Cardiology

Signs of ischemia on the ECG: how to determine

What is ischemia and how does it affect the myocardium

Ischemia is a decrease in blood supply to an organ or tissues due to insufficient arterial blood flow. Short-term current limitation does not lead to irreversible damage, long-term - causes consequences in the form of tissue death (necrosis) of the area that supplies the diseased vessel.

Organs with a high level of oxygen consumption (heart and brain) are most sensitive to insufficient blood flow.

IHD is an acute or persistent inadequacy of the oxygen demand of cardiomyocytes and the ability of the circulatory system to deliver oxygen due to coronary artery disease. In ischemia, a decrease in blood flow occurs due to a combination of vascular stenosis and wall tone abnormalities caused by endothelial dysfunction (inner lining of arterioles).

In most patients with coronary artery disease, the main pathological process in the coronary vessels is atherosclerosis. A specific symptom of the disease is pain in the chest during physical and emotional stress, which pass at rest or after the "Nitroglycerin" tablet.

Myocardial ischemia develops when the lumen of the coronary artery is blocked by a cholesterol plaque by 70% or more. In such cases, even the maximum dilation of small vessels does not provide cardiomyocytes with sufficient blood, and signs of oxygen starvation develop during physical or emotional stress. Arteries narrowed by 90% do not supply the heart with oxygen even at rest.

Drawing. The reasons for the narrowing of the lumen of the coronary vessels.

The process is aggravated by impaired microcirculation due to increased blood clotting and the formation of small blood clots in the branches of the coronary artery.

Ischemic damage to cardiomyocytes causes:

  1. Disorders of the energy supply of cardiomyocytes.
  2. Changes in the properties and structure of cell membranes, enzyme activity and electrolyte imbalance.
  3. Failures of the genetic program of myocardial cells.
  4. Disorders of autonomic innervation of cardiac activity.
  5. Remodeling of the myocardium (disordered growth of cardiomyocytes, an increase in the mass of connective tissue).

Such changes lead to a progressive decrease in myocardial contractility, limitation of its functionality and the development of heart failure.

Ischemia does not persist for a long time. Either adequate blood flow to the organ is restored, or muscle fiber damage occurs. The most vulnerable is the subendocardial (inner) layer of the myocardium, which is poorly supplied with blood and is exposed to pressure.

IHD classification according to ICD-10:

  1. Angina pectoris:
    • Stable.
    • Unstable.
    • With vasospasm.
    • Unspecified.
  1. Acute myocardial infarction (MI):
    • Transmural.
    • Subendocardial.
    • Repeated.
  1. Complications of MI.
  2. Other forms:
    • Painless ischemia.
    • Coronary thrombosis.
    • Acute ischemic heart disease.
    • Dressler's Syndrome.

Electrocardiographic signs of coronary artery disease

Changes in the ECG in ischemic heart disease are caused by oxygen deficiency arising from the pathology of the coronary vessels and energy disturbances in cardiomyocytes.

Methods for detecting ischemia:

  1. Simple 12-lead ECG.
  2. With additional leads - for the diagnosis of certain localizations of ischemia, which are not recorded with a conventional ECG.
  3. Holter monitoring (ECG recording for 24-48 hours).
  4. Exercise ECG (stress test) - to determine latent pathology.
  5. With medicinal samples.

In 50% of patients with coronary artery disease at rest, there are no signs of ischemia on the ECG. Therefore, the "gold standard" in the outpatient diagnosis of such a disease is an exercise test. This procedure solves several problems at the same time:

  • detection of latent coronary insufficiency;
  • registration of fleeting rhythm disturbances;
  • designation of the threshold of exercise tolerance.

Photo 1. Bicycle ergometry.

The most commonly used are bicycle ergometry or treadmill test (treadmill). In a person with healthy vessels, such a load causes dilatation of the coronary arteries and an increase in myocardial contractility, which is necessary to ensure adequate blood flow. In the case of coronary artery disease, the coronary arteries are already in a dilated state before loading and do not compensate for the needs. As a result, angina pectoris occurs and ischemia is recorded on the ECG.

Bicycle ergometry is done on a special exercise bike. ECG sensors and a tonometer cuff are fixed on the patient to monitor hemodynamic parameters. The procedure takes 15-20 minutes. During this time, the load gradually increases from 25 to 50 watts. Patients with severe heart disease are allowed to take short breaks.

The test is stopped if:

  • ECG changes in the ST segment;
  • an attack of chest pain;
  • drop in blood pressure;
  • increase in blood pressure more than 200 mm Hg. Art .;
  • reaching the threshold heart rate for a given age;
  • severe shortness of breath;
  • serious rhythm disturbances;
  • dizziness, severe weakness, nausea;
  • patient refusal.

Photo 2. Treadmill test.

The treadmill test differs from bicycle ergometry only in that the patient performs physical activity on a treadmill with a changing angle of inclination.

Exercise tests are contraindicated for:

  • acute coronary syndrome;
  • unstable course of angina pectoris;
  • severe circulatory failure;
  • stroke;
  • thrombophlebitis;
  • hypertensive crisis;
  • severe arrhythmias;
  • decompensated heart defects;
  • severe pain in diseases of the musculoskeletal system.

Ischemia slows down the processes of repolarization in the cardiomyocyte or changes the direction of the electrical wave. On the ECG in IHD, these violations correspond to widening, depression and changes in the configuration of the ST segment. In acute coronary syndrome, the main pathological changes are observed in the QRS complex and the S-T segment.

