Myocardial infarction on ECG
The content of the article:
- ECG signs of myocardial infarction
- Stages of myocardial infarction on the ECG
- The main types of heart attack on the ECG
- Video
Myocardial infarction on the ECG has a number of characteristic features that help differentiate it from other conduction and excitability disorders of the heart muscle. It is very important to conduct ECG diagnostics in the first few hours after the attack in order to obtain data on the depth of the lesion, the degree of functional heart failure, and the possible localization of the focus. Therefore, the cardiogram is removed, if possible, while still in the ambulance, and if this is not possible, then immediately upon the patient's arrival at the hospital.
Electrocardiography is the main method for diagnosing myocardial infarction
ECG signs of myocardial infarction
The electrocardiogram reflects the electrical activity of the heart - by interpreting the data of such a study, one can obtain comprehensive information about the work of the conducting system of the heart, its ability to contract, pathological foci of excitation, as well as the course of various diseases.
The classic ECG pattern consists of several sections that can be seen on any normal tape. Each of them is responsible for a separate process in the heart.
- P wave - visualization of atrial contraction. By its height and shape, one can judge the state of the atria, their well-coordinated work with other parts of the heart.
- PQ interval - shows the propagation of the excitation pulse from the atria to the ventricles, from the sinus node down to the atrioventricular. The lengthening of this interval indicates a violation of conductivity.
- The QRST complex is a ventricular complex that provides complete information about the state of the most important chambers of the heart, ventricles. Analysis and description of this part of the ECG is the most important part of the diagnosis of a heart attack, the main data is obtained from here.
- The ST segment is an important part, which is normally an isoline (a straight horizontal line on the main axis of the ECG that does not have teeth), with pathologies capable of rising and falling. This may be evidence of myocardial ischemia, i.e., insufficient blood supply to the heart muscle.
Any changes in the cardiogram and deviations from the norm are associated with pathological processes in the heart tissue. In the case of a heart attack - with necrosis, that is, the death of myocardial cells with their subsequent replacement with connective tissue. The stronger and deeper the damage, the wider the zone of necrosis, the more noticeable the changes in the ECG will be.
The first sign that you should pay attention to is the deformation of the QRST complex, in particular, a significant decrease in the R wave or its complete absence. This indicates a violation of ventricular depolarization (an electrophysical process responsible for the contraction of the heart).
Further, the changes affect the Q wave - it becomes pathologically deep, which indicates a disruption in the work of pacemakers - nodes of special cells in the thickness of the myocardium, which begin to contract the ventricles.
The ST segment also changes - it is normally on the isoline, but with a heart attack it can rise higher or lower. In this case, one speaks of segment elevation or depression, which is a sign of ischemia of the heart tissues. By this parameter, it is possible to determine the localization of the ischemic injury area - the segment is raised in those parts of the heart where the necrosis is most pronounced, and is omitted in opposite leads.
Also, after some time, especially closer to the stage of scarring, a negative deep T wave is observed. This wave reflects massive necrosis of the heart muscle and allows you to establish the depth of damage.
Photo ECG with myocardial infarction with decoding allows you to consider the described signs in detail.
Typical ECG signs of myocardial infarction are found at all stages
The tape can move at a speed of 50 and 25 mm per second, a lower speed with better detail is of greater diagnostic value. When making a diagnosis of a heart attack, not only changes in leads I, II and III are taken into account, but also in enhanced ones. If the device allows you to record chest leads, then V1 and V2 will display information from the right heart - the right ventricle and atrium, as well as the apex, V3 and V4 about the apex of the heart, and V5 and V6 will indicate the pathology of the left sections.
Stages of myocardial infarction on the ECG
A heart attack occurs in several stages, and each period is marked by special changes in the ECG.
