ECG in pathology
Last reviewed: 23.04.2024
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The electrical activity of the atria is evaluated by the tooth P. This prong is normally positive (directed upwards) in most leads (except for the aVR lead).
The enlargement of the left atrium and its hypertrophy are characterized by the following features: the tooth P increases, expands and becomes serrate in the leads I and II (P mitrale).
ECG after exercise
ECG registration after exercise is used to detect changes that are not at rest. For this purpose, use a load on a bicycle ergometer or treadmill (treadmill). The load is carried out to a sub-maximal increase in the heart rate, the appearance of anginal pain or significant depression of the ST segment, the occurrence of various arrhythmias and conduction disorders. The load also stops when there are signs of impaired circulation with a decrease in the filling of the pulse, a decrease in blood pressure. The most common, positive reaction to the load, indicating the presence of ischemic changes, is horizontal or descending depression, less often the rise of the ST segment. The sensitivity of this test is approximately 50% and the specificity is 90%. This means that among patients with stenotic atherosclerosis and myocardial ischemia (in every second) this test will be positive. With a positive test with physical exertion from 10 patients, 9 have stenosing lesions of the coronary arteries.
A test with physical activity allows a differential diagnosis for pain in the heart, confirming or excluding their ischemic genesis with a high degree of probability. The test also makes it possible to evaluate the functional capabilities of a patient suffering from coronary heart disease and, in particular, after a previous myocardial infarction. Rapid, within 6 minutes, the appearance of signs of ischemia indicates an unfavorable prognosis. In this case, calculate the power developed by the patient and the work that he performs. Normally, with physical exertion, the heart rate increases, systolic and diastolic pressure increases. On the ECG, the teeth T remain positive, and the ST segment in individual leads is only slightly depressed, but within 1 mm. Pathological changes in the ECG under load are characterized by a decrease in the ST segment by more than 1 mm. A marked manifestation of pathology can also be rhythm disturbances. In addition to the previously indicated symptoms of ischemia, there may also be the appearance of gallop rhythm at the height of physical activity, as well as systolic noise as a result of papillary muscle dysfunction. ECG after exercise has a lower diagnostic value in patients with pre-existing ST segment changes, left ventricular hypertrophy, and digoxin treatment. It should not be performed with physical exertion in unstable angina, acute myocardial infarction, severe aortic stenosis, severe hypertension, heart failure and other serious heart lesions, as well as previously proven stenosing coronarosclerosis.
ECG monitoring
Continuous ECG recording ( Holter monitoring ) is used to recognize transient rhythm disturbances, in particular to evaluate the effectiveness of antiarrhythmic therapy, as well as the diagnosis of myocardial ischemia. The frequency of episodes of arrhythmia or extrasystole and their nature can be quantified and compared with clinical manifestations. In this case, the ECG is recorded in the usual, habitual for the patient physical activity. Changes in the segment of the ST and the T wave detected during monitoring are important for the diagnosis of ischemia, especially when they are associated with the load.
Indication for ECG monitoring is the presence of symptoms such as palpitations, fainting or pre-stupor states, dizziness, indicating the possibility of arrhythmia and in the absence of the latter on a registered ECG. If the described symptoms occur, and if there is no arrhythmia, you should look for other causes of these manifestations.
Magnetic recording of the ECG in Holter monitoring is carried out within 6-24 hours. At the same time, the patient leads a habitual way of life. In the future, magnetic recording is read on a special device at a high speed, and individual parts of this record can be played on paper.
Explanation of results
P wave P becomes biphasic in lead V1. The enlargement and hypertrophy of the right atrium can be established by the appearance of a high, spike-shaped P wave with an amplitude exceeding 2.5 mm in the leads II, III (P pulmonale). In normal conditions, the right atrium first develops, later on the left atrium. However, these processes are brought together in time, and therefore the tooth P looks only slightly bifurcate. With hypertrophy of the right atrium, its electrical activity increases, while the processes of excitation of both atriums are folded, which is expressed in the appearance of the P wave of a higher amplitude. With hypertrophy of the left atrium, the component of the P-wave associated with it increases in time and amplitude, which is manifested in the appearance of a broadened and two-humped P wave in the leads I and II.
The tooth P can disappear, be replaced by several small waves, which is observed in atrial arrhythmias.
Hypertrophy and an increase in the ventricles of the heart can be diagnosed by ECG analysis, but not always accurately enough. Hypertrophy of the left ventricle is established by the following features: the electric axis of the heart deviates to the left, the amplitude of the tooth R1 + S3 is more than 2.5 mV. RV5 (or RV6) + SV6 is greater than 3.5 mV. In addition, the ST segment decreases in I, II and V5.6, leads.
Hypertrophy of the right ventricle is recognized by the following features: high R in right thoracic leads and deep S in left thoracic leads (ratio R: S in lead V1 greater than 1); deviation of the electric axis of the heart to the right; decrease in the ST segment; negative T wave in right thoracic leads.
The increase in the voltage of the QRS complex is possible in young people and is normal.
Violations of intracardiac conduction are diagnosed most reliably by ECG. Interval PQ, reflecting the atrioventricular conduction, with its violation is prolonged. When there is a violation of intraventricular conduction, which is associated with lesions of the legs of the bundle, a deformation of the QRS complex and its elongation to 0.12 s and higher are noted.
ECG is important for diagnosing and monitoring patients with coronary heart disease. The most characteristic sign of myocardial ischemia is horizontal depression (decrease) by 1 mm and below the ST segment in I, II and thoracic leads. In typical cases, this is clearly manifested with physical activity. Another sign is the presence of a negative T wave in the same leads, and there may be no ST segment depression. However, these changes are in principle nonspecific, and therefore they should be evaluated in conjunction with clinical data, primarily with the nature of the pain syndrome in the heart.
The appearance of the focus of necrosis in the myocardium (myocardial infarction) is accompanied by characteristic ECG changes, especially in those leads that best reflect the electrical activity of the affected area of the heart. In the lead, reflecting the activity of the sites of the myocardium located against the affected (for example, the anterior wall of the left ventricle is opposed to the posterior wall), there are opposite changes, especially the ST segment. With the transmural focal point, a pronounced Q wave appears, sometimes with a decrease in the R wave and a characteristic rise in the ST segment. When observing the process, a gradual return of the ST segment to the isoelectric line with the dynamics of the QRS complex is noted in the dynamics. With myocardial infarction of the anterior wall, these changes are best seen in the thoracic leads V4-6, in the form of a decrease in the R wave. With infarction of the posterior wall of the left ventricle, they are best seen in leads using the electrode from the left leg, ie II, III and aVF.
In many patients with a variety of cardiac abnormalities, nonspecific changes in the ST segment and in the T wave are observed, which should be assessed in comparison with clinical data. A variety of ECG changes are associated with metabolic disorders, electrolyte balance and the influence of drugs. Hyperkalemia is characterized by a high symmetrical peak-shaped T-wave with a narrow base, hypokalemia - depression of the ST segment, flattening of the T wave, appearance of a pronounced U wave. Hypercalcemia is expressed in shortening of the QT interval. Prolonged treatment with cardiac glycosides may be accompanied by depression of the ST segment, a decrease in the T wave, a shortening of the QT. Expressed violations of repolarization, ie ST-T, can occur with a cerebral infarction or cerebral hemorrhage.
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