The degree of changes on the ECG is directly related to the extent of the process and the duration of ischemia. With stable angina pectoris, the signs of coronary insufficiency on the cardiogram taken in the interictal period may not be determined. And in the case of myocardial infarction, violations are recorded in the acute phase, and after several years.

One of the early signs of coronary blood flow insufficiency is the appearance of a distinct sharp border of the transition of the S-T segment into the T wave. Further growth of atherosclerotic plaque aggravates the S-T depression below the isoline.

Types of depression of the S-T interval in coronary artery disease:

Offset typeS-T intervalT wave
HorizontalParallel and below the isolinePositive (+), negative (-) or biphasic
Oblique downwardWith distance from the ORS complex, the degree of S-T depression increases.+/-, smoothed
Arc, roundness upThe degree of displacement varies throughout, in the form of an arcOf any kind
Oblique ascendingMost S-T depression is just behind the QRSPositive, smoothed
Trough-shapedArc shape with convexity, top downAny kind
Rise of the S-T segment above the contourRounded, arched with apex downwardsPositive, smoothed

Changes in the S-T segment in coronary artery disease are most clearly visible in the leads:

  • V4-V6;
  • II, III;
  • aVF, I, aVL.

Unlike acute coronary syndrome in IHD, S-T changes are stable over months and even years.

S-T segment depression is present when:

  • ventricular hypertrophy;
  • myocarditis;
  • pericarditis;
  • Digitalis therapy;
  • hypokalemia;
  • myocardial dystrophy;
  • bundle branch block, WPW syndrome;
  • acute pancreatitis, cholecystitis, gallstone disease, diaphragmatic hernia (reflex reaction);
  • pulmonary insufficiency;
  • pulmonary embolism;
  • poisoning with nicotine;
  • Prinzmetal's angina;
  • vegetative dystonia.

The greatest stability in coronary artery disease in changes in the T wave (the so-called "coronary"). It is negative, symmetrical, with an amplitude of more than 5 mm T, which signals serious ischemic damage to the myocardium. A rounded and irregularly shaped tooth indicates less pronounced changes in the heart muscle.

The further the electrode is installed from the place that is supplied with blood by the damaged vessel, the less pronounced the signs of ischemia on the ECG.

T wave changes are recorded in:

  • left chest leads;
  • I;
  • aVL;
  • III;
  • aVF.

But similar changes in the T waves are also observed with:

  • pulmonary embolism;
  • myxoma;
  • myocarditis;
  • constrictive pericarditis;
  • ventricular hypertrophy;
  • blockages of cardiac conduction;
  • electrolyte imbalance;
  • excessive smoking;
  • hypokalemia;
  • dyshormonal processes;
  • stress;
  • taking certain medications.

With a long course of ischemic heart disease on the ECG, the widening of the P wave is manifested. This is an unfavorable prognostic sign regarding the risk of acute coronary syndrome and atrial fibrillation.

A slowdown in electrical conduction is also observed during ventricular systole (Q-T). The heart in conditions of oxygen starvation, which is caused by atherosclerotic cardiosclerosis, takes more and more time to contract.

Due to a decrease in coronary blood flow, arrhythmias and blockages occur:

  • extrasystoles;
  • sinus tachy, bradycardia;
  • atrial flutter;
  • paroxysmal tachycardia;
  • atrioventricular block;
  • blockade of the legs of the bundle of His.

The extreme degree of ischemia of the heart muscle is myocardial infarction. If necrosis affects all layers of muscle, there is a high likelihood of fatal arrhythmias, cardiac arrest, ruptured papillary muscles, thromboembolism, ventricular aneurysm, acute circulatory failure, and cardiogenic pulmonary edema.

With the help of a standard ECG, reliable data on the location and area of ​​the lesion are obtained already at the pre-hospital stage.

The diagnosis of posterior and basal myocardial infarction, when the left ventricle is affected at the point of contact with the diaphragm, is very difficult. In such cases, additional leads V7-V9 and dorsal leads across the sky are required.

How often should a cardiogram be done for a patient with ischemic disease?

The diagnosis of ischemic heart disease is established only on the basis of a detailed survey, examination, description of the ECG at rest and taken during an attack, with physical exertion and, if necessary, performed echocardiography and coronary angiography.

Often, in the early stages of coronary artery disease, ischemic signs on an ECG taken in the interictal period are not detected. Pathology is found during functional exercise testing or Holter monitoring. These methods help to reveal hidden areas of damage and register a painless form of ischemia, which is of great danger.

According to the rules of clinical examination, patients with a stable course of coronary artery disease perform an ECG annually.

Patients with a newly diagnosed diagnosis, who are selected for adequate therapy, have a cardiogram performed more often.

An unscheduled ECG is indicated for:

  • pain attacks atypical for a particular patient;
  • prolonged episodes of angina pectoris;
  • the occurrence of rhythm disturbances.

Additionally, an ECG for myocardial ischemia is indicated before performing veloergometry, coronary angiography, stenting and coronary artery bypass grafting.

Conclusions

ECG is a safe and painless study that can be performed on all patients without exception. Electrocardiography does not require prior preparation.

But remember that the diagnosis of ischemic heart disease by ECG is conditionally reliable only if the study was performed at the time of an attack of angina pectoris. Several pathologies at once have similar indicators when deciphered. A set of diagnostic measures can confirm ischemic heart disease.