Diagnostics of the acute myocardial infarction

Patient interview

An appeal of a cardiological patient to a doctor with complaints of chest pain should always alert the specialist. A detailed questioning with the details of complaints and the course of the pathology helps to establish the direction of the diagnostic search.

The main points that indicate the possibility of a heart attack in a patient:

• the presence of coronary heart disease (stable angina pectoris, diffuse cardiosclerosis, myocardial infarction);
• risk factors: smoking, obesity, hypertension, atherosclerosis, diabetes mellitus;
• provoking factors: excessive physical activity, infectious disease, psychoemotional stress;
• complaints: chest pain of squeezing or burning character, which lasts more than 30 minutes and is not stopped by "Nitroglycerin".

In addition, a number of patients notice an "aura" 2-3 days before the disaster (more about it in the article "Pre-infarction state"):

• general weakness, unmotivated fatigue, fainting, dizziness;
• increased sweating;
• palpitations.

Inspection

Physical (general) examination of the patient is carried out in the doctor's office using the methods of percussion (tapping), palpation and auscultation ("listening" to heart sounds using a phonendoscope).

Myocardial infarction is a pathology that does not differ in specific clinical signs that make it possible to diagnose without using additional methods. Physical examination is used to assess the state of the cardiovascular system and determine the degree of hemodynamic (blood circulation) impairment on prehospital stage.

Frequent clinical signs of a heart attack and its complications:

• pallor and high moisture content of the skin;
• cyanosis (cyanosis) of the skin and mucous membranes, cold fingers and toes - indicate the development of acute heart failure;
• expansion of the boundaries of the heart (percussion phenomenon) - speaks of aneurysm (thinning and protrusion of the myocardial wall);
• precordial pulsation is characterized by a visible heartbeat on the anterior chest wall;
• auscultatory picture - muffled tones (due to reduced muscle contractility), systolic murmur at the apex (with the development of relative valve insufficiency with the expansion of the cavity of the affected ventricle);
• tachycardia (heart palpitations) and hypertension (high blood pressure readings) are caused by activation of the sympathoadrenal system.

More rare phenomena - bradycardia and hypotension - are characteristic of posterior wall infarction.

Changes in other organs are recorded infrequently and are mainly associated with the development of acute circulatory failure. For instance, pulmonary edemawhich is auscultatory characterized by moist rales in the lower segments.

Changes in blood count and body temperature

Measurement of body temperature and a detailed blood test are generally available methods for assessing the patient's condition to exclude acute inflammatory processes.

In the case of myocardial infarction, the temperature may rise to 38.0 ° C for 1-2 days, the condition persists for 4-5 days. However, hyperthermia occurs in large-focal muscle necrosis with the release of inflammatory mediators. For small-focal heart attacks, the increased temperature is uncharacteristic.

The most characteristic changes in a detailed blood test for myocardial infarction:

• leukocytosis - an increase in the level of white blood cells to 12-15 * 10⁹/ l (norm - 4-9 * 10⁹/ l);
• stab shift to the left: an increase in the number of rods (normally up to 6%), young forms and neutrophils;
• aneosinophilia - the absence of eosinophils (the norm is 0-5%);
• erythrocyte sedimentation rate (ESR) increases to 20-25 mm / hour by the end of the first week (the norm is 6-12 mm / hour).

The combination of these signs with high leukocytosis (up to 20 * 10⁹/ l and more) indicate an unfavorable prognosis for the patient.

Coronary angiography

According to modern standards, a patient with suspected myocardial infarction is subject to urgent coronary angiography (introduction of contrast into the vascular bed and followed by X-ray examination of the patency of the heart vessels). You can read more about this survey and the peculiarities of its implementation here.

Electrocardiography

Electrocardiography (ECG) is still considered the main method for diagnosing acute myocardial infarction.

The ECG method allows not only to diagnose myocardial infarction, but also to establish the stage of the process (acute, subacute or scar) and the localization of damage.

International recommendations of the European Society of Cardiology identify the following criteria for myocardial infarction on film:

1. Acute myocardial infarction (in the absence of left ventricular hypertrophy and left bundle branch block):
   • Increase (rise) of the ST segment above the isoline:> 1 mm (> 0.1 mV) in two or more leads. For V₂-V₃ criteria> 2 mm (0.2 mV) in men and> 1.5 mm (0.15 mV) in women.
   • ST segment depression> 0.05 mV in two or more leads.
   • Inversion ("flip" relative to the isoline) of the T wave is more than 0.1 mV in two consecutive leads.
   • Convex R and R: S ratio> 1.

