Diagnosis of localization and stage of myocardial infarction using ECG

Myocardial infarction is the necrosis of part of the myocardium, which occurs due to impaired blood circulation, which provokes a lack of oxygen supplied to the myocardium. According to statistics, it is a heart attack that provokes the majority of deaths. If changes occur in the heart that can lead to the death of myocardial tissue, then it is important to notice them in time. ECG (electrocardiography) helps to diagnose serious heart problems in a timely manner and prevent them from developing into a dangerous condition.

Heart attack symptoms

A heart attack is classified according to its manifestations.

• Anginal. This type of heart attack is the most common. In such a situation, the pain is very intense and lasts more than thirty minutes. The pains are of a pressing or contracting nature and are localized behind the chest, and it is impossible to get rid of it even with the help of medications. Pain is given to the left side of the sternum, the left upper limb, jaw and even the spine. A patient with such a diagnosis experiences weakness, anxiety, is afraid of an imminent death, and sweating occurs in an enhanced mode.
• Asthmatic infarction. The main symptoms of such a problem are breathing problems and an accelerated heartbeat. Often such a heart attack is painless, but sometimes painful sensations occur before bouts of difficulty breathing. The asthmatic type mainly affects the elderly and patients who have already experienced a heart attack at least once.
• gastralgic. This type is distinguished by a specific localization of pain, since unpleasant sensations occur at the top of the peritoneum. Sometimes the pain goes to the shoulder blades and back. In such a situation, the patient hiccups, he has an eructation, he is sick and even vomits. If there is intestinal obstruction, then the stomach may swell.

• Cerebrovascular infarction. A sign of such a disease is the manifestation of cerebral ischemia. The patient often feels dizzy, nauseous and vomits, he loses consciousness, and there are bouts of disorientation in space. In such a situation, it is difficult for doctors to make a correct diagnosis, as they are confused by neurological symptoms, and it becomes possible to accurately determine the presence of the disease only after ECG diagnostics.
• arrhythmic infarction. Symptoms of this type are manifested in changes in the heart rhythm. The patient notices short cardiac arrests and disturbances in its functioning. A person does not notice any special painful sensations, or they appear very little. With arrhythmic infarction, there is a feeling of weakness, respiratory failure, loss of consciousness and other manifestations that are provoked by a decrease in pressure.
• Asymptomatic infarction. It becomes possible to detect a transferred asymptomatic myocardial infarction after an ECG. It is impossible to notice a heart attack after the fact without an ECG, but before it occurs, the patient sometimes has symptoms of a heart attack, albeit weak, but still. Such manifestations include sudden loss of strength, problems with breathing and heartbeat.

Any type of heart attack requires an ECG for an accurate diagnosis. Also, this procedure will help prevent such serious problems at the first manifestations of disorders of the cardiovascular system.

Causes of myocardial infarction

In most cases, a heart attack is a consequence of circulatory disorders of the coronary arteries.

• Thrombosis of the coronary arteries of the heart. The lumen of the artery is clogged so much that the walls of the heart begin to die. Often, such a death is of a macrofocal nature.

• Stenosis of the coronary vessels of the heart. This pathology is a narrowing of the arterial opening due to a plaque or thrombus. This problem leads to a macrofocal infarction of the heart muscle.
• Stenosing coronary sclerosis. With such a deviation, the lumen between the coronary arteries is greatly narrowed, resulting in small-focal heart attacks (often these heart attacks are subendocardial).

Among all cases of a heart attack, the majority occurs due to atherosclerosis, hypertension, and diabetes. The approach of a heart attack is also affected by bad habits, excess weight, and inactivity. Cause a heart attack conditions in which the heart muscle requires more oxygen.

• stress;
• excessive physical activity;
• anxiety state;
• sudden changes in atmospheric pressure;
• surgical intervention.

The beginning of the development of a heart attack often becomes hypothermia. In this regard, the statistics of heart attacks depends on the time of year. Most heart attacks occur in the winter, and the least in the summer. Despite such temperature statistics, hot weather can also provoke a heart attack.

