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Electrocardiogram, Waves, Types, Working and Why it is Done

Electrocardiogram is a simple, non-invasive test that monitors the electrical activity of the heart. An ECG can help diagnose specific heart conditions, such as abnormal heart rhythms and coronary heart disease (heart attack and angina).
authorImageKrati Saraswat30 May, 2025
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Electrocardiogram

Electrocardiogram: An electrocardiogram, also known as an EKG or ECG, is a quick and easy diagnostic procedure that evaluates how well the heart is working.  Electrodes, or tiny, sticky patches, are applied to particular parts of the arms, legs, and chest and then lead wires are used to connect them to an ECG machine. The machine records and prints the electrical activity of the heart without sending any electricity into the body.

The heart's natural electrical impulses coordinate its contractions to maintain proper blood circulation. An ECG records these impulses, indicating the heart's rate, rhythm (regular or irregular), and the timing of electrical impulses as they pass through various parts of the heart. ECG changes can indicate a variety of heart conditions. This article provides detailed information on electrocardiograms and their functions.

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Electrocardiogram Types

There are various types of electrocardiograms (ECGs) used to assess heart health. The most common ones include::
  1. Resting ECG: This is the most commonly used ECG method. It requires placing electrodes on the chest, arms, and legs while the patient lies down. The heart's electrical activity is recorded for a brief period, typically around 10 minutes. A resting ECG aids in detecting abnormal heart rhythms, heart attacks, and other cardiac issues.
  2. Stress ECG (exercise stress test): The doctor monitors the patient's heart rate and rhythm while they exercise on a treadmill or stationary bike to see how the heart responds to exertion. A stress ECG helps in identifying blood flow issues to the heart, such as coronary artery disease.
  3. Holter Monitor: This portable ECG device is worn for 24 to 48 hours during normal daily activities. It continuously records the heart's electrical activity, which can reveal irregular heartbeats not captured by a resting ECG.
  4. Event Recorder: A small, portable ECG device worn for a few weeks or months. Patients press a button when experiencing symptoms like chest pain or palpitations, enabling the device to record the heart's electrical activity at that moment, aiding in identifying the symptom's cause.
  5. Signal-averaged ECG (SAECG): A specialized ECG used to diagnose arrhythmogenic right ventricular cardiomyopathy (ARVC), a condition that can lead to sudden death. SAECG is a more intricate test than a standard ECG and is not as widely accessible.
These are just a few of the available ECG types. The choice of ECG depends on the patient's specific needs and medical history.

Electrocardiogram (ECG) Working

An electrocardiogram (ECG) is a non-invasive diagnostic test that records the heart's electrical activity. It plays a vital role in evaluating cardiac health and detecting various heart conditions.

How Does an ECG Function?

The heart produces small electrical impulses that trigger muscle contractions, enabling it to pump blood. An ECG machine detects these impulses through electrodes placed on the chest, arms, and legs. The electrodes capture the electrical signals, which are then amplified and displayed as a graph by the ECG machine. This graph, known as an electrocardiogram, illustrates the electrical waves as they travel through the heart's chambers.

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Electrocardiogram Waves

A standard ECG trace reveals distinct wave patterns, each indicating a specific stage of the electrical impulse's journey through the heart:
  • P wave: Indicates the spread of the electrical impulse through the atria (upper chambers), causing them to contract.
  • QRS complex: Reflects the impulse's passage through the ventricles (lower chambers), stimulating their contraction.
  • T wave: Represents the ventricles' relaxation.
  • U wave: Reflects atrial repolarization (may not always be visible on a normal ECG).
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What Information Does an EKG Detect?

By analysing the ECG trace, a physician can assess:
  • Heart rate: The number of heartbeats per minute.
  • Heart rhythm : Whether the heart rhythm is regular or irregular.
  • Size and positioning of the heart chambers.
  • Blood flow to the heart muscle.
  • Prior heart muscle damage from a past heart attack.
  • Other cardiac issues, such as arrhythmias (irregular heart rhythms) or conduction abnormalities.
An abnormal ECG can indicate various heart conditions, including:
  • Coronary artery disease
  • Heart attack
  • Arrhythmias
  • Heart valve disorders
  • Heart muscle abnormalities
The ECG is an essential tool for diagnosing and monitoring heart conditions. It is a safe, painless procedure that provides valuable insights into cardiac health.

