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Electrocardiogram - Uses, Types, and Performance

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

Written by

Dr. Narmatha. A

Medically reviewed by

Dr. Ruchi Sharma

Published At January 11, 2023
Reviewed AtMay 11, 2023


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

  • Chest pain.

  • Difficulty in breathing.

  • Arrhythmia (irregular heartbeat).

  • Dizziness.

  • Fatigue.

  • Hypertension (increased blood pressure).

  • Hypotension (decreased blood pressure).

  • Tachycardia (abnormally increased heart rate).

  • Bradycardia (abnormally decreased heart rate).

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).

Frequently Asked Questions


Which ECG Leads Are Between Two Points?

Bipolar ECG (it stands for electrocardiogram, which measures the electrical activity of the heart) leads to measuring the electrical activity of the heart between the negative and positive points. There are three bipolar leads in ECG, which include:
 - Lead One: It measures the electrical activity between the left and right arms. The positive electrode is placed on the left arm and the negative on the right arm.
 - Lead Two: It measures the electrical activity between the right arm and left leg. The positive electrode is placed on the right arm and the negative on the left leg.
 - Lead Three: It measures the electrical activity between the left arm and the left leg. The positive electrode is placed on the left arm and the negative electrode is placed on the left leg.


What Type of ECG Lead Is in Apple Watch?

Apple watch does not contain traditional ECG lead. It consists of a standard 12-lead ECG machine. It contains a single lead ECG system that measures the electrical activity of the heart between the right arm and left wrist. The Apple watch series has four, and later models have an inbuilt ECG app that allows an individual to take ECG readings using an electrical sensor in the watch. An individual may touch the digital crown over the watch. After the circuit's completion, the watch records the electrical activity of the heart and provides information about the heart's rhythm.


How Long Does an ECG Test Take?

The ECG test lasts for a few minutes, usually around five to ten minutes. The ECG test recording is quick. The total time depends on the number of leads used and the reason for testing. The test is done by removing any clothing because of interference with ECG electrodes.


What Is the Validity of the ECG Test?

The validity of an ECG test depends on the test's purpose. The ECG test is valid for a specific moment in time. It captures the electrical activity of the heart and detects any abnormalities if present. In the case of a diagnostic evaluation, the validity depends on the patient's symptoms. In some cases, a doctor may recommend repeated ECG testing if there are changes in the patient's heart function.


How to Place the ECG Leads?

ECG leads are placed on the patient’s chest, legs, and arms to measure the electrical activity of the heart. There are 12 leads for the standard ECG test. Four leads are placed on the patient's limbs, two on the legs and two on the arms. Eight leads are placed on the chest. The doctor may clean the skin with alcohol, and electrodes are placed on the selected locations. The electrodes are attached to the ECG machine and record the heart's electrical activity.


What Is the Work Procedure of ECG?

ECG is a test that measures the heart's electrical activity. The heart beats and generates electrical impulses. The electrodes are situated on the chest, arms, and legs and detect impulses. The electrodes are connected to a machine and record the electrical activity of the heart. The ECG tracing shows the strength and timing of the electrical signals. The ECG tracing is divided into several segments in which the P wave represents the electrical activity that causes the atrium to contract. The QRS simplex causes ventricles to contract and a T wave occurs when the ventricles recover from contraction.


What Does an ECG Show?

ECG shows several things about the heart's electrical activity. The ECG shows the slow and fast heartbeat by measuring the time it takes. It also shows regular and irregular heartbeat. Any blockage or delay in the electrical signals can be diagnosed by the ECG. It also shows any enlargement of the part of the heart, which may be an indication of heart disease. In the case of a heart attack, an ECG will show any damage in the heart.


What Is the Procedure for ECG Test in Ladies?

The procedure for ECG is the same for men and women. The process only differs based on the clothing worn. The patient is asked to put on a gown and the electrodes are placed directly on the skin. The women's chest is cleaned with alcohol to remove any oils or sweat. The electrodes are put down on the patient’s chest, arms, and legs. The electrodes machine will turn on and the patient is asked to breathe normally. It measures the electrical activity and the graph is printed out for the doctor to interpret.


What Are the Signs of an ECG Showing Heart Attack?

An ECG can detect the signs of a heart attack by showing changes in electrical activity. During a heart attack, the blood flow is blocked, leading to damage to the area of the heart. During a heart attack, the ECG may show:
 - ST-Segment Elevation: The most common sign of heart attack is ST-segment elevation. The ST segment represents the ventricular repolarization phase (when the heart muscles relax). 
 - T Wave Inversion: During a heart attack, the T wave may be upside down. 
 - Q Wave: A downward deflection of the Q wave represents the initial contraction of the heart muscle. This indicates the heart muscle is damaged.


How Long Do ECG Results Normally Take?

The time to get ECG results varies depending on several factors including the urgency of the test, the location of the test, and the interpretation process. ECG results may be available immediately after the test. More time is consumed in the interpretation of the results. In the case of cardiac arrest or any heart attack, the results may be processed quickly.


How to Read an ECG Report?

It is a complex process and needs specialized knowledge and training. Some steps to read the ECG graph.
 - Examine the paper speed and calibration.
 - The ECG graph displays 12 leads and each lead shows electrical activity from a different angle. 
 - The baseline of the ECG graph can be examined and should be straight and free from any movement.
 - The P wave represents the heart’s top chamber electrical activity.
 - The QRS complex represents the heart’s bottom chamber's electrical activity.
 - The ST segment represents the period between contraction and relaxation.
 - The T wave represents ventricular contraction.


How Coronary Artery Disease Is Detected by an ECG?

An ECG can diagnose coronary artery disease in several ways.
 - During a heart attack, a coronary artery gets blocked, leading to changes in the ST segment. The changes lead to a decrease in the blood flow of the heart muscle.
 - An inverted or flat T-wave is a sign of coronary artery disease.
 - A downward deflection of the Q-wave is a sign of coronary artery disease.
 - An ECG can detect abnormalities in the heart rate, which is a sign of coronary artery disease.
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