Staged ECG changes in myocardial infarction
The main method for diagnosing myocardial infarction is the analysis of electrocardiographic criteria for coronary circulation disorders. ECG - an indispensable study in case of a heart attack, confirming the diagnosis of the disease. It can not be replaced by any other, like the ECG in blockades.
Myocardial infarction or necrosis is characterized by non-recurrent changes in muscle fibers. Necrotic tissue does not participate in the excitation. Therefore, on the ECG over the necrosis site, there is a violation of the ventricular myocardial depolarization, which is manifested by a change in the QRS complex. This change consists in a decrease in the R wave and deepening of the Q wave. Myocardial infarction is characterized by the dynamics of changes in the electrocardiogram. It shows the presence of three zones of a heart attack - the central site of necrosis, the zone of damage surrounding necrosis, and the ischemic zone around the area of injury.
A section of necrotically altered tissue with myocardial infarction can cover the entire thickness of the muscular wall of the heart. Such a heart attack is called transmural. If necrosis is located under the endocardium - subendocardial, under the epicardium - subepicardial, in the thickness of the heart muscle - intramural.
On the ECG, regardless of the clinical form of the infarct, a regular pattern is observed, which is determined by the localization, depth, spread of the heart muscle damage and the stage of the process. ECG signs of myocardial infarction vary depending on the stage of the disease.
A typical course of myocardial infarction is divided into four stages: acute, acute, subacute and stage scarring.
ECG with myocardial infarction in the most acute stage
The disease begins with the acute stage of myocardial infarction. This is the time from the onset of severe myocardial ischemia to the formation of signs of necrosis. On the ECG, this stage is characterized by the appearance of an arched ST segment that merges with the tooth R on one side and the T tooth on the other. Thus, the Pardi arc typical for myocardial infarction or the "cat's back" symptom is formed.
ECG with myocardial infarction in the acute stage
In the acute stage of the infarction, the necrosis site is finally formed and myomalation develops( softening of the altered myocardium).The pathological Q wave forms on the ECG. It gradually becomes broad and deep, which indicates the development of the necrosis zone. Simultaneously with the appearance of this wave, the ST segment begins to decrease, which indicates a reduction in the damage zone. At the same time, the acute negative tooth T.
ECG begins to form with myocardial infarction in the subacute stage of
. During the subacute stage, the initial processes of scar organization are completed. The main ECG symptom of this stage is the gradual reduction of the ST segment to the isoline and the final formation of a deep, symmetrically pointed, so-called coronary wave. At this time, Zubets Q acquires its shape, which remains unchanged for many years or remains for life.
ECG with myocardial infarction in the cicatricial stage
In the cicatrical stage, the scar is compacted. A characteristic feature of this stage is the location of the ST segment on the isoelectric line. About the transferred infarction is indicated by pathological Q wave and stably negative T wave. With time, the magnitude of the negative T wave can decrease, and even a positive T wave may appear.
With small-focal myocardial infarction, ECG changes are limited by a slight shift of the ST segment from the isoline upwards or downwards, dependingfrom the location of the infarction, and inversion of the T wave.
Myocardial infarction develops mainly in the left ventricle. The localization of the focus of necrosis in the myocardium is indicated by the appearance of electrocardiographic signs characteristic of the infarction in the corresponding leads.