- The ischemic stage (the stage of injury, the most acute) is associated with the development of acute circulatory failure in the tissues of the heart. This stage does not last long, so it is rarely recorded on the cardiogram tape, but its diagnostic value is quite high. The T wave at the same time increases, sharpens - they speak of a giant coronary T, which is a harbinger of a heart attack. Then ST rises above the isoline, its position is stable here, but further elevation is possible. When this phase lasts longer and becomes acute, a decrease in the T wave can be observed, as the necrosis focus extends to the deeper layers of the heart. Reciprocal, reverse changes are possible.
- The acute stage (necrosis stage) occurs 2-3 hours after the onset of the attack and lasts up to several days. On the ECG, it looks like a deformed, wide QRS complex, forming a monophasic curve, where it is almost impossible to distinguish individual teeth. The deeper the Q wave on the ECG, the deeper the layers were affected by ischemia. At this stage, a transmural infarction can be recognized, which will be discussed later. Rhythm disturbances are characteristic - arrhythmias, extrasystoles.
- The onset of the subacute stage can be recognized by the stabilization of the ST segment. When it returns to the baseline, the infarction no longer progresses due to ischemia, the recovery process begins. Of greatest importance in this period is the comparison of the existing sizes of the T wave with the original ones. It can be either positive or negative, but will slowly return to the baseline in sync with the healing process. The secondary deepening of the T wave in the subacute stage indicates inflammation around the zone of necrosis and does not last long, with proper drug therapy.
- In the stage of scarring, the R wave rises again to its characteristic indicators, and the T is already on the isoline. In general, the electrical activity of the heart is weakened, because some of the cardiomyocytes have died and are replaced by connective tissue, which does not have the ability to conduct and contract. Pathological Q, if present, is normalized. This stage lasts up to several months, sometimes six months.
The main types of heart attack on the ECG
In the clinic, a heart attack is classified depending on the size and location of the lesion. This is important in the management and prevention of delayed complications.
Depending on the size of the damage, a distinction is made between:
- Large focal, or Q-infarction. This means that a circulatory disorder has occurred in a large coronary vessel, and a large volume of tissue is affected. The main feature is deep and widened Q, and the R wave cannot be seen. If the infarction is transmural, that is, affecting all layers of the heart, the ST segment is located high above the isoline, in the subacute period there is a deep T. If the damage is subepicardial, that is, not deep and located next to the outer shell, then R will be recorded, albeit small.
- Small focal, non-Q-infarction. Ischemia has developed in areas fed by the terminal branches of the coronary arteries; this type of disease has a more favorable prognosis. With intramural infarction (damage does not extend beyond the heart muscle) Q and R do not change, but a negative T wave is present. In this case, the ST segment is on the isoline. With subendocardial infarction (focus in the inner membrane), T is normal, and ST is depressed.
Q-infarction is one of the most dangerous lesions of the heart muscle
Depending on the location, the following types of heart attack are determined:
- Antero-septal Q-infarction - noticeable changes in 1-4 chest leads, where there is no R in the presence of a wide QS, ST elevation. In I and II standard - classic for this type of pathological Q.
- Lateral Q-infarction - identical changes affect 4-6 chest leads.
- Posterior, or diaphragmatic Q-infarction, it is also lower - pathological Q and high T in II and III leads, as well as enhanced from the right leg.
- Ventricular septal infarction - in I standard deep Q, ST elevation and high T. In 1 and 2 chest pathologically high R, AV block is also characteristic.
- Anterior non-Q-infarction - in I and 1-4 chest T1 / 2 higher than the stored R, and in II and III, a decrease in all waves along with ST depression.
- Posterior non-Q infarction - in standard II, III and chest 5-6 positive T, decrease in R and ST depression.
Video
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Nikita Gaidukov About the author
Education: 4th year student of the Faculty of Medicine No. 1, specializing in General Medicine, Vinnitsa National Medical University. N. I. Pirogov.
Work experience: Nurse of the cardiology department of the Tyachiv Regional Hospital No. 1, geneticist / molecular biologist in the Polymerase Chain Reaction Laboratory at VNMU named after N. I. Pirogov.
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