis Troponin test for myocardial infarction does not apply to the methods of early diagnosis of the disease. If the test result is negative in patients with suspected acute coronary syndrome (exacerbation of ischemic heart disease, clinically manifested by the development of unstable angina pectoris or myocardial infarction without / with ST segment elevation), a second study is performed 6-12 hours after the attack. At the same time, even a slight increase in the indicator indicates a risk for the patient due to the correlation between the level of troponin increase in the peripheral blood and the volume of myocardial damage..

Myoglobin The specificity of myoglobin for the diagnosis of heart attack is approximately the same as that of creatine phosphokinase.. An increase in the level of myoglobin by 10 times or more is considered diagnostically significant. In myocardial infarction, the increase in the concentration of myoglobin in the blood begins earlier than creatine phosphokinase.

Laboratory diagnostics of myocardial infarction is based on the detection in the patient's blood of markers of myocardial infarction - indicators of the inflammatory process and tissue necrosis.

To a diagnostically significant level, myoglobin in the blood rises 4-6 hours after the onset of an attack and remains high only for several hours. Therefore, it is advisable to perform the analysis for myoglobin no later than 6-8 hours after the onset of a heart attack..

General blood test The general blood test according to the instructions should be carried out when the patient is admitted to the hospital, and then weekly in order to timely detect the development of infectious or autoimmune complications of myocardial infarction.

In a general blood test, leukocytosis is usually detected, not exceeding 15?

109 / l, the absence of eosinophils in the peripheral blood, a slight shift in the leukocyte formula to the left, an increase in the erythrocyte sedimentation rate. An adequate interpretation of these indicators is possible only when compared with the existing clinical manifestations and electrocardiographic data.. Prolonged (more than 1 week) persistence of leukocytosis and / or moderate fever in patients with myocardial infarction may indicate the development of complications (pericarditis, pleurisy, thromboembolism of small branches of the pulmonary artery, pneumonia).

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