How is a heart attack classified?

A heart attack is distinguished immediately by several signs.

• according to the anatomical characteristics of dying tissues;
• according to the location of the foci of infarction;
• by the number of affected tissues;
• according to the stage of injury.

To prescribe adequate treatment, the doctor needs not only to determine the presence of the heart attack itself, but also to correctly classify it.

How does a heart attack affect ECG readings?

ECG is considered to be the main method for diagnosing a heart attack. Special electrodes are attached to the subject's body, which poison the signals to the ECG device. Such a system captures the electrical signals of the myocardium. There are six leads taken from electrodes that are applied to the limbs. Often this amount is enough for the doctor to be able to diagnose a heart attack. For a detailed diagnosis of the work of the cardiovascular system, it is customary to look at twice as many leads, which include additional chest leads.

During the development of a heart attack, the ECG shows only manifestations of the initial stage of impaired blood flow, unless, of course, they developed right at the time of the procedure.

1. Problems with the conduction of excitation through the tissue of the heart muscle. This complication appears due to complete cell necrosis.
2. Changes in the electrolyte composition. This feature is accompanied by the release of potassium from the affected tissue.

These features require a certain time, so noticeable manifestations of a heart attack are detected only if an ECG is performed several hours after the onset of an attack.

The ECG readings change due to the processes occurring in the zone of the infarct state, distributing it to the following areas:

1. Tissue death. This feature is present only in Q-heart attacks.
2. Cellular damage. Such damage over time can turn into tissue necrosis.
3. Insufficient amount of incoming blood or coronary heart disease. This deviation is only a temporary manifestation, it will disappear soon after a heart attack.

The most informative diagnosis using an ECG device will be in the first few hours after the onset of a heart muscle infarction, since during this period symptoms of impaired blood flow to the heart tissues will be noticeable on the electrocardiogram.

Signs of a heart attack on the ECG

• the absence of an R-wave, or at least its significant decrease;
• the presence of a deep Q-wave;
• elevation above the isoline of the S–T interval;
• negative T-wave value.

Changes are also noticeable in the area opposite the infarction zone. The most noticeable manifestation of a heart attack is considered to be a decrease in the ST interval below the isoline. It should be taken into account that the size of the area with impaired blood flow and its localization in relation to the membranes of the heart on the ECG does not fix all of these changes.

• determine the presence of pathology;
• determine the localization of the infarction;
• find out when a heart attack occurred;

• prescribe an adequate treatment that is best suited in each case;
• make a forecast regarding possible complications (even the risks of death of the patient are calculated).

Any professional physician who has suspicions about a deviation in the work of the heart muscle can send a patient to an ECG. The procedure is carried out by emergency workers in the prehospital period or nurses of resuscitation rooms in a hospital. The decoding of the data is carried out by paramedics in the ambulance or by doctors during hospitalization.

Temporal classification of infarction

1. acute stage. This stage lasts from the first hours to three days. On the film, the acute stage is seen as an elevated ST interval above the infarcted area. Due to this increase, the T-wave becomes invisible.
2. Subacute stage. This stage lasts from three days to three weeks. On the electrocardiogram, a gradual decrease in the ST interval becomes noticeable, and as soon as it reaches the line, the subacute stage is considered over. The T-wave is negative at this time.
3. Scarring stage. Scarring lasts from the first week to several months. At this stage, the T-wave slowly stabilizes, reaching the isoline, and sometimes even acquires a positive value. The R-wave rises, and Q, on the contrary, decreases (unless, of course, it was originally there).

Some believe that an ECG is akin to fluorography to show the state of the internal organs, as in the photo, but in fact the device gives a long printout of a graph that reflects the state of the heart as a curved line.

Classification of a heart attack depending on the size of the focus

The infarct condition also differs in location and the number of tissues that have been affected:

1. Large-focal infarction (it is also called Q-infarction). This pathology has two possible types of development. The first is called transmural, and its affected area covers the entire wall of the heart. On the film, this is manifested by the absence of an R-wave, an extended Q-wave, an increased ST gap, which merges with the T-wave over the focus of the infarction. Also, the ST interval falls below the isoline (this can be recognized by indications from the opposite part of the myocardial infarction), and in the subacute stage, the T-wave is negative. The second variant of Q-infarction is subepicardial. With such a lesion, the focus takes place next to the outer shell. The ECG shows that the R-wave has become smaller, but it can still be fixed, the Q-wave has become wider and larger, the ST interval gradually begins to rise above the infarction zone, the ST interval decreases relative to other leads, and the T-wave, going through the subacute stage, has negative character.
2. Small-focal infarction (another name is heart attack without Q). There are also two types of heart attack. Intramural infarction is a lesion of the inner muscle layer. With such a deviation, the readings of the R- and Q-teeth, as well as the ST gap, do not change in any way. Also, the ECG for at least two weeks shows a negative T-wave. The second option is called subendocardial. The focus of such a heart attack is located near the inner heart membrane. On the film, the R- and Q-teeth remain unchanged, the S-T gap falls below the isoline by 0.02 mV or more, and the T-wave is smoothed out or remains unchanged.

Classification of a heart attack depending on the location of the foci

It is possible to determine where a heart attack has developed thanks to the ECG readings. This effect is achieved using electrodes that are attached to various places around the myocardium.

• basic three electrodes;
• three reinforced electrodes (right arm and leg, as well as the left arm);
• six chest electrodes.

ECG readings vary greatly in different foci of a heart attack.

1. The base two leads and the electrode on the left hand show that the Q wave is unusually deep and the ST gap is above the line and creates one solid curve with the T wave.
2. The base three leads and the electrode on the right arm detect that the S-T gap has dropped below the line, creating a negative T-wave.
3. Three chest leads (located at the transition to the top and the 4th chest). They register the absence of an R-wave, but in its place there is an extended QS-complex, and the ST gap rises above the isoline by more than a few millimeters.
4. Right arm lead and 4th, 5th, 6th chest lead showing a flat T-wave and slight ST gap depression.

With a lateral Q-infarction, the indications also have differences.

• deepened and extended Q-prong;
• higher than normal S-T gap;
• The T-tooth creates a single line with an S-T gap.

• deep and extended Q-tooth;
• significant elevation above the ST interval line;

Q-infarction of the posterior or diaphragmatic nature is detected according to the following indications:

• Basic 2nd, 3rd leads and the electrode on the right leg show that the Q-tooth is deepened and widened, the S-T gap rises above the line, merging with the T-tooth, and the T-tooth itself has a positive appearance.

• Base lead 1 captures the shift of the ST gap under the isoline.
• Often, chest electrodes from the 1st to the 6th register a decrease in the S-T gap below the level of the line and a change in the T-wave (becomes similar to negative).

1. Baseline lead 1, left arm electrode, chest lead 1, 2 show that the Q wave is deepened, the S-T gap is raised, and the T wave looks positive.
2. The 1st and 2nd chest electrodes show an increased state of the R-wave, a decrease in the S-T gap to the level of the isoline or even below it, and atrioventricular block is often detected.

1. Baseline 1, left arm lead, and chest electrodes 1 to 4 describe a positive T-wave value (even higher than the R-wave).
2. Basic 2nd and 3rd leads fix a smooth decrease in the ST interval, a negative T-wave, and a decrease in the R-wave.
3. The thoracic 5th and 6th electrodes show a semi-positive T-wave value with a decrease in the second part below the line.

Posterior subendocardial non-Q infarction has the following characteristics.

• R-tooth goes down;
• T-prong is positive;
• the S-T gap gradually decreases.

Right ventricular infarctions also occur, which complement anterior left ventricular pathology due to a single source of blood flow. It is difficult to recognize such a lesion on an ECG, since additional leads are often required for diagnosis (although even with additional electrodes, the chance of detection is low). In this case, the best diagnosis will be an ultrasound of the heart. If an acute violation of blood flow to the heart muscle is suspected, then there must be twelve electrodes. A standard six-electrode examination will not show the required data.