2. Previously transferred MI:
   • Q wave with a duration of more than 0.02 s in leads V₂-V₃; more than 0.03 s and 0.1 mV in I, II, aVL, aVF, V₄-V₆.
   • QS complex in V₂-V
   • R> 0.04 s in V₁-V₂, the R: S ratio> 1 and a positive T wave in these leads without signs of rhythm disturbance.

Determination of the localization of violations by ECG is presented in the table below.

The arrhythmic variant of a heart attack occurs without characteristic chest pain, but with rhythm disturbances, which are recorded on the ECG.

Biochemical tests for markers of cardiac muscle necrosis

The “gold standard” for confirming the diagnosis of MI in the first hours after the onset of a pain attack is the determination of biochemical markers.

Laboratory diagnosis of myocardial infarction using enzymes includes:

• troponins (fractions I, T and C) - proteins that are inside the fibers of cardiomyocytes and enter the bloodstream when the myocardium is destroyed (read how to perform the test here;
• creatine phosphokinase, cardiac fraction (CPK-MB);
• fatty acid binding protein (FFA).

Also, laboratory assistants determine less specific indicators: aspartate aminotransferase (AST, which is also a marker of liver damage) and lactate dehydrogenase (LDH_1-2).

The time of appearance and dynamics of the concentration of cardiac markers are presented in the table below.

According to the above data, for the diagnosis of a recurrence of a heart attack (in the first 28 days), it is advisable to determine the CPK-MB or BSFA, the concentration of which decreases within 1-2 days after the attack.

Blood sampling for cardiac markers is carried out depending on the time of the onset of the attack and the specifics of changes in enzyme concentrations: do not expect high values ​​of CPK-MB in the first 2 hours.

Emergency care for patients is provided regardless of the results of laboratory diagnostics, based on clinical and electrocardiographic data.

Chest x-ray

X-ray methods are rarely used in the practice of cardiologists to diagnose myocardial infarction.

According to protocols, chest x-rays are indicated for:

• suspected pulmonary edema (shortness of breath and moist rales in the lower regions);
• acute aneurysm of the heart (expansion of the boundaries of cardiac dullness, pericardial pulsation).

Ultrasound of the heart (echocardiography)

Comprehensive diagnosis of acute myocardial infarction involves early ultrasound examination of the heart muscle. The echocardiography (EchoCG) method is informative already on the first day, when the following are determined:

• decreased contractility of the myocardium (hypokinesia zone), which makes it possible to establish a topical (by localization) diagnosis;
• drop in the ejection fraction (EF) - the relative volume that enters the circulatory system with one contraction;
• acute aneurysm of the heart - expansion of the cavity with the formation of a blood clot in non-functioning areas.

In addition, the method is used to identify complications of myocardial infarction: valvular regurgitation (insufficiency), pericarditis, the presence of blood clots in the chambers.

Radioisotope methods

Diagnosis of myocardial infarction in the presence of a dubious ECG pattern (for example, with blockade of the left bundle branch, paroxysmal arrhythmias) involves the use of radionuclide methods.

The most common option is scintigraphy using technetium pyrophosphate (99mTc), which accumulates in necrotic areas of the myocardium. When scanning such an area, the infarction zone acquires the most intense color. The study is informative from 12 hours after the onset of a painful attack and up to 14 days.

MRI and multislice computed tomography

CT and MRI in the diagnosis of heart attack are used relatively rarely due to the technical complexity of the study and low information content.

Computed tomography is most indicative for the differential diagnosis of MI with pulmonary embolism, dissection of the thoracic aortic aneurysm, and other pathologies of the heart and great vessels.

Magnetic resonance imaging of the heart is highly safe and informative in determining the etiology of myocardial damage: ischemic (with a heart attack), inflammatory or traumatic. However, the duration of the procedure and the specifics of the procedure (the patient must be immobile) do not allow MRI to be performed in the acute period of myocardial infarction.

Differential diagnosis

The most life-threatening pathologies that need to be distinguished from MI, their signs and the studies used are presented in the table below.