Cardiac ischemia electrocardiogram

This is an automatically translated article.

The article was professionally consulted by Specialist Doctor II Nguyen Quoc Viet - Interventional Cardiologist - Department of Medical Examination & Internal Medicine - Vinmec Danang International General Hospital.
Electrocardiogram is a very valuable medical technique, used to diagnose and localize coronary artery occlusion in ischemic heart disease. On the other hand, the electrocardiogram also plays an important role in monitoring and evaluating the progress of coronary revascularization in ST-segment elevation myocardial infarction.

1. What is an electrocardiogram?

An electrocardiogram (ECG) is a method of monitoring the activity, speed, and rhythm of the heart. When the heart contracts, it generates fluctuations in electrical current. An electrocardiogram is a curve that records these variations. Through the electrocardiogram, the doctor can see the heart's ability to eject blood, the rhythm and speed of the heart.
The leads will examine different myocardial regions:
V1, V2: "look" in front of the interventricular septum. V3, V4: “look at” the anterior apex. V5, V6: “look at” the lower left ventricular wall. D1, aVL: “look at” the left ventricular superior wall. V7, V8, V9: “look at” the posterior wall of the left ventricle. D2, D3, aVF: “look at” the left ventricular inferior wall. V3R, V4R: “look at” the right ventricle.

Electrocardiogram ischemic myocardial
ST depression. T wave inversion becomes negative, symmetric Pathological Q wave: Q wave is > 2mm deep, > 0.04s wide, this is a late sign after myocardial infarction. If no ST segment elevation is detected, the ECG changes over time or upon recovery such as: ST depression, transient ST elevation, T wave reversal are also very valuable in diagnosing myocardial ischemia. . However, up to 20% of cases of myocardial ischemia have no ECG changes. Therefore, monitoring the evolution of electrocardiographic changes according to the progression of angina and symptoms of myocardial ischemia is extremely necessary.
The ischemic electrocardiogram will be repeated after 90 minutes in cases of thrombolysis or immediately after PCI to assess the extent of revascularization and reperfusion of the patient. coronary artery.

2. Electrocardiogram of acute myocardial infarction

Myocardial ischemia: high-positive or negative-pointed T waves, symmetrical. Signs of myocardial necrosis: Appearance of new Q waves (at least 40 ms wide or ≥ 1⁄4 R waves) in 1 of the following lead domains: D2, D3, and aVF; V1 to V6... ST segment elevation or depression in one of the above lead domains.

Stages of myocardial infarction:
fulminant stage: in the first 24 hours, ST segment elevation, arch arch, high and sharp T intermingled with ST segment. Acute stage: in the first 1, 2 days, arch wave may appear, pathological Q wave may appear, QT lengthening, ST elevation decreased, T wave is more negative. Subacute phase: From a few days to a few weeks is the most common stage, the ST segment is lower, the T negative is deep, pointed, and symmetrical. Simultaneously, a distinct pathological Q wave and QT interval prolongation were observed. During this stage, arrhythmias or atrioventricular block are often present, especially in septal (interventricular) infarction. Chronic phase: From a few months to several years, ST returns to isoelectric, T may become positive again, and pathological Q is often permanent.

3. Types of myocardial infarction

The above signs are not always present in all the same leads, but only clearly seen in the lead where the electrode is placed (directly) on the infarcted myocardium, called imaging. direct. In contrast, leads with electrodes placed in the contralateral radial region of the infarct region will obtain contrasting, "mirrored" findings of these or indirect images.

Infarction can occur in many different areas of narrowing of the left ventricle (right ventricle rarely occurs). Depending on the affected area, people are divided into 4 main and most common types (subepicardial) with the following stage 2 (subacute) signs:
Anterior septal infarction: anterior wall of the left ventricle and anterior portion of the interventricular septum. Image of QS wave, ST elevation, negative T in V2, V3, V4. Sometimes T waves are low or negative in V5, V6, aVL, D1 (T1>T3) because the ischemic area spreads to the lateral (left) wall of the left ventricle. Lateral wall infarction of the anterior and lateral wall of the left ventricle. Deep and wide Q, ST elevation, and deep negative T in V5, V6, D1, aVL. ST segment depression, very high positive T at D3, sometimes aVF. Posterior infarction: in the posterior and inferior walls of the left ventricle. Deep, wide Q, ST elevation, deep negative T in D2, D3, aVF. Indirect images: T is high positive, can be pointed, symmetrical, ST can be depressed in V1, V2, V3, V4. Non-ST-elevated myocardial infarction (NSTEMI) or Subendocardial infarction (left ventricle): Primarily anterior-lateral: ST depression, sometimes T deformity in V5, V6, D1 , aVL. Sometimes the posterior wall is below the ST segment depression at D3, D2, aVF.

3.1. ST segment elevation in any position will indicate the location of myocardial infarction V1, V2: myocardial infarction in the anterior septum.
V3, V4: myocardial infarction in the anterior apex.
V1, V2, V3, V4: anterior apical myocardial infarction.
V5, V6: low lateral myocardial infarction.
D1, aVL: high lateral myocardial infarction.
V5, V6, D1, aVL: lateral myocardial infarction.
V3, V4, V5, V6: anterolateral myocardial infarction.
From V1 to V6, with D1, aVL: large anterior myocardial infarction.
D2, D3, aVF: myocardial infarction of the lower wall (diaphragm)
V7, V8, V9: myocardial infarction of the posterior wall.
D2, D3, aVF with V7, V8, V9: posterior inferior myocardial infarction.
V3R, V4R: right ventricular myocardial infarction.

3.2. Case of electrocardiographic changes not due to coronary artery disease Acute pericarditis. Electrolyte disorders: hyperkalemia. Digoxin poisoning. WPW syndrome. Brugada syndrome. ST elevation in traumatic brain injury. Use a pacemaker. Electrocardiogram is a very valuable medical technique, used to diagnose and localize coronary artery occlusion in ischemic heart disease. In addition, they also play an important role in monitoring and evaluating the progress of coronary revascularization in ST-segment elevation myocardial infarction. Therefore, the patient should choose reputable and well-qualified examination addresses to perform this method, thereby giving the results, the doctor will determine the best treatment regimen for the patient.
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