What Is Electrocardiogram?
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Electrocardiogram - Uses, Types, and Performance

Published on Jan 11, 2023 and last reviewed on May 11, 2023   -  4 min read


An electrocardiogram is a test that detects the heart's electrical activity. Read this article to know more about electrocardiograms.


Electrocardiography is the process of obtaining an electrocardiogram or electrocardiograph. An electrocardiogram is a test used to measure the heart's electrical activity. EKG is commonly used to determine the heart rate, heart rhythm, atrial abnormalities, ventricular hypertrophy, and pericarditis. The main components are the P wave (atrial depolarization), QRS complex, and T wave (ventricular repolarization).

What Are the Uses of Electrocardiograms?

  • To detect heart diseases such as myocardial infarction (a heart disease caused by the decreased blood flow to the heart muscles) and coronary artery disease (a disease caused by a blocked or narrowed coronary artery).

  • To detect how well the pacemaker is working.

  • To detect whether a patient had a previous heart attack.

  • To detect the function of the heart after heart surgery or medications.

  • To detect the overall health of the heart before heart surgery.

  • The electrocardiogram is often used in patients with symptoms of heart diseases such as

What Are the Different Types of ECG Leads?

The 12- lead ECG is the standard electrocardiogram performed in patients. The ECG leads are divided into limb leads and precordial leads. Limb leads are divided into standard bipolar limb leads l, ll, lll, and augmented unipolar leads aVL, aVF, and aVR.The limb leads are placed distal to the shoulders and hips of each limb. A aVR lead is placed over the right arm, aVL lead is placed over the left arm, and aVF lead is placed over the left leg.

The precordial leads are classified into V1 to V6. V1 is placed over the right sternal border at the fourth intercostal space. V2 is placed across V1 at the left sternal border and in the fourth intercostal space. V4 is placed over the midclavicular line at the fifth intercostal space. V3 is placed midway between V2 and V4. V6 is placed at the midaxillary line and the horizontal plane of V4. Finally, V5 is placed midway between V4 and V6 at the horizontal plane of V4.

How Do the Patients Prepare for an Electrocardiogram Procedure?

  • The health provider may ask the patients to sign a consent form before the electrocardiogram.

  • Patients should inform their doctor whether they have pacemakers.

  • Patients can normally eat and drink before their electrocardiogram.

  • Sometimes patients are instructed to remove the metal objects or jewels from the examination site before the test.

  • Medical conditions and regular medicines of the patient should be informed to the doctor. Sometimes the physician might ask them to stop their medication, interfering with the test result.

How Is an Electrocardiogram Performed?

Patients are instructed to remove their clothes above their waist before the procedure. They are given a hospital gown or sheet to cover the unnecessarily exposed area. Patients' hair over the chest, legs, and arms should be removed and cleaned before the procedure, as it may alter the tracing results. During the test, patients are asked to lie flat on the procedure table, and a number of sensors called electrodes are stuck over the arms, legs, and chest. These electrodes are connected to the lead wires of an ECG machine. The electrodes should be placed close to the skin to detect the electrical signals of the heartbeat. The electrical signals recorded by the computer are displayed as waves on the paper or monitor. Patients should not move or talk during the procedure as it may alter the test result. Once the electrocardiogram is done, the technician will remove the electrodes placed over the skin.

What Are the Interpretations of Electrocardiograms?

  • The 12- lead ECG shows the heart rate, heart rhythm, PQRS-T morphology, and PQRS-T intervals and detects the presence of an ST segment.

  • When the heart rate is normal, the interval between two successive QRS complexes determines the heart rate. The heart rate is calculated on paper by dividing the boxes between two QRS complexes by 300. For abnormal heart rate, the average heart rate in beats per minute is determined by counting the number of QRS complexes and multiplying it by six.

  • P wave refers to atrial depolarization. The normal P wave is upright in leads l, ll, and aVF and is inverted in lead aVR. The P wave is usually biphasic and contains both positive and negative components. When the negative component of the P wave exceeds one small box (0.04 seconds), it is abnormal. The increased P wave duration is seen in left atrial enlargement. The P wave is taller than 2.5 mm (millimeter) in inferior (below) leads and taller than 1.5 mm in leads V1 and V2 are seen in right atrial enlargement.

  • The PR interval is measured from the P wave to the first part of the QRS complex. The average PR interval is between 0.12 to 0.20 seconds.

  • The QRS complex refers to ventricular depolarization. The average duration of a QRS complex is 0.06 to 0.10 seconds. Q wave is the first QRS vector directed away from a positive electrode. The first positive deflection refers to the R wave, and the negative deflection refers to the S wave.

  • QT interval is used to measure the depolarization and repolarization of the ventricles. Prolonged QT interval refers to ventricular arrhythmia and causes sudden death. QT interval depends on the heart rate. Shorter QT interval results from an increased heart rate, and longer QT interval results from a slower heart rate.

What Are the Possible Interfering Factors in Electrocardiogram Procedure?

  • Obesity.

  • Pregnancy.

  • Ascites (collection of fluid inside the abdominal cavity).

  • Movement during the procedure.

  • Exercise before the test.

  • Smoking.

  • Electrolyte imbalance.

  • Certain medications, such as beta-blockers and antidepressants.

  • Size of the chest and location of heart inside the chest.


An electrocardiogram is a noninvasive diagnostic tool used to determine the severity of heart diseases. The electrocardiogram is a simple and easy procedure and does not require hospitalization. For women with large breasts, the electrodes are placed beneath the breast and not over the breast. ECG and EKG both refer to the same procedure, electrocardiogram. The abbreviation EKG comes from the German spelling of electrocardiogram (elektrokardiogramm). Health professionals commonly prefer the term EKG to avoid confusion between ECG and EEG (electroencephalogram).

Last reviewed at:
11 May 2023  -  4 min read




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