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Why ECG is Done?

The electrocardiogram (ECG) provides two primary types of data:
  1. Determining Conduction Time: Surgeons use the ECG to measure the time it takes for an electromagnetic pulse to traverse the heart. They do this by calculating time intervals on the ECG, and observing whether the electrical activity is natural, sluggish, fast, or erratic. This helps determine how long a pulse takes to travel from one part of the heart to another.
  2. Assessing Heart Condition: Cardiologists can assess if areas of the heart are enlarged or overworked by measuring the electrical activity flowing through the heart muscle. A traditional 12-lead ECG involves placing ten electrodes on the patient's arms and chest. The average strength of the heart's electrical potential is then calculated from 12 different angles (known as "leads") over a period, typically 10 seconds. This process allows for the observation of the total intensity and trajectory of the heart's electrical depolarization during the cardiac cycle.
While ECGs are useful diagnostic tools, there is no evidence to support their routine use as a preventive measure in people who have no symptoms or are at low risk of cardiovascular disease. This is because ECG readings can be misinterpreted, resulting in misdiagnosis, unnecessary invasive procedures, and overtreatment. Individuals in certain professions requiring high levels of safety, such as airline pilots, may undergo routine ECG evaluations as part of their occupational health assessments.

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Difference Between ECG and EKG Test

The two terms refer to the same medical procedure: an electrocardiogram (ECG). The term "EKG" is derived from the German word, which has "k" instead of "c" in both parts of it. It is important to note that an EKG differs from an echocardiogram, which is a type of ultrasound that produces images of the heart as it beats.

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Electrocardiograms Risks

Electrocardiograms are generally safe procedures with minimal risks. Since an ECG does not administer electricity to the body, there is no risk of receiving an electric shock. However, some individuals may experience a rash or skin irritation at the sites where the electrodes were placed. Several factors can interfere with the accuracy of ECG results, including:
  • Movement or talking during the ECG test
  • Smoking or engaging in vigorous exercise prior to the test
  • Pregnancy
  • Obesity
  • Certain medications
  • Abdominal swelling caused by fluid accumulation (ascites)
  • Electrolyte imbalances, such as abnormal levels of calcium, potassium, or magnesium in the blood
Before undergoing an ECG, you should inform your doctor of any health conditions you may have, including pregnancy, as well as any medications or supplements you are currently using. Physics Wallah NEET Online Coaching will help you get ready for the exam. PW offers comprehensive NEET UG prep courses with live classes, PDF notes, and practice problems for Class 12 aspirants.
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Electrocardiogram FAQs

What is an electrocardiogram used to diagnose?

An electrocardiogram (ECG) is utilised to diagnose various heart conditions, such as abnormal heart rhythms and coronary heart disease (including heart attacks and angina), by recording the heart's electrical activity.

What are the types of ECG?

The two main types of ECG. Resting ECG, performed most frequently, involves placing electrodes on the chest, arms, and legs while the patient lies down. Stress ECG which is also known as an exercise stress test, this ECG monitors the heart's activity during physical activities like walking or running on a treadmill.

Is there a difference between an EKG and an electrocardiogram?

"EKG" and "ECG" are different spellings for the same diagnostic test that monitors the heart's electrical activity. "EKG" is derived from the German spelling of "electrocardiogram," with the abbreviation "EKG" originating from the test's initial invention location.

What is a normal ECG?

A normal ECG should indicate that the heart is beating at a regular rate of 60 to 100 beats per minute. However, an ECG can reveal various heart conditions, including abnormal heart rhythms, heart defects, coronary artery disease, heart valve issues, or an enlarged heart.

What is a normal ECG value?

Normal ECG values for waves and intervals are as follows: 1. RR interval: 0.6-1.2 seconds. 2. P wave: 80 milliseconds. 3. PR interval: 120-200 milliseconds.

Can ECG detect heart blockage?

No, an ECG (electrocardiogram) cannot directly detect heart blockages. Its primary purpose is to record the heart's electrical activity.
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