Electrocardiogram (ECG): what is it for and how is it done?


What is the electrocardiogram?

Electrocardiogram , or ECG, is an examination that assesses the electrical activity of the heart from electrodes attached to the skin. This activity is characterized by the variation in the amount of sodium ions inside and outside the cardiac muscle cells.

The result of this examination is recorded on graphs that compare the patient’s cardiac activity with the standard, indicating whether cardiac activity is within normal limits or if there are changes in the muscles and nerves of the heart.

What is the ECG exam for?

This test is able to detect the heart rhythm and the number of beats per minute, so it is used to identify arrhythmias, enlarged heart cavities, coronary pathologies, myocardial infarction, disturbances in the electrical conduction of the organ, problems in the heart valves , pericarditis, hypertrophy of the cardiac chambers and diseases that isolate the heart.

It can also be indicated to check the health of the heart when the patient has other conditions, such as:

  • High pressure;
  • High cholesterol;
  • Smoking;
  • Diabetes;
  • Family history of early heart disease.

How is the electrocardiograph (electrocardiogram device)?

The device used for the exam is called a digital electrocardiograph and is usually compact and portable. It can be used connected to a desktop or notebook computer. By connecting to notebooks, the electrocardiograph can be used even without power, as it will work with the battery of the portable computer.

This device captures electrical activity through the patient’s skin, generating linear images in waves that demonstrate a pattern. Such waves are given a specific name and represent a meaning recognized by the cardiologist.

Types and how the electrocardiogram is done

There are three different types of electrocardiogram , all have the same purpose and are capable of achieving the same purpose.

The main difference between each type is the ways in which each is made. However, there are points in common between them, such as:

  • The indications, the patient must not smoke in the last 30 minutes, nor practice physical activities in the last 10 minutes before the exam;
  • The application of a conductive gel to facilitate the capture of stimuli in all types.

Standard ECG

Also known as resting or surface ECG, it is the most common form of the exam, simple and painless. Its maximum duration is 5 minutes.

In this method, the patient lies on a stretcher, with his chest bare, and his skin is clean and defatted to receive the electrodes. If the patient has a lot of hair on the body, a waxing will be done, and in cases of a lot of oil on the skin, it should be cleaned with alcohol.

With the skin ready, the electrodes are connected to specific parts of the body, such as breasts, arms and legs. On the arms and legs the electrodes are fixed by bracelets and on the chest by a kind of rubber suction cup.

Exercise ECG

Also known as exercise testing, in this type of electrocardiogram the test is performed while the patient performs some type of physical exercise, usually on a treadmill or on a bicycle. For the proper performance of this exam, the patient’s diet should be light for at least 2 hours before the exam. The patient should also wear appropriate clothing for physical exercise and not smoke for 2 hours before the exam. Women should wear a bra or top.

Exercise usually starts out slow and easy, and gradually intensifies. The patient can stop during exercise, in case of exhaustion, and its duration does not exceed 20 minutes.

From this examination, it is possible to define how the individual’s heart generates stress , in addition to diagnosing coronary heart disease and determining its severity.


Also known as ambulatory ECG monitoring, in this type of examination a device records the patient’s cardiac activity for 24 hours. This device, called a holter, works as a recording device with electrode wires that are connected to the patient’s chest.

During the 24-hour exam, the patient must also take notes of his daily activities and his symptoms or experiences.

When should the electrocardiogram be done?

The exam should be performed periodically, depending on the age group and biological sex. Women over 50 and men over 40 must have the standard ECG performed annually. Based on it, the stress test can be recommended, if necessary, for example for individuals who intend to start exercising at the gym.

The test can also be recommended if any of these symptoms appear:

  • Lack of air;
  • Dizziness;
  • Irregular heartbeat;
  • Fainting.

Examination contraindications

Contraindications for the exam are rare. One of the factors that could prevent its performance would be the impossibility of connecting the electrodes to the patient’s skin. It is also not recommended to practice physical exercises just before the exam, as it can change the level of your heartbeat.

In general, any individual in any situation can take the exam.

Can pregnant women take the exam?

Yes, there are no contraindications regarding the examination in pregnant or lactating women.

How to prepare for the exam?

You should always report the medications the patient is using to the doctor, as some of them can cause changes in the test result. In addition, it is important to clarify doubts about the reason for the test, its risks and how it will be done.

The test should not be done with jewelry on the neck, arms or wrist. For men with a lot of chest hair, it may be necessary to cut them.

Is special care necessary after the exam?

No special care is required after the exam. If necessary, the patient can work normally after the test.

The result is ready quickly and can be expected in the office.

Electrocardiogram results

The test result describes, in a technical way, cardiac rhythm, intervals, blocks, conduction disorders, cavity overload and other factors that make the patient concerned about the organ.

If the results show any irregularity, it may be necessary to repeat the exam or perform others, such as an echocardiogram , holter or more complex exams.

Normal results

When the tracking seems normal, as well as when the heart beats at a common pace, usually between 60 and 100 beats per minute. In such cases the test result will be normal.

Abnormal results

When the tracking doesn’t seem normal, as well as when you notice some of these cases:

  • Heart beats slowly, below 60 beats per minute;
  • Heart beats very fast, above 100 beats per minute;
  • The rhythm of the heart is irregular.

Possible meanings for abnormal results

Through this examination, several diseases or problems in the heart can be discovered, all of them from an abnormal result. Some possibilities are:

  • Cardiac arrhythmia;
  • Angina;
  • Ischemia;
  • Congenital heart diseases;
  • Injuries to the heart valves;
  • Blockages in the impulse conduction system;
  • Modification of electrolytes in the body;
  • Parts of the heart that have been damaged and the extent of the damage.

What can affect the results of the electrocardiogram?

Some cases can influence the results of the exam, they are:

  • If the electrodes are not well connected to the patient’s skin;
  • If the patient moves or talks during the exam;
  • If the patient exercises before the exam;
  • If the patient is anxious or breathes deeply or rapidly during the examination.

Risks of the electrocardiogram

The exam does not present any risk. In rare cases, dermatological reactions may occur depending on the gel or the electrodes in contact with the skin., There may also be slight discomfort when they are removed from the skin.

There is no risk of shock during the examination, as the electrodes do not emit any electrical current, they only record the activity of the heart.

The electrocardiogram is a very common exam and without any contraindications. Share this article with your friends and family so that they also get to know the types of exams and how each exam is done!