Angina pectoris or angina is a temporary pain or discomfort in the chest. Clinically, it is defined as a syndrome resulting from myocardial ischemia (injury or disease in the major blood vessels of the heart), caused by a decrease in blood flow to the heart muscle. It is characterized by discomfort near the sternum, but can be felt anywhere in the body, from the epigastrium, jaws, shoulders, back or arms that appears on exercise or stress. Symptoms are usually described as tension, tightness, or heaviness and may be accompanied by a feeling of constriction, strangulation, or burning.

Angina can be stable when it develops during physical activity, or unstable when it occurs during periods of rest, the latter manifestation can be more severe. It should be noted that angina is not a heart attack, but it is a sign of cardiac risk, so the patient must eliminate possible factors that cause the disease to progress and the symptoms to reappear or worsen. Tests used to diagnose and confirm angina include electrocardiogram, chest x-ray, blood tests, stress test, echocardiogram, heart computed tomography, cardiac magnetic resonance imaging, and coronary angiography.

Electrocardiogram as initial diagnostic test for angina pectoris detection

To detect this syndrome, any patient with suspected angina should initially undergo an electrocardiogram. The study technique allows to determine signs of ischemic heart disease, such as a previous myocardial infarction or repolarization disturbances, shows the rhythm of heart function. It should be noted, this test at rest is quite frequent even in patients with severe angina and does not exclude the diagnosis of ischemia. The methodology is characterized by being quick and painless, sensitive and specific to measure the electrical activity of the heart. It is preferably used to identify inducible ischemia in most patients with stable angina.

What is an Electrocardiogram and how is it performed?

The electrocardiogram is the graphic representation of the heart’s electrical activity, in which voltage variations are studied as a function of time, which usually does not exceed about 30 seconds. These changes are the result of depolarization and repolarization of the cardiac muscle, which produce electric fields when they reach the surface of the body where the electrodes are placed. This electrical activity is recorded in a special format on strips of millimeter paper, or on a screen if the equipment is modern.

To perform an electrocardiogram is a simple procedure. For this, an electrocardiograph with the respective accessories for the measurement is needed, and the procedure is as follows:

• The patient lies on a stretcher horizontally, with the chest uncovered.
• The technical professional places a total of ten electrode patches distributed on the chest, and sometimes on the arms and legs. Of these, six patches are placed on six specific points on the chest in the so-called precordial region, and four on the leads on each extremity. The information obtained in each region provides a different electrocardiographic view.
• The electrodes are connected to a computer that displays the results. The cardiac activity is displayed on the computer monitor or printed on paper. The procedure may take one to three minutes.

What is an electrocardiograph and how does it work?

The electrocardiograph is an electronic device that captures and amplifies the electrical activity of the heart through electrodes and the information captured is recorded on an electrocardiogram. The electrocardiograph was described by the Dutch physician Willem Einthoven in 1903, who was awarded the Nobel Prize in medicine in 1924 for his contributions to the field of health.

This type of medical equipment is part of bioinstrumentation in biomedical engineering, which is dedicated to recording specific biosignals from the human body and processing them for use by healthcare specialists, so that the diagnostic process is non-invasive.

An electrocardiograph uses electrodes to detect and convert the flow of ions through the heart muscle into electrical current. Because the captured signal is almost imperceptible, a preamplifier is used, which increases the magnitude of the signal to work better with it. Then, the signal is cleaned through filters and a final amplification is performed for its respective digitization.

There are several types of electrocardiographs, among them are:

• Single-channel electrocardiograph: characterized by recording and printing the results of the electrical activity of the heart from a single lead per recording.
• Multichannel electrocardiograph: distinguished by having 3, 6 or 12 channels and recording each of the 12 leads within 2.5 seconds.
• Multichannel with printing: it differs from the previous ones because it has a computer with recognition patterns that identify normal and abnormal electrocardiogram